WorldWideScience

Sample records for driven collisionless shocks

  1. Electron Weibel Instability Mediated Laser Driven Electromagnetic Collisionless Shock

    Science.gov (United States)

    Jia, Qing; Mima, Kunioki; Cai, Hong-Bo; Taguchi, Toshihiro; Nagatomo, Hideo; He, X. T.

    2015-11-01

    As a fundamental nonlinear structure, collisionless shock is widely studied in astrophysics. Recently, the rapidly-developing laser technology provides a good test-bed to study such shock physics in laboratory. In addition, the laser driven shock ion acceleration is also interested due to its potential applications. We explore the effect of external parallel magnetic field on the collisionless shock formation and resultant particle acceleration by using the 2D3V PIC simulations. We show that unlike the electrostatic shock generated in the unmagnetized plasma, the shock generated in the weakly-magnetized laser-driven plasma is mostly electromagnetic (EM)-like with higher Mach number. The generation mechanism is due to the stronger transverse magnetic field self-generated at the nonlinear stage of the electron Weibel instability which drastically scatters particles and leads to higher energy dissipation. Simulation results also suggest more ions are reflected by this EM shock and results in larger energy transfer rate from the laser to ions, which is of advantage for applications such as neutron production and ion fast ignition.

  2. Collisionless Relativistic Shocks:current driven turbulence and particle acceleration

    CERN Document Server

    Pelletier, Guy; Gremillet, Laurent; Plotnikov, Illya

    2014-01-01

    The physics of collisionless relativistic shocks with a moderate magnetization is presented. Micro-physics is relevant to explain the most energetic radiative phenomena of Nature, namely that of the termination shock of Gamma Ray Bursts. A transition towards Fermi process occurs for decreasing magnetization around a critical value which turns out to be the condition for the scattering to break the mean field inhibition. Scattering is produced by magnetic micro-turbulence driven by the current carried by returning particles, which had not been considered till now, but turns out to be more intense than Weibel's one around the transition. The current is also responsible for a buffer effect on the motion of the incoming flow, on which the threshold for the onset of turbulence depends.

  3. Current-driven filamentation upstream of magnetized relativistic collisionless shocks

    CERN Document Server

    Lemoine, M; Gremillet, L; Plotnikov, I

    2014-01-01

    The physics of instabilities in the precursor of relativistic collisionless shocks is of broad importance in high energy astrophysics, because these instabilities build up the shock, control the particle acceleration process and generate the magnetic fields in which the accelerated particles radiate. Two crucial parameters control the micro-physics of these shocks: the magnetization of the ambient medium and the Lorentz factor of the shock front; as of today, much of this parameter space remains to be explored. In the present paper, we report on a new instability upstream of electron-positron relativistic shocks and we argue that this instability shapes the micro-physics at moderate magnetization levels and/or large Lorentz factors. This instability is seeded by the electric current carried by the accelerated particles in the shock precursor as they gyrate around the background magnetic field. The compensation current induced in the background plasma leads to an unstable configuration, with the appearance of ...

  4. Intense laser driven collision-less shock and ion acceleration in magnetized plasmas

    Science.gov (United States)

    Mima, K.; Jia, Q.; Cai, H. B.; Taguchi, T.; Nagatomo, H.; Sanz, J. R.; Honrubia, J.

    2016-05-01

    The generation of strong magnetic field with a laser driven coil has been demonstrated by many experiments. It is applicable to the magnetized fast ignition (MFI), the collision-less shock in the astrophysics and the ion shock acceleration. In this paper, the longitudinal magnetic field effect on the shock wave driven by the radiation pressure of an intense short pulse laser is investigated by theory and simulations. The transition of a laminar shock (electro static shock) to the turbulent shock (electromagnetic shock) occurs, when the external magnetic field is applied in near relativistic cut-off density plasmas. This transition leads to the enhancement of conversion of the laser energy into high energy ions. The enhancement of the conversion efficiency is important for the ion driven fast ignition and the laser driven neutron source. It is found that the total number of ions reflected by the shock increases by six time when the magnetic field is applied.

  5. Weibel instability mediated collisionless shocks using intense laser-driven plasmas

    Science.gov (United States)

    Palaniyappan, Sasi; Huang, Chengkun; Gautier, Donald; Fernandez, Juan; Ma, Wenjun; Schreiber, Jorg; LANL Collaboration; LMU Team

    2016-10-01

    The origin of cosmic rays remains a long-standing challenge in astrophysics and continues to fascinate physicists. It is believed that ``collisionless shocks'' - where the particle Coulomb mean free path is much larger that the shock transition - are a dominant source of energetic cosmic rays. These shocks are ubiquitous in astrophysical environments such as gamma-ray bursts, supernova remnants, pulsar wind nebula and coronal mass ejections from the sun. Several spacecraft observations have revealed acceleration of charged particles, mostly electrons, to very high energies with in the shock front. There is now also clear observational evidence that supernova remnant shocks accelerate both protons and electrons. The understanding of the microphysics behind collisionless shocks and their particle acceleration is tightly related with nonlinear basic plasma processes and remains a grand challenge. In this poster, we will present results from recent experiments at the LANL Trident laser facility studying collisionless shocks using intense ps laser (80J, 650 fs - peak intensity of 1020 W/cm2) driven near-critical plasmas using carbon nanotube foam targets. A second short pulse laser driven protons from few microns thick aluminum foil is used to image the laser-driven plasma.

  6. Collisionless electrostatic shocks

    DEFF Research Database (Denmark)

    Andersen, H.K.; Andersen, S.A.; Jensen, Vagn Orla

    1970-01-01

    An attempt was made in the laboratory to observe the standing collisionless electrostatic shocks in connection with the bow shock of the earth......An attempt was made in the laboratory to observe the standing collisionless electrostatic shocks in connection with the bow shock of the earth...

  7. Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Device

    Energy Technology Data Exchange (ETDEWEB)

    Schaeffer, D. B., E-mail: dschaeffer@physics.ucla.edu; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Gekelman, W.; Niemann, C. [Department of Physics and Astronomy, University of California - Los Angeles, Los Angeles, California 90095 (United States); Winske, D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2014-05-15

    The interaction of a laser-driven super-Alfvénic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations.

  8. Generation and Evolution of High-Mach Number, Laser-Driven Magnetized Collisionless Shocks in the Laboratory

    CERN Document Server

    Schaeffer, Derek; Haberberger, Dan; Fiksel, Gennady; Bhattacharjee, Amitava; Barnak, Daniel; Hu, Suxing; Germaschewski, Kai

    2016-01-01

    Shocks act to convert incoming supersonic flows to heat, and in collisionless plasmas the shock layer forms on kinetic plasma scales through collective electromagnetic effects. These collisionless shocks have been observed in many space and astrophysical systems [Smith 1975, Smith 1980, Burlaga 2008, Sulaiman 2015], and are believed to accelerate particles, including cosmic rays, to extremely high energies [Kazanas 1986, Loeb 2000, Bamba 2003, Masters 2013, Ackermann 2013]. Of particular importance are the class of high-Mach number, supercritical shocks [Balogh 2013] ($M_A\\gtrsim4$), which must reflect significant numbers of particles back into the upstream to accommodate entropy production, and in doing so seed proposed particle acceleration mechanisms [Blandford 1978, McClements 2001, Caprioli 2014, Matsumoto 2015]. Here we present the first laboratory generation of high-Mach number magnetized collisionless shocks created through the interaction of an expanding laser-driven plasma with a magnetized ambient ...

  9. Collisionless shocks and particle acceleration in laser-driven laboratory plasmas

    Science.gov (United States)

    Fiuza, Frederico

    2012-10-01

    Collisionless shocks are pervasive in space and astrophysical plasmas, from the Earth's bow shock to Gamma Ray Bursters; however, the microphysics underlying shock formation and particle acceleration in these distant sites is not yet fully understood. Mimicking these extreme conditions in laboratory is a grand challenge that would allow for a better understanding of the physical processes involved. Using ab initio multi-dimensional particle-in-cell simulations, shock formation and particle acceleration are investigated for realistic laboratory conditions associated with the interaction of intense lasers with high-energy-density plasmas. Weibel-instability-mediated shocks are shown to be driven by the interaction of an ultraintense laser with overcritical plasmas. In this piston regime, the laser generates a relativistic flow that is Weibel unstable. The strong Weibel magnetic fields deflect the incoming flow, compressing it, and forming a shock. The resulting shock structure is consistent with previous simulations of relativistic astrophysical shocks, demonstrating for the first time the possibility of recreating these structures in laboratory. As the laser intensity is decreased and near-critical density plasmas are used, electron heating dominates over radiation pressure and electrostatic shocks can be formed. The electric field associated with the shock front can reflect ions from the background accelerating them to high energies. It is shown that high quality 200 MeV proton beams, required for tumor therapy, can be generated by using an exponentially decaying plasma profile to control competing accelerating fields. These results pave the way for the experimental exploration of space and astrophysical relevant shocks and particle acceleration with current laser systems.

  10. Generation and Evolution of High-Mach-Number Laser-Driven Magnetized Collisionless Shocks in the Laboratory

    Science.gov (United States)

    Schaeffer, D. B.; Fox, W.; Haberberger, D.; Fiksel, G.; Bhattacharjee, A.; Barnak, D. H.; Hu, S. X.; Germaschewski, K.

    2017-07-01

    We present the first laboratory generation of high-Mach-number magnetized collisionless shocks created through the interaction of an expanding laser-driven plasma with a magnetized ambient plasma. Time-resolved, two-dimensional imaging of plasma density and magnetic fields shows the formation and evolution of a supercritical shock propagating at magnetosonic Mach number Mms≈12 . Particle-in-cell simulations constrained by experimental data further detail the shock formation and separate dynamics of the multi-ion-species ambient plasma. The results show that the shocks form on time scales as fast as one gyroperiod, aided by the efficient coupling of energy, and the generation of a magnetic barrier between the piston and ambient ions. The development of this experimental platform complements present remote sensing and spacecraft observations, and opens the way for controlled laboratory investigations of high-Mach number collisionless shocks, including the mechanisms and efficiency of particle acceleration.

  11. Experimental study of subcritical laboratory magnetized collisionless shocks using a laser-driven magnetic piston

    Science.gov (United States)

    Schaeffer, D. B.; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Winske, D.; Gekelman, W.; Niemann, C.

    2015-11-01

    Recent experiments at the University of California, Los Angeles have successfully generated subcritical magnetized collisionless shocks, allowing new laboratory studies of shock formation relevant to space shocks. The characteristics of these shocks are compared with new data in which no shock or a pre-shock formed. The results are consistent with theory and 2D hybrid simulations and indicate that the observed shock or shock-like structures can be organized into distinct regimes by coupling strength. With additional experiments on the early time parameters of the laser plasma utilizing Thomson scattering, spectroscopy, and fast-gate filtered imaging, these regimes are found to be in good agreement with theoretical shock formation criteria.

  12. Collisionless parallel shocks

    Science.gov (United States)

    Khabibrakhmanov, I. KH.; Galeev, A. A.; Galinskii, V. L.

    1993-01-01

    Consideration is given to a collisionless parallel shock based on solitary-type solutions of the modified derivative nonlinear Schroedinger equation (MDNLS) for parallel Alfven waves. The standard derivative nonlinear Schroedinger equation is generalized in order to include the possible anisotropy of the plasma distribution and higher-order Korteweg-de Vies-type dispersion. Stationary solutions of MDNLS are discussed. The anisotropic nature of 'adiabatic' reflections leads to the asymmetric particle distribution in the upstream as well as in the downstream regions of the shock. As a result, nonzero heat flux appears near the front of the shock. It is shown that this causes the stochastic behavior of the nonlinear waves, which can significantly contribute to the shock thermalization.

  13. High Mach-number collisionless shock driven by a laser with an external magnetic field

    Directory of Open Access Journals (Sweden)

    Morita T.

    2013-11-01

    Full Text Available Collisionless shocks are produced in counter-streaming plasmas with an external magnetic field. The shocks are generated due to an electrostatic field generated in counter-streaming laser-irradiated plasmas, as reported previously in a series of experiments without an external magnetic field [T. Morita et al., Phys. Plasmas, 17, 122702 (2010, Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011] via laser-irradiation of a double-CH-foil target. A magnetic field is applied to the region between two foils by putting an electro-magnet (∼10 T perpendicular to the direction of plasma expansion. The generated shocks show different characteristics later in time (t > 20ns.

  14. Vlasov modelling of laser-driven collisionless shock acceleration of protons

    Energy Technology Data Exchange (ETDEWEB)

    Svedung Wettervik, B.; DuBois, T. C.; Fülöp, T. [Department of Applied Physics, Chalmers University of Technology, Gothenburg (Sweden)

    2016-05-15

    Ion acceleration due to the interaction between a short high-intensity laser pulse and a moderately overdense plasma target is studied using Eulerian Vlasov–Maxwell simulations. The effects of variations in the plasma density profile and laser pulse parameters are investigated, and the interplay of collisionless shock and target normal sheath acceleration is analyzed. It is shown that the use of a layered-target with a combination of light and heavy ions, on the front and rear side, respectively, yields a strong quasi-static sheath-field on the rear side of the heavy-ion part of the target. This sheath-field increases the energy of the shock-accelerated ions while preserving their mono-energeticity.

  15. Collisionless shocks driven by 800 nm laser pulses generate high-energy carbon ions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H.; Shen, B. F., E-mail: bfshen@mail.shcnc.ac.cn; Wang, W. P.; Xu, Y.; Liu, Y. Q.; Liang, X. Y.; Leng, Y. X.; Li, R. X., E-mail: ruxinli@mail.shcnc.ac.cn; Xu, Z. Z. [State Key Laboratory of High Filed Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Yan, X. Q.; Chen, J. E. [State Key Laboratory of Nuclear Physics and Technology, Institute of Heavy Ion Physics, Peking University, Beijing 100871 (China)

    2015-01-15

    We present experimental studies on ion acceleration from diamond-like carbon (DLC) foils irradiated by 800 nm, linearly polarized laser pulses with peak intensity of 1.7 × 10{sup 19 }W/cm{sup 2} to 3.5 × 10{sup 19 }W/cm{sup 2} at oblique incidence. Diamond-like carbon foils are heated by the prepulse of a high-contrast laser pulse and expand to form plasmas of near-critical density caused by thermal effect before the arrival of the main pulse. It is demonstrated that carbon ions are accelerated by a collisionless shock wave in slightly overdense plasma excited by forward-moving hot electrons generated by the main pulse.

  16. Simulation of laser-driven, ablated plasma flows in collisionless shock experiments on OMEGA and the NIF

    Science.gov (United States)

    Grosskopf, M. J.; Drake, R. P.; Kuranz, C. C.; Rutter, E. M.; Ross, J. S.; Kugland, N. L.; Plechaty, C.; Remington, B. A.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C. D.; Meinecke, J.; Reville, B.; Sakawa, Y.; Kuramitsu, Y.; Takabe, H.; Froula, D. H.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Liang, E.; Fu, W.; Woolsey, N.; Park, H.-S.

    2013-03-01

    Experiments investigating the physics of interpenetrating, collisionless, ablated plasma flows have become an important area of research in the high-energy-density field. In order to evaluate the feasibility of designing experiments that will generate a collisionless shock mediated by the Weibel instability on the National Ignition Facility (NIF) laser, computer simulations using the Center for Radiative Shock Hydrodynamics (CRASH) radiation-hydrodynamics model have been carried out. This paper reports assessment of whether the experiment can reach the required scale size while maintaining the low interflow collisionality necessary for the collisionless shock to form. Comparison of simulation results with data from Omega experiments shows the ability of the CRASH code to model these ablated systems. The combined results indicate that experiments on the NIF are capable of reaching the regimes necessary for the formation of a collisionless shock in a laboratory experiment.

  17. Collisionless Electrostatic Shock Modeling and Simulation

    Science.gov (United States)

    2016-10-21

    Briefing Charts 3. DATES COVERED (From - To) 30 September 2016 – 21 October 2016 4. TITLE AND SUBTITLE Collisionless Electrostatic Shock Modeling and...release: distribution unlimited. PA#16490 Air Force Research Laboratory Collisionless Electrostatic Shock Modeling and Simulation Daniel W. Crews In-Space...unlimited. PA#16490 Overview • Motivation and Background • What is a Collisionless Shock Wave? • Features of the Collisionless Shock • The Shock Simulation

  18. Gamma-ray bursts and collisionless shocks

    CERN Document Server

    Waxman, E

    2006-01-01

    Particle acceleration in collisionless shocks is believed to be responsible for the production of cosmic-rays over a wide range of energies, from few GeV to >10^{20} eV, as well as for the non-thermal emission of radiation from a wide variety of high energy astrophysical sources. A theory of collisionless shocks based on first principles does not, however, exist. Observations of gamma-ray burst (GRB) "afterglows" provide a unique opportunity for diagnosing the physics of relativistic collisionless shocks. Most GRBs are believed to be associated with explosions of massive stars, and their "afterglows," delayed low energy emission following the prompt burst of gamma-rays, are produced by relativistic collisionless shock waves driven by the explosion into the surrounding plasma. Some of the striking characteristics of these shocks include the generation of downstream magnetic fields with energy density exceeding that of the upstream field by ~8 orders of magnitude, the survival of this strong field at distances ...

  19. Physics of collisionless shocks - theory and simulation

    CERN Document Server

    Novo, A Stockem; Fonseca, R A; Silva, L O

    2015-01-01

    Collisionless shocks occur in various fields of physics. In the context of space and astrophysics they have been investigated for many decades. However, a thorough understanding of shock formation and particle acceleration is still missing. Collisionless shocks can be distinguished into electromagnetic and electrostatic shocks. Electromagnetic shocks are of importance mainly in astrophysical environments and they are mediated by the Weibel or filamentation instability. In such shocks, charged particles gain energy by diffusive shock acceleration. Electrostatic shocks are characterized by a strong electrostatic field, which leads to electron trapping. Ions are accelerated by reflection from the electrostatic potential. Shock formation and particle acceleration will be discussed in theory and simulations.

  20. Self-Similar Collisionless Shocks

    CERN Document Server

    Katz, B; Waxman, E; Katz, Boaz; Keshet, Uri; Waxman, Eli

    2006-01-01

    Observations of gamma-ray burst afterglows suggest that the correlation length of magnetic field fluctuations downstream of relativistic non-magnetized collisionless shocks grows with distance from the shock to scales much larger than the plasma skin depth. We argue that this indicates that the plasma properties are described by a self-similar solution, and derive constraints on the scaling properties of the solution. For example, we find that the scaling of the characteristic magnetic field amplitude with distance from the shock is B \\propto D^{s_B} with -1 \\propto x^{2s_B} (for x>>D). We show that the plasma may be approximated as a combination of two self-similar components: a kinetic component of energetic particles and an MHD-like component representing "thermal" particles. We argue that the latter may be considered as infinitely conducting, in which case s_B=0 and the scalings are completely determined (e.g. dn/dE \\propto E^{-2} and B \\propto D^0). Similar claims apply to non- relativistic shocks such a...

  1. The microphysics of collisionless shock waves

    CERN Document Server

    Marcowith, A; Bykov, A; Dieckman, M E; Drury, L O C; Lembege, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem

    2016-01-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebul\\ae, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in-situ observations, analytical and numerical developments. A particular emphasize is made on the different instabilities triggered during the shock formation and in a...

  2. The microphysics of collisionless shock waves

    DEFF Research Database (Denmark)

    Marcowith, Alexandre; Bret, Antoine; Bykov, Andrei;

    2016-01-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active...... galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space....... It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments...

  3. Collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near critical density plasmas

    CERN Document Server

    Liu, M; Li, Y T; Yuan, D W; Chen, M; Mulser, P; Sheng, Z M; Murakami, M; Yu, L L; Zheng, X L; Zhang, J

    2016-01-01

    Laser-driven collisonless electrostatic shock formation and the subsequent ion acceleration have been studied in near critical density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near critical density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near critical density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strongly time-oscillating electric field accompanying laser-driven collisionless shock in a near critical density plasma...

  4. The microphysics of collisionless shock waves

    DEFF Research Database (Denmark)

    Marcowith, Alexandre; Bret, Antoine; Bykov, Andrei

    2016-01-01

    galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space...... the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights...... in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics....

  5. Parallel collisionless shocks forming in simulations of the LAPD experiment

    Science.gov (United States)

    Weidl, Martin S.; Jenko, Frank; Niemann, Chris; Winske, Dan

    2016-10-01

    Research on parallel collisionless shocks, most prominently occurring in the Earth's bow shock region, has so far been limited to satellite measurements and simulations. However, the formation of collisionless shocks depends on a wide range of parameters and scales, which can be accessed more easily in a laboratory experiment. Using a kJ-class laser, an ongoing experimental campaign at the Large Plasma Device (LAPD) at UCLA is expected to produce the first laboratory measurements of the formation of a parallel collisionless shock. We present hybrid kinetic/MHD simulations that show how beam instabilities in the background plasma can be driven by ablating carbon ions from a target, causing non-linear density oscillations which develop into a propagating shock front. The free-streaming carbon ions can excite both the resonant right-hand instability and the non-resonant firehose mode. We analyze their respective roles and discuss optimizing their growth rates to speed up the process of shock formation.

  6. Study of astrophysical collisionless shocks at NIF

    Science.gov (United States)

    Park, Hye-Sook; Higginson, D. P.; Huntington, C. M.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H.; Ross, J. S.; Ryutov, D. D.; Swadling, G. F.; Wilks, S. C.; Sakawa, Y.; Spitkovsky, A.; Petrasso, R.; Li, C. K.; Zylstra, A. B.; Lamb, D.; Tzeferacos, P.; Gregori, G.; Meinecke, J.; Manuel, M.; Froula, D.; Fiuza, F.

    2016-10-01

    High Mach number astrophysical plasmas can create collisionless shocks via plasma instabilities and turbulence that are responsible for magnetic field generations and cosmic ray acceleration. Recently, many laboratory experiments were successful to observe the Weibel instabilities and self-generated magnetic fields using high-power lasers that generated interpenetrating plasma flows. In order to create a fully formed shock, a series of NIF experiments have begun. The characteristics of flow interaction have been diagnosed by the neutrons and protons generated via beam-beam deuteron interactions, the x-ray emission from the hot plasmas and proton probe generated by imploding DHe3 capsules. This paper will present the latest results from the NIF collisionless shock experiments. Prepared by LLNL under Contract DE-AC52-07NA27344.

  7. The microphysics of collisionless shock waves

    Science.gov (United States)

    Marcowith, A.; Bret, A.; Bykov, A.; Dieckman, M. E.; O'C Drury, L.; Lembège, B.; Lemoine, M.; Morlino, G.; Murphy, G.; Pelletier, G.; Plotnikov, I.; Reville, B.; Riquelme, M.; Sironi, L.; Stockem Novo, A.

    2016-04-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

  8. The microphysics of collisionless shock waves.

    Science.gov (United States)

    Marcowith, A; Bret, A; Bykov, A; Dieckman, M E; Drury, L O'C; Lembège, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem

    2016-04-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

  9. Collisionless shock waves mediated by Weibel Instability

    Science.gov (United States)

    Naseri, Neda; Ruan, Panpan; Zhang, Xi; Khudik, Vladimir; Shvets, Gennady

    2015-11-01

    Relativistic collisionless shocks are common events in astrophysical environments. They are thought to be responsible for generating ultra-high energy particles via the Fermi acceleration mechanism. It has been conjectured that the formation of collisionless shocks is mediated by the Weibel instability that takes place when two initially cold, unmagnetized plasma shells counter-propagate into each other with relativistic drift velocities. Using a PIC code, VLPL, which is modified to suppress numerical Cherenkov instabilities, we study the shock formation and evolution for asymmetric colliding shells with different densities in their own proper reference frame. Plasma instabilities in the region between the shock and the precursor are also investigated using a moving-window simulation that advances the computational domain at the shock's speed. This method helps both to save computation time and avoid severe numerical Cherenkov instabilities, and it allows us to study the shock evolution in a longer time period. Project is supported by US DOE grants DE-FG02-04ER41321 and DE-FG02-07ER54945.

  10. Simulations of Relativistic Collisionless Shocks: Shock Structure and Particle Acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2006-04-10

    We discuss 3D simulations of relativistic collisionless shocks in electron-positron pair plasmas using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the shock's magnetization (''sigma'' parameter). We demonstrate how the structure of the shock varies as a function of sigma for perpendicular shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magnetic fields that can exceed the initial field. At larger magnetizations the shock is dominated by magnetic reflections. We demonstrate where the transition occurs and argue that it is impossible to have very low magnetization collisionless shocks in nature (in more than one spatial dimension). We further discuss the acceleration properties of these shocks, and show that higher magnetization perpendicular shocks do not efficiently accelerate nonthermal particles in 3D. Among other astrophysical applications, this may pose a restriction on the structure and composition of gamma-ray bursts and pulsar wind outflows.

  11. Physics of Collisionless Shocks Space Plasma Shock Waves

    CERN Document Server

    Balogh, André

    2013-01-01

    The present book provides a contemporary systematic treatment of shock waves in high-temperature collisionless plasmas as are encountered in near Earth space and in Astrophysics. It consists of two parts. Part I develops the complete theory of shocks in dilute hot plasmas under the assumption of absence of collisions among the charged particles when the interaction is mediated solely by the self-consistent electromagnetic fields. Such shocks are naturally magnetised implying that the magnetic field plays an important role in their evolution and dynamics. This part treats both subcritical shocks, which dissipate flow energy by generating anomalous resistance or viscosity, and supercritical shocks. The main emphasis is, however, on super-critical shocks where the anomalous dissipation is insufficient to retard the upstream flow. These shocks, depending on the direction of the upstream magnetic field, are distinguished as quasi-perpendicular and quasi-parallel shocks which exhibit different behaviours, reflecti...

  12. Towards a parallel collisionless shock in LAPD

    Science.gov (United States)

    Weidl, M. S.; Heuer, P.; Schaeffer, D.; Dorst, R.; Winske, D.; Constantin, C.; Niemann, C.

    2017-09-01

    Using a high-energy laser to produce a super-Alfvénic carbon-ion beam in a strongly magnetized helium plasma, we expect to be able to observe the formation of a collisionless parallel shock inside the Large Plasma Device. We compare early magnetic-field measurements of the resonant right-hand instability with analytical predictions and find excellent agreement. Hybrid simulations show that the carbon ions couple to the background plasma and compress it, although so far the background ions are mainly accelerated perpendicular to the mean-field direction.

  13. Collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near critical density plasmas

    Science.gov (United States)

    Liu, M.; Weng, S. M.; Li, Y. T.; Yuan, D. W.; Chen, M.; Mulser, P.; Sheng, Z. M.; Murakami, M.; Yu, L. L.; Zheng, X. L.; Zhang, J.

    2016-11-01

    Laser-driven collisionless electrostatic shock formation and the subsequent ion acceleration have been studied in near critical density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near critical density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near critical density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strong time-oscillating electric field accompanying the laser-driven collisionless shock in a near critical density plasma.

  14. Fundamentals of collisionless shocks for astrophysical application, 2. Relativistic shocks

    CERN Document Server

    Bykov, A M

    2011-01-01

    We review recent progress on collisionless relativistic shocks. Kinetic instability theory is briefed including its predictions and limitations. The main focus is on numerical experiments in (i) pair and (ii) electron-nucleon plasmas. The main results are: (i) confirmation of shock evolution in non-magnetised relativistic plasma in 3D due to either the lepton-Weibel instability or the ion-Weibel instability; (ii) sensitive dependence on upstream magnetisation ; (iii) the sensitive dependence of particle dynamics on the upstream magnetic inclination angle $\\thetabn$, where particles of $\\thetabn>34^\\circ$ cannot escape upstream, leading to the distinction between `sub-luminal' and `super-luminal' shocks; (iv) particles in ultra-relativistic shocks can hardly overturn the shock and escape to upstream; they may oscillate around the shock ramp for a long time, so to speak `surfing it' and thereby becoming accelerated by a kind of SDA; (v) these particles form a power law tail on the downstream distribution; their...

  15. Collisionless Weibel shocks: Full formation mechanism and timing

    Energy Technology Data Exchange (ETDEWEB)

    Bret, A. [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain); Stockem, A. [GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal); Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum (Germany); Narayan, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51 Cambridge, Massachusetts 02138 (United States); Silva, L. O. [GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal)

    2014-07-15

    Collisionless shocks in plasmas play an important role in space physics (Earth's bow shock) and astrophysics (supernova remnants, relativistic jets, gamma-ray bursts, high energy cosmic rays). While the formation of a fluid shock through the steepening of a large amplitude sound wave has been understood for long, there is currently no detailed picture of the mechanism responsible for the formation of a collisionless shock. We unravel the physical mechanism at work and show that an electromagnetic Weibel shock always forms when two relativistic collisionless, initially unmagnetized, plasma shells encounter. The predicted shock formation time is in good agreement with 2D and 3D particle-in-cell simulations of counterstreaming pair plasmas. By predicting the shock formation time, experimental setups aiming at producing such shocks can be optimised to favourable conditions.

  16. Formation and evolution of a pair of collisionless shocks in counter-streaming flows

    Science.gov (United States)

    Yuan, Dawei; Li, Yutong; Liu, Meng; Zhong, Jiayong; Zhu, Baojun; Li, Yanfei; Wei, Huigang; Han, Bo; Pei, Xiaoxing; Zhao, Jiarui; Li, Fang; Zhang, Zhe; Liang, Guiyun; Wang, Feilu; Weng, Suming; Li, Yingjun; Jiang, Shaoen; Du, Kai; Ding, Yongkun; Zhu, Baoqiang; Zhu, Jianqiang; Zhao, Gang; Zhang, Jie

    2017-01-01

    A pair of collisionless shocks that propagate in the opposite directions are firstly observed in the interactions of laser-produced counter-streaming flows. The flows are generated by irradiating a pair of opposing copper foils with eight laser beams at the Shenguang-II (SG-II) laser facility. The experimental results indicate that the excited shocks are collisionless and electrostatic, in good agreement with the theoretical model of electrostatic shock. The particle-in-cell (PIC) simulations verify that a strong electrostatic field growing from the interaction region contributes to the shocks formation. The evolution is driven by the thermal pressure gradient between the upstream and the downstream. Theoretical analysis indicates that the strength of the shocks is enhanced with the decreasing density ratio during both flows interpenetration. The positive feedback can offset the shock decay process. This is probable the main reason why the electrostatic shocks can keep stable for a longer time in our experiment. PMID:28266497

  17. Magnetic field amplification by collisionless shocks in partially ionized plasmas

    CERN Document Server

    Ohira, Yutaka

    2015-01-01

    In this paper, we study shock structures of collisionless shocks in partially ionized plasmas by means of two-dimensional hybrid simulations, where the shock is a perpendicular shock with shock velocity Vsh ~ 40 Va ~ 1333 km/s and the upstream ionization fraction is 0.5. We find that large density fluctuations and large magnetic fields fluctuations are generated both in the upstream and downstream regions. In addition, we find that the velocity distribution of downstream hydrogen atoms has three components. Observed shock structures suggest that diffusive shock acceleration can operate at perpendicular shocks propagating into partially ionized plasmas in real three-dimensional systems.

  18. Kelvin-Helmholtz turbulence associated with collisionless shocks in laser produced plasmas.

    Science.gov (United States)

    Kuramitsu, Y; Sakawa, Y; Dono, S; Gregory, C D; Pikuz, S A; Loupias, B; Koenig, M; Waugh, J N; Woolsey, N; Morita, T; Moritaka, T; Sano, T; Matsumoto, Y; Mizuta, A; Ohnishi, N; Takabe, H

    2012-05-11

    We report the experimental results of a turbulent electric field driven by Kelvin-Helmholtz instability associated with laser produced collisionless shock waves. By irradiating an aluminum double plane target with a high-power laser, counterstreaming plasma flows are generated. As the consequence of the two plasma interactions, two shock waves and the contact surface are excited. The shock electric field and transverse modulation of the contact surface are observed by proton radiography. Performing hydrodynamic simulations, we reproduce the time evolutions of the reverse shocks and the transverse modulation driven by Kelvin-Helmholtz instability.

  19. Laboratory astrophysical collisionless shock experiments on Omega and NIF

    Science.gov (United States)

    Park, Hye-Sook; Ross, J. S.; Huntington, C. M.; Fiuza, F.; Ryutov, D.; Casey, D.; Drake, R. P.; Fiksel, G.; Froula, D.; Gregori, G.; Kugland, N. L.; Kuranz, C.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R.; Plechaty, C.; Remington, B.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Zylstra, A. B.

    2016-03-01

    We are performing scaled astrophysics experiments on Omega and on NIF. Laser driven counter-streaming interpenetrating supersonic plasma flows can be studied to understand astrophysical electromagnetic plasma phenomena in a controlled laboratory setting. In our Omega experiments, the counter-streaming flow plasma state is measured using Thomson scattering diagnostics, demonstrating the plasma flows are indeed super-sonic and in the collisionless regime. We observe a surprising additional electron and ion heating from ion drag force in the double flow experiments that are attributed to the ion drag force and electrostatic instabilities. [1] A proton probe is used to image the electric and magnetic fields. We observe unexpected large, stable and reproducible electromagnetic field structures that arise in the counter-streaming flows [2]. The Biermann battery magnetic field generated near the target plane, advected along the flows, and recompressed near the midplane explains the cause of such self-organizing field structures [3]. A D3He implosion proton probe image showed very clear filamentary structures; three-dimensional Particle-In-Cell simulations and simulated proton radiography images indicate that these filamentary structures are generated by Weibel instabilities and that the magnetization level (ratio of magnetic energy over kinetic energy in the system) is ∼0.01 [4]. These findings have very high astrophysical relevance and significant implications. We expect to observe true collisionless shock formation when we use >100 kJ laser energy on NIF.

  20. High-power laser experiments to study collisionless shock generation

    Science.gov (United States)

    Sakawa, Y.; Kuramitsu, Y.; Morita, T.; Kato, T.; Tanji, H.; Ide, T.; Nishio, K.; Kuwada, M.; Tsubouchi, T.; Ide, H.; Norimatsu, T.; Gregory, C.; Woolsey, N.; Schaar, K.; Murphy, C.; Gregori, G.; Diziere, A.; Pelka, A.; Koenig, M.; Wang, S.; Dong, Q.; Li, Y.; Park, H.-S.; Ross, S.; Kugland, N.; Ryutov, D.; Remington, B.; Spitkovsky, A.; Froula, D.; Takabe, H.

    2013-11-01

    A collisionless Weibel-instability mediated shock in a self-generated magnetic field is studied using two-dimensional particle-in-cell simulation [Kato and Takabe, Astophys. J. Lett. 681, L93 (2008)]. It is predicted that the generation of the Weibel shock requires to use NIF-class high-power laser system. Collisionless electrostatic shocks are produced in counter-streaming plasmas using Gekko XII laser system [Kuramitsu et al., Phys. Rev. Lett. 106, 175002 (2011)]. A NIF facility time proposal is approved to study the formation of the collisionless Weibel shock. OMEGA and OMEGA EP experiments have been started to study the plasma conditions of counter-streaming plasmas required for the NIF experiment using Thomson scattering and to develop proton radiography diagnostics.

  1. High-power laser experiments to study collisionless shock generation

    Directory of Open Access Journals (Sweden)

    Sakawa Y.

    2013-11-01

    Full Text Available A collisionless Weibel-instability mediated shock in a self-generated magnetic field is studied using two-dimensional particle-in-cell simulation [Kato and Takabe, Astophys. J. Lett. 681, L93 (2008]. It is predicted that the generation of the Weibel shock requires to use NIF-class high-power laser system. Collisionless electrostatic shocks are produced in counter-streaming plasmas using Gekko XII laser system [Kuramitsu et al., Phys. Rev. Lett. 106, 175002 (2011]. A NIF facility time proposal is approved to study the formation of the collisionless Weibel shock. OMEGA and OMEGA EP experiments have been started to study the plasma conditions of counter-streaming plasmas required for the NIF experiment using Thomson scattering and to develop proton radiography diagnostics.

  2. On the generation of magnetized collisionless shocks in the large plasma device

    Science.gov (United States)

    Schaeffer, D. B.; Winske, D.; Larson, D. J.; Cowee, M. M.; Constantin, C. G.; Bondarenko, A. S.; Clark, S. E.; Niemann, C.

    2017-04-01

    Collisionless shocks are common phenomena in space and astrophysical systems, and in many cases, the shocks can be modeled as the result of the expansion of a magnetic piston though a magnetized ambient plasma. Only recently, however, have laser facilities and diagnostic capabilities evolved sufficiently to allow the detailed study in the laboratory of the microphysics of piston-driven shocks. We review experiments on collisionless shocks driven by a laser-produced magnetic piston undertaken with the Phoenix laser laboratory and the Large Plasma Device at the University of California, Los Angeles. The experiments span a large parameter space in laser energy, background magnetic field, and ambient plasma properties that allow us to probe the physics of piston-ambient energy coupling, the launching of magnetosonic solitons, and the formation of subcritical shocks. The results indicate that piston-driven magnetized collisionless shocks in the laboratory can be characterized with a small set of dimensionless formation parameters that place the formation process in an organized and predictive framework.

  3. Scaled Laboratory Collisionless Shock Experiments in the Large Plasma Device

    Science.gov (United States)

    Clark, S. E.; Schaeffer, D.; Everson, E.; Bondarenko, A.; Winske, D.; Constantin, C.; Niemann, C.

    2013-12-01

    Collisionless shocks in space plasmas have been investigated since the fifties and are typically studied via in-situ satellite observations, which are limited due to the large structure of collisionless shocks in space environments relative to the satellite observation platform. Scaled, repeatable experiments in the Large Plasma Device (LAPD) at UCLA provide a test bed for studying collisionless shocks in the laboratory, where questions of ion and electron heating and acceleration can be addressed and examined in detail. The experiments are performed by ablating a graphite or plastic target using the Raptor kilojoule-class laser facility at UCLA. The laser provides an on-target energy in the range of 100-500 J that drives a super-Alfvénic (MA > 1) debris plasma across a background magnetic field (200-800 G) into the ambient, magnetized LAPD plasma. Typical plasma parameters in the LAPD consist of a H+ or He+ ambient plasma with a core column (diameter > 20 cm ) density ni ~ 1013 cm-3 and electron temperature Te ~ 10 eV embedded in a larger plasma discharge (diameter ~ 80 cm) of density ni ~ 1012 cm-3 and Te ~ 5 eV. The ambient ion temperature is Ti ~ 1 eV. Experimental results from the latest collisionless shock campaign will be presented and compared with two dimensional hybrid simulations of the experiment. Fielded diagnostics include Thomson scattering, ion spectroscopy, magnetic flux probes, Langmuir probes, and microwave reflectometry.

  4. Partical acceleration at collisionless shock fronts; Teilchenbeschleunigung an kollisionsfreien Schockfronten

    Energy Technology Data Exchange (ETDEWEB)

    Kilian, Patrick

    2015-09-14

    The magnetic field of the sun is not a simple static dipole field but comprises much more complicated structures. When magnetic reconnection changes the topology of a structure the large amount of energy that was stored in the magnetic field is released and can eject the remainder of the magnetic structure and the plasma that is frozen to the magnetic field lines from the solar corona at large velocities. This event is called a coronal mass ejection (CME). Given that the upward motion happens at velocities larger than the local Alfven speed, the critical speed in the solar wind, the CME will act as a piston that drives a shock front through the solar wind ahead of itself. Satellites that monitor solar wind conditions detect an enhanced flux of high energy particles associated with the shock front. Radio instruments typically pick up bursts of electromagnetic emission, termed radio bursts, that are also consistent with processes driven by energetic particles. Thus, and due to theoretical considerations, it is safe to assume that particles can be accelerated at the shock front. Particle acceleration at collisionless shock fronts is an interesting topic for another reason. Earth is constantly bombarded by very energetic particles called (due to historical reasons) cosmic rays. The leading theory for the production of at least the fraction of cosmic rays that originate in our galaxy is acceleration at shock fronts, e.g. in super nova remnants. The large distance and consequently limited observation of these shock fronts restrict more detailed investigations. It is therefore useful to study the process of shock acceleration at shocks in the solar system that are much closer and more approachable to develop and test models and simulation methods that can be applied in different regimes. This dissertation aims at simulations of shock fronts with parameters that are close to the ones occurring in CME driven shocks. Since the goal is the investigation of the changing

  5. Magnetic field evolution in relativistic unmagnetized collisionless shocks

    CERN Document Server

    Keshet, Uri; Spitkovsky, Anatoly; Waxman, Eli

    2008-01-01

    We study relativistic unmagnetized collisionless shocks using unprecedentedly large particle-in-cell simulations of two-dimensional pair plasma. High energy particles accelerated by the shock are found to drive magnetic field evolution on a time scale >10^4 plasma times. Progressively stronger magnetic fields are generated on larger scales in a growing region around the shock. Shock-generated magnetic fields and accelerated particles carry >1% and >10% of the downstream energy flux respectively. Our results suggest limits on the magnetization of relativistic astrophysical flows.

  6. Collisionless ion dynamics in the shock front

    Science.gov (United States)

    Gedalin, Michael

    2016-07-01

    In the vicinity of the shock front the dynamics of ions is governed by the macroscopic regular electric and magnetic field of the shock. Upon crossing the shock the thermal ions form a non-gyrotropic distribution. The pressure of these non-gyrotropic ions shapes the downstream magnetic field. High-energy ions behave in the shock front as test particles under the influence on the macroscopic fields. The reflection and transmission coefficients of high-energy ions at an oblique shock front is not sensitive to the shock structure and depends only on the global magnetic field change at the shock.

  7. Ion Injection at Non-relativistic Collisionless Shocks

    CERN Document Server

    Caprioli, Damiano; Spitkovsky, Anatoly

    2014-01-01

    We use kinetic hybrid simulations (kinetic ions - fluid electrons) to characterize the fraction of ions that are accelerated to non-thermal energies at non-relativistic collisionless shocks. We investigate the properties of the shock discontinuity and show that shocks propagating almost along the background magnetic field (quasi-parallel shocks) reform quasi-periodically on ion cyclotron scales. Ions that impinge on the shock when the discontinuity is the steepest are specularly reflected. This is a necessary condition for being injected, but it is not sufficient. Also by following the trajectories of reflected ions, we calculate the minimum energy needed for injection into diffusive shock acceleration, as a function of the shock inclination. We construct a minimal model that accounts for the ion reflection from quasi-periodic shock barrier, for the fraction of injected ions, and for the ion spectrum throughout the transition from thermal to non-thermal energies. This model captures the physics relevant for i...

  8. Collisionless shocks in space plasmas structure and accelerated particles

    CERN Document Server

    Burgess, David

    2015-01-01

    Shock waves are an important feature of solar system plasmas, from the solar corona out to the edge of the heliosphere. This engaging introduction to collisionless shocks in space plasmas presents a comprehensive review of the physics governing different types of shocks and processes of particle acceleration, from fundamental principles to current research. Motivated by observations of planetary bow shocks, interplanetary shocks and the solar wind termination shock, it emphasises the physical theory underlying these shock waves. Readers will develop an understanding of the complex interplay between particle dynamics and the electric and magnetic fields that explains the observations of in situ spacecraft. Written by renowned experts in the field, this up-to-date text is the ideal companion for both graduate students new to heliospheric physics and researchers in astrophysics who wish to apply the lessons of solar system shocks to different astrophysical environments.

  9. Visualizing electromagnetic fields in laser-produced counter-streaming plasma experiments for collisionless shock laboratory astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Kugland, N. L.; Ross, J. S.; Glenzer, S. H.; Huntington, C.; Martinez, D.; Plechaty, C.; Remington, B. A.; Ryutov, D. D.; Park, H.-S. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States); Chang, P.-Y.; Fiksel, G.; Froula, D. H. [Laboratory for Laser Energetics, University of Rochester, 250 E. River Road, Rochester, New York 14636 (United States); Drake, R. P.; Grosskopf, M.; Kuranz, C. [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Gregori, G.; Meinecke, J.; Reville, B. [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Koenig, M.; Pelka, A. [Laboratoire pour l' Utilisation des Lasers Intenses (LULI), École Polytechnique-Univ, Paris VI, 91128 Palaiseau (France); and others

    2013-05-15

    Collisionless shocks are often observed in fast-moving astrophysical plasmas, formed by non-classical viscosity that is believed to originate from collective electromagnetic fields driven by kinetic plasma instabilities. However, the development of small-scale plasma processes into large-scale structures, such as a collisionless shock, is not well understood. It is also unknown to what extent collisionless shocks contain macroscopic fields with a long coherence length. For these reasons, it is valuable to explore collisionless shock formation, including the growth and self-organization of fields, in laboratory plasmas. The experimental results presented here show at a glance with proton imaging how macroscopic fields can emerge from a system of supersonic counter-streaming plasmas produced at the OMEGA EP laser. Interpretation of these results, plans for additional measurements, and the difficulty of achieving truly collisionless conditions are discussed. Future experiments at the National Ignition Facility are expected to create fully formed collisionless shocks in plasmas with no pre-imposed magnetic field.

  10. Collisionless shock formation, spontaneous electromagnetic fluctuations and streaming instabilities

    CERN Document Server

    Bret, A; Fiuza, F; Ruyer, C; Gremillet, L; Narayan, R; Silva, L O

    2013-01-01

    Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic PIC simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.

  11. Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities

    Energy Technology Data Exchange (ETDEWEB)

    Bret, A. [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Instituto de Investigaciones Energeticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain); Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51 Cambridge, Massachusetts 02138 (United States); Stockem, A.; Fiuza, F.; Silva, L. O. [GoLP/Instituto de Plasmas e Fusao Nuclear-Laboratorio Associado, Instituto Superior Tecnico, Lisboa (Portugal); Ruyer, C.; Gremillet, L. [CEA, DAM, DIF F-91297 Arpajon (France); Narayan, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51 Cambridge, Massachusetts 02138 (United States)

    2013-04-15

    Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.

  12. Particle Acceleration in Relativistic Magnetized Collisionless Electron-Ion Shocks

    CERN Document Server

    Sironi, Lorenzo

    2010-01-01

    We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5D particle-in-cell simulations with ion-to-electron mass ratios (m_i/m_e) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In "subluminal" shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via a Fermi-like mechanism. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains ~5% of ions and ~30% of ion energy. Its slope is -2.1. Upstream electrons enter the shock with lower energy than ions, so they are more strongly tied to the field. As a result, only ~1% of the incoming electrons are Fermi-accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5). For "superluminal" shocks, where relativistic particles ca...

  13. Weibel-instability-mediated collisionless shocks in laboratory with ultraintense lasers

    CERN Document Server

    Fiuza, F; Tonge, J; Mori, W B; Silva, L O

    2012-01-01

    The formation of non-relativistic collisionless shocks in laboratory with ultrahigh intensity lasers is studied via \\emph{ab initio} multi-dimensional particle-in-cell simulations. The microphysics behind shock formation and dissipation, and the detailed shock structure are analyzed, illustrating that the Weibel instability plays a crucial role in the generation of strong subequipartition magnetic fields that isotropize the incoming flow and lead to the formation of a collisionless shock, similarly to what occurs in astrophysical scenarios. The possibility of generating such collisionless shocks in laboratory opens the way to the direct study of the physics associated with astrophysical shocks.

  14. Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks

    Energy Technology Data Exchange (ETDEWEB)

    Medvedev, Mikhail M.

    2008-08-31

    This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general.

  15. Collisionless shock experiments with lasers and observation of Weibel instabilities

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.-S., E-mail: park1@llnl.gov; Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Drake, R. P.; Kuranz, C. C. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Froula, D. H.; Rosenberg, M. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14636 (United States); Gregori, G.; Meinecke, J. [University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Koenig, M. [LULI, Ecole Polytechnique, Palaiseau (France); Kugland, N. L. [Lam Research Corporation, Fremont, California 94538 (United States); Lamb, D. Q.; Tzeferacos, P. [University of Chicago, Chicago, California 94538 (United States); and others

    2015-05-15

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  16. Cross-scale coupling at a perpendicular collisionless shock

    CERN Document Server

    Umeda, Takayuki; Yamazaki, Ryo; 10.1016/j.pss.2010.01.007

    2011-01-01

    A full particle simulation study is carried out on a perpendicular collisionless shock with a relatively low Alfven Mach number (M_A=5). In the present study, we have performed a two-dimensional (2D) electromagnetic full particle simulation with a "shock-rest-frame model". The simulation domain is taken to be larger than the ion inertial length in order to include full kinetics of both electrons and ions. The present simulation result has confirmed the transition of shock structures from the cyclic self-reformation to the quasi-stationary shock front. During the transition, electrons and ions are thermalized in the direction parallel to the shock magnetic field. Ions are thermalized by low-frequency electromagnetic waves (or rippled structures) excited by strong ion temperature anisotropy at the shock foot, while electrons are thermalized by high-frequency electromagnetic waves (or whistler mode waves) excited by electron temperature anisotropy at the shock overshoot. Ion acoustic waves are also excited at th...

  17. Final report for the NSF/DOE partnership in basic plasma science grant DE-FG02-06ER54906 'Laser-driven collisionless shocks in the Large Plasma Device'

    Energy Technology Data Exchange (ETDEWEB)

    Niemann, Christoph [UCLA, CA (United States); Gekelman, W. [UCLA, CA (United States); Winske, D. [LANL, NM (United States); Larsen, D. [LLNL, CA (United States)

    2012-12-14

    We have performed several thousand high-energy laser shots in the LAPD to investigate the dynamics of an exploding laser-produced plasma in a large ambient magneto-plasma. Debris-ions expanding at super-Alfvenic velocity (up to MA=1.5) expel the ambient magnetic field, creating a large (> 20 cm) diamagnetic cavity. We observed field compressions of up to B/B{sub 0} = 1.5 at the edge of the bubble, consistent with the MHD jump conditions, as well as localized electron heating at the edge of the bubble. Two-dimensional hybrid simulations reproduce these measurements well and show that the majority of the ambient ions are energized by the magnetic piston to super-Alfvenic speeds and swept outside the bubble volume. Nonlinear shear-Alfven waves ({delta}B/B{sub 0} > 25%) are radiated from the cavity with a coupling efficiency of 70% from magnetic energy in the bubble to the wave. While the data is consistent with a weak magneto-sonic shock, the experiments were severely limited by the low ambient plasma densities (10{sup 12} cm{sup -3}). 2D hybrid simulations indicate that future experiments with the new LAPD plasma source and densities in excess of 10{sup 13} cm{sup -3} will drive full-blown collisionless shocks with MA>10 over several c/wpi and shocked Larmor radii. In a separate experiment at the LANL Trident laser facility we have performed a proof-of-principle experiment at higher densities to demonstrate key elements of collisionless shocks in laser-produced magnetized plasmas with important implications to NIF. Simultaneously we have upgraded the UCLA glass-laser system by adding two large amplitude disk amplifiers from the NOVA laser and boost the on-target energy from 30 J to up to 1 kJ, making this one of the world’s largest university-scale laser systems. We now have the infrastructure in place to perform novel and unique high-impact experiments on collision-less shocks at the LAPD.

  18. Neutron Generation Simulations of Collisionless Shock Experiments on NIF

    Science.gov (United States)

    Wilks, S. C.; Higginson, D. P.; Weber, S. V.; Ryutov, D. D.; Ross, J. S.; Park, H.-S.; Fiuza, F.

    2015-11-01

    A series of simulations that model recent collisionless shock experiments at the NIF will be presented. In these experiments, two opposing CD plasmas flow into each other, both plasmas arising from lasers hitting planar CD targets separated by 6, 8, and 10mm. Where the plasma flows overlap, a symmetric peak of neutron generation was observed about the mid-plane. When one of the CD foils was replaced by CH, neutron generation was still observed, but with an asymmetry about the mid-plane. The hybrid PIC code LSP is used to model this interaction. Neutron yields, temporal profiles and burn widths obtained from simulation compare favorably with experimental measurements from NTOF and PTOF diagnostics. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-675193.

  19. On the electron-ion temperature ratio established by collisionless shocks

    CERN Document Server

    Vink, Jacco; Bykov, Andrei; Gabici, Stefano

    2014-01-01

    Astrophysical shocks are often collisionless shocks, in which the changes in plasma flow and temper- atures across the shock are established not through Coulomb interactions, but through electric and mag- netic fields. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature (non-equilibration of temperatures), or whether they quickly equilibrate in the shock region. Here we provide a simple relation for the minimal amount of equilibration to expect. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all parti- cle species should undergo the same density jump across the the shock, in order for the plasma to remain charge neutral. This assumption results in an analytic treatment of electron-ion equilibration that agrees with observations of collisionless shocks: at low Mach numbers < 2 the electrons and ions are close to equilibration, whereas for Mach numbers above M ~ 60 the electron-ion tempera...

  20. Microstructure in two- and three-dimensional hybrid simulations of perpendicular collisionless shocks

    CERN Document Server

    Burgess, David; Gingell, Peter W; Trávníček, Pavel M

    2016-01-01

    Supercritical collisionless perpendicular shocks have an average macrostructure determined primarily by the dynamics of ions specularly reflected at the magnetic ramp. Within the overall macrostructure, instabilities, both linear and nonlinear, generate fluctuations and microstructure. To identify the sources of such microstructure, high-resolution two- and three-dimensional simulations have been carried out using the hybrid method, wherein the ions are treated as particles and the electron response is modelled as a massless fluid. We confirm the results of earlier 2-D simulations showing both field-parallel aligned propagating fluctuations and fluctuations carried by the reflected-gyrating ions. In addition, it is shown that, for 2-D simulations of the shock coplanarity plane, the presence of short-wavelength fluctuations in all magnetic components is associated with the ion Weibel instability driven at the upstream edge of the foot by the reflected-gyrating ions. In 3-D simulations we show for the first tim...

  1. Electron force balance in steady collisionless-driven reconnection.

    Science.gov (United States)

    Li, Bin; Horiuchi, Ritoku

    2008-11-21

    Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfvén velocity averaged over the electron dissipation region.

  2. Studying astrophysical collisionless shocks with counterstreaming plasmas from high power lasers

    Science.gov (United States)

    Park, Hye-Sook; Ryutov, D. D.; Ross, J. S.; Kugland, N. L.; Glenzer, S. H.; Plechaty, C.; Pollaine, S. M.; Remington, B. A.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C.; Sakawa, Y.; Kuramitsu, Y.; Morita, T.; Takabe, H.; Froula, D. H.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Pelka, A.; Liang, E.; Woolsey, N.; Kuranz, C. C.; Drake, R. P.; Grosskopf, M. J.

    2012-03-01

    Collisions of high Mach number flows occur frequently in astrophysics, and the resulting shock waves are responsible for the properties of many astrophysical phenomena, such as supernova remnants, Gamma Ray Bursts and jets from Active Galactic Nuclei. Because of the low density of astrophysical plasmas, the mean free path due to Coulomb collisions is typically very large. Therefore, most shock waves in astrophysics are "collisionless", since they form due to plasma instabilities and self-generated magnetic fields. Laboratory experiments at the laser facilities can achieve the conditions necessary for the formation of collisionless shocks, and will provide a unique avenue for studying the nonlinear physics of collisionless shock waves. We are performing a series of experiments at the Omega and Omega-EP lasers, in Rochester, NY, with the goal of generating collisionless shock conditions by the collision of two high-speed plasma flows resulting from laser ablation of solid targets using ˜1016 W/cm2 laser irradiation. The experiments will aim to answer several questions of relevance to collisionless shock physics: the importance of the electromagnetic filamentation (Weibel) instabilities in shock formation, the self-generation of magnetic fields in shocks, the influence of external magnetic fields on shock formation, and the signatures of particle acceleration in shocks. Our first experiments using Thomson scattering diagnostics studied the plasma state from a single foil and from double foils whose flows collide "head-on". Our data showed that the flow velocity and electron density were 108 cm/s and 1019 cm-3, respectively, where the Coulomb mean free path is much larger than the size of the interaction region. Simulations of our experimental conditions show that weak Weibel mediated current filamentation and magnetic field generation were likely starting to occur. This paper presents the results from these first Omega experiments.

  3. Microstructure in two- and three-dimensional hybrid simulations of perpendicular collisionless shocks

    Science.gov (United States)

    Burgess, David; Hellinger, Petr; Gingell, Imogen; Trávníček, Pavel M.

    2016-08-01

    Supercritical collisionless perpendicular shocks have an average macrostructure determined primarily by the dynamics of ions specularly reflected at the magnetic ramp. Within the overall macrostructure, instabilities, both linear and nonlinear, generate fluctuations and microstructure. To identify the sources of such microstructure, high-resolution two- and three-dimensional simulations have been carried out using the hybrid method, wherein the ions are treated as particles and the electron response is modelled as a massless fluid. We confirm the results of earlier two-dimensional (2-D) simulations showing both field-parallel aligned propagating fluctuations and fluctuations carried by the reflected-gyrating ions. In addition, it is shown that, for 2-D simulations of the shock coplanarity plane, the presence of short-wavelength fluctuations in all magnetic components is associated with the ion Weibel instability driven at the upstream edge of the foot by the reflected-gyrating ions. In 3-D simulations we show for the first time that the dominant microstructure is due to a coupling between field-parallel propagating fluctuations in the ramp and the motion of the reflected ions. This results in a pattern of fluctuations counter-propagating across the surface of the shock at an angle inclined to the magnetic field direction, due to a combination of field-parallel motion at the Alfvén speed of the ramp and motion in the sense of gyration of the reflected ions.

  4. Acoustic instability in the neutral precursor region of collisionless shocks propagating into partially ionized plasmas

    CERN Document Server

    Ohira, Yutaka

    2014-01-01

    Recent studies about collisionless shocks in partially ionized plasmas showed that some of neutral particles leak into the shock upstream region from the downstream region. In this paper, we perform a linear analysis and show that acoustic waves are unstable in the neutral precursor region. The acoustic instability amplifies fluctuations of magnetic field and density in the upstream region. The fluctuations are indispensable for the diffusive shock acceleration and could be important for the downstream turbulence.

