Injection into electron plasma traps

International Nuclear Information System (INIS)

Gorgadze, Vladimir; Pasquini, Thomas A.; Fajans, Joel; Wurtele, Jonathan S.

2003-01-01

Computational studies and experimental measurements of plasma injection into a Malmberg-Penning trap reveal that the number of trapped particles can be an order of magnitude higher than predicted by a simple estimates based on a ballistic trapping model. Enhanced trapping is associated with a rich nonlinear dynamics generated by the space-charge forces of the evolving trapped electron density. A particle-in-cell simulation is used to identify the physical mechanisms that lead to the increase in trapped electrons. The simulations initially show strong two-stream interactions between the electrons emitted from the cathode and those reflected off the end plug of the trap. This is followed by virtual cathode oscillations near the injection region. As electrons are trapped, the initially hollow longitudinal phase-space is filled, and the transverse radial density profile evolves so that the plasma potential matches that of the cathode. Simple theoretical arguments are given that describe the different dynamical regimes. Good agreement is found between simulation and theory

THE EFFECT OF LARGE-SCALE MAGNETIC TURBULENCE ON THE ACCELERATION OF ELECTRONS BY PERPENDICULAR COLLISIONLESS SHOCKS

International Nuclear Information System (INIS)

Guo Fan; Giacalone, Joe

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 two-dimensional hybrid simulations (kinetic ions and 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 occurring 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 injection problem for electron acceleration by collisionless shocks. It is also shown that the spatial distribution of energetic electrons is similar to in situ observations. The process may be important to our understanding of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures seen in some type II solar radio bursts.

The inversion layer of electric fields and electron phase-space-hole structure during two-dimensional collisionless magnetic reconnection

International Nuclear Information System (INIS)

Chen Lijen; Lefebvre, Bertrand; Torbert, Roy B.; Daughton, William S.

2011-01-01

Based on two-dimensional fully kinetic simulations that resolve the electron diffusion layer in undriven collisionless magnetic reconnection with zero guide field, this paper reports the existence and evolution of an inversion layer of bipolar electric fields, its corresponding phase-space structure (an electron-hole layer), and the implication to collisionless dissipation. The inversion electric field layer is embedded in the layer of bipolar Hall electric field and extends throughout the entire length of the electron diffusion layer. The electron phase-space hole structure spontaneously arises during the explosive growth phase when there exist significant inflows into the reconnection layer, and electrons perform meandering orbits across the layer while being cyclotron-turned toward the outflow directions. The cyclotron turning of meandering electrons by the magnetic field normal to the reconnection layer is shown to be a primary factor limiting the current density in the region where the reconnection electric field is balanced by the gradient (along the current sheet normal) of the off-diagonal electron pressure-tensor.

Electron trapping during irradiation in reoxidized nitrided oxide

International Nuclear Information System (INIS)

Mallik, A.; Vasi, J.; Chandorkar, A.N.

1993-01-01

Isochronal detrapping experiments have been performed following irradiation under different gate biases in reoxidized nitrided oxide (RNO) MOS capacitors. These show electron trapping by the nitridation-induced electron traps at low oxide fields during irradiation. A difference in the detrapping behavior of trapped holes and electrons is observed, with trapped holes being detrapped at relatively lower temperatures compared to trapped electrons. Electron trapping shows a strong dependence on tile magnitude of the applied gate bias during irradiation but is independent of its polarity. Conventional oxide devices, as expected, do not show any electron trapping during irradiation by the native electron traps. Finally, a comparison of the isochronal detrapping behavior following irradiation and following avalanche injection of electrons has been made to estimate the extent of electron trapping. The results show that electron trapping by the nitridation-induced electron traps does not play the dominant role in improving radiation performance of RNO, though its contribution cannot be completely neglected for low oxide field irradiations

New evidence for efficient collisionless heating of electrons at the reverse shock of a young supernova remnant

Energy Technology Data Exchange (ETDEWEB)

Yamaguchi, Hiroya; Petre, Robert [NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Eriksen, Kristoffer A. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 (United States); Badenes, Carles [Department of Physics and Astronomy and Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O' Hara St, Pittsburgh, PA 15260 (United States); Hughes, John P. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Slane, Patrick O.; Smith, Randall K., E-mail: hiroya.yamaguchi@nasa.gov [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2014-01-10

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 Kβ (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 Kα (2p → 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 Kα morphology from the Chandra observations. Since strong Fe Kβ 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.

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.

Neoclassical transport caused by collisionless scattering across an asymmetric separatrix.

Science.gov (United States)

Dubin, Daniel H E; Driscoll, C F; Tsidulko, Yu A

2010-10-29

Plasma loss due to apparatus asymmetries is a ubiquitous phenomenon in magnetic plasma confinement. When the plasma equilibrium has locally trapped particle populations partitioned by a separatrix from one another and from passing particles, the asymmetry transport is enhanced. The trapped and passing particle populations react differently to the asymmetries, leading to the standard 1/ν and sqrt[ν] transport regimes of superbanana orbit theory as particles collisionally scatter from one orbit type to another. However, when the separatrix is itself asymmetric, particles can collisionlessly transit from trapped to passing and back, leading to enhanced transport.

Electron traps in semiconducting polymers : Exponential versus Gaussian trap distribution

NARCIS (Netherlands)

Nicolai, H. T.; Mandoc, M. M.; Blom, P. W. M.

2011-01-01

The low electron currents in poly(dialkoxy-p-phenylene vinylene) (PPV) derivatives and their steep voltage dependence are generally explained by trap-limited conduction in the presence of an exponential trap distribution. Here we demonstrate that the electron transport of several PPV derivatives can

Electron traps in semiconducting polymers: exponential versus Gaussian trap distribution

NARCIS (Netherlands)

Nicolai, H.T.; Mandoc, M.M.; Blom, P.W.M.

2011-01-01

The low electron currents in poly(dialkoxy-p-phenylene vinylene) (PPV) derivatives and their steep voltage dependence are generally explained by trap-limited conduction in the presence of an exponential trap distribution. Here we demonstrate that the electron transport of several PPV derivatives can

Stability of trapped electrons in SiO2

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.; Flament, O.; Leray, J.L.

1998-01-01

Electron trapping near the Si/SiO 2 interface plays a crucial role in mitigating the response of MOS devices to ionizing radiation or high-field stress. These electrons offset positive charge due to trapped holes, and can be present at densities exceeding 10 12 cm -2 in the presence of a similar density of trapped positive charge. The nature of the defects that serve as hosts for trapped electrons in the near-interfacial SiO 2 is presently unknown, although there is compelling evidence that these defects are often intimately associated with trapped holes. This association is depicted most directly in the model of Lelis et al., which suggests that trapped electrons and holes occupy opposite sides of a compensated E center in SiO 2 . Charge exchange between electron traps and the Si can occur over a wide range of time scales, depending on the trap depth and location relative to the Si/SiO 2 interface. Here the authors report a detailed study of the stability of electron traps associated with trapped holes near the Si/SiO 2 interface

Collisionless shock waves

International Nuclear Information System (INIS)

Sagdeev, R.Z.; Kennel, C.F.

1991-01-01

Collisionless shocks cannot occur naturally on the earth, because nearly all matter here consists of electrically neutral atoms and molecules. In space, however, high temperatures and ultraviolet radiation from hot stars decompose atoms into their constituent nuclei and electrons, producing a soup of electrically charged particles known as a plasma. Plasma physicists proposed that the collective electrical and magnetic properties of plasmas could produce interactions that take the place of collisions and permit shocks to form. In 1964 the theoretical work found its first experimental confirmation. Norman F. Ness and his colleagues at the Goddard Space Flight Center, using data collected from the iMP-1 spacecraft, detected clear signs that a collisionless shock exists where the solar wind encounters the earth's magnetic field. More recent research has demonstrated that collisionless shocks appear in a dazzling array of astronomical settings. For example, shocks have been found in the solar wind upstream (sunward) of all the planet and comets that have been visited by spacecraft. Violent flares on the sun generate shocks that propagate to the far reaches of the solar system; tremendous galactic outbursts create disruptions in the intergalactic medium that are trillions of times larger. In addition, many astrophysicists think that shocks from supernova explosions in our galaxy accelerate cosmic rays, a class of extraordinarily energetic elementary particles and atomic nuclei that rain down on the earth from all directions

Stability of Trapped Electrons in SiO(2)

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.

1999-01-01

Thermally stimulated current and capacitance voltage methods are used to investigate the thermal stability of trapped electrons associated with radiation-induced trapped positive charge in metal-oxide-semiconductor capacitors. The density of deeply trapped electrons in radiation-hardened 45 nm oxides exceeds that of shallow electrons by a factor of ∼3 after radiation exposure, and by up to a factor of 10 or more during biased annealing. Shallow electron traps anneal faster than deep traps, and seem to be at least qualitatively consistent with the model of Lelis et al. Deeper traps maybe part of a fundamentally distinct dipole complex, and/or have shifted energy levels that inhibit charge exchange with the Si

A new fast reconnection model in a collisionless regime

International Nuclear Information System (INIS)

Tsiklauri, David

2008-01-01

Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm's law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnetic reconnection in a collisionless regime is formulated. The model is general, resembling its collisional Sweet-Parker analog in that it is not specific to any initial configuration, e.g., Harris-type tearing unstable current sheet, X-point collapse or otherwise. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate [M c ' less =(c/ω pe ) 2 /(r L,e L)] 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 δ c ' less =(c/ω pe ) 2 /r L,e , which is independent of the global reconnection scale L and is only prescribed by microphysics (electron inertial length, c/ω pe , and electron Larmor radius, r L,e ). Amongst other issues, the fastness of the reconnection rate 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 a few minutes, as opposed to Sweet-Parker's equivalent value of less than a day. The new theoretical reconnection rate is compared to the Magnetic Reconnection Experiment device experimental data by Yamada et al. [Phys. Plasmas 13, 052119 (2006)] and Ji et al. [Geophys. Res. Lett. 35, 13106 (2008)], and a good agreement is obtained.