  5. Collisionless Shocks and TeV Neutrinos before Supernova Shock Breakout from an Optically Thick Wind

    CERN Document Server

    Giacinti, G

    2015-01-01

    During a supernova explosion, a radiation-dominated shock (RDS) travels through its progenitor. A collisionless shock (CS) is usually assumed to replace it during shock breakout (SB). We demonstrate here that for some realistic progenitors enshrouded in optically thick winds, such as possibly SN 2008D, a CS forms deep inside the wind, soon after the RDS leaves the core, and therefore significantly before SB. The RDS does not survive the transition from the core to the thick wind when the wind close to the core is not sufficiently dense to compensate for the $r^{-2}$ dilution of photons due to shock curvature. This typically happens when the shock velocity is $\\lesssim 0.1 {\\rm c} \\, (\\frac{u_{\\rm w}}{10\\,{\\rm km/s}}) (\\frac{\\dot{M}}{5 \\cdot 10^{-4} \\, {\\rm M}_\\odot {\\rm /yr}})^{-1} (\\frac{r_\\ast}{10^{13}\\,{\\rm cm}})$, where $u_{\\rm w}$, $\\dot{M}$ and $r_\\ast$ are respectively the wind velocity, mass-loss rate and radius of the progenitor star. The radiative CS results in a hard spectrum of the photon flash at...

  6. Density filament and helical field line structures in three dimensional Weibel-mediated collisionless shocks

    Science.gov (United States)

    Moritaka, Toseo; Sakawa, Youichi; Kuramitsu, Yasuhiro; Morita, Taichi; Yamaura, Yuta; Ishikawa, Taishi; Takabe, Hideaki

    2016-03-01

    Collisionless shocks mediated by Weibel instability are attracting attention for their relevance to experimental demonstrations of astrophysical shocks in high-intensity laser facilities. The three dimensional structure of Weibel-mediated shocks is investigated through a fully kinetic particle-in-cell simulation. The structures obtained are characterized by the following features: (i) helical magnetic field lines elongated in the direction upstream of the shock region, (ii) high and low density filaments inside the helical field lines. These structures originate from the interaction between counter-streaming plasma flow and magnetic vortexes caused by Weibel instability, and potentially affect the shock formation mechanism.

  7. Simulation of Experiments Generating Collisionless Shocks With Intense Lasers Using the CRASH Code

    Science.gov (United States)

    Grosskopf, M. J.; Drake, R. P.; Kuranz, C. C.; Rutter, E. M.; Park, H. S.; Kugland, N. L.; Pollaine, S.; Ross, J. S.; Remington, B. A.; Ryutov, D.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C.; Sakawa, Y.; Kuramitsu, Y.; Takabe, H.; Froula, D. H.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Liang, E.; Woosley, N.

    2011-10-01

    Collisionless shocks, shocks generated by plasma wave interactions in regions where the collisional mean-free-path for particles is long compared to the length scale for shock interaction, are found ubiquitously in astrophysics. Experiments to investigate collisionless shocks in a laboratory-scale system are being carried out on intense lasers; measuring the density, temperature, magnetic field, and velocity of counter-streaming flows generated by laser ablation. This poster reports hydrodynamic simulations modeling the ablative flow of plasma generated in order to assess potential designs and infer properties of collected data from previous single foil experiments. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52-08NA28616.

  8. The properties and causes of rippling in quasi-perpendicular collisionless shock fronts

    Directory of Open Access Journals (Sweden)

    R. E. Lowe

    Full Text Available The overall structure of quasi-perpendicular, high Mach number collisionless shocks is controlled to a large extent by ion reflection at the shock ramp. Departure from a strictly one-dimensional structure is indicated by simulation results showing that the surface of such shocks is rippled, with variations in the density and all field components. We present a detailed analysis of these shock ripples, using results from a two-dimensional hybrid (particle ions, electron fluid simulation. The process that generates the ripples is poorly understood, because the large gradients at the shock ramp make it difficult to identify instabilities. Our analysis reveals new features of the shock ripples, which suggest the presence of a surface wave mode dominating the shock normal magnetic field component of the ripples, as well as whistler waves excited by reflected ions.

    Key words. Space plasma physics (numerical simulation studies; shock waves; waves and instabilities

  9. Density bump formation in a collisionless electrostatic shock wave in a laser-ablated plasma

    CERN Document Server

    Garasev, M A; Kocharovsky, V V; Malkov, Yu A; Murzanev, A A; Nechaev, A A; Stepanov, A N

    2016-01-01

    The emergence of a density bump at the front of a collisionless electrostatic shock wave have been observed experimentally during the ablation of an aluminium foil by a femtosecond laser pulse. We have performed numerical simulations of the dynamics of this phenomena developing alongside the generation of a package of ion-acoustic waves, exposed to a continual flow of energetic electrons, in a collisionless plasma. We present the physical interpretation of the observed effects and show that the bump consists of transit particles, namely, the accelerated ions from the dense plasma layer, and the ions from the diluted background plasma, formed by a nanosecond laser prepulse during the ablation.

  10. Weibel instability-mediated collisionless shocks in laser-irradiated dense plasmas:Prevailing role of the electrons in the turbulence generation

    CERN Document Server

    Ruyer, C; Bonnaud, G

    2015-01-01

    We present a particle-in-cell simulation of the generation of a collisionless turbulent shock in a dense plasma driven by an ultra-high-intensity laser pulse. From the linear analysis, we highlight the crucial role of the laser-heated and return-current electrons in triggering a strong Weibel-like instability, giving rise to a magnetic turbulence able to isotropize the target ions.

  11. The Link Between Shocks, Turbulence, and Magnetic Reconnection in Collisionless Plasmas

    Science.gov (United States)

    Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.

    2014-01-01

    Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, 'stir' the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space, and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.

  12. Ultra-intense laser-plasma interaction toward Weibel-mediated collisionless shocks formation

    Science.gov (United States)

    Grassi, Anna; Grech, M.; Amiranoff, F.; Macchi, A.; Riconda, C.

    2016-10-01

    The rapid developments in laser technology will soon offer the opportunity to study in the laboratory the processes driving Weibel-mediated collisionless shocks, typical of various astrophysical scenarii. The interaction of an ultra-intense laser with an overdense plasma has been identified as the preferential configuration. Yet, the experimental requirements still need to be properly investigated. High performance computing simulations are a necessary tool for this study. In this work, we present a series of kinetic simulations performed with the PIC code SMILEI, varying the laser and plasma parameters. In particular, we will study the effect of the laser polarisation and plasma density to obtain the best conditions for the creation of a collisionless shock. The role of the electrons heated at the interaction surface and of particles accelerated via the Hole Boring (laser-piston) mechanism on the generation of the current filamentation instability and the subsequent shock front formation will be highlighted.

  13. The Maximum Energy of Accelerated Particles in Relativistic Collisionless Shocks

    CERN Document Server

    Sironi, Lorenzo; Arons, Jonathan

    2013-01-01

    The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from electrons accelerated at the GRB external shock, that propagates with relativistic velocities into the magnetized interstellar medium. By means of multi-dimensional particle-in-cell simulations, we investigate the acceleration performance of weakly magnetized relativistic shocks, in the magnetization range 0shock magnetic field is orthogonal to the flow, as generically expected for relativistic shocks. We find that relativistic perpendicular shocks propagating in electron-positron plasmas are efficient particle accelerators if the magnetization is sigma<1e-3. For electron-ion plasmas, the transition to efficient acceleration occurs for sigma<3e-5. Here, the acceleration process proceeds similarly for the two species, since the electrons enter the shock nearly in equipartition with the ions, as a result of strong pre-heating in the self-generated upstream turbulence. In both...

  14. Role of Magnetosonic Solitons in Perpendicular Collisionless Shock Reformation

    Science.gov (United States)

    Gueroult, Renaud; Ohsawa, Yukiharu; Fisch, Nathaniel J.

    2017-03-01

    The nature of the magnetic structure arising from ion specular reflection in shock compression studies is examined by means of 1D particle-in-cell simulations. Propagation speed, field profiles, and supporting currents for this magnetic structure are shown to be consistent with a magnetosonic soliton. Coincidentally, this structure and its evolution are typical of foot structures observed in perpendicular shock reformation. To reconcile these two observations, we propose, for the first time, that shock reformation can be explained as the result of the formation, growth, and subsequent transition to a supercritical shock of a magnetosonic soliton. This argument is further supported by the remarkable agreement found between the period of the soliton evolution cycle and classical reformation results. This new result suggests that the unique properties of solitons can be used to shed new light on the long-standing issue of shock nonstationarity and its role on particle acceleration.

  15. Collisionless shock in a partially ionized medium. II. Balmer emission

    CERN Document Server

    Morlino, G; Blasi, P; Amato, E

    2012-01-01

    Strong shocks propagating into a partially ionized medium are often associated with optical Balmer lines. This emission is due to impact excitation of neutral hydrogen by hot protons and electrons in the shocked gas. The structure of such Balmer-dominated shocks has been computed in a previous paper (Blasi et al. 2012), where the distribution function of neutral particles was derived from the appropriate Boltzmann equation including coupling with ions and electrons through charge exchange and ionization. This calculation showed how the presence of neutrals can significantly modify the shock structure through the formation of a "neutral-induced" precursor ahead of the shock. Here we follow up on our previous work and investigate the properties of the resulting Balmer emission, with the aim of using the observed radiation as a diagnostic tool for shock parameters. Our main focus is on Supernova Remnant shocks, and we find that, for typical parameters, the H{\\alpha} emission typically has a three-component spect...

  16. Analytical model of Weibel-mediated electron-ion collisionless shock formation

    Science.gov (United States)

    Ruyer, C.; Gremillet, L.; Bonnaud, G.; Riconda, C.

    2015-11-01

    We address the formation of ion-electron collisionless shocks in the non-relativistic regime. The shocks formed by the non-linear evolution of the Weibel-type instabilities, arise during plasma collisions in numerous high-energy astrophysical scenario such as pulsar wind nebulae or supernova remnants. For the first time, a predictive fully analytical model of the ion Weibel saturation based on the coalescence of filaments is presented and allows to describe the evolution of the plasma and its characteristics until shock-formation. It is compared successfully to Weibel-mediated shock simulations until quasi-isotropisation of the ions, and close to shock formation. Our model compares well with two different recent experiments and allows us to pinpoint the role of the electron screening on the ion-Weibel dynamics. Our theoretical results, supported by both experiments and simulations, proves for the first time the effect of an artificially low ion to electron mass ratio on the formation of collisionless shocks commonly used in many numerical works.

  17. COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. II. BALMER EMISSION

    Energy Technology Data Exchange (ETDEWEB)

    Morlino, G.; Bandiera, R.; Blasi, P.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy)

    2012-12-01

    Strong shocks propagating into a partially ionized medium are often associated with optical Balmer lines. This emission is due to impact excitation of neutral hydrogen by hot protons and electrons in the shocked gas. The structure of such Balmer-dominated shocks has been computed in a previous paper, where the distribution function of neutral particles was derived from the appropriate Boltzmann equation including coupling with ions and electrons through charge exchange and ionization. This calculation showed how the presence of neutrals can significantly modify the shock structure through the formation of a neutral-induced precursor ahead of the shock. Here we follow up on our previous work and investigate the properties of the resulting Balmer emission, with the aim of using the observed radiation as a diagnostic tool for shock parameters. Our main focus is on supernova remnant shocks, and we find that, for typical parameters, the H{alpha} emission typically has a three-component spectral profile, where (1) a narrow component originates from upstream cold hydrogen atoms, (2) a broad component comes from hydrogen atoms that have undergone charge exchange with shocked protons downstream of the shock, and (3) an intermediate component is due to hydrogen atoms that have undergone charge exchange with warm protons in the neutral-induced precursor. The relative importance of these three components depends on the shock velocity, on the original degree of ionization, and on the electron-ion temperature equilibration level. The intermediate component, which is the main signature of the presence of a neutral-induced precursor, becomes negligible for shock velocities {approx}< 1500 km s{sup -1}. The width of the intermediate line reflects the temperature in the precursor, while the width of the narrow one is left unaltered by the precursor. In addition, we show that the profiles of both the intermediate and broad components generally depart from a thermal distribution, as a

  18. The Effect of Large Scale Magnetic Turbulence on the Acceleration of Electrons by Perpendicular Collisionless Shocks

    CERN Document Server

    Guo, Fan

    2010-01-01

    We study the physics of electron acceleration at collisionless shocks that move through a plasma containing large-scale magnetic fluctuations. We numerically integrate the trajectories of a large number of electrons, which are treated as test particles moving in the time dependent electric and magnetic fields determined from 2-D hybrid simulations (kinetic ions, fluid electron). The large-scale magnetic fluctuations effect the electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to cross the shock front several times, leading to efficient acceleration. Ripples in the shock front occuring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The current study is also helpful in understanding the inje...

  19. THE MAXIMUM ENERGY OF ACCELERATED PARTICLES IN RELATIVISTIC COLLISIONLESS SHOCKS

    Energy Technology Data Exchange (ETDEWEB)

    Sironi, Lorenzo [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Spitkovsky, Anatoly [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544-1001 (United States); Arons, Jonathan, E-mail: lsironi@cfa.harvard.edu [Department of Astronomy, Department of Physics, and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States)

    2013-07-01

    The afterglow emission from gamma-ray bursts (GRBs) is usually interpreted as synchrotron radiation from electrons accelerated at the GRB external shock that propagates with relativistic velocities into the magnetized interstellar medium. By means of multi-dimensional particle-in-cell simulations, we investigate the acceleration performance of weakly magnetized relativistic shocks, in the magnetization range 0 {approx}< {sigma} {approx}< 10{sup -1}. The pre-shock magnetic field is orthogonal to the flow, as generically expected for relativistic shocks. We find that relativistic perpendicular shocks propagating in electron-positron plasmas are efficient particle accelerators if the magnetization is {sigma} {approx}< 10{sup -3}. For electron-ion plasmas, the transition to efficient acceleration occurs for {sigma} {approx}< 3 Multiplication-Sign 10{sup -5}. Here, the acceleration process proceeds similarly for the two species, since the electrons enter the shock nearly in equipartition with the ions, as a result of strong pre-heating in the self-generated upstream turbulence. In both electron-positron and electron-ion shocks, we find that the maximum energy of the accelerated particles scales in time as {epsilon}{sub max}{proportional_to}t {sup 1/2}. This scaling is shallower than the so-called (and commonly assumed) Bohm limit {epsilon}{sub max}{proportional_to}t, and it naturally results from the small-scale nature of the Weibel turbulence generated in the shock layer. In magnetized plasmas, the energy of the accelerated particles increases until it reaches a saturation value {epsilon}{sub sat}/{gamma}{sub 0} m{sub i}c {sup 2} {approx} {sigma}{sup -1/4}, where {gamma}{sub 0} m{sub i}c {sup 2} is the mean energy per particle in the upstream bulk flow. Further energization is prevented by the fact that the self-generated turbulence is confined within a finite region of thickness {proportional_to}{sigma}{sup -1/2} around the shock. Our results can provide physically

  20. Ion streaming instabilities with application to collisionless shock wave structure

    Science.gov (United States)

    Golden, K. I.; Linson, L. M.; Mani, S. A.

    1973-01-01

    The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. Magnetic effects on the ion beams are included, but the electrons are treated as a magnetized fluid. The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k-U space (U is the relative velocity between the two ion beams) are presented. These results are extensions of Kovner's analysis for weak beams. The parameters are then chosen to be applicable for parallel shocks. It is found that unstable waves with zero group velocity in the shock frame can exist near the leading edge of the shock for upstream Alfven Mach numbers greater than 5.5.

  1. Laboratory studies of magnetized collisionless flows and shocks using accelerated plasmoids

    Science.gov (United States)

    Weber, T. E.; Smith, R. J.; Hsu, S. C.

    2015-11-01

    Magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those found in both space and astrophysical shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to high velocities (100s of km/s); resulting in β ~ 1, collisionless plasma flows with sonic and Alfvén Mach numbers of ~10. The FRC subsequently impacts a static target such as a strong parallel or anti-parallel (reconnection-wise) magnetic mirror, a solid obstacle, or neutral gas cloud to create shocks with characteristic length and time scales that are both large enough to observe yet small enough to fit within the experiment. This enables study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental capabilities of MSX will be presented, including diagnostics, selected recent results, and future directions. Supported by the DOE Office of Fusion Energy Sciences under contract DE-AC52-06NA25369.

  2. Simulations and Theory of Ion Injection at Non-relativistic Collisionless Shocks

    Science.gov (United States)

    Caprioli, Damiano; Pop, Ana-Roxana; Spitkovsky, Anatoly

    2015-01-01

    We use kinetic hybrid simulations (kinetic ions-fluid electrons) to characterize the fraction of ions that are accelerated to non-thermal energies at non-relativistic collisionless shocks. We investigate the properties of the shock discontinuity and show that shocks propagating almost along the background magnetic field (quasi-parallel shocks) reform quasi-periodically on ion cyclotron scales. Ions that impinge on the shock when the discontinuity is the steepest are specularly reflected. This is a necessary condition for being injected, but it is not sufficient. Also, by following the trajectories of reflected ions, we calculate the minimum energy needed for injection into diffusive shock acceleration, as a function of the shock inclination. We construct a minimal model that accounts for the ion reflection from quasi-periodic shock barrier, for the fraction of injected ions, and for the ion spectrum throughout the transition from thermal to non-thermal energies. This model captures the physics relevant for ion injection at non-relativistic astrophysical shocks with arbitrary strengths and magnetic inclinations, and represents a crucial ingredient for understanding the diffusive shock acceleration of cosmic rays.

  3. Collisionless Weibel Shocks and Electron Acceleration in Gamma-Ray Bursts

    Science.gov (United States)

    Ardaneh, Kazem; Cai, Dongsheng; Nishikawa, Ken-Ichi; Lembége, Bertrand

    2015-09-01

    A study of collisionless external shocks in gamma-ray bursts is presented. The shock structure, electromagnetic field, and process of electron acceleration are assessed by performing a self-consistent 3D particle-in-cell simulation. In accordance with hydrodynamic shock systems, the shock consists of a reverse shock (RS) and forward shock separated by a contact discontinuity. The development and structure are controlled by the ion Weibel instability. The ion filaments are sources of strong transverse electromagnetic fields at both sides of the double shock structure over a length of 30-100 ion skin depths. Electrons are heated up to a maximum energy {ɛ }{ele}≈ \\sqrt{{ɛ }{{b}}}, where ɛ is the energy normalized to the total incoming energy. Jet electrons are trapped in the RS transition region due to the presence of an ambipolar electric field and reflection by the strong transverse magnetic fields in the shocked region. In a process similar to shock surfing acceleration for ions, electrons experience drift motion and acceleration by ion filament transverse electric fields in the plane perpendicular to the shock propagation direction. Ultimately, accelerated jet electrons are convected back into the upstream.

  4. Collisionless Weibel shocks and electron acceleration in gamma-ray bursts

    CERN Document Server

    Ardaneh, Kazem; Nishikawa, Ken-Ichi; Lembége, Bertrand

    2015-01-01

    A study of collisionless external shocks in gamma-ray bursts is presented. The shock structure, electromagnetic fields, and process of electron acceleration are assessed by using a self-consistent 3D particle-in-cell simulation. In accordance with hydrodynamic shock systems, the formed shock is composed of a forward and reverse shock separated by a contact discontinuity. The establishment of the shock transitions is controlled by the ion Weibel instability. The ion filaments are sources the strong transversal electromagnetic fields at the two sides of the double shock structure with a length about 30-100 ion skin depths. In regard to the electrons, they are heated up to a maximum energy $\\epsilon_{ele}\\approx \\sqrt{\\epsilon_b}$ (normalized to the total incoming energy). Moreover, the jet electrons behind the reverse shock are trapped due to the presence of an ambipolar electric field accompanying with reflection by the strong transversal magnetic fields in the shocked region. In a similar process to the shock...

  5. Laser plasma physics in shock ignition – transition from collisional to collisionless absorption

    Directory of Open Access Journals (Sweden)

    Klimo O.

    2013-11-01

    Full Text Available Shock Ignition is considered as a relatively robust and efficient approach to inertial confinement fusion. A strong converging shock, which is used to ignite the fuel, is launched by a high power laser pulse with intensity in the range of 1015 − 1016 W/cm2 (at the wavelength of 351 nm. In the lower end of this intensity range the interaction is dominated by collisions while the parametric instabilities are playing a secondary role. This is manifested in a relatively weak reflectivity and efficient electron heating. The interaction is dominated by collective effects at the upper edge of the intensity range. The stimulated Brillouin and Raman scattering (SBS and SRS respectively take place in a less dense plasma and cavitation provides an efficient collisionless absorption mechanism. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied here with the help of large scale one-dimensional Particle-in-Cell (PIC simulations. The relation between the collisional and collisionless processes is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light.

  6. Cosmic-ray acceleration at collisionless astrophysical shocks using Monte-Carlo simulations

    CERN Document Server

    Wolff, M

    2015-01-01

    Context. The diffusive shock acceleration mechanism has been widely accepted as the acceleration mechanism for galactic cosmic rays. While self-consistent hybrid simulations have shown how power-law spectra are produced, detailed information on the interplay of diffusive particle motion and the turbulent electromagnetic fields responsible for repeated shock crossings are still elusive. Aims. The framework of test-particle theory is applied to investigate the effect of diffusive shock acceleration by inspecting the obtained cosmic-ray energy spectra. The resulting energy spectra can be obtained this way from the particle motion and, depending on the prescribed turbulence model, the influence of stochastic acceleration through plasma waves can be studied. Methods. A numerical Monte-Carlo simulation code is extended to include collisionless shock waves. This allows one to trace the trajectories of test particle while they are being accelerated. In addition, the diffusion coefficients can be obtained directly fro...

  7. Collisionless shocks in a partially ionized medium: III. Efficient cosmic ray acceleration

    CERN Document Server

    Morlino, G; Bandiera, R; Amato, E; Caprioli, D

    2012-01-01

    In this paper we present the first formulation of the theory of non-linear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification and the magnetic dynamical effects on the shock are also included. The main new aspect consists however in accounting for charge exchange and ionization of neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated to the so-called neutral return flux, namely the return of hot neutrals from the downstream region to the upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer the cosmic ray accelera...

  8. Impact of continuous particle injection on generation and decay of the magnetic field in collisionless shocks

    Science.gov (United States)

    Garasev, Mikhail; Derishev, Evgeny

    2016-09-01

    We present numerical simulations of the magnetic field turbulence in a collisionless electron-positron plasma with continuous injection of new pairs, which maintains the anisotropy in the particle distribution over a long time. With these simulations, we follow the evolution of a small (and, therefore, uniform) region in the fluid comoving frame to model the generation and decay of the magnetic field in shocks. The upstream is modified by two-photon pair production due to self-absorption of the shock's high-energy radiation. We find that the overall picture of the magnetic field build-up is consistent with the development of Weibel instability. However, the long-term injection of anisotropic pairs in the upstream leads to the formation of large-scale structures in the magnetic field, while small-scale structures are almost absent. We find that being amplified at the shock front, this magnetic field mostly preserves its large spatial scale and then slowly decays in the downstream on a time-scale approximately equal to the duration of the injection phase. The observed decay of the magnetic field is in exceptionally good agreement with predictions of the so-called phase mixing model. The generation of a long-lived magnetic field in relativistic collisionless shocks with an injection-modified upstream explains how they can efficiently produce the synchrotron radiation in gamma-ray bursts.

  9. Electron acceleration in collisionless shocks and magnetic reconnection by laser-produced plasma ablation

    Science.gov (United States)

    Park, Jaehong; Spitkovksy, Anatoly; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    We perform particle-in-cell simulations of collisionless shocks and magnetic reconnection generated by ablated plasma expanding into a magnetized background plasma. We find: (1) The simulated proton radiography produces different morphology of the shock structure depending on the orientation of the magnetic field and can be used to identify a shock in the experiment. Electrons are accelerated by the whistler waves generated at oblique sites of the shock. (2) Forced collisionless magnetic reconnection is induced when the expanding plumes carry opposite magnetic polarities and interact with a background plasma. Electrons are accelerated at the reconnection X line and reveal a power-law distribution as the plasma beta is lowered, β = 0.08 . As the plasma beta is increased, β = 0.32 , the 1st order Fermi mechanism against the two plasma plumes contributes to the electron acceleration as well as the X line acceleration. Using 3-D simulations, we also explore the effect of 3-D instabilities (Weibel instability or drift-kink) on particle acceleration and magnetic field annihilation between the colliding magnetized plumes

  10. More than mass proportional heating of heavy ions by supercritical collisionless shocks in the solar corona

    CERN Document Server

    Zimbardo, Gaetano

    2009-01-01

    We propose a new model for explaining the observations of more than mass proportional heating of heavy ions in the polar solar corona. We point out that a large number of small scale intermittent shock waves can be present in the solar corona. The energization mechanism is, essentially, the ion reflection off supercritical quasi-perpendicular collisionless shocks in the corona and the subsequent acceleration by the motional electric field ${\\bf E} = - (1/c) {\\bf V} \\times {\\bf B}$. The acceleration due to ${\\bf E}$ is perpendicular to the magnetic field, in agreement with observations, and is more than mass proportional with respect to protons, because the heavy ion orbit is mostly upstream of the quasi-perpendicular shock foot. The observed temperature ratios between O$^{5+}$ ions and protons in the polar corona, and between $\\alpha$ particles and protons in the solar wind are easily recovered.

  11. Laboratory astrophysical collisionless shock experiments with interpenetrating plasma flows on Omega and NIF

    Science.gov (United States)

    Ross, James; Park, H.-S.; Huntington, C.; Ryutov, D.; Drake, R. P.; Froula, D.; Gregori, G.; Levy, M.; Lamb, D.; Fiuza, F.; Petrasso, R.; Li, C.; Zylastra, A.; Rinderknecht, H.; Sakawa, Y.; Spitkovsky, A.

    2015-11-01

    Shock formation from high-Mach number plasma flows is observed in many astrophysical objects such as supernova remnants and gamma ray bursts. These are collisionless shocks as the ion-ion collision mean free path is much larger than the system size. It is believed that seed magnetic fields can be generated on a cosmologically fast timescale via the Weibel instability when such environments are initially unmagnetized. Here we present laboratory experiments using high-power lasers whose ultimate goal is to investigate the dynamics of collisionless shock formation in two interpenetrating plasma streams. Particle-in-cell numerical simulations have confirmed that the strength and structure of the generated magnetic field are consistent with the Weibel mediated electromagnetic nature and that the inferred magnetization level could be as high as ~ 1%. This paper will review recent experimental results from various laser facilities as well as the simulation results and the theoretical understanding of these observations. Taken together, these results imply that electromagnetic instabilities can be significant in both inertial fusion and astrophysical conditions. We will present results from initial NIF experiments, where we observe the neutrons and x-rays generated from the hot plasmas at the center of weakly collisional, counterstreaming flows. Prepared by LLNL under Contract DE-AC52-07NA27344.

  12. Cosmic-ray acceleration at collisionless astrophysical shocks using Monte-Carlo simulations

    Science.gov (United States)

    Wolff, M.; Tautz, R. C.

    2015-08-01

    Context. The diffusive shock acceleration mechanism has been widely accepted as the acceleration mechanism for galactic cosmic rays. While self-consistent hybrid simulations have shown how power-law spectra are produced, detailed information on the interplay of diffusive particle motion and the turbulent electromagnetic fields responsible for repeated shock crossings are still elusive. Aims: The framework of test-particle theory is applied to investigate the effect of diffusive shock acceleration by inspecting the obtained cosmic-ray energy spectra. The resulting energy spectra can be obtained this way from the particle motion and, depending on the prescribed turbulence model, the influence of stochastic acceleration through plasma waves can be studied. Methods: A numerical Monte-Carlo simulation code is extended to include collisionless shock waves. This allows one to trace the trajectories of test particle while they are being accelerated. In addition, the diffusion coefficients can be obtained directly from the particle motion, which allows for a detailed understanding of the acceleration process. Results: The classic result of an energy spectrum with E-2 is only reproduced for parallel shocks, while, for all other cases, the energy spectral index is reduced depending on the shock obliqueness. Qualitatively, this can be explained in terms of the diffusion coefficients in the directions that are parallel and perpendicular to the shock front.

  13. Spatial Structure and Collisionless Electron Heating in Balmer-dominated Shocks

    CERN Document Server

    van Adelsberg, Matthew; McCray, Richard; Raymond, John C

    2008-01-01

    Balmer-dominated shocks in supernova remnants (SNRs) produce strong hydrogen lines with a two-component profile composed of a narrow contribution from cold upstream hydrogen atoms, and a broad contribution from hydrogen atoms that have undergone charge transfer reactions with hot protons. Observations of emission lines from edge-wise shocks in SNRs can constrain the gas velocity and collisionless electron heating at the shock front. Downstream hydrogen atoms engage in charge transfer, excitation and ionization reactions, defining an interaction region called the shock transition zone, with characteristic width l_{zone} \\sim 10^{15} cm, for shock velocity v_s \\sim 1000 km s^{-1} and upstream density n_0 \\sim 1 cm^{-3}. The properties of hot hydrogen atoms undergoing charge transfer (called broad neutrals) are critical for accurately calculating the structure and radiation from the shock transition zone. This paper is the third in a series describing the kinetic, fluid and emission properties of Balmer-dominate...

  14. Characterizing counter-streaming interpenetrating plasmas relevant to astrophysical collisionless shocks

    Science.gov (United States)

    Ross, J. S.; Glenzer, S. H.; Amendt, P.; Berger, R.; Divol, L.; Kugland, N. L.; Landen, O. L.; Plechaty, C.; Remington, B.; Ryutov, D.; Rozmus, W.; Froula, D. H.; Fiksel, G.; Sorce, C.; Kuramitsu, Y.; Morita, T.; Sakawa, Y.; Takabe, H.; Drake, R. P.; Grosskopf, M.; Kuranz, C.; Gregori, G.; Meinecke, J.; Murphy, C. D.; Koenig, M.; Pelka, A.; Ravasio, A.; Vinci, T.; Liang, E.; Presura, R.; Spitkovsky, A.; Miniati, F.; Park, H.-S.

    2012-05-01

    A series of Omega experiments have produced and characterized high velocity counter-streaming plasma flows relevant for the creation of collisionless shocks. Single and double CH2 foils have been irradiated with a laser intensity of ~ 1016 W/cm2. The laser ablated plasma was characterized 4 mm from the foil surface using Thomson scattering. A peak plasma flow velocity of 2000 km/s, an electron temperature of ~ 110 eV, an ion temperature of ~ 30 eV, and a density of ~ 1018 cm-3 were measured in the single foil configuration. Significant increases in electron and ion temperatures were seen in the double foil geometry. The measured single foil plasma conditions were used to calculate the ion skin depth, c/ωpi~0.16 mm, the interaction length, lint, of ~ 8 mm, and the Coulomb mean free path, λmfp~27mm. With c/ωpi<collisionless shock formation is possible.

  15. On the electron-ion temperature ratio established by collisionless shocks

    Science.gov (United States)

    Vink, Jacco; Broersen, Sjors; Bykov, Andrei; Gabici, Stefano

    2015-07-01

    Astrophysical shocks are often collisionless shocks, in which the changes in plasma flow and temperatures across the shock are established not through Coulomb interactions, but through electric and magnetic fields. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature (non-equilibration of temperatures), or whether they quickly equilibrate in the shock region. Here we provide a simple, thermodynamic, relation for the minimum electron-ion temperature ratios that should be expected as a function of Mach number. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all particle species should undergo the same density jump across the shock, in order for the plasma to remain charge neutral. The only form of additional electron heating that we allow for is adiabatic heating, caused by the compression of the electron gas. These assumptions result in an analytic treatment of expected electron-ion temperature ratio that agrees with observations of collisionless shocks: at low sonic Mach numbers, Ms ≲ 2, the electron-ion temperature ratio is close to unity, whereas for Mach numbers above Ms ≈ 60 the electron-ion temperature ratio asymptotically approaches a temperature ratio of Te/Ti = me/ ⟨ mi ⟩. In the intermediate Mach number range the electron-ion temperature ratio scales as Te/Ti ∝ Ms-2. In addition, we calculate the electron-ion temperature ratios under the assumption of adiabatic heating of the electrons only, which results in a higher electron-ion temperature ratio, but preserves the Te/Ti ∝ Ms-2 scaling. We also show that for magnetised shocks the electron-ion temperature ratio approaches the asymptotic value Te/Ti = me/ ⟨ mi ⟩ for lower magnetosonic Mach numbers (Mms), mainly because for a strongly magnetised shock the sonic Mach number is larger than the magnetosonic Mach number (Mms ≤ Ms). The predicted scaling of the electron

  16. Microinstabilities at perpendicular collisionless shocks: A comparison of full particle simulations with different ion to electron mass ratio

    CERN Document Server

    Umeda, Takayuki; Matsukiyo, Shuichi; Yamazaki, Ryo

    2012-01-01

    A full particle simulation study is carried out for studying microinstabilities generated at the shock front of perpendicular collisionless shocks. The structure and dynamics of shock waves are determined by Alfven Mach number and plasma beta, while microinstabilities are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the plasma-to-cyclotron frequency. Thus, growth rates of microinstabilities are changed by the ion-to-electron mass ratio, even with the same Mach number and plasma beta. The present two-dimensional simulations show that the electron cyclotron drift instability is dominant for a lower mass ratio, and electrostatic electron cyclotron harmonic waves are excited. For a higher mass ratio, the modified two-stream instability is dominant and oblique electromagnetic whistler waves are excited, which can affect the structure and dynamics of collisionless shocks by modifying shock magnetic fields.

  17. Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock

    CERN Document Server

    Ohira, Yutaka

    2008-01-01

    Electrostatic behavior of a collisionless plasma in the foot region of high Mach number perpendicular shocks is investigated through the two-dimensional linear analysis and electrostatic particle-in-cell (PIC) simulation. The simulations are double periodic and taken as a proxy for the situation in the foot. The linear analysis for relatively cold unmagnetized plasmas with a reflected proton beam shows that obliquely propagating Buneman instability is strongly excited. We also found that when the electron temperature is much higher than the proton temperature, the most unstable mode is the highly obliquely propagating ion two-stream instability excited through the resonance between ion plasma oscillations of the background protons and of the beam protons, rather than the ion acoustic instability that is dominant for parallel propagation. To investigate nonlinear behavior of the ion two-stream instability, we have made PIC simulations for the shock foot region in which the initial state satisfies the Buneman i...

  18. DESIGN CONSIDERATIONS FOR UNMAGNETIZED COLLISIONLESS-SHOCK MEASUREMENTS IN HOMOLOGOUS FLOWS

    Energy Technology Data Exchange (ETDEWEB)

    Drake, R. P. [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Gregori, G., E-mail: rpdrake@umich.edu [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

    2012-04-20

    The subject of this paper is the design of practical laser experiments that can produce collisionless shocks mediated by the Weibel instability. Such shocks may be important in a wide range of astrophysical systems. Three issues are considered. The first issue is the implications of the fact that such experiments will produce expanding flows that are approximately homologous. As a result, both the velocity and the density of the interpenetrating plasma streams will be time dependent. The second issue is the implications of the linear theory of the Weibel instability. For the experiments, the instability is in a regime where standard simplifications do not apply. It appears feasible but non-trivial to obtain adequate growth. The third issue is collisionality. The need to keep resistive magnetic-field dissipation small enough implies that the plasmas should not be allowed to cool substantially.

  19. Hybrid simulation of a parallel collisionless shock in the Large Plasma Device

    CERN Document Server

    Weidl, M S; Jenko, F; Niemann, C

    2016-01-01

    We present two-dimensional hybrid kinetic/magnetohydrodynamic simulations of planned laser-ablation experiments in the Large Plasma Device (LAPD). Our results, based on parameters which have been validated in previous experiments, show that a parallel collisionless shock can begin forming within the available space. Carbon-debris ions that stream along the magnetic-field direction with a blow-off speed of four times the Alfven velocity excite strong magnetic fluctuations, eventually transfering part of their kinetic energy to the surrounding hydrogen ions. This acceleration and compression of the background plasma creates a shock front, which satisfies the Rankine-Hugoniot conditions and can therefore propagate on its own. Furthermore, we analyze the upstream turbulence and show that it is dominated by the right-hand resonant instability.

  20. Bifurcation Theory of the Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Kolesnikov, R.A.; Krommes, J.A.

    2005-09-22

    The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for the model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.

  1. Weibel-mediated collisionless shocks in laser-irradiated dense plasmas: Prevailing role of the electrons in generating the field fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Ruyer, C., E-mail: charles.ruyer@polytechnique.edu; Gremillet, L., E-mail: laurent.gremillet@cea.fr [CEA, DAM, DIF, F-91297 Arpajon (France); Bonnaud, G. [CEA, Saclay, INSTN, F-91191 Gif-sur-Yvette (France)

    2015-08-15

    We present a particle-in-cell simulation of the generation of a collisionless strong shock in a dense plasma driven by an ultra-intense, plane-wave laser pulse. A linear theory analysis, based on a multi-waterbag model of the particle distributions, highlights the role of the laser-heated electrons in triggering the Weibel-like instability causing shock formation. It is demonstrated that the return-current electrons play a major role in the instability development as well as in the determination of the saturated magnetic field. By contrast, the ions are found of minor importance in driving the instability and the magnetic field fluctuations responsible for their isotropization. Finally, we show that a Weibel-mediated shock can also be generated by a focused laser pulse of large enough spot size.

  2. Weibel-mediated collisionless shocks in laser-irradiated dense plasmas: Prevailing role of the electrons in generating the field fluctuations

    Science.gov (United States)

    Ruyer, C.; Gremillet, L.; Bonnaud, G.

    2015-08-01

    We present a particle-in-cell simulation of the generation of a collisionless strong shock in a dense plasma driven by an ultra-intense, plane-wave laser pulse. A linear theory analysis, based on a multi-waterbag model of the particle distributions, highlights the role of the laser-heated electrons in triggering the Weibel-like instability causing shock formation. It is demonstrated that the return-current electrons play a major role in the instability development as well as in the determination of the saturated magnetic field. By contrast, the ions are found of minor importance in driving the instability and the magnetic field fluctuations responsible for their isotropization. Finally, we show that a Weibel-mediated shock can also be generated by a focused laser pulse of large enough spot size.

  3. An in situ Comparison of Electron Acceleration at Collisionless Shocks under Differing Upstream Magnetic Field Orientations

    Science.gov (United States)

    Masters, A.; Sulaiman, A. H.; Stawarz, Ł.; Reville, B.; Sergis, N.; Fujimoto, M.; Burgess, D.; Coates, A. J.; Dougherty, M. K.

    2017-07-01

    A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn’s bow shock have revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream-downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ˜100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures.

  4. Conditions for Debris-Background Ion Interactions and Collisionless Shock Wave Generation

    Energy Technology Data Exchange (ETDEWEB)

    Winske, Dan [Los Alamos National Laboratory; Cowee, Misa [Los Alamos National Laboratory

    2012-07-10

    We use hybrid simulations and simple theoretical arguments to determine when debris ions streaming relative to background ions in a collisionless, magnetized plasma couple strongly enough to generate a magnetosonic shock wave. We consider three types of configurations: one-dimensional, the two-dimensional extension of the 1-D case, and a more complex 2-D geometry that contains some effects that would be found in a laser-produced, laboratory plasma. We show that the simulation results as well as previous Russian and LLNL results reduce to a simple condition (R{sub m}/{rho}{sub d} = equal mass radius/debris ion gyroradius {ge} 0.7) for the generation of a shock wave. Strong debris interaction with the background is characterized by the formation of a magnetic pulse that steepens and speeds up as it encounters the debris ions deflected by the magnetic field. The pulse further evolves into a shock. As the earlier work has indicated, the process also involves the generation of a transverse electric field perpendicular to the flow and the magnetic field that accelerates the background ions radially outward, which in turn causes the speedup of the pulse. With electric and magnetic field probes, the UCLA laser experiments should be able to detect these signatures of coupling as well as the generation of the shock wave.

  5. Laser plasma simulations of the generation processes of Alfven and collisionless shock waves in space plasma

    Science.gov (United States)

    Prokopov, P. A.; Zakharov, Yu P.; Tishchenko, V. N.; Shaikhislamov, I. F.; Boyarintsev, E. L.; Melekhov, A. V.; Ponomarenko, A. G.; Posukh, V. G.; Terekhin, V. A.

    2016-11-01

    Generation of Alfven waves propagating along external magnetic field B0 and Collisionless Shock Waves propagating across B0 are studied in experiments with laser- produced plasma and magnetized background plasma. The collisionless interaction of interpenetrating plasma flows takes place through a so-called Magnetic Laminar Mechanism (MLM) or Larmor Coupling. At the edge of diamagnetic cavity LP-ions produce induction electric field Eφ which accelerates BP-ions while LP-ions rotate in opposite direction. The ions movement generates sheared azimuthal magnetic field Bφ which could launches torsional Alfven wave. In previous experiments at KI-1 large scale facility a generation of strong perturbations propagating across B0 with magnetosonic speed has been studied at a moderate value of interaction parameter δ∼0.3. In the present work we report on experiments at conditions of 5∼R2 and large Alfven-Mach number MA∼10 in which strong transverse perturbations traveling at a scale of ∼1 m in background plasma at a density of ∼3*1013 cm-3 is observed. At the same conditions but smaller MA ∼ 2 a generation, the structure and dynamic of Alfven wave with wavelength ∼0.5 m propagating along fields B0∼100÷500 G for a distance of ∼2.5 m is studied.

  6. New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant

    CERN Document Server

    Yamaguchi, Hiroya; Badenes, Carles; Hughes, John P; Brickhouse, Nancy S; Foster, Adam R; Patnaude, Daniel J; Petre, Robert; Slane, Patrick O; Smith, Randall K

    2013-01-01

    Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe-K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K-beta (3p->1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe K-alpha (2p->1s) emission dominated by a relatively highly-ionized component. Comparison with our hydrodynamical simulations implies instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating w...

  7. Manually operated piston-driven shock tube

    OpenAIRE

    Reddy, KPJ; Sharath, N

    2013-01-01

    A simple hand-operated shock tube capable of producing Mach 2 shock waves is described. Performance of this miniature shock tube using compressed high pressure air created by a manually operated piston in the driver section of the shock tube as driver gas with air at 1 atm pressure as the test gas in the driven tube is presented. The performance of the shock tube is found to match well with the theoretically estimated values using normal shock relations. Applications of this shock tube named ...

  8. COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. III. EFFICIENT COSMIC RAY ACCELERATION

    Energy Technology Data Exchange (ETDEWEB)

    Morlino, G.; Blasi, P.; Bandiera, R.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, I-50125 Firenze (Italy); Caprioli, D. [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2013-05-10

    In this paper, we present the first formulation of the theory of nonlinear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification, and the magnetic dynamical effects on the shock are also included. The main new aspect of this study, however, consists of accounting for charge exchange and the ionization of a neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated with the so-called neutral return flux, namely the return of hot neutrals from the downstream region to upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer cosmic ray acceleration efficiency in supernova remnants showing Balmer emission: the broad Balmer line, which is due to charge exchange of hydrogen atoms with hot ions downstream of the shock, is shown to become narrower as a result of the energy drainage into cosmic rays, while the narrow Balmer line, due to charge exchange in the cosmic-ray-induced precursor, is shown to become broader. In addition to these two well-known components, the neutral return flux leads to the formation of a third component with an intermediate width: this too contains information on ongoing processes at the shock.

  9. Long wavelength unstable modes in the far upstream of relativistic collisionless shocks

    CERN Document Server

    Rabinak, Itay; Waxman, Eli

    2010-01-01

    The growth rate of long wavelength kinetic instabilities arising due to the interaction of a collimated beam of relativistic particles and a cold unmagnetized plasma are calculated in the ultra relativistic limit. For sufficiently culminated beams, all long wave-length modes are shown to be Weibel-unstable, and a simple analytic expression for their growth rate is derived. For large transverse velocity spreads, these modes become stable. An analytic condition for stability is given. These analytic results, which generalize earlier ones given in the literature, are shown to be in agreement with numerical solutions of the dispersion equation and with the results of novel PIC simulations in which the electro-magnetic fields are restricted to a given k-mode. The results may describe the interaction of energetic cosmic rays, propagating into the far upstream of a relativistic collisionless shock, with a cold unmagnetized upstream. The long wavelength modes considered may be efficient in deflecting particles and co...

  10. X-ray Emission from Supernovae in Dense Circumstellar Matter Environments: a Search for Collisionless Shocks

    Science.gov (United States)

    Ofek, E. O.; Fox, D.; Cenko, Stephen B.; Sullivan, M; Gnat, O.; Frail, D. A.; Horesh, A.; Corsi, A.; Quimby, R. M.; Gehrels, N.; Kulkarni, S. R.; Gal-Yam, A.; Nugent, P. E.; Yaron, O.; Fillippenko, A. V; Kasliwal, M. M.; Bildsten, L.; Bloom, J. S.; Poznanski, D.; Arcavi, I.; Laher, R. R.; Levitan, D.; Sesar, B.; Surace, J..

    2013-01-01

    The optical light curve of some supernovae (SNe) may be powered by the outward diffusion of the energy deposited by the explosion shock (the so-called shock breakout) in optically thick (Tau approx > 30) circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and radiation-dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift/XRT and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM. Our sample includes 19 Type IIn SNe, one Type Ibn SN, and eight hydrogen-poor superluminous SNe (SLSN-I such as SN 2005ap). Two SNe (SN 2006jc and SN 2010jl) have X-ray properties that are roughly consistent with the expectation for X-rays from a collisionless shock in optically thick CSM. However, the X-ray emission from SN 2006jc can also be explained as originating in an optically thin region. Thus, we propose that the optical light curve of SN 2010jl is powered by shock breakout in CSM. We suggest that two other events (SN 2010al and SN 2011ht) were too X-ray bright during the SN maximum optical light to be explained by the shock-breakout model.We conclude that the light curves of some, but not all, SNe IIn/Ibn are powered by shock breakout in CSM. For the rest of the SNe in our sample, including all of the SLSN-I events, our X-ray limits are not deep enough and were typically obtained too early (i.e., near the SN maximum light) for definitive conclusions about their nature. Late-time X-ray observations are required in order to further test whether these SNe are indeed embedded in dense CSM. We review the conditions required for a shock breakout in a wind profile. We argue that the timescale, relative to maximum light, for the SN to peak in X-rays is a probe of the column density and the density profile above

  11. Heating heavy ions in the polar corona by collisionless shocks: A one-dimensional simulation

    Science.gov (United States)

    Nisticò, Giuseppe; Zimbardo, Gaetano

    2012-01-01

    Recently a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona was proposed (Zimbardo, 2010, 2011). In that model the ion energization mechanism is the ion reflection off supercritical quasi-perpendicular collisionless shocks in the corona and the subsequent acceleration by the motional electric field E = -V × B/c. The mechanism of heavy ion reflection is based on ion gyration in the magnetic overshoot of the shock. The acceleration due to the motional electric field is perpendicular to the magnetic field, giving rise to large temperature anisotropy with T⊥ ≫ T∥, in agreement with SoHO observations. Such a model is tested here by means of a one dimensional test particle simulation where ions are launched toward electric and magnetic profiles representing the shock transition. We study the dynamics of O5+, as representative of coronal heavy ions for Alfvénic Mach numbers of 2-4, as appropriate to solar corona. It is found that O5+ ions are easily reflected and gain more than mass proportional energy with respect to protons.

  12. Time-dependence in Relativistic Collisionless Shocks: Theory of the Variable "Wisps" in the Crab Nebula

    CERN Document Server

    Spitkovsky, A; Spitkovsky, Anatoly; Arons, Jonathan

    2004-01-01

    We describe results from time-dependent numerical modeling of the collisionless reverse shock terminating the pulsar wind in the Crab Nebula. We treat the upstream relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. The relativistic cyclotron instability of the ion gyrational orbit downstream of the leading shock in the electron-positron pairs launches outward propagating magnetosonic waves. Because of the fresh supply of ions crossing the shock, this time-dependent process achieves a limit-cycle, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in the magnetic field and pair density associated with these waves, as well as their propagation speed, semi-quantitatively reproduce the behavior of the wisp and ring features described in recent observations obtained using the Hubble Space Telescope and the Chandra X-Ray Observator...

  13. Impact of continuous particle injection on generation and decay of the magnetic field in collisionless shocks

    CERN Document Server

    Garasev, Mikhail

    2016-01-01

    We present numerical simulations of the magnetic field turbulence in collisionless electron-positron plasma with continuous injection of new pairs, which maintains anisotropy in the particle distribution over long time. With these simulations we model generation and decay of the magnetic field in shocks, where the upstream is modified by two-photon pair production due to self-absorption of the shock's high-energy radiation. We find that the overall picture of magnetic field build-up is consistent with development of Weibel instability. However, the long-term injection of anisotropic pairs in the upstream leads to formation of large-scale structures in the magnetic field, while the small-scale structures are almost absent. Furthermore, we find that being amplified at the shock front this magnetic field mostly preserves its large spatial scale and then slowly decays in the downstream on a timescale approximately equal to duration of the injection phase. We observe that the decay of the magnetic field is in exce...

  14. Under and over-adiabatic electrons through a perpendicular collisionless shock: theory versus simulations

    Directory of Open Access Journals (Sweden)

    P. Savoini

    2005-12-01

    Full Text Available Test particle simulations are performed in order to analyze in detail the dynamics of transmitted electrons through a supercritical, strictly perpendicular, collisionless shock. In addition to adiabatic particles, two distinct nonadiabatic populations are observed surprisingly: (i first, an over-adiabatic population characterized by an increase in the gyrating velocity higher than that expected from the conservation of the magnetic moment µ, and (ii second, an under-adiabatic population characterized by a decrease in this velocity. Results show that both nonadiabatic populations have their pitch angle more aligned along the magnetic field than the adiabatic one at the time these hit the shock front. The formation of "under" and "over-adiabatic" particles strongly depends on their local injection conditions through the large amplitude cross-shock potential present within the shock front. A simplified theoretical model validates these results and points out the important role of the electric field as seen by the electrons. A classification shows that both nonadiabatic electrons are issued from the core part of the upstream distributionÊ function. In contrast, suprathermal and tail electrons only contribute to the adiabatic population; nevertheless, the core part of the upstream distribution contributes at a lower percentage to the adiabatic electrons. Under-adiabatic electrons are characterized by small injection angles θinj≤90°, whereas "over-adiabatic" particles have high injection angles θinj>90° (where θinj is the angle between the local gyrating velocity vector and the shock normal.

  15. New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant

    Science.gov (United States)

    Yamaguchi, Hiroya; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Petre, Robert; Slane, Patrick O.; Smith, Randall K.

    2013-01-01

    Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K beta (3p yields 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe K alpha (2p yields 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe K alpha morphology from the Chandra observations. Since strong Fe K beta fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.

  16. The structure of a collisionless shock in a partially ionized medium: I. Cosmic rays as test particles

    CERN Document Server

    Blasi, P; Bandiera, R; Amato, E; Caprioli, D

    2012-01-01

    A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, that we refer to as "the neutral return flux", is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge exchange interaction lengths of fast neutrals moving towards upstream infinity. In the case of a shock propagating in the interstellar m...

  17. Hybrid Simulations and Scaling Laws for Shock Formation in the UCLA Collisionless Shock Experiment

    Science.gov (United States)

    Larson, David; Winske, Dan; Cowee, Misa; Clark, S. Eric; Niemann, Christoph; Brecht, Stephen

    2015-11-01

    Two- and three-dimensional simulations are used to compare and contrast the plasma expansion, formation of a magnetic cavity, and generation of an outgoing shock wave for conditions relevant to the laser experiment at UCLA, as a function of the background ion mass. A model of the shock formation process is constructed that yields an expression for the speed of the shock, which we show is in good agreement with the simulations. In addition, the criteria for generating strongly-coupled shocks are derived and simulations are used to examine the velocity scaling obtained via momentum conservation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by DTRA10027-6759.

  18. Width dependent collisionless electron dynamics in the static fields of the shock ramp, 2, Phase space portrait

    Directory of Open Access Journals (Sweden)

    M. Gedalin

    1997-01-01

    Full Text Available We study numerically in detail the behaviour of electrons in the strongly inhomogeneous static magnetic and electric fields, which are typical for thin quasiperpendicular collisionless shocks. We pay particular attention to the dependence of the final electron velocities on their initial velocities, for different shock widths. Electrons are completely magnetized when the shock is wide, but become demagnetized, and the energies that they acquire rapidly increase with the steepening of the field structure. One of the clear manifestations of the electron demagnetization is the loss of even approximate one-to-one correspondence of the downstream perpendicular velocity to the upstream perpendicular velocity. Electron reflection occurs despite the large cross-shock potential which accelerates electrons along the magnetic field (the regime of complete magnetization or across the shock (strong demagnetization. The reflected ion fraction is sensitive to the potential, magnetic field jump, and ramp width.

  19. Nuclear Fusion in Laser-Driven Counter-Streaming Collisionless Plasmas

    CERN Document Server

    Zhang, Xiaopeng; Yuan, Dawei; Fu, Changbo; Bao, Jie; Chen, Liming; He, Jianjun; Hou, Long; Li, Liang; Li, Yanfei; Li, Yutong; Liao, Guoqiang; Rhee, Yongjoo; Sun, Yang; Xu, Skiwei; Zhao, Gang; Zhu, Baojun; Zhu, Jianqiang; Zhang, Zhe; Zhang, Jie

    2016-01-01

    Nuclear fusion reactions are the most important processes in nature to power stars and produce new elements, and lie at the center of the understanding of nucleosynthesis in the universe. It is critically important to study the reactions in full plasma environments that are close to true astrophysical conditions. By using laser-driven counter-streaming collisionless plasmas, we studied the fusion D$+$D$\\rightarrow n +^3$He in a Gamow-like window around 27 keV. The results show that astrophysical nuclear reaction yield can be modulated significantly by the self-generated electromagnetic fields and the collective motion of the plasma. This plasma-version mini-collider may provide a novel tool for studies of astrophysics-interested nuclear reactions in plasma with tunable energies in earth-based laboratories.

  20. COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. I. NEUTRAL RETURN FLUX AND ITS EFFECTS ON ACCELERATION OF TEST PARTICLES

    Energy Technology Data Exchange (ETDEWEB)

    Blasi, P.; Morlino, G.; Bandiera, R.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, I-50125 Firenze (Italy); Caprioli, D. [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08540 (United States)

    2012-08-20

    A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high-velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, which we refer to as the neutral return flux, is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge-exchange interaction lengths of fast neutrals moving toward upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities <3000 km s{sup -1}. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test particles accelerated at the shock. We find that, for shocks slower than {approx}3000 km s{sup -1}, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely, {proportional_to}E{sup -2}.

  1. Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

    CERN Document Server

    Melville, S; Kunz, M W

    2015-01-01

    The nonlinear state of a high-beta collisionless plasma is investigated when an imposed linear shear amplifies or diminishes a uniform magnetic field, driving pressure anisotropies and hence firehose/mirror instabilities. The evolution of the resulting microscale turbulence is considered when the shear is switched off or reversed after one shear time (mimicking local behaviour of a macroscopic flow), so a new macroscale configuration is superimposed on the microscale state left behind by the previous one. There is a threshold value of plasma beta: when $\\beta\\ll\\Omega/S$ (ion cyclotron frequency/shear rate), the emergence of firehose/mirror fluctuations driven unstable by shear and their disappearance when the shear is removed/reversed are quasi-instantaneous compared to the shear time, viz., the decay time of these fluctuations is $\\sim\\beta/\\Omega \\ll 1/S$ (this result follows from the free decay of the fluctuations being constrained by the same marginal-stability thresholds as their growth). In contrast, w...

  2. Dispersive nature of high mach number collisionless plasma shocks: Poynting flux of oblique whistler waves.

    Science.gov (United States)

    Sundkvist, David; Krasnoselskikh, V; Bale, S D; Schwartz, S J; Soucek, J; Mozer, F

    2012-01-13

    Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.

  3. The adiabatic energy change of plasma electrons and the frame dependence of the cross-shock potential at collisionless magnetosonic shock waves

    Science.gov (United States)

    Goodrich, C. C.; Scudder, J. D.

    1984-01-01

    The adiabatic energy gain of electrons in the stationary electric and magnetic field structure of collisionless shock waves was examined analytically in reference to conditions of the earth's bow shock. The study was performed to characterize the behavior of electrons interacting with the cross-shock potential. A normal incidence frame (NIF) was adopted in order to calculate the reversible energy change across a time stationary shock, and comparisons were made with predictions made by the de Hoffman-Teller (HT) model (1950). The electron energy gain, about 20-50 eV, is demonstrated to be consistent with a 200-500 eV potential jump in the bow shock quasi-perpendicular geometry. The electrons lose energy working against the solar wind motional electric field. The reversible energy process is close to that modeled by HT, which predicts that the motional electric field vanishes and the electron energy gain from the electric potential is equated to the ion energy loss to the potential.

  4. Magnetic field generation, Weibel-mediated collisionless shocks, and magnetic reconnection in colliding laser-produced plasmas

    Science.gov (United States)

    Fox, W.; Bhattacharjee, A.; Fiksel, G.

    2016-10-01

    Colliding plasmas are ubiquitous in astrophysical environments and allow conversion of kinetic energy into heat and, most importantly, the acceleration of particles to extremely high energies to form the cosmic ray spectrum. In collisionless astrophysical plasmas, kinetic plasma processes govern the interaction and particle acceleration processes, including shock formation, self-generation of magnetic fields by kinetic plasma instabilities, and magnetic field compression and reconnection. How each of these contribute to the observed spectra of cosmic rays is not fully understood, in particular both shock acceleration processes and magnetic reconnection have been proposed. We will review recent results of laboratory astrophysics experiments conducted at high-power, inertial-fusion-class laser facilities, which have uncovered significant results relevant to these processes. Recent experiments have now observed the long-sought Weibel instability between two interpenetrating high temperature plasma plumes, which has been proposed to generate the magnetic field necessary for shock formation in unmagnetized regimes. Secondly, magnetic reconnection has been studied in systems of colliding plasmas using either self-generated magnetic fields or externally applied magnetic fields, and show extremely fast reconnection rates, indicating fast destruction of magnetic energy and further possibilities to accelerate particles. Finally, we highlight kinetic plasma simulations, which have proven to be essential tools in the design and interpretation of these experiments.

  5. Diffusive shock acceleration at laser driven shocks: studying cosmic-ray accelerators in the laboratory

    CERN Document Server

    Reville, B; Gregori, G

    2012-01-01

    The non-thermal particle spectra responsible for the emission from many astrophysical systems are thought to originate from shocks via a first order Fermi process otherwise known as diffusive shock acceleration. The same mechanism is also widely believed to be responsible for the production of high energy cosmic rays. With the growing interest in collisionless shock physics in laser produced plasmas, the possibility of reproducing and detecting shock acceleration in controlled laboratory experiments should be considered. The various experimental constraints that must be satisfied are reviewed. It is demonstrated that several currently operating laser facilities may fulfil the necessary criteria to confirm the occurrence of diffusive shock acceleration of electrons at laser produced shocks. Successful reproduction of Fermi acceleration in the laboratory could open a range of possibilities, providing insight into the complex plasma processes that occur near astrophysical sources of cosmic rays.

  6. Physical processes of driven magnetic reconnection in collisionless plasmas: Zero guide field case

    Science.gov (United States)

    Cheng, C. Z.; Inoue, S.; Ono, Y.; Horiuchi, R.

    2015-10-01

    The key physical processes of the electron and ion dynamics, the structure of the electric and magnetic fields, and how particles gain energy in the driven magnetic reconnection in collisionless plasmas for the zero guide field case are presented. The key kinetic physics is the decoupling of electron and ion dynamics around the magnetic reconnection region, where the magnetic field is reversed and the electron and ion orbits are meandering, and around the separatrix region, where electrons move mainly along the field line and ions move mainly across the field line. The decoupling of the electron and ion dynamics causes charge separation to produce a pair of in-plane bipolar converging electrostatic electric field ( E→ e s ) pointing toward the neutral sheet in the magnetic field reversal region and the monopolar E→ e s around the separatrix region. A pair of electron jets emanating from the reconnection current layer generate the quadrupole out-of-plane magnetic field, which causes the parallel electric field ( E→ || ) from E→ i n d to accelerate particles along the magnetic field. We explain the electron and ion dynamics and their velocity distributions and flow structures during the time-dependent driven reconnection as they move from the upstream to the downstream. In particular, we address the following key physics issues: (1) the decoupling of electron and ion dynamics due to meandering orbits around the field reversal region and the generation of a pair of converging bipolar electrostatic electric field ( E→ e s ) around the reconnection region; (2) the slowdown of electron and ion inflow velocities due to acceleration/deceleration of electrons and ions by E→ e s as they move across the neutral sheet; (3) how the reconnection current layer is enhanced and how the orbit meandering particles are accelerated inside the reconnection region by E→ i n d ; (4) why the electron outflow velocity from the reconnection region reaches super-Alfvenic speed

  7. Collisionless shock waves in space - A very high beta structure. [solar wind measurements

    Science.gov (United States)

    Formisano, V.; Russell, C. T.; Means, J. D.; Greenstadt, E. W.; Scarf, F. L.; Neugebauter, M.

    1975-01-01

    Measurements from six OGO-5 particle and field experiments are used to examine the structure of the earth's bow shock during a period of extremely high beta (the ratio of plasma thermal to magnetic energy density), as determined from simultaneous measurements of the upstream plasma on board the HEOS satellite. Even though the interplanetary field is nearly perpendicular to the shock normal, the shock is extremely turbulent. Large field increases are observed up to a factor of 20 above the upstream values. Ahead of these large enhancements, smaller magnetic effects accompanied by electrostatic noise, electron heating, and ion deflection are observed for several minutes. These observations suggest that a steady-state shock may not be able to form at very high beta. Further, they show that while the magnetic energy density may be relatively unimportant in the upstream flow, it can become very significant within the shock structure, and hence the magnetic field should not be ignored in theoretical treatments of very high beta shocks.

  8. 3D PIC Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

    Science.gov (United States)

    Bamford, R. A.; Alves, E. P.; Cruz, F.; Kellett, B. J.; Fonseca, R. A.; Silva, L. O.; Trines, R. M. G. M.; Halekas, J. S.; Kramer, G.; Harnett, E.; Cairns, R. A.; Bingham, R.

    2016-10-01

    Investigation of the lunar crustal magnetic anomalies offers a comprehensive long-term data set of observations of small-scale magnetic fields and their interaction with the solar wind. In this paper a review of the observations of lunar mini-magnetospheres is compared quantifiably with theoretical kinetic-scale plasma physics and 3D particle-in-cell simulations. The aim of this paper is to provide a complete picture of all the aspects of the phenomena and to show how the observations from all the different and international missions interrelate. The analysis shows that the simulations are consistent with the formation of miniature (smaller than the ion Larmor orbit) collisionless shocks and miniature magnetospheric cavities, which has not been demonstrated previously. The simulations reproduce the finesse and form of the differential proton patterns that are believed to be responsible for the creation of both the “lunar swirls” and “dark lanes.” Using a mature plasma physics code like OSIRIS allows us, for the first time, to make a side-by-side comparison between model and space observations. This is shown for all of the key plasma parameters observed to date by spacecraft, including the spectral imaging data of the lunar swirls. The analysis of miniature magnetic structures offers insight into multi-scale mechanisms and kinetic-scale aspects of planetary magnetospheres.

  9. Note: A table-top blast driven shock tube.

    Science.gov (United States)

    Courtney, Michael W; Courtney, Amy C

    2010-12-01

    The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer that explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

  10. A Table-top Blast Driven Shock Tube

    CERN Document Server

    Courtney, Michael; 10.1063/1.3518970

    2011-01-01

    The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer which explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

  11. Laser-driven shock acceleration of monoenergetic ion beams

    CERN Document Server

    Fiuza, F; Boella, E; Fonseca, R A; Silva, L O; Haberberger, D; Tochitsky, S; Gong, C; Mori, W B; Joshi, C

    2012-01-01

    We show that monoenergetic ion beams can be accelerated by moderate Mach number collisionless, electrostatic shocks propagating in a long scale-length exponentially decaying plasma profile. Strong plasma heating and density steepening produced by an intense laser pulse near the critical density can launch such shocks that propagate in the extended plasma at high velocities. The generation of a monoenergetic ion beam is possible due to the small and constant sheath electric field associated with the slowly decreasing density profile. The conditions for the acceleration of high-quality, energetic ion beams are identified through theory and multidimensional particle-in-cell simulations. The scaling of the ion energy with laser intensity shows that it is possible to generate $\\sim 200$ MeV proton beams with state-of-the-art 100 TW class laser systems.

  12. Shock driven multiphase flow with particle evaporation

    Science.gov (United States)

    Dahal, Jeevan; McFarland, Jacob

    2016-11-01

    The computational study of the shock driven instability of a multiphase system with particle evaporation is presented. The particle evaporation modifies the evolution of the interface due to the addition of the vapor phase to the gas. The effects can be quantitatively measured by studying various gas parameters like density, temperature, vorticity and particle properties like diameter and temperature. In addition, the size distribution of particles also modifies the development of instability as the larger size particles damp the evolution of interface in comparison to the smaller size particles. The simulation results are presented to study these effects using FLASH developed at the FLASH Center at the University of Chicago. The capabilities of FLASH for particle modeling were extended using the Particle in Cell (PIC) technique for coupling of mass, momentum, and energy between the particle and carrier gas. A seeded cylinder of gas with particles having either a single radius or a distribution of radii was studied. The enstrophy production and destruction mechanisms were explored to understand the reason for change in vorticity with particle size.

  13. A Table-top Blast Driven Shock Tube

    OpenAIRE

    Courtney, Michael; Courtney, Amy

    2011-01-01

    The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The d...

  14. Weak turbulence theory of collisionless trapped electron driven drift instability in tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Hahm, T.S.; Tang, W.M.

    1990-10-01

    The toroidal collisionless trapped electron modes are analyzed in the weak turbulence regime treating both ions and trapped electrons nonlinearly in the presence of ion and electron temperature gradients. The spectral intensity of the density fluctuations in the nonlinearly saturated state is analytically obtained from the steady state solution of the wave-kinetic equation. Distant nonlinear interactions between low-k{sub {theta}} and high-k{sub {theta}} modes of similar frequencies via trapped electron scattering (the resonance between the beat wave and the trapped electron precession drift frequencies) suppress the low-k{sub {theta}} (k{sub {theta}}{rho}{sub s} {much lt} (L{sub n}/R){sup 1/2}) modes while close interactions via ion Compton scattering (nonlinear ion Landau damping) produce a monotonically decreasing spectrum from k{sub {theta}}{rho}{sub s} {congruent} (L{sub n}/R){sup 1/2} to k{sub {theta}}{rho}{sub s} {congruent} 1 according to an approximate power law k{sub {theta}}{sup {minus}3}. Various fluctuation amplitudes at saturation and the fluctuation-induced anomalous particle and heat fluxes are found to be smaller than the mixing length estimates. The plasma confinement is predicted to improve with higher T{sub i}/T{sub e}, more peaked density profile, larger aspect ratio, and higher plasma current. Also, a significant dependence of transport on the electron temperature gradient is found which could contribute to the rigidity of the electron temperature profile often experimentally observed.

  15. Radiative Interaction Between Driver and Driven Gases in an Arc-Driven Shock Tube

    Science.gov (United States)

    Bogdanoff, David W.; Park, Chul

    2001-01-01

    An electric-arc driven shock tube was operated with hydrogen as the driven gas and either hydrogen or helium as the driver gas. Electron density was measured behind the primary shock wave spectroscopically from the width of the Beta line of hydrogen. The measured electron density values were many times greater than the values calculated by the Rankine - Hugoniot relations. By accounting for the radiative transfer from the driver gas to the driven gas, the measured electron density values were numerically recreated.

  16. Coherent Structures and Reconnection in Collisionless Turbulence

    Science.gov (United States)

    Roytershteyn, Vadim; Karimabadi, Homa

    2014-10-01

    The sub-proton range of collisionless turbulence has attracted considerable attention in the last decades due to its role in the dissipation of cascading energy and increased availability of high-quality measurements capable of constraining the relevant models. Coherent structures, such as current sheets, have long been considered important sites for the dissipation of energy. However, a self-consistent treatment of their formation and of the relevant collisionless dissipation mechanisms has only become possible recently. Here we discuss several examples from recent kinetic simulations of turbulence focusing on the role of current sheets and magnetic reconnection. In the 3D fully kinetic simulations with initial conditions relevant to solar wind turbulence, current sheets form over a large range of scales and are shown to be sites of increased energy transfer between fluctuating fields and particles. Moreover, depending on the initial conditions and the type of driving, other types of coherent structures are possible, such as magnetic holes. 2D and 3D global hybrid simulations of the interaction between solar wind and planetary magnetospheres demonstrate inherent connection between collisionless shocks, turbulence, and magnetic reconnection. Specifically, the interaction of foreshock turbulence driven by reflected ions with the shock itself leads to a variety of fascinating phenomena in the magnetosheath, seeding both small-scale turbulence and large-scale global perturbations.

  17. Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. III. Collisionless tearing mode

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Dongjian [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); Southwestern Institution of Physics, Chengdu 610041 (China); Bao, Jian [Fusion Simulation Center, Peking University, Beijing 100871 (China); Han, Tao; Wang, Jiaqi [College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China); Lin, Zhihong, E-mail: zhihongl@uci.edu [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States)

    2016-02-15

    A finite-mass electron fluid model for low frequency electromagnetic fluctuations, particularly the collisionless tearing mode, has been implemented in the gyrokinetic toroidal code. Using this fluid model, linear properties of the collisionless tearing mode have been verified. Simulations verify that the linear growth rate of the single collisionless tearing mode is proportional to D{sub e}{sup 2}, where D{sub e} is the electron skin depth. On the other hand, the growth rate of a double tearing mode is proportional to D{sub e} in the parameter regime of fusion plasmas.

  18. Dynamics and microinstabilities at perpendicular collisionless shock: A comparison of large-scale two-dimensional full particle simulations with different ion to electron mass ratio

    CERN Document Server

    Umeda, Takayuki; Matsukiyo, Shuichi; Yamazaki, Ryo

    2014-01-01

    Large-scale two-dimensional (2D) full particle-in-cell simulations are carried out for studying the relationship between the dynamics of a perpendicular shock and microinstabilities generated at the shock foot. The structure and dynamics of collisionless shocks are generally determined by Alfven Mach number and plasma beta, while microinstabilities at the shock foot are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the ratio of the plasma-to-cyclotron frequency. With a fixed Alfven Mach number and plasma beta, the ratio of the upstream bulk velocity to the electron thermal velocity is given as a function of the ion-to-electron mass ratio. The present 2D full PIC simulations with a relatively low Alfven Mach number (M_A ~ 6) show that the modified two-stream instability is dominant with higher ion-to-electron mass ratios. It is also confirmed that waves propagating downstream are more enhanced at the shock foot near the shock ramp as the mass ratio becomes higher. T...

  19. Explosively driven air blast in a conical shock tube

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, Joel B., E-mail: joel.b.stewart2.civ@mail.mil; Pecora, Collin, E-mail: collin.r.pecora.civ@mail.mil [U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States)

    2015-03-15

    Explosively driven shock tubes present challenges in terms of safety concerns and expensive upkeep of test facilities but provide more realistic approximations to the air blast resulting from free-field detonations than those provided by gas-driven shock tubes. Likewise, the geometry of conical shock tubes can naturally approximate a sector cut from a spherically symmetric blast, leading to a better agreement with the blast profiles of free-field detonations when compared to those provided by shock tubes employing constant cross sections. The work presented in this article documents the design, fabrication, and testing of an explosively driven conical shock tube whose goal was to closely replicate the blast profile seen from a larger, free-field detonation. By constraining the blast through a finite area, large blasts (which can add significant damage and safety constraints) can be simulated using smaller explosive charges. The experimental data presented herein show that a close approximation to the free-field air blast profile due to a 1.5 lb charge of C4 at 76 in. can be achieved by using a 0.032 lb charge in a 76-in.-long conical shock tube (which translates to an amplification factor of nearly 50). Modeling and simulation tools were used extensively in designing this shock tube to minimize expensive fabrication costs.

  20. Explosively driven air blast in a conical shock tube.

    Science.gov (United States)

    Stewart, Joel B; Pecora, Collin

    2015-03-01

    Explosively driven shock tubes present challenges in terms of safety concerns and expensive upkeep of test facilities but provide more realistic approximations to the air blast resulting from free-field detonations than those provided by gas-driven shock tubes. Likewise, the geometry of conical shock tubes can naturally approximate a sector cut from a spherically symmetric blast, leading to a better agreement with the blast profiles of free-field detonations when compared to those provided by shock tubes employing constant cross sections. The work presented in this article documents the design, fabrication, and testing of an explosively driven conical shock tube whose goal was to closely replicate the blast profile seen from a larger, free-field detonation. By constraining the blast through a finite area, large blasts (which can add significant damage and safety constraints) can be simulated using smaller explosive charges. The experimental data presented herein show that a close approximation to the free-field air blast profile due to a 1.5 lb charge of C4 at 76 in. can be achieved by using a 0.032 lb charge in a 76-in.-long conical shock tube (which translates to an amplification factor of nearly 50). Modeling and simulation tools were used extensively in designing this shock tube to minimize expensive fabrication costs.

  1. On Poor Separation in Magnetically Driven Shock Tube

    DEFF Research Database (Denmark)

    Chang, C.T.

    1973-01-01

    Observations made at steady-state running conditions in a magnetically driven shock tube, with parallel-plate electrodes, showed that for a given discharge voltage, sufficient separation between the shock and the current-sheet occurred only at relatively high discharge pressures. As a comparison......, poor separations were also noted in conventional diaphragm-type shock tubes running at low initial pressures. It is demonstrated that the observed poor separation can be explained by a mass leakage, instead of through the wall boundary layer, but through the current-sheet itself....

  2. The effect of intermediate frequency on sheath dynamics in collisionless current driven triple frequency capacitive plasmas

    Science.gov (United States)

    Sharma, S.; Mishra, S. K.; Kaw, P. K.; Turner, M. M.

    2017-01-01

    The Capacitively Coupled Plasma discharge featuring operation in current driven triple frequency configuration has analytically been investigated, and the outcome is verified by utilising the 1D3V particle-in-cell (PIC) simulation code. In this analysis, the role of middle frequency component of the applied signal has precisely been explored. The discharge parameters are seen to be sensitive to the ratio of the chosen middle frequency to lower and higher frequencies for fixed amplitudes of the three frequency components. On the basis of analysis and PIC simulation results, the middle frequency component is demonstrated to act as additional control over sheath potential, electron sheath heating, and ion energy distribution function (iedf) of the plasma discharge. For the electron sheath heating, effect of the middle frequency is seen to be pronounced as it approaches to the lower frequency component. On the other hand, for the iedf, the control is more sensitive as the middle frequency approaches towards the higher frequency. The PIC estimate for the electron sheath heating is found to be in reasonably good agreement with the analytical prediction based on the Kaganovich formulation.

  3. Generation of laser plasma bunches with a high efficiency of energy concentration for laboratory simulation of collisionless shock waves in magnetised cosmic plasma

    Science.gov (United States)

    Zakharov, Yu P.; Ponomarenko, A. G.; Tishchenko, V. N.; Antonov, V. M.; Melekhov, A. V.; Posukh, V. G.; Prokopov, P. A.; Terekhin, V. A.

    2016-05-01

    We present the results of first experiments on the formation of collisionless shock waves (CSWs) in background plasma by injecting laser plasma bunches transverse to the magnetic field (as a piston) with a maximum energy up to 100 J per unit of solid angle and with a high enough degree of ion magnetisation. With this aim in view, on a unique KI-1 facility at the Institute of Laser Physics, Siberian Branch of the Russian Academy of Sciences (ILP), a plastic (polyethylene) target irradiated by a CO2 laser in the most energy-efficient regime (near the plasma formation threshold) and a highly ionised hydrogen plasma with a high concentration in a large volume (not less than 1 m3) have been employed. As a result of model experiments performed on the basis of a model of collisionless interaction of plasma flows, developed at the VNIIEF and being adequate to the problem under consideration, not only an intensive, background-induced, deceleration of a super-Alfven laser plasma flow, but also the formation in that flow of a strong perturbation having the properties of a subcritical CSW and propagating transverse to the magnetic field, have been first registered in the laboratory conditions.

  4. Shock wave driven microparticles for pharmaceutical applications

    Science.gov (United States)

    Menezes, V.; Takayama, K.; Gojani, A.; Hosseini, S. H. R.

    2008-10-01

    Ablation created by a Q-switched Nd:Yttrium Aluminum Garnet (Nd:YAG) laser beam focusing on a thin aluminum foil surface spontaneously generates a shock wave that propagates through the foil and deforms it at a high speed. This high-speed foil deformation can project dry micro- particles deposited on the anterior surface of the foil at high speeds such that the particles have sufficient momentum to penetrate soft targets. We used this method of particle acceleration to develop a drug delivery device to deliver DNA/drug coated microparticles into soft human-body targets for pharmaceutical applications. The device physics has been studied by observing the process of particle acceleration using a high-speed video camera in a shadowgraph system. Though the initial rate of foil deformation is over 5 km/s, the observed particle velocities are in the range of 900-400 m/s over a distance of 1.5-10 mm from the launch pad. The device has been tested by delivering microparticles into liver tissues of experimental rats and artificial soft human-body targets, modeled using gelatin. The penetration depths observed in the experimental targets are quite encouraging to develop a future clinical therapeutic device for treatments such as gene therapy, treatment of cancer and tumor cells, epidermal and mucosal immunizations etc.

  5. On the energy source of a magnetically driven shock tube

    DEFF Research Database (Denmark)

    Chang, C.T.; Kofoed-Hansen, O.

    1968-01-01

    In order to study the effect of the variation in load due to the motion of the current sheet on the driving current of a magnetically driven shock tube, we first demonstrate that the usual `snow-plough' model is adequate for the purpose. On the basis of this model it is shown theoretically...... that a shock moving at a constant speed can be obtained by using a constant voltage source. The result of the analysis shows that the value of the steady-state current Î depends on a single parameter epsilon related to the voltage and resistance of the battery, the geometry of the electrodes and the initial...

  6. Impact-driven shock waves and thermonuclear neutron generation

    Energy Technology Data Exchange (ETDEWEB)

    Gus' kov, S Yu; Demchenko, N N; Doskoch, I Ya; Rozanov, V B [P.N. Lebedev Physical Institute of Russian Academy of Sciences, Moscow (Russian Federation); Azechi, H; Murakami, M; Sakaiya, T; Watari, T [Institute of Laser Engineering, Osaka University, Suita, Osaka (Japan); Zmitrenko, N V, E-mail: guskov@sci.lebedev.r [Institute for Mathematical Modeling of Russian Academy of Sciences, Moscow (Russian Federation)

    2009-09-15

    Impact-driven shock waves, thermonuclear plasma and neutron yield were investigated. The results of 2D numerical simulations and Gekko/HIPER laser experiments on the collision of a laser-accelerated disk-projectile with a massive target, both containing (CD){sub n}-material, are discussed. A two-temperature model of the non-equilibrium plasma created by impact-driven shock waves due to the collision of a laser-accelerated planar projectile with a massive target was developed and used for analysis of the numerical and experimental results. The model defines the characteristics of shock waves and plasmas (including their lifetime) as well as neutron yields in both the colliding objects as functions of velocity, density and mass of the projectile-impactor just before collision. The neutron yield generated during the period of laser-driven acceleration of the impactor was also determined. Two effects were discovered that exert a substantial influence on the plasma parameters and neutron yield. The first of them relates to the formation of the pre-impact state of the impactor. It decreases the projectile density due to thermal expansion of its matter through a free boundary during the period of laser-driven acceleration. The other relates to the formation of impact-produced plasma. Predominant heating of the ion component of plasma leads to the existence of a non-equilibrium two-temperature plasma during the period of electron-ion relaxation.

  7. Implicit large eddy simulation of shock-driven material mixing.

    Science.gov (United States)

    Grinstein, F F; Gowardhan, A A; Ristorcelli, J R

    2013-11-28

    Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.

  8. Initial Conditions and Modeling for Shock Driven Turbulence

    Science.gov (United States)

    Grinstein, Fernando

    2016-11-01

    We focus on the simulation of shock-driven material mixing driven by flow instabilities and initial conditions. Beyond complex multi-scale resolution of shocks and variable density turbulence, me must address the equally difficult problem of predicting flow transition promoted by energy deposited at the material interfacial layer during the shock interface interactions. Transition involves unsteady large-scale coherent-structure dynamics which can be captured by LES, but not by URANS based on equilibrium turbulence assumptions and single-point-closure modeling. Such URANS is frequently preferred on the engineering end of computation capabilities for full-scale configurations - and with reduced 1D/2D dimensionality being also a common aspect. With suitable initialization around each transition - e.g., reshock, URANS can be used to simulate the subsequent near-equilibrium weakly turbulent flow. We demonstrate 3D state-of-the-art URANS performance in one such flow regime. We simulate the CEA planar shock-tube experiments by Poggi et al. (1998) with an ILES strategy. Laboratory turbulence and mixing data are used to benchmark ILES. In turn, the ILES generated data is used to initialize and as reference to assess state-of-the-art 3D URANS. We find that by prescribing physics-based 3D initial conditions and allowing for 3D flow convection with just enough resolution, the additionally computed dissipation in 3D URANS effectively blends with the modeled dissipation to yield significantly improved statistical predictions.

  9. Magnetar Driven Shock Breakout and Double Peaked Supernova Light Curves

    CERN Document Server

    Kasen, Daniel; Bildsten, Lars

    2015-01-01

    The light curves of some luminous supernovae are suspected to be powered by the spindown energy of a rapidly rotating magnetar. Here we describe a possible signature of the central engine: a burst of shock breakout emission occurring several days after the supernova explosion. The energy input from the magnetar inflates a high-pressure bubble that drives a shock through the pre-exploded supernova ejecta. If the magnetar is powerful enough, that shock will near the ejecta surface and become radiative. At the time of shock breakout, the ejecta will have expanded to a large radius (~10^{14} cm) so that the radiation released is at optical/ultraviolet wavelengths (T ~ 20,000 K) and lasts for several days. The luminosity and timescale of this magnetar driven shock breakout are similar to the first peak observed recently in the double-peaked light curve of SN-LSQ14BDQ. However, for a large region of model parameter space, the breakout emission is predicted to be dimmer than the diffusive luminosity from direct magn...

  10. Non-thermal Electron Acceleration in Low Mach Number Collisionless Shocks. I. Particle Energy Spectra and Acceleration Mechanism

    Science.gov (United States)

    Guo, Xinyi; Sironi, Lorenzo; Narayan, Ramesh

    2014-10-01

    Electron acceleration to non-thermal energies in low Mach number (Ms Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with Ms = 3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15% of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p ~= 2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration (SDA). The accelerated electrons are then reflected back upstream where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock for further energization via SDA. In summary, the self-generated waves allow for repeated cycles of SDA, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  11. Quantitative Measurements of CME-driven Shocks from LASCO Observations

    CERN Document Server

    Ontiveros, Veronica

    2008-01-01

    In this paper, we demonstrate that CME-driven shocks can be detected in white light coronagraph images and in which properties such as the density compression ratio and shock direction can be measured. Also, their propagation direction can be deduced via simple modeling. We focused on CMEs during the ascending phase of solar cycle 23 when the large-scale morphology of the corona was simple. We selected events which were good candidates to drive a shock due to their high speeds (V>1500 km/s). The final list includes 15 CMEs. For each event, we calibrated the LASCO data, constructed excess mass images and searched for indications of faint and relatively sharp fronts ahead of the bright CME front. We found such signatures in 86% (13/15) of the events and measured the upstream/downstream densities to estimate the shock strength. Our values are in agreement with theoretical expectations and show good correlations with the CME kinetic energy and momentum. Finally, we used a simple forward modeling technique to esti...

  12. Explosive-driven shock wave and vortex ring interaction with a propane flame

    Science.gov (United States)

    Giannuzzi, P. M.; Hargather, M. J.; Doig, G. C.

    2016-11-01

    Experiments were performed to analyze the interaction of an explosively driven shock wave and a propane flame. A 30 g explosive charge was detonated at one end of a 3-m-long, 0.6-m-diameter shock tube to produce a shock wave which propagated into the atmosphere. A propane flame source was positioned at various locations outside of the shock tube to investigate the effect of different strength shock waves. High-speed retroreflective shadowgraph imaging visualized the shock wave motion and flame response, while a synchronized color camera imaged the flame directly. The explosively driven shock tube was shown to produce a repeatable shock wave and vortex ring. Digital streak images show the shock wave and vortex ring propagation and expansion. The shadowgrams show that the shock wave extinguishes the propane flame by pushing it off of the fuel source. Even a weak shock wave was found to be capable of extinguishing the flame.

  13. Non-Thermal Electron Acceleration in Low Mach Number Collisionless Shocks. I. Particle Energy Spectra and Acceleration Mechanism

    CERN Document Server

    Guo, Xinyi; Narayan, Ramesh

    2014-01-01

    Electron acceleration to non-thermal energies in low Mach number (M<5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M=3. We find that about 15 percent of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p~2.4. Initially, thermal electrons are energized at the shock front via shock drift a...

  14. Collisionless Electron-ion Shocks in Relativistic Unmagnetized Jet-ambient Interactions: Non-thermal Electron Injection by Double Layer

    Science.gov (United States)

    Ardaneh, Kazem; Cai, Dongsheng; Nishikawa, Ken-Ichi

    2016-08-01

    The course of non-thermal electron ejection in relativistic unmagnetized electron-ion shocks is investigated by performing self-consistent particle-in-cell simulations. The shocks are excited through the injection of a relativistic jet into ambient plasma, leading to two distinct shocks (referred to as the trailing shock and leading shock) and a contact discontinuity. The Weibel-like instabilities heat the electrons up to approximately half of the ion kinetic energy. The double layers formed in the trailing and leading edges then accelerate the electrons up to the ion kinetic energy. The electron distribution function in the leading edge shows a clear, non-thermal power-law tail which contains ˜1% of electrons and ˜8% of the electron energy. Its power-law index is -2.6. The acceleration efficiency is ˜23% by number and ˜50% by energy, and the power-law index is -1.8 for the electron distribution function in the trailing edge. The effect of the dimensionality is examined by comparing the results of three-dimensional simulations with those of two-dimensional simulations. The comparison demonstrates that electron acceleration is more efficient in two dimensions.

  15. Collisionless electron-ion shocks in relativistic unmagnetized jet-ambient interactions: Non-thermal electron injection by double layer

    CERN Document Server

    Ardaneh, Kazem; Nishikawa, Ken-Ichi

    2016-01-01

    The course of non-thermal electron ejection in relativistic unmagnetized electron-ion shocks is investigated by performing self-consistent particle-in-cell simulations. The shocks are excited through the injection of relativistic jet into ambient plasma, leading to two distinct shocks (named as the trailing shock and leading shock) and a contact discontinuity. The Weibel-like instabilities heat the electrons up to approximately half of ion kinetic energy. The double layers formed in the trailing and leading edges then accelerated the electrons by the ion kinetic energy. The electron distribution function in the leading edge shows a clear non-thermal power-law tail which contains $\\sim1\\%$ of electrons and $\\sim8\\%$ of electron energy. Its power-law index is -2.6. The acceleration efficiency is $\\sim23\\%$ by number and $\\sim50\\%$ by energy and the power-law index is -1.8 for electron distribution function in the trailing edge. The effect of the dimensionality is examined by comparing results of 3D simulation w...

  16. Non-adiabatic electron behaviour due to short-scale electric field structures at collisionless shock waves

    Directory of Open Access Journals (Sweden)

    V. See

    2013-04-01

    Full Text Available Under sufficiently high electric field gradients, electron behaviour within exactly perpendicular shocks is unstable to the so-called trajectory instability. We extend previous work paying special attention to short-scale, high-amplitude structures as observed within the electric field profile. Via test particle simulations, we show that such structures can cause the electron distribution to heat in a manner that violates conservation of the first adiabatic invariant. This is the case even if the overall shock width is larger than the upstream electron gyroradius. The spatial distance over which these structures occur therefore constitutes a new scale length relevant to the shock heating problem. Furthermore, we find that the spatial location of the short-scale structure is important in determining the total effect of non-adiabatic behaviour – a result that has not been previously noted.

  17. Origin of the Ion Foreshock in a Quasi-perpendicular Curved Collisionless Shock: Particles Trajectory Analysis in 2D PIC Simulations

    Science.gov (United States)

    Savoini, P.; Lembege, B.

    2015-12-01

    The ion foreshock located upstream of the Earth's shock wave is populated with ions having interacted with the shock, and then, reflected back with an high energy gain. Spacecrafts have clearly established the existence of two distinct populations in the quasi-perpendicular shock region (i.e. for 45° ≤ ΘBn ≤ 90°, where ΘBn is the angle between the shock normal and the upstream magnetic field) : (i) field-aligned ion beams or « FAB » characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions or « GPB » characterized by a NON gyrotropic distribution. One of the important unresolved problem is the exact origin of the particles contributing to these two populations. To our knowledge, it was the first time that full-particle simulations have been performed including self-consistently the shock front curvature and nonstationarity, and the time-of-flight effects. Our analysis evidences that these two backstreaming populations may be reflected by the front itself and can be differentiated both in terms of interaction time and trajectory within the shock front. In particular, simulations evidence that "GPB" population is characterized by a short interaction time (ΔTinter = 1 to 2 τci) while the "FAB" population corresponds to a much larger time range (from 1 τci to 10 τci), where tci is the upstream ion gyroperiod. Present individual ion trajectories evidence that "FAB" population shows a strong perpendicular drift at the shock front (i.e. strong dependence of the pitch angle to the perpendicular velocity) whereas the "GPB" population shows no perpendicular drift (i.e. its pitch angle is mainly driven by the parallel velocity). Such differences explain why the "FAB" population loses their gyro-phase coherency and become gyrotropic which is not the case for the "GPB". This important result was not expected and greatly simplifies the question of their origin.

  18. Collisionless plasmas in astrophysics

    CERN Document Server

    Belmont, Gerard; Mottez, Fabrice; Pantellini, Filippo; Pelletier, Guy

    2013-01-01

    Collisionless Plasmas in Astrophysics examines the unique properties of media without collisions in plasma physics. Experts in this field, the authors present the first book to concentrate on collisionless conditions in plasmas, whether close or not to thermal equilibrium. Filling a void in scientific literature, Collisionless Plasmas in Astrophysics explains the possibilities of modeling such plasmas, using a fluid or a kinetic framework. It also addresses common misconceptions that even professionals may possess, on phenomena such as "collisionless (Landau) damping". Abundant illustrations

  19. Probabilistic events in shock driven multiphase hydrodynamic instabilities

    Science.gov (United States)

    Black, Wolfgang; Denissen, Nick; McFarland, Jacob

    2016-11-01

    Multiphase flows are an important and complex topic of research with a rich parameter space. Historically many simplifications and assumptions have been made to allow simulation techniques to be applied to these systems. Some common assumptions include no partilce-particle effects, evenly distributed particle fields, no phase change, or even constant particle radii. For some flows, these assumptions may be applicable but as the systems undergo complex accelerations and eventually become turbulent these multiphase parameters can create significant effects. Through the use of FLAG, a multiphysics hydrodynamics code developed at Los Alamos national laboratory, these assumptions can be relaxed or eliminated to increase fidelity and guide the development of experiments. This talk will build on our previous work utilizing simulations on the shock driven multiphase instability with a new investigation into a greater parameter space provided by additional multiphase effects; including a probabilistic particle field, various particle radii, and particle-particle effects on the evolution of commonly studied interfaces. Los Alamos National Laboratory LA-UR-16-25652.

  20. Shock induced damage and damage threshold of optical K9 glass investigated by laser-driven shock wave

    Science.gov (United States)

    Song, Yunfei; Yu, Guoyang; Jiang, Lilin; Zheng, Xianxu; Liu, Yuqiang; Yang, Yanqiang

    2011-04-01

    The shock wave driven by short laser pulse is used to study the damage of brittle material K9 glass. The damage morphology of K9 glass surface indicates that the material has experienced different loading modes, respectively, at the central area and the surrounding area of the shock wave. At the central area of shock wave, the wavefront is plane and has a uniform pressure distribution, the material mainly suffers a longitudinal shock pressure; but on the edge the shock wave, the wavefront is approximately spherical, besides longitudinal pressure, transverse tensile stress will emerge inside the material. In the latter case, the damage threshold of the material is much smaller than that in the case of compressing by longitudinal pressure only. According to the relationship between damage area and shock pressure, an experimental method is proposed to measure the damage threshold of materials under shock loading. The damage threshold of K9 glass under spherical shock wave is measured to be about 1.12 GPa; and the damage threshold under plane shock wave is estimated to be between 1.82 and 1.98 GPa. They are much bigger than the damage threshold under static pressure. This method could also be used to measure the damage threshold of other materials when loaded by dynamic pressure.

  1. Evolutionary signatures in complex ejecta and their driven shocks

    Science.gov (United States)

    Farrugia, C.; Berdichevsky, D.

    2004-10-01

    We examine interplanetary signatures of ejecta-ejecta interactions. To this end, two time intervals of inner-heliospheric (≤1AU) observations separated by 2 solar cycles are chosen where ejecta/magnetic clouds are in the process of interacting to form complex ejecta. At the Sun, both intervals are characterized by many coronal mass ejections (CMEs) and flares. In each case, a complement of observations from various instruments on two spacecraft are examined in order to bring out the in-situ signatures of ejecta-ejecta interactions and their relation to solar observations. In the first interval (April 1979), data are shown from Helios-2 and ISEE-3, separated by ~0.33AU in radial distance and 28° in heliographic longitude. In the second interval (March-April 2001), data from the SOHO and Wind probes are combined, relating effects at the Sun and their manifestations at 1AU on one of Wind's distant prograde orbits. At ~0.67AU, Helios-2 observes two individual ejecta which have merged by the time they are observed at 1AU by ISEE-3. In March 2001, two distinct Halo CMEs (H-CMEs) are observed on SOHO on 28-29 March approaching each other with a relative speed of 500kms-1 within 30 solar radii. In order to isolate signatures of ejecta-ejecta interactions, the two event intervals are compared with expectations for pristine (isolated) ejecta near the last solar minimum, extensive observations on which were given by Berdichevsky et al. (2002). The observations from these two event sequences are then intercompared. In both event sequences, coalescence/merging was accompanied by the following signatures: heating of the plasma, acceleration of the leading ejecta and deceleration of the trailing ejecta, compressed field and plasma in the leading ejecta, disappearance of shocks and the strengthening of shocks driven by the accelerated ejecta. A search for reconnection signatures at the interface between the two ejecta in the March 2001 event was inconclusive because the

  2. The effect of diffusion on the current-sheet speed in a magnetically driven shock tube

    DEFF Research Database (Denmark)

    Chang, C.T.; Popovic, M.; Korsbech, Uffe

    1970-01-01

    The lowering of the current-sheet speed in a magnetically driven shock tube is attributed to the diffusion effect of the current and not to the anchoring of a large fraction of the total current near the driving end.......The lowering of the current-sheet speed in a magnetically driven shock tube is attributed to the diffusion effect of the current and not to the anchoring of a large fraction of the total current near the driving end....

  3. Note: A high Mach number arc-driven shock tube for turbulence studies.

    Science.gov (United States)

    Titus, J B; Alexander, A B; Johnson, J A

    2013-04-01

    A high Mach arc-driven shock tube has been built at the Center for Plasma Science and Technology of Florida A&M University to study shock waves. A larger apparatus with higher voltage was built to study more stable shock waves and subsequent plasmas. Initial measurements of the apparatus conclude that the desired Mach numbers can be reached using only two-thirds the maximum possible energy that the circuit can provide.

  4. Quasiperpendicular high Mach number Shocks

    CERN Document Server

    Sulaiman, A H; Dougherty, M K; Burgess, D; Fujimoto, M; Hospodarsky, G B

    2015-01-01

    Shock waves exist throughout the universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasi-perpendicular shocks across two orders of magnitude in Alfven Mach number (MA) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted timescale of ~0.3 {\\tau}c, where {\\tau}c is the ion gyroperio...

  5. Filamentation Instability of Counterstreaming Laser-Driven Plasmas

    Science.gov (United States)

    Fox, W.; Fiksel, G.; Bhattacharjee, A.; Chang, P.-Y.; Germaschewski, K.; Hu, S. X.; Nilson, P. M.

    2013-11-01

    Filamentation due to the growth of a Weibel-type instability was observed in the interaction of a pair of counterstreaming, ablatively driven plasma flows, in a supersonic, collisionless regime relevant to astrophysical collisionless shocks. The flows were created by irradiating a pair of opposing plastic (CH) foils with 1.8 kJ, 2-ns laser pulses on the OMEGA EP Laser System. Ultrafast laser-driven proton radiography was used to image the Weibel-generated electromagnetic fields. The experimental observations are in good agreement with the analytical theory of the Weibel instability and with particle-in-cell simulations.

  6. Filamentation instability of counter-streaming laser-driven plasmas

    CERN Document Server

    Fox, W; Bhattacharjee, A; Chang, P -Y; Germaschewski, K; Hu, S X; Nilson, P M

    2013-01-01

    Filamentation due to the growth of a Weibel-type instability was observed in the interaction of a pair of counter-streaming, ablatively-driven plasma flows, in a supersonic, collisionless regime relevant to astrophysical collisionless shocks. The flows were created by irradiating a pair of opposing plastic (CH) foils with 1.8 kJ, 2-ns laser pulses on the OMEGA EP laser system. Ultrafast laser-driven proton radiography was used to image the Weibel-generated electromagnetic fields. The experimental observations are in good agreement with the analytical theory of the Weibel instability and with particle-in-cell simulations.

  7. Oxy-acetylene driven laboratory scale shock tubes for studying blast wave effects.

    Science.gov (United States)

    Courtney, Amy C; Andrusiv, Lubov P; Courtney, Michael W

    2012-04-01

    This paper describes the development and characterization of modular, oxy-acetylene driven laboratory scale shock tubes. Such tools are needed to produce realistic blast waves in a laboratory setting. The pressure-time profiles measured at 1 MHz using high-speed piezoelectric pressure sensors have relevant durations and show a true shock front and exponential decay characteristic of free-field blast waves. Descriptions are included for shock tube diameters of 27-79 mm. A range of peak pressures from 204 kPa to 1187 kPa (with 0.5-5.6% standard error of the mean) were produced by selection of the driver section diameter and distance from the shock tube opening. The peak pressures varied predictably with distance from the shock tube opening while maintaining both a true blast wave profile and relevant pulse duration for distances up to about one diameter from the shock tube opening. This shock tube design provides a more realistic blast profile than current compression-driven shock tubes, and it does not have a large jet effect. In addition, operation does not require specialized personnel or facilities like most blast-driven shock tubes, which reduces operating costs and effort and permits greater throughput and accessibility. It is expected to be useful in assessing the response of various sensors to shock wave loading; assessing the reflection, transmission, and absorption properties of candidate armor materials; assessing material properties at high rates of loading; assessing the response of biological materials to shock wave exposure; and providing a means to validate numerical models of the interaction of shock waves with structures. All of these activities have been difficult to pursue in a laboratory setting due in part to lack of appropriate means to produce a realistic blast loading profile.

  8. Evolutionary signatures in complex ejecta and their driven shocks

    Directory of Open Access Journals (Sweden)

    C. J. Farrugia

    2004-11-01

    Full Text Available We examine interplanetary signatures of ejecta-ejecta interactions. To this end, two time intervals of inner-heliospheric (≤1AU observations separated by 2 solar cycles are chosen where ejecta/magnetic clouds are in the process of interacting to form complex ejecta. At the Sun, both intervals are characterized by many coronal mass ejections (CMEs and flares. In each case, a complement of observations from various instruments on two spacecraft are examined in order to bring out the in-situ signatures of ejecta-ejecta interactions and their relation to solar observations. In the first interval (April 1979, data are shown from Helios-2 and ISEE-3, separated by ~0.33AU in radial distance and 28° in heliographic longitude. In the second interval (March-April 2001, data from the SOHO and Wind probes are combined, relating effects at the Sun and their manifestations at 1AU on one of Wind's distant prograde orbits. At ~0.67AU, Helios-2 observes two individual ejecta which have merged by the time they are observed at 1AU by ISEE-3. In March 2001, two distinct Halo CMEs (H-CMEs are observed on SOHO on 28-29 March approaching each other with a relative speed of 500kms-1 within 30 solar radii. In order to isolate signatures of ejecta-ejecta interactions, the two event intervals are compared with expectations for pristine (isolated ejecta near the last solar minimum, extensive observations on which were given by Berdichevsky et al. (2002. The observations from these two event sequences are then intercompared. In both event sequences, coalescence/merging was accompanied by the following signatures: heating of the plasma, acceleration of the leading ejecta and deceleration of the trailing ejecta, compressed field and plasma in the leading ejecta, disappearance of shocks and the strengthening of shocks driven by the accelerated ejecta. A search for reconnection signatures at the interface between the two ejecta in the March 2001 event was

  9. Laser Driven Compression to Investigate Shock-Induced Melting of Metals

    Directory of Open Access Journals (Sweden)

    Thibaut de Rességuier

    2014-10-01

    Full Text Available High pressure shock compression induces a large temperature increase due to the dissipation within the shock front. Hence, a solid sample subjected to intense shock loading can melt, partially or fully, either on compression or upon release from the shocked state. In particular, such melting is expected to be associated with specific damage and fragmentation processes following shock propagation. In this paper, we show that laser driven shock experiments can provide a procedure to investigate high pressure melting of metals at high strain rates, which is an issue of key interest for various engineering applications as well as for geophysics. After a short description of experimental and analytical tools, we briefly review some former results reported for tin, then we present more recent observations for aluminum and iron.

  10. Investigating Vaporization of Silica through Laser Driven Shock Wave Experiments

    Science.gov (United States)

    Kraus, R. G.; Swift, D. C.; Stewart, S. T.; Smith, R.; Bolme, C. A.; Spaulding, D. K.; Hicks, D.; Eggert, J.; Collins, G.

    2010-12-01

    Giant impacts melt and vaporize a significant amount of the bolide and target body. However, our ability to determine how much melt or vapor a given impact creates depends strongly on our understanding of the liquid-vapor phase boundary of geologic materials. Our current knowledge of the liquid-vapor equilibrium for one of the most important minerals, SiO2, is rather limited due to the difficulty of performing experiments in this area of phase space. In this study, we investigate the liquid-vapor coexistence region by shocking quartz into a supercritical fluid state and allowing it to adiabatically expand to a state on the liquid-vapor phase boundary. Although shock compression and release has been used to study the liquid-vapor equilibrium of metals [1], few attempts have been made at studying geologic materials by this method [2]. Shock waves were produced by direct ablation of the quartz sample using the Jupiter Laser Facility of Lawrence Livermore National Laboratory. Steady shock pressures of 120-360 GPa were produced in the quartz samples: high enough to force the quartz into a supercritical fluid state. As the shock wave propagates through the sample, we measure the shock velocity using a line imaging velocity interferometer system for any reflector (VISAR) and shock temperature using a streaked optical pyrometer (SOP). When the shock wave reaches the free surface of the sample, the material adiabatically expands. Upon breakout of the shock at the free surface, the SOP records a distinct drop in radiance due to the lower temperature of the expanded material. For a subset of experiments, a LiF window is positioned downrange of the expanding silica. When the expanding silica impacts the LiF window, the velocity at the interface between the expanding silica and LiF window is measured using the VISAR. From the shock velocity measurements, we accurately determine the shocked state in the quartz. The post-shock radiance measurements are used to constrain the

  11. Theory of the corrugation instability of a piston-driven shock wave.

    Science.gov (United States)

    Bates, J W

    2015-01-01

    We analyze the two-dimensional stability of a shock wave driven by a steadily moving corrugated piston in an inviscid fluid with an arbitrary equation of state. For h≤-1 or h>h(c), where h is the D'yakov parameter and h(c) is the Kontorovich limit, we find that small perturbations on the shock front are unstable and grow--at first quadratically and later linearly--with time. Such instabilities are associated with nonequilibrium fluid states and imply a nonunique solution to the hydrodynamic equations. The above criteria are consistent with instability limits observed in shock-tube experiments involving ionizing and dissociating gases and may have important implications for driven shocks in laser-fusion, astrophysical, and/or detonation studies.

  12. Effects of Initial Condition Spectral Content on Shock Driven Turbulent Mixing

    CERN Document Server

    Nelson, Nicholas J

    2015-01-01

    The mixing of materials due to the Richtmyer-Meshkov instability and the ensuing turbulent behavior is of intense interest in a variety of physical systems including inertial confinement fusion, combustion, and the final stages of stellar evolution. Extensive numerical and laboratory studies of shock-driven mixing have demonstrated the rich behavior associated with the onset of turbulence due to the shocks. Here we report on progress in understanding shock-driven mixing at interfaces between fluids of differing densities through 3D numerical simulations using the RAGE code in the implicit large eddy simulation context. We consider a shock tube configuration with a band of high density gas (SF$_6$) embedded in low density gas (air). Shocks with a Mach number of 1.26 are passed through SF$_6$ bands, resulting in transition to turbulence driven by the Richtmyer-Meshkov instability. The system is followed as a rarefaction wave and a reflected secondary shock from the back wall pass through the SF$_6$ band. We app...

  13. Laser driven single shock compression of fluid deuterium from 45 to 220 GPa

    Energy Technology Data Exchange (ETDEWEB)

    Hicks, D; Boehly, T; Celliers, P; Eggert, J; Moon, S; Meyerhofer, D; Collins, G

    2008-03-23

    The compression {eta} of liquid deuterium between 45 and 220 GPa under laser-driven shock loading has been measured using impedance matching to an aluminum (Al) standard. An Al impedance match model derived from a best fit to absolute Hugoniot data has been used to quantify and minimize the systematic errors caused by uncertainties in the high-pressure Al equation of state. In deuterium below 100 GPa results show that {eta} {approx_equal} 4.2, in agreement with previous impedance match data from magnetically-driven flyer and convergent-explosive shock wave experiments; between 100 and 220 GPa {eta} reaches a maximum of {approx}5.0, less than the 6-fold compression observed on the earliest laser-shock experiments but greater than expected from simple extrapolations of lower pressure data. Previous laser-driven double-shock results are found to be in good agreement with these single-shock measurements over the entire range under study. Both sets of laser-shock data indicate that deuterium undergoes an abrupt increase in compression at around 110 GPa.

  14. Oxy-acetylene driven laboratory scale shock tubes for studying blast wave effects

    CERN Document Server

    Courtney, Michael

    2011-01-01

    Instrumentation is needed to produce realistic blast waves in a laboratory setting. This paper describes the development and characterization of oxy-acetylene driven, laboratory scale shock tubes for use in studying blast injury, candidate armor materials, and material properties at blast loading rates. The pressure-time profiles show a true shock front and exponential decay characteristic of blast waves and have relevant durations. The modular design includes shock tube diameters of 27 mm and 41 mm, and a selection of peak pressures from 204 kPa to 920 kPa can be produced by selection of the driver section diameter and placement of the test sample. Characterization studies of several driver/driven section combinations showed consistent results, with peak pressures having 0.8 - 6.9 percent uncertainty in the mean. This shock tube design provides a more realistic blast profile than current air-driven shock tubes. In addition, operation does not require specialized personnel or facilities like most blast-driven...

  15. Optical diagnostics of turbulent mixing in explosively-driven shock tube

    Science.gov (United States)

    Anderson, James; Hargather, Michael

    2016-11-01

    Explosively-driven shock tube experiments were performed to investigate the turbulent mixing of explosive product gases and ambient air. A small detonator initiated Al / I2O5 thermite, which produced a shock wave and expanding product gases. Schlieren and imaging spectroscopy were applied simultaneously along a common optical path to identify correlations between turbulent structures and spatially-resolved absorbance. The schlieren imaging identifies flow features including shock waves and turbulent structures while the imaging spectroscopy identifies regions of iodine gas presence in the product gases. Pressure transducers located before and after the optical diagnostic section measure time-resolved pressure. Shock speed is measured from tracking the leading edge of the shockwave in the schlieren images and from the pressure transducers. The turbulent mixing characteristics were determined using digital image processing. Results show changes in shock speed, product gas propagation, and species concentrations for varied explosive charge mass. Funded by DTRA Grant HDTRA1-14-1-0070.

  16. Shock-driven Accretion in Circumplanetary Disks: Observables and Satellite Formation

    CERN Document Server

    Zhu, Zhaohuan; Stone, James M

    2016-01-01

    Circumplanetary disks (CPDs) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. We have carried out two dimensional hydrodynamical simulations with radiative cooling to study CPDs, and suggested a new mechanism to drive the disk accretion. Two spiral shocks are present in CPDs, excited by the central star. We find that spiral shocks can at least contribute to, if not dominate the angular momentum transport and energy dissipation in CPDs. Meanwhile, dissipation and heating by spiral shocks have a positive feedback on shock-driven accretion itself. As the disk is heated up by spiral shocks, the shocks become more open, leading to more efficient angular momentum transport. This shock driven accretion is, on the other hand, unsteady on a timescale of months/years due to production and destruction of vortices in disks. After being averaged over time, a quasi-steady accretion is reached from the planet's Hill radius all the way to th...

  17. Shock-driven fluid-structure interaction for civil design

    Energy Technology Data Exchange (ETDEWEB)

    Wood, Stephen L [ORNL; Deiterding, Ralf [ORNL

    2011-11-01

    The multiphysics fluid-structure interaction simulation of shock-loaded structures requires the dynamic coupling of a shock-capturing flow solver to a solid mechanics solver for large deformations. The Virtual Test Facility combines a Cartesian embedded boundary approach with dynamic mesh adaptation in a generic software framework of flow solvers using hydrodynamic finite volume upwind schemes that are coupled to various explicit finite element solid dynamics solvers (Deiterding et al., 2006). This paper gives a brief overview of the computational approach and presents first simulations that utilize the general purpose solid dynamics code DYNA3D for complex 3D structures of interest in civil engineering. Results from simulations of a reinforced column, highway bridge, multistory building, and nuclear reactor building are presented.

  18. Modeling of PZT Ferroelectric Ceramic Depolarization Driven by Shock Stress

    Institute of Scientific and Technical Information of China (English)

    LAN Chao-Hui; PENG Yu-Fei; LONG Ji-Dong; WANG Qiang; WANG Wen-Dou

    2011-01-01

    @@ Shock-induced phase transition of ferroelectric ceramic PZT 95/5 causes elastic stiffening and depolarization,releasing stored electrostatic energy into the load circuit.We develop a model to describe the response of the PZT ferroelectric ceramic and implement it into simulation codes.The model is based on the phenomenological theory of phase transition dyynamics and takes into account the effects of the self-generated intensive electrical field and stress.Connected with the discharge model and external circuit, the whole transient process of PZT ceramic depoling can be investigated.The results show the finite transition velocity of the ferroelectric phase and the double wave structure caused by phase transition.Simulated currents are compared with the results from experiments with shock pressures varying from 0.4 to 2.8GPa.

  19. THE JET-DRIVEN BOW SHOCK IN OUTFLOWS

    Institute of Scientific and Technical Information of China (English)

    ZhangQing; ZhengXingwu

    1999-01-01

    Recent high resolution observations show the high collimated bipolar molecular outflows from young stellar objects, such as NGC 2 264G and NGC 2 024. Existing models can not yet give complete interpretations of the structure and properties of the observed flow. Here, we propose a jet-driven bow

  20. BOW SHOCK FRAGMENTATION DRIVEN BY A THERMAL INSTABILITY IN LABORATORY ASTROPHYSICS EXPERIMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki-Vidal, F.; Lebedev, S. V.; Pickworth, L. A.; Swadling, G. F.; Skidmore, J.; Hall, G. N.; Bennett, M.; Bland, S. N.; Burdiak, G.; De Grouchy, P.; Music, J.; Suttle, L. [Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom); Ciardi, A. [Sorbonne Universités, UPMC Univ. Paris 6, UMR 8112, LERMA, F-75005, Paris (France); Rodriguez, R.; Gil, J. M.; Espinosa, G. [Departamento de Fisica de la Universidad de Las Palmas de Gran Canaria, E-35017 Las Palmas de Gran Canaria (Spain); Hartigan, P. [Department of Physics and Astronomy, Rice University, 6100 S. Main, Houston, TX 77521-1892 (United States); Hansen, E.; Frank, A., E-mail: f.suzuki@imperial.ac.uk [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)

    2015-12-20

    The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counterstreaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame, and the experiments are driven over many times the characteristic cooling timescale. The initially smooth bow shock rapidly develops small-scale nonuniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with the radiative packages ABAKO/RAPCAL.

  1. Bow shock fragmentation driven by a thermal instability in laboratory-astrophysics experiments

    CERN Document Server

    Suzuki-Vidal, F; Ciardi, A; Pickworth, L A; Rodriguez, R; Gil, J M; Espinosa, G; Hartigan, P; Swadling, G F; Skidmore, J; Hall, G N; Bennett, M; Bland, S N; Burdiak, G; de Grouchy, P; Music, J; Suttle, L; Hansen, E; Frank, A

    2015-01-01

    The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counter-streaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame and the experiments are driven over many times the characteristic cooling time-scale. The initially smooth bow shock rapidly develops small-scale non-uniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with...

  2. Collisionless magnetic reconnection under anisotropic MHD approximation

    Science.gov (United States)

    Hirabayashi, Kota; Hoshino, Masahiro

    We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{⊥}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{⊥})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.

  3. The behavior of iron under ultrafast shock loading driven by a femtosecond laser

    Science.gov (United States)

    Ashitkov, S. I.; Zhakhovsky, V. V.; Inogamov, N. A.; Komarov, P. S.; Agranat, M. B.; Kanel, G. I.

    2017-01-01

    The results of experimental and theoretical investigations of shock-wave propagation in bcc iron under ultra-short loads driven by femtosecond laser pulses are presented. Chirped pulse interferometry was used for continuous diagnostics of movement in a picosecond range of the rear-side surface of thin iron films. The evolution of ultra-short elastic-plastic shock waves in samples with different thicknesses and purity has been studied. The obtained HEL and spall strength are close to ultimate values of shear and tensile stresses. Response of single-crystal iron to ultra-short shock loading/unloading was also explored in micron-sized films by molecular dynamics simulations. The experimental and simulation results on shock-induced elastic-plastic transformation and phase transition from bcc to hcp iron in a picosecond range of loading are discussed.

  4. Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-Driven Instabilities and the Electron Heating Mechanism

    CERN Document Server

    Sironi, Lorenzo

    2014-01-01

    In systems accreting well below the Eddington rate, the plasma in the innermost regions of the disk is collisionless and two-temperature, with the ions hotter than the electrons. Yet, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities, by means of multi-dimensional particle-in-cell (PIC) simulations. A large-scale compression - embedded in a novel form of the PIC equations - continuously amplifies the field. This constantly drives a pressure anisotropy P_perp > P_parallel, due to the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values beta_i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows, mirror modes dominate if the electron-to-proton temperature ratio is > 0.2, whereas if it is m_e/m_i - governed by the conservation of the magnetic moment in the growing fields ...

  5. Periodic shock-emission from acoustically driven cavitation clouds: a source of the subharmonic signal.

    Science.gov (United States)

    Johnston, Keith; Tapia-Siles, Cecilia; Gerold, Bjoern; Postema, Michiel; Cochran, Sandy; Cuschieri, Alfred; Prentice, Paul

    2014-12-01

    Single clouds of cavitation bubbles, driven by 254kHz focused ultrasound at pressure amplitudes in the range of 0.48-1.22MPa, have been observed via high-speed shadowgraphic imaging at 1×10(6) frames per second. Clouds underwent repetitive growth, oscillation and collapse (GOC) cycles, with shock-waves emitted periodically at the instant of collapse during each cycle. The frequency of cloud collapse, and coincident shock-emission, was primarily dependent on the intensity of the focused ultrasound driving the activity. The lowest peak-to-peak pressure amplitude of 0.48MPa generated shock-waves with an average period of 7.9±0.5μs, corresponding to a frequency of f0/2, half-harmonic to the fundamental driving. Increasing the intensity gave rise to GOC cycles and shock-emission periods of 11.8±0.3, 15.8±0.3, 19.8±0.2μs, at pressure amplitudes of 0.64, 0.92 and 1.22MPa, corresponding to the higher-order subharmonics of f0/3, f0/4 and f0/5, respectively. Parallel passive acoustic detection, filtered for the fundamental driving, revealed features that correlated temporally to the shock-emissions observed via high-speed imaging, p(two-tailed) subharmonic spectral peaks, in the frequency domain. The larger cavitation clouds (>200μm diameter, at maximum inflation), that developed under insonations of peak-to-peak pressure amplitudes >1.0MPa, emitted shock-waves with two or more fronts suggesting non-uniform collapse of the cloud. The observations indicate that periodic shock-emissions from acoustically driven cavitation clouds provide a source for the cavitation subharmonic signal, and that shock structure may be used to study intra-cloud dynamics at sub-microsecond timescales.