Electron scattering by trapped fermionic atoms

International Nuclear Information System (INIS)

Wang Haijun; Jhe, Wonho

2002-01-01

Considering the Fermi gases of alkali-metal atoms that are trapped in a harmonic potential, we study theoretically the elastic and inelastic scattering of the electrons by the trapped Fermi atoms and present the corresponding differential cross sections. We also obtain the stopping power for the cases that the electronic state as well as the center-of-mass state are excited both separately and simultaneously. It is shown that the elastic scattering process is no longer coherent in contrast to the electron scattering by the atomic Bose-Einstein condensate (BEC). For the inelastic scattering process, on the other hand, the differential cross section is found to be proportional to the 2/3 power of the number of the trapped atoms. In particular, the trapped fermionic atoms display the effect of ''Fermi surface,'' that is, only the energy levels near the Fermi energy have dominant contributions to the scattering process. Moreover, it is found that the stopping power scales as the 7/6 power of the atomic number. These results are fundamentally different from those of the electron scattering by the atomic BEC, mainly due to the different statistics obeyed by the trapped atomic systems

Study on intense relativistic electron beam propagation in a low density collisionless plasma

International Nuclear Information System (INIS)

Korenev, S.A.; Rubin, N.B.; Khodataev, K.V.

1982-01-01

The results of investigations into the increase in effectivity of transport of an intensive relativistic electron beam (IREB) in a collisionless plasma of low density are presented. The electron beam with the current of 1.5 kA, energy of 300 keV, radius of 1.5 cm is in ected into a plasma channel 180 cm long which is a metallic cylinder covered with a biniplast layer from inside 0.5 cm thickness on which there is a metallic net from the vacuum side. Plasma production is carried out during the supply of voltage pulse to the net. A condition of the optimum IREB distribution is found. It is sohwn that self-focusing IREB transport in plasma of low density can be effective if equilibrium conditions are carried out in plasma with the concentration of electrons less (or equal) to the concentration of electrons in a beam

The Inner Structure of Collisionless Magnetic Reconnection: The Electron-Frame Dissipation Measure and Hall Fields

Science.gov (United States)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha

2011-01-01

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron s rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

International Nuclear Information System (INIS)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha

2011-01-01

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

Energy Technology Data Exchange (ETDEWEB)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)

2011-12-15

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

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

Non-thermal particle acceleration in collisionless relativistic electron-proton reconnection

Science.gov (United States)

Werner, G. R.; Uzdensky, D. A.; Begelman, M. C.; Cerutti, B.; Nalewajko, K.

2018-02-01

Magnetic reconnection in relativistic collisionless plasmas can accelerate particles and power high-energy emission in various astrophysical systems. Whereas most previous studies focused on relativistic reconnection in pair plasmas, less attention has been paid to electron-ion plasma reconnection, expected in black hole accretion flows and relativistic jets. We report a comprehensive particle-in-cell numerical investigation of reconnection in an electron-ion plasma, spanning a wide range of ambient ion magnetizations σi, from the semirelativistic regime (ultrarelativistic electrons but non-relativistic ions, 10-3 ≪ σi ≪ 1) to the fully relativistic regime (both species are ultrarelativistic, σi ≫ 1). We investigate how the reconnection rate, electron and ion plasma flows, electric and magnetic field structures, electron/ion energy partitioning, and non-thermal particle acceleration depend on σi. Our key findings are: (1) the reconnection rate is about 0.1 of the Alfvénic rate across all regimes; (2) electrons can form concentrated moderately relativistic outflows even in the semirelativistic, small-σi regime; (3) while the released magnetic energy is partitioned equally between electrons and ions in the ultrarelativistic limit, the electron energy fraction declines gradually with decreased σi and asymptotes to about 0.25 in the semirelativistic regime; and (4) reconnection leads to efficient non-thermal electron acceleration with a σi-dependent power-law index, p(σ _i)˜eq const+0.7σ _i^{-1/2}. These findings are important for understanding black hole systems and lend support to semirelativistic reconnection models for powering non-thermal emission in blazar jets, offering a natural explanation for the spectral indices observed in these systems.

Balmer line diagnostic of electron heating at collisionless shocks in supernova remnants

International Nuclear Information System (INIS)

Rakowski, C.

2008-01-01

The mechanism and extent of electron heating at collisionless shocks has recently been under intense investigation. H α Balmer line emission is excited immediately behind the shock front and provides the best diagnostic for the electron to proton temperature ratio at supernova remnant shocks. Two components of emission are produced, a narrow component from electron and proton impact excitation of cold neutrals, and a broad component produced through charge exchange between the cold neutrals and the shock heated protons. Thus the broad and narrow component fluxes reflect the competition between electron and proton impact ionization, electron and proton impact excitation and charge exchange. This diagnostic has led to the discovery of an approximate inverse square relationship between the electron to proton temperature ratio and the shock velocity. In turn, this implies a constant level of electron heating, independent of shock speed above ∼ 450 km/s. In this talk I will present the observational evidence to date. Time permitting, I will introduce how lower-hybrid waves in an extended cosmic ray precursor could explain such a relationship, and how this and other parameters in the H α profile might relate to properties of cosmic rays and magnetic field amplification ahead of the shock. (author)

Collisionless emission of radiation by an inhomogeneous plasma

International Nuclear Information System (INIS)

Mejerovich, B.Eh.

1976-01-01

Collisionless emission of radiation by an inhomogeneous plasma due to the finite motion of charges in the field of external forces and collective interaction forces is studied. The intensity of the radiation is inversely proportional to the square of the transverse dimensions of the plasma. It apparently makes the main contribution to the radiation from a vacuum spark and other relativitstic beams compressed to a small size by collective interaction forces. The intensity of the collisionless radiation is calculated by taking into account Fermi statistics of the electrons. The spectral radiance in the low frequency range increases with frequency, reaches a maximum at the frequency of the finite motion of the emitters and then decreases. Measurement of collisionless radiation emission by a plasma compressed to a small size by the pinch effect is a natural way of diagnosing the plasma

The generalized Ohm's law in collisionless magnetic reconnection

International Nuclear Information System (INIS)

Cai, H.J.; Lee, L.C.

1997-01-01

The generalized Ohm close-quote s law and the force balance near neutral lines in collisionless magnetic reconnection is studied based on two-dimensional full particle simulations in which the ion endash electron mass ratio is set to be 1836. The off-diagonal elements of a plasma pressure tensor are found to be responsible for the breakdown of the frozen-in condition in collisionless reconnection. While the off-diagonal elements of the electron pressure tensor are dominant terms in the generalized Ohm close-quote s law near neutral lines, the ion off-diagonal pressure terms are of significant importance when ions are main current carriers. The spatial scale of electron off-diagonal pressure term P xy (e) is also found to be proportional to the Dungey length scale, (m e E y /eβ 2 ) 1/3 , where β=∂B z /∂x. copyright 1997 American Institute of Physics

A nonlinear bounce kinetic equation for trapped electrons

International Nuclear Information System (INIS)

Gang, F.Y.

1990-03-01

A nonlinear bounce averaged drift kinetic equation for trapped electrons is derived. This equation enables one to compute the nonlinear response of the trapped electron distribution function in terms of the field-line projection of a potential fluctuation left-angle e -inqθ φ n right-angle b . It is useful for both analytical and computational studies of the nonlinear evolution of short wavelength (n much-gt 1) trapped electron mode-driven turbulence. 7 refs

Collisionless stopping of electron current in an inhomogeneous ...

Indian Academy of Sciences (India)

Ampere's law we can express b in terms of the typical incoming current filament dimension a and the electron velocity u. Thus b ∼ au. This shows that. Q ∼ KLb2aLzu ∼ (L/Ln)aLzu. (9). The energy dissipation depends on the same parameter ratio (Ln/L) which determined the criteria for trapping vs. transmission, noted ...

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...

Novel extension of the trap model for electrons in liquid hydrocarbons

International Nuclear Information System (INIS)

Jamal, M.A.; Watt, D.E.

1981-01-01

A novel extension for the trap model of electron mobilities in liquid hydrocarbons is described. The new model assumes: (a) two main types of electron trap exist in liquid hydrocarbons, one is deep and the second is shallow; (b) these traps are the same in all liquid alkanes. The difference in electron mobilities in different alkanes is accounted for by the difference in the frequency of electron trapping in each state. The probability of trapping in each state has been evaluated from the known structures of the normal alkanes. Electron mobilities in normal alkanes (C 3 -C 10 ) show a very good correlation with the probability of trapping in deep traps, suggesting that the C-C bonds are the main energy sinks of the electron. A mathematical formula which expresses the electron mobility in terms of the probability of trapping in deep traps has been found from the Arrhenius relationship between electron mobilities and probability of trapping. The model has been extended for branched alkanes and the relatively high electron mobilities in globular alkanes has been explained by the fact that each branch provides some degree of screening to the skeleton structure of the molecule resulting in reduction of the probability of electron interaction with the molecular skeleton. (author)

Numerical studies of electron dynamics in oblique quasi-perpendicular collisionless shock waves

International Nuclear Information System (INIS)

Liewer, P.C.; Decyk, V.K.; Dawson, J.M.; Lembege, B.

1991-01-01

Linear and nonlinear electron damping of the whistler precursor wave train to low Mach number quasi-perpendicular oblique shocks is studied using a one-dimensional electromagnetic plasma simulation code with particle electrons and ions. In some parameter regimes, electrons are observed to trap along the magnetic field lines in the potential of the whistler precursor wave train. This trapping can lead to significant electron heating in front of the shock for β e (∼10% or less). Use of the 64-processor Caltech/JPL Mark IIIfp hypercube concurrent computer has enables us to make long runs using realistic mass ratios (m i /m e = 1,600) in the full particle in-cell code and thus simulate shock parameter regimes and phenomena not previously studied numerically

Collisionless magnetic reconnection associated with coalescence of flux bundles

International Nuclear Information System (INIS)

Tanaka, Motohiko.

1994-11-01

The basic process of collisionless reconnection is studied in terms of coalescence of magnetized flux bundles using an implicit particle simulation of two-dimensions. The toroidal electric field that directly relates to magnetic reconnection is generated solenoidally in a region much broader than the current sheet whose width is a few electron skin depths. The reconnected flux increases linearly in time, but it is insensitive to finite Larmor radii of the ions in this Sweet-Parker regime. The toroidal electric field is controlled by a balance of transit acceleration of finite-mass electrons and their removal by sub-Alfvenic E x B drift outflow. The simulation results supports the collisionless Ohm's law E t ≅η eq J t with η eq the inertia resistivity. (author)

Electron Cooling of Protons in a Nested Penning Trap

International Nuclear Information System (INIS)

Hall, D.S.; Gabrielse, G.