  6. Reverse Undercompressive Shock Structures in Wetting Films Driven by a Marangoni Flow

    Science.gov (United States)

    Sur, Jeanman; Bertozzi, Andrea; Behringer, Robert

    2002-11-01

    We experimentally investigate the pinch-off transition in thin liquid films driven by a thermally induced Marangoni force against the gravity. In the experiments, a partially immersed non-isothermal solid substrate is pulled out from a liquid bath and allowed to drain. A uniform temperature gradient drives the film up the substrate. The film just above the meniscus becomes thin and pinches off from the bulk fluid. This pinch-off transition was first observed by Ludviksson and Lightfoot [AIChE J. 17, 1166(1971)] and recently analyzed by Andrea Muench [preprint]. Muench predicts that the pinch-off transition gives rise to a leading undercompressive shock, followed by a reverse undercompressive shock and a trailing rarefaction wave. Our experiments confirm his prediction and show that the reverse undercompressive shock is unstable to transverse perturbations while the leading undercompressive shock is stable. Depending on the pinch-off film thickness, as controlled by the meniscus, either a trailing rarefaction wave or a compressive shock separates from the reverse undercompressive shock. This is the first experimental evidence of a scalar shock structure involving two undercompressive waves.

  7. Side-Pinch Effect of a Magnetically Driven Shock Tube with Parallel Plate Electrodes

    DEFF Research Database (Denmark)

    Chang, C. T.; Korsbech, Uffe C C; Mondrup, K.

    1969-01-01

    To study the possible effect of the side pinch on the steady-state current and the steady-state shock speed of a magnetically driven shock tube, a semiempirical model is formulated. The time history of the current, the radial and the translational motion of the current-carrying region are expressed...... show that the current-carrying region oscillates radially, but the current and the translational velocity of the current-carrying region approach the quasi-steady state rapidly. The deviation of the current from its “steady-state” value (when the pinch effect is absent) in no case amounts to more than...

  8. Shock-driven Accretion in Circumplanetary Disks: Observables and Satellite Formation

    Science.gov (United States)

    Zhu, Zhaohuan; Ju, Wenhua; Stone, James M.

    2016-12-01

    Circumplanetary disks (CPDs) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. We have carried out two-dimensional hydrodynamical simulations with radiative cooling to study CPDs and suggested a new mechanism to drive the disk accretion. Two spiral shocks are present in CPDs, excited by the central star. We find that spiral shocks can at least contribute to, if not dominate, the angular momentum transport and energy dissipation in CPDs. Meanwhile, dissipation and heating by spiral shocks have a positive feedback on shock-driven accretion itself. As the disk is heated up by spiral shocks, the shocks become more open, leading to more efficient angular momentum transport. This shock-driven accretion is, on the other hand, unsteady due to production and destruction of vortices in disks. After being averaged over time, a quasi-steady accretion is reached from the planet’s Hill radius all the way to the planet surface, and the disk α coefficient characterizing angular momentum transport is ˜0.001-0.02. The disk surface density ranges from 10 to 1000 g cm-2 in our simulations, which is at least three orders of magnitude smaller than the “minimum-mass subnebula” model used to study satellite formation; instead it is more consistent with the “gas-starved” satellite formation model. Finally, we calculate the millimeter flux emitted by CPDs at ALMA and EVLA wavelength bands and predict the flux for several recently discovered CPD candidates, which suggests that ALMA is capable of discovering these accreting CPDs.

  9. Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-driven Instabilities and the Electron Heating Mechanism

    Science.gov (United States)

    Sironi, Lorenzo; Narayan, Ramesh

    2015-02-01

    In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the electron-to-proton temperature ratio is T 0e /T 0i >~ 0.2, whereas for T 0e /T 0i ~ 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the initial electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.

  10. Evaluation of standoff distance method to determine the coronal magnetic field using CME-driven shocks

    Science.gov (United States)

    Suresh, K.; Shanmugaraju, A.; Syed Ibrahim, M.

    2016-11-01

    We have analyzed the propagation characteristics of four limb coronal mass ejections (CMEs) with their shocks. These CMEs were observed in 18 frames up to 18 solar radii using LASCO white light images. Gopalswamy and Yashiro (Astrophys. J. 736:L17, 2011) introduced the standoff distance method (SOD) to find the magnetic field in the corona using CME-driven shock. In this paper, we have used this technique to determine the magnetic field strength and to study the propagation/shock formation condition of these CMEs at 18 different locations. Since the thickness of shock sheath (standoff distance or SOD) is not constant around CME, we estimate the shock parameters and their variation in large and small SOD regions of the shock. The Mach number ranges from 1.7 to 2.8 and Alfvén speed varies from 197 to 857 km s^{-1}. Finally, we estimate the magnetic field variation in the corona. The magnetic field strength ranges from 4.9 to 26.2 mG from 8.3 to 17.5 solar radii. The estimated magnetic field strength in this study is consistent with the literature value (7.6 to 45.8 mG from Gopalswamy and Yashiro (Astrophys. J. 736:L17, 2011), and 6 to 105 mG from Kim et al. (Astrophys. J. 746:118, 2012)) and it smoothly follows the general coronal magnetic field profile.

  11. Numerical investigation of Richtmyer-Meshkov instability driven by cylindrical shocks

    Institute of Scientific and Technical Information of China (English)

    Baolin Tian; Dexun FU; Yanwen Ma

    2006-01-01

    In this Paper,a numerical method with high order accuracy and high resolution was developed to simulate the Richtmyer-Meshkov(RM) instability driven by cylindrical shock waves.Compressible Euler equations in cylindrical coordinate were adopted for the cylindrical geometry and a third order accurate group control scheme was adopted to discretize the equations.Moreover,an adaptive grid technique was developed to refine the grid near the moving interface to improve the resolution of numerical solutions.The results of simulation exhibited the evolution process of RM instability,and the effect of Atwood number was studied.The larger the absolute value of Atwood number,the larger the perturbation amplitude.The nonlinear effect manifests more evidently in cylindrical geometry.The shock reflected from the pole center accelerates the interface for the second time,considerably complicating the interface evolution process,and such phenomena of reshock and secondary shock were studied.

  12. Picosecond dynamics of a shock-driven displacive phase transformation in Zr

    Science.gov (United States)

    Swinburne, T. D.; Glavicic, M. G.; Rahman, K. M.; Jones, N. G.; Coakley, J.; Eakins, D. E.; White, T. G.; Tong, V.; Milathianaki, D.; Williams, G. J.; Rugg, D.; Sutton, A. P.; Dye, D.

    2016-04-01

    High-pressure solid-state transformations at high strain rates are usually observed after the fact, either during static holding or after unloading, or inferred from interferometry measurements of the sample surface. The emergence of femtosecond x-ray diffraction techniques provides insight into the dynamics of short-time-scale events such as shocks. We report laser pump-probe experiments of the response of Zr to laser-driven shocks over the first few nanoseconds of the shock event, enabling the α →ω transition and orientation relationship to be observed in real time with picosecond resolution. A clear orientation relationship of (101 ¯0 ) α|| (101 ¯1 ) ω is found, in conflict with ω →α annealing experiments in zirconium and the two α →ω pathways proposed for titanium.

  13. A Data-Driven Analytic Model for Proton Acceleration by Large-Scale Solar Coronal Shocks

    CERN Document Server

    Kozarev, Kamen A

    2016-01-01

    We have recently studied the development of an eruptive filament-driven, large-scale off-limb coronal bright front (OCBF) in the low solar corona (Kozarev et al. 2015), using remote observations from Solar Dynamics Observatory's Advanced Imaging Assembly EUV telescopes. In that study, we obtained high-temporal resolution estimates of the OCBF parameters regulating the efficiency of charged particle acceleration within the theoretical framework of diffusive shock acceleration (DSA). These parameters include the time-dependent front size, speed, and strength, as well as the upstream coronal magnetic field orientations with respect to the front's surface normal direction. Here we present an analytical particle acceleration model, specifically developed to incorporate the coronal shock/compressive front properties described above, derived from remote observations. We verify the model's performance through a grid of idealized case runs using input parameters typical for large-scale coronal shocks, and demonstrate ...

  14. Maximum initial growth-rate of strong-shock-driven Richtmyer-Meshkov instability

    Science.gov (United States)

    Dell, Z. R.; Pandian, A.; Bhowmick, A. K.; Swisher, N. C.; Stanic, M.; Stellingwerf, R. F.; Abarzhi, S. I.

    2017-09-01

    We focus on the classical problem of the dependence on the initial conditions of the initial growth-rate of strong shock driven Richtmyer-Meshkov instability (RMI) by developing a novel empirical model and by employing rigorous theories and Smoothed Particle Hydrodynamics simulations to describe the simulation data with statistical confidence in a broad parameter regime. For the given values of the shock strength, fluid density ratio, and wavelength of the initial perturbation of the fluid interface, we find the maximum value of the RMI initial growth-rate, the corresponding amplitude scale of the initial perturbation, and the maximum fraction of interfacial energy. This amplitude scale is independent of the shock strength and density ratio and is characteristic quantity of RMI dynamics. We discover the exponential decay of the ratio of the initial and linear growth-rates of RMI with the initial perturbation amplitude that excellently agrees with available data.

  15. Continuum modelling of piston driven shock waves through granular gases and ensuing pattern formations

    Science.gov (United States)

    Sirmas, Nick; Radulescu, Matei

    2015-11-01

    Two-dimensional event-driven Molecular Dynamics (MD) simulations were previously completed to investigate the stability of piston driven shock waves through dilute granular gases. By considering viscoelastic collisions, allowing for finite dissipation within the shock wave, instabilities were found in the form of distinctive high density non-uniformities and convective rolls within the shock structure. This work is now extended to the continuum level. Euler and Navier-Stokes equations for granular gases are modelled with a modified cooling rate to include an impact threshold necessary for inelastic collisions. The shock structure predicted by the continuum formulation is found in good agreement with the structure obtained by MD. Non-linear stability analyses of the travelling wave solution are performed, showing a neutrally stable structure and responding only to fluctuations in the upstream state. Introducing strong perturbations to the incoming density field, in accordance with the spacial fluctuations in upstream state seen in MD, yields similar instabilities as those previously observed. While the inviscid model predicts a highly turbulent structure from these perturbations, the inclusion of viscosity yields comparable wavelengths of pattern formations to those seen in MD.

  16. Analysis of the CME-driven shock from the SEP event that occurred on 2006 December 14

    Institute of Scientific and Technical Information of China (English)

    Xin Wang; Yi-Hua Yan

    2012-01-01

    In a solar flare or coronal mass ejection (CME),observations of the subsequent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV,even up to GeV.Diffusive shock acceleration is an efficient mechanism for particle acceleration.For investigating the shock structure,the energy injection and energy spectrum of a CME-driven shock,we perform a dynamical Monte Carlo simulation of the CME-driven shock that occurred on 2006 December 14 using an anisotropic scattering law.The simulated results of the shock's fine structure,particle injection,and energy spectrum are presented.We find that our simulation results give a good fit to the observations from multiple spacecraft.

  17. Emergence of power-law scalings in shock-driven mixing transition

    Science.gov (United States)

    Vorobieff, Peter; Wayne, Patrick; Olmstead, Dell; Simons, Dylan; Truman, C. Randall; Kumar, Sanjay

    2016-11-01

    We present an experimental study of transition to turbulence due to shock-driven instability evolving on an initially cylindrical, diffuse density interface between air and a mixture of sulfur hexafluoride (SF6) and acetone. The plane of the shock is at an initial angle θ with the axis of the heavy-gas cylinder. We present the cases of planar normal (θ = 0) and oblique (θ =20°) shock interaction with the initial conditions. Flow is visualized in two perpendicular planes with planar laser-induced fluorescence (PLIF) triggered in acetone with a pulsed ultraviolet laser. Statistics of the flow are characterized in terms of the second-order structure function of the PLIF intensity. As instabilities in the flow evolve, the structure functions begin to develop power-law scalings, at late times manifesting over a range of scales spanning more than two orders of magnitude. We discuss the effects of the initial conditions on the emergence of these scalings, comparing the fully three-dimensional case (oblique shock interaction) with the quasi-two-dimensional case (planar normal shock interaction). We also discuss the flow anisotropy apparent in statistical differences in data from the two visualization planes. This work is funded by NNSA Grant DE-NA0002913.

  18. Quasiperpendicular High Mach Number Shocks

    Science.gov (United States)

    Sulaiman, A. H.; Masters, A.; Dougherty, M. K.; Burgess, D.; Fujimoto, M.; Hospodarsky, G. B.

    2015-09-01

    Shock waves exist throughout the Universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this Letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasiperpendicular shocks across 2 orders of magnitude in Alfvén Mach number (MA ) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted time scale of ˜0.3 τc , where τc is the ion gyroperiod. In addition, we experimentally reveal the relationship between reformation and MA and focus on the magnetic structure of such shocks to further show that for the same MA , a reforming shock exhibits stronger magnetic field amplification than a shock that is not reforming.

  19. Properties of the Fast Forward Shock Driven by the July 23 2012 Extreme Coronal Mass Ejection

    CERN Document Server

    Riley, Pete; Giacalone, Joe; Lario, David; Liu, Ying

    2015-01-01

    Late on July 23, 2012, the STEREO-A spacecraft encountered a fast forward shock driven by a coronal mass ejection launched from the Sun earlier that same day. The estimated travel time of the disturbance ($\\sim 20$ hrs), together with the massive magnetic field strengths measured within the ejecta ($> 100$nT), made it one of the most extreme events observed during the space era. In this study, we examine the properties of the shock wave. Because of an instrument malfunction, plasma measurements during the interval surrounding the CME were limited, and our approach has been modified to capitalize on the available measurements and suitable proxies, where possible. We were able to infer the following properties. First, the shock normal was pointing predominantly in the radial direction (${\\bf n} = 0.97 {\\bf e}_r -0.09 {\\bf e}_t -0.23 {\\bf e}_n$). Second, the angle between ${\\bf n}$ and the upstream magnetic field, $\\theta_{Bn}$, was estimated to be $\\approx 34^{\\circ}$, making the shock "quasi-parallel," and sup...

  20. Ion acceleration at CME-driven shocks near the Earth and the Sun

    Energy Technology Data Exchange (ETDEWEB)

    Desai, Mihir; Dayeh, Maher; Ebert, Robert; Smith, Charles; Mason, Glenn; Li, G. [Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas, 78238 (United States); University of New Hampshire, Durham, New Hampshire, 03824 (United States); Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, 20724 (United States); Center for Space Plasma and Aeronomic Research, University of Alabama, Huntsville, Al 35899 (United States)

    2012-11-20

    We compare the behavior of heavy ion spectra during an Energetic Storm Particle (ESP) event that exhibited clear evidence of wave excitation with that observed during an intense, large gradual Solar Energetic Particle (SEP) event in which the associated <0.2 MeV/nucleon ions are delayed >12 hr. We interpret that the ESP event is an example of the first-order Fermi acceleration process where enhancements in the magnetic field power spectral densities around local ion cyclotron frequency {nu}{sub pc} indicate the presence of Alfven waves excited by accelerated protons streaming away from the in-situ interplanetary shock. The softening or unfolding of the CNO energy spectrum below {approx}200 keV/nucleon and the systematic organization of the Fe and O spectral roll-overs with the E/q ratio during the ESP event are likely due to M/Q-dependent trapping and scattering of the heavy ions by the proton-excited waves. Based on striking similarities in the spectral behavior observed upstream of both, the ESP and the SEP event, we suggest that coupling between proton-generated Alfven waves and energetic ions is also operating at the distant CME shock during the large, gradual SEP event, thereby providing us with a new, powerful tool to remotely probe the roles of shock geometries and wave-particle interactions at near-Sun CME-driven shocks.

  1. Study of spallation by sub-picosecond laser driven shocks in metals

    Directory of Open Access Journals (Sweden)

    Combis P.

    2011-01-01

    Full Text Available Spallation induced by a laser driven shock has been studied for two decades on time scales of nanosecond order. The evolution of laser technologies now provides access to sources whose pulse duration is under the picosecond, corresponding to characteristic times of numerous microscopic phenomena. In this ultra-short irradiation regime, spallation experiments have been performed with time-resolved measurements of the free surface. In this solicitation type, damage occurs at small scale, leading to micrometric spalls. The VISAR measurements have been complemented with post-test observations and microtomography and compared with numerical simulations to check the models consistency of the laser-matter interaction, shock wave propagation and the dynamic damage criteria ability to reproduce spallation at this ultra-short time scale, inducing strong tensile stress states at very high strain rates.

  2. A numerical method for shock driven multiphase flow with evaporating particles

    Science.gov (United States)

    Dahal, Jeevan; McFarland, Jacob A.

    2017-09-01

    A numerical method for predicting the interaction of active, phase changing particles in a shock driven flow is presented in this paper. The Particle-in-Cell (PIC) technique was used to couple particles in a Lagrangian coordinate system with a fluid in an Eulerian coordinate system. The Piecewise Parabolic Method (PPM) hydrodynamics solver was used for solving the conservation equations and was modified with mass, momentum, and energy source terms from the particle phase. The method was implemented in the open source hydrodynamics software FLASH, developed at the University of Chicago. A simple validation of the methods is accomplished by comparing velocity and temperature histories from a single particle simulation with the analytical solution. Furthermore, simple single particle parcel simulations were run at two different sizes to study the effect of particle size on vorticity deposition in a shock-driven multiphase instability. Large particles were found to have lower enstrophy production at early times and higher enstrophy dissipation at late times due to the advection of the particle vorticity source term through the carrier gas. A 2D shock-driven instability of a circular perturbation is studied in simulations and compared to previous experimental data as further validation of the numerical methods. The effect of the particle size distribution and particle evaporation is examined further for this case. The results show that larger particles reduce the vorticity deposition, while particle evaporation increases it. It is also shown that for a distribution of particles sizes the vorticity deposition is decreased compared to single particle size case at the mean diameter.

  3. Magnetar-driven Shock Breakout and Double-peaked Supernova Light Curves

    Science.gov (United States)

    Kasen, Daniel; Metzger, Brian D.; Bildsten, Lars

    2016-04-01

    The light curves of some luminous supernovae are suspected to be powered by the spindown energy of a rapidly rotating magnetar. Here we describe a possible signature of the central engine: a burst of shock breakout emission occurring several days after the supernova explosion. The energy input from the magnetar inflates a high-pressure bubble that drives a shock through the pre-exploded supernova ejecta. If the magnetar is powerful enough, that shock will near the ejecta surface and become radiative. At the time of shock breakout, the ejecta will have expanded to a large radius (∼ {10}14 cm) so that the radiation released is at optical/ultraviolet wavelengths ({T}{{eff}} ≈ 20,000 K) and lasts for several days. The luminosity and timescale of this magnetar-driven shock breakout are similar to the first peak observed recently in the double-peaked light curve of SN-LSQ14BDQ. However, for a large region of model parameter space, the breakout emission is predicted to be dimmer than the diffusive luminosity from direct magnetar heating. A distinct double-peaked light curve may therefore only be conspicuous if thermal heating from the magnetar is suppressed at early times. We describe how such a delay in heating may naturally result from inefficient dissipation and thermalization of the pulsar wind magnetic energy. Without such suppression, the breakout may only be noticeable as a small bump or kink in the early luminosity or color evolution, or as a small but abrupt rise in the photospheric velocity. A similar breakout signature may accompany other central engines in supernovae, such as a black hole accreting fallback material.

  4. Numerical simulations of energy transfer in two collisionless interpenetrating plasmas

    Directory of Open Access Journals (Sweden)

    Davis S.

    2013-11-01

    Full Text Available Ion stream instabilities are essential for collisionless shock formation as seen in astrophysics. Weakly relativistic shocks are considered as candidates for sources of high energy cosmic rays. Laboratory experiments may provide a better understanding of this phenomenon. High intensity short pulse laser systems are opening possibilities for efficient ion acceleration to high energies. Their collision with a secondary target could be used for collisionless shock formation. In this paper, using particle-in-cell simulations we are studying interaction of a sub-relativistic, laser created proton beam with a secondary gas target. We show that the ion bunch initiates strong electron heating accompanied by the Weibel-like filamentation and ion energy losses. The energy repartition between ions, electrons and magnetic fields are investigated. This yields insight on the processes occurring in the interstellar medium (ISM and gamma-ray burst afterglows.

  5. A Data-driven Analytic Model for Proton Acceleration by Large-scale Solar Coronal Shocks

    Science.gov (United States)

    Kozarev, Kamen A.; Schwadron, Nathan A.

    2016-11-01

    We have recently studied the development of an eruptive filament-driven, large-scale off-limb coronal bright front (OCBF) in the low solar corona, using remote observations from the Solar Dynamics Observatory’s Advanced Imaging Assembly EUV telescopes. In that study, we obtained high-temporal resolution estimates of the OCBF parameters regulating the efficiency of charged particle acceleration within the theoretical framework of diffusive shock acceleration (DSA). These parameters include the time-dependent front size, speed, and strength, as well as the upstream coronal magnetic field orientations with respect to the front’s surface normal direction. Here we present an analytical particle acceleration model, specifically developed to incorporate the coronal shock/compressive front properties described above, derived from remote observations. We verify the model’s performance through a grid of idealized case runs using input parameters typical for large-scale coronal shocks, and demonstrate that the results approach the expected DSA steady-state behavior. We then apply the model to the event of 2011 May 11 using the OCBF time-dependent parameters derived by Kozarev et al. We find that the compressive front likely produced energetic particles as low as 1.3 solar radii in the corona. Comparing the modeled and observed fluences near Earth, we also find that the bulk of the acceleration during this event must have occurred above 1.5 solar radii. With this study we have taken a first step in using direct observations of shocks and compressions in the innermost corona to predict the onsets and intensities of solar energetic particle events.

  6. Magnetic field amplification in nonlinear diffusive shock acceleration including resonant and non-resonant cosmic-ray driven instabilities

    CERN Document Server

    Bykov, Andrei M; Osipov, Sergei M; Vladimirov, Andrey E

    2014-01-01

    We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration (DSA) where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short- and long-wavelength CR-current-driven instabilities. We include the backpressure from CRs interacting with the strongly amplified magnetic turbulence which decelerates and heats the super-alfvenic flow in the extended shock precursor. Uniquely, in our plane-parallel, steady-state, multi-scale model, the full range of particles, from thermal (~eV) injected at the viscous subshock, to the escape of the highest energy CRs (~PeV) from the shock precursor, are calculated consistently with the shock structure, precursor heating, magnetic field amplification (MFA), and scattering center drift relative to the background plasma. In addition, we show how the cascade of turbulence to shorter wavelengths influences the total shock compression, the d...

  7. Laser heating of solid matter by light pressure-driven shocks

    Energy Technology Data Exchange (ETDEWEB)

    Akli, K; Hansen, S B; Kemp, A J; Freeman, R R; Beg, F N; Clark, D; Chen, S; Hey, D; Highbarger, K; Giraldez, E; Green, J; Gregori, G; Lancaster, K; Ma, T; MacKinnon, A J; Norreys, P A; Patel, N; Patel, P; Shearer, C; Stephens, R B; Stoeckl, C; Storm, M; Theobald, W; Van Woerkom, L; Weber, R; Key, M H

    2007-05-04

    Heating by irradiation of a solid surface in vacuum with 5 x 10{sup 20} W cm{sup -2}, 0.8 ps, 1.05 {micro}m wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo and V. A surface layer is heated to {approx} 5 keV with an axial temperature gradient of 0.6 {micro}m scale length. Images of Ni Ly{sub {alpha}} show the hot region has a {approx} 25 {micro}m diameter, much smaller than {approx} 70 {micro}m region of K{sub {alpha}} emission. 2D particle-in-cell (PIC) simulations suggest that the surface heating is due to a light pressure driven shock.

  8. Shearing Box Simulations of the MRI in a Collisionless Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Prateek; Hammett, Gregory, W.; Quataert, Eliot; Stone, James, M.

    2005-08-31

    We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Galactic Center. The MHD version of ZEUS is modified to evolve an anisotropic pressure tensor. A fluid closure approximation is used to calculate heat conduction along magnetic field lines. The anisotropic pressure tensor provides a qualitatively new mechanism for transporting angular momentum in accretion flows (in addition to the Maxwell and Reynolds stresses). We estimate limits on the pressure anisotropy due to pitch angle scattering by kinetic instabilities. Such instabilities provide an effective ''collision'' rate in a collisionless plasma and lead to more MHD-like dynamics. We find that the MRI leads to efficient growth of the magnetic field in a collisionless plasma, with saturation amplitudes comparable to those in MHD. In the saturated state, the anisotropic stress is comparable to the Maxwell stress, implying that the rate of angular momentum transport may be moderately enhanced in a collisionless plasma.

  9. Small Ground-Level Enhancement of 6 January 2014: Acceleration by CME-Driven Shock?

    Science.gov (United States)

    Li, C.; Miroshnichenko, L. I.; Sdobnov, V. E.

    2016-03-01

    Available spectral data for solar energetic particles (SEPs) measured near the Earth's orbit (GOES-13) and on the terrestrial surface (polar neutron monitors) on 6 January 2014 are analyzed. A feature of this solar proton event (SPE) and weak ground-level enhancement (GLE) is that the source was located behind the limb. For the purpose of comparison, we also use the Advanced Composition Explorer (ACE) data on sub-relativistic electrons and GOES-13 measurements of a strong and extended proton event on 8 - 9 January 2014. It was found that the surface observations at energies {>} 433 MeV and GOES-13 data at {>} 30 - {>} 700 MeV may be satisfactorily reconciled by a power-law time-of-maximum (TOM) spectrum with a characteristic exponential tail (cutoff). Some methodological difficulties of spectrum determination are discussed. Assuming that the TOM spectrum near the Earth is a proxy of the spectrum of accelerated particles in the source, we critically consider the possibility of shock acceleration to relativistic energies in the solar corona. Finally, it is suggested to interpret the observational features of this GLE under the assumption that small GLEs may be produced by shocks driven by coronal mass ejections. However, the serious limitations of such an approach to the problem of the SCR spectrum prevent drawing firm conclusions in this controversial field.

  10. Nonlinear Acceleration Mechanism of Collisionless Magnetic Reconnection

    CERN Document Server

    Hirota, M; Ishii, Y; Yagi, M; Aiba, N

    2012-01-01

    A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges. Nonlinear growth of the tearing mode driven by electron inertia is analytically estimated by invoking the energy principle for the first time. Decrease of potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in acceleration of the reconnection. Release of free energy by such ideal fluid motion leads to unsteady and strong convective flow, which theoretically corroborates the inertia-driven collapse model of the sawtooth crash [D. Biskamp and J. F. Drake, Phys. Rev. Lett. 73, 971 (1994)].

  11. Atypical Particle Heating at a Supercritical Interplanetary Shock

    Science.gov (United States)

    Wilson, Lynn B., III

    2010-01-01

    We present the first observations at an interplanetary shock of large amplitude (> 100 mV/m pk-pk) solitary waves and large amplitude (approx.30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

  12. Laser-driven shock experiments in pre-compressed water: Implications for magnetic field generation in Icy Giant planets

    Energy Technology Data Exchange (ETDEWEB)

    Lee, K; Benedetti, L R; Jeanloz, R; Celliers, P M; Eggert, J H; Hicks, D G; Moon, S J; Mackinnon, A; Henry, E; Koenig, M; Benuzzi-Mounaix, A; Collins, G W

    2005-11-10

    Laser-driven shock compression of pre-compressed water (up to 1 GPa precompression) produces high-pressure, -temperature conditions in the water inducing two optical phenomena: opacity and reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semi-conductor to electronic conductor transition in water and is found at pressures above {approx}130 GPa for single-shocked samples pre-compressed to 1 GPa. This electronic conduction provides an additional contribution to the conductivity required for magnetic field generation in Icy Giant planets like Uranus and Neptune.

  13. NASA Ames's electric arc-driven shock tube facility and research on nonequilibrium phenomena in low density hypersonic flows

    Science.gov (United States)

    Sharma, Surendra P.

    1992-01-01

    Basic requirements for a ground test facility simulating low density hypersonic flows are discussed. Such facilities should be able to produce shock velocities in the range of 10-17 km/sec in an initial pressure of 0.010 to 0.050 Torr. The facility should be equipped with diagnostics systems to be able to measure the emitted radiation, characteristic temperatures and populations in various energy levels. In the light of these requirements, NASA Ames's electric arc-driven low density shock tube facility is described and available experimental diagnostics systems and computational tools are discussed.

  14. An Application of the Stereoscopic Self-Similar-Expansion Model to the Determination of CME-Driven Shock Parameters

    CERN Document Server

    Volpes, L

    2015-01-01

    We present an application of the stereoscopic self-similar-expansion model (SSSEM) to Solar Terrestrial Relations Observatory (STEREO)/Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) observations of the 03 April 2010 CME and its associated shock. The aim is to verify whether CME-driven shock parameters can be inferred from the analysis of j-maps. For this purpose we use the SSSEM to derive the CME and the shock kinematics. Arrival times and speeds, inferred assuming either propagation at constant speed or with uniform deceleration, show good agreement with Advanced Composition Explorer (ACE) measurements. The shock standoff distance $[\\Delta]$, the density compression $[\\frac{\\rho_d}{\\rho_u}]$ and the Mach number $[M]$ are calculated combining the results obtained for the CME and shock kinematics with models for the shock location. Their values are extrapolated to $\\textrm{L}_1$ and compared to in-situ data. The in-situ standoff distance is obtained from ACE solar-wind measurements, and t...

  15. Effects of laser polarization on electrostatic shock ion acceleration in near-critical plasmas

    Science.gov (United States)

    Kim, Young-Kuk; Kang, Teyoun; Hur, Min Sup

    2016-10-01

    Collisionless electrostatic shock ion acceleration has become a major regime of laser-driven ion acceleration owing to generation of quasi-monoenergetic ion beams from moderate parametric conditions of lasers and plasmas in comparison with target-normal-sheath-acceleration or radiation pressure acceleration. In order to construct the shock, plasma heating is an essential condition for satisfying Mach number condition 1.5 Weibel instability. This work was supported by the Basic Science Research Program (NRF- 2013R1A1A2006353) and the Creative Allied Project (CAP-15-06-ETRI).

  16. Role of spall in microstructure evolution during laser-shock-driven rapid undercooling and resolidification

    Science.gov (United States)

    Colvin, Jeffrey D.; Jankowski, Alan F.; Kumar, Mukul; MoberlyChan, Warren J.; Reed, Bryan W.; Paisley, Dennis L.; Tierney, Thomas E.

    2009-01-01

    We previously reported [Colvin et al., J. Appl. Phys. 101, 084906 (2007)] on the microstructure morphology of pure Bi metal subjected to rapid laser-shock-driven melting and subsequent resolidification upon release of pressure, where the estimated effective undercooling rates were of the order of 109-1010 K/s. More recently, we repeated these experiments, but with a Bi/Zn alloy (Zn atomic fraction of 2%-4%) instead of elemental Bi and with a change in target design to suppress spall in the Bi/Zn samples. We observed a similar microstructure morphology in the two sets of experiments, with initially columnar grains recrystallizing to larger equiaxed grains. The Bi samples, however, exhibited micron-scale dendrites on the spall surfaces, whereas there were no dendritic structures anywhere in the nonspalled Bi/Zn, even down to the nanometer scale as observed by transmission electron microscopy. We present the simulations and the interferometry data that show that the samples in the two sets of experiments followed nearly identical hydrodynamic and thermodynamic paths apart from the presence of (probably partially liquid) spall in pure Bi. Simulations also show that the spall occurs right at the moving phase front and, hence, the spall itself cuts off the principal direction for latent heat dissipation across the phase boundary. We suggest that it is the liquid spall itself that creates the conditions for dendrite formation.

  17. Multichannel emission spectrometer for high dynamic range optical pyrometry of shock-driven materials

    Science.gov (United States)

    Bassett, Will P.; Dlott, Dana D.

    2016-10-01

    An emission spectrometer (450-850 nm) using a high-throughput, high numerical aperture (N.A. = 0.3) prism spectrograph with stepped fiberoptic coupling, 32 fast photomultipliers and thirty-two 1.25 GHz digitizers is described. The spectrometer can capture single-shot events with a high dynamic range in amplitude and time (nanoseconds to milliseconds or longer). Methods to calibrate the spectrometer and verify its performance and accuracy are described. When a reference thermal source is used for calibration, the spectrometer can function as a fast optical pyrometer. Applications of the spectrometer are illustrated by using it to capture single-shot emission transients from energetic materials or reactive materials initiated by kmṡs-1 impacts with laser-driven flyer plates. A log (time) data analysis method is used to visualize multiple kinetic processes resulting from impact initiation of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) or a Zr/CuO nanolaminate thermite. Using a gray body algorithm to interpret the spectral radiance from shocked HMX, a time history of temperature and emissivity was obtained, which could be used to investigate HMX hot spot dynamics. Finally, two examples are presented showing how the spectrometer can avoid temperature determination errors in systems where thermal emission is accompanied by atomic or molecular emission lines.

  18. Spall strength and ejecta production of gold under explosively driven shock wave compression

    Energy Technology Data Exchange (ETDEWEB)

    La Lone, B. M. [National Security Technologies, LLC. (NSTec), Mercury, NV (United States); Stevens, G. D. [National Security Technologies, LLC. (NSTec), Mercury, NV (United States); Turley, W. D. [National Security Technologies, LLC. (NSTec), Mercury, NV (United States); Veeser, L. R. [National Security Technologies, LLC. (NSTec), Mercury, NV (United States); Holtkamp, D. B. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2013-12-16

    Explosively driven shock wave experiments were conducted to characterize the spall strength and ejecta production of high-purity cast gold samples. The samples were from 0.75 to 1.84 mm thick and 30 mm in diameter. Peak stresses up to 44 GPa in gold were generated using PBX-9501 high explosive. Sample free surface and ejecta velocities were recorded using photonic Doppler velocimetry techniques. Lithium niobate pins were used to quantify the time dependence of the ejecta density and the total ejected mass. An optical framing camera for time-resolved imaging and a single-image x-ray radiograph were used for additional characterization. Free surface velocities exhibited a range of spall strengths from 1.7 to 2.4 GPa (mean: 2.0 ±0.3 GPa). The pullback signals were faint, minimal ringing was observed in the velocity records, and the spall layer continued to decelerate after first pull back. These results suggest finite tensile strength was present for some time after the initial void formation. Ejecta were observed for every sample with a roughened free surface, and the ejecta density increased with increased surface roughness, which was different in every experiment. The total ejected mass is consistent with the missing mass model.

  19. Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations

    CERN Document Server

    Liljegren, S; Nowotny, W; Eriksson, K

    2016-01-01

    Winds of AGB stars are thought to be driven by a combination of pulsation-induced shock waves and radiation pressure on dust. In dynamic atmosphere and wind models, the stellar pulsation is often simulated by prescribing a simple sinusoidal variation in velocity and luminosity at the inner boundary of the model atmosphere. We experiment with different forms of the luminosity variation in order to assess the effects on the wind velocity and mass-loss rate, when progressing from the simple sinusoidal recipe towards more realistic descriptions. Using state-of-the-art dynamical models of C-rich AGB stars, a range of different asymmetric shapes of the luminosity variation and a range of phase shifts of the luminosity variation relative to the radial variation are tested. These tests are performed on two stellar atmosphere models. The first model has dust condensation and, as a consequence, a stellar wind is triggered, while the second model lacks both dust and wind. The first model with dust and stellar wind is ve...

  20. Evaluation of a Two-Length Scale Turbulence Model with Experiments on Shock-Driven Turbulent Mixing

    Science.gov (United States)

    Carter, John; Gore, Rob; Ranjan, Devesh

    2015-11-01

    A new second moment turbulence model which uses separate transport and decay length scales is used to model the shock-driven instability. The ability of the model to capture the evolution of turbulence statistics and mixing is discussed. Evaluation is based on comparison to the Georgia Tech shock tube experiments. In the experiments a membraneless light-over-heavy interface is created. There is a long-wavelength perturbation which exists due to inclination of the entire shock tube. By limiting calculations to one dimension, there is not a geometric description of the incline, and the ability of the transport length scale alone to capture the effect of the long-wavelength perturbation is tested.

  1. Study on the dynamic behavior of matters using laser-driven shock waves in the water confinement

    Science.gov (United States)

    Yu, Hyeonju; Yoh, Jack J.

    2015-06-01

    The strain rates achievable in laser-driven shock experiments overlap with gas gun and can reach much higher values. The laser-based method also has advantages in terms of system size, cost, repeatability, and controllability. In this research, we aim to measure equation of state, Hugoniot elastic limit, strain rate, and compressive yield strength of target samples by making use of the velocity interferometer or the VISAR. High pressure shock wave is generated by a Q-switched Nd:YAG laser operating at 1.064 μm wavelength with pulse energy up to 3 joules and 9 ns pulse duration. All the experiments are conducted in the water confinement to increase the peak stresses to an order of GPa. Furthermore, quantitative comparisons are made to the existing shock data in order to emphasize the novelty of the proposed setup which is relatively simple and reliable. Corresponding author.

  2. Laser-Driven Ultra-Relativistic Plasmas - Nuclear Fusion in Coulomb Shock Waves, Rouge Waves, and Background Matter

    Science.gov (United States)

    2015-05-05

    AND SUBTITLE LASER-DRIVEN ULTRA-RELATIVISTIC PLASMAS - NUCLEAR FUSION IN COULOMB SHOCK WAVES, ROUGE WAVES, AND BACKGROUND MATTER. 5a.  CONTRACT...blackbody radiation on free electrons .........................9 2.vi. Proposal of ultimate test of laser nuclear fusion efficiency in clusters...domain of energies and temperatures, with applications in particular to controlled nuclear fusion . 2. Final technical report on the grant #F49620-11-1

  3. Weibel instability driven by spatially anisotropic density structures

    CERN Document Server

    Tomita, Sara

    2016-01-01

    Observations of afterglows of gamma-ray bursts suggest (GRBs) that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating of the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron--positron plasmas with the spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by the spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that the temperature ...

  4. Operating characteristics of a 60 cm and a 10 cm electric arc-driven shock-tube

    Science.gov (United States)

    Sharma, Surendra P.; Park, Chul; Dannenberg, Robert E.

    1988-01-01

    This paper describes the current status of the operating characteristics of the electric arc-driven shock-tube facility at Ames Research Center, focusing on its potential usefulness in the current and anticipated future applications. The paper specifically addresses the questions as to: (1) how well the behavior of the arc driver is understood and controlled, (2) how well the facility is equipped to test low-density, very-high-velocity nonequilibrium flow regimes, and (3) how closely the facility is expected to produce an equilibrium hypersonic flow when operated in shock-tunnel modes. For these issues, it is shown that: (1) a plasma kinetics model of the exploding wire closely describes the arc behavior in the driver, (2) the facility can produce a spectroscopically-clean flow in a low density regime with a shock velocity of 13 km/sec in air when used with an aluminum driven tube, and (3) when operated as a shock-tunnel, the high enthalpy flow in the test section is expected to deviate only slightly from the perfect equilibrium flow conditions at enthalpies corresponding to flight speeds of 5 km/sec or less.

  5. Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets

    CERN Document Server

    Moser, A L

    2014-01-01

    We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex ...

  6. Shock

    Science.gov (United States)

    Shock can be caused by any condition that reduces blood flow, including: Heart problems (such as heart attack or heart failure ) Low blood volume (as with heavy bleeding or dehydration ) Changes in blood vessels (as with infection ...

  7. Radiation-Hydrodynamic Simulation of Experiments With Intense Lasers Generating Collisionless Interpenetrating Plasmas

    Science.gov (United States)

    Grosskopf, Michael; Drake, R.; Kuranz, C.; Park, H.; Kugland, N.; Pollaine, S.; Ross, J.; Remington, B.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C.; Meinecke, J.; Reville, B.; Sakawa, Y.; Kuramitsu, Y.; Takabe, H.; Froula, D.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Liang, E.; Woolsey, N.

    2012-05-01

    Collisionless shocks, shocks generated by plasma wave interactions in regions where the collisional mean-free-path for ions is long compared to the length scale for instabilities that generate magnetic fields, are found in many astrophysical systems such as supernova remnants and planetary bow shocks. Generating conditions to investigate collisionless shock physics is difficult to achieve in a laboratory setting; however, high-energy-density physics facilities have made this a possibility. Experiments whose goal is to investigate the production and growth of magnetic fields in collisionless shocks in laboratory-scale systems are being carried out on intense lasers, several of which are measuring the plasma properties and magnetic field strength in counter-streaming, collisionless flows generated by laser ablation. This poster reports radiation-hydrodynamic simulations using the CRASH code to model the ablative flow of plasma generated in order to assess potential designs, as well as infer properties of collected data from previous experiments. This work is funded by the Predictive Sciences Academic Alliances Program in NNSA-ASC via grant DEFC52- 08NA28616, by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-FG52-09NA29548, and by the National Laser User Facility Program, grant number DE-NA0000850.

  8. Entropy production and collisionless fluid closure

    Energy Technology Data Exchange (ETDEWEB)

    Sarazin, Y; Zarzoso, D; Garbet, X; Ghendrih, Ph; Grandgirard, V [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Dif-Pradalier, G, E-mail: yanick.sarazin@cea.f [Center for Astrophysics and Space Science, U.C.S.D., La Jolla, CA 92093 (United States)

    2009-11-15

    A novel method is proposed to construct collisionless fluid closures accounting for some kinetic properties. The idea consists in optimizing the agreement between the fluid and kinetic quasi-linear entropy production rates, so as to constrain the closure coefficients. This procedure is applied to the slab branch of the ion temperature gradient driven instability. Focusing on the kinetic regime characterized by slow waves, the closure proposed by Hammett and Perkins (Hammett and Perkins 1990 Phys. Rev. Lett. 64 3019) naturally emerges from the systematic identification of the kinetic and fluid entropy production rates. This closure is revealed to be extremely powerful well beyond the kinetic regime. Besides, it reconciles the fluid and kinetic linear stability diagrams in the two-dimensional space of the density and temperature gradient lengths. Such a method is systematic and generic. As such, it is applicable to other models and classes of instabilities.

  9. Entropy production and collisionless fluid closure

    Science.gov (United States)

    Sarazin, Y.; Dif-Pradalier, G.; Zarzoso, D.; Garbet, X.; Ghendrih, Ph; Grandgirard, V.

    2009-11-01

    A novel method is proposed to construct collisionless fluid closures accounting for some kinetic properties. The idea consists in optimizing the agreement between the fluid and kinetic quasi-linear entropy production rates, so as to constrain the closure coefficients. This procedure is applied to the slab branch of the ion temperature gradient driven instability. Focusing on the kinetic regime characterized by slow waves, the closure proposed by Hammett and Perkins (Hammett and Perkins 1990 Phys. Rev. Lett. 64 3019) naturally emerges from the systematic identification of the kinetic and fluid entropy production rates. This closure is revealed to be extremely powerful well beyond the kinetic regime. Besides, it reconciles the fluid and kinetic linear stability diagrams in the two-dimensional space of the density and temperature gradient lengths. Such a method is systematic and generic. As such, it is applicable to other models and classes of instabilities.

  10. Development of a novel miniature detonation-driven shock tube assembly that uses in situ generated oxyhydrogen mixture

    Science.gov (United States)

    Janardhanraj, S.; Jagadeesh, G.

    2016-08-01

    A novel concept to generate miniature shockwaves in a safe, repeatable, and controllable manner in laboratory confinements using an in situ oxyhydrogen generator has been proposed and demonstrated. This method proves to be more advantageous than existing methods because there is flexibility to vary strength of the shockwave, there is no need for storage of high pressure gases, and there is minimal waste disposal. The required amount of oxyhydrogen mixture is generated using alkaline electrolysis that produces hydrogen and oxygen gases in stoichiometric quantity. The rate of oxyhydrogen mixture production for the newly designed oxyhydrogen generator is found to be around 8 ml/s experimentally. The oxyhydrogen generator is connected to the driver section of a specially designed 10 mm square miniature shock tube assembly. A numerical code that uses CANTERA software package is used to predict the properties of the driver gas in the miniature shock tube. This prediction along with the 1-D shock tube theory is used to calculate the properties of the generated shockwave and matches reasonably well with the experimentally obtained values for oxyhydrogen mixture fill pressures less than 2.5 bars. The miniature shock tube employs a modified tri-clover clamp assembly to facilitate quick changing of diaphragm and replaces the more cumbersome nut and bolt system of fastening components. The versatile nature of oxyhydrogen detonation-driven miniature shock tube opens up new horizons for shockwave-assisted interdisciplinary applications.

  11. Sub-photospheric shocks in relativistic explosions

    CERN Document Server

    Beloborodov, Andrei M

    2016-01-01

    This paper examines the mechanism of shocks in opaque outflows from astrophysical explosions, in particular in cosmological gamma-ray bursts. Sub-photospheric shocks can produce neutrino emission and affect the observed photospheric radiation from the explosion. Shocks develop from internal compressive waves and can be of different types depending on the composition of the flow: (1) Shocks in `photon gas' with small plasma inertial mass have a unique structure determined by the `force-free' condition -- zero radiation flux in the plasma rest frame. Radiation dominance over plasma inertia suppresses formation of collisionless shocks mediated by collective electromagnetic fields. (2) Strong collisionless subshocks develop in the opaque flow if it is sufficiently magnetized. We evaluate the critical magnetization for this to happen. The collisionless subshock is embedded in a thicker radiation-mediated shock structure. (3) Shocks in outflows carrying a free neutron component involve dissipation through nuclear c...

  12. Fabrication of visible-light-driven Ag/TiO{sub 2} heterojunction composites induced by shock wave

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Chunxiao [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Chen, Pengwan, E-mail: pwchen@bit.edu.cn [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 (China); Liu, Jianjun [State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Yin, Hao [Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang 612900, Sichuan Province (China); Gao, Xin; Mei, Xiaofeng [State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 (China)

    2016-09-15

    Using metatitanic acid (H{sub 2}TiO{sub 3}) and silver nitrate (AgNO{sub 3}) as titanium precursor and silver source respectively, a visible-light responsible Ag/TiO{sub 2} heterojunction photocatalyst is successfully prepared by shock wave with detonation-driven flyer impact. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) and photoluminescence (PL) emission spectra are employed to characterize the phase structure, morphology, chemical composition and optical property of the recovered samples. The results indicate the metatitanic acid transforms to pure rutile TiO{sub 2} phase by shock wave which possess large surface area. Ag nanoparticles cover on the surface of TiO{sub 2} uniformly and a nanojunction structure is formed efficiently, which play important roles as an electron-conduction bridge and in the surface plasmon resonance effect. Ag modification feasibly improves the separation efficiency for photoinduced electron–hole pairs and enhances the visible-light response. Furthermore, due to the further enhanced separation for photogenerated charges resulting from close interfacial contact of the hetero structure, the obtained Ag/TiO{sub 2} photocatalyst exhibit remarkably improved photocatalytic activities (88% within 2 h) than that of P25 and shock induced pure TiO{sub 2} for the degradation of Rhodamine B under simulated sunlight irradiation. The experimental result shows the shock loading is an effective method to get Ag/TiO{sub 2} photocatalyst and offers new ideas to fabricate other heterojunction composite materials. - Highlights: • Shock wave was a new method of material modification. • The Ag/TiO{sub 2} hetero structure was formed efficiently by shock loading. • The visible-light responsible sample showed an enhanced photocatalytic activity. • This work gave new ideas to fabricate other heterojunction materials.

  13. Rayleigh Taylor growth at an embedded interface driven by a radiative shock

    Science.gov (United States)

    Huntington, Channing

    2016-10-01

    Radiative shocks are those where the radiation generated by the shock influences the hydrodynamics of the matter in the system. Radiative shocks are common in astrophysics, including during type II supernovae, and have also been observed in the rebound phase of a compressed inertial confinement fusion (ICF) capsule. It is predicted that the radiative heating serves to stabilize hydrodynamic instabilities in these systems, but studying the effect is challenging. Only in recent experiments at the National Ignition Facility has the energy been available to drive a radiative shock across a planar, Rayleigh-Taylor unstable interface in solid-density materials. Because the generation of radiation at the shock front is a strong function of shock velocity (v8) , the RT growth rates in the presence of fast and slow shockas were directly compared. We observe reduced RT spike development when the driving shock is expected to be radiative. Both low drive (225 eV) hydrodynamic RT growth and high drive (325 eV), radiatively-stabilized growth rates are in good agreement with 2D models. This NIF Discovery Science result has important implications for our understanding of astrophysical radiative shocks, as well as the dynamics of ICF capsules. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  14. Reverse Shock Emission Driven By Post-Merger Millisecond Magnetar Winds: Effects of the Magnetization Parameter

    CERN Document Server

    Liu, L D; Dai, Z G

    2016-01-01

    The study of short-duration gamma-ray bursts provides growing evidence that a good fraction of double neutron star mergers lead to the formation of stable millisecond magnetars. The launch of Poynting flux by the millisecond magnetars could leave distinct electromagnetic signatures that reveal the energy dissipation processes in the magnetar wind. In previous studies (Wang & Dai 2013b; Wang et al. 2015), we assume that the magnetar wind becomes completely lepton-dominated so that electrons/positrons in the magnetar wind are accelerated by a diffusive shock. However, theoretical modeling of pulsar wind nebulae shows that in many cases the magnetic field energy in the pulsar wind may be strong enough to suppress diffusive shock acceleration. In this paper, we investigate the reverse shock emission as well as the forward shock emission with an arbitrary magnetization parameter $\\sigma$ of a magnetar wind. We find that the reverse shock emission strongly depends on $\\sigma$, and in particular, $\\sigma \\sim 0....

  15. Observation and analysis of emergent coherent structures in a high-energy-density shock-driven planar mixing layer experiment

    Science.gov (United States)

    Doss, F. W.; Flippo, K. A.; Merritt, E. C.

    2016-08-01

    Coherent emergent structures have been observed in a high-energy-density supersonic mixing layer experiment. A millimeter-scale shock tube uses lasers to drive Mbar shocks into the tube volume. The shocks are driven into initially solid foam (60 mg /cm3 ) hemicylinders separated by an Al or Ti metal tracer strip; the components are vaporized by the drive. Before the experiment disassembles, the shocks cross at the tube center, creating a very fast (Δ U > 200 km/s) shear-unstable zone. After several nanoseconds, an expanding mixing layer is measured, and after 10+ ns we observe the appearance of streamwise-periodic, spanwise-aligned rollers associated with the primary Kelvin-Helmholtz instability of mixing layers. We additionally image roller pairing and spanwise-periodic streamwise-aligned filaments associated with secondary instabilities. New closures are derived to connect length scales of these structures to estimates of fluctuating velocity data otherwise unobtainable in the high-energy-density environment. This analysis indicates shear-induced specific turbulent energies 103-104 times higher than the nearest conventional experiments. Because of difficulties in continuously driving systems under these conditions and the harshness of the experimental environment limiting the usable diagnostics, clear evidence of these developing structures has never before been observed in this regime.

  16. THE CHESS SURVEY OF THE L1157-B1 SHOCK REGION: CO SPECTRAL SIGNATURES OF JET-DRIVEN BOW SHOCKS

    Energy Technology Data Exchange (ETDEWEB)

    Lefloch, B.; Codella, C.; Ceccarelli, C. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et dAstrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Cabrit, S. [Observatoire de Paris, LERMA, UMR 8112 du CNRS, ENS, UPMC, UCP, 61 Av. de l' Observatoire, F-75014 Paris (France); Busquet, G.; Benedettini, M. [INAF, Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, I-00133 Roma (Italy); Cernicharo, J.; Pardo, J. R. [Centro de Astrobiologia, INTA, Ctra de Torrejon a Ajalvir, km 4, E-28850 Torrejon de Ardoz, E-28850 Madrid (Spain); Lis, D. C. [California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125 (United States); Nisini, B., E-mail: lefloch@obs.ujf-grenoble.fr [INAF, Osservatorio Astronomico di Roma, Via di Frascati 33, I-00040 Monte, Porzio Catone (Italy)

    2012-10-01

    The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. Over the course of the CHESS Key Program, we have observed toward the bright bow shock region L1157-B1, the CO rotational transitions between J = 5-4 and J = 16-15 with HIFI, and the J = 1-0, 2-1, and 3-2 with the IRAM 30 m and the Caltech Submillimeter Observatory telescopes. We find that all the line profiles I{sub CO}(v) are well fit by a linear combination of three exponential laws {proportional_to}exp (- |v/v{sub 0}|) with v{sub 0} = 12.5, 4.4, and 2.5 km s{sup -1}. The first component dominates the CO emission at J {>=} 13, as well as the high-excitation lines of SiO and H{sub 2}O. The second component dominates for 3 {<=} J{sub up} {<=} 10 and the third one for J{sub up} {<=} 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components: the impact of the jet against the L1157-B1 bow shock (T{sub k} {approx_equal} 210 K), the walls of the outflow cavity associated with B1 (T{sub k} {approx_equal} 64 K), and the older cavity L1157-B2 (T{sub k} {approx_equal} 23 K), respectively. Analysis of the CO line flux in the large-velocity gradient approximation further shows that the emission arises from dense gas (n(H{sub 2}) {>=} 10{sup 5}-10{sup 6} cm{sup -3}) close to LTE up to J = 20. We find that the CO J = 2-1 intensity-velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.

  17. Collisionless Relaxation of Stellar Systems

    CERN Document Server

    Kandrup, H E

    1998-01-01

    The objective of the work summarised here has been to exploit and extend ideas from plasma physics and accelerator dynamics to formulate a unified description of collisionless relaxation that views violent relaxation, Landau damping, and phase mixing as (manifestations of) a single phenomenon. This approach embraces the fact that the collisionless Boltzmann equation (CBE), the basic object of the theory, is an infinite-dimensional Hamiltonian system, with the distribution function f playing the role of the fundamental dynamical variable, and that, interpreted appropriately, an evolution described by the other Hamiltonian system. Equilibrium solutions correspond to extremal points of the Hamiltonian subject to the constraints associated with Liouville's Theorem. Stable equilibria correspond to energy minima. The evolution of a system out of equilibrium involves (in general nonlinear) phase space oscillations which may -- or may not -- interfere destructively so as to damp away.

  18. Collisionless Relaxation of Stellar Systems

    Science.gov (United States)

    Kandrup, Henry E.

    1999-08-01

    The objective of the work summarized here has been to exploit and extend ideas from plasma physics and accelerator dynamics to formulate a unified description of collisionless relaxation of stellar systems that views violent relaxation, Landau damping, and phase mixing as (manifestations of) a single phenomenon. This approach embraces the fact that the collisionless Boltzmann equation (CBE), the basic object of the theory, is an infinite-dimensional Hamiltonian system, with the distribution function f playing the role of the fundamental dynamical variable, and that, interpreted appropriately, an evolution described by the CBE is no different fundamentally from an evolution described by any other Hamiltonian system. Equilibrium solutions f0 correspond to extremal points of the Hamiltonian subject to the constraints associated with Liouville's Theorem. Stable equilibria correspond to energy minima. The evolution of a system out of equilibrium involves (in general nonlinear) phase space oscillations which may - or may not - interfere destructively so as to damp away.

  19. Modeling properties of chromospheric evaporation driven by thermal conduction fronts from reconnection shocks

    CERN Document Server

    Brannon, Sean

    2014-01-01

    Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks so produced drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the "flow reversal point" or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These properties may provide a diagnostic tool to determine parameters of the coronal energy release mechanism and the loop atmosphere. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere/transition region/corona), with TCFs initiated by shocks introduced in the corona. We investigate the effect of two different flare loop parameters (post-shock temperature and tra...

  20. Experimental approach to shape field relevant blast wave profiles in compressed gas-driven shock tube

    Directory of Open Access Journals (Sweden)

    Aravind eSundaramurthy

    2014-12-01

    Full Text Available Detonation of a high explosive produces shock-blast wave, shrapnel, and gaseous products. While direct exposure to blast is a concern near the epicenter, shock-blast can affect subjects even at farther distances, which is termed as primary blast injury, which is the theme of this work. The shock-blast profile is characterized with blast overpressure, positive time duration, and impulse as shock-blast wave parameters (SWPs. These parameters in turn are a function of field factors, such as the strength of high explosive and the distance of the human subjects from the epicenter. The shape and magnitude of the profile determine the severity of injury to the subjects. As shown in some of our recent works (Chandra et al., 2011;Sundaramurthy et al., 2012;Skotak et al., 2013, the profile not only determines the survival of the animal but also the acute and chronic biomechanical injuries along with the following bio-chemical sequelae. It is extremely important to carefully design and operate the shock tube to produce field relevant SWPs. Furthermore, it is vital to identify and eliminate the artifacts that are inadvertently introduced in the shock-blast profile that may affect the results. In this work, we examine the relationship between shock tube adjustable parameters (SAPs and SWPs that can be used to control the blast profile; the results can be easily applied to many of the laboratory shock tubes. Further, exact replication of shock profile (magnitude and shape can be related to field explosions and can be a standard in comparing results across different laboratories. 40 experiments are carried out by judiciously varying SAPs such as membrane thickness, breech length (66.68 to 1209.68 mm, measurement location, and type of driver gas (nitrogen, helium. The relationships between SAPs and the resulting shock-blast profiles are characterized. Finally, shock-blast profiles of a TNT explosion from ConWep software is compared with the profiles obtained

  1. Reverse shock emission driven by post-merger millisecond magnetar winds: Effects of the magnetization parameter

    Science.gov (United States)

    Liu, L. D.; Wang, L. J.; Dai, Z. G.

    2016-08-01

    The study of short-duration gamma-ray bursts provides growing evidence that a good fraction of double neutron star mergers lead to the formation of stable millisecond magnetars. The launch of Poynting flux by the millisecond magnetars could leave distinct electromagnetic signatures that reveal the energy dissipation processes in the magnetar wind. In previous studies, we assume that the magnetar wind becomes completely lepton-dominated so that electrons/positrons in the magnetar wind are accelerated by a diffusive shock. However, theoretical modeling of pulsar wind nebulae shows that in many cases the magnetic field energy in the pulsar wind may be strong enough to suppress diffusive shock acceleration. In this paper, we investigate the reverse shock emission and the forward shock emission with an arbitrary magnetization parameter σ of a magnetar wind. We find that the reverse shock emission strongly depends on σ, and in particular that σ ~ 0.3 leads to the strongest reverse shock emission. Future observations would be helpful to diagnose the composition of the magnetar wind.

  2. Large-Amplitude Electrostatic Waves Observed at a Supercritical Interplanetary Shock

    Science.gov (United States)

    Wilson, L. B., III; Cattell, C. A.; Kellogg, P. J.; Goetz, K.; Kersten, K.; Kasper, J. C.; Szabo, A.; Wilber, M.

    2010-01-01

    We present the first observations at an interplanetary shock of large-amplitude (> 100 mV/m pk-pk) solitary waves and large-amplitude (approx.30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

  3. Modeling Properties Of Chromospheric Evaporation Driven By Thermal Conduction Fronts From Reconnection Shocks

    Science.gov (United States)

    Brannon, Sean; Longcope, D.

    2013-07-01

    Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. These hydrodynamic shocks drive thermal conduction fronts (TCFs), which deposit energy into the chromosphere, driving upflows (evaporation) and downflows (condensation) across a range of temperatures. Observations have revealed that the transition between evaporation and condensation, the "velocity reversal point" (VRP), occurs at a characteristic temperature and with a characteristic slope, which vary between different flares. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere / transition region (TR) / corona), with TCFs initiated by piston shocks introduced in the corona. We investigate the effect of three different flare loop parameters (post-shock temperature, TR temperature ratio, and TR thickness) on the temperature and slope of the VRP. We find that both of the evaporation characteristics have power-law relationships to the varied flare parameters, and we report the scaling exponents for our model. Finally, we develop a method to determine the best-fit post-shock temperature and TR temperature ratio based on the observed quantities, and discuss the results for two sets of published data.

  4. Measure the Propagation of a Halo CME and Its Driven Shock with the Observations from a Single Perspective at Earth

    Science.gov (United States)

    Lu, Lei; Inhester, Bernd; Feng, Li; Liu, Siming; Zhao, Xinhua

    2017-02-01

    We present a detailed study of an Earth-directed coronal mass ejection (full-halo CME) event that happened on 2011 February 15, making use of white-light observations by three coronagraphs and radio observations by Wind/WAVES. We applied three different methods to reconstruct the propagation direction and traveling distance of the CME and its driven shock. We measured the kinematics of the CME leading edge from white-light images observed by Solar Terrestrial Relations Observatory (STEREO) Aand B, tracked the CME-driven shock using the frequency drift observed by Wind/WAVES together with an interplanetary density model, and obtained the equivalent scattering centers of the CME by the polarization ratio (PR) method. For the first time, we applied the PR method to different features distinguished from LASCO/C2 polarimetric observations and calculated their projections onto white-light images observed by STEREO-A and STEREO-B. By combining the graduated cylindrical shell (GCS) forward modeling with the PR method, we proposed a new GCS-PR method to derive 3D parameters of a CME observed from a single perspective at Earth. Comparisons between different methods show a good degree of consistence in the derived 3D results.

  5. Neutrino-driven Turbulent Convection and Standing Accretion Shock Instability in Three-Dimensional Core-Collapse Supernovae

    CERN Document Server

    Abdikamalov, E; Radice, D; Roberts, L F; Haas, R; Reisswig, C; Moesta, P; Klion, H; Schnetter, E

    2014-01-01

    We conduct a series of numerical experiments into the nature of three-dimensional (3D) hydrodynamics in the postbounce stalled-shock phase of core-collapse supernovae using 3D general-relativistic hydrodynamic simulations of a $27$-$M_\\odot$ progenitor star with a neutrino leakage/heating scheme. We vary the strength of neutrino heating and find three cases of 3D dynamics: (1) neutrino-driven convection, (2) initially neutrino-driven convection and subsequent development of the standing accretion shock instability (SASI), (3) SASI dominated evolution. This confirms previous 3D results of Hanke et al. 2013, ApJ 770, 66 and Couch & Connor 2014, ApJ 785, 123. We carry out simulations with resolutions differing by up to a factor of $\\sim$4 and demonstrate that low resolution is artificially favorable for explosion in the 3D convection-dominated case, since it decreases the efficiency of energy transport to small scales. Low resolution results in higher radial convective fluxes of energy and enthalpy, more ful...

  6. Design and analysis of x-ray driven shock wave equation-of-state experiments on the National Ignition Facility

    Science.gov (United States)

    London, R. A.; Lazicki, A.; Celliers, P. M.; Erskine, D. J.; Fratanduono, D. E.; Meezan, N. B.; Peterson, J. L.; NIF EOS Team

    2016-10-01

    The equation-of-state (EOS) is important for describing and predicting material properties in the field of high energy density physics. Especially important is the EOS of materials compressed and heated from ambient conditions by shockwaves. For most materials, experimental data at high pressures, much above 10 Mbar, is sparse. The large energy and power of the National Ignition Facility readily enable EOS experiments in a new regime, at pressures on order of 100 Mbar. We describe a platform for EOS measurements using planar shockwaves driven by x rays within a hohlraum target. The EOS is determined by an impedance matching method, using a reference material of known EOS. For transparent materials, the shock velocity is measured directly by optical interferometry, while for opaque materials, the measurement is done by timing the entrance and exit of the shock and correcting for time variations with an adjacent transparent reference. We describe the computational design and analysis of experiments. Predicted shock velocities and transit times are used to set the target layer thicknesses and interferometer timing. Data from several NIF shots are compared to post-shot calculations. New, high pressure EOS data is presented for several materials. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  7. A comparative analysis of reticular crack on ceramic plate driven by thermal shock

    Science.gov (United States)

    Xu, XiangHong; Sheng, ShiLong; Tian, Cheng; Yuan, WenJun

    2016-07-01

    Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain, it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.

  8. On Collisionless Damping of Ion Acoustic Waves

    DEFF Research Database (Denmark)

    Jensen, Vagn Orla; Petersen, P.I.

    1973-01-01

    Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero.......Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero....

  9. Non-linear collisionless damping of Weibel turbulence in relativistic blast waves

    CERN Document Server

    Lemoine, Martin

    2014-01-01

    The Weibel/filamentation instability is known to play a key role in the physics of weakly magnetized collisionless shock waves. From the point of view of high energy astrophysics, this instability also plays a crucial role because its development in the shock precursor populates the downstream with a small-scale magneto-static turbulence which shapes the acceleration and radiative processes of suprathermal particles. The present work discusses the physics of the dissipation of this Weibel-generated turbulence downstream of relativistic collisionless shock waves. It calculates explicitly the first-order non-linear terms associated to the diffusive nature of the particle trajectories. These corrections are found to systematically increase the damping rate, assuming that the scattering length remains larger than the coherence length of the magnetic fluctuations. The relevance of such corrections is discussed in a broader astrophysical perspective, in particular regarding the physics of the external relativistic ...

  10. On the interplanetary evolution of CME-driven shocks: a comparison between remote sensing observations and in-situ data

    Science.gov (United States)

    Volpes, Laura; Bothmer, Volker

    2015-08-01

    Fast coronal mass ejections (CMEs) are a prime driver of major space weather effects and strong geomagnetic storms. When the CME propagation speed is higher than the Alfvén speed a shock forms in front of the CME leading edge. CME-driven shocks are observed in in-situ data and, with the advent of increasingly sensitive imaging instruments, also in remote sensing observations in the form of bright fronts ahead of the CMEs.In this work we present the study of 4 Earth-directed CMEs which drove shocks detected in STEREO COR 2 and HI observations. For each event we identify the source region and the signatures of CME eruption such as waves, EUV dimmings, flare and prominence eruptions. The shock and CME interplanetary evolution is determined from COR2 and HI observations via an application of triangulation techniques. Furthermore, propagation speed and arrival times are inferred. The CME geometry is modelled in COR2 via the graduated cylindrical shell (GCS) model and the assumption on self-similar expansion is tested by expanding the flux rope to the HI1 field of view. A combination of these results with models for the shock location allows to infer the time evolution of the compression ratio ρd/ρu across the shock and of the upstream Mach number M at locations where no direct plasma measurements are available. These values, as well as the arrival time and speed, are compared to ACE in-situ measurements to validate the results. For the 03 April 2010 event, e.g., the values of the Mach number and the compression ratio extrapolated to the position of ACE are respectively 2.1 situ values found in literature, ρd/ρu = 2.84 and M = 2.2. This study is carried out in conjunction to simulations of CME initiation. Combined results from observations and simulations allow to connect the interplanetary and near-Earth properties of CMEs to those of their source regions, and to the mechanisms of CME onset.

  11. Shock induced ignition and DDT in the presence of mechanically driven fluctuations

    Science.gov (United States)

    Wang, Wentian; McDonald, James G.; Radulescu, Matei I.

    2015-11-01

    The present study addresses the problem of shock induced ignition and transition to detonation in the presence of mechanical and thermal fluctuations. These departures from a homogeneous medium are of significant importance in practical situations, where such fluctuations may promote hot-spot ignition and favor the flame transition to detonation. The problem is studied in 1D, where a piston-induced shock ignites the gas. The fluctuations in the shock-compressed medium are controlled by allowing the piston's speed to oscillate around a mean, with controllable frequency and amplitude. A Lagrangian numerical formulation is used, which allows to treat exactly the transient boundary condition at the piston head. The hydrodynamic solver is coupled with the reactive dynamics of the gas using Cantera. The code was verified by comparison with steady state ZND solutions and previous shock induced ignition results in homogeneous media. Results obtained for different fuels illustrate the strong relation of the DDT amplification length to mechanical fluctuations in systems with a high effective activation energy and fast rate of energy deposition, consistent with experiments performed on fast flame acceleration in the presence of strong mechanical perturbations. Financial support from NSERC and Shell, with A. Pekalski and M. Levin as technical monitors, are greatly acknowledged.

  12. THE ROLE OF PICKUP IONS ON THE STRUCTURE OF THE VENUSIAN BOW SHOCK AND ITS IMPLICATIONS FOR THE TERMINATION SHOCK

    Energy Technology Data Exchange (ETDEWEB)

    Lu Quanming; Shan Lican; Zhang Tielong; Wu Mingyu; Wang Shui [CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei 230026 (China); Zank, Gary P. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Yang Zhongwei [SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai (China); Du Aimin, E-mail: qmlu@ustc.edu.cn [Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)

    2013-08-20

    The recent crossing of the termination shock by Voyager 2 has demonstrated the important role of pickup ions (PUIs) in the physics of collisionless shocks. The Venus Express (VEX) spacecraft orbits Venus in a 24 hr elliptical orbit that crosses the bow shock twice a day. VEX provides a unique opportunity to investigate the role of PUIs on the structure of collisionless shocks more generally. Using VEX observations, we find that the strength of the Venusian bow shock is weaker when solar activity is strong. We demonstrate that this surprising anti-correlation is due to PUIs mediating the Venusian bow shock.

  13. Shock-Driven Hydrodynamic Instability Growth Near Phase Boundaries and Material Property Transitions: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Peralta, Pedro [Arizona State Univ., Tempe, AZ (United States); Fortin, Elizabeth [Arizona State Univ., Tempe, AZ (United States); Opie, Saul [Arizona State Univ., Tempe, AZ (United States); Gautam, Sudrishti [Arizona State Univ., Tempe, AZ (United States); Gopalakrishnan, Ashish [Arizona State Univ., Tempe, AZ (United States); Lynch, Jenna [Arizona State Univ., Tempe, AZ (United States); Chen, Yan [Arizona State Univ., Tempe, AZ (United States); Loomis, Eric [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-01

    Activities for this grant included: 1) Development of dynamic impact experiments to probe strength and phase transition influence on dynamic deformation, 2) development of modern strength and phase aware simulation capabilities, 3) and post-processing of experimental data with simulation and closed form analytical techniques. Two different dynamic experiments were developed to probe material strengths in solid metals (largely copper and iron in this effort). In the first experiment a flyer plate impacts a flat target with an opposite rippled surface that is partially supported by a weaker window material. Post mortem analysis of the target sample showed a strong and repeatable residual plastic deformation dependence on grain orientation. Yield strengths for strain rates near 105 s-1 and plastic strains near ~50% were estimated to be around 180 to 240 MPa, varying in this range with grain orientation. Unfortunately dynamic real-time measurements were difficult with this setup due to diagnostic laser scattering; hence, an additional experimental setup was developed to complement these results. In the second set of experiments a rippled surface was ablated by a controlled laser pulsed, which launched a rippled shock front to an opposite initially flat diagnostic surface that was monitored in real-time with spatially resolved velocimetry techniques, e.g., line VISAR in addition to Transient Imaging Displacement Interferometry (TIDI) displacement measurements. This setup limited the displacements at the diagnostic surface to a reasonable level for TIDI measurements (~ less than one micrometer). These experiments coupled with analytical and numerical solutions provided evidence that viscous and elastic deviatoric strength affect shock front perturbation evolution in clearly different ways. Particularly, normalized shock front perturbation amplitudes evolve with viscosity (η) and perturbation wavelength (λ) as η/λ, such that increasing viscosity

  14. Collisionless reconnection: Mechanism of self-ignition in thin current sheets

    OpenAIRE

    2010-01-01

    The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  15. Collisionless reconnection: Mechanism of self-ignition in thin current sheets

    CERN Document Server

    Treumann, R A; Baumjohann, W

    2010-01-01

    The spontaneous onset of magnetic reconnection in thin collisionless current sheets is shown to result from a thermal-anisotropy driven magnetic Weibel-mode, generating seed-magnetic field {\\sf X}-points in the centre of the current layer.

  16. Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

    Science.gov (United States)

    Treumann, R. A.; Nakamura, R.; Baumjohann, W.

    2010-10-01

    The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  17. A physics informed emulator for laser-driven radiating shock simulations

    KAUST Repository

    McClarren, Ryan G.

    2011-09-01

    This work discusses the uncertainty quantification aspect of quantification of margin and uncertainty (QMU) in the context of two linked computer codes. Specifically, we present a physics based reduction technique to deal with functional data from the first code and then develop an emulator for this reduced data. Our particular application deals with conditions created by laser deposition in a radiating shock experiment modeled using the Lagrangian, radiation-hydrodynamics code Hyades. Our goal is to construct an emulator and perform a sensitivity analysis of the functional output from Hyades to be used as an initial condition for a three-dimensional code that will compute the evolution of the radiating shock at later times. Initial attempts at purely statistical data reduction techniques, were not successful at reducing the number of parameters required to describe the Hyades output. We decided on an alternate approach using physical arguments to decide what features/locations of the output were relevant (e.g., the location of the shock front or the location of the maximum pressure) and then used a piecewise linear fit between these locations. This reduced the number of outputs needed from the emulator to 40, down from the O(1000) points in the Hyades output. Then, using Bayesian MARS and Gaussian process regression, we were able to build emulators for Hyades and study sensitivities to input parameters. © 2011 Elsevier Ltd. All rights reserved.

  18. Microjetting from grooved surfaces in metallic samples subjected to laser driven shocks

    Energy Technology Data Exchange (ETDEWEB)

    Rességuier, T. de, E-mail: resseguier@ensma.fr [Institut PPRIME, UPR 3346, CNRS, ENSMA, Université de Poitiers, 1 ave. Clément Ader, 86961 Futuroscope Cedex (France); Lescoute, E.; Sollier, A.; Prudhomme, G.; Mercier, P. [CEA, DAM, DIF, 91297 Arpajon (France)

    2014-01-28

    When a shock wave propagating in a solid sample reflects from a free surface, geometrical effects predominantly governed by the roughness and defects of that surface may lead to the ejection of tiny jets that may breakup into high velocity, approximately micrometer-size fragments. This process referred to as microjetting is a major safety issue for engineering applications such as pyrotechnics or armour design. Thus, it has been widely studied both experimentally, under explosive and impact loading, and theoretically. In this paper, microjetting is investigated in the specific loading conditions associated to laser shocks: very short duration of pressure application, very high strain rates, small spatial scales. Material ejection from triangular grooves in the free surface of various metallic samples is studied by combining transverse optical shadowgraphy and time-resolved velocity measurements. The influences of the main parameters (groove angle, shock pressure, nature of the metal) on jet formation and ejection velocity are quantified, and the results are compared to theoretical estimates.

  19. Microjetting from grooved surfaces in metallic samples subjected to laser driven shocks

    Science.gov (United States)

    de Rességuier, T.; Lescoute, E.; Sollier, A.; Prudhomme, G.; Mercier, P.

    2014-01-01

    When a shock wave propagating in a solid sample reflects from a free surface, geometrical effects predominantly governed by the roughness and defects of that surface may lead to the ejection of tiny jets that may breakup into high velocity, approximately micrometer-size fragments. This process referred to as microjetting is a major safety issue for engineering applications such as pyrotechnics or armour design. Thus, it has been widely studied both experimentally, under explosive and impact loading, and theoretically. In this paper, microjetting is investigated in the specific loading conditions associated to laser shocks: very short duration of pressure application, very high strain rates, small spatial scales. Material ejection from triangular grooves in the free surface of various metallic samples is studied by combining transverse optical shadowgraphy and time-resolved velocity measurements. The influences of the main parameters (groove angle, shock pressure, nature of the metal) on jet formation and ejection velocity are quantified, and the results are compared to theoretical estimates.

  20. Turbulent dynamo in a collisionless plasma.

    Science.gov (United States)

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco

    2016-04-12

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.

  1. Molecular dynamics simulation of a piston driven shock wave in a hard sphere gas. Final Contractor ReportPh.D. Thesis

    Science.gov (United States)

    Woo, Myeung-Jouh; Greber, Isaac

    1995-01-01

    Molecular dynamics simulation is used to study the piston driven shock wave at Mach 1.5, 3, and 10. A shock tube, whose shape is a circular cylinder, is filled with hard sphere molecules having a Maxwellian thermal velocity distribution and zero mean velocity. The piston moves and a shock wave is generated. All collisions are specular, including those between the molecules and the computational boundaries, so that the shock development is entirely causal, with no imposed statistics. The structure of the generated shock is examined in detail, and the wave speed; profiles of density, velocity, and temperature; and shock thickness are determined. The results are compared with published results of other methods, especially the direct simulation Monte-Carlo method. Property profiles are similar to those generated by direct simulation Monte-Carlo method. The shock wave thicknesses are smaller than the direct simulation Monte-Carlo results, but larger than those of the other methods. Simulation of a shock wave, which is one-dimensional, is a severe test of the molecular dynamics method, which is always three-dimensional. A major challenge of the thesis is to examine the capability of the molecular dynamics methods by choosing a difficult task.

  2. The dynamics of neutrino-driven supernova explosions after shock revival in 2D and 3D

    Science.gov (United States)

    Müller, B.

    2015-10-01

    We study the growth of the explosion energy after shock revival in neutrino-driven explosions in two and three dimensions (2D/3D) using multi-group neutrino hydrodynamics simulations of an 11.2 M⊙ star. The 3D model shows a faster and steadier growth of the explosion energy and already shows signs of subsiding accretion after one second. By contrast, the growth of the explosion energy in 2D is unsteady, and accretion lasts for several seconds as confirmed by additional long-time simulations of stars of similar masses. Appreciable explosion energies can still be reached, albeit at the expense of rather high neutron star masses. In 2D, the binding energy at the gain radius is larger because the strong excitation of downward-propagating g modes removes energy from the freshly accreted material in the downflows. Consequently, the mass outflow rate is considerably lower in 2D than in 3D. This is only partially compensated by additional heating by outward-propagating acoustic waves in 2D. Moreover, the mass outflow rate in 2D is reduced because much of the neutrino energy deposition occurs in downflows or bubbles confined by secondary shocks without driving outflows. Episodic constriction of outflows and vertical mixing of colder shocked material and hot, neutrino-heated ejecta due to Rayleigh-Taylor instability further hamper the growth of the explosion energy in 2D. Further simulations will be necessary to determine whether these effects are generic over a wider range of supernova progenitors.

  3. Kinetic Simulations of Particle Acceleration at Shocks

    Energy Technology Data Exchange (ETDEWEB)

    Caprioli, Damiano [Princeton University; Guo, Fan [Los Alamos National Laboratory

    2015-07-16

    Collisionless shocks are mediated by collective electromagnetic interactions and are sources of non-thermal particles and emission. The full particle-in-cell approach and a hybrid approach are sketched, simulations of collisionless shocks are shown using a multicolor presentation. Results for SN 1006, a case involving ion acceleration and B field amplification where the shock is parallel, are shown. Electron acceleration takes place in planetary bow shocks and galaxy clusters. It is concluded that acceleration at shocks can be efficient: >15%; CRs amplify B field via streaming instability; ion DSA is efficient at parallel, strong shocks; ions are injected via reflection and shock drift acceleration; and electron DSA is efficient at oblique shocks.

  4. Experimental studies of collisional plasma shocks and plasma interpenetration via merging supersonic plasma jets

    Science.gov (United States)

    Hsu, S. C.; Moser, A. L.; Merritt, E. C.; Adams, C. S.

    2015-11-01

    Over the past 4 years on the Plasma Liner Experiment (PLX) at LANL, we have studied obliquely and head-on-merging supersonic plasma jets of an argon/impurity or hydrogen/impurity mixture. The jets are formed/launched by pulsed-power-driven railguns. In successive experimental campaigns, we characterized the (a) evolution of plasma parameters of a single plasma jet as it propagated up to ~ 1 m away from the railgun nozzle, (b) density profiles and 2D morphology of the stagnation layer and oblique shocks that formed between obliquely merging jets, and (c) collisionless interpenetration transitioning to collisional stagnation between head-on-merging jets. Key plasma diagnostics included a fast-framing CCD camera, an 8-chord visible interferometer, a survey spectrometer, and a photodiode array. This talk summarizes the primary results mentioned above, and highlights analyses of inferred post-shock temperatures based on observations of density gradients that we attribute to shock-layer thickness. We also briefly describe more recent PLX experiments on Rayleigh-Taylor-instability evolution with magnetic and viscous effects, and potential future collisionless shock experiments enabled by low-impurity, higher-velocity plasma jets formed by contoured-gap coaxial guns. Supported by DOE Fusion Energy Sciences and LANL LDRD.

  5. Generation of quasi-monoenergetic heavy ion beams via staged shock wave acceleration driven by intense laser pulses in near-critical plasmas

    Science.gov (United States)

    Zhang, W. L.; Qiao, B.; Shen, X. F.; You, W. Y.; Huang, T. W.; Yan, X. Q.; Wu, S. Z.; Zhou, C. T.; He, X. T.

    2016-09-01

    Laser-driven ion acceleration potentially offers a compact, cost-effective alternative to conventional accelerators for scientific, technological, and health-care applications. A novel scheme for heavy ion acceleration in near-critical plasmas via staged shock waves driven by intense laser pulses is proposed, where, in front of the heavy ion target, a light ion layer is used for launching a high-speed electrostatic shock wave. This shock is enhanced at the interface before it is transmitted into the heavy ion plasmas. Monoenergetic heavy ion beam with much higher energy can be generated by the transmitted shock, comparing to the shock wave acceleration in pure heavy ion target. Two-dimensional particle-in-cell simulations show that quasi-monoenergetic {{{C}}}6+ ion beams with peak energy 168 MeV and considerable particle number 2.1 × {10}11 are obtained by laser pulses at intensity of 1.66 × {10}20 {{W}} {{cm}}-2 in such staged shock wave acceleration scheme. Similarly a high-quality {{Al}}10+ ion beam with a well-defined peak with energy 250 MeV and spread δ E/{E}0=30 % can also be obtained in this scheme.

  6. First results of radiation-driven, layered deuterium-tritium implosions with a 3-shock adiabat-shaped drive at the National Ignition Facility

    Energy Technology Data Exchange (ETDEWEB)

    Smalyuk, V. A.; Robey, H. F.; Döppner, T.; Jones, O. S.; Milovich, J. L.; Bachmann, B.; Baker, K. L.; Berzak Hopkins, L. F.; Bond, E.; Callahan, D. A.; Casey, D. T.; Celliers, P. M.; Cerjan, C.; Clark, D. S.; Dixit, S. N.; Edwards, M. J.; Haan, S. W.; Hamza, A. V.; Hurricane, O. A.; Jancaitis, K. S. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); and others

    2015-08-15

    Radiation-driven, layered deuterium-tritium plastic capsule implosions were carried out using a new, 3-shock “adiabat-shaped” drive on the National Ignition Facility. The purpose of adiabat shaping is to use a stronger first shock, reducing hydrodynamic instability growth in the ablator. The shock can decay before reaching the deuterium-tritium fuel leaving it on a low adiabat and allowing higher fuel compression. The fuel areal density was improved by ∼25% with this new drive compared to similar “high-foot” implosions, while neutron yield was improved by more than 4 times, compared to “low-foot” implosions driven at the same compression and implosion velocity.

  7. Feedback under the microscope: thermodynamic structure and AGN driven shocks in M87

    CERN Document Server

    Million, E T; Simionescu, A; Allen, S W; Nulsen, P E J; Fabian, A C; Bohringer, H; Sanders, J S

    2010-01-01

    (abridged) Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of $\\sim$16,000 independent regions, each with $\\sim$1,000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. Excluding the 'X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift, or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions. We confirm the presence of a thick ($\\sim$40 arcsec or $\\sim$3 kpc) ring of high pressure gas at a radius of $\\sim$180 arcsec ($\\sim$14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of $\\sim$40 arcsec ($\\sim$3 kpc...

  8. Experimental models of acute infection and Toll-like receptor driven septic shock.

    Science.gov (United States)

    Ferstl, Ruth; Spiller, Stephan; Fichte, Sylvia; Dreher, Stefan; Kirschning, Carsten J

    2009-01-01

    Mainly Gram-negative and Gram-positive bacterial infections, but also other infections such as with fungal or viral pathogens, can cause the life-threatening clinical condition of septic shock. Transgression of the host immune response from a local level limited to the pathogen's place of entry to the systemic level is recognised as a major mode of action leading to sepsis. This view has been established upon demonstration of the capacity of specific pathogen-associated molecular patterns (PAMPs) to elicit symptoms of septic shock upon systemic administration. Immune stimulatory PAMPs are agonists of soluble, cytoplasmic, as well as/or cell membrane-anchored and/or -spanning pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs). However, reflection of pathogen-host crosstalk triggering sepsis pathogenesis upon an infection by a host response to challenge with an isolated PAMP is incomplete. Therefore, an experimental model more reflective of pathogen-host interaction requires experimental host confrontation with a specific pathogen in its viable form resulting in a collective stimulation of a variety of specific PRRs. This chapter describes methods to analyse innate pathogen sensing by the host on both a cellular and systemic level.

  9. The shocked outflow in NGC 4051 - momentum-driven feedback, UFO's and warm absorbers

    CERN Document Server

    Pounds, Ken

    2013-01-01

    An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009 revealed an unusually rich absorption spectrum with outflow velocities, in both RGS and EPIC spectra, up to ~ 9000 km/s (Pounds and Vaughan 2011). Evidence was again seen for a fast ionised wind with velocity ~ 0.12c (Tombesi 2010, Pounds and Vaughan 2012). Detailed modelling with the XSTAR photoionisation code now confirms the general correlation of velocity and ionisation predicted by mass conservation in a Compton-cooled shocked wind (King 2010). We attribute the strong column density gradient in the model to the addition of strong two-body cooling in the later stages of the flow, causing the ionisation (and velocity) to fall more quickly, and confining the lower ionisation gas to a narrower region. The column density and recombination timescale of the highly ionised flow component, seen mainly in Fe K lines, determine the primary shell thickness which, when compared with the theoretical Compton cooling length, determines a shock r...

  10. Physics of collisionless phase mixing

    CERN Document Server

    Tsiklauri, D

    2008-01-01

    A previous study [Tsiklauri et al., 2005, Astron. Astrophys., 435, 1105] of phase mixing of ion cyclotron (IC), Alfvenic, waves in the collisionless regime has established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we bridge the gap in understanding by establishing the following: (i) Using the generalised Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20% respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to b...

  11. Shear-driven instabilities and shocks in the atmospheres of hot Jupiters

    Science.gov (United States)

    Fromang, Sébastien; Leconte, Jeremy; Heng, Kevin

    2016-07-01

    Context. General circulation models of the atmosphere of hot Jupiters have shown the existence of a supersonic eastward equatorial jet. These results have been obtained using numerical schemes that filter out vertically propagating sound waves and assume vertical hydrostatic equilibrium, or were acquired with fully compressive codes that use large dissipative coefficients. Aims: We remove these two limitations and investigate the effects of compressibility on the atmospheric dynamics by solving the standard Euler equations. Methods: This was done by means of a series of simulations performed in the framework of the equatorial β-plane approximation using the finite-volume shock-capturing code RAMSES. Results: At low resolution, we recover the classical results described in the literature: we find a strong and steady supersonic equatorial jet of a few km s-1 that displays no signature of shocks. We next show that the jet zonal velocity depends significantly on the grid meridional resolution. When this resolution is fine enough to properly resolve the jet, the latter is subject to a Kelvin-Helmholtz instability. The jet zonal mean velocity displays regular oscillations with a typical timescale of a few days and a significant amplitude of about 15% of the jet velocity. We also find compelling evidence for the development of a vertical shear instability at pressure levels of a few bars. It seems to be responsible for an increased downward kinetic energy flux that significantly affects the temperature of the deep atmosphere and appears to act as a form of drag on the equatorial jet. This instability also creates velocity fluctuations that propagate upward and steepen into weak shocks at pressure levels of a few mbars. Conclusions: We conclude that hot-Jupiter equatorial jets are potentially unstable to both a barotropic Kelvin-Helmholtz instability and a vertical shear instability. Upon confirmation using more realistic models, these two instabilities could result in

  12. Laser Heating of Solid Matter by Light-Pressure-Driven Shocks at Ultrarelativistic Intensities

    Energy Technology Data Exchange (ETDEWEB)

    Akli, K.U.; Hansen, S.B.; Kemp, A.J.; Freeman, R.R.; Beg, F.N.; Clark, D.C.; Chen, S.D.; Hey, D.; Hatchett, S.P.; Highbarger, K.; Giraldez, E.; Green, J.S.; Gregori, G.; Lancaster, K.L.; Ma, T.; MacKinnon, A.J.; Norreys, P.; Patel, N.; Pasley, J.; Shearer, C.; Stephens, R.B.; Stoeckl, C.; Storm, M.; Theobald, W.; Van Woerkom, L.D.; Weber, R.; Key, M.H.

    2008-04-29

    The heating of solid targets irradiated by 5 x 10^20 W cm^-2, 0.8 ps, 1.05 um wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to ~5 keV with an axial temperature gradient of 0.6 um scale length. Images of Ni Ly sub-alpha show the hot region has <25 um diameter. These data are consistent with collisional particle-in-cell simulations using preformed plasma density profiles from hydrodynamic modeling which show that the >100 Gbar light pressure compresses the preformed plasma and dries a shock into the solid, heating a thin layer.

  13. Constitutively active heat shock factor 1 enhances glucose-driven insulin secretion.

    Science.gov (United States)

    Uchiyama, Tsuyoshi; Tomono, Shoichi; Utsugi, Toshihiro; Ohyama, Yoshio; Nakamura, Tetsuya; Tomura, Hideaki; Kawazu, Shoji; Okajima, Fumikazu; Kurabayashi, Masahiko

    2011-06-01

    Weak pancreatic β-cell function is a cause of type 2 diabetes mellitus. Glucokinase regulates insulin secretion via phosphorylation of glucose. The present study focused on a system for the self-protection of pancreatic cell by expressing heat shock factor (HSF) and heat shock protein (HSP) to improve insulin secretion without inducing hypoglycemia. We previously generated a constitutively active form of human HSF1 (CA-hHSF1). An adenovirus expressing CA-hHSF1 using the cytomegalovirus promoter was generated to infect mouse insulinoma cells (MIN6 cells). An adenovirus expressing CA-hHSF1 using a human insulin promoter (Ins-CA-hHSF1) was also generated to infect rats. We investigated whether CA-hHSF1 induces insulin secretion in MIN6 cells and whether Ins-CA-hHSF1 can improve blood glucose and serum insulin levels in healthy Wister rats and type 2 diabetes mellitus model rats. CA-hHSF1 expression increased insulin secretion 1.27-fold compared with the overexpression of wild-type hHSF1 in MIN6 cells via induction of HSP90 expression and subsequent activation of glucokinase. This mechanism is associated with activation of both glucokinase and neuronal nitric oxide synthase. Ins-CA-hHSF1 improved blood glucose levels in neonatal streptozotocin-induced diabetic rats. Furthermore, Ins-CA-hHSF1 reduced oral glucose tolerance testing results in healthy Wister rats because of an insulin spike at 15 minutes; however, it did not induce hypoglycemia. CA-hHSF1 induced insulin secretion both in vitro and in vivo. These findings suggest that gene therapy with Ins-CA-hHSF1 will be able to be used to treat patients with type 2 diabetes mellitus and impaired glucose tolerance without causing hypoglycemia at fasting. Copyright © 2011 Elsevier Inc. All rights reserved.

  14. High pressure generation by hot electrons driven ablation

    Energy Technology Data Exchange (ETDEWEB)

    Piriz, A. R. [E.T.S.I. Industriales, CYTEMA, and Instituto de Investigaciones Energéticas, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Piriz, S. A. [Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Tahir, N. A. [GSI Helmholtzzentrum für Schwerionenforschung, Planckstrasse 1, 64291 Darmstadt (Germany)

    2013-11-15

    A previous model [Piriz et al. Phys. Plasmas 19, 122705 (2012)] for the ablation driven by the hot electrons generated in collisionless laser-plasma interactions in the framework of shock ignition is revisited. The impact of recent results indicating that for a laser wavelength λ = 0.35 μm the hot electron temperature θ{sub H} would be independent of the laser intensity I, on the resulting ablation pressure is considered. In comparison with the case when the scaling law θ{sub H}∼(Iλ{sup 2}){sup 1/3} is assumed, the generation of the high pressures needed for driving the ignitor shock may be more demanding. Intensities above 10{sup 17} W/cm{sup 2} would be required for θ{sub H}=25−30 keV.

  15. Performance experiments with a shock-tunnel-driven argon-cesium MHD disk generator

    Energy Technology Data Exchange (ETDEWEB)

    Veefkind, A.; Karavasilev, P.; Wang, D.

    1988-08-01

    An extensive amount of data has been collected concerning MHD disk generator performance under different operation conditions. The results are obtained from a large number of runs with the Eindhoven shock tunnel facility. The runs are carried out at different stagnation temperatures, stagnation pressures, external loads, and seed fractions. Two channels have been used, one with and one without inlet swirl. Voltage, pressure, and radiation measurements have been employed. Current to voltage characteristics have been measured for different seed ratios. The enthalpy extractions of the disk with inlet swirl are found to be comparable with similar experiments with linear channels. The enthalpy extractions of the radial disk are found to be lower. A high enthalpy extraction (18 percent at a stagnation temperature of 2100 K) is reported at a comparatively low stagnation pressure (4.2 bar). A one-dimensional-gasdynamical analysis using measured voltages as an input is discussed. The measured fluctuations of electron temperature and density indicate that the results are obtained in a nonuniform plasma. 10 references.

  16. Effects of laser polarization on electrostatic shock ion acceleration in near-critical plasmas

    Science.gov (United States)

    Kim, Young-Kuk; Kang, Teyoun; Hur, Min Sup

    2016-10-01

    Ion acceleration from laser-driven collisionless electrostatic shock (CES) is attracting much attention, as quasi-monoenergetic, tens of MeV ion beams are expected to be available from relatively moderate laser power and near-critical density plasmas. For generation of a high-speed shock by a laser pulse, it is important to compress a high-contrast density layer by hole-boring process, and to heat the electrons in the upstream, where the hole-boring speed should match the Mach number condition 1.5 boring speed is higher in lower density plasmas, we observed consistently higher speed of the shock and accelerated ion energy when driven by CP pulses. Interesting point is that the CP-shock generation is determined predominantly by the transmittance only, while the LP-shock formation depends on other parameters such as plasma scale length. In 2D simulations, we found that Weibel instability is less effective in CP than LP, which enables more stable shock formation for given conditions of the laser and plasma. This work was supported by the Basic Science Research Program (NRF-2013R1A1A2006353) and the Creative Allied Project (CAP-15-06-ETRI).

  17. Collisionless Reconnection and Electron Demagnetization

    Science.gov (United States)

    Scudder, J. D.

    Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.

  18. The Dynamics of Neutrino-Driven Supernova Explosions after Shock Revival in 2D and 3D

    CERN Document Server

    Müller, Bernhard

    2015-01-01

    We study the growth of the explosion energy after shock revival in neutrino-driven explosions in two and three dimensions (2D/3D) using multi-group neutrino hydrodynamics simulations of an $11.2 M_\\odot$ star. The 3D model shows a faster and steadier growth of the explosion energy and already shows signs of subsiding accretion after one second. By contrast, the growth of the explosion energy in 2D is unsteady, and accretion lasts for several seconds as confirmed by additional long-time simulations of stars of similar masses. Appreciable explosion energies can still be reached, albeit at the expense of rather high neutron star masses. In 2D, the binding energy at the gain radius is larger because the strong excitation of downward-propagating $g$-modes removes energy from the freshly accreted material in the downflows. Consequently, the mass outflow rate is considerably lower in 2D than in 3D. This is only partially compensated by additional heating by outward-propagating acoustic waves in 2D. Moreover, the mas...

  19. Internal shocks driven by accretion flow variability in the compact jet of the black hole binary GX 339-4

    CERN Document Server

    Drappeau, S; Belmont, J; Gandhi, P; Corbel, S

    2014-01-01

    In recent years, compact jets have been playing a growing role in the understanding of accreting black hole engines. In the case of X-ray binary systems, compact jets are usually associated with the hard state phase of a source outburst. Recent observations of GX 339-4 have demonstrated the presence of a variable synchrotron spectral break in the mid-infrared band that was associated with its compact jet. In the model used in this study, we assume that the jet emission is produced by electrons accelerated in internal shocks driven by rapid fluctuations of the jet velocity. The resulting spectral energy distribution (SED) and variability properties are very sensitive to the Fourier power spectrum density (PSD) of the assumed fluctuations of the jet Lorentz factor. These fluctuations are likely to be triggered by the variability of the accretion flow which is best traced by the X-ray emission. Taking the PSD of the jet Lorentz factor fluctuations to be identical to the observed X-ray PSD, our study finds that t...

  20. The dynamic quasiperpendicular shock: Cluster discoveries

    CERN Document Server

    Krasnoselskikh, V; Walker, S N; Schwartz, S; Sundkvist, D; Lobzin, V; Gedalin, M; Bale, S D; Mozer, F; Soucek, J; Hobara, Y; Comisel, H

    2013-01-01

    The physics of collisionless shocks is a very broad topic which has been studied for more than five decades. However, there are a number of important issues which remain unresolved. The energy repartition amongst particle populations in quasiperpendicular shocks is a multi-scale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. The most important processes take place in the close vicinity of the major magnetic transition or ramp region. The distribution of electromagnetic fields in this region determines the characteristics of ion reflection and thus defines the conditions for ion heating and energy dissipation for supercritical shocks and also the region where an important part of electron heating takes place. All of these processes are crucially dependent upon the characteristic spatial scales of the ramp and foot region provided that the shock is stationary. The earliest studies of collisionless shocks identified nonlinearity, dissipation, and dispe...

  1. Weibel Instability Driven by Spatially Anisotropic Density Structures

    Science.gov (United States)

    Tomita, Sara; Ohira, Yutaka

    2016-07-01

    Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron-positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.

  2. Ion-acoustic shocks with reflected ions: modeling and PIC simulations

    CERN Document Server

    Liseykina, T; Vshivkov, V; Malkov, M

    2015-01-01

    Non-relativistic collisionless shock waves are widespread in space and astrophysical plasmas and are known as efficient particle accelerators. However, our understanding of collisionless shocks, including their structure and the mechanisms whereby they accelerate particles remains incomplete. We present here the results of numerical modeling of an ion-acoustic collisionless shock based on one-dimensional (1D) kinetic approximation both for electrons and ions with a real mass ratio. Special emphasis is made on the shock-reflected ions as the main driver of shock dissipation. The reflection efficiency, velocity distribution of reflected particles and the shock electrostatic structure are studied in terms of the shock parameters. Applications to particle acceleration in geophysical and astrophysical shocks are discussed.

  3. Experimental Demonstration of the Collisionless Plasmoid Instability below the Ion Kinetic Scale during Magnetic Reconnection.

    Science.gov (United States)

    Olson, J; Egedal, J; Greess, S; Myers, R; Clark, M; Endrizzi, D; Flanagan, K; Milhone, J; Peterson, E; Wallace, J; Weisberg, D; Forest, C B

    2016-06-24

    The spontaneous formation of magnetic islands is observed in driven, antiparallel magnetic reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that the plasmoid instability is active at the electron scale inside the ion diffusion region in a low collisional regime. The experiments show the island formation occurs at a smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding of magnetic islands emphasizes their importance to reconnection in naturally occurring 3D plasmas.

  4. Experimental Demonstration of the Collisionless Plasmoid Instability below the Ion Kinetic Scale during Magnetic Reconnection

    Science.gov (United States)

    Olson, J.; Egedal, J.; Greess, S.; Myers, R.; Clark, M.; Endrizzi, D.; Flanagan, K.; Milhone, J.; Peterson, E.; Wallace, J.; Weisberg, D.; Forest, C. B.

    2016-06-01

    The spontaneous formation of magnetic islands is observed in driven, antiparallel magnetic reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that the plasmoid instability is active at the electron scale inside the ion diffusion region in a low collisional regime. The experiments show the island formation occurs at a smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding of magnetic islands emphasizes their importance to reconnection in naturally occurring 3D plasmas.

  5. Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2010-10-01

    Full Text Available The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  6. Assessment of ion kinetic effects in shock-driven inertial confinement fusion implosions using fusion burn imaging

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, M. J., E-mail: mros@lle.rochester.edu; Séguin, F. H.; Rinderknecht, H. G.; Zylstra, A. B.; Li, C. K.; Sio, H.; Johnson, M. Gatu; Frenje, J. A.; Petrasso, R. D. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Amendt, P. A.; Wilks, S. C.; Pino, J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Atzeni, S. [Dipartimento SBAI, Università di Roma “La Sapienza” and CNISM, Via A. Scarpa 14-16, I-00161 Roma (Italy); Hoffman, N. M.; Kagan, G.; Molvig, K. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Glebov, V. Yu.; Stoeckl, C.; Seka, W.; Marshall, F. J. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); and others

    2015-06-15

    The significance and nature of ion kinetic effects in D{sup 3}He-filled, shock-driven inertial confinement fusion implosions are assessed through measurements of fusion burn profiles. Over this series of experiments, the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number, N{sub K}) was varied from 0.3 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured the observed yield trends [Rosenberg et al., Phys. Rev. Lett. 112, 185001 (2014)]. Here, spatially resolved measurements of the fusion burn are used to examine kinetic ion transport effects in greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional integrated quantities to one-dimensional profiles. In agreement with the previous findings, a comparison of measured and simulated burn profiles shows that models including ion transport effects are able to better match the experimental results. In implosions characterized by large Knudsen numbers (N{sub K} ∼ 3), the fusion burn profiles predicted by hydrodynamics simulations that exclude ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally observed profiles, which are centrally peaked. In contrast, a hydrodynamics simulation that includes a model of ion diffusion is able to qualitatively match the measured profile shapes. Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the observed trends, though further refinement of the models is needed for a more complete and quantitative understanding of ion kinetic effects.

  7. Absence of caveolin-1 alters heat shock protein expression in spontaneous mammary tumors driven by Her-2/neu expression.

    Science.gov (United States)

    Ciocca, Daniel R; Cuello-Carrión, F Darío; Natoli, Anthony L; Restall, Christina; Anderson, Robin L

    2012-02-01

    In a previous study, we measured caveolin-1 protein levels, both in the normal breast and in breast cancer. The study revealed no association between caveolin-1 expression in the epithelial compartment and clinical disease outcome. However, high levels of caveolin-1 in the stromal tissue surrounding the tumor associated strongly with reduced metastasis and improved survival. Using an animal model, we found that the onset of mammary tumors driven by Her-2/neu expression was accelerated in mice lacking caveolin-1. We have analysed the heat shock protein (Hsp) response in the tumors of mice lacking caveolin-1. In all cases, the mammary tumors were estrogen and progesterone receptor negative, and the levels of Her-2/neu (evaluated by immunohistochemistry) were not different between the caveolin-1 +/+ (n = 8) and the caveolin-1 -/- (n = 7) tumors. However, a significant reduction in the extent of apoptosis was observed in mammary tumors from animals lacking caveolin-1. While Bcl-2, Bax, and survivin levels in the tumors were not different, the amount of HSPA (Hsp70) was almost double in the caveolin-1 -/- tumors. In contrast, HSPB1 (Hsp27/Hsp25) levels were significantly lower in the caveolin-1 -/- tumors. The mammary tumors from caveolin-1 null mice expressed more HSPC4 (gp96 or grp94), but HSPC1 (Hsp90), HSPA5 (grp78), HSPD1 (Hsp60), and CHOP were not altered. No significant changes in these proteins were found in the stroma surrounding these tumors. These results demonstrate that the disruption of the Cav-1 gene can cause alterations of specific Hsps as well as tumor development.

  8. Properties of a Coronal Shock Wave as A Driver of Early SEP Acceleration

    CERN Document Server

    Kozarev, Kamen A; Lobzin, Vasili V; Hammer, Michael

    2014-01-01

    Coronal mass ejections (CMEs) are thought to drive collisionless shocks in the solar corona, which in turn have been shown capable of accelerating solar energetic particles (SEPs) in minutes. It has been notoriously difficult to extract information about energetic particle spectra in the corona, due to lack of in-situ measurements. It is possible, however, to combine remote observations with data-driven models in order to deduce coronal shock properties relevant to the local acceleration of SEPs and their heliospheric connectivity to near-Earth space. We present such novel analysis applied to the May 11, 2011 CME event on the western solar limb, focusing on the evolution of the eruption-driven, dome-like shock wave observed by the Atmospheric Imaging Assembly (AIA) EUV telescopes on board the Solar Dynamics Observatory spacecraft. We analyze the shock evolution and estimate its strength using emission measure modeling. We apply a new method combining a geometric model of the shock front with a potential field...

  9. The formation and evolution of reconnection-driven, slow-mode shocks in a partially ionised plasma

    Science.gov (United States)

    Hillier, A.; Takasao, S.; Nakamura, N.

    2016-06-01

    The role of slow-mode magnetohydrodynamic (MHD) shocks in magnetic reconnection is of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we use numerical simulations to investigate the role of collisional coupling between a proton-electron, charge-neutral fluid and a neutral hydrogen fluid for the one-dimensional (1D) Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves. The first is a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock wave. The system evolves through four stages: initiation, weak coupling, intermediate coupling, and a quasi-steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. Because of the nature of the system, the neutral fluid is overpressured by the shock when compared to a purely hydrodynamic shock, which results in the neutral fluid expanding to form the shock precursor. Once it has formed, the thickness of the shock front is proportional to ξ i-1.2 , which is a smaller exponent than would be naively expected from simple scaling arguments. One interesting result is that the shock front is a continuous transition of the physical variables of subsonic velocity upstream of the shock front (a c-shock) to a sharp jump in the physical variables followed by a relaxation to the downstream values for supersonic upstream velocity (a j-shock). The frictional heating that results from the velocity drift across the shock front can amount to ~2 per cent of the reference magnetic energy.

  10. Firehose and Mirror Instabilities in a Collisionless Shearing Plasma

    CERN Document Server

    Kunz, Matthew W; Stone, James M

    2014-01-01

    The first hybrid-kinetic numerical simulations of the firehose and mirror instabilities in a collisionless plasma are performed in which pressure anisotropy is driven as the magnetic field is changed by a persistent linear shear S. For a decreasing field, it is found that mostly oblique firehose fluctuations grow at Larmor scales and saturate with energies ~S^{1/2}; the pressure anisotropy is pinned at the stability threshold by anomalous particle scattering. In contrast, nonlinear mirror fluctuations are large compared to the Larmor scale and grow secularly in time; marginality is maintained by an increasing population of resonant particles trapped in magnetic mirrors. After one shear time, saturated order-unity magnetic mirrors are formed and particles scatter off their sharp edges. Both instabilities drive sub-Larmor-scale fluctuations, which appear to be kinetic-Alfven-wave turbulence. Our results impact theories of momentum and heat transport in astrophysical and space plasmas, in which the stretching of...

  11. Umklapp superradiance with a collisionless quantum degenerate Fermi gas.

    Science.gov (United States)

    Piazza, Francesco; Strack, Philipp

    2014-04-11

    The quantum dynamics of the electromagnetic light mode of an optical cavity filled with a coherently driven Fermi gas of ultracold atoms strongly depends on the geometry of the Fermi surface. Superradiant light generation and self-organization of the atoms can be achieved at low pumping threshold due to resonant atom-photon umklapp processes, where the fermions are scattered from one side of the Fermi surface to the other by exchanging photon momenta. The cavity spectrum exhibits sidebands that, despite strong atom-light coupling and cavity decay, retain narrow linewidth, due to absorptionless transparency windows outside the atomic particle-hole continuum and the suppression of broadening and thermal fluctuations in the collisionless Fermi gas.

  12. Magnetic guide field generation in collisionless current sheets

    Directory of Open Access Journals (Sweden)

    W. Baumjohann

    2010-03-01

    Full Text Available In thin (Δ< few λi collisionless current sheets in a space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal fluctuation level by the action of the non-magnetic Weibel instability (Weibel, 1959. The instability is driven by the counter-streaming electron inflow from the "ion diffusion" (ion inertial Hall region into the inner current (electron inertial region after thermalisation by the two-stream instability. Under magnetospheric tail conditions it takes ~50 e-folding times (~100 s for the Weibel field to reach observable amplitudes |bW|~1 nT. In counter-streaming inflows these fields are of guide field type.

  13. DIFFUSIVE SHOCK ACCELERATION AT COSMOLOGICAL SHOCK WAVES

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Hyesung [Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of); Ryu, Dongsu, E-mail: kang@uju.es.pusan.ac.kr, E-mail: ryu@canopus.cnu.ac.kr [Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of)

    2013-02-10

    We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological shocks in the large-scale structure of the universe, incorporating wave-particle interactions that are expected to operate in collisionless shocks. Adopting simple phenomenological models for magnetic field amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfvenic drift, we perform kinetic DSA simulations for a wide range of sonic and Alfvenic Mach numbers and evaluate the CR injection fraction and acceleration efficiency. In our DSA model, the CR acceleration efficiency is determined mainly by the sonic Mach number M{sub s} , while the MFA factor depends on the Alfvenic Mach number and the degree of shock modification by CRs. We show that at strong CR modified shocks, if scattering centers drift with an effective Alfven speed in the amplified magnetic field, the CR energy spectrum is steepened and the acceleration efficiency is reduced significantly, compared to the cases without such effects. As a result, the postshock CR pressure saturates roughly at {approx}20% of the shock ram pressure for strong shocks with M{sub s} {approx}> 10. In the test-particle regime (M{sub s} {approx}< 3), it is expected that the magnetic field is not amplified and the Alfvenic drift effects are insignificant, although relevant plasma physical processes at low Mach number shocks remain largely uncertain.

  14. Transition from Collisionless to Collisional MRI

    Energy Technology Data Exchange (ETDEWEB)

    Prateek Sharma; Gregory W. Hammett; Eliot Quataert

    2003-07-24

    Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.

  15. The internal propagation of fusion flame with the strong shock of a laser driven plasma block for advanced nuclear fuel ignition

    Institute of Scientific and Technical Information of China (English)

    B.Malekynia; S.S.Razavipour

    2013-01-01

    An accelerated skin layer may be used to ignite solid state fuels.Detailed analyses were clarified by solving the hydrodynamic equations for nonlinear force driven plasma block ignition.In this paper,the complementary mechanisms are included for the advanced fuel ignition:external factors such as lasers,compression,shock waves,and sparks.The other category is created within the plasma fusion as reheating of an alpha particle,the Bremsstrahlung absorption,expansion,conduction,and shock waves generated by explosions.With the new condition for the control of shock waves,the spherical deuterium-tritium fuel density should be increased to 75 times that of the solid state.The threshold ignition energy flux density for advanced fuel ignition may be obtained using temperature equations,including the ones for the density profile obtained through the continuity equation and the expansion velocity for the r ≠ 0 layers.These thresholds are significantly reduced in comparison with the ignition thresholds at x =0 for solid advanced fuels.The quantum correction for the collision frequency is applied in the case of the delay in ion heating.Under the shock wave condition,the spherical protonboron and proton-lithium fuel densities should be increased to densities 120 and 180 times that of the solid state.These plasma compressions are achieved through a longer duration laser pulse or X-ray.

  16. The plasma physics of shock acceleration

    Science.gov (United States)

    Jones, Frank C.; Ellison, Donald C.

    1991-01-01

    The history and theory of shock acceleration is reviewed, paying particular attention to theories of parallel shocks which include the backreaction of accelerated particles on the shock structure. The work that computer simulations, both plasma and Monte Carlo, are playing in revealing how thermal ions interact with shocks and how particle acceleration appears to be an inevitable and necessary part of the basic plasma physics that governs collisionless shocks is discussed. Some of the outstanding problems that still confront theorists and observers in this field are described.

  17. Hybrid Simulations of Particle Acceleration at Shocks

    CERN Document Server

    Caprioli, Damiano

    2014-01-01

    We present the results of large hybrid (kinetic ions - fluid electrons) simulations of particle acceleration at non-relativistic collisionless shocks. Ion acceleration efficiency and magnetic field amplification are investigated in detail as a function of shock inclination and strength, and compared with predictions of diffusive shock acceleration theory, for shocks with Mach number up to 100. Moreover, we discuss the relative importance of resonant and Bell's instability in the shock precursor, and show that diffusion in the self-generated turbulence can be effectively parametrized as Bohm diffusion in the amplified magnetic field.

  18. A parametric approach to shape field-relevant blast wave profiles in compressed-gas-driven shock tube.

    Science.gov (United States)

    Sundaramurthy, Aravind; Chandra, Namas

    2014-01-01

    Detonation of a high-explosive produces shock-blast wave, shrapnel, and gaseous products. While direct exposure to blast is a concern near the epicenter, shock-blast can affect subjects, even at farther distances. When a pure shock-blast wave encounters the subject, in the absence of shrapnels, fall, or gaseous products the loading is termed as primary blast loading and is the subject of this paper. The wave profile is characterized by blast overpressure, positive time duration, and impulse and called herein as shock-blast wave parameters (SWPs). These parameters in turn are uniquely determined by the strength of high explosive and the distance of the human subjects from the epicenter. The shape and magnitude of the profile determine the severity of injury to the subjects. As shown in some of our recent works (1-3), the profile not only determines the survival of the subjects (e.g., animals) but also the acute and chronic biomechanical injuries along with the following bio-chemical sequelae. It is extremely important to carefully design and operate the shock tube to produce field-relevant SWPs. Furthermore, it is vital to identify and eliminate the artifacts that are inadvertently introduced in the shock-blast profile that may affect the results. In this work, we examine the relationship between shock tube adjustable parameters (SAPs) and SWPs that can be used to control the blast profile; the results can be easily applied to many of the laboratory shock tubes. Further, replication of shock profile (magnitude and shape) can be related to field explosions and can be a standard in comparing results across different laboratories. Forty experiments are carried out by judiciously varying SAPs such as membrane thickness, breech length (66.68-1209.68 mm), measurement location, and type of driver gas (nitrogen, helium). The effects SAPs have on the resulting shock-blast profiles are shown. Also, the shock-blast profiles of a TNT explosion from ConWep software is compared

  19. Thomson scattering measurement of a shock in laser-produced counter-streaming plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Morita, T.; Kuramitsu, Y.; Moritaka, T. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Sakawa, Y.; Takabe, H. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Graduate School of Science, Osaka University, 1-1 Machikane-yama, Toyonaka, Osaka 560-0043 (Japan); Tomita, K.; Nakayama, K.; Inoue, K.; Uchino, K. [Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasugakoen, Kasuga, Fukuoka 816-8580 (Japan); Ide, T.; Tsubouchi, K. [Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Nishio, K.; Ide, H.; Kuwada, M. [Graduate School of Science, Osaka University, 1-1 Machikane-yama, Toyonaka, Osaka 560-0043 (Japan)

    2013-09-15

    We report the first direct measurement of temporally and spatially resolved plasma temperatures at a shock as well as its spatial structure and propagation in laser-produced counter-streaming plasmas. Two shocks are formed in counter-streaming collisionless plasmas early in time, and they propagate opposite directions. This indicates the existence of counter-streaming collisionless flows to keep exciting the shocks, even though the collisional effects increase later in time. The shock images are observed with optical diagnostics, and the upstream and downstream plasma parameters of one of the shocks are measured using Thomson scattering technique.

  20. P-ρ-T measurements of H{sub 2}O up to 260 GPa under laser-driven shock loading

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, T. [Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577 (Japan); Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Ozaki, N.; Kodama, R. [Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Photon Pioneers Center, Osaka University, Suita, Osaka 565-0871 (Japan); Sano, T.; Sakawa, Y. [Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Okuchi, T. [Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori 682-0193 (Japan); Sano, T.; Miyanishi, K.; Terai, T.; Kakeshita, T. [Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Shimizu, K. [KYOKUGEN, Center for Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531 (Japan)

    2015-04-28

    Pressure, density, and temperature data for H{sub 2}O were obtained up to 260 GPa by using laser-driven shock compression technique. The shock compression technique combined with the diamond anvil cell was used to assess the equation of state models for the P-ρ-T conditions for both the principal Hugoniot and the off-Hugoniot states. The contrast between the models allowed for a clear assessment of the equation of state models. Our P-ρ-T data totally agree with those of the model based on quantum molecular dynamics calculations. These facts indicate that this model is adopted as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range.