1996-01-01

Trapped protons cool via collisions with trapped electrons at 4 K.This first demonstration of sympathetic cooling by trapped species of opposite sign of charge utilizes a nested Penning trap. The demonstrated interaction of electrons and protons at very low relative velocities, where recombination is predicted to be most rapid, indicates that this may be a route towards the study of low temperature recombination. The production of cold antihydrogen is of particular interest, and electron cooling of highly stripped ions may also be possible. copyright 1996 The American Physical Society

Study on the intense relativistic electron beam propagation in a collisionless plasma of small density

International Nuclear Information System (INIS)

Korenev, S.A.; Rubin, N.B.; Khodataev, K.V.

1982-01-01

The results of the experimental studies of the intense relativistic electron beam (IREB) propagation with ν/γ approximately 0.1, and γ approximately 1.6 (γ is an electron beam relativistic factor) in a collisionless plasma of small density over the 180 cm length are presented. Plasma is generated with the incomplete discharge over dielectric surface at the residual gas pressure of P approximately 10 -5 Torr. It is shown that the transportation efficiency may be essentially high, if the electron concentration in plasma satisfies the equilibrium conditions and if it is less or equal to the electron concentration in a beam. At concentration less than optimum one, the transportation efficiency decreases due to violations of equilibrium conditions. At high concentration the transportation efficiency also decreased due to the scattering and breaking on excited small-scale and plasma oscillations. The IREB propagation occurs without essential time delay under optimum conditions

Gyrokinetic Electron and Fully Kinetic Ion Particle Simulation of Collisionless Plasma Dynamics

Energy Technology Data Exchange (ETDEWEB)

Yu Lin; Xueyi Wang; Liu Chen; Zhihong Lin

2009-08-11

Fully kinetic-particle simulations and hybrid simulations have been utilized for decades to investigate various fundamental plasma processes, such as magnetic reconnection, fast compressional waves, and wave-particle interaction. Nevertheless, due to disparate temporal and spatial scales between electrons and ions, existing fully kinetic-particle codes have to employ either unrealistically high electron-to-ion mass ratio, me/mi, or simulation domain limited to a few or a few ten's of the ion Larmor radii, or/and time much less than the global Alfven time scale in order to accommodate available computing resources. On the other hand, in the hybrid simulation, the ions are treated as fully kinetic particles but the electrons are treated as a massless fluid. The electron kinetic effects, e.g., wave-particle resonances and finite electron Larmor radius effects, are completely missing. Important physics, such as the electron transit time damping of fast compressional waves or the triggering mechanism of magnetic reconnection in collisionless plasmas is absent in the hybrid codes. Motivated by these considerations and noting that dynamics of interest to us has frequencies lower than the electron gyrofrequency, we planned to develop an innovative particle simulation model, gyrokinetic (GK) electrons and fully kinetic (FK) ions. In the GK-electron and FK-ion (GKe/FKi) particle simulation model, the rapid electron cyclotron motion is removed, while keeping finite electron Larmor radii, realistic me/mi ratio, wave-particle interactions, and off-diagonal components of electron pressure tensor. The computation power can thus be significantly improved over that of the full-particle codes. As planned in the project DE-FG02-05ER54826, we have finished the development of the new GK-electron and FK-ion scheme, finished its benchmark for a uniform plasma in 1-D, 2-D, and 3-D systems against linear waves obtained from analytical theories, and carried out a further convergence

Gyrokinetic Electron and Fully Kinetic Ion Particle Simulation of Collisionless Plasma Dynamics

International Nuclear Information System (INIS)

Lin, Yu; Wang, Xueyi; Chen, Liu; Lin, Zhihong

2009-01-01

Fully kinetic-particle simulations and hybrid simulations have been utilized for decades to investigate various fundamental plasma processes, such as magnetic reconnection, fast compressional waves, and wave-particle interaction. Nevertheless, due to disparate temporal and spatial scales between electrons and ions, existing fully kinetic-particle codes have to employ either unrealistically high electron-to-ion mass ratio, me/mi, or simulation domain limited to a few or a few ten's of the ion Larmor radii, or/and time much less than the global Alfven time scale in order to accommodate available computing resources. On the other hand, in the hybrid simulation, the ions are treated as fully kinetic particles but the electrons are treated as a massless fluid. The electron kinetic effects, e.g., wave-particle resonances and finite electron Larmor radius effects, are completely missing. Important physics, such as the electron transit time damping of fast compressional waves or the triggering mechanism of magnetic reconnection in collisionless plasmas is absent in the hybrid codes. Motivated by these considerations and noting that dynamics of interest to us has frequencies lower than the electron gyrofrequency, we planned to develop an innovative particle simulation model, gyrokinetic (GK) electrons and fully kinetic (FK) ions. In the GK-electron and FK-ion (GKe/FKi) particle simulation model, the rapid electron cyclotron motion is removed, while keeping finite electron Larmor radii, realistic me/mi ratio, wave-particle interactions, and off-diagonal components of electron pressure tensor. The computation power can thus be significantly improved over that of the full-particle codes. As planned in the project DE-FG02-05ER54826, we have finished the development of the new GK-electron and FK-ion scheme, finished its benchmark for a uniform plasma in 1-D, 2-D, and 3-D systems against linear waves obtained from analytical theories, and carried out a further convergence test

Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator

Energy Technology Data Exchange (ETDEWEB)

Kirby, Neil; /SLAC

2009-10-30

Plasma-based accelerators use the propagation of a drive bunch through plasma to create large electric fields. Recent plasma wakefield accelerator (PWFA) experiments, carried out at the Stanford Linear Accelerator Center (SLAC), successfully doubled the energy for some of the 42 GeV drive bunch electrons in less than a meter; this feat would have required 3 km in the SLAC linac. This dissertation covers one phenomenon associated with the PWFA, electron trapping. Recently it was shown that PWFAs, operated in the nonlinear bubble regime, can trap electrons that are released by ionization inside the plasma wake and accelerate them to high energies. These trapped electrons occupy and can degrade the accelerating portion of the plasma wake, so it is important to understand their origins and how to remove them. Here, the onset of electron trapping is connected to the drive bunch properties. Additionally, the trapped electron bunches are observed with normalized transverse emittance divided by peak current, {epsilon}{sub N,x}/I{sub t}, below the level of 0.2 {micro}m/kA. A theoretical model of the trapped electron emittance, developed here, indicates that the emittance scales inversely with the square root of the plasma density in the non-linear 'bubble' regime of the PWFA. This model and simulations indicate that the observed values of {epsilon}{sub N,x}/I{sub t} result from multi-GeV trapped electron bunches with emittances of a few {micro}m and multi-kA peak currents. These properties make the trapped electrons a possible particle source for next generation light sources. This dissertation is organized as follows. The first chapter is an overview of the PWFA, which includes a review of the accelerating and focusing fields and a survey of the remaining issues for a plasma-based particle collider. Then, the second chapter examines the physics of electron trapping in the PWFA. The third chapter uses theory and simulations to analyze the properties of the trapped

Trapped electron losses by interactions with coherent VLF waves

International Nuclear Information System (INIS)

Walt, M.; Inan, U.S.; Voss, H.D.

1996-01-01

VLF whistler waves from lightning enter the magnetosphere and cause the precipitation of energetic trapped electrons by pitch angle scattering. These events, known as Lightning-induced Electron Precipitation (LEP) have been detected by satellite and rocket instruments and by perturbations of VLF waves traveling in the earth-ionosphere waveguide. Detailed comparison of precipitating electron energy spectra and time dependence are in general agreement with calculations of trapped electron interactions with ducted whistler waves. In particular the temporal structure of the precipitation and the dynamic energy spectra of the electrons confirm this interpretation of the phenomena. There are discrepancies between observed and measured electron flux intensities and pitch angle distributions, but these quantities are sensitive to unknown wave intensities and trapped particle fluxes near the loss cone angle. The overall effect of lightning generated VLF waves on the lifetime of trapped electrons is still uncertain. The flux of electrons deflected into the bounce loss cone by a discrete whistler wave has been measured in a few cases. However, the area of the precipitation region is not known, and thus the total number of electrons lost in an LEP event can only be estimated. While the LEP events are dramatic, more important effects on trapped electrons may arise from the small but numerous deflections which increase the pitch angle diffusion rate of the electron population. copyright 1996 American Institute of Physics

Trapped electron losses by interactions with coherent VLF waves

Science.gov (United States)

Walt, M.; Inan, U. S.; Voss, H. D.

1996-07-01

VLF whistler waves from lightning enter the magnetosphere and cause the precipitation of energetic trapped electrons by pitch angle scattering. These events, known as Lightning-induced Electron Precipitation (LEP) have been detected by satellite and rocket instruments and by perturbations of VLF waves traveling in the earth-ionosphere waveguide. Detailed comparison of precipitating electron energy spectra and time dependence are in general agreement with calculations of trapped electron interactions with ducted whistler waves. In particular the temporal structure of the precipitation and the dynamic energy spectra of the electrons confirm this interpretation of the phenomena. There are discrepancies between observed and measured electron flux intensities and pitch angle distributions, but these quantities are sensitive to unknown wave intensities and trapped particle fluxes near the loss cone angle. The overall effect of lightning generated VLF waves on the lifetime of trapped electrons is still uncertain. The flux of electrons deflected into the bounce loss cone by a discrete whistler wave has been measured in a few cases. However, the area of the precipitation region is not known, and thus the total number of electrons lost in an LEP event can only be estimated. While the LEP events are dramatic, more important effects on trapped electrons may arise from the small but numerous deflections which increase the pitch angle diffusion rate of the electron population.

An Introduction to the Physics of Collisionless Shocks

International Nuclear Information System (INIS)

Russell, C.T.

2005-01-01

Collisionless shocks are important in astrophysical, heliospheric and magnetospheric settings. They deflect flows around obstacles; they heat the plasma, and they alter the properties of the flow as it intersects those obstacles. The physical processes occurring at collisionless shocks depend on the Mach number (strength) and beta (magnetic to thermal pressure) of the shocks and the direction of the magnetic field relative to the shock normal. Herein we review how the shock has been modeled in numerical simulations, the basic physical processes at work, including dissipation and thermalization, the electric potential drop at the shock, and the formation of the electron and ion foreshocks

Electron plasma waves and plasma resonances

International Nuclear Information System (INIS)

Franklin, R N; Braithwaite, N St J

2009-01-01

In 1929 Tonks and Langmuir predicted of the existence of electron plasma waves in an infinite, uniform plasma. The more realistic laboratory environment of non-uniform and bounded plasmas frustrated early experiments. Meanwhile Landau predicted that electron plasma waves in a uniform collisionless plasma would appear to be damped. Subsequent experimental work verified this and revealed the curious phenomenon of plasma wave echoes. Electron plasma wave theory, extended to finite plasmas, has been confirmed by various experiments. Nonlinear phenomena, such as particle trapping, emerge at large amplitude. The use of electron plasma waves to determine electron density and electron temperature has not proved as convenient as other methods.

Trapped electrons in irradiated single crystals of polyhydroxy compounds

International Nuclear Information System (INIS)

Box, H.C.; Budzinski, E.E.; Freund, H.G.; Potter, W.R.

1979-01-01

The intermolecular trapping of electrons has been observed in single crystals of dulcitol and L(+) arabinose x-irradiated at 4.2 0 K. Attribution of a major component of the ESR absorption to trapped electrons is based upon the character of the hyperfine pattern, which arises from multiple anisotropic hyperfine interactions with exchangeable protons, and on the g value of the absorption, which is always less than the free spin value. The removal of the trapped electron absorption upon irradiation with visible light has also been demonstrated. In these experiments all of the electrons are trapped in identical sites. This circumstance provides some important advantages in the study of the factors affecting the stabilization of charge in an environment of polarizable molecules

Spectroscopic analysis of electron trapping levels in pentacene field-effect transistors

International Nuclear Information System (INIS)

Bum Park, Chang

2014-01-01

Electron trapping phenomena have been investigated with respect to the energy levels of localized trap states and bias-induced device instability effects in pentacene field-effect transistors. The mechanism of the photoinduced threshold voltage shift (ΔV T ) is presented by providing a ΔV T model governed by the electron trapping. The trap-and-release behaviour functionalized by photo-irradiation also shows that the trap state for electrons is associated with the energy levels in different positions in the forbidden gap of pentacene. Spectroscopic analysis identifies two kinds of electron trap states distributed above and below the energy of 2.5 eV in the band gap of the pentacene crystal. The study of photocurrent spectra shows the specific trap levels of electrons in energy space that play a substantial role in causing device instability. The shallow and deep trapping states are distributed at two centroidal energy levels of ∼1.8 and ∼2.67 eV in the pentacene band gap. Moreover, we present a systematic energy profile of electron trap states in the pentacene crystal for the first time. (paper)

Collisionless damping of nonlinear dust ion acoustic wave due to dust charge fluctuation

International Nuclear Information System (INIS)

Ghosh, Samiran; Chaudhuri, Tushar K.; Sarkar, Susmita; Khan, Manoranjan; Gupta, M.R.

2002-01-01

A dissipation mechanism for the damping of the nonlinear dust ion acoustic wave in a collisionless dusty plasma consisting of nonthermal electrons, ions, and variable charge dust grains has been investigated. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust ion acoustic wave propagation to be described by the damped Korteweg-de Vries equation. Due to the presence of nonthermal electrons, the dust ion acoustic wave admits both positive and negative potential and it suffers less damping than the dust acoustic wave, which admits only negative potential

Trapping of Electron Cloud LLC/Cesrta Quadrupole and Sextupole Magnets

International Nuclear Information System (INIS)

Wang, L.

2011-01-01

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R and D (1). One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in CESRTA and ILC quadrupole and sextupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with a long lifetime in a quadrupole and sextupole magnet due to the mirror field trapping mechanism. We study the effects of magnet strength, bunch current, ante-chamber effect, bunch spacing effect and secondary emission yield (SEY) in great detail. The development of an electron cloud in magnets is the main concern where a weak solenoid field is not effective. Quadrupole and sextupole magnets have mirror field configurations which may trap electrons by the mirror field trapping mechanism (2). Fig.1 shows the orbit of a trapped electron in a quadrupole magnet. The electron makes gyration motion (called transverse motion) and also moves along the field line (called longitudinal motion). At the mirror point (middle of the field line), there is a maximum longitudinal energy and minimum transverse energy. When the electron moves away from the mirror point, its longitudinal energy reduces and the transverse energy increases as the magnetic field increases. If the magnetic field is strong enough, the longitudinal energy becomes zero at one point and then the electron is turned back by the strong field. Note that the electrons are trapped in the region near the middle of the field lines. Although all quadrupole and sextupole magnets can trap electrons in principle, the

Self-reinforcing process of the reconnection electric field in the electron diffusion region and onset of collisionless magnetic reconnection

International Nuclear Information System (INIS)

Lu Quanming; Lu San; Huang Can; Wu Mingyu; Wang Shui

2013-01-01

The onset of collisionless magnetic reconnection is considered to be controlled by electron dynamics in the electron diffusion region, where the reconnection electric field is balanced mainly by the off-diagonal electron pressure tensor term. Two-dimensional particle-in-cell simulations are employed in this paper to investigate the self-reinforcing process of the reconnection electric field in the electron diffusion region, which is found to grow exponentially. A theoretical model is proposed to demonstrate such a process in the electron diffusion region. In addition the reconnection electric field in the pileup region, which is balanced mainly by the electromotive force term, is also found to grow exponentially and its growth rate is twice that in the electron diffusion region. (paper)

Weakly Collisional and Collisionless Astrophysical Plasmas

DEFF Research Database (Denmark)

Berlok, Thomas

are used to study weakly collisional, stratified atmospheres which offer a useful model of the intracluster medium of galaxy clusters. Using linear theory and computer simulations, we study instabilities that feed off thermal and compositional gradients. We find that these instabilities lead to vigorous...... investigate helium mixing in the weakly collisional intracluster medium of galaxy clusters using Braginskii MHD. Secondly, we present a newly developed Vlasov-fluid code which can be used for studying fully collisionless plasmas such as the solar wind and hot accretions flows. The equations of Braginskii MHD...... associated with the ions and is thus well suited for studying collisionless plasmas. We have developed a new 2D-3V Vlasov-fluid code which works by evolving the phase-space density distribution of the ions while treating the electrons as an inertialess fluid. The code uses the particle-incell (PIC) method...

Hydration of excess electrons trapped in charge pockets on molecular surfaces

Science.gov (United States)

Jalbout, Abraham F.; Del Castillo, R.; Adamowicz, Ludwik

2007-01-01

In this work we strive to design a novel electron trap located on a molecular surface. The process of electron trapping involves hydration of the trapped electron. Previous calculations on surface electron trapping revealed that clusters of OH groups can form stable hydrogen-bonded networks on one side of a hydrocarbon surface (i.e. cyclohexane sheets), while the hydrogen atoms on the opposite side of the surface form pockets of positive charge that can attract extra negative charge. The excess electron density on such surfaces can be further stabilized by interactions with water molecules. Our calculations show that these anionic systems are stable with respect to vertical electron detachment (VDE).

Hydrodynamics of ponderomotive interactions in a collisionless plasma

International Nuclear Information System (INIS)

Kono, M.; Skoric, M.M.; ter Haar, D.

1987-01-01

A hydrodynamic treatment of ponderomotive interactions in a collisionless plasma is presented and it is shown that consistent hydrodynamics leads to the correct expression for the solenoidal ponderomotive electron current density, a result previously thought to be derivable only in the framework of the warm-plasma kinetic theory

Slow electron acoustic double layer (SEADL) structures in bi-ion plasma with trapped electrons

Science.gov (United States)

Shan, Shaukat Ali; Imtiaz, Nadia

2018-05-01

The properties of ion acoustic double layer (IADL) structures in bi-ion plasma with electron trapping are investigated by using the quasi-potential analysis. The κ-distributed trapped electrons number density expression is truncated to some finite order of the electrostatic potential. By utilizing the reductive perturbation method, a modified Schamel equation which describes the evolution of the slow electron acoustic double layer (SEADL) with the modified speed due to the presence of bi-ion species is investigated. The Sagdeev-like potential has been derived which accounts for the effect of the electron trapping and superthermality in a bi-ion plasma. It is found that the superthermality index, the trapping efficiency of electrons, and ion to electron temperature ratio are the inhibiting parameters for the amplitude of the slow electron acoustic double layers (SEADLs). However, the enhanced population of the cold ions is found to play a supportive role for the low frequency DLs in bi-ion plasmas. The illustrations have been presented with the help of the bi-ion plasma parameters in the Earth's ionosphere F-region.

Nonlocal collisionless and collisional electron transport in low temperature plasmas

Science.gov (United States)

Kaganovich, Igor

2009-10-01

The purpose of the talk is to describe recent advances in nonlocal electron kinetics in low-pressure plasmas. A distinctive property of partially ionized plasmas is that such plasmas are always in a non-equilibrium state: the electrons are not in thermal equilibrium with the neutral species and ions, and the electrons are also not in thermodynamic equilibrium within their own ensemble, which results in a significant departure of the electron velocity distribution function from a Maxwellian. These non-equilibrium conditions provide considerable freedom to choose optimal plasma parameters for applications, which make gas discharge plasmas remarkable tools for a variety of plasma applications, including plasma processing, discharge lighting, plasma propulsion, particle beam sources, and nanotechnology. Typical phenomena in such discharges include nonlocal electron kinetics, nonlocal electrodynamics with collisionless electron heating, and nonlinear processes in the sheaths and in the bounded plasmas. Significant progress in understanding the interaction of electromagnetic fields with real bounded plasma created by this field and the resulting changes in the structure of the applied electromagnetic field has been one of the major achievements of the last decade in this area of research [1-3]. We show on specific examples that this progress was made possible by synergy between full scale particle-in-cell simulations, analytical models, and experiments. In collaboration with Y. Raitses, A.V. Khrabrov, Princeton Plasma Physics Laboratory, Princeton, NJ, USA; V.I. Demidov, UES, Inc., 4401 Dayton-Xenia Rd., Beavercreek, OH 45322, USA and AFRL, Wright-Patterson AFB, OH 45433, USA; and D. Sydorenko, University of Alberta, Edmonton, Canada. [4pt] [1] D. Sydorenko, A. Smolyakov, I. Kaganovich, and Y. Raitses, IEEE Trans. Plasma Science 34, 895 (2006); Phys. Plasmas 13, 014501 (2006); 14 013508 (2007); 15, 053506 (2008). [0pt] [2] I. D. Kaganovich, Y. Raitses, D. Sydorenko, and

Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis

Directory of Open Access Journals (Sweden)

Shigeru Kohtani

2017-10-01

Full Text Available Electrons, photogenerated in conduction bands (CB and trapped in electron trap defects (Tids in titanium dioxide (TiO2, play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO2. Particularly, the reactivity of electrons accumulated in CB and trapped at Tids on TiO2 is highlighted in the reduction of molecular oxygen and molecular nitrogen, and the hydrogenation and dehalogenation of organic substrates. Finally, the prospects for developing highly active TiO2 photocatalysts are discussed.