  1. A STUDY OF THE HELIOCENTRIC DEPENDENCE OF SHOCK STANDOFF DISTANCE AND GEOMETRY USING 2.5D MAGNETOHYDRODYNAMIC SIMULATIONS OF CORONAL MASS EJECTION DRIVEN SHOCKS

    Energy Technology Data Exchange (ETDEWEB)

    Savani, N. P. [University Corporation for Atmospheric Research (UCAR), Boulder, CO 80307 (United States); Shiota, D. [Computational Astrophysics Laboratory, Advanced Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Kusano, K. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan); Vourlidas, A. [Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States); Lugaz, N., E-mail: neel.savani02@imperial.ac.uk [Experimental Space Plasma Group, University of New Hampshire, Durham, NH 03824 (United States)

    2012-11-10

    We perform four numerical magnetohydrodynamic simulations in 2.5 dimensions (2.5D) of fast coronal mass ejections (CMEs) and their associated shock fronts between 10 Rs and 300 Rs. We investigate the relative change in the shock standoff distance, {Delta}, as a fraction of the CME radial half-width, D {sub OB} (i.e., {Delta}/D {sub OB}). Previous hydrodynamic studies have related the shock standoff distance for Earth's magnetosphere to the density compression ratio (DR; {rho} {sub u}/{rho} {sub d}) measured across the bow shock. The DR coefficient, k {sub dr}, which is the proportionality constant between the relative standoff distance ({Delta}/D {sub OB}) and the compression ratio, was semi-empirically estimated as 1.1. For CMEs, we show that this value varies linearly as a function of heliocentric distance and changes significantly for different radii of curvature of the CME's leading edge. We find that a value of 0.8 {+-} 0.1 is more appropriate for small heliocentric distances (<30 Rs) which corresponds to the spherical geometry of a magnetosphere presented by Seiff. As the CME propagates its cross section becomes more oblate and the k {sub dr} value increases linearly with heliocentric distance, such that k {sub dr} = 1.1 is most appropriate at a heliocentric distance of about 80 Rs. For terrestrial distances (215 Rs) we estimate k {sub dr} = 1.8 {+-} 0.3, which also indicates that the CME cross-sectional structure is generally more oblate than that of Earth's magnetosphere. These alterations to the proportionality coefficients may serve to improve investigations into the estimates of the magnetic field in the corona upstream of a CME as well as the aspect ratio of CMEs as measured in situ.

  2. Quantified Energy Dissipation Rates in the Terrestrial Bow Shock. 2; Waves and Dissipation

    Science.gov (United States)

    Wilson, L. B., III; Sibeck, D. G.; Breneman, A. W.; Le Contel, O.; Cully, C.; Turner, D. L.; Angelopoulos, V.; Malaspina, D. M.

    2014-01-01

    We present the first quantified measure of the energy dissipation rates, due to wave-particle interactions, in the transition region of the Earth's collision-less bow shock using data from the Time History of Events and Macro-Scale Interactions during Sub-Storms spacecraft. Our results show that wave-particle interactions can regulate the global structure and dominate the energy dissipation of collision-less shocks. In every bow shock crossing examined, we observed both low-frequency (less than 10 hertz) and high-frequency (approximately or greater than10 hertz) electromagnetic waves throughout the entire transition region and into the magnetosheath. The low-frequency waves were consistent with magnetosonic-whistler waves. The high-frequency waves were combinations of ion-acoustic waves, electron cyclotron drift instability driven waves, electrostatic solitary waves, and whistler mode waves. The high-frequency waves had the following: (1) peak amplitudes exceeding delta B approximately equal to 10 nanoteslas and delta E approximately equal to 300 millivolts per meter, though more typical values were delta B approximately equal to 0.1-1.0 nanoteslas and delta E approximately equal to 10-50 millivolts per meter (2) Poynting fluxes in excess of 2000 microWm(sup -2) (micro-waves per square meter) (typical values were approximately 1-10 microWm(sup -2) (micro-waves per square meter); (3) resistivities greater than 9000 omega meters; and (4) associated energy dissipation rates greater than 10 microWm(sup -3) (micro-waves per cubic meter). The dissipation rates due to wave-particle interactions exceeded rates necessary to explain the increase in entropy across the shock ramps for approximately 90 percent of the wave burst durations. For approximately 22 percent of these times, the wave-particle interactions needed to only be less than or equal to 0.1 percent efficient to balance the nonlinear wave steepening that produced the shock waves. These results show that wave

  3. Collisionless loss-cone refilling: there is no final parsec problem

    CERN Document Server

    Gualandris, Alessia; Dehnen, Walter; Bortolas, Elisa

    2016-01-01

    Coalescing massive black hole binaries, formed during galaxy mergers, are expected to be a primary source of low frequency gravitational waves. Yet in isolated gas-free spherical stellar systems, the hardening of the binary stalls at parsec-scale separations owing to the inefficiency of relaxation-driven loss-cone refilling. Repopulation via collisionless orbit diffusion in triaxial systems is more efficient, but published simulation results are contradictory. While sustained hardening has been reported in simulations of galaxy mergers with $N \\sim 10^6$ stars and in early simulations of rotating models, in isolated non-rotating triaxial models the hardening rate continues to fall with increasing N, a signature of spurious two-body relaxation. We present a novel approach for studying loss cone repopulation in galactic nuclei. Since loss cone repopulation in triaxial systems owes to orbit diffusion, it is a purely collisionless phenomenon and can be studied with an approximated force calculation technique, pro...

  4. Collisional and collisionless expansion of Yukawa balls.

    Science.gov (United States)

    Piel, Alexander; Goree, John A

    2013-12-01

    The expansion of Yukawa balls is studied by means of molecular dynamics simulations of collisionless and collisional situations. High computation speed was achieved by using the parallel computing power of graphics processing units. When the radius of the Yukawa ball is large compared to the shielding length, the expansion process starts with the blow-off of the outermost layer. A rarefactive wave subsequently propagates radially inward at the speed of longitudinal phonons. This mechanism is fundamentally different from Coulomb explosions, which employ a self-similar expansion of the entire system. In the collisionless limit, the outer layers carry away most of the available energy. The simulations are compared with analytical estimates. In the collisional case, the expansion process can be described by a nonlinear diffusion equation that is a special case of the porous medium equation.

  5. Lessons on collisionless reconnection from quantum fluids

    Directory of Open Access Journals (Sweden)

    Yasuhito eNarita

    2014-12-01

    Full Text Available Magnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.

  6. Structure of Energetic Particle Mediated Shocks Revisited

    Science.gov (United States)

    Mostafavi, P.; Zank, G. P.; Webb, G. M.

    2017-05-01

    The structure of collisionless shock waves is often modified by the presence of energetic particles that are not equilibrated with the thermal plasma (such as pickup ions [PUIs] and solar energetic particles [SEPs]). This is relevant to the inner and outer heliosphere and the Very Local Interstellar Medium (VLISM), where observations of shock waves (e.g., in the inner heliosphere) show that both the magnetic field and thermal gas pressure are less than the energetic particle component pressures. Voyager 2 observations revealed that the heliospheric termination shock (HTS) is very broad and mediated by energetic particles. PUIs and SEPs contribute both a collisionless heat flux and a higher-order viscosity. We show that the incorporation of both effects can completely determine the structure of collisionless shocks mediated by energetic ions. Since the reduced form of the PUI-mediated plasma model is structurally identical to the classical cosmic ray two-fluid model, we note that the presence of viscosity, at least formally, eliminates the need for a gas sub-shock in the classical two-fluid model, including in that regime where three are possible. By considering parameters upstream of the HTS, we show that the thermal gas remains relatively cold and the shock is mediated by PUIs. We determine the structure of the weak interstellar shock observed by Voyager 1. We consider the inclusion of the thermal heat flux and viscosity to address the most general form of an energetic particle-thermal plasma two-fluid model.

  7. Finite-dimensional collisionless kinetic theory

    CERN Document Server

    Burby, J W

    2016-01-01

    A collisionless kinetic plasma model may often be cast as an infinite-dimensional noncanonical Hamiltonian system. I show that, when this is the case, the model can be discretized in space and particles while preserving its Hamiltonian structure, thereby producing a finite-dimensional Hamiltonian system that approximates the original kinetic model. I apply the general theory to two example systems: the relativistic Vlasov-Maxwell system with spin, and a gyrokinetic Vlasov-Maxwell system.

  8. Studying astrophysical particle acceleration with laser-driven plasmas

    Science.gov (United States)

    Fiuza, Frederico

    2016-10-01

    The acceleration of non-thermal particles in plasmas is critical for our understanding of explosive astrophysical phenomena, from solar flares to gamma ray bursts. Particle acceleration is thought to be mediated by collisionless shocks and magnetic reconnection. The microphysics underlying these processes and their ability to efficiently convert flow and magnetic energy into non-thermal particles, however, is not yet fully understood. By performing for the first time ab initio 3D particle-in-cell simulations of the interaction of both magnetized and unmagnetized laser-driven plasmas, it is now possible to identify the optimal parameters for the study of particle acceleration in the laboratory relevant to astrophysical scenarios. It is predicted for the Omega and NIF laser conditions that significant non-thermal acceleration can occur during magnetic reconnection of laser-driven magnetized plasmas. Electrons are accelerated by the electric field near the X-points and trapped in contracting magnetic islands. This leads to a power-law tail extending to nearly a hundred times the thermal energy of the plasma and that contains a large fraction of the magnetic energy. The study of unmagnetized interpenetrating plasmas also reveals the possibility of forming collisionless shocks mediated by the Weibel instability on NIF. Under such conditions, both electrons and ions can be energized by scattering out of the Weibel-mediated turbulence. This also leads to power-law spectra that can be detected experimentally. The resulting experimental requirements to probe the microphysics of plasma particle acceleration will be discussed, paving the way for the first experiments of these important processes in the laboratory. As a result of these simulations and theoretical analysis, there are new experiments being planned on the Omega, NIF, and LCLS laser facilities to test these theoretical predictions. This work was supported by the SLAC LDRD program and DOE Office of Science, Fusion

  9. Characteristics of Weak Interplanetary Shocks and Shock-like Events

    Science.gov (United States)

    Balogh, A.; Gloag, J. M.

    The variation of magnetic and plasma parameters across the discontinuity of a colli- sionless shock wave are clearly understood and presented in MHD theory. The anal- ysis of 116 shock waves appearing on the Ulysses shock list in the period mid 1996 to the end of 1999 show that in the cases of the stronger shock waves, measured by the ratio of downstream to upstream magnetic field magnitudes, this MHD descrip- tion is adequate. However in the case of many of the weaker shocks there are events which are not clearly characterised in MHD terms and in these cases plasma param- eters are particularly difficult to interpret. To explore the issues associated with these very weak shocks further, a set of shock-like events is considered which have shock characteristics in the high frequency wave data measured by the plasma wave inves- tigation(URAP) but are not considered to be clearly shock waves purely considering magnetic and plasma data. These shock-like events are thought to extend the spectrum of interplanetary shocks at the very weakest end and possibly beyond what should be considered a collisionless shock wave.

  10. The Strength and Radial Profile of Coronal Magnetic Field from the Standoff Distance of a CME-driven Shock

    CERN Document Server

    Gopalswamy, Nat

    2011-01-01

    We determine the coronal magnetic field strength in the heliocentric distance range 6 to 23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection (CME) imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfven Mach number, and hence the Alfven speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from ~48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.

  11. Shock breakout driven by the remnant of a neutron star binary merger: An X-ray precursor of mergernova emission

    CERN Document Server

    Li, Shao-Ze

    2015-01-01

    A supra-massive neutron star (NS) spinning extremely rapidly could survive from a merger of NS-NS binary. The spin-down of this remnant NS that is highly magnetized would power the isotropic merger ejecta to produce a bright mergernova emission in ultraviolet/optical bands. Before the mergernova, the early interaction between the NS wind and the ejecta can drive a forward shock to propagate outwards into the ejecta. As a result, a remarkable amount of heat can be accumulated to be deposited behind the shock front, the final escaping of which can produce a shock breakout emission. We describe the dynamics and thermal emission of this shock with a semi-analytical model. It is found that a sharp and luminous breakout emission, which is mainly in soft X-rays with a luminosity of $\\sim10^{45}~\\rm erg~s^{-1}$, appears at a few hours after the merger, by leading the mergernova emission as a precursor. Therefore, detections of such X-ray precursors would provide a smoking-gun evidence for identifying NS-powered merge...

  12. Shock Breakout Driven by the Remnant of a Neutron Star Binary Merger: An X-Ray Precursor of Mergernova Emission

    Science.gov (United States)

    Li, Shao-Ze; Yu, Yun-Wei

    2016-03-01

    A supra-massive neutron star (NS) spinning extremely rapidly could survive from a merger of an NS-NS binary. The spin-down of this remnant NS that is highly magnetized could power the isotropic merger ejecta to produce a bright mergernova emission in the ultraviolet/optical bands. Before the mergernova, the early interaction between the NS wind and the ejecta could drive a forward shock propagating outward into the ejecta. As a result, a remarkable amount of heat can be accumulated behind the shock front and the final escape of this heat could produce a shock breakout emission. We describe the dynamics and thermal emission of this shock with a semi-analytical model. It is found that a few hours after the merger, by leading the mergernova emission as a precursor, sharp and luminous breakout emission appears mainly in soft X-rays, with a luminosity of ∼ {10}45 {erg} {{{s}}}-1. Therefore, the detection of such an X-ray precursor could provide evidence for identifying NS-powered mergernovae and distinguishing them from radioactivity-powered novae (i.e., kilonovae or macronovae). The discovery of NS-powered mergernovae could finally help to confirm the gravitational wave signals due to the mergers and the existence of supra-massive NSs.

  13. Diagnosing collisionless energy transfer using field-particle correlations: gyrokinetic turbulence

    Science.gov (United States)

    Klein, Kristopher G.; Howes, Gregory G.; Tenbarge, Jason M.

    2017-08-01

    Determining the physical mechanisms that extract energy from turbulent fluctuations in weakly collisional magnetized plasmas is necessary for a more complete characterization of the behaviour of a variety of space and astrophysical plasmas. Such a determination is complicated by the complex nature of the turbulence as well as observational constraints, chiefly that in situ measurements of such plasmas are typically only available at a single point in space. Recent work has shown that correlations between electric fields and particle velocity distributions constructed from single-point measurements produce a velocity-dependent signature of the collisionless damping mechanism. We extend this work by constructing field-particle correlations using data sets drawn from single points in strongly driven, turbulent, electromagnetic gyrokinetic simulations to demonstrate that this technique can identify the collisionless mechanisms operating in such systems. The velocity-space structure of the correlation between proton distributions and parallel electric fields agrees with expectations of resonant mechanisms transferring energy collisionlessly in turbulent systems. This work motivates the eventual application of field-particle correlations to spacecraft measurements in the solar wind, with the ultimate goal to determine the physical mechanisms that dissipate magnetized plasma turbulence.

  14. Relativistic Electron Shock Drift Acceleration in Low Mach Number Galaxy Cluster Shocks

    CERN Document Server

    Matsukiyo, Shuichi; Yamazaki, Ryo; Umeda, Takayuki

    2011-01-01

    An extreme case of electron shock drift acceleration in low Mach number collisionless shocks is investigated as a plausible mechanism of initial acceleration of relativistic electrons in large-scale shocks in galaxy clusters where upstream plasma temperature is of the order of 10 keV and a degree of magnetization is not too small. One-dimensional electromagnetic full particle simulations reveal that, even though a shock is rather moderate, a part of thermal incoming electrons are accelerated and reflected through relativistic shock drift acceleration and form a local nonthermal population just upstream of the shock. The accelerated electrons can self-generate local coherent waves and further be back-scattered toward the shock by those waves. This may be a scenario for the first stage of the electron shock acceleration occurring at the large-scale shocks in galaxy clusters such as CIZA J2242.8+5301 which has well defined radio relics.

  15. Should Elliptical Galaxies Be Idealised as Collisionless Equilibria?

    OpenAIRE

    Kandrup, Henry E.

    2000-01-01

    This talk summarises several different lines of argument suggesting that one should not expect cuspy nonaxisymmetric galaxies to exist as robust, long-lived collisionless equilibria, i.e., that such objects should not be idealised as time-independent solutions to the collisionless Boltzmann equation.

  16. Transport of parallel momentum by collisionless drift wave turbulence

    DEFF Research Database (Denmark)

    Diamond, P.H.; McDevitt, C.J.; Gurcan, O.E.

    2008-01-01

    This paper presents a novel, unified approach to the theory of turbulent transport of parallel momentum by collisionless drift waves. The physics of resonant and non‐resonant off‐diagonal contributions to the momentum flux is emphasized, and collisionless momentum exchange between waves and parti...

  17. Transport of parallel momentum by collisionless drift wave turbulence

    DEFF Research Database (Denmark)

    Diamond, P.H.; McDevitt, C.J.; Gürcan, O.D.

    2008-01-01

    This paper presents a novel, unified approach to the theory of turbulent transport of parallel momentum by collisionless drift waves. The physics of resonant and nonresonant off-diagonal contributions to the momentum flux is emphasized, and collisionless momentum exchange between waves and partic...

  18. Diffusive Shock Acceleration at Cosmological Shock Waves

    CERN Document Server

    Kang, Hyesung

    2012-01-01

    We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological shocks in the large scale structure of the Universe, incorporating wave-particle interactions that are expected to operate in collisionless shocks. Adopting simple phenomenological models for magnetic field amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfv'enic drift, we perform kinetic DSA simulations for a wide range of sonic and Alfv'enic Mach numbers and evaluate the CR injection fraction and acceleration efficiency. In our DSA model the CR acceleration efficiency is determined mainly by the sonic Mach number Ms, while the MFA factor depends on the Alfv'enic Mach number and the degree of shock modification by CRs. We show that at strong CR modified shocks, if scattering centers drift with an effective Alfv'en speed in the amplified magnetic field, the CR energy spectrum is steepened and the acceleration efficiency is reduced significantly, compared to the cases without such effects. As a result, the postshock C...

  19. New Expression for Collisionless Magnetic Reconnection Rate

    Science.gov (United States)

    Klimas, Alexander J.

    2014-01-01

    For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, a new expression for the reconnection rate in the electron diffusion region is introduced. It is shown that this expression can be derived in just a few simple steps from a physically intuitive starting point; the derivation is given in its entirety and the validity of each step is confirmed. The predictions of this expression are compared to the results of several long-duration, open-boundary PIC reconnection simulations to demonstrate excellent agreement.

  20. Whistler Mode Waves in Collisionless Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    GUO Jun; LU Quan-Ming; WANG Shui; WANG Yu-Ming; DOU Xian-Kang

    2004-01-01

    A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the wave phenomena in the plasma sheet of collisionless magnetic reconnection. The results show that these waves have the following characteristics: they are right-hand circularity polarized, with propagation direction nearly parallel to local magnetic field, and frequency between 0.07 and 0.17 times of local electron cyclotron frequency. Therefore we conclude that such waves are Whistler waves, and their possible excitation mechanisms are also discussed.

  1. Evidence for collisionless magnetic reconnection at Mars

    Science.gov (United States)

    Eastwood, J. P.; Brain, D. A.; Halekas, J. S.; Drake, J. F.; Phan, T. D.; Øieroset, M.; Mitchell, D. L.; Lin, R. P.; Acuña, M.

    2008-01-01

    Using data from Mars Global Surveyor (MGS) in combination with Particle-In-Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion - the Hall magnetic field - that uniquely indicate the reconnection process. These are the first such in-situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars' recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.

  2. ON SHOCKS DRIVEN BY HIGH-MASS PLANETS IN RADIATIVELY INEFFICIENT DISKS. II. THREE-DIMENSIONAL GLOBAL DISK SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Lyra, Wladimir [Department of Physics and Astronomy, California State University Northridge, 18111 Nordhoff St, Northridge, CA 91330 (United States); Richert, Alexander J. W. [Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802 (United States); Boley, Aaron [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Turner, Neal; Okuzumi, Satoshi; Flock, Mario [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Mac Low, Mordecai-Mark, E-mail: wlyra@csun.edu, E-mail: neal.j.turner@jpl.nasa.gov, E-mail: mario.flock@jpl.nasa.gov, E-mail: ajr327@psu.edu, E-mail: acboley@phas.ubc.ca, E-mail: mordecai@amnh.org, E-mail: okuzumi@geo.titech.ac.jp [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192 (United States)

    2016-02-01

    Recent high-resolution, near-infrared images of protoplanetary disks have shown that these disks often present spiral features. Spiral arms are among the structures predicted by models of disk–planet interaction and thus it is tempting to suspect that planetary perturbers are responsible for these signatures. However, such interpretation is not free of problems. The observed spirals have large pitch angles, and in at least one case (HD 100546) it appears effectively unpolarized, implying thermal emission of the order of 1000 K (465 ± 40 K at closer inspection). We have recently shown in two-dimensional models that shock dissipation in the supersonic wake of high-mass planets can lead to significant heating if the disk is sufficiently adiabatic. Here we extend this analysis to three dimensions in thermodynamically evolving disks. We use the Pencil Code in spherical coordinates for our models, with a prescription for thermal cooling based on the optical depth of the local vertical gas column. We use a 5M{sub J} planet, and show that shocks in the region around the planet where the Lindblad resonances occur heat the gas to substantially higher temperatures than the ambient gas. The gas is accelerated vertically away from the midplane to form shock bores, and the gas falling back toward the midplane breaks up into a turbulent surf. This turbulence, although localized, has high α values, reaching 0.05 in the inner Lindblad resonance, and 0.1 in the outer one. We find evidence that the disk regions heated up by the shocks become superadiabatic, generating convection far from the planet’s orbit.

  3. The formation and evolution of reconnection-driven slow-mode shocks in a partially ionised plasma

    CERN Document Server

    Hillier, Andrew; Nakamura, Naoki

    2016-01-01

    The role of slow-mode MHD shocks in magnetic reconnection is one of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we investigate, using numerical simulations, the role of collisional coupling between a proton-electron charge-neutral fluid and a neutral hydrogen fluid for the 1D Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves: a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock. The system evolves through four stage: initiation, weak coupling, intermediate coupling and a quasi steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. D...

  4. Effect of a relative phase of waves constituting the initial perturbation and the wave interference on the dynamics of strong-shock-driven Richtmyer-Meshkov flows

    Science.gov (United States)

    Pandian, Arun; Stellingwerf, Robert F.; Abarzhi, Snezhana I.

    2017-07-01

    While it is a common wisdom that initial conditions influence the evolution of the Richtmyer-Meshkov instability (RMI), the research in this area is focused primarily on the effects of the wavelength and amplitude of the interface perturbation. The information has hitherto largely ignored the influences on RMI dynamics of the relative phase of waves constituting a multiwave initial perturbation and the interference of the perturbation waves. In this work we systematically study the influence of the relative phase and the interference of waves constituting a multiwave initial perturbation on a strong-shock-driven Richtmyer-Meshkov unstable interface separating ideal fluids with contrast densities. We apply group theory analysis and smoothed particle hydrodynamics numerical simulations. For verification and validation of the simulations, qualitative and quantitative comparisons are performed with rigorous zeroth-order, linear, and nonlinear theories as well as with gas dynamics experiments achieving good agreement. For a sample case of a two-wave (two-mode) initial perturbation we select the first-wave amplitude enabling the maximum initial growth rate of the RMI and we vary the second-wave amplitude from 1% to 100% of the first-wave amplitude. We also vary the relative phase of the first and second waves and consider the in-phase, the antiphase and the random-phase cases. We find that the relative phase and the interference of waves are important factors of RMI dynamics influencing qualitatively and quantitatively the symmetry, morphology, and growth rate of the Richtmyer-Meshkov unstable interface, as well as the order and disorder in strong-shock-driven RMI.

  5. Experimental Studies on Shock Pressure of Laser-driven Flyer System%激光驱动飞片冲击应力实验研究

    Institute of Scientific and Technical Information of China (English)

    王猛; 何碧; 蒋明; 覃文志

    2013-01-01

    PVDF stress gauge was made for experimental studies on shock pressure of laser-driven flyer. The dynamic calibration curve was given. Measurement for pressure wave profile in the experiment research of single and multiple flyer has been made and analyzed, it showed that using more thicker multiple flyer would obtain higher shock pressure and longer duration. Meanwhile, points for attention in the measurement of PVDF have been put forward.%  为了对激光驱动飞片的冲击应力进行测试,利用PVDF 压电材料,自制了满足测试需要的应力计,并给出了应力计的动态标定曲线。通过对激光驱动复合飞片和单层飞片的冲击应力进行测试分析,可知对于激光驱动飞片起爆系统,应用较厚复合飞片可获得较大的冲击应力以及较长的持续时间,并指出了 PVDF 应力计测试中的若干注意事项。

  6. Particle acceleration around SNR shocks

    Energy Technology Data Exchange (ETDEWEB)

    Morlino, G., E-mail: morlino@arcetri.astro.it [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze (Italy)

    2013-08-21

    We review the basic features of particle acceleration theory around collisionless shocks in supernova remnants (SNRs). We show how non-linear effects induced by the back reaction of accelerated particles onto the shock dynamics are of paramount importance to support the hipotesys that SNRs are the factories of Galactic cosmic rays. Recent developments in the modeling of the mechanism of diffusive shock acceleration are discussed, with emphasis on the role of magnetic field amplification and the presence of neutrals in the circumstellar environment. Special attention will be devoted to observational consequences of non-linear effects on the multi-wavelength spectrum of SNRs, with emphasis on X-ray and gamma-ray emission. Finally we also discuss how Balmer lines, detected from several young SNRs, can be used to estimate the shock dynamical properties and the efficiency of CR acceleration.

  7. Particle acceleration around SNR shocks

    CERN Document Server

    Morlino, Giovanni

    2012-01-01

    We review the basic features of particle acceleration theory around collisionless shocks in supernova remnants (SNRs). We show how non linear effects induced by the back reaction of accelerated particles onto the shock dynamics are of paramount importance to support the hipotesys that SNRs are the factories of Galactic cosmic rays. Recent developments in the modeling of the mechanism of diffusive shock acceleration are discussed, with emphasis on the role of magnetic field amplification and the presence of neutrals in the circumstellar environment. Special attention will be devoted to observational consequences of non linear effects on the multi-wavelength spectrum of SNRs, with emphasis on X-ray and gamma-ray emission. Finally we also discuss how Balmer lines, detected from several young SNRs, can be used to estimate the shock dynamical properties and the efficiency of CR acceleration.

  8. Electron Acceleration in Collisionless Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    GUO Jun; LU Quan-Ming; WANG Shui; FU Xiang-Rong

    2005-01-01

    @@ A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the electron acceleration in collisionless magnetic reconnection. The results show that the electrons are accelerated in the diffusion region near the X point, and the acceleration process can be roughly divided into two procedures: firstly the electrons are accelerated in the z direction due to the electric field in the negative z direction. Then the electrons gyrate surrounding the magnetic field with the action of the Lorentz force, through this procedure the electrons reach higher velocity in the x direction and then flow out of the diffusion region. After being accelerated away from the diffusion region, part of electrons is trapped near the O point, and the other part of electrons flows into plasma sheet boundary layer along the magnetic field.

  9. Collisionless evaporation from cluster elliptical galaxies

    CERN Document Server

    Muccione, V

    2003-01-01

    We describe a particular aspect of the effects of the parent cluster tidal field (CTF) on stellar orbits inside cluster Elliptical galaxies. In particular we discuss, with the aid of a simple numerical model, the possibility that collisionless stellar evaporation from elliptical galaxies is an effective mechanism for the production of the recently discovered intracluster stellar populations. A preliminary investigation, based on very idealized galaxy density profiles (Ferrers density distributions), showed that over an Hubble time, the amount of stars lost by a representative galaxy may sum up to the 10% of the initial galaxy mass, a fraction in interesting agreement with observational data. The effectiveness of this mechanism is due to the fact that the galaxy oscillation periods near equilibrium configurations in the CTF are comparable to stellar orbital times in the external galaxy regions. Here we extend our previous study to more realistic galaxy density profiles, in particular by adopting a triaxial Her...

  10. A collisionless plasma thruster plume expansion model

    Science.gov (United States)

    Merino, Mario; Cichocki, Filippo; Ahedo, Eduardo

    2015-06-01

    A two-fluid model of the unmagnetized, collisionless far region expansion of the plasma plume for gridded ion thrusters and Hall effect thrusters is presented. The model is integrated into two semi-analytical solutions valid in the hypersonic case. These solutions are discussed and compared against the results from the (exact) method of characteristics; the relative errors in density and velocity increase slowly axially and radially and are of the order of 10-2-10-3 in the cases studied. The plasma density, ion flux and ambipolar electric field are investigated. A sensitivity analysis of the problem parameters and initial conditions is carried out in order to characterize the far plume divergence angle in the range of interest for space electric propulsion. A qualitative discussion of the physics of the secondary plasma plume is also provided.

  11. Nanoflare heating model for collisionless solar corona

    Indian Academy of Sciences (India)

    U L VISAKH KUMAR; BILIN SUSAN VARGHESE; P J KURIAN

    2017-02-01

    The problem of coronal heating remains one of the greatest unresolved problems in space science. Magnetic reconnection plays a significant role in heating the solar corona. When two oppositely directed magnetic fields come closer to form a current sheet, the current density of the plasma increases due to which magnetic reconnection and conversion of magnetic energy into thermal energy takes place. The present paper deals with a model for reconnection occurring in the solar corona under steady state in collisionless regime. The model predicts that reconnection time in the solar corona varies inversely with the cube of magnetic field and varies directly with the Lindquist number. Our analysis shows that reconnections are occurring within a time interval of600 s in the solar corona, producing nanoflares in the energy range $10^{21}–10^{23}$ erg/s which matches with Yohkoh X-ray observations.

  12. Nanoflare heating model for collisionless solar corona

    Science.gov (United States)

    Visakh Kumar, U. L.; Varghese, Bilin Susan; Kurian, P. J.

    2017-02-01

    The problem of coronal heating remains one of the greatest unresolved problems in space science. Magnetic reconnection plays a significant role in heating the solar corona. When two oppositely directed magnetic fields come closer to form a current sheet, the current density of the plasma increases due to which magnetic reconnection and conversion of magnetic energy into thermal energy takes place. The present paper deals with a model for reconnection occurring in the solar corona under steady state in collisionless regime. The model predicts that reconnection time in the solar corona varies inversely with the cube of magnetic field and varies directly with the Lindquist number. Our analysis shows that reconnections are occurring within a time interval of 600 s in the solar corona, producing nanoflares in the energy range 10 21-10 23 erg /s which matches with Yohkoh X-ray observations.

  13. Collisionless Dynamics and the Cosmic Web

    CERN Document Server

    Hahn, Oliver

    2014-01-01

    I review the nature of three-dimensional collapse in the Zeldovich approximation, how it relates to the underlying nature of the three-dimensional Lagrangian manifold and naturally gives rise to a hierarchical structure formation scenario that progresses through collapse from voids to pancakes, filaments and then halos. I then discuss how variations of the Zeldovich approximation (based on the gravitational or the velocity potential) have been used to define classifications of the cosmic large-scale structure into dynamically distinct parts. Finally, I turn to recent efforts to devise new approaches relying on tessellations of the Lagrangian manifold to follow the fine-grained dynamics of the dark matter fluid into the highly non-linear regime and both extract the maximum amount of information from existing simulations as well as devise new simulation techniques for cold collisionless dynamics.

  14. Collisionless Dynamics and the Cosmic Web

    Science.gov (United States)

    Hahn, Oliver

    2016-10-01

    I review the nature of three-dimensional collapse in the Zeldovich approximation, how it relates to the underlying nature of the three-dimensional Lagrangian manifold and naturally gives rise to a hierarchical structure formation scenario that progresses through collapse from voids to pancakes, filaments and then halos. I then discuss how variations of the Zeldovich approximation (based on the gravitational or the velocity potential) have been used to define classifications of the cosmic large-scale structure into dynamically distinct parts. Finally, I turn to recent efforts to devise new approaches relying on tessellations of the Lagrangian manifold to follow the fine-grained dynamics of the dark matter fluid into the highly non-linear regime and both extract the maximum amount of information from existing simulations as well as devise new simulation techniques for cold collisionless dynamics.

  15. Collisionless microinstabilities in stellarators II - numerical simulations

    CERN Document Server

    Proll, Josefine Henriette Elise; Helander, Per

    2013-01-01

    Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-$J$ geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment (NCSX) and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduce...

  16. Multiscale dynamics based on kinetic simulation of collisionless magnetic reconnection

    Science.gov (United States)

    Fujimoto, Keizo; Takamoto, Makoto

    2016-07-01

    Magnetic reconnection is a natural energy converter which allows explosive energy release of the magnetic field energy into plasma kinetic energy. The reconnection processes inherently involve multi-scale process. The breaking of the field lines takes place predominantly in a small region called the diffusion region formed near the x-line, while the fast plasma jets resulting from reconnection extend to a distance far beyond the ion kinetic scales from the x-line. There has been a significant gap in understanding of macro-scale and micro-scale processes. The macro-scale model of reconnection has been developed using the magnetohydrodynamics (MHD) equations, while the micro-scale processes around the x-line have been based on kinetic equations including the ion and electron inertia. The problem is that these two kinds of model have significant discrepancies. It has been believed without any guarantee that the microscopic model near the x-line would connect to the macroscopic model far downstream of the x-line. In order to bridge the gap between the macro and micro-scale processes, we have performed large-scale particle-in-cell simulations with the adaptive mesh refinement. The simulation results suggest that the microscopic processes around the x-line do not connect to the previous MHD model even in the region far downstream of the x-line. The slow mode shocks and the associated plasma acceleration do not appear at the exhaust boundary of kinetic reconnection. Instead, the ions are accelerated due to the Speiser motion in the current layer extending to a distance beyond the kinetic scales. The different acceleration mechanisms between the ions and electrons lead to the Hall current system in broad area of the exhaust. Therefore, the previous MHD model could be inappropriate for collisionless magnetic reconnection. Ref. K. Fujimoto & M. Takamoto, Phys. Plasmas, 23, 012903 (2016).

  17. Measurement of scaling laws for shock waves in thermal nonlocal media

    CERN Document Server

    Ghofraniha, N; Folli, V; Trillo, S; DelRe, E; Conti, C

    2012-01-01

    We are able to detect the details of spatial optical collisionless wave-breaking through the high aperture imaging of a beam suffering shock in a fluorescent nonlinear nonlocal thermal medium. This allows us to directly measure how nonlocality and nonlinearity affect the point of shock formation and compare results with numerical simulations.

  18. Global scale-invariant dissipation in collisionless plasma turbulence.

    Science.gov (United States)

    Kiyani, K H; Chapman, S C; Khotyaintsev, Yu V; Dunlop, M W; Sahraoui, F

    2009-08-14

    A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.

  19. On shocks driven by high-mass planets in radiatively inefficient disks. II. Three-dimensional global disk simulations

    CERN Document Server

    Lyra, Wladimir; Boley, Aaron; Turner, Neal; Mac Low, Mordecai-Mark; Okuzumi, Satoshi; Flock, Mario

    2015-01-01

    Recent high-resolution, near-infrared images of protoplanetary disks have shown that these disks often present spiral features. Spiral arms are among the structures predicted decades ago by numerical simulations of disk-planet interaction and thus it is tempting to suspect that planetary perturbers are responsible for the observed signatures. However, such interpretation is not free of problems. The spirals are found to have large pitch angles, and in at least one case the spiral feature appears effectively unpolarized, which implies thermal emission at roughly 1000 K. We have recently shown in two-dimensional models that shock dissipation in the supersonic wake of high-mass planets can lead to significant heating if the disk is sufficiently adiabatic. In this paper we extend this analysis to three dimensions in thermodynamically evolving disks. We use the Pencil Code in spherical coordinates for our models, with a prescription for thermal cooling based on the optical depth of the local vertical gas column. W...

  20. Entropy Generation Across Earth's Bow Shock

    Science.gov (United States)

    Parks, George K.; McCarthy, Michael; Fu, Suiyan; Lee E. s; Cao, Jinbin; Goldstein, Melvyn L.; Canu, Patrick; Dandouras, Iannis S.; Reme, Henri; Fazakerley, Andrew; Lin, Naiguo; Wilber, Mark

    2011-01-01

    Earth's bow shock is a transition layer that causes an irreversible change in the state of plasma that is stationary in time. Theories predict entropy increases across the bow shock but entropy has never been directly measured. Cluster and Double Star plasma experiments measure 3D plasma distributions upstream and downstream of the bow shock that allow calculation of Boltzmann's entropy function H and his famous H-theorem, dH/dt O. We present the first direct measurements of entropy density changes across Earth's bow shock. We will show that this entropy generation may be part of the processes that produce the non-thermal plasma distributions is consistent with a kinetic entropy flux model derived from the collisionless Boltzmann equation, giving strong support that solar wind's total entropy across the bow shock remains unchanged. As far as we know, our results are not explained by any existing shock models and should be of interests to theorists.

  1. Suprathermal electrons at Saturn's bow shock

    CERN Document Server

    Masters, A; Sergis, N; Stawarz, L; Fujimoto, M; Coates, A J; Dougherty, M K

    2016-01-01

    The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically onl...

  2. Electron acceleration to relativistic energies at a strong quasi-parallel shock wave

    CERN Document Server

    Masters, A; Fujimoto, M; Schwartz, S J; Sergis, N; Thomsen, M F; Retinò, A; Hasegawa, H; Lewis, G R; Coates, A J; Canu, P; Dougherty, M K

    2013-01-01

    Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron accele...

  3. Miniature 100-kV Explosively Driven Prime Power Sources Based on Transverse Shock-Wave Depolarization of Pb(Zr0.95Ti0.05)O3 Ferroelectric Ceramics

    Science.gov (United States)

    2011-06-01

    MINIATURE 100-kV EXPLOSIVELY DRIVEN PRIME POWER SOURCES BASED ON TRANSVERSE SHOCK-WAVE DEPOLARIZATION OF Pb(Zr0.95Ti0.05)O3 FERROELECTRIC CERAMICS...1,8,9]. Earlier [2-5] we reported on the development of compact prime power sources utilizing quasi-planar-shock-wave depolarization of Pb...engineering projects it is important to develop miniature prime power sources that reliably generate ultrahigh (up to 100 kV) output voltages. We work on

  4. STEREO interplanetary shocks and foreshocks

    Energy Technology Data Exchange (ETDEWEB)

    Blanco-Cano, X. [Instituto de Geofisica, UNAM, CU, Coyoacan 04510 DF (Mexico); Kajdic, P. [IRAP-University of Toulouse, CNRS, Toulouse (France); Aguilar-Rodriguez, E. [Instituto de Geofisica, UNAM, Morelia (Mexico); Russell, C. T. [ESS and IGPP, University of California, Los Angeles, 603 Charles Young Drive, Los Angeles, CA 90095 (United States); Jian, L. K. [NASA Goddard Space Flight Center, Greenbelt, MD and University of Maryland, College Park, MD (United States); Luhmann, J. G. [SSL, University of California Berkeley (United States)

    2013-06-13

    We use STEREO data to study shocks driven by stream interactions and the waves associated with them. During the years of the extended solar minimum 2007-2010, stream interaction shocks have Mach numbers between 1.1-3.8 and {theta}{sub Bn}{approx}20-86 Degree-Sign . We find a variety of waves, including whistlers and low frequency fluctuations. Upstream whistler waves may be generated at the shock and upstream ultra low frequency (ULF) waves can be driven locally by ion instabilities. The downstream wave spectra can be formed by both, locally generated perturbations, and shock transmitted waves. We find that many quasiperpendicular shocks can be accompanied by ULF wave and ion foreshocks, which is in contrast to Earth's bow shock. Fluctuations downstream of quasi-parallel shocks tend to have larger amplitudes than waves downstream of quasi-perpendicular shocks. Proton foreshocks of shocks driven by stream interactions have extensions dr {<=}0.05 AU. This is smaller than foreshock extensions for ICME driven shocks. The difference in foreshock extensions is related to the fact that ICME driven shocks are formed closer to the Sun and therefore begin to accelerate particles very early in their existence, while stream interaction shocks form at {approx}1 AU and have been producing suprathermal particles for a shorter time.

  5. Collisionless relaxation in beam-plasma systems

    Energy Technology Data Exchange (ETDEWEB)

    Backhaus, Ekaterina Yu. [Univ. of California, Berkeley, CA (United States)

    2001-01-01

    This thesis reports the results from the theoretical investigations, both numerical and analytical, of collisionless relaxation phenomena in beam-plasma systems. Many results of this work can also be applied to other lossless systems of plasma physics, beam physics and astrophysics. Different aspects of the physics of collisionless relaxation and its modeling are addressed. A new theoretical framework, named Coupled Moment Equations (CME), is derived and used in numerical and analytical studies of the relaxation of second order moments such as beam size and emittance oscillations. This technique extends the well-known envelope equation formalism, and it can be applied to general systems with nonlinear forces. It is based on a systematic moment expansion of the Vlasov equation. In contrast to the envelope equation, which is derived assuming constant rms beam emittance, the CME model allows the emittance to vary through coupling to higher order moments. The CME model is implemented in slab geometry in the absence of return currents. The CME simulation yields rms beam sizes, velocity spreads and emittances that are in good agreement with particle-in-cell (PIC) simulations for a wide range of system parameters. The mechanism of relaxation is also considered within the framework of the CME system. It is discovered that the rapid relaxation or beam size oscillations can be attributed to a resonant coupling between different modes of the system. A simple analytical estimate of the relaxation time is developed. The final state of the system reached after the relaxation is complete is investigated. New and accurate analytical results for the second order moments in the phase-mixed state are obtained. Unlike previous results, these connect the final values of the second order moments with the initial beam mismatch. These analytical estimates are in good agreement with the CME model and PIC simulations. Predictions for the final density and temperature are developed that show

  6. FAST MAGNETIC FIELD AMPLIFICATION IN THE EARLY UNIVERSE: GROWTH OF COLLISIONLESS PLASMA INSTABILITIES IN TURBULENT MEDIA

    Energy Technology Data Exchange (ETDEWEB)

    Falceta-Gonçalves, D. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom); Kowal, G. [Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, Rua Arlindo Bettio, 1000, São Paulo, SP 03828-000 (Brazil)

    2015-07-20

    In this work we report on a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of the magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that (i) amplification of the magnetic field was efficient in firehose-unstable turbulent regimes, but not in the mirror-unstable models; (ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo; and (iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales and pressure anisotropy is confirmed by the numerical simulations. These results reinforce the idea that pressure anisotropies—driven naturally in a turbulent collisionless medium, e.g., the intergalactic medium, could efficiently amplify the magnetic field in the early universe (post-recombination era), previous to the collapse of the first large-scale gravitational structures. This mechanism, though fast for the small-scale fields (∼kpc scales), is unable to provide relatively strong magnetic fields at large scales. Other mechanisms that were not accounted for here (e.g., collisional turbulence once instabilities are quenched, velocity shear, or gravitationally induced inflows of gas into galaxies and clusters) could operate afterward to build up large-scale coherent field structures in the long time evolution.

  7. Expansion Techniques for Collisionless Stellar Dynamical Simulations

    CERN Document Server

    Meiron, Yohai; Holley-Bockelmann, Kelly; Spurzem, Rainer

    2014-01-01

    We present GPU implementations of two fast force calculation methods, based on series expansions of the Poisson equation. One is the Self-Consistent Field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other is the Multipole Expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field method and optimized for collisionless galactic dynamics, but while SCF is a "pure" expansion, MEX is an expansion in just the angular part; it is thus capable of capturing radial structure easily, where SCF needs a large number of radial terms. We show that despite the expansion bias, these methods are more accurate than direct techniques for the same number of particles. The performance of our GPU code, which we call ETICS, is profiled and compared to a CPU implementation. On the tested GPU hardware, a full force calculation for one million particles took...

  8. Efficiency in Collisionless Growth of Planetesimals

    CERN Document Server

    Shannon, Andrew; Lithwick, Yoram

    2013-01-01

    We study the efficiency of growing large bodies, starting from a sea of equal-sized planetesimal seeds. This is likely one of the earlier steps of planet formation and is related to the origin of the asteroid belt, the Kuiper belt and extra-solar debris disks. Here we study the case that the seeds do not collide frequently enough for dynamical cooling to be important (the collisionless limit), using a newly constructed conglomeration code, and by carefully comparing numerical results with analytical scalings. We find that large bodies grow primarily by accreting small seeds (and not by accreting each other). As the velocity dispersion of the small bodies (u) is increasingly excited by the growing big bodies, growth passes from the well-known run-away stage (when u is higher than the big bodies' hill velocity) to the newly discovered trans-hill stage (when u and big bodies both grow, but u remains at the big bodies' hill velocity). We find, concurring with analytical understandings developed in Lithwick (2013)...

  9. Collisionless reconnection: magnetic field line interaction

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2012-10-01

    Full Text Available Magnetic field lines are quantum objects carrying one quantum Φ0 = 2πh/e of magnetic flux and have finite radius λm. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.

  10. Relativistic soliton-like collisionless ionization wave

    Science.gov (United States)

    Arefiev, Alexey; McCormick, Matthew; Quevedo, Hernan; Bengtson, Roger; Ditmire, Todd

    2014-10-01

    It has been observed in recent experiments with laser-irradiated gas jets that a plasma filament produced by the laser and containing energetic electrons can launch a relativistic ionization wave into ambient gas. Here we present a self-consistent theory that explains how a collisionless ionization wave can propagate in a self-sustaining regime. A population of hot electrons necessarily generates a sheath electric field at the plasma boundary. This field penetrates the ambient gas, ionizing the gas atoms and thus causing the plasma boundary to expand. We show that the motion of the newly generated electrons can form a potential well adjacent to the plasma boundary. The outwards motion of the well causes a bunch of energetic electrons to become trapped, while allowing the newly generated electrons to escape into the plasma without retaining much energy. The resulting soliton-like ionizing field structure propagates outwards with a bunch of hot electrons that maintain a strong sheath field despite significant plasma expansion. We also present 1D and 2D particle-in-cell simulations that illustrate the described mechanism. The simulations were performed using HPC resources provided by the Texas Advanced Computing Center. This work was supported by NNSA Contract No. DE-FC52-08NA28512 and U.S. DOE Contract No. DE-FG02-04ER54742.

  11. Expansion techniques for collisionless stellar dynamical simulations

    Energy Technology Data Exchange (ETDEWEB)

    Meiron, Yohai [Kavli Institute for Astronomy and Astrophysics at Peking University, Beijing 100871 (China); Li, Baile; Holley-Bockelmann, Kelly [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Spurzem, Rainer, E-mail: ymeiron@pku.edu.cn [National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing 100012 (China)

    2014-09-10

    We present graphics processing unit (GPU) implementations of two fast force calculation methods based on series expansions of the Poisson equation. One method is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other method is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a 'pure' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms. We show that despite the expansion bias, these methods are more accurate than direct techniques for the same number of particles. The performance of our GPU code, which we call ETICS, is profiled and compared to a CPU implementation. On the tested GPU hardware, a full force calculation for one million particles took ∼0.1 s (depending on expansion cutoff), making simulations with as many as 10{sup 8} particles fast for a comparatively small number of nodes.

  12. Proton and Helium Injection Into First Order Fermi Acceleration at Shocks: Hybrid Simulation and Analysis

    Science.gov (United States)

    Dudnikova, Galina; Malkov, Mikhail; Sagdeev, Roald; Liseykina, Tatjana; Hanusch, Adrian

    2016-10-01

    Elemental composition of galactic cosmic rays (CR) probably holds the key to their origin. Most likely, they are accelerated at collisionless shocks in supernova remnants, but the acceleration mechanism is not entirely understood. One complicated problem is ``injection'', a process whereby the shock selects a tiny fraction of particles to keep on crossing its front and gain more energy. Comparing the injection rates of particles with different mass to charge ratio is a powerful tool for studying this process. Recent advances in measurements of CR He/p ratio have provided particularly important new clues. We performed a series of hybrid simulations and analyzed a joint injection of protons and Helium, in conjunction with upstream waves they generate. The emphasis of this work is on the bootstrap aspects of injection manifested in particle confinement to the shock and, therefore, their continuing acceleration by the self-driven waves. The waves are initially generated by He and protons in separate spectral regions, and their interaction plays a crucial role in particle acceleration. The work is ongoing and new results will be reported along with their analysis and comparison with the latest data from the AMS-02 space-based spectrometer. Work supported Grant RFBR 16-01-00209, NASA ATP-program under Award NNX14AH36G, and by the US Department of Energy under Award No. DE-FG02-04ER54738.

  13. On the role of wave-particle interactions in the macroscopic dynamics of collisionless plasmas

    CERN Document Server

    Wilson, Lynn B; Osmane, Adnane; Malaspina, David M

    2015-01-01

    What is the relative importance of small-scale (i.e., electron to sub-electron scales), microphysical plasma processes to the acceleration of particles from thermal to suprathermal or even to cosmic-ray energies? Additionally, can these microphysical plasma processes influence or even dominate macroscopic (i.e., greater than ion scales) processes, thus affecting global dynamics? These are fundamental and unresolved questions in plasma and astrophysical research. Recent observations of large amplitude electromagnetic waves in the terrestrial radiation belts [i.e., Cattell et al., 2008; Kellogg et al., 2010; Wilson III et al., 2011] and in collisionless shock waves [i.e., Wilson III et al., 2014a,b] have raised questions regarding the macrophysical effect of these microscopic waves. The processes thought to dominate particle acceleration and the macroscopic dynamics in both regions have been brought into question with these recent observations. The relative importance of wave-particle interactions has recently ...

  14. GRB060218: A Relativistic Supernova Shock Breakout

    CERN Document Server

    Waxman, E; Campana, S

    2007-01-01

    We show that the prompt and afterglow X-ray emission of GRB060218, as well as its early (t<=1 d) optical-UV emission, can be explained by a model in which a radiation- mediated shock propagates through a compact progenitor star into a dense wind. The prompt thermal X-ray emission is produced in this model as the mildly relativistic shock, v/c=0.85 carrying few x 10^49 erg, reaches the wind (Thomson) photosphere, where the post-shock thermal radiation is released and the shock becomes collisionless. Adopting this interpretation of the thermal X-ray emission, a subsequent X-ray afterglow is predicted, due to synchrotron emission and inverse-Compton scattering of SN UV photons by electrons accelerated in the collisionless shock. Early optical-UV emission is also predicted, due to the cooling of the outer \\delta M ~10^{-3} M_sun envelope of the star, which was heated to high temperature during shock passage. The observed X-ray afterglow and the early optical-UV emission are both consistent with those expected ...

  15. Injection to rapid diffusive shock acceleration at perpendicular shocks in partially ionized plasmas

    CERN Document Server

    Ohira, Yutaka

    2016-01-01

    We present a three-dimensional hybrid simulation of a collisionless perpendicular shock in a partially ionized plasma for the first time. In this simulation, the shock velocity and the upstream ionization fraction are Vsh ~ 1333 km/s and fi ~ 0.5, that are typical values for isolated young supernova remnants in the interstellar medium. We confirm previous two-dimensional simulation results that downstream hydrogen atoms leak into the upstream region, they are accelerated by the pickup process in the upstream region, and large magnetic field fluctuations are generated both in the upstream and downstream regions. In addition, we find that the magnetic field fluctuations have three-dimensional structures and the leaking hydrogen atoms are injected to the diffusive shock acceleration at the perpendicular shock after the pickup process. The observed diffusive shock acceleration can be interpreted as the shock drift acceleration with scattering. Particles are accelerated to v ~ 100 Vsh ~ 0.3c within ~ 100 gyroperio...

  16. Ion Acceleration at the Quasi-Parallel Shock: Injection Unveiled

    CERN Document Server

    Sundberg, Torbjörn; Burgess, David; Mazelle, Christian X

    2015-01-01

    Collisionless shocks are efficient particle accelerators. At Earth, ions with energies exceeding 100 keV are seen upstream of the bow shock when the magnetic geometry is quasi-parallel, and large-scale supernova remnant shocks can accelerate ions into cosmic rays energies. This energization is attributed to diffusive shock acceleration, however, for this process to become active the ions must first be sufficiently energized. How and where this initial acceleration takes place has been one of the key unresolved issues in shock acceleration theory. Using Cluster spacecraft observations, we study the signatures of ion reflection events in the turbulent transition layer upstream of the shock, and with the support of a hybrid simulation of the shock, we show that these reflection signatures are characteristic of the first step in the ion injection process. These reflection events develop in particular in the region where the trailing edge of large-amplitude upstream waves intercept the local shock ramp and the ups...

  17. Collisionless loss-cone refilling: there is no final parsec problem

    Science.gov (United States)

    Gualandris, Alessia; Read, Justin I.; Dehnen, Walter; Bortolas, Elisa

    2017-01-01

    Coalescing massive black hole binaries, formed during galaxy mergers, are expected to be a primary source of low-frequency gravitational waves. Yet in isolated gas-free spherical stellar systems, the hardening of the binary stalls at parsec-scale separations owing to the inefficiency of relaxation-driven loss-cone refilling. Repopulation via collisionless orbit diffusion in triaxial systems is more efficient, but published simulation results are contradictory. While sustained hardening has been reported in simulations of galaxy mergers with N ˜ 106 stars and in early simulations of rotating models, in isolated non-rotating triaxial models the hardening rate continues to fall with increasing N, a signature of spurious two-body relaxation. We present a novel approach for studying loss-cone repopulation in galactic nuclei. Since loss-cone repopulation in triaxial systems owes to orbit diffusion, it is a purely collisionless phenomenon and can be studied with an approximated force calculation technique, provided the force errors are well behaved and sufficiently small. We achieve this using an accurate fast multipole method and define a proxy for the hardening rate that depends only on stellar angular momenta. We find that the loss cone is efficiently replenished even in very mildly triaxial models (with axis ratios 1:0.9:0.8). Such triaxiality is unavoidable following galactic mergers and can drive binaries into the gravitational wave regime. We conclude that there is no `final parsec problem'.

  18. Collisionless loss-cone refilling: there is no final parsec problem

    Science.gov (United States)

    Gualandris, Alessia; Read, Justin I.; Dehnen, Walter; Bortolas, Elisa

    2016-10-01

    Coalescing massive black hole binaries, formed during galaxy mergers, are expected to be a primary source of low frequency gravitational waves. Yet in isolated gas-free spherical stellar systems, the hardening of the binary stalls at parsec-scale separations owing to the inefficiency of relaxation-driven loss-cone refilling. Repopulation via collisionless orbit diffusion in triaxial systems is more efficient, but published simulation results are contradictory. While sustained hardening has been reported in simulations of galaxy mergers with N ˜ 106 stars and in early simulations of rotating models, in isolated non-rotating triaxial models the hardening rate continues to fall with increasing N, a signature of spurious two-body relaxation. We present a novel approach for studying loss cone repopulation in galactic nuclei. Since loss cone repopulation in triaxial systems owes to orbit diffusion, it is a purely collisionless phenomenon and can be studied with an approximated force calculation technique, provided the force errors are well behaved and sufficiently small. We achieve this using an accurate fast multipole method and define a proxy for the hardening rate that depends only on stellar angular momenta. We find that the loss cone is efficiently replenished even in very mildly triaxial models (with axis ratios 1 : 0.9 : 0.8). Such triaxiality is unavoidable following galactic mergers and can drive binaries into the gravitational wave regime. We conclude that there is no `final parsec problem'.

  19. Increase of the Density, Temperature and Velocity of Plasma Jets driven by a Ring of High Energy Laser Beams

    CERN Document Server

    Fu, Wen; Fatenejad, Milad; Lamb, Donald Q; Grosskopf, Michael; Park, Hye-Sook; Remington, Bruce; Spitkovsky, Anatoly

    2012-01-01

    Supersonic plasma outflows driven by multi-beam, high-energy lasers, such as Omega and NIF, have been and will be used as platforms for a variety of laboratory astrophysics experiments. Here we propose a new way of launching high density and high velocity, plasma jets using multiple intense laser beams in a hollow ring formation. We show that such jets provide a more flexible and versatile platform for future laboratory astrophysics experiments. Using high resolution hydrodynamic simulations, we demonstrate that the collimated jets can achieve much higher density, temperature and velocity when multiple laser beams are focused to form a hollow ring pattern at the target, instead of focused onto a single spot. We carried out simulations with different ring radii and studied their effects on the jet properties. Implications for laboratory collisionless shock experiments are discussed.

  20. Plasmoid-induced turbulence in collisionless magnetic reconnection.

    Science.gov (United States)

    Fujimoto, Keizo; Sydora, Richard D

    2012-12-28

    The dissipation mechanism in collisionless magnetic reconnection in a quasisteady period is investigated for the antiparallel field configuration. A three-dimensional simulation in a fully kinetic system reveals that a current-aligned electromagnetic mode produces turbulent electron flow that facilitates the transport of the momentum responsible for the current density. It is found that the electromagnetic turbulence is drastically enhanced by plasmoid formations and has a significant impact on the dissipation at the magnetic x-line. The linear analyses confirm that the mode survives in the real ion-to-electron mass ratio, which assures the importance of the turbulence in collisionless reconnection.

  1. Equations of state for collisionless guide-field reconnection.

    Science.gov (United States)

    Le, A; Egedal, J; Daughton, W; Fox, W; Katz, N

    2009-02-27

    Direct in situ observation of magnetic reconnection in the Earth's magnetotail as well as kinetic numerical studies have recently shown that the electron pressure in a collisionless reconnection region is strongly anisotropic. This anisotropy is mainly caused by the trapping of electrons in parallel electric fields. We present new equations of state for the parallel and perpendicular pressures for magnetized electrons. This model-derived here and tested against a kinetic simulation-allows a fluid description in a collisionless regime where parallel electric fields and the dynamics of both passing and trapped electrons are essential.

  2. Simulating radiative shocks in nozzle shock tubes

    Science.gov (United States)

    van der Holst, B.; Tóth, G.; Sokolov, I. V.; Daldorff, L. K. S.; Powell, K. G.; Drake, R. P.