Landau Damping and Anomalous Skin Effect in Low-pressure Gas Discharges: Self-consistent Treatment of Collisionless Heating

International Nuclear Information System (INIS)

Kaganovich, Igor D.; Polomarov, Oleg V.; Theodosiou, Constantine E.

2004-01-01

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for the nonuniform plasma density profile for computing the current density profile and the EEDF is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the potential well and the external radio-frequency electric field is investigated. It is shown that a nonlinear and self-consistent treatment is necessary for the correct description of collisionless heating

Comparison of collisionless macroscopic models and application to the ion-electron instability

International Nuclear Information System (INIS)

Ahedo, E.; Lapuerta, V.

2001-01-01

In a first part, different macroscopic models of linear Landau damping are compared using a concise one-dimensional (1-D) collisionless formulation. The three-moment model of Chang and Callen (CC) [Phys. Fluids B 4, 1167 (1992)] with two closure relations (complex in the Fourier space) for the viscous stress and the heat conduction is found to be equivalent to the two-moment model of Stubbe-Sukhorukov (SS) [Phys. Plasmas 6, 2976 (1999)], which uses a single (complex) closure relation for the pressure. The comparison of the respective closure relations favors clearly the SS pressure law, which associates an anomalous resistivity to the Landau damping. In a second part, a macroscopic interpretation, with the SS model, of the ion-electron instability shows its resistive character for low and intermediate drift velocities, and the transition to the reactive Buneman limit. The pressure law for the electrons is found to verify a simple law, whereas approximate laws are discussed for the ion pressure. These laws are used to close a macroscopic model for stability analyses of nonhomogeneous plasma structures, where SS and CC models are not applicable easily

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.

Heating and generation of suprathermal particles at collisionless shocks

International Nuclear Information System (INIS)

Thomsen, M.F.

1985-01-01

Collisionless plasma shocks are different from ordinary collisional fluid shocks in several important respects. They do not in general heat the electrons and ions equally, nor do they produce Maxwellian velocity distributions downstream. Furthermore, they commonly generate suprathermal particles which propagate into the upstream region, giving advance warning of the presence of the shock and providing a ''seed'' population for further acceleration to high energies. Recent space observations and theory have revealed a great deal about the heating mechanisms which occur in collisionless shocks and about the origin of the various suprathermal particle populations which are found in association with them. An overview of the present understanding of these subjects is presented herein. 83 refs., 8 figs

Atomic physics measurements in an electron Beam Ion Trap

International Nuclear Information System (INIS)

Marrs, R.E.; Beiersdorfer, P.; Bennett, C.

1989-01-01

An electron Beam Ion Trap at Lawrence Livermore National Laboratory is being used to produce and trap very-highly-charged ions (q ≤ 70/+/) for x-ray spectroscopy measurements. Recent measurements of transition energies and electron excitation cross sections for x-ray line emission are summarized. 13 refs., 10 figs

Trapped-particle instabilities in quasi-isodynamic stellarators

Energy Technology Data Exchange (ETDEWEB)

Proll, Josefine Henriette Elise

2014-01-28

approximately in quasi-isodynamic stellarators, for example Wendelstein 7-X. In such configurations the precessional drift of the trapped particles is in the opposite direction from the direction of propagation of drift waves. Instabilities that are driven by the trapped particles usually rely on a resonance between these two frequencies. Here it is shown analytically by analysing the electrostatic energy transfer between the particles and the instability that, thanks to the absence of the resonance, a particle species draws energy from the mode if the frequency of the mode is well below the characteristic bounce frequency. Due to the low electron mass and the fast bounce motion, electrons are almost always found to be stabilising. Most of the trapped-particle instabilities are therefore predicted to be absent in maximum- J configurations in large parts of parameter space. Analytical theory thus predicts enhanced linear stability of trapped-particle modes in quasi-isodynamic stellarators compared with tokamaks. Moreover, since the electrons are expected to be stabilising, or at least less destabilising, for all instabilities whose frequency lies below the trapped-electron bounce frequency, other modes might benefit from the enhanced stability as well. In reality, however, 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 another, non-quasiisodynamic stellarator, the National Compact Stellarator Experiment (NCSX) and a typical tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, several microinstabilities, driven by the density as well as both ion and electron temperature gradients, are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all

Trapped-particle instabilities in quasi-isodynamic stellarators

International Nuclear Information System (INIS)

Proll, Josefine Henriette Elise

2014-01-01

approximately in quasi-isodynamic stellarators, for example Wendelstein 7-X. In such configurations the precessional drift of the trapped particles is in the opposite direction from the direction of propagation of drift waves. Instabilities that are driven by the trapped particles usually rely on a resonance between these two frequencies. Here it is shown analytically by analysing the electrostatic energy transfer between the particles and the instability that, thanks to the absence of the resonance, a particle species draws energy from the mode if the frequency of the mode is well below the characteristic bounce frequency. Due to the low electron mass and the fast bounce motion, electrons are almost always found to be stabilising. Most of the trapped-particle instabilities are therefore predicted to be absent in maximum- J configurations in large parts of parameter space. Analytical theory thus predicts enhanced linear stability of trapped-particle modes in quasi-isodynamic stellarators compared with tokamaks. Moreover, since the electrons are expected to be stabilising, or at least less destabilising, for all instabilities whose frequency lies below the trapped-electron bounce frequency, other modes might benefit from the enhanced stability as well. In reality, however, 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 another, non-quasiisodynamic stellarator, the National Compact Stellarator Experiment (NCSX) and a typical tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, several microinstabilities, driven by the density as well as both ion and electron temperature gradients, are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all

Physics of collisionless scrape-off-layer plasma during normal and off-normal Tokamak operating conditions

International Nuclear Information System (INIS)

Hassanein, A.; Konkashbaev, I.

1999-01-01

The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of a plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker-Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte-Carlo methods. The analytical solutions provide an insight to the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters

Highly Supersonic Ion Pulses in a Collisionless Magnetized Plasma

DEFF Research Database (Denmark)

Juul Rasmussen, Jens; Schrittwieser, R.

1982-01-01

The initial transient response of a collisionless plasma to a high positive voltage step is investigated. Four different pulses are observed. An electron plasma wave pulse is followed by an ion burst. The latter is overtaken and absorbed by a highly supersonic ion pulse. Thereafter, an ion...

The Role of Electron Transport and Trapping in MOS Total-Dose Modeling

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.; Riewe, L.C.; Flament, O.; Paillet, P.; Leray, J.L.

1999-01-01

Radiation-induced hole and electron transport and trapping are fundamental to MOS total-dose models. Here we separate the effects of electron-hole annihilation and electron trapping on the neutralization of radiation-induced charge during switched-bias irradiation for hard and soft oxides, via combined thermally stimulated current (TSC) and capacitance-voltage measurements. We also show that present total-dose models cannot account for the thermal stability of deeply trapped electrons near the Si/SiO 2 interface, or the inability of electrons in deep or shallow traps to contribute to TSC at positive bias following (1) room-temperature, (2) high-temperature, or (3) switched-bias irradiation. These results require revisions of modeling parameters and boundary conditions for hole and electron transport in SiO 2 . The nature of deep and shallow electron traps in the near-interfacial SiO 2 is discussed

Collisionless plasma expansion into a vacuum

International Nuclear Information System (INIS)

Denavit, J.

1979-01-01

Particle simulations of the expansion of a collisionless plasma into vacuum are presented. The cases of a single-electron-temperature plasma and of a two-electron-temperature plasma are considered. The results confirm the existence of an ion front and verify the general features of self-similar solutions behind this front. A cold electron front is clearly observed in the two-electron-temperatures case. The computations also show that for a finite electron-to-ion mass ratio, m/sub e//m/sub i/, the electron thermal velocity in the expansion region is not constant, but decreases approximately linearly with xi 0 -(γ-1) xi/2, and comparison with computer simulation results show that the constant γ-1 is proportional to (Zm/sub e//m/sub i/)atsup 1/2at, where Z is the ion charge number

Collisionless analogs of Riemann S ellipsoids with halo

International Nuclear Information System (INIS)

Abramyan, M.G.

1987-01-01

A spheroidal halo ensures equilibrium of the collisionless analogs of the Riemann S ellipsoids with oscillations of the particles along the direction of their rotation. Sequences of collisionless triaxial ellipsoids begin and end with dynamically stable members of collisionless embedded spheroids. Both liquid and collisionless Riemann S ellipsoids with weak halo have properties that resemble those of bars of SB galaxies

Ion trapping in one-minimum potentials via charge-exchange collisions

International Nuclear Information System (INIS)

Maier, H.; Kuhn, S.

1994-01-01

A (1 d, 2 v), electrostatic, kinetics model for time-independent single-ended Q-machine states with a positively biased cold plate and a single internal minimum near the hot plate is presented. While the electrons are treated as collisionless, charge-exchange collisions between the ions and the neutral background gas atoms are taken into account by means of a linearized Boltzmann collision operator. The self-consistent plasma states are found by using an iterative analytic-numerical trajectory-simulation method in which the charge-density and potential distributions are alternately determined numerical results clearly demonstrate the sensitive role that trapped ions play in shaping the microscopic and macroscopic properties of the dc states under study. The trapped-ion distributions themselves are shown to be controlled critically by the detailed scattering conditions, which in turn are determined by the choice of the background properties. (author). 10 refs, 3 figs

The Child-Langmuir law and analytical theory of collisionless to collision-dominated sheaths

International Nuclear Information System (INIS)

Benilov, M S

2009-01-01

This paper is concerned with summarizing simple analytical models of space-charge sheaths and tracing their relation to the Child-Langmuir model of an ion sheath. The topics discussed include the Child-Langmuir law and model of a collisionless ion sheath, the Mott-Gurney law and model of a collision-dominated ion sheath, the Bohm model of a collisionless ion-electron sheath, the Su-Lam-Cohen model of a collision-dominated ion-electron sheath, ion sheaths with arbitrary collisionality, high-accuracy boundary conditions for the Child-Langmuir and Mott-Gurney models of an ion sheath and the mathematical sense of Child-Langmuir type models of an ion sheath from the point of view of modern theoretical physics.

Pressure gradient turbulent transport and collisionless reconnection

International Nuclear Information System (INIS)

Connor, J.W.

1993-01-01

The scale invariance technique is employed to discuss pressure gradient driven turbulent transport when an Ohm's law with electron inertia, rather than resistivity, is relevant. An expression for thermal diffusivity which has many features appropriate to L-mode transport in tokamaks, is seen to have greater generality than indicated by their particular calculation. The results of applying the technique to a more appropriate collisionless Ohm's law are discussed. (Author)

Universal collisionless transport of graphene

Science.gov (United States)

Link, Julia M.; Orth, Peter P.; Sheehy, Daniel E.; Schmalian, Jörg

2016-06-01

The impact of the electron-electron Coulomb interaction on the optical conductivity of graphene has led to a controversy that calls into question the universality of collisionless transport in this and other Dirac materials. Using a lattice calculation that avoids divergences present in previous nodal Dirac approaches, our work settles this controversy and obtains results in quantitative agreement with experiment over a wide frequency range. We also demonstrate that dimensional regularization methods agree, if the regularization of the theory in modified dimensions is correctly implemented. Tight-binding lattice and nodal Dirac theory calculations are shown to coincide at low energies even when the nonzero size of the atomic orbital wave function is included, conclusively demonstrating the universality of the optical conductivity of graphene.

Electrons in feldspar I: On the wavefunction of electrons trapped at simple lattice defects

DEFF Research Database (Denmark)

Poolton, H.R.J.; Wallinga, J.; Murray, A.S.

2002-01-01

The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states. It is sh......The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states...

Saturation of drift instabilities by ExB advection of resonant electrons

International Nuclear Information System (INIS)

Dimits, A.M.

1990-01-01

Saturation of the collisionless and weakly collisional drift instabilities by nonlinear ExB advection of resonant electrons is considered. The nonlinear ExB advection of the resonant electrons around the O points and X points of the potential shuts off the linear phase shift between the electron density and the potential, and hence the linear growth, and produces residual oscillations at the ExB-trapping frequency. Two analytical solutions of a three-mode model of Lee et al. [Phys. Fluids 27, 2652 (1984)], which describes the saturation of drift waves by this mechanism, are found. The first is an exact solution in the form of a steadily propagating wave of constant amplitude, and is relevant when electron pitch-angle scattering is present. The second is an approximate time-dependent analytical solution, obtained using the method of O'Neil [Phys. Fluids 8, 2255 (1965)], and is relevant to the collisionless case. The predictions that follow from this solution for the saturation level and for the amplitude oscillation frequency are in excellent agreement with the direct numerical solutions of the three-mode system

Whistler dominated quasi-collisionless magnetic reconnection

International Nuclear Information System (INIS)

Biskamp, D.; Drake, J.F.

1995-05-01

A theory of fast quasi-collisionless reconnection is presented. For spatial scales smaller than the ion inertia length the electrons decouple from the ions and the dynamics is described by electron magnetohydrodynamics (EMHD). A qualitative analysis of the reconnection region is obtained, which is corroborated by numerical simulations. The main results are that in contrast to resistive reconnection no macroscopic current sheet is generated, and the reconnection rate is independent of the smallness parameters of the system, i.e. the electron inertia length and the dissipation coefficients. At larger scales the coupling to the ions is important, which, however, does not change the small-scale dynamics. The reconnection rate is only limited by ion inertia being independent of the electron inertia scale and the dissipation coefficients. Reconnection is much faster than in the absence of the whistler mode. (orig.)

Spectral measurements of few-electron uranium ions produced and trapped in a high-energy electron beam ion trap

International Nuclear Information System (INIS)

Beiersdorfer, P.

1994-01-01

Measurements of 2s l/2 -2p 3/2 electric dipole and 2p 1/2 -2p 3/2 magnetic dipole and electric quadrupole transitions in U 82+ through U 89+ have been made with a high-resolution crystal spectrometer that recorded the line radiation from stationary ions produced and trapped in a high-energy electron beam ion trap. From the measurements we infer -39.21 ± 0.23 eV for the QED contribution to the 2s 1/2 -2p 3/2 transition energy of lithiumlike U 89+ . A comparison between our measurements and various computations illustrates the need for continued improvements in theoretical approaches for calculating the atomic structure of ions with two or more electrons in the L shell

High-speed photography of a 'switch-on' collisionless shock

International Nuclear Information System (INIS)

El-Khalafawy, T.A.; El-Nicklawy, M.M.; Bashara, A.B.; El-Masry, M.A.; Rudnev, N.J.

1975-01-01

The paper presents the results of the investigation of a 'switch-on' shock profile and the measurement of the wave velocity in the collisionless regime employing high-speed photography. Data for the electron temperature (Tsub(e)) ahead of and behind the wave front are presented here, and a Table with estimated and measured characteristic physical quantities. (author)

A model for precursor structure in supercritical perpendicular, collisionless shock waves

International Nuclear Information System (INIS)

Sherwell, D.; Cairns, R.A.

1978-01-01

Magnetosonic solitons may be given smooth increasing profiles by assuming the presence within the wave of a current distribution Jsub(y)(x) of trapped ions perpendicular to Bsub(z)(x) and the wave velocity Vsub(x). Suitable ions are found immediately upstream of perpendicular collisionless shock waves and these are coincident with the often observed 'foot' in magnetic field profiles of moderately supercritical shocks. The theory is applied to previous experiments by modelling Jsub(y)(x), where Jsub(y)(x) is observed, the profiles in the foot are reproduced and explained. Insight into a number of features of fast shocks is obtained. (author)

Collisionless current sheet equilibria

Science.gov (United States)

Neukirch, T.; Wilson, F.; Allanson, O.

2018-01-01

Current sheets are important for the structure and dynamics of many plasma systems. In space and astrophysical plasmas they play a crucial role in activity processes, for example by facilitating the release of magnetic energy via processes such as magnetic reconnection. In this contribution we will focus on collisionless plasma systems. A sensible first step in any investigation of physical processes involving current sheets is to find appropriate equilibrium solutions. The theory of collisionless plasma equilibria is well established, but over the past few years there has been a renewed interest in finding equilibrium distribution functions for collisionless current sheets with particular properties, for example for cases where the current density is parallel to the magnetic field (force-free current sheets). This interest is due to a combination of scientific curiosity and potential applications to space and astrophysical plasmas. In this paper we will give an overview of some of the recent developments, discuss their potential applications and address a number of open questions.

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.

Sawtooth activity of the ion cloud in an electron-beam ion trap

International Nuclear Information System (INIS)

Radtke, R.; Biedermann, C.

2003-01-01

The dynamics of an ensemble of highly charged Ar and Ba ions in an electron-beam ion trap (EBIT) was studied by recording time-resolved x-ray spectra emitted from trapped ions. Sawtoothlike signatures manifest in the spectra for a variety of EBIT operating conditions indicating a sudden collapse of the ion inventory in the trap. The collapse occurs on a time scale of approximately 100 ms and the evolution of the sawteeth is very sensitive to parameters such as electron-beam current and axial trap depth. Analysis of the measurements is based on a time-dependent calculation of the trapping process showing that sawtooth activity is caused by the feedback between the low-Z argon and high-Z barium ions. This unexpected behavior demonstrates the importance of nonlinear effects in electron-beam traps containing more than a single ion species

High-Mach number, laser-driven magnetized collisionless shocks

International Nuclear Information System (INIS)

Schaeffer, Derek B.; Fox, W.; Haberberger, D.; Fiksel, G.; Bhattacharjee, A.

2017-01-01

Collisionless shocks are ubiquitous in space and astrophysical systems, and the class of supercritical shocks is of particular importance due to their role in accelerating particles to high energies. While these shocks have been traditionally studied by spacecraft and remote sensing observations, laboratory experiments can provide reproducible and multi-dimensional datasets that provide complementary understanding of the underlying microphysics. We present experiments undertaken on the OMEGA and OMEGA EP laser facilities that show the formation and evolution of high-Mach number collisionless shocks created through the interaction of a laser-driven magnetic piston and magnetized ambient plasma. Through time-resolved, 2-D imaging we observe large density and magnetic compressions that propagate at super-Alfvenic speeds and that occur over ion kinetic length scales. Electron density and temperature of the initial ambient plasma are characterized using optical Thomson scattering. Measurements of the piston laser-plasma are modeled with 2-D radiation-hydrodynamic simulations, which are used to initialize 2-D particle-in-cell simulations of the interaction between the piston and ambient plasmas. The numerical results show the formation of collisionless shocks, including the separate dynamics of the carbon and hydrogen ions that constitute the ambient plasma and their effect on the shock structure. Furthermore, the simulations also show the shock separating from the piston, which we observe in the data at late experimental times.

Accessing the Asymmetric Collisionless Reconnection Regime in the Terrestrial Reconnection Experiment (TREX)

Science.gov (United States)

Greess, S.; Egedal, J.; Olson, J.; Millet-Ayala, A.; Myers, R.; Wallace, J.; Clark, M.; Forest, C.

2017-12-01

Kinetic effects are expected to dominate the collisionless reconnection regime, where the mean free path is large enough that the anisotropic electron pressure can develop without being damped away by collisional pitch angle scattering. In simulations, the anisotropic pressure drives the formation of outflow jets [1]. These jets are expected to play a role in the reconnection layer at the Earth's magnetopause, which is currently being explored by Magnetospheric Multiscale Mission (MMS) [2]. Until recently, this regime of anisotropic pressure was inaccessible by laboratory experiments, but new data from the Terrestrial Reconnection Experiment (TREX) shows that fully collisionless reconnection can now be achieved in the laboratory. Future runs at TREX will delve deeper into this collisionless regime in both the antiparallel and guide-field cases. [1] Le, A. et al. JPP, 81(1). doi: 10.1017/S0022377814000907. [2] Burch, J. L. et al. Space Sci. Rev. 199,5. doi: 10.1007/s11214-015-0164-9 Supported in part by NSF/DOE award DE-SC0013032.

Electron trap annealing in neutron transmutation doped silicon

DEFF Research Database (Denmark)

Guldberg, J.

1977-01-01

Silicon doped by neutron transmutation to 1.2×1014 phosphorus atoms/cm3 was investigated with deep level transient spectroscopy using evaporated Au/n-Si diodes. Seven bulk electron traps were identified which appear after 30 min N2 anneal at temperatures between 425 and 725 °C. Five of these anne......Silicon doped by neutron transmutation to 1.2×1014 phosphorus atoms/cm3 was investigated with deep level transient spectroscopy using evaporated Au/n-Si diodes. Seven bulk electron traps were identified which appear after 30 min N2 anneal at temperatures between 425 and 725 °C. Five...

Plasma and energetic particle structure of a collisionless quasi-parallel shock

Science.gov (United States)

Kennel, C. F.; Scarf, F. L.; Coroniti, F. V.; Russell, C. T.; Smith, E. J.; Wenzel, K. P.; Reinhard, R.; Sanderson, T. R.; Feldman, W. C.; Parks, G. K.

1983-01-01

The quasi-parallel interplanetary shock of November 11-12, 1978 from both the collisionless shock and energetic particle points of view were studied using measurements of the interplanetary magnetic and electric fields, solar wind electrons, plasma and MHD waves, and intermediate and high energy ions obtained on ISEE-1, -2, and -3. The interplanetary environment through which the shock was propagating when it encountered the three spacecraft was characterized; the observations of this shock are documented and current theories of quasi-parallel shock structure and particle acceleration are tested. These observations tend to confirm present self consistent theories of first order Fermi acceleration by shocks and of collisionless shock dissipation involving firehouse instability.

Electron-trapping probability in natural dosemeters as a function of irradiation temperature

DEFF Research Database (Denmark)

Wallinga, J.; Murray, A.S.; Wintle, A.G.

2002-01-01

The electron-trapping probability in OSL traps as a function of irradiation temperature is investigated for sedimentary quartz and feldspar. A dependency was found for both minerals; this phenomenon could give rise to errors in dose estimation when the irradiation temperature used in laboratory...... procedures is different from that in the natural environment. No evidence was found for the existence of shallow trap saturation effects that Could give rise to a dose-rate dependency of electron trapping....

Electron transfer from electronic excited states to sub-vacuum electron traps in amorphous ice

International Nuclear Information System (INIS)

Vichnevetski, E.; Bass, A.D.; Sanche, L.

2000-01-01

We investigate the electron stimulated yield of electronically excited argon atoms (Ar * ) from monolayer quantities of Ar deposited onto thin films of amorphous ice. Two peaks of narrow width ( - electron-exciton complex into exciton states, by the transfer of an electron into a sub-vacuum electron state within the ice film. However, the 10.7 eV feature is shifted to lower energy since electron attachment to Ar occurs within small pores of amorphous ice. In this case, the excess electron is transferred into an electron trap below the conduction band of the ice layer

Origin and behavior of main electron traps in Si-implanted GaAs

International Nuclear Information System (INIS)

Fang, Z.Q.; Yamamoto, H.; Look, D.C.

1990-01-01

The electron traps in Si-implanted active layers (n ∼ 10 17 cm -3 ) have been studied by capacitance and conductance DLTS techniques in conjunction with different anneal conditions, which include rapid thermal anneals at different temperatures and furnace anneals with Si 3 N 4 cap or capless in an AsH 3 atmosphere. As compared to the electron traps in as-grown bulk n-GaAs (n ∼ 4 x 10 16 cm -3 ), nearly the same electron traps, i.e. EL2, EL3, EL4, EL5, EL6, and EL9 can be observed in the Si-implanted layers. Through a comparison with the annealing behavior of the main electron traps in bulk n-GaAs, the processing associated origins of some of the traps (EL2, EL3, EL4, EL5 and EL9) observed in Si-implanted GaAs layers have been determined. For some Si-implanted capped with Si 3 N 4 and furnace annealed, traps EL3 and EL4 dominate the trap EL2. In such layers it is found that emission due to EL3 is reduced while emission from EL12 is augmented by increasing the filling pulse width from 10 μs to 5 x 10 3 μs. In this paper phenomenon is explained in terms of a defect reaction enhanced by electron capture, showing a metastability or bistability

Neutralizing trapped electrons on the hydrogenated surface of a diamond amplifier

Directory of Open Access Journals (Sweden)

Xiangyun Chang

2012-01-01

Full Text Available We discuss our investigation of electron trapping in a diamond amplifier (DA. Our previous work demonstrated that some electrons reaching the DA’s hydrogenated surface are not emitted. The state and the removal of these electrons is important for DA applications. We found that these stopped electrons are trapped, and cannot be removed by a strong reversed-polarity electric field; to neutralize this surface charge, holes must be sent to the hydrogenated surface to recombine with the trapped electrons through the Shockley-Read-Hall surface-recombination mechanism. We measured the time taken for such recombination on the hydrogenated surface, viz. the recombination time, as less than 5 ns, limited by the resolution of our test system. With this measurement, we demonstrated that DA could be operated in an rf cavity with frequency of a few hundred megahertz.

ELECTRON TRAPPING IN WIGGLER AND QUADRUPOLE MAGNETS OF CESRTA

International Nuclear Information System (INIS)

Wang, Lanfa

2010-01-01

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R and D (1). One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in the wiggler and quadrupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with long lifetime in a quadrupole magnet due to the mirror field trapping mechanism and photoelectrons produced in the wiggler zero field zone have long lifetime due to their complicated trajectory.

Intrinsic electron traps in atomic-layer deposited HfO{sub 2} insulators

Energy Technology Data Exchange (ETDEWEB)

Cerbu, F.; Madia, O.; Afanas' ev, V. V.; Houssa, M.; Stesmans, A. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Andreev, D. V. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Bauman Moscow State Technical University—Kaluga Branch, 248000 Kaluga, Moscow obl. (Russian Federation); Fadida, S.; Eizenberg, M. [Department of Materials Science and Engineering, Technion-Israel Institute of Technology, 32000 Haifa (Israel); Breuil, L. [imec, 3001 Leuven (Belgium); Lisoni, J. G. [imec, 3001 Leuven (Belgium); Institute of Physics and Mathematics, Faculty of Science, Universidad Austral de Chile, Valdivia (Chile); Kittl, J. A. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Advanced Logic Lab, Samsung Semiconductor, Inc., Austin, 78754 Texas (United States); Strand, J.; Shluger, A. L. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

2016-05-30

Analysis of photodepopulation of electron traps in HfO{sub 2} films grown by atomic layer deposition is shown to provide the trap energy distribution across the entire oxide bandgap. The presence is revealed of two kinds of deep electron traps energetically distributed at around E{sub t} ≈ 2.0 eV and E{sub t} ≈ 3.0 eV below the oxide conduction band. Comparison of the trapped electron energy distributions in HfO{sub 2} layers prepared using different precursors or subjected to thermal treatment suggests that these centers are intrinsic in origin. However, the common assumption that these would implicate O vacancies cannot explain the charging behavior of HfO{sub 2}, suggesting that alternative defect models should be considered.

Radiation of electrons in an electromagnetic axial trap

International Nuclear Information System (INIS)

Toropova, A.I.

1998-01-01

The version of a trap. wherein particles move in a homogeneous constant magnetic field and electrostatic field, formed by two equipotential planes and rotation axial surface, is proposed. The solution of canonic equations is found. It is shown that interaction of electrons with the radiation field leads to damping parametric resonance. The trap model, accounting for the finite conductivity of the resonator walls and losses by collisions with gas, is studied

Role of trapped and solvated electrons in Ps formation

International Nuclear Information System (INIS)

Stepanov, S.V.; Byakov, V.M.; Mikhin, K.V.; He, C.; Hirade, T.

2005-01-01

Role of trapped and solvated electrons in Ps formation is discussed. Combination of thermalized positron with such electrons is possible from the view point of the energy balance and may results in Ps formation. This process proceeds during all e = lifetime matter. Fitting of raw experimental e + -e - annihilation spectra has to be based on an adequate physical input, which often leads to necessity of nonexponential deconvolution of the spectra. We have interpreted the Ps formation data in polyethylene, ethylene-methylmethacrylate and polymethylmethacrylate in dark and in light vs. tome of the measurement and temperature. parameters characterized accumulation of trapped electrons and their recombination with counter ions and positrons are obtained. (author)

A closed set of conservation laws and the evolution of the electron magnetic moment in the collisionless solar wind

International Nuclear Information System (INIS)

Alexander, P.

1993-01-01

A hydromagnetic equation system for the interplanetary collisionless solar wind is used to derive a set of conservation laws for that medium. It is found that every equation of the original system, including the closure relation, is related to one conservation law. The set that has been derived does not only include the traditional laws, but also a new one for the magnetic moment of the electrons. The conservation set is then used to obtain the space constants for the solar coronal expansion. The new law yields a constant that has not been predicted by other models

Self-generated zonal flows in the plasma turbulence driven by trapped-ion and trapped-electron instabilities

Energy Technology Data Exchange (ETDEWEB)

Drouot, T.; Gravier, E.; Reveille, T.; Collard, M. [Institut Jean Lamour, UMR 7198 CNRS - Université de Lorraine, 54 506 Vandoeuvre-lès-Nancy Cedex (France)

2015-10-15

This paper presents a study of zonal flows generated by trapped-electron mode and trapped-ion mode micro turbulence as a function of two plasma parameters—banana width and electron temperature. For this purpose, a gyrokinetic code considering only trapped particles is used. First, an analytical equation giving the predicted level of zonal flows is derived from the quasi-neutrality equation of our model, as a function of the density fluctuation levels and the banana widths. Then, the influence of the banana width on the number of zonal flows occurring in the system is studied using the gyrokinetic code. Finally, the impact of the temperature ratio T{sub e}/T{sub i} on the reduction of zonal flows is shown and a close link is highlighted between reduction and different gyro-and-bounce-average ion and electron density fluctuation levels. This reduction is found to be due to the amplitudes of gyro-and-bounce-average density perturbations n{sub e} and n{sub i} gradually becoming closer, which is in agreement with the analytical results given by the quasi-neutrality equation.

Effect of Single-Electron Interface Trapping in Decanano MOSFETs: A 3D Atomistic Simulation Study

Science.gov (United States)

Asenov, Asen; Balasubramaniam, R.; Brown, A. R.; Davies, J. H.

2000-01-01

We study the effect of trapping/detrapping of a single-electron in interface states in the channel of n-type MOSFETs with decanano dimensions using 3D atomistic simulation techniques. In order to highlight the basic dependencies, the simulations are carried out initially assuming continuous doping charge, and discrete localized charge only for the trapped electron. The dependence of the random telegraph signal (RTS) amplitudes on the device dimensions and on the position of the trapped charge in the channel are studied in detail. Later, in full-scale, atomistic simulations assuming discrete charge for both randomly placed dopants and the trapped electron, we highlight the importance of current percolation and of traps with strategic position where the trapped electron blocks a dominant current path.