    2012-06-01

    We use the recently developed Center for Radiative Shock Hydrodynamics (CRASH) code to numerically simulate laser-driven radiative shock experiments. These shocks are launched by an ablated beryllium disk and are driven down xenon-filled plastic tubes. The simulations are initialized by the two-dimensional version of the Lagrangian Hyades code which is used to evaluate the laser energy deposition during the first 1.1 ns. Later times are calculated with the CRASH code. CRASH solves for the multi-material hydrodynamics with separate electron and ion temperatures on an Eulerian block-adaptive-mesh and includes a multi-group flux-limited radiation diffusion and electron thermal heat conduction. The goal of the present paper is to demonstrate the capability to simulate radiative shocks of essentially three-dimensional experimental configurations, such as circular and elliptical nozzles. We show that the compound shock structure of the primary and wall shock is captured and verify that the shock properties are consistent with order-of-magnitude estimates. The synthetic radiographs produced can be used for comparison with future nozzle experiments at high-energy-density laser facilities.

  3. Simulating radiative shocks in nozzle shock tubes

    CERN Document Server

    van der Holst, B; Sokolov, I V; Daldorff, L K S; Powell, K G; Drake, R P

    2011-01-01

    We use the recently developed Center for Radiative Shock Hydrodynamics (CRASH) code to numerically simulate laser-driven radiative shock experiments. These shocks are launched by an ablated beryllium disk and are driven down xenon-filled plastic tubes. The simulations are initialized by the two-dimensional version of the Lagrangian Hyades code which is used to evaluate the laser energy deposition during the first 1.1ns. The later times are calculated with the CRASH code. This code solves for the multi-material hydrodynamics with separate electron and ion temperatures on an Eulerian block-adaptive-mesh and includes a multi-group flux-limited radiation diffusion and electron thermal heat conduction. The goal of the present paper is to demonstrate the capability to simulate radiative shocks of essentially three-dimensional experimental configurations, such as circular and elliptical nozzles. We show that the compound shock structure of the primary and wall shock is captured and verify that the shock properties a...

  4. Structure, Propagation, and Expansion of a CME-driven Shock in the Heliosphere: A Revisit of the 2012 July 23 Extreme Storm

    Science.gov (United States)

    Liu, Ying D.; Hu, Huidong; Zhu, Bei; Luhmann, Janet G.; Vourlidas, Angelos

    2017-01-01

    We examine the structure, propagation, and expansion of the shock associated with the 2012 July 23 extreme coronal mass ejection. Characteristics of the shock determined from multi-point imaging observations are compared to in situ measurements at different locations and a complex radio type II burst, which according to our definition has multiple branches that may not all be fundamental-harmonic related. The white-light shock signature can be modeled reasonably well by a spherical structure and was expanding backward even on the opposite side of the Sun. The expansion of the shock, which was roughly self-similar after the first ∼1.5 hr from launch, largely dominated over the translation of the shock center for the time period of interest. Our study also suggests a bow-shock morphology around the nose at later times due to the outward motion in combination with the expansion of the ejecta. The shock decayed and failed to reach Mercury in the backward direction and the Solar Terrestrial Relations Observatory B (STEREO B) and Venus in the lateral directions, as indicated by the imaging and in situ observations. The shock in the nose direction, however, may have persisted to the far outer heliosphere, with predicted impact on Dawn around 06:00 UT on July 25 and on Jupiter around 23:30 UT on July 27 by a magnetohydrodynamic model. The type II burst shows properties generally consistent with the spatial/temporal variations of the shock deduced from imaging and in situ observations. In particular, the low-frequency bands agree well with the in situ measurements of a very low density ahead of the shock at STEREO A.

  5. Characterization of Saturn's bow shock: Magnetic field observations of quasi-perpendicular shocks

    CERN Document Server

    Sulaiman, A H; Dougherty, M K

    2016-01-01

    Collisionless shocks vary drastically from terrestrial to astrophysical regimes resulting in radically different characteristics. This poses two complexities. Firstly, separating the influences of these parameters on physical mechanisms such as energy dissipation. Secondly, correlating observations of shock waves over a wide range of each parameter, enough to span across different regimes. Investigating the latter has been restricted since the majority of studies on shocks at exotic regimes (such as supernova remnants) have been achieved either remotely or via simulations, but rarely by means of in-situ observations. Here we present the parameter space of MA bow shock crossings from 2004-2014 as observed by the Cassini spacecraft. We find that Saturn's bow shock exhibits characteristics akin to both terrestrial and astrophysical regimes (MA of order 100), which is principally controlled by the upstream magnetic field strength. Moreover, we determined the {\\theta}Bn of each crossing to show that Saturn's (days...

  6. A new fast reconnection model in a collisionless regime

    CERN Document Server

    Tsiklauri, David

    2008-01-01

    Based on the first principles (by balancing the advection with the electron pressure tensor in the generalised Ohm's law, and using the conservation of mass) a simple model of magnetic reconnection in a collisionless regime is formulated. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate ($M_{c'less}={(d_i/2)}^{1/2}$) than Sweet-Parker's classical one ($M_{sp}=S^{-1/2}$). The width of the diffusion region (current sheet) in the collisionless regime is found to be $\\delta_{c'less}={(d_i/2)}^{1/2}L$, which is much larger than the Sweet-Parker width ($\\delta_{sp}=S^{-1/2}L$) for the space plasma conditions. Amongst other issues, this alleviates e.g. the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be $< 10$ minutes, as opposed to Sweet-Parker's equivalent value of $<$ year. The new theoretical reconnec...

  7. The Q,G-method in physics of collisionless plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetsov, V. I., E-mail: victor.kuznetsov@mail.ioffe.ru; Ender, A. Ya. [Russian Academy of Sciences, Ioffe Institute (Russian Federation)

    2015-03-15

    An analytic method for analyzing nonstationary processes in collisionless one-dimensional bounded plasma—the Q,G-method—is proposed. Formulas for the distribution function of charged particles escaping from the boundary and moving without collisions in a nonstationary electric field of arbitrary form are obtained. Specific features of the distribution function are revealed and analyzed.

  8. Relativistic electrons produced by foreshock disturbances observed upstream of the Earth's bow shock

    Science.gov (United States)

    Wilson, Lynn Bruce, III; Sibeck, David G.; Turner, Drew L.; Osmane, Adnane; Caprioli, Damiano; Angelopoulos, Vassilis

    2017-04-01

    It has been known for years that charged particles can be accelerated by high Mach number collisionless shock waves. The accelerated particles can stream away upstream to form a foreshock region in communication with the shock. Due to differences in gyroradii, ions are more readily accelerated than electrons by collisionless shocks. These energetic, suprathermal ions stream against the incident flow providing free energy that can generate foreshock disturbances - large-scale (i.e., tens to thousands of thermal ion gyroradii), transient ( 5-10 per day) structures. They have recently been found to accelerate ions to energies of several keV [e.g., Wilson et al., 2013] and even produce their own mini foreshocks [e.g., Liu et al., 2016]. While the high Mach number (M > 40) Kronian bow shock can generate MeV electrons [e.g., Masters et al., 2013], the much weaker Earth's bow shock (1 ≤ M questions in heliospheric and astrophysical plasmas.

  9. Diffusive Shock Acceleration the Fermi Mechanism

    CERN Document Server

    Baring, M G

    1997-01-01

    The mechanism of diffusive Fermi acceleration at collisionless plasma shock waves is widely invoked in astrophysics to explain the appearance of non-thermal particle populations in a variety of environments, including sites of cosmic ray production, and is observed to operate at several sites in the heliosphere. This review outlines the principal results from the theory of diffusive shock acceleration, focusing first on how it produces power-law distributions in test-particle regimes, where the shock dynamics are dominated by the thermal populations that provide the seed particles for the acceleration process. Then the importance of non-linear modifications to the shock hydrodynamics by the accelerated particles is addressed, emphasizing how these subsequently influence non-thermal spectral formation.

  10. Structure, Propagation and Expansion of a CME-Driven Shock in the Heliosphere: A Revisit of the 2012 July 23 Extreme Storm

    CERN Document Server

    Liu, Ying D; Zhu, Bei; Luhmann, Janet G; Vourlidas, Angelos

    2016-01-01

    We examine the structure, propagation and expansion of the shock associated with the 2012 July 23 extreme coronal mass ejection (CME). Characteristics of the shock determined from multi-point imaging observations are compared to in situ measurements at different locations and a complex radio type II burst, which according to our definition has multiple branches that may not all be fundamental-harmonic related. The white-light shock signature can be modeled reasonably well by a spherical structure and was expanding backward even on the opposite side of the Sun. The expansion of the shock, which was roughly self-similar after the first $\\sim$1.5 hours from launch, largely dominated over the translation of the shock center for the time period of interest. Our study also suggests a bow-shock morphology around the nose at later times due to the outward motion in combination with the expansion of the ejecta. The shock decayed and failed to reach Mercury in the backward direction and STEREO B and Venus in the latera...

  11. Evidence of magnetic field switch-off in Particle In Cell simulations of collisionless magnetic reconnection with guide field

    Science.gov (United States)

    Innocenti, M. E.; Goldman, M. V.; Newman, D. L.; Markidis, S.; Lapenta, G.

    2015-12-01

    The long term evolution of large domain Particle In Cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: towards a Petschek-like configuration (Gosling 2007) or towards multiple X points (Eriksson et al. 2014). In the simulations presented here and described in [Innocenti2015*], a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminding of Petschek's switch-off then ensues. Switch-off is obtained through a slow shock / rotational discontinuity (SS/RD) compound structure, with the rotation discontinuity downstreamthe slow shock. Two external slow shocks located in correspondence of the separatrices reduce the in plane tangential component of the magnetic field, but not to zero. Two transitions reminding of rotational discontinuities in the internal part of the exhausts then perform the final switch-off. Both the slow shocks and the rotational discontinuities are characterized as such through the analysis of their Rankine-Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust that prevented switch off in [Liu2012]. Compound SS/RD structures, with the RD located downstream the SS, have been observed in both the solar wind and the magnetosphere in Wind and Geotail data respectively [Whang1998, Whang2004]. Ion trajectiories across the SS/RD structure are followed and the kinetic origin of the SS/RD structure is investigated. * Innocenti, Goldman, Newman, Markidis, Lapenta, Evidence of magnetic field switch-off in collisionless magnetic reconnection, accepted in Astrophysical Journal Letters, 2015 Acknowledgements: NERSC, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of

  12. Computer modeling of test particle acceleration at oblique shocks

    Science.gov (United States)

    Decker, Robert B.

    1988-01-01

    The present evaluation of the basic techniques and illustrative results of charged particle-modeling numerical codes suitable for particle acceleration at oblique, fast-mode collisionless shocks emphasizes the treatment of ions as test particles, calculating particle dynamics through numerical integration along exact phase-space orbits. Attention is given to the acceleration of particles at planar, infinitessimally thin shocks, as well as to plasma simulations in which low-energy ions are injected and accelerated at quasi-perpendicular shocks with internal structure.

  13. Quantified Energy Dissipation Rates: Electromagnetic Wave Observations in the Terrestrial Bow Shock

    CERN Document Server

    Wilson, L B; Breneman, A W; Contel, O Le; Cully, C; Turner, D L; Angelopoulos, V

    2013-01-01

    We present the first quantified measure of the rate of energy dissipated per unit volume by high frequency electromagnetic waves in the transition region of the Earth's collisionless bow shock using data from the THEMIS spacecraft. Every THEMIS shock crossing examined with available wave burst data showed both low frequency ( 10 Hz) electromagnetic and electrostatic waves throughout the entire transition region and into the magnetosheath. The waves in both frequency ranges had large amplitudes, but the higher frequency waves, which are the focus of this study, showed larger contributions to both the Poynting flux and the energy dissipation rates. The higher frequency waves were identified as combinations of ion-acoustic waves, electron cyclotron drift instability driven waves, electrostatic solitary waves, and whistler mode waves. These waves were found to have: (1) amplitudes capable of exceeding dB ~ 10 nT and dE ~ 300 mV/m, though more typical values were dB ~ 0.1-1.0 nT and dE ~ 10-50 mV/m; (2) energy flu...

  14. Two-temperature radiative shocks with electron thermal conduction

    Science.gov (United States)

    Borkowski, Kazimierz J.; Shull, J. Michael; Mckee, Christopher F.

    1989-01-01

    The influence of electron thermal conduction on radiative shock structure is studied for both one- and two-temperature plasmas. The dimensionless ratio of the conductive length to the cooling length determines whether or not conduction is important, and shock jump conditions with conduction are established for a collisionless shock front. Approximate solutions are obtained, with the assumptions that the ionization state of the gas is constant and the cooling rate is a function of temperature alone. In the absence of magnetic fields, these solutions indicate that conduction noticeably influences normal-abundance interstellar shocks with velocities 50-100 km/s and dramatically affects metal-dominated shocks over a wide range of shock velocities.

  15. Downstream plasma parameters in laminar shocks from ion kinetics

    Science.gov (United States)

    Gedalin, M.

    2016-10-01

    Ion dynamics in oblique shocks is governed by the macroscopic electric and magnetic fields of the shock front. In laminar shocks, these fields are time-independent and depend only on the coordinate along the shock normal. The shock ramp is narrow and the ion motion across the shock is manifestly non-adiabatic. The ion distribution just behind the ramp is significantly non-gyrotropic. Gyrotropy is achieved well behind the ramp mainly due to the gyrophase mixing. The asymptotic values of the ion density and temperature are determined by the eventual collisionless relaxation of the gyrating ion distribution. Given a distribution at the downstream edge of the ramp, the moments of the distribution after gyrophase mixing are derived using proper spatial averaging. The obtained expressions can be used for independent determination of the downstream plasma state and implementation in Rankine-Hugoniot relations.

  16. Shock Formation in Electron-Ion Plasmas: Mechanism and Timing

    Science.gov (United States)

    Bret, Antoine; Stockem Novo, Anne; Ricardo, Fonseca; Luis, Silva

    2016-10-01

    We analyze the formation of a collisionless shock in electron-ion plasmas in theory and simulations. In initially un-magnetized relativistic plasmas, such shocks are triggered by the Weibel instability. While in pair plasmas the shock starts forming right after the instability saturates, it is not so in electron-ion plasmas because the Weibel filaments at saturation are too small. An additional merging phase is therefore necessary for them to efficiently stop the flow. We derive a theoretical model for the shock formation time, taking into account filament merging in the nonlinear phase of the Weibel instability. This process is much slower than in electron-positron pair shocks, and so the shock formation is longer by a factor proportional to √{mi /me } ln(mi /me).

  17. Sub-ion scale plasmoids during collisionless reconnection on TREX

    Science.gov (United States)

    Olson, Joseph; Egedal, Jan; Myers, Rachel; Greess, Sam; Clark, Mike; Wallace, John; Forest, Cary; Wisconsin Plasma Astrophysics Laboratory Collaboration

    2016-10-01

    The Terrestrial Reconnection Experiment (TREX), operating at the Wisconsin Plasma Astrophysics Laboratory, is able to explore a collisionless regime inaccessible to previous reconnection experiments. To date, TREX has already achieved Lundquist numbers up to 104 where kinetic effects, such as electron pressure anisotropy, become important to the reconnection dynamics. During a recent run campaign in this collisionless regime, the spontaneous formation of magnetic islands (plasmoids) inside the ion diffusion region was observed. It is known that long current layers are susceptible to tearing, leading to the formation of plasmoids, and that these plasmoids have strong effects on the reconnection rate and particle energization. However, contrary to theoretical and numerical predictions, the TREX experiments show that the plasmoid instability is active even when the current layer is less than one di long. Analysis of these events shows that smaller plasmoids occur at a higher rate than larger ones, suggesting that magnetic islands could be seeded in plasmas more effectively than previously thought.

  18. 长试验时间爆轰驱动激波风洞技术研究%INVESTIGATING INTO TECHNIQUES FOR EXTENDING THE TEST-DURATION OF DETONATION-DRIVEN SHOCK TUNNELS

    Institute of Scientific and Technical Information of China (English)

    姜宗林; 李进平; 赵伟; 刘云峰; 俞鸿儒

    2012-01-01

    地面试验是先进高超声速飞行器研制的主要手段之一,获得满足高超声速气动实验研究的长时间高焓气流是发展激波风洞技术的关键难题之一.依据反向爆轰驱动方法,针对满足超燃试验有效时问的要求,讨论了爆轰驱动激波风洞运行缝合条件匹配、喷管起动激波干扰控制和激波管末端激波边界层相互作用等因素对激波风洞试验时间的制约及其相应的解决方法.应用这些延长试验时间的激波风洞创新技术,成功研制了基于反向爆轰驱动方法的超大型激波风洞,试验时间长达100ms,并有复现高超声速飞行条件的流动模拟能力.%Ground test is the important and indispensable method for the research and development of hypersonic vehicle, and the acquisition of the high-enthalpy test flow with long enough test time in the test is one of the key challenges for the shock tunnel. Based on detonation-driven shock tunnel, several factors that are of significant influences on the test time are discussed and the corresponding solutions for extending test time are proposed in this paper, including the tailored condition, the shock starting process in the nozzle and the interaction of reflected shock and boundary layer, aiming to meet the requirement for the test time of supersonic combustion experiments. Through the application of the proposed methods, a large detonation-driven shock tunnel has been successfully developed, which can provide the test time of more than 100 microseconds and are capable of duplicating the hypersonic flight conditions.

  19. Collisionless damping of electron waves in non-Maxwellian plasma

    OpenAIRE

    Soshnikov, V. N.

    2007-01-01

    In this paper we have criticized the so-called Landau damping theory. We have analyzed solutions of the standard dispersion equations for longitudinal (electric) and transversal (electromagnetic and electron) waves in half-infinite slab of the uniform collisionless plasmas with non-Maxwellian and Maxwellian-like electron energy distribution functions. One considered the most typical cases of both the delta-function type distribution function (the plasma stream with monochromatic electrons) an...

  20. On the linear stability of collisionless microtearing modes

    CERN Document Server

    Predebon, I

    2013-01-01

    Microtearing modes are an important drive of turbulent heat transport in present-day fusion plasmas. We investigate their linear stability under very-low collisionality regimes, expected for the next generations of devices, using gyrokinetic and drift-kinetic approaches. At odds with current opinion, we show that collisionless microtearing instabilities may occur in certain experimental conditions, particularly relevant for such devices as reversed field pinches and spherical tokamaks.

  1. Stability analysis of collisionless plasmas with specularly reflecting boundary

    CERN Document Server

    Nguyen, Toan

    2011-01-01

    In this paper we provide sharp criteria for linear stability or instability of equilibria of collisionless plasmas in the presence of boundaries. Specifically, we consider the relativistic Vlasov-Maxwell system with specular reflection at the boundary for the particles and with the perfectly conducting boundary condition for the electromagnetic field. Here we initiate our investigation in the simple geometry of radial and longitudinal symmetry.

  2. Suprathermal Electrons at Saturn's Bow Shock

    Science.gov (United States)

    Masters, A.; Sulaiman, A. H.; Sergis, N.; Stawarz, L.; Fujimoto, M.; Coates, A. J.; Dougherty, M. K.

    2016-07-01

    The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (process involves interaction with whistler waves at the shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ˜1 MeV).

  3. The Strength and Radial Profile of the Coronal Magnetic Field from the Standoff Distance of a Coronal Mass Ejection-driven Shock

    Science.gov (United States)

    Gopalswamy, Nat; Yashiro, Seiji

    2011-07-01

    We determine the coronal magnetic field strength in the heliocentric distance range 6-23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfvén Mach number, and hence the Alfvén speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from ~48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.

  4. The Strength and Radial Profile of the Coronal Magnetic Field from the Standoff Distance of a Coronal Mass Ejection-Driven Shock

    Science.gov (United States)

    Gopalswamy, Nat; Yashiro, Seiji

    2011-01-01

    We determine the coronal magnetic field strength in the heliocentric distance range 6-23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfven Mach number, and hence the Alfven speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from approximately 48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.

  5. Plasma physics. Stochastic electron acceleration during spontaneous turbulent reconnection in a strong shock wave.

    Science.gov (United States)

    Matsumoto, Y; Amano, T; Kato, T N; Hoshino, M

    2015-02-27

    Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.

  6. Simulation Study of Magnetic Fields generated by the Electromagnetic Filamentation Instability driven by Pair Loading

    Science.gov (United States)

    Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hededal, C.; Hardee, P.; Mizuno, Y.; Fishman, G. J.

    2007-01-01

    Using a 3-D relativistic particle-in-cell (RPIC) code, we have investigated particle acceleration associated with a relativistic electron-positron (cold) jet propagating into ambient electron-positron and electron-ion plasmas without initial magnetic fields in order to investigate the nonlinear stage of the Weibel instability. We have also performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which are assumed to be created by the photon annihilation. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions and ambient plasma. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities, currents, electric, and magnetic fields in the electron-ion ambient plasma are larger than those in the electron-positron ambient plasma. We have shown that plasma instabilities driven by these streaming electron-positron pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. These fields maintain a strong saturated level on timescales much longer than the electron skin depth at least for the duration of the simulations. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between electron-positron pairs and ions, and may help explain the origin of large upstream fields in GRB shock.

  7. Cardiogenic shock

    Science.gov (United States)

    Shock - cardiogenic ... electrical system of the heart (heart block) Cardiogenic shock occurs when the heart is unable to pump ... orthostatic hypotension) Weak (thready) pulse To diagnose cardiogenic shock, a catheter (tube) may be placed in the ...

  8. Stereoscopic study of the kinematic evolution of a coronal mass ejection and its driven shock from the sun to the earth and the prediction of their arrival times

    Energy Technology Data Exchange (ETDEWEB)

    Hess, Phillip; Zhang, Jie, E-mail: phess4@gmu.edu [School of Physics, Astronomy and Computational Sciences, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States)

    2014-09-01

    We present a detailed study of the complete evolution of a coronal mass ejection (CME). We have tracked the evolution of both the ejecta and its shock, and further fit the evolution of the fronts to a simple but physics-based analytical model. This study focuses on the CME initiated on the Sun on 2012 July 12 and arriving at the Earth on 2012 July 14. Shock and ejecta fronts were observed by white light images, as well as in situ by the Advanced Composition Explorer satellite. We find that the propagation of the two fronts is not completely dependent upon one another, but can each be modeled in the heliosphere with a drag model that assumes the dominant force of affecting CME evolution to be the aerodynamic drag force of the ambient solar wind. Results indicate that the CME ejecta front undergoes a more rapid deceleration than the shock front within 50 R {sub ☉} and therefore the propagation of the two fronts is not completely coupled in the heliosphere. Using the graduated cylindrical shell model, as well as data from time-elongation stack plots and in situ signatures, we show that the drag model can accurately describe the behavior of each front, but is more effective with the ejecta. We also show that without the in situ data, based on measurements out to 80 R {sub ☉} combined with the general values for drag model parameters, the arrival of both the shock and ejecta can be predicted within four hours of arrival.

  9. Shock Dynamics in Stellar Outbursts. I. Shock Formation

    Science.gov (United States)

    Ro, Stephen; Matzner, Christopher D.

    2017-05-01

    Wave-driven outflows and non-disruptive explosions have been implicated in pre-supernova outbursts, supernova impostors, luminous blue variable eruptions, and some narrow-line and superluminous supernovae. To model these events, we investigate the dynamics of stars set in motion by strong acoustic pulses and wave trains, focusing on nonlinear wave propagation, shock formation, and an early phase of the development of a weak shock. We identify the shock formation radius, showing that a heuristic estimate based on crossing characteristics matches an exact expansion around the wave front and verifying both with numerical experiments. Our general analytical condition for shock formation applies to one-dimensional motions within any static environment, including both eruptions and implosions. We also consider the early phase of shock energy dissipation. We find that waves of super-Eddington acoustic luminosity always create shocks, rather than damping by radiative diffusion. Therefore, shock formation is integral to super-Eddington outbursts.

  10. Gamma-Rays from Intergalactic Shocks

    CERN Document Server

    Keshet, U; Loeb, A; Springel, V; Hernquist, L E; Keshet, Uri; Waxman, Eli; Loeb, Abraham; Springel, Volker; Hernquist, Lars

    2003-01-01

    Structure formation in the intergalactic medium (IGM) produces large-scale, collisionless shock waves, where electrons can be accelerated to highly relativistic energies. Such electrons can Compton scatter cosmic microwave background photons up to gamma-ray energies. We study the radiation emitted in this process using a hydrodynamic cosmological simulation of a LCDM universe. The resulting radiation, extending beyond TeV energies, has roughly constant energy flux per decade in photon energy, in agreement with the predictions of Loeb & Waxman (2000). Assuming that a fraction \\xi_e=0.05 of the shock energy is transferred to the relativistic electrons, as inferred from collisionless non-relativistic shocks in the interstellar medium, we find that the radiation energy flux, e^2 (dJ/de) ~ 50-160 eV cm^{-2} s^{-1} sr^{-1}, constitutes ~10% of the extragalactic gamma-ray background flux. The associated gamma-ray point-sources are too faint to account for the ~60 unidentified EGRET gamma-ray sources, but GLAST s...

  11. Particle transport in microturbulence and acceleration performances of relativistic shocks

    CERN Document Server

    Plotnikov, Illya; Lemoine, Martin

    2012-01-01

    Collisionless relativistic shocks have been the focus of intense theoretical and numerical investigations and these interesting physics have a direct impact on the generation of energetic particles and the interpretation of gamma ray spectra. The Fermi acceleration process that takes place in these shocks is intimately linked with the excitation of micro-turbulence responsible for the shock formation, electron heating and supra-thermal tail generation that in turn excites micro-turbulence, developing thus a self-sustaining phenomenon. In this paper we discuss the development of the micro-turbulence and we investigate two important issues: firstly the transport of supra-thermal particles in the excited microturbulence upstream of the shock and its consequences for the efficiency of the Fermi process; secondly, the preheating process of the incoming background electrons as they cross the shock precursor and experience relativistic oscillations in the electric field of the micro-turbulence.We emphasize the impor...

  12. Turbulence in Collisionless Space Plasmas: a Comparative Study Between the Solar Wind and the Magnetosheath

    Science.gov (United States)

    Sahraoui, F.; Huang, S.; Goldstein, M. L.

    2013-12-01

    Recent studies of kinetic scales solar wind turbulence have revealed new features of the processes of energy cascade and dissipation at electron scales. However, several instrumental limitations have been found and shown to prevent one from deducing firm conclusions about the nature of the turbulence (e.g., scaling, anisotropy) at those scales. These limitations stem in particular from the low SNR (Signal-to-Noise-Ratio) in the solar wind due to the small amplitude of the electric and magnetic field fluctuations. To overcome this difficulty, we study the turbulence in the terrestrial magnetosheath (i.e., the region of the solar wind that is downstream of the Earth's bow shock), where the turbulent fluctuations become enhanced, which yields a higher SNR. We have performed a statistical study using the Cluster wave data (1Hzcollisionless plasmas.

  13. Collisionless and Kinetic Phenomena of Interpenetrating Plasma Streams via Neutron Self-Emission

    Science.gov (United States)

    Ross, J. S.; Higginson, D. P.; Hatarik, R.; Link, A.; Park, H.-S.; Ryutov, D. D.; Weber, S. V.; Wilks, S. C.; Fiuza, F.; Li, C. K.; Sio, H.; Zylstra, A. B.

    2016-10-01

    Recent NIF experiments focus on the generation and diagnosis of collisionless shocks relevant to astrophysical phenomena such as supernova remnants and gamma ray bursts. In the experiments, two opposing CD laser-generated plasmas flow into each other at high velocity ( 1000 km/s). As the ion-ion collisional mean-free-path is near to or greater than the system size, the flows interpenetrate and neutrons are generated via beam-beam deuteron interactions. We model this system using the hybrid particle-in-cell code LSP with electric and magnetic fields suppressed to capture the full temporal and spatial size of the experiment. These simulations show good agreement with the yield, spectrum and spatial/temporal profiles of the neutrons observed in the experiment. When one CD foil is replaced with CH an asymmetry develops in the neutron spectrum that is caused by the Doppler shift related to the flow velocity. Additionally, in this case the neutron yield is found to be lower in the simulations than is observed experimentally, which indicates that the deuterons thermalize more efficiently in the experiment. This suggests that another mechanism is responsible for this yield enhancement other than small angle scattering since it is included in the simulations. Possible mechanisms such as scattering across Weibel-mediated magnetic filaments and large-angle Coulomb scattering will be evaluated and discussed. Prepared by LLNL under Contract DE-AC52-07NA27344.

  14. Particle acceleration, magnetization and radiation in relativistic shocks

    Science.gov (United States)

    Derishev, Evgeny V.; Piran, Tsvi

    2016-08-01

    The mechanisms of particle acceleration and radiation, as well as magnetic field build-up and decay in relativistic collisionless shocks, are open questions with important implications to various phenomena in high-energy astrophysics. While the Weibel instability is possibly responsible for magnetic field build-up and diffusive shock acceleration is a model for acceleration, both have problems and current particle-in-cell simulations show that particles are accelerated only under special conditions and the magnetic field decays on a very short length-scale. We present here a novel model for the structure and the emission of highly relativistic collisionless shocks. The model takes into account (and is based on) non-local energy and momentum transport across the shock front via emission and absorption of high-energy photons. This leads to a pre-acceleration of the fluid and pre-amplification of the magnetic fields in the upstream region. Both have drastic implications on the shock structure. The model explains the persistence of the shock-generated magnetic field at large distances from the shock front. The dissipation of this magnetic field results in a continuous particle acceleration within the downstream region. A unique feature of the model is the existence of an `attractor', towards which any shock will evolve. The model is applicable to any relativistic shock, but its distinctive features show up only for sufficiently large compactness. We demonstrate that prompt and afterglow gamma-ray bursts' shocks satisfy the relevant conditions, and we compare their observations with the predictions of the model.

  15. Collisionless magnetic reconnection via Alfvén eigenmodes.

    Science.gov (United States)

    Dai, Lei

    2009-06-19

    We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields.

  16. New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

    Science.gov (United States)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha

    2012-01-01

    A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron s rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

  17. Time-dependent closure relations for relativistic collisionless fluid equations.

    Science.gov (United States)

    Bendib-Kalache, K; Bendib, A; El Hadj, K Mohammed

    2010-11-01

    Linear fluid equations for relativistic and collisionless plasmas are derived. Closure relations for the fluid equations are analytically computed from the relativistic Vlasov equation in the Fourier space (ω,k), where ω and k are the conjugate variables of time t and space x variables, respectively. The mathematical method used is based on the projection operator techniques and the continued fraction mathematical tools. The generalized heat flux and stress tensor are calculated for arbitrary parameter ω/kc where c is the speed of light, and for arbitrary relativistic parameter z=mc²/T , where m is the particle rest mass and T, the plasma temperature in energy units.

  18. How to Patch Active Plasma and Collisionless Sheath: Pragmatical Guide

    Science.gov (United States)

    Shneider, Mikhail N.; Kaganovich, Igor D.

    2002-11-01

    Most plasmas have very thin sheath compared with plasma dimension. This necessitates separate calculation of plasma and sheath. Bohm criterion provides boundary condition for calculation of plasma profiles. To calculate sheath properties a value of electric field at the plasma-sheath interface has to be specified in addition to Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy is reported. Additional information on the subject will be posted in http://www.pppl.gov/pub/report/2002/ http://arxiv.org/abs/physics/ Work supported by the Princeton Plasma Physics Laboratory through a University Research Support Program.

  19. Entropy production rate as a constraint for collisionless fluid closures

    Science.gov (United States)

    Fleurence, E.; Sarazin, Y.; Garbet, X.; Dif-Pradalier, G.; Ghendrih, Ph.; Grandgirard, V.; Ottaviani, M.

    2006-11-01

    A novel method is proposed to construct collisionless fluid closures accounting for some kinetic properties. The first dropped fluid moment is assumed to be a linear function of the lower order ones. Optimizing the agreement between the fluid and kinetic entropy production rates is used to constrain the coefficients of the linear development. This procedure is applied to a reduced version of the interchange instability. The closure, involving the absolute value of the wave vector, is non-local in real space. In this case, the linear instability thresholds are the same, and the linear growth rates exhibit similar characteristics. Such a method is applicable to other models and classes of instabilities.

  20. Extending Magnetohydrodynamics to the Slow Dynamics of Collisionless Plasmas

    Science.gov (United States)

    Passot, T.; Sulem, P. L.; Hunana, P.

    2012-01-01

    A fluid approach aimed to provide a consistent description of the slow dynamics of a collisionless plasma, is presented. In this regime, both Landau damping and finite Larmor radius effects cannot be ignored. Two models are discussed; one retains the dynamics at sub-ionic scales, while the other is restricted to scales larger than the ion gyroscale. Special attention is paid to the capability of these approaches to accurately reproduce the properties of linear waves that are known to play an important role, for example, in the small-scale dynamics of solar wind turbulence.

  1. 冲击波在铝靶中传播的数值模拟研究%NUMERICAL SIMULATION STUDY OF LASER-DRIVEN SHOCK WAVE PROPAGATION IN PLANAR Al FOIL TARGETS

    Institute of Scientific and Technical Information of China (English)

    张杰; 王薇; 等

    2001-01-01

    利用一维辐射流体力学数值模拟程序对激光驱动的冲击波在平面铝靶中传播的实验结果进行了模拟研究.分析了空间单元层的厚度对模拟结果的影响,给出了最佳单元层厚度.通过将数值模拟与实验结果相比较给出了实验中两种激光光强的实际的吸收系数.结果显示,波长为1.053μm, 强度分别为0.81×1014和1.65×1014W/cm2的激光驱动的冲击波在铝靶中传播速度分别为16.52,18.56μm/ns,冲击波的峰值压力分别为0.386和0.537?TPa, 这些模拟结果与实验结果是一致的.%The numerical simulation study of an experimental result of laser-driven shock wave propagation in a planar aluminum foil target is performed using a one-dimensional radiation hydrodynamic code MULTI. The effect of spatial mesh size on numerical simulation resulits is found to be significant and optimum mesh size is obtained. Series of simulations are performed using different sets of laser absorption coefficients and the most appropriate laser absorption coefficients value for two laser intensity values used in the experiment is obtained .The results suggest that shock velocities and peak shock pressures are in good agreement with the experimental results.

  2. Application of Single Spacecraft Methods to Study the Motion of the Venusian Bow Shock

    Science.gov (United States)

    Giagkiozis, Stefanos; Pope, Simon

    2016-07-01

    Collisionless shockwaves are associated with a plethora of processes throughout the universe. Supernova remnant shocks are considered one of the main mechanisms that are capable to accelerate particles at high enough energies as the ones observed in cosmic rays. It is still unknown how these shocks accelerate particle to such high energies. By studying shocks in the heliosphere in order to define as much as possible of their parameter space, we could find the answer to this question. One important collisionless shock parameter is the velocity that the shock is travelling. This velocity can be used to define the spatial scales of the shock. The spatial scale in turn is closely related to the processes that govern the energy dissipation and in turn the nature of the shock. The use of multi-spacecraft measurements are the most reliable method to determine the shock velocity. However single spacecraft measurements are often only available, particularly for planetary missions. In a previous study we examined the accuracy of some of the single spacecraft methods that have been developed. Here we apply these approaches to a series of observations of the Venusian bow shock at different locations using Venus Express magnetic field data.

  3. Optimizing laser-driven proton acceleration from overdense targets

    Science.gov (United States)

    Stockem Novo, A.; Kaluza, M. C.; Fonseca, R. A.; Silva, L. O.

    2016-01-01

    We demonstrate how to tune the main ion acceleration mechanism in laser-plasma interactions to collisionless shock acceleration, thus achieving control over the final ion beam properties (e. g. maximum energy, divergence, number of accelerated ions). We investigate this technique with three-dimensional particle-in-cell simulations and illustrate a possible experimental realisation. The setup consists of an isolated solid density target, which is preheated by a first laser pulse to initiate target expansion, and a second one to trigger acceleration. The timing between the two laser pulses allows to access all ion acceleration regimes, ranging from target normal sheath acceleration, to hole boring and collisionless shock acceleration. We further demonstrate that the most energetic ions are produced by collisionless shock acceleration, if the target density is near-critical, ne ≈ 0.5 ncr. A scaling of the laser power shows that 100 MeV protons may be achieved in the PW range. PMID:27435449

  4. Magneto-Hydro-Dynamic Waves In The Collisionless Space Plasma

    Science.gov (United States)

    Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J.

    2007-12-01

    The instability of magneto-hydro-dynamic (MHD) waves in an anisotropic, collisionless, rarefied hot plasma is studied. Anisotropy properties of such a plasma are caused by a strong magnetic field, when the thermal gas pressures across and along the field become unequal. Moreover, there appears an anisotropy of the thermal fluxes. The study of the anisotropy features of the plasma are motivated by observed solar coronal data. The 16 moments equations derived from the Boltzmann-Vlasov kinetic equation are used. These equations strongly differ from the usual isotropic MHD case. For linear disturbances the wave equations in homogenous anisotropic plasma are deduced. The general dispersion relation for the incompressible wave modes is derived, solved and analyzed. It is shown that a wide wave spectrum with stable and unstable behavior is possible, in contrast to the usual isotropic MHD case. The dependence of the instability on magnetic field, pressure anisotropy, and heat fluxes is investigated. The general instability condition is obtained. The results can be applied to the theory of solar and stellar coronal heating, to wind models and in other modeling, where the collisionless approximation is valid.

  5. Simplex-in-Cell Technique for Collisionless Plasma Simulations

    CERN Document Server

    Kates-Harbeck, Julian; Zrake, Jonathan; Abel, Tom

    2015-01-01

    We extend the simplex-in-cell (SIC) technique recently introduced in the context of collisionless dark matter fluids (Abel et al. 2012; Hahn et al. 2012) to the case of collisionless plasmas. The six-dimensional phase space distribution function $f(\\mathbf x,\\mathbf v)$ is represented by an ensemble of three-dimensional manifolds, which we refer to as sheets. The electric potential field is obtained by solving the Poisson equation on a uniform mesh, where the charge density is evaluated by a spatial projection of the phase space sheets. The SIC representation of phase space density facilitates robust, high accuracy numerical evolution of the Vlasov-Poisson system using significantly fewer tracer particles than comparable particle-in-cell (PIC) approaches by reducing the numerical shot-noise associated with the latter. We introduce the SIC formulation and describe its implementation in a new code, which we validate using standard test problems including plasma oscillations, Landau damping, and two stream insta...

  6. Electron Whistler Mode Waves Associated with Collisionless Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    GUO Jun; YU Bin; GUO Guang-Hai; ZHAO Bo

    2011-01-01

    @@ The results of particle-in-cell (PIC) simulations are presented on the evolution of the electron whistler waves during the collisionless magnetic reconnection.The simulation results show that the electron whistler waves with frequency higher than the lower hybrid frequency are found to occur in the electrons outflow region.Moreover, the present results indicate that these electron whistler waves with high-frequency in the region greater than an ion inertial scale of the x-line are irrelevant to the fast reconnection, but are generated as a result of the reconnection processes.%The results of particle-in-cell (PIC) simulations are presented on the evolution of the electron whistler waves during the collisionless magnetic reconnection. The simulation results show that the electron whistler waves with frequency higher than the lower hybrid frequency are found to occur in the electrons outflow region. Moreover,the present results indicate that these electron whistler waves with high-frequency in the region greater than an ion inertial scale of the x-line are irrelevant to the fast reconnection, but are generated as a result of the reconnection processes.

  7. Collisionless reconnection in Jupiter's magnetotail

    Energy Technology Data Exchange (ETDEWEB)

    Zimbardo, G. (Univ. ' della Calabria (Italy))

    1991-04-01

    The authors present the first quantitative study of collisionless reconnection in Jupiter's magnetotail. Recently it has been shown that collisionless reconnection can occur in the Earth's magnetotail quasi-neutral sheet when the electrons are subject to chaotic pitch angle diffusion. This happens when the curvature parameter K{sub e} = B{sub z}/B{sub 0}(L{sub z}/{rho}{sub e0}){sup 1/2} decreases to {approximately} 1.6. For Jupiter's magnetotail, a self-consistent axisymmetric equilibrium model is used to compute the magnetic field and K{sub e}, and it is found that the condition for electron chaotization is satisfied in a region large enough to allow the growth of a tearing instability. The favorite site for reconnection is situated at about 60 R{sub j}, and the growth time is estimated to be about 370 s, i.e., much shorter than the plasma transit time through the chaotization region. The inductive e.m.f. along a 20 R{sub j} X line is estimated to be of order 100 kV - 1 MV, and should accelerate the ions dawnward and the electrons duskward.

  8. Simplex-in-cell technique for collisionless plasma simulations

    Science.gov (United States)

    Kates-Harbeck, Julian; Totorica, Samuel; Zrake, Jonathan; Abel, Tom

    2016-01-01

    We extend the simplex-in-cell (SIC) technique recently introduced in the context of collisionless dark matter fluids [1,2] to the case of collisionless plasmas. The six-dimensional phase space distribution function f (x , v) is represented by an ensemble of three-dimensional manifolds, which we refer to as sheets. The electric potential field is obtained by solving the Poisson equation on a uniform mesh, where the charge density is evaluated by a spatial projection of the phase space sheets. The SIC representation of phase space density facilitates robust, high accuracy numerical evolution of the Vlasov-Poisson system using significantly fewer tracer particles than comparable particle-in-cell (PIC) approaches by reducing the numerical shot-noise associated with the latter. We introduce the SIC formulation and describe its implementation in a new code, which we validate using standard test problems including plasma oscillations, Landau damping, and two stream instabilities in one dimension. Merits of the new scheme are shown to include higher accuracy and faster convergence rates in the number of particles. We finally motivate and outline the efficient application of SIC to higher dimensional problems.

  9. (Quasi-)collisional Magneto-optic Effects in Collisionless Plasmas with sub-Larmor-scale Electromagnetic Fluctuations

    CERN Document Server

    Keenan, Brett D; Medvedev, Mikhail V

    2015-01-01

    High-amplitude, chaotic/turbulent electromagnetic fluctuations are ubiquitous in high-energy-density laboratory and astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on "sub-Larmor scales" -- scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch-angles, thus establishing diffusive transport on long time-scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective "collision" frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma "quasicollisionality", may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified mag...

  10. Collisionless Isotropization of the Solar-wind Protons by Compressive Fluctuations and Plasma Instabilities

    Science.gov (United States)

    Verscharen, Daniel; Chandran, Benjamin D. G.; Klein, Kristopher G.; Quataert, Eliot

    2016-11-01

    Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in {β }\\parallel {{p}}\\equiv 8π {n}{{p}}{k}{{B}}{T}\\parallel {{p}}/{B}2 and in {R}{{p}}\\equiv {T}\\perp {{p}}/{T}\\parallel {{p}}, where {T}\\perp {{p}} and {T}\\parallel {{p}} are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and {n}{{p}} is the proton density. If the amplitude of the compressive fluctuations is large enough, {R}{{p}} crosses one or more instability thresholds for anisotropy-driven microinstabilities. The enhanced field fluctuations from these microinstabilities scatter the protons so as to reduce the anisotropy of the pressure tensor. We propose that this scattering drives the average value of {R}{{p}} away from the marginal stability boundary until the fluctuating value of {R}{{p}} stops crossing the boundary. We model this “fluctuating-anisotropy effect” using linear Vlasov-Maxwell theory to describe the large-scale compressive fluctuations. We argue that this effect can explain why, in the nearly collisionless solar wind, the average value of {R}{{p}} is close to unity.

  11. Hypovolemic shock

    Science.gov (United States)

    ... thready Tests that may be done include: Blood chemistry, including kidney function tests and those tests looking ... severe shock. Severe hypovolemic shock may lead to death, even with immediate medical attention. Older adults are ...

  12. Kinetic structures of quasi-perpendicular shocks in global particle-in-cell simulations

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Ivy Bo, E-mail: bopeng@kth.se; Markidis, Stefano; Laure, Erwin [KTH Royal Institute of Technology, Stockholm (Sweden); Johlander, Andreas; Vaivads, Andris; Khotyaintsev, Yuri [Swedish Institute of Space Physics, Uppsala (Sweden); Henri, Pierre [LPC2E-CNRS, Orléans (France); Lapenta, Giovanni [Centre for mathematical Plasma-Astrophysics, KU Leuven, Leuven (Belgium)

    2015-09-15

    We carried out global Particle-in-Cell simulations of the interaction between the solar wind and a magnetosphere to study the kinetic collisionless physics in super-critical quasi-perpendicular shocks. After an initial simulation transient, a collisionless bow shock forms as a result of the interaction of the solar wind and a planet magnetic dipole. The shock ramp has a thickness of approximately one ion skin depth and is followed by a trailing wave train in the shock downstream. At the downstream edge of the bow shock, whistler waves propagate along the magnetic field lines and the presence of electron cyclotron waves has been identified. A small part of the solar wind ion population is specularly reflected by the shock while a larger part is deflected and heated by the shock. Solar wind ions and electrons are heated in the perpendicular directions. Ions are accelerated in the perpendicular direction in the trailing wave train region. This work is an initial effort to study the electron and ion kinetic effects developed near the bow shock in a realistic magnetic field configuration.

  13. Kinetic Structures of Quasi-Perpendicular Shocks in Global Particle-in-Cell Simulations

    Science.gov (United States)

    Peng, I. B.; Markidis, S.; Laure, E.; Johlander, A.; Vaivads, A.; Khotyaintsev, Y. V.; Pierre, H.; Lapenta, G.

    2015-12-01

    We carried out global Particle-in-Cell simulations of the interaction between the solar wind and a magnetosphere to study the kinetic collisionless physics in super-critical quasi-perpendicular shocks. After an initial simulation transient, a collisionless bow shock forms as a result of the interaction of the solar wind and a planet magnetic dipole. The shock ramp has a thickness of approximately one ion skin depth and is followed by a trailing wave train in the shock downstream. At the downstream edge of the bow shock, whistler waves propagate along the magnetic field lines and the presence of electron cyclotron waves has been identified. A small part of the solar wind ion population is specularly reflected by the shock while a larger part is deflected and heated by the shock. Solar wind ions and electrons are heated in the perpendicular directions. Ions are accelerated in the perpendicular direction in the trailing wave train region. This work is an initial effort to study the electron and ion kinetic effects developed near the bow shock in a realistic magnetic field configuration.

  14. Modeling the Lyman-alpha Forest in Collisionless Simulations

    CERN Document Server

    Sorini, Daniele; Lukić, Zarija; Hennawi, Joseph F

    2016-01-01

    Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present Iteratively Matched Statistics (IMS), a novel method to accurately model the Lyman-alpha forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyman-alpha forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can perfectly reproduce line-of-sight observables, such as the PDF and power spe...

  15. Three dimensional density cavities in guide field collisionless magnetic reconnection

    CERN Document Server

    Markidis, Stefano; Divin, Andrey; Goldman, Martin V; Newman, D; Andersson, Laila

    2012-01-01

    Particle-in-Cell simulations of collisionless magnetic reconnection with a guide field reveal for the first time the three dimensional features of the low density regions along the magnetic reconnection separatrices, the so-called "cavities". It is found that structures with further lower density develop within the cavities. Because their appearance is similar to the rib shape, these formations are here called "low density ribs". Their location remains approximately fixed in time and their density progressively decreases, as electron currents along the cavities evacuate them. They develop along the magnetic field lines and are supported by a strong perpendicular electric field that oscillates in space. In addition, bipolar parallel electric field structures form as isolated spheres between the cavities and the outflow plasma, along the direction of the low density ribs and of magnetic field lines.

  16. Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons

    Energy Technology Data Exchange (ETDEWEB)

    Swamy, Aditya K.; Ganesh, R., E-mail: ganesh@ipr.res.in [Institute for Plasma Research, Bhat, Gandhinagar, 382428 (India); Brunner, S.; Vaclavik, J.; Villard, L. [CRPP, EPFL, 1015 Lausanne (Switzerland)

    2015-07-15

    Collisionless microtearing modes have recently been found linearly unstable in sharp temperature gradient regions of large aspect ratio tokamaks. The magnetic drift resonance of passing electrons has been found to be sufficient to destabilise these modes above a threshold plasma β. A global gyrokinetic study, including both passing electrons as well as trapped electrons, shows that the non-adiabatic contribution of the trapped electrons provides a resonant destabilization, especially at large toroidal mode numbers, for a given aspect ratio. The global 2D mode structures show important changes to the destabilising electrostatic potential. The β threshold for the onset of the instability is found to be generally downshifted by the inclusion of trapped electrons. A scan in the aspect ratio of the tokamak configuration, from medium to large but finite values, clearly indicates a significant destabilizing contribution from trapped electrons at small aspect ratio, with a diminishing role at larger aspect ratios.

  17. Reconnection Rate in Collisionless Magnetic Reconnection under Open Boundary Conditions

    Institute of Scientific and Technical Information of China (English)

    HUANG Jun; MA Zhi-Wei

    2008-01-01

    Collisionless magnetic reconnection is studied by using two-dimensional Darwin particle-in-cell simulations with different types of open boundary conditions.The simulation results indicate that reconnection rates are strongly dependent on the imposed boundary conditions of the magnetic field Bx in the inward side. Under the zerogradient Bx boundary condition,the reconnection rate quickly decreases after reaching its maximum and no steady-state is found.Under both electromagnetic and magnetosonic boundary conditions,the system can reach a quasi-steady state.However,the reconnection rate Er≈ 0.08 under the electromagnetic boundary condition is weaker than Er≈ 0.13 under the magnetosonic boundary condition.

  18. Magnetorotational Turbulence and Dynamo in a Collisionless Plasma

    CERN Document Server

    Kunz, Matthew W; Quataert, Eliot

    2016-01-01

    We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disc. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatio-temporally variable. Energy spectra suggest an Alfv\\'en-wave cascade at large scales and a kinetic-Alfv\\'en-wave cascade at small scales, with strong small-scale density fluctuations and weak non-axisymmetric density waves. Ions undergo n...

  19. Effects of electron inertia in collisionless magnetic reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel [Instituto de Astronomía y Física del Espacio, CC. 67, suc. 28, 1428, Buenos Aires (Argentina); Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina); Martin, Luis; Dmitruk, Pablo [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina)

    2014-07-15

    We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

  20. Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas

    Science.gov (United States)

    Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael

    2015-01-01

    Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.

  1. Collisionless Spectral Kinetic Simulation of Ideal Multipole Resonance Probe

    Science.gov (United States)

    Gong, Junbo; Wilczek, Sebastian; Szeremley, Daniel; Oberrath, Jens; Eremin, Denis; Dobrygin, Wladislaw; Schilling, Christian; Friedrichs, Michael; Brinkmann, Ralf Peter

    2016-09-01

    Active Plasma Resonance Spectroscopy denotes a class of industry-compatible plasma diagnostic methods which utilize the natural ability of plasmas to resonate on or near the electron plasma frequency ωpe. One particular realization of APRS with a high degree of geometric and electric symmetry is the Multipole Resonance Probe (MRP). The Ideal MRP(IMRP) is an even more symmetric idealization which is suited for theoretical investigations. In this work, a spectral kinetic scheme is presented to investigate the behavior of the IMRP in the low pressure regime. However, due to the velocity difference, electrons are treated as particles whereas ions are only considered as stationary background. In the scheme, the particle pusher integrates the equations of motion for the studied particles, the Poisson solver determines the electric field at each particle position. The proposed method overcomes the limitation of the cold plasma model and covers kinetic effects like collisionless damping.

  2. The final-parsec problem in the collisionless limit

    CERN Document Server

    Vasiliev, Eugene; Merritt, David

    2015-01-01

    A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triax...

  3. Development of numerical model to investigate the laser driven shock waves from aluminum target into ambient air at atmospheric pressure and its comparison with experiment

    Science.gov (United States)

    Shiva, S. Sai; Leela, Ch.; Chaturvedi, S.; Sijoy, C. D.; Kiran, P. Prem

    2017-01-01

    A one-dimensional, three-temperature (electron, ion and thermal radiation) numerical model was developed to study the laser induced shock wave (LISW) propagation from aluminum target in ambient air at atmospheric pressure. The hydrodynamic equations of mass, momentum and energy are solved by using an implicit scheme in Lagrangian form. The model considers the laser absorption to take place via inverse-bremsstrahlung due to electron-ion (e-i) process. The flux limited electron thermal energy transport due e-i and e-n thermal energy relaxation equations are solved implicitly. The experimental characterization of spatio-temporal evolution of the LISW in air generated by focusing a second harmonic (532 nm, 7ns) of Nd:YAG laser on to surface of Al is performed using shadowgraphy technique with a temporal resolution of 1.5 ns. The velocity of SW observed in the experiments over 0.2 µs-8 µs time scales was compared with the numerical results to understand the SW transition from planar to spherical evolution.

  4. Determination of the Heliospheric Radial Magnetic Field from the Standoff Distance of a CME-driven Shock Observed by the STEREO Spacecraft

    Science.gov (United States)

    Poomvises, Watanachak; Gopalswamy, Nat; Yashiro, Seiji; Kwon, Ryun-Young; Olmedo, Oscar

    2012-10-01

    We report on the determination of radial magnetic field strength in the heliocentric distance range from 6 to 120 solar radii (R ⊙) using data from Coronagraph 2 (COR2) and Heliospheric Imager I (HI1) instruments on board the Solar Terrestrial Relations Observatory spacecraft following the standoff-distance method of Gopalswamy & Yashiro. We measured the shock standoff distance of the 2008 April 5 coronal mass ejection (CME) and determined the flux-rope curvature by fitting the three-dimensional shape of the CME using the Graduated Cylindrical Shell model. The radial magnetic field strength is computed from the Alfvén speed and the density of the ambient medium. We also compare the derived magnetic field strength with in situ measurements made by the Helios spacecraft, which measured the magnetic field at the heliocentric distance range from 60 to 215 R ⊙. We found that the radial magnetic field strength decreases from 28 mG at 6 R ⊙ to 0.17 mG at 120 R ⊙. In addition, we found that the radial profile can be described by a power law.

  5. Numerical Simulations of Collisionless Shock Formation in Merging Plasma Jet Experiments

    Science.gov (United States)

    2013-06-01

    experiment [5], which uses counter-propagating hydrogen plasma jets formed and launched by plasma railguns [11] mounted on opposite sides of a...hydrogen plasma jet propagating from the railgun nozzle to the center of the chamber in order to connect the plasma jet parameters at the railgun exit...the jet at the railgun exit and center of the chamber (z = 0 cm) are given in Table 1. So this simulation determines the approximate parameter regime

  6. Collisionless Stellar Hydrodynamics as an Efficient Alternative to N-body Methods

    CERN Document Server

    Mitchell, Nigel L; Hensler, Gerhard

    2012-01-01

    For simulations that deal only with dark matter or stellar systems, the conventional N-body technique is fast, memory efficient, and relatively simple to implement. However when including the effects of gas physics, mesh codes are at a distinct disadvantage compared to SPH. Whilst implementing the N-body approach into SPH codes is fairly trivial, the particle-mesh technique used in mesh codes to couple collisionless stars and dark matter to the gas on the mesh, has a series of significant scientific and technical limitations. These include spurious entropy generation resulting from discreteness effects, poor load balancing and increased communication overhead which spoil the excellent scaling in massively parallel grid codes. We propose the use of the collisionless Boltzmann moment equations as a means to model collisionless material as a fluid on the mesh, implementing it into the massively parallel FLASH AMR code. This approach, which we term "collisionless stellar hydrodynamics" enables us to do away with ...

  7. Transport of Solar Wind H+ and He++ Ions across Earth’s Bow Shock

    Science.gov (United States)

    Parks, G. K.; Lee, E.; Fu, S. Y.; Kim, H. E.; Ma, Y. Q.; Yang, Z. W.; Liu, Y.; Lin, N.; Hong, J.; Canu, P.; Dandouras, I.; Rème, H.; Goldstein, M. L.

    2016-07-01

    We have investigated the dependence of mass, energy, and charge of solar wind (SW) transport across Earth’s bow shock. An examination of 111 crossings during quiet SW in both quasi-perpendicular and quasi-parallel shock regions shows that 64 crossings had various degrees of heating and thermalization of SW. We found 22 crossings where the SW speed was flat top distribution is ˜50 Volts. We find that the temperatures of H+ and He++ beams that penetrate the shock can sometimes be nearly the same in the upstream and downstream regions, indicating little or no heating had occurred crossing the bow shock. None of the models predict that the SW can cross the bow shock without heating. Our observations are important constraints for new models of collisionless shocks.

  8. Electromagnetic field generation in the downstream of electrostatic shocks due to electron trapping

    CERN Document Server

    Stockem, A; Fonseca, R A; Silva, L O

    2014-01-01

    A new magnetic field generation mechanism in electrostatic shocks is found, which can produce fields with magnetic energy density as high as 0.01 of the kinetic energy density of the flows on time scales $ \\tilde \\, 10^4 \\, {\\omega}_{pe}^{-1}$. Electron trapping during the shock formation process creates a strong temperature anisotropy in the distribution function, giving rise to the pure Weibel instability. The generated magnetic field is well-confined to the downstream region of the electrostatic shock. The shock formation process is not modified and the features of the shock front responsible for ion acceleration, which are currently probed in laser-plasma laboratory experiments, are maintained. However, such a strong magnetic field determines the particle trajectories downstream and has the potential to modify the signatures of the collisionless shock.

  9. Oscillating nonlinear acoustic shock waves

    DEFF Research Database (Denmark)

    Gaididei, Yuri; Rasmussen, Anders Rønne; Christiansen, Peter Leth

    2016-01-01

    We investigate oscillating shock waves in a tube using a higher order weakly nonlinear acoustic model. The model includes thermoviscous effects and is non isentropic. The oscillating shock waves are generated at one end of the tube by a sinusoidal driver. Numerical simulations show...... that at resonance a stationary state arise consisting of multiple oscillating shock waves. Off resonance driving leads to a nearly linear oscillating ground state but superimposed by bursts of a fast oscillating shock wave. Based on a travelling wave ansatz for the fluid velocity potential with an added 2'nd order...... polynomial in the space and time variables, we find analytical approximations to the observed single shock waves in an infinitely long tube. Using perturbation theory for the driven acoustic system approximative analytical solutions for the off resonant case are determined....

  10. Does the Rate of Collisionless Magnetic Reconnection Depend on the Dissipation Mechanism?

    Science.gov (United States)

    Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria

    2012-01-01

    The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and the macroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.