MOS Capacitance—Voltage Characteristics II. Sensitivity of Electronic Trapping at Dopant Impurity from Parameter Variations

International Nuclear Information System (INIS)

Jie Binbin; Sah Chihtang

2011-01-01

Low-frequency and high-frequency Capacitance—Voltage (C—V) curves of Metal—Oxide—Semiconductor Capacitors (MOSC), including electron and hole trapping at the dopant donor and acceptor impurities, are presented to illustrate giant trapping capacitances, from > 0.01C OX to > 10C OX . Five device and materials parameters are varied for fundamental trapping parameter characterization, and electrical and optical signal processing applications. Parameters include spatially constant concentration of the dopant-donor-impurity electron trap, N DD , the ground state electron trapping energy level depth measured from the conduction band edge, E C –E D , the degeneracy of the trapped electron at the ground state, g D , the device temperature, T, and the gate oxide thickness, x OX . (invited papers)

Ultralow-Power Electronic Trapping of Nanoparticles with Sub-10 nm Gold Nanogap Electrodes.

Science.gov (United States)

Barik, Avijit; Chen, Xiaoshu; Oh, Sang-Hyun

2016-10-12

We demonstrate nanogap electrodes for rapid, parallel, and ultralow-power trapping of nanoparticles. Our device pushes the limit of dielectrophoresis by shrinking the separation between gold electrodes to sub-10 nm, thereby creating strong trapping forces at biases as low as the 100 mV ranges. Using high-throughput atomic layer lithography, we manufacture sub-10 nm gaps between 0.8 mm long gold electrodes and pattern them into individually addressable parallel electronic traps. Unlike pointlike junctions made by electron-beam lithography or larger micron-gap electrodes that are used for conventional dielectrophoresis, our sub-10 nm gold nanogap electrodes provide strong trapping forces over a mm-scale trapping zone. Importantly, our technology solves the key challenges associated with traditional dielectrophoresis experiments, such as high voltages that cause heat generation, bubble formation, and unwanted electrochemical reactions. The strongly enhanced fields around the nanogap induce particle-transport speed exceeding 10 μm/s and enable the trapping of 30 nm polystyrene nanoparticles using an ultralow bias of 200 mV. We also demonstrate rapid electronic trapping of quantum dots and nanodiamond particles on arrays of parallel traps. Our sub-10 nm gold nanogap electrodes can be combined with plasmonic sensors or nanophotonic circuitry, and their low-power electronic operation can potentially enable high-density integration on a chip as well as portable biosensing.

Nonlinear collisionless electron cyclotron interaction in the pre-ionisation stage

Science.gov (United States)

Farina, D.

2018-06-01

Electron cyclotron (EC) wave-particle interaction is theoretically investigated in the pre-ionisation phase, much before collisions and other mechanisms can play a role. In the very first phase of a plasma discharge with EC-assisted breakdown, the motion of an electron at room temperature in a static magnetic field under the action of a localised microwave beam is nonlinear, and transition to states of larger energy can occur via wave trapping. Within a Hamiltonian adiabatic formalism, the conditions at which the particles gain energy in single beam crossing are derived in a rigorous way, and the energy variation is characterized quantitatively as a function of the wave frequency, harmonic number, polarisation and EC power and beam width. Estimates of interest for applications to tokamak start-up are obtained for the first, second and third cyclotron harmonic. The investigation confirms that electrons can easily gain energies well above the ionisation energy in most conditions at the first two harmonics, while not at the third harmonic, as observed in experiments.

Regulation of electron temperature gradient turbulence by zonal flows driven by trapped electron modes

Science.gov (United States)

Asahi, Y.; Ishizawa, A.; Watanabe, T.-H.; Tsutsui, H.; Tsuji-Iio, S.

2014-05-01

Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger than or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.

Electron spin resonance from NV centers in diamonds levitating in an ion trap

International Nuclear Information System (INIS)

Delord, T; Nicolas, L; Schwab, L; Hétet, G

2017-01-01

We report observations of the electron spin resonance (ESR) of nitrogen vacancy centers in diamonds that are levitating in an ion trap. Using a needle Paul trap operating under ambient conditions, we demonstrate efficient microwave driving of the electronic spin and show that the spin properties of deposited diamond particles measured by the ESR are retained in the Paul trap. We also exploit the ESR signal to show angle stability of single trapped mono-crystals, a necessary step towards spin-controlled levitating macroscopic objects. (paper)

The energy distribution function of excess electrons trapped in the pulse irradiated low density polyethylene (LDPE)

International Nuclear Information System (INIS)

Wysocki, S.; Mazurek, L.; Karolczak, S.; Kroh, J.

1995-01-01

Distribution function D (E) of electrons trapped in irradiated LDPE was calculated on the basis of time resolved absorption spectra recorded at temperatures of 20-250 K. Variation of absorption spectra with time and temperature were observed and discussed in terms of simultaneous decay and relocation of electrons from shallow to deeper traps. Results obtained imply domination of trap limited transport for shallowly trapped electrons. For deeper traps, hopping mechanism is prevailing. (author)

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

Energy Technology Data Exchange (ETDEWEB)

Masters, A.; Dougherty, M. K. [The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom); Sulaiman, A. H. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); Stawarz, Ł. [Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow (Poland); Reville, B. [School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN (United Kingdom); Sergis, N. [Office of Space Research and Technology, Academy of Athens, Soranou Efesiou 4, 11527 Athens (Greece); Fujimoto, M. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Burgess, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom); Coates, A. J., E-mail: a.masters@imperial.ac.uk [Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom)

2017-07-10

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.

Time-dependence hole and electron trapping effects in SIMOX buried oxides

International Nuclear Information System (INIS)

Boesch, H.E. Jr.; Taylor, T.L.; Hite, L.R.; Bailey, W.E.

1990-01-01

Back-channel threshold shift associated with the buried oxide layers of separation by implanted oxygen (SIMOX) and zone-melted recrystallization (ZMR) field-effect transistors (FETs) was measured following pulsed irradiation as a function of temperature and back-gate bias using a fast time-resolved I-V measurement technique. The SIMOX FETs showed large initial negative voltage shifts at 0.2 ms after irradiation followed by temperature- and bias-dependent additional negative shifts to 800s. Analysis and modeling of the results indicate efficient deep trapping of radiation-generated holes in the bulk of the oxide, substantial initial trapping of radiation-generated electrons in the oxide, and rapid removal of the trapped electrons by a thermal detrapping process. The ZMR FETs showed evidence of substantial trapping of holes alone in the oxide bulk

Transition from Collisionless to Collisional MRI

International Nuclear Information System (INIS)

Sharma, Prateek; Hammett, Gregory W.; Quataert, Eliot

2003-01-01

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

The role of electron-phonon interaction and non-Gaussian transport in spectral changes of trapped electrons in glasses

International Nuclear Information System (INIS)

Funabishi, K.; Hamill, W.H.

The continuous-time-random-walk (CTRW) model which was developed for electron scavenging reactions in polar glasses is extended to the phenomenon of spectral relaxation of electrons in shallow traps esub(t) - in a wider range of systems. The central role of electron-phonon coupling in understanding the initial electron localization, the ''pre-existing trap'', and electron transfer processes are emphasized. The reactivity of esub(t) - with scavengers, including protons, is discussed in terms of the theory of multi-phonon non-radiative transitions. (author)

A poloidal non-uniformity of the collisionless parallel current in a tokamak plasma

Energy Technology Data Exchange (ETDEWEB)

Romannikov, A.; Fenzi-Bonizec, C

2005-07-01

The collisionless distortion of the ion (electron) distribution function at certain points on a magnetic surface is studied in the framework of a simple model of a large aspect ratio tokamak plasma. The flow velocity driven by this distortion is calculated. The possibility of an additional non-uniform collisionless parallel current density on a magnetic surface, other than the known neo-classical non-uniformity is shown. The difference between the parallel current density on the low and high field side of a magnetic surface is close to the neoclassical bootstrap current density. The first Tore-Supra experimental test indicates the possibility of the poloidal non-uniformity of the parallel current density. (authors)

FRC collisionless resistivity

International Nuclear Information System (INIS)

Tajima, T.; Horton, W.

1990-01-01

Ions in the field reversed configuration (FRC) exhibit stochastic orbits due to the field null and the curvature of poloidal field lines. Velocity correlations of these particles decay in a power law fashion t -m where 1 ≤ m ≤ 2. This decay of the single particle correlation function is characteristic of the long tail correlations of strongly chaotic or nonlinear systems found in other problems of statistical physics. This decay of correlations gives rise to a collisionless resistivity that can far exceed the collisional resistivity in an FRC plasma. The finite correlation τ c of a single particle limits the acceleration in the electric field producing the finite resistivity. Maxwellian test particle distributions are integrated to find the measure of the set of stochastic ions that contribute to the collisionless resistivity. The computed conductivity is proportional to the square root of the characteristic ion gyroradius in both simulation and theory

The electron trap parameter extraction-based investigation of the relationship between charge trapping and activation energy in IGZO TFTs under positive bias temperature stress

Science.gov (United States)

Rhee, Jihyun; Choi, Sungju; Kang, Hara; Kim, Jae-Young; Ko, Daehyun; Ahn, Geumho; Jung, Haesun; Choi, Sung-Jin; Myong Kim, Dong; Kim, Dae Hwan

2018-02-01

Experimental extraction of the electron trap parameters which are associated with charge trapping into gate insulators under the positive bias temperature stress (PBTS) is proposed and demonstrated for the first time in amorphous indium-gallium-zinc-oxide thin-film transistors. This was done by combining the PBTS/recovery time-evolution of the experimentally decomposed threshold voltage shift (ΔVT) and the technology computer-aided design (TCAD)-based charge trapping simulation. The extracted parameters were the trap density (NOT) = 2.6 × 1018 cm-3, the trap energy level (ΔET) = 0.6 eV, and the capture cross section (σ0) = 3 × 10-19 cm2. Furthermore, based on the established TCAD framework, the relationship between the electron trap parameters and the activation energy (Ea) is comprehensively investigated. It is found that Ea increases with an increase in σ0, whereas Ea is independent of NOT. In addition, as ΔET increases, Ea decreases in the electron trapping-dominant regime (low ΔET) and increases again in the Poole-Frenkel (PF