  11. A quasilinear formulation of turbulence driven current

    Energy Technology Data Exchange (ETDEWEB)

    McDevitt, C. J.; Tang, Xian-Zhu; Guo, Zehua [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2014-02-15

    Non-inductive current drive mechanisms, such as the familiar neoclassical bootstrap current correspond to an essential component to the realization of steady state tokamak operation. In this work, we discuss a novel collisionless mechanism through which a mean plasma current may be driven in the presence of microturbulence. In analogy with the traditional neoclassical bootstrap current drive mechanism, in which the collisional equilibrium established between trapped and passing electrons results in the formation of a steady state plasma current, here we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons. The resulting collisionless equilibrium is shown to result in the formation of an equilibrium current whose magnitude is a function of the thermodynamic forces. A mean field formulation is utilized to incorporate the above components into a unified framework through which both collisional as well as collisionless current drive mechanisms may be self-consistently treated. Utilizing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions as well as turbulent stresses is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.

  12. Design of indirectly driven, high-compression Inertial Confinement Fusion implosions with improved hydrodynamic stability using a 4-shock adiabat-shaped drive

    Energy Technology Data Exchange (ETDEWEB)

    Milovich, J. L., E-mail: milovich1@llnl.gov; Robey, H. F.; Clark, D. S.; Baker, K. L.; Casey, D. T.; Cerjan, C.; Field, J.; MacPhee, A. G.; Pak, A.; Patel, P. K.; Peterson, J. L.; Smalyuk, V. A.; Weber, C. R. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

    2015-12-15

    Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm{sup 2}, but with significantly lower total neutron yields (between 1.5 × 10{sup 14} and 5.5 × 10{sup 14}) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the “high-foot” experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expense of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3–10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm{sup 2}. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.

  13. Design of indirectly driven, high-compression Inertial Confinement Fusion implosions with improved hydrodynamic stability using a 4-shock adiabat-shaped drive

    Science.gov (United States)

    Milovich, J. L.; Robey, H. F.; Clark, D. S.; Baker, K. L.; Casey, D. T.; Cerjan, C.; Field, J.; MacPhee, A. G.; Pak, A.; Patel, P. K.; Peterson, J. L.; Smalyuk, V. A.; Weber, C. R.

    2015-12-01

    Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm2, but with significantly lower total neutron yields (between 1.5 × 1014 and 5.5 × 1014) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the "high-foot" experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expense of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3-10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm2. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.

  14. Heat shock protein 90 is involved in the regulation of HMGA2-driven growth and epithelial-to-mesenchymal transition of colorectal cancer cells

    Directory of Open Access Journals (Sweden)

    Chun-Yu Kao

    2016-02-01

    Full Text Available High Mobility Group AT-hook 2 (HMGA2 is a nonhistone chromatin-binding protein which acts as a transcriptional regulating factor involved in gene transcription. In particular, overexpression of HMGA2 has been demonstrated to associate with neoplastic transformation and tumor progression in Colorectal Cancer (CRC. Thus, HMGA2 is a potential therapeutic target in cancer therapy. Heat Shock Protein 90 (Hsp90 is a chaperone protein required for the stability and function for a number of proteins that promote the growth, mobility, and survival of cancer cells. Moreover, it has shown strong positive connections were observed between Hsp90 inhibitors and CRC, which indicated their potential for use in CRC treatment by using combination of data mining and experimental designs. However, little is known about the effect of Hsp90 inhibition on HMGA2 protein expression in CRC. In this study, we tested the hypothesis that Hsp90 may regulate HMGA2 expression and investigated the relationship between Hsp90 and HMGA2 signaling. The use of the second-generation Hsp90 inhibitor, NVP-AUY922, considerably knocked down HMGA2 expression, and the effects of Hsp90 and HMGA2 knockdown were similar. In addition, Hsp90 knockdown abrogates colocalization of Hsp90 and HMGA2 in CRC cells. Moreover, the suppression of HMGA2 protein expression in response to NVP-AUY922 treatment resulted in ubiquitination and subsequent proteasome-dependant degradation of HMGA2. Furthermore, RNAi-mediated silencing of HMGA2 reduced the survival of CRC cells and increased the sensitivity of these cells to chemotherapy. Finally, we found that the NVP-AUY922-dependent mitigation of HMGA2 signaling occurred also through indirect reactivation of the tumor suppressor microRNA (miRNA, let-7a, or the inhibition of ERK-regulated HMGA2 involved in regulating the growth of CRC cells. Collectively, our studies identify the crucial role for the Hsp90-HMGA2 interaction in maintaining CRC cell survival and

  15. [Cardiogenic shock].

    Science.gov (United States)

    Houegnifioh, Komlanvi Kafui; Gfeller, Etienne; Garcia, Wenceslao; Ribordy, Vincent

    2014-08-13

    Cardiogenic shock, especially when it complicates a myocardial infarction, is still associated with high mortality rate. Emergency department or first care physicians are often the first providers to assess the cardiogenic shock patient, and plays thereby a key role in achieving a timely diagnosis and treatment. This review will detail the actual physiopathology understanding of the cardiogenic shock, its diagnosis and management focusing on the care within the emergency department.

  16. Cluster observations of structures at quasi-parallel bow shocks

    Directory of Open Access Journals (Sweden)

    E. A. Lucek

    2004-07-01

    Full Text Available Collisionless quasi-parallel shocks are thought to be composed of a patchwork of short, large-amplitude magnetic structures (SLAMS which act to thermalise the plasma, giving rise to a spatially extended and time varying shock transition. With the launch of Cluster, new observations of the three-dimensional shape and size of shock structures are available. In this paper we present SLAMS observations made when the Cluster tetrahedron scale size was ~100km. The SLAMS magnetic field enhancement is typically well correlated between spacecraft on this scale, although small differences are observed. The statistical characteristics of these differences contain information on the typical gradients of magnetic field changes within the SLAM structure which, in the case studied here, occur on scales of 100-150km, comparable with the upstream ion inertial length.

  17. Reentry Shock

    Institute of Scientific and Technical Information of China (English)

    Dorine; Houston

    1998-01-01

    Dear Xiao Lan, You remember the pain of culture and reentry shock; humor me please; let mereview the facts for the sake of the students you are sending here in greater numbers.Culture shock is the emotional pain that people experience when they visit a newcountry and find customs, experiences, smells, and non-verbal communication stylesto be different from their own country.

  18. Modeling the Lyα Forest in Collisionless Simulations

    Science.gov (United States)

    Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.

    2016-08-01

    Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%-80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.

  19. The Impact of Geometrical Constraints on Collisionless Magnetic Reconnection

    Science.gov (United States)

    Hesse, Michael; Aunai, Nico; Kuznetsova, Masha; Frolov, Rebekah; Black, Carrrie

    2012-01-01

    One of the most often cited features associated with collisionless magnetic reconnection is a Hall-type magnetic field, which leads, in antiparallel geometries, to a quadrupolar magnetic field signature. The combination of this out of plane magnetic field with the reconnection in-plane magnetic field leads to angling of magnetic flux tubes out of the plane defined by the incoming magnetic flux. Because it is propagated by Whistler waves, the quadrupolar field can extend over large distances in relatively short amounts of time - in fact, it will extend to the boundary of any modeling domain. In reality, however, the surrounding plasma and magnetic field geometry, defined, for example, by the overall solar wind flow, will in practice limit the extend over which a flux tube can be angled out of the main plain. This poses the question to what extent geometric constraints limit or control the reconnection process and this is the question investigated in this presentation. The investigation will involve a comparison of calculations, where open boundary conditions are set up to mimic either free or constrained geometries. We will compare momentum transport, the geometry of the reconnection regions, and the acceleration if ions and electrons to provide the current sheet in the outflow jet.

  20. A multi-model plasma simulation of collisionless magnetic reconnection

    Science.gov (United States)

    Datta, I. A. M.; Shumlak, U.; Ho, A.; Miller, S. T.

    2016-10-01

    Collisionless magnetic reconnection is a process relevant to many areas of plasma physics in which energy stored in magnetic fields within highly conductive plasmas is rapidly converted to plasma energy. A full understanding of this phenomenon, however, is currently incomplete as models developed to date have difficulty explaining the fast reconnection rates often seen in nature, such as in the case of solar flares. Therefore, this behavior represents an area of much research in which various plasma models have been tested in order to understand the proper physics explaining the reconnection process. In this research, the WARPXM code developed at the University of Washington is used to study the problem using a hybrid multi-model simulation employing Hall-MHD and two-fluid plasma models. The simulation is performed on a decomposed domain where different plasma models are solved in different regions, depending on a trade-off between each model's physical accuracy and associated computational expense in each region. The code employs a discontinuous Galerkin (DG) finite element spatial discretization coupled with a Runge-Kutta scheme for time advancement and uses boundary conditions to couple the different plasma models. This work is supported by a Grant from the United States Air Force Office of Scientific Research.

  1. Critical Collapse of Collisionless Matter in Spherical Symmetry

    CERN Document Server

    Olabarrieta, I

    2002-01-01

    We perform a numerical study of the critical regime for the general relativistic collapse of collisionless matter in spherical symmetry. The evolution of the matter is given by the Vlasov equation (or Boltzmann equation) and the geometry by Einstein's equations. This system of coupled differential equations is solved using a particle-mesh (PM) method. This method approximates the distribution function which describes the matter in phase space with a set of particles moving along the characteristics of the Vlasov equation. The individual particles are allowed to have angular momentum different from zero but the total angular momentum has to be zero to retain spherical symmetry. In accord wih previous work by Rein, Rendall and Schaeffer, our results give some indications that the critical behaviour in this model is of Type I (the smallest black hole in each family has a finite mass). For the families of initial data that we have studied it seems that in the critical regime the solution is a static spacetime wit...

  2. Electron dynamics in collisionless magnetic reconnection with a PIC simulation

    Institute of Scientific and Technical Information of China (English)

    GUO Jun

    2009-01-01

    Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli-sionless magnetic reconnection, and the proton/electron mass ratio is taken to be ml/me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re-gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating elec-trons than those fields located in the density cavities.

  3. Magnetorotational Turbulence and Dynamo in a Collisionless Plasma

    Science.gov (United States)

    Kunz, Matthew W.; Stone, James M.; Quataert, Eliot

    2016-12-01

    We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disk. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. These results have implications for the properties of low-collisionality accretion flows, such as that near the black hole at the Galactic center.

  4. The Morphology of Collisionless Galactic Rings Exterior to Evolving Bars

    CERN Document Server

    Bagley, Micaela; Quillen, Alice C

    2008-01-01

    The morphology of the outer rings of early-type spiral galaxies is compared to integrations of massless collisionless particles initially in nearly circular orbits. Particles are perturbed by a quadrupolar gravitational potential corresponding to a growing and secularly evolving bar. We find that outer rings with R1R2 morphology and pseudorings are exhibited by the simulations even though they lack gaseous dissipation. Simulations with stronger bars form pseudorings earlier and more quickly than those with weaker bars. We find that the R1 ring, perpendicular to the bar, is fragile and dissolves after a few bar rotation periods if the bar pattern speed increases by more than ~ 8%, bar strength increases (by >~ 140%) after bar growth, or the bar is too strong (Q_T>0.3). If the bar slows down after formation, pseudoring morphology persists and the R2 ring perpendicular to the bar is populated due to resonance capture. The R2 ring remains misaligned with the bar and increases in ellipticity as the bar slows down....

  5. Statistical mechanics of collisionless orbits. IV. Distribution of angular momentum

    CERN Document Server

    Williams, Liliya L R; Wojtak, Radoslaw

    2014-01-01

    It has been shown in previous work that DARKexp, which is a theoretically derived, maximum entropy, one shape parameter model for isotropic collisionless systems, provides very good fits to simulated and observed dark-matter halos. Specifically, it fits the energy distribution, N(E), and the density profiles, including the central cusp. Here, we extend DARKexp N(E) to include the distribution in angular momentum, L^2, for spherically symmetric systems. First, we argue, based on theoretical, semi-analytical, and simulation results, that while dark-matter halos are relaxed in energy, they are not nearly as relaxed in angular momentum, which precludes using maximum entropy to uniquely derive N(E,L^2). Instead, we require that when integrating N(E,L^2) over squared angular momenta one retrieves the DARKexp N(E). Starting with a general expression for N(E,L^2) we show how the distribution of particles in L^2 is related to the shape of the velocity distribution function, VDF, and velocity anisotropy profile, \\beta(...

  6. Collisionless magnetic reconnection: analytical model and PIC simulation comparison

    Directory of Open Access Journals (Sweden)

    V. Semenov

    2009-03-01

    Full Text Available Magnetic reconnection is believed to be responsible for various explosive processes in the space plasma including magnetospheric substorms. The Hall effect is proved to play a key role in the reconnection process. An analytical model of steady-state magnetic reconnection in a collisionless incompressible plasma is developed using the electron Hall MHD approximation. It is shown that the initial complicated system of equations may split into a system of independent equations, and the solution of the problem is based on the Grad-Shafranov equation for the magnetic potential. The results of the analytical study are further compared with a two-dimensional particle-in-cell simulation of reconnection. It is shown that both methods demonstrate a close agreement in the electron current and the magnetic and electric field structures obtained. The spatial scales of the acceleration region in the simulation and the analytical study are of the same order. Such features like particles trajectories and the in-plane electric field structure appear essentially similar in both models.

  7. Langmuir probe in collisionless and collisional plasma including dusty plasma

    Science.gov (United States)

    Bose, Sayak; Kaur, Manjit; Chattopadhyay, P. K.; Ghosh, J.; Saxena, Y. C.; Pal, R.

    2017-04-01

    Measurements of local plasma parameters in dusty plasma are crucial for understanding the physics issues related to such systems. The Langmuir probe, a small electrode immersed in the plasma, provides such measurements. However, designing of a Langmuir probe system in a dusty plasma environment demands special consideration. First, the probe has to be miniaturized enough so that its perturbation on the ambient dust structure is minimal. At the same time, the probe dimensions must be such that a well-defined theory exists for interpretation of its characteristics. The associated instrumentation must also support the measurement of current collected by the probe with high signal to noise ratio. The most important consideration, of course, comes from the fact that the probes are prone to dust contamination, as the dust particles tend to stick to the probe surface and alter the current collecting area in unpredictable ways. This article describes the design and operation of a Langmuir probe system that resolves these challenging issues in dusty plasma. In doing so, first, different theories that are used to interpret the probe characteristics in collisionless as well as in collisional regimes are discussed, with special emphasis on application. The critical issues associated with the current-voltage characteristics of Langmuir probe obtained in different operating regimes are discussed. Then, an algorithm for processing these characteristics efficiently in presence of ion-neutral collisions in the probe sheath is presented.

  8. Turbulent transport in 2D collisionless guide field reconnection

    CERN Document Server

    Muñoz, P A; Kilian, P

    2016-01-01

    Transport in collisionless plasmas is usually called anomalous, being due to the interaction between the particles and the self-generated turbulence by their collective interactions. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood, yet. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell (PiC) code simulations. We split off the mean, slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by st...

  9. Initial conditions of radiative shock experiments

    Energy Technology Data Exchange (ETDEWEB)

    Kuranz, C. C.; Drake, R. P.; Krauland, C. M.; Marion, D. C.; Grosskopf, M. J.; Rutter, E.; Torralva, B.; Holloway, J. P. [Department of Atmospheric, Oceanic and Space Science, University of Michigan, Center for Radiative Shock Hydrodynamics, 2455 Hayward Dr., Ann Arbor, Michigan 48109 (United States); Bingham, D.; Goh, J. [Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 (Canada); Boehly, T. R.; Sorce, A. T. [Laboratory for Laser Energetics, University of Rochester, New York 14623 (United States)

    2013-05-15

    We performed experiments at the Omega Laser Facility to characterize the initial, laser-driven state of a radiative shock experiment. These experiments aimed to measure the shock breakout time from a thin, laser-irradiated Be disk. The data are then used to inform a range of valid model parameters, such as electron flux limiter and polytropic γ, used when simulating radiative shock experiments using radiation hydrodynamics codes. The characterization experiment and the radiative shock experiment use a laser irradiance of ∼7 × 10{sup 14} W cm{sup −2} to launch a shock in the Be disk. A velocity interferometer and a streaked optical pyrometer were used to infer the amount of time for the shock to move through the Be disk. The experimental results were compared with simulation results from the Hyades code, which can be used to model the initial conditions of a radiative shock system using the CRASH code.

  10. Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock

    Science.gov (United States)

    Wilson, L. B.; Sibeck, D. G.; Turner, D. L.; Osmane, A.; Caprioli, D.; Angelopoulos, V.

    2016-11-01

    Charged particles can be reflected and accelerated by strong (i.e., high Mach number) astrophysical collisionless shock waves, streaming away to form a foreshock region in communication with the shock. Foreshocks are primarily populated by suprathermal ions that can generate foreshock disturbances—large-scale (i.e., tens to thousands of thermal ion Larmor radii), transient (˜5 - 10 per day ) structures. They have recently been found to accelerate ions to energies of several keV. Although electrons in Saturn's high Mach number (M >40 ) bow shock can be accelerated to relativistic energies (nearly 1000 keV), it has hitherto been thought impossible to accelerate electrons beyond a few tens of keV at Earth's low Mach number (1 ≤M events. These relativistic electrons are not associated with any solar or magnetospheric activity. Further, due to their relatively small Larmor radii (compared to magnetic gradient scale lengths) and large thermal speeds (compared to shock speeds), no known shock acceleration mechanism can energize thermal electrons up to relativistic energies. The discovery of relativistic electrons associated with foreshock structures commonly generated in astrophysical shocks could provide a new paradigm for electron injections and acceleration in collisionless plasmas.

  11. On the proper Mach number and ratio of specific heats for modeling the Venus bow shock

    Science.gov (United States)

    Tatrallyay, M.; Russell, C. T.; Luhmann, J. G.; Barnes, A.; Mihalov, J. D.

    1984-01-01

    Observational data from the Pioneer Venus Orbiter are used to investigate the physical characteristics of the Venus bow shock, and to explore some general issues in the numerical simulation of collisionless shocks. It is found that since equations from gas-dynamic (GD) models of the Venus shock cannot in general replace MHD equations, it is not immediately obvious what the optimum way is to describe the desired MHD situation with a GD code. Test case analysis shows that for quasi-perpendicular shocks it is safest to use the magnetospheric Mach number as an input to the GD code. It is also shown that when comparing GD predicted temperatures with MHD predicted temperatures total energy should be compared since the magnetic energy density provides a significant fraction of the internal energy of the MHD fluid for typical solar wind parameters. Some conclusions are also offered on the properties of the terrestrial shock.

  12. Particle Acceleration at a Flare Termination Shock: Effect of Large-scale Magnetic Turbulence

    CERN Document Server

    Guo, Fan

    2012-01-01

    We investigate the acceleration of charged particles (both electrons and protons) at collisionless shocks predicted to exist in the vicinity of solar flares. The existence of standing termination shocks has been examined by flare models and numerical simulations e.g., Shibata,Forbes. We study electron energization by numerically integrating the equations of motion of a large number of test-particle electrons in the time-dependent two-dimensional electric and magnetic fields generated from hybrid simulations (kinetic ions and fluid electron) using parameters typical of the solar flare plasma environment. The shock is produced by injecting plasma flow toward a rigid piston. Large-scale magnetic fluctuations -- known to exist in plasmas and known to have important effects on the nonthermal electron acceleration at shocks -- are also included in our simulations. For the parameters characteristic of the flaring region, our calculations suggest that the termination shock formed in the reconnection outflow region (a...

  13. X-rays, gamma-rays and neutrinos from collisoinless shocks in supernova wind breakouts

    CERN Document Server

    Katz, Boaz; Waxman, Eli

    2011-01-01

    We show that a collisionless shock necessarily forms during the shock breakout of a supernova (SN) surrounded by an optically thick wind. An intense non-thermal flash of <~ MeV gamma rays, hard X-rays and multi-TeV neutrinos is produced simultaneously with and following the soft X-ray breakout emission, carrying similar or larger energy than the soft emission. The non-thermal flash is detectable by current X-ray telescopes and may be detectable out to 10's of Mpc by km-scale neutrino telescopes.

  14. Are gauge shocks really shocks?

    CERN Document Server

    Alcubierre, M

    2005-01-01

    The existence of gauge pathologies associated with the Bona-Masso family of generalized harmonic slicing conditions is proven for the case of simple 1+1 relativity. It is shown that these gauge pathologies are true shocks in the sense that the characteristic lines associated with the propagation of the gauge cross, which implies that the name ``gauge shock'' usually given to such pathologies is indeed correct. These gauge shocks are associated with places where the spatial hypersurfaces that determine the foliation of spacetime become non-smooth.

  15. Collisionless Coupling between Explosive Debris Plasma and Magnetized Ambient Plasma

    Science.gov (United States)

    Bondarenko, Anton

    2016-10-01

    The explosive expansion of a dense debris plasma cloud into relatively tenuous, magnetized, ambient plasma characterizes a wide variety of astrophysical and space phenomena, including supernova remnants, interplanetary coronal mass ejections, and ionospheric explosions. In these rarified environments, collective electromagnetic processes rather than Coulomb collisions typically mediate the transfer of momentum and energy from the debris plasma to the ambient plasma. In an effort to better understand the detailed physics of collisionless coupling mechanisms in a reproducible laboratory setting, the present research jointly utilizes the Large Plasma Device (LAPD) and the Phoenix laser facility at UCLA to study the super-Alfvénic, quasi-perpendicular expansion of laser-produced carbon (C) and hydrogen (H) debris plasma through preformed, magnetized helium (He) ambient plasma via a variety of diagnostics, including emission spectroscopy, wavelength-filtered imaging, and magnetic field induction probes. Large Doppler shifts detected in a He II ion spectral line directly indicate initial ambient ion acceleration transverse to both the debris plasma flow and the background magnetic field, indicative of a fundamental process known as Larmor coupling. Characterization of the laser-produced debris plasma via a radiation-hydrodynamics code permits an explicit calculation of the laminar electric field in the framework of a ``hybrid'' model (kinetic ions, charge-neutralizing massless fluid electrons), thus allowing for a simulation of the initial response of a distribution of He II test ions. A synthetic Doppler-shifted spectrum constructed from the simulated velocity distribution of the accelerated test ions excellently reproduces the spectroscopic measurements, confirming the role of Larmor coupling in the debris-ambient interaction.

  16. Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating

    CERN Document Server

    Uzdensky, Dmitri A

    2007-01-01

    I propose that solar coronal heating is a self-regulating process that keeps the coronal plasma roughly marginally collisionless. The self-regulating mechanism is based on the interplay of two effects. First, plasma density controls coronal energy release via the transition between the slow collisional Sweet--Parker regime and the fast collisionless reconnection regime. This transition takes place when the Sweet--Parker layer becomes thinner than the characteristic collisionless reconnection scale. I present a simple criterion for this transition in terms of the upstream plasma density and magnetic field and the global length of the reconnection layer. Second, coronal energy release by reconnection raises the ambient plasma density via chromospheric evaporation and this, in turn, temporarily inhibits subsequent reconnection involving the newly-reconnected loops. Over time, however, radiative cooling gradually lowers the density again below the critical value and fast reconnection again becomes possible. As a ...

  17. Experiments on a Miniature Hypervelocity Shock Tube

    Science.gov (United States)

    Tasker, Douglas; Johnson, Carl; Murphy, Michael; Lieber, Mark; MIMS Team

    2013-06-01

    A miniature explosively-driven shock tube, based on the Voitenko compressor design, has been designed to produce shock speeds in light gases in excess of 80 km/s. Voitenko compressors over 1 meter in diameter have been reported but here experiments on miniature shock tubes with ~1-mm bore diameters are described. In this design a 12-mm diameter explosive pellet drives a metal plate into a hemispherical gas compression chamber. Downstream from the piston a mica diaphragm separates the gas from an evacuated shock tube which is confined by a massive polymethylmethacrylate (PMMA) block. The diaphragm eventually ruptures under the applied pressure loading and the compressed gases escape into the evacuated shock tube at hyper velocities. The progress of gas shocks in the tube and bow shocks in the PMMA are monitored with an ultra-high-speed imaging system, the Shock Wave Image Framing Technique (SWIFT). The resulting time-resolved images yield two-dimensional visualizations of shock geometry and progression. By measuring both the gas and bow shocks, accurate and unequivocal measurements of shock position history are obtained. The experimental results were compared with those of hydrocode modeling to optimize the design. The first experiments were suboptimum in that the velocities were ~16 km/s. Progress with these experiments will be reported.

  18. THE EFFECTS OF AREA CONTRACTION ON SHOCK WAVE STRENGTH AND PEAK PRESSURE IN SHOCK TUBE

    Directory of Open Access Journals (Sweden)

    A. M. Mohsen

    2012-06-01

    Full Text Available This paper presents an experimental investigation into the effects of area contraction on shock wave strength and peak pressure in a shock tube. The shock tube is an important component of the short duration, high speed fluid flow test facility, available at the Universiti Tenaga Nasional (UNITEN, Malaysia. The area contraction was facilitated by positioning a bush adjacent to the primary diaphragm section, which separates the driver and driven sections. Experimental measurements were performed with and without the presence of the bush, at various diaphragm pressure ratios, which is the ratio of air pressure between the driver (high pressure and driven (low pressure sections. The instantaneous static pressure variations were measured at two locations close to the driven tube end wall, using high sensitivity pressure sensors, which allow the shock wave strength, shock wave speed and peak pressure to be analysed. The results reveal that the area contraction significantly reduces the shock wave strength, shock wave speed and peak pressure. At a diaphragm pressure ratio of 10, the shock wave strength decreases by 18%, the peak pressure decreases by 30% and the shock wave speed decreases by 8%.

  19. Laboratory studies of stagnating plasma flows with applications to inner solar system and stellar bow shocks

    Science.gov (United States)

    Weber, T. E.; Smith, R. J.; Hsu, S. C.

    2016-10-01

    Supercritical magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe by converting flow kinetic energy to other forms such as thermal and supra-thermal populations, magnetic field enhancement, turbulence, and energetic particles. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those of inner solar system and stellar bow shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to 100s of km/s; resulting in β 1, collisionless plasma flows with Msonic and MAlfvén 10. The drifting FRC can be made to impinge upon a variety of static obstacles including: a strong mirror or cusp magnetic field (mimicking magnetically excited shocks such as the Earth's bow shock), plasma pileup from a solid obstacle (similar to the bow shocks of Mercury and the Moon), and a neural gas puff (bow shocks of Venus or the comets). Characteristic shock length and time scales that are both large enough to observe yet small enough to fit within the experiment, enabling study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental program will be presented, including recent results. This work is supported by the U.S. DOE, Office of Science, Office of Fusion Energy Sciences under Contract No. DE-AC52-06NA25369.

  20. Dislocation structure produced by an ultrashort shock pulse

    Energy Technology Data Exchange (ETDEWEB)

    Matsuda, Tomoki, E-mail: t-matsu@mapse.eng.osaka-u.ac.jp; Hirose, Akio [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Sano, Tomokazu [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); JST, CREST, Suita, Osaka 565-0871 (Japan); Arakawa, Kazuto [JST, CREST, Suita, Osaka 565-0871 (Japan); Department of Material Science, Interdisciplinary Faculty of Science and Engineering, Shimane University, Matsue, Shimane 690-8504 (Japan)

    2014-11-14

    We found an ultrashort shock pulse driven by a femtosecond laser pulse on iron generates a different dislocation structure than the shock process which is on the nanosecond timescale. The ultrashort shock pulse produces a highly dense dislocation structure that varies by depth. According to transmission electron microscopy, dislocations away from the surface produce microbands via a network structure similar to a long shock process, but unlike a long shock process dislocations near the surface have limited intersections. Considering the dislocation motion during the shock process, the structure near the surface is attributed to the ultrashort shock duration. This approach using an ultrashort shock pulse will lead to understanding the whole process off shock deformation by clarifying the early stage.

  1. Turbulent transport in 2D collisionless guide field reconnection

    Science.gov (United States)

    Muñoz, P. A.; Büchner, J.; Kilian, P.

    2017-02-01

    Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic

  2. Advances in Fluid Modeling of the Solar Wind. Part 1: Electron and Anisotropic Proton Temperatures from the Collisionless Dissipation of Alfven Wave Turbulence

    CERN Document Server

    Chandran, Benjamin D G; Quataert, Eliot; Bale, Stuart D

    2011-01-01

    We develop a 1D solar-wind model that includes separate energy equations for the electrons and protons, proton temperature anisotropy, collisional and collisionless heat flux, and an analytical treatment of low-frequency, reflection-driven, Alfven-wave turbulence. To partition the turbulent heating between electron heating, parallel proton heating, and perpendicular proton heating, we employ results from the theories of linear wave damping and nonlinear stochastic heating. We account for mirror and oblique firehose instabilities by increasing the proton pitch-angle scattering rate when the proton temperature anisotropy exceeds the threshold for either instability. We numerically integrate the equations of the model forward in time until a steady state is reached, focusing on two fast-solar-wind-like solutions. These solutions are consistent with a number of observations, supporting the idea that Alfven-wave turbulence plays an important role in the origin of the solar wind.

  3. [Neurogenic shock].

    Science.gov (United States)

    Meister, Rafael; Pasquier, Mathieu; Clerc, David; Carron, Pierre-Nicolas

    2014-08-13

    The neurogenic shock is a common complication of spinal cord injury, especially when localized at the cervical level. Characterized by a vasoplegia (hypotension) and bradycardia, the neurogenic shock is secondary to the damage of the sympathetic nervous system. The clinical presentation often includes tetraplegia, with or without respiratory failure. Early treatment aims to minimize the occurrence of secondary spinal cord lesions resulting from systemic ischemic injuries. Medical management consists in a standardized ABCDE approach, in order to stabilize vital functions and immobilize the spine. The hospital care includes performing imaging, further measures of neuro-resuscitation, and coordinated surgical assessment and treatment of any other injury.

  4. High pressure generation by laser driven shock waves: application to equation of state measurement; Generation de hautes pressions par choc laser: application a la mesure d'equations d'etat

    Energy Technology Data Exchange (ETDEWEB)

    Benuzzi, A

    1997-12-15

    This work is dedicated to shock waves and their applications to the study of the equation of state of compressed matter.This document is divided into 6 chapters: 1) laser-produced plasmas and abrasion processes, 2) shock waves and the equation of state, 3) relative measuring of the equation of state, 4) comparison between direct and indirect drive to compress the target, 5) the measurement of a new parameter: the shock temperature, and 6) control and measurement of the pre-heating phase. In this work we have reached relevant results, we have shown for the first time the possibility of generating shock waves of very high quality in terms of spatial distribution, time dependence and of negligible pre-heating phase with direct laser radiation. We have shown that the shock pressure stays unchanged as time passes for targets whose thickness is over 10 {mu}m. A relative measurement of the equation of state has been performed through the simultaneous measurement of the velocity of shock waves passing through 2 different media. The great efficiency of the direct drive has allowed us to produce pressures up to 40 Mbar. An absolute measurement of the equation of state requires the measurement of 2 parameters, we have then performed the measurement of the colour temperature of an aluminium target submitted to laser shocks. A simple model has been developed to infer the shock temperature from the colour temperature. The last important result is the assessment of the temperature of the pre-heating phase that is necessary to know the media in which the shock wave propagates. The comparison of the measured values of the reflectivity of the back side of the target with the computed values given by an adequate simulation has allowed us to deduce the evolution of the temperature of the pre-heating phase. (A.C.)

  5. Higher-Order Corrections to Earthʼs Ionosphere Shocks

    Science.gov (United States)

    Abdelwahed, H. G.; El-Shewy, E. K.

    2017-01-01

    Nonlinear shock wave structures in unmagnetized collisionless viscous plasmas composed fluid of positive (negative) ions and nonthermally electron distribution are examined. For ion shock formation, a reductive perturbation technique applied to derive Burgers equation for lowest-order potential. As the shock amplitude decreasing or enlarging, its steepness and velocity deviate from Burger equation. Burgers type equation with higher order dissipation must be obtained to avoid this deviation. Solution for the compined two equations has been derived using renormalization analysis. Effects of higher-order, positive- negative mass ratio Q, electron nonthermal parameter δ and kinematic viscosities coefficient of positive (negative) ions {η }1 and {η }2 on the electrostatic shocks in Earth’s ionosphere are also argued. Supported by the Deanship of Scientific Research at Prince Sattam Bin Abdulaziz University under the Research Project No. 2015/01/4787

  6. Erratum: A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma

    Science.gov (United States)

    Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex

    2011-01-01

    The following describes a list of errata in our paper, "A simple, analytical model of collisionless magnetic reconnection in a pair plasma." It supersedes an earlier erratum. We recently discovered an error in the derivation of the outflow-to-inflow density ratio.

  7. Strong cosmic censorship for T^2-symmetric cosmological spacetimes with collisionless matter

    CERN Document Server

    Dafermos, M; Dafermos, Mihalis; Rendall, Alan D.

    2006-01-01

    We prove strong cosmic censorship for T^2-symmetric cosmological spacetimes (with spatial topology T^3 and vanishing cosmological constant Lambda) with collisionless matter. Gowdy symmetric spacetimes constitute a special case. The formulation of the conjecture is in terms of generic C^2-inextendibility of the metric. Our argument exploits a rigidity property of Cauchy horizons, inherited from Killing fields.

  8. Particle-in-cell simulations of particle energization from low Mach number fast mode shocks

    CERN Document Server

    Park, Jaehong; Blackman, Eric G; Ren, Chuang; Siller, Robert

    2012-01-01

    Astrophysical shocks are often studied in the high Mach number limit but weakly compressive fast shocks can occur in magnetic reconnection outflows and are considered to be a site of particle energization in solar flares. Here we study the microphysics of such perpendicular, low Mach number collisionless shocks using two-dimensional particle-in-cell (PIC) simulations with a reduced ion/electron mass ratio and employ a moving wall boundary method for initial generation of the shock. This moving wall method allows for more control of the shock speed, smaller simulation box sizes, and longer simulation times than the commonly used fixed wall, reflection method of shock formation. Our results, which are independent of the shock formation method, reveal the prevalence shock drift acceleration (SDA) of both electron and ions in a purely perpendicular shock with Alfv\\'en Mach number $M_A=6.8$ and ratio of thermal to magnetic pressure $\\beta=8$. We determine the respective minimum energies required for electrons and ...

  9. Hydrodynamic shocks in microroller suspensions

    Science.gov (United States)

    Delmotte, Blaise; Driscoll, Michelle; Chaikin, Paul; Donev, Aleksandar

    2017-09-01

    We combine experiments, large-scale simulations, and continuum models to study the emergence of coherent structures in a suspension of magnetically driven microrollers sedimented near a floor. Collective hydrodynamic effects are predominant in this system, leading to strong density-velocity coupling. We characterize a uniform suspension and show that density waves propagate freely in all directions in a dispersive fashion. When sharp density gradients are introduced in the suspension, we observe the formation of a shock. Unlike Burgers' shocklike structures observed in other active and driven confined hydrodynamic systems, the shock front in our system has a well-defined finite width and moves rapidly compared to the mean suspension velocity. We introduce a continuum model demonstrating that the finite width of the front is due to far-field nonlocal hydrodynamic interactions and governed by a geometric parameter, the average particle height above the floor.

  10. Lower hybrid waves at the shock front: a reassessment

    Directory of Open Access Journals (Sweden)

    S. N. Walker

    2008-03-01

    Full Text Available The primary process occurring at a collisionless shock is the redistribution of the bulk upstream energy into other degrees of freedom. One part of this process results in the acceleration of electrons at the shock front. Accelerated electrons are observed at the terrestrial and other planetary shocks, comets, and their effects are observed in astrophysical phenomena such as supernova remnants and jets in the form of X-ray bremsstrahlung radiation. One of the physical models for electron acceleration at supercritical shocks is based on low-hybrid turbulence due to the presence of reflected ions in the foot region. Since lower hybrid waves propagate almost perpendicular to the magnetic field they can be simultaneously in resonance with both the unmagnetised ions (ω=Vik and magnetised electrons (ω=Vek||. In this paper, Cluster observations of the electric field are used to study the occurrence of lower hybrid waves in the front of the terrestrial bow shock. It is shown that the lower hybrid waves exist as isolated wave packets. However, the very low level of the observed lower hybrid turbulence is too small to impart significant energisation to the electron population.

  11. Particle acceleration, magnetization and radiation in relativistic shocks

    CERN Document Server

    Derishev, Evgeny V

    2015-01-01

    What are the mechanisms of particle acceleration and radiation, as well as magnetic field build up and decay in relativistic shocks are open questions with important implications to various phenomena in high energy astrophysics. While the Weibel instability is possibly responsible for magnetic field build up and diffusive shock acceleration is a model for acceleration, both have problems and current PIC simulation show that particles are accelerated only under special conditions and the magnetic field decays on a short length scale. We present here a novel model for the structure and the emission of highly relativistic collisionless shocks. The model takes into account (and is based on) non-local energy and momentum transport across the shock front via emission and absorption of high-energy photons. This leads to a pre-acceleration of the fluid and pre-amplificaiton of the magnetic fields in the upstream region. Both have drastic implications on the shock structure. The model explains the persistence of the s...

  12. Intrinsic rotation drive by collisionless trapped electron mode turbulence

    CERN Document Server

    Wang, Lu; Diamond, P H

    2016-01-01

    Both the parallel residual stress and parallel turbulent acceleration driven by electrostatic collisionsless trapped electron mode (CTEM) turbulence are calculated analytically using gyrokinetic theory. Quasilinear results show that the parallel residual stress contributes an outward flux of co-current rotation for normal magnetic shear and turbulence intensity profile increasing outward. This may induce intrinsic counter-current rotation or flattening of the co-current rotation profile. The parallel turbulent acceleration driven by CTEM turbulence vanishes, due to the absence of a phase shift between density fluctuation and ion pressure fluctuation. This is different from the case of ion temperature gradient (ITG) turbulence, for which the turbulent acceleration can provide co-current drive for normal magnetic shear and turbulence intensity profile increasing outward. Its order of magnitude is predicted to be the same as that of the divergence of the residual stress [Lu Wang and P.H. Diamond, Phys. Rev. Lett...

  13. Culture Shock

    Institute of Scientific and Technical Information of China (English)

    宋文玲

    2004-01-01

    Specialists say that it is not easy to get used to life in a new culture.“Culture shock”is the term these specialists use when talking about the feelings that people have in a new environment.There are three stages of culture shock,say the specialists.In the first stage,the newcomers like their new environment,Then when the fresh experience

  14. Shock Waves

    CERN Document Server

    Jiang, Z

    2005-01-01

    The International Symposium on Shock Waves (ISSW) is a well established series of conferences held every two years in a different location. A unique feature of the ISSW is the emphasis on bridging the gap between physicists and engineers working in fields as different as gas dynamics, fluid mechanics and materials sciences. The main results presented at these meetings constitute valuable proceedings that offer anyone working in this field an authoritative and comprehensive source of reference.

  15. Experimental investigation of collisionless electron-electron microinstabilities. Final technical report for the period August 1, 1997-October 31, 2000

    Energy Technology Data Exchange (ETDEWEB)

    Scime, Earl E. [West Virginia Univ., Morgantown, WV (United States)

    2000-12-11

    This is the final report for the Office of Fusion Energy sponsored project entitled, "Experimental Investigation of Collisionless Electron-Electron Microinstabilities." The report summarizes the scientific and human resource development accomplishments supported through this project.

  16. Condensate Accretion in Shock Tube's Expansion Fan

    Science.gov (United States)

    Mezonlin, Ephrem-Denis; DeSilva, Upul P.; Hunte, F.; Johnson, Joseph A., III

    1997-01-01

    It has been shown that turbulence and temperature influence the droplet sizes in expansion fan induced condensation by studying the Rayleigh scattering from one port in our shock tube's test section. We have modified our set-up so as to allow, using two ports, the real time measurement of the influence of turbulence and temperature on the rate at which these droplets grow. To do this, we looked at the Rayleigh scattering from two different ports for ten Reynolds numbers at five different temperatures. We modeled the time of flight of droplets, using the equations of one-dimensional gas dynamics and the measured shock wave speed in shock tube's driven section.

  17. [Definition of shock types].

    Science.gov (United States)

    Adams, H A; Baumann, G; Gänsslen, A; Janssens, U; Knoefel, W; Koch, T; Marx, G; Müller-Werdan, U; Pape, H C; Prange, W; Roesner, D; Standl, T; Teske, W; Werner, G; Zander, R

    2001-11-01

    Definitions of shock types. Hypovolaemic shock is a state of insufficient perfusion of vital organs with consecutive imbalance of oxygen supply and demand due to an intravascular volume deficiency with critically impaired cardiac preload. Subtypes are haemorrhagic shock, hypovolaemic shock in the narrow sense, traumatic-haemorrhagic shock and traumatic-hypovolaemic shock. Cardiac shock is caused by a primary critical cardiac pump failure with consecutive inadequate oxygen supply of the organism. Anaphylactic shock is an acute failure of blood volume distribution (distributive shock) and caused by IgE-dependent, type-I-allergic, classical hypersensibility, or a physically, chemically, or osmotically induced IgE-independent anaphylactoid hypersensibility. The septic shock is a sepsis-induced distribution failure of the circulating blood volume in the sense of a distributive shock. The neurogenic shock is a distributive shock induced by generalized and extensive vasodilatation with consecutive hypovolaemia due to an imbalance of sympathetic and parasympathetic regulation of vascular smooth muscles.

  18. Ion-acoustic shocks with self-regulated ion reflection and acceleration

    Science.gov (United States)

    Malkov, M. A.; Sagdeev, R. Z.; Dudnikova, G. I.; Liseykina, T. V.; Diamond, P. H.; Papadopoulos, K.; Liu, C.-S.; Su, J. J.

    2016-04-01

    An analytic solution describing an ion-acoustic collisionless shock, self-consistently with the evolution of shock-reflected ions, is obtained. The solution extends the classic soliton solution beyond a critical Mach number, where the soliton ceases to exist because of the upstream ion reflection. The reflection transforms the soliton into a shock with a trailing wave and a foot populated by the reflected ions. The solution relates parameters of the entire shock structure, such as the maximum and minimum of the potential in the trailing wave, the height of the foot, as well as the shock Mach number, to the number of reflected ions. This relation is resolvable for any given distribution of the upstream ions. In this paper, we have resolved it for a simple "box" distribution. Two separate models of electron interaction with the shock are considered. The first model corresponds to the standard Boltzmannian electron distribution in which case the critical shock Mach number only insignificantly increases from M ≈1.6 (no ion reflection) to M ≈1.8 (substantial reflection). The second model corresponds to adiabatically trapped electrons. They produce a stronger increase, from M ≈3.1 to M ≈4.5 . The shock foot that is supported by the reflected ions also accelerates them somewhat further. A self-similar foot expansion into the upstream medium is described analytically.

  19. The evolution of a spatially homogeneous and isotropic universe filled with a collisionless gas

    CERN Document Server

    Astorga, Francisco; Zannias, Thomas

    2014-01-01

    We review the evolution of a spatially homogeneous and isotropic universe described by a Friedmann-Robertson-Walker spacetime filled with a collisionless, neutral, simple, massive gas. The gas is described by a one-particle distribution function which satisfies the Liouville equation and is assumed to be homogeneous and isotropic. Making use of the isometries of the spacetime, we define precisely the homogeneity and isotropicity property of the distribution function, and based on this definition we give a concise derivation of the most general family of such distribution functions. For this family, we construct the particle current density and the stress-energy tensor and consider the coupled Einstein-Liouville system of equations. We find that as long as the distribution function is collisionless, homogenous and isotropic, the evolution of a Friedmann-Robertson-Walker universe exhibits a singular origin. Its future development depends upon the curvature of the spatial sections: spatially flat or hyperboloid ...

  20. Turbulence in collisionless plasmas: statistical analysis from numerical simulations with pressure anisotropy

    CERN Document Server

    Kowal, Grzegorz; Lazarian, A

    2010-01-01

    In the past years we have experienced an increasing interest in understanding of the physical properties of collisionless plasmas, mostly because of the large number of astrophysical environments, e.g. the intracluster medium (ICM), containing magnetic fields which are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions a new class of kinetic instabilities arises, such as firehose and mirror ones, which were extensively studied in the literature. Their role in the turbulence evolution and cascade process in the presence of pressure anisotropy, however, is still unclear. In this work we present the first statistical analysis of turbulence in collisionless plasmas using three dimensional double isothermal magnetohydrodynamical with the Chew-Goldberger-Low closure (CGL-MHD) numerical simulations. We study models with different initial conditions to account for th...

  1. Time-of-flight expansion of trapped dipolar Fermi gases: from collisionless to hydrodynamic regime

    CERN Document Server

    Veljic, Vladimir; Pelster, Axel

    2016-01-01

    A recent time-of-flight (TOF) expansion experiment with polarized fermionic erbium atoms measured a Fermi surface deformation from a sphere to an ellipsoid due to dipole-dipole interaction, thus confirming previous theoretical predictions. Here we perform a systematic study of the ground-state properties and TOF dynamics for trapped dipolar Fermi gases from the collisionless to the hydrodynamic regime at zero temperature. To this end we solve analytically the underlying Boltzmann-Vlasov equation within the relaxation-time approximation in the vicinity of equilibrium by using a suitable rescaling of the equilibrium distribution. The resulting ordinary differential equations for the respective scaling parameters are then solved numerically for experimentally realistic parameters and relaxation times that correspond to the collisionless, collisional, and hydrodynamic regime. The equations for the collisional regime are first solved in the approximation of a fixed relaxation time, and then this approach is extend...

  2. Quasilinear theory of collisionless Fermi acceleration in a multicusp magnetic confinement geometry

    Science.gov (United States)

    Dewar, R. L.; Ciubotariu, C. I.

    1999-12-01

    Particle motion in a cylindrical multiple-cusp magnetic field configuration is shown to be highly (though not completely) chaotic, as expected by analogy with the Sinai billiard. This provides a collisionless, linear mechanism for phase randomization during monochromatic wave heating. A general quasilinear theory of collisionless energy diffusion is developed for particles with a Hamiltonian of the form H0+H1, motion in the unperturbed Hamiltonian H0 being assumed chaotic, while the perturbation H1 can be coherent (i.e., not stochastic). For the multicusp geometry, two heating mechanisms are identified-cyclotron resonance heating of particles temporarily mirrortrapped in the cusps, and nonresonant heating of nonadiabatically reflected particles (the majority). An analytically solvable model leads to an expression for a transit-time correction factor, exponentially decreasing with increasing frequency. The theory is illustrated using the geometry of a typical laboratory experiment.

  3. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta

    Energy Technology Data Exchange (ETDEWEB)

    Allanson, O., E-mail: oliver.allanson@st-andrews.ac.uk; Neukirch, T., E-mail: tn3@st-andrews.ac.uk; Wilson, F., E-mail: fw237@st-andrews.ac.uk; Troscheit, S., E-mail: s.troscheit@st-andrews.ac.uk [School of Mathematics and Statistics, University of St Andrews, St. Andrews, KY16 9SS (United Kingdom)

    2015-10-15

    We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely, the force-free Harris sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.

  4. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta

    CERN Document Server

    Allanson, O; Wilson, F; Troscheit, S

    2015-01-01

    We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely the Force-Free Harris Sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite Polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.

  5. Accretion of a relativistic, collisionless kinetic gas into a Schwarzschild black hole

    CERN Document Server

    Rioseco, Paola

    2016-01-01

    We provide a systematic study for the accretion of a collisionless, relativistic kinetic gas into a nonrotating black hole. To this end, we first solve the relativistic Liouville equation on a Schwarzschild background spacetime. The most general solution for the distribution function is given in terms of appropriate symplectic coordinates on the cotangent bundle, and the associated observables, including the particle current density and stress energy-momentum tensor, are determined. Next, we explore the case where the flow is steady-state and spherically symmetric. Assuming that in the asymptotic region the gas is described by an equilibrium distribution function, we determine the relevant parameters of the accretion flow as a function of the particle density and the temperature of the gas at infinity. In particular, we find that in the low temperature limit the tangential pressure at the horizon is about an order of magnitude larger than the radial one, showing explicitly that a collisionless gas, despite ex...

  6. Collisionless damping of dust-acoustic waves in a charge varying dusty plasma with nonextensive ions

    Energy Technology Data Exchange (ETDEWEB)

    Amour, Rabia; Tribeche, Mouloud [Faculty of Physics, Theoretical Physics Laboratory (TPL), Plasma Physics Group (PPG), University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria)

    2014-12-15

    The charge variation induced nonlinear dust-acoustic wave damping in a charge varying dusty plasma with nonextensive ions is considered. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust acoustic wave propagation to be described by a damped Korteweg-de Vries (dK-dV) equation the coefficients of which depend sensitively on the nonextensive parameter q. The damping term, solely due to the dust charge variation, is affected by the ion nonextensivity. For the sake of completeness, the possible effects of nonextensivity and collisionless damping on weakly nonlinear wave packets described by the dK-dV equation are succinctly outlined by deriving a nonlinear Schrödinger-like equation with a complex nonlinear coefficient.

  7. Self-Regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition

    CERN Document Server

    Uzdensky, Dmitri A

    2007-01-01

    I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly-reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nano-flares), evaporation episodes, and long periods of slow magnetic stress build-up and radiative cooling of the coronal plasma.

  8. Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations

    CERN Document Server

    Klein, Kristopher G

    2016-01-01

    An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both estimates the local rate of energy transfer f...

  9. Fast magnetic field amplification in the early Universe: growth of collisionless plasma instabilities in turbulent media

    CERN Document Server

    Falceta-Goncalves, D

    2015-01-01

    In this work we report a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that i) amplification of magnetic field was efficient in firehose unstable turbulent regimes, but not in the mirror unstable models, ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo, iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales with pressure anisotropy ratio is confirmed by the numerical simulations. These results reinforce the idea that pres...

  10. Shock induced cavity collapse

    Science.gov (United States)

    Skidmore, Jonathan; Doyle, Hugo; Tully, Brett; Betney, Matthew; Foster, Peta; Ringrose, Tim; Ramasamy, Rohan; Parkin, James; Edwards, Tom; Hawker, Nicholas

    2016-10-01

    Results from the experimental investigation of cavity collapse driven by a strong planar shock (>6km/s) are presented. Data from high speed framing cameras, laser backlit diagnostics and time-resolved pyromety are used to validate the results of hydrodynamic front-tracking simulations. As a code validation exercise, a 2-stage light gas gun was used to accelerate a 1g Polycarbonate projectile to velocities exceeding 6km/s; impact with a PMMA target containing a gas filled void results in the formation of a strong shockwave with pressures exceeding 1Mbar. The subsequent phenomena associated with the collapse of the void and excitation of the inert gas fill are recorded and compared to simulated data. Variation of the mass density and atomic number of the gas fill is used to alter the plasma parameters furthering the extent of the code validation.

  11. Localized shocks

    CERN Document Server

    Roberts, Daniel A; Susskind, Leonard

    2014-01-01

    We study products of precursors of spatially local operators, $W_{x_{n}}(t_{n}) ... W_{x_1}(t_1)$, where $W_x(t) = e^{-iHt} W_x e^{iHt}$. Using chaotic spin-chain numerics and gauge/gravity duality, we show that a single precursor fills a spatial region that grows linearly in $t$. In a lattice system, products of such operators can be represented using tensor networks. In gauge/gravity duality, they are related to Einstein-Rosen bridges supported by localized shock waves. We find a geometrical correspondence between these two descriptions, generalizing earlier work in the spatially homogeneous case.

  12. INVESTIGATION ON NONEQULIBRIUM RADIATION AND RELAXATION PHENOMENA IN SHOCK TUBES

    Institute of Scientific and Technical Information of China (English)

    竺乃宜; 杨乾锁; 张恒利; 余西龙; 黄立舜

    2003-01-01

    The experimental results for the excited time of the nonequlibrium radiation andthe ionization behind strong shock waves are presented. Using an optical multichannel analyzer, InSb infrared detectors and near-free-molecular Langmuir probes, the infrared radiation, the electron density of air and the nonequlibrium radiation spectra at different moments of the relaxation process in nitrogen test gas behind normal shock waves were obtained, respectively, in hydrogen oxygen combustion driven shock tubes.

  13. Observation of ion acceleration and heating during collisionless magnetic reconnection in a laboratory plasma.

    Science.gov (United States)

    Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Myers, Clayton E

    2013-05-24

    The ion dynamics in a collisionless magnetic reconnection layer are studied in a laboratory plasma. The measured in-plane plasma potential profile, which is established by electrons accelerated around the electron diffusion region, shows a saddle-shaped structure that is wider and deeper towards the outflow direction. This potential structure ballistically accelerates ions near the separatrices toward the outflow direction. Ions are heated as they travel into the high-pressure downstream region.

  14. The equilibrium probability distribution of a conductive sphere's floating charge in a collisionless, drifting Maxwellian plasma

    CERN Document Server

    Thomas, Drew M

    2013-01-01

    A dust grain in a plasma has a fluctuating electric charge, and past work concludes that spherical grains in a stationary, collisionless plasma have an essentially Gaussian charge probability distribution. This paper extends that work to flowing plasmas and arbitrarily large spheres, deriving analytic charge probability distributions up to normalizing constants. We find that these distributions also have good Gaussian approximations, with analytic expressions for their mean and variance.

  15. Collisionless stopping of electron current in an inhomogeneous electron magnetohydrodynamics plasma

    Indian Academy of Sciences (India)

    Amita Das; Sharad K Yadav; Predhiman Kaw; Sudip Sengupta

    2011-11-01

    A brief review of a recent work on a novel collisionless scheme for stopping electron current pulse in plasma is presented. This scheme relies on the inhomogeneity of the plasma medium. This mechanism can be used for heating an overdense regime of plasma where lasers cannot penetrate. The method can ensure efficient localized heating at a desired location. The suitability of the scheme to the frontline fast ignition laser fusion experiment has been illustrated.

  16. Laboratory study of collisionless coupling between explosive debris plasma and magnetized ambient plasma

    Science.gov (United States)

    Bondarenko, A. S.; Schaeffer, D. B.; Everson, E. T.; Clark, S. E.; Lee, B. R.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Winske, D.; Niemann, C.

    2017-08-01

    The explosive expansion of a localized plasma cloud into a relatively tenuous, magnetized, ambient plasma characterizes a variety of astrophysical and space phenomena. In these rarified environments, collisionless electromagnetic processes rather than Coulomb collisions typically mediate the transfer of momentum and energy from the expanding "debris" plasma to the surrounding ambient plasma. In an effort to better understand the detailed physics of collisionless coupling mechanisms, compliment in situ measurements of space phenomena, and provide validation of previous computational and theoretical work, the present research jointly utilizes the Large Plasma Device and the Raptor laser facility at the University of California, Los Angeles to study the super-Alfvénic, quasi-perpendicular expansion of laser-produced carbon (C) and hydrogen (H) debris plasma through preformed, magnetized helium (He) ambient plasma via a variety of diagnostics, including emission spectroscopy, wavelength-filtered imaging, and a magnetic flux probe. Doppler shifts detected in a He1+ ion spectral line indicate that the ambient ions initially accelerate transverse to both the debris plasma flow and the background magnetic field. A qualitative analysis in the framework of a "hybrid" plasma model (kinetic ions and inertia-less fluid electrons) demonstrates that the ambient ion trajectories are consistent with the large-scale laminar electric field expected to develop due to the expanding debris. In particular, the transverse ambient ion motion provides direct evidence of Larmor coupling, a collisionless momentum exchange mechanism that has received extensive theoretical and numerical investigation. In order to quantitatively evaluate the observed Doppler shifts, a custom simulation utilizing a detailed model of the laser-produced debris plasma evolution calculates the laminar electric field and computes the initial response of a distribution of ambient test ions. A synthetic Doppler

  17. Type II Shocks Characteristics: Comparison with associated CMEs and Flares

    CERN Document Server

    Pothitakis, G; Preka-Papadema, P; Moussas, X; Caroubalos, C; Alissandrakis, C E; Hillaris, A; Tsitsipis, P; Kontogeorgos, A; Bougeret, J -L; Dumas, G; 10.1063/1.2347985

    2010-01-01

    A number of metric (100-650 MHz) typeII bursts was recorded by the ARTEMIS-IV radiospectrograph in the 1998-2000 period; the sample includes both CME driven shocks and shocks originating from flare blasts. We study their characteristics in comparison with characteristics of associated CMEs and flares.

  18. Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations

    Science.gov (United States)

    Klein, K. G.; Howes, G. G.

    2016-08-01

    An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.

  19. Quasi-Separatrix Layers and Line-tied Reconnection in Collisionless Plasmas

    Science.gov (United States)

    Billey, Zachary; Zweibel, Ellen; Finn, John; Daughton, William

    2015-11-01

    Many plasmas undergoing magnetic reconnection have boundaries that have constant magnetic flux on the dynamical timescales of the system, such as coronal loops and planetary magnetospheres. Systems where the boundary magnetic flux is constant are called line-tied systems. We conduct collisionless fully 3D particle-in-cell simulations in slab geometry to study how line-tying changes the dynamics relative non-tied systems. We confirm Quasi-Separatrix Layers (QSLs) as a model for predicting potential reconnection sites in 3D systems. Based on this theory, we use line-integrated diagnostics to investigate the collisionless physics relating to the parallel electric field. Here we find non-gyrotopic terms in the pressure tensor are important at the center of the reconnection layer. We investigate the effect of varying the length of the line-tied plasma on the growth rate and reconnection process and compare oblique modes with equivalent periodic systems. We discuss the extension into collisionless regimes of the geometric width vs tearing width theory, developed to explain line-tied suppression of tearing in MHD reconnection. Work supported by the NSF and U.S. DoE through CMSO.

  20. Effects of laser polarizations on shock generation and shock ion acceleration in overdense plasmas

    Science.gov (United States)

    Kim, Young-Kuk; Kang, Teyoun; Jung, Moon Youn; Hur, Min Sup

    2016-09-01

    The effects of laser-pulse polarization on the generation of an electrostatic shock in an overdense plasma were investigated using particle-in-cell simulations. We found, from one-dimensional simulations, that total and average energies of reflected ions from a circular polarization- (CP) driven shock front are a few times higher than those from a linear polarization- (LP) driven one for a given pulse energy. Moreover, it was discovered that the pulse transmittance is the single dominant factor for determining the CP-shock formation, while the LP shock is affected by the plasma scale length as well as the transmittance. In two-dimensional simulations, it is observed that the transverse instability, such as Weibel-like instability, can be suppressed more efficiently by CP pulses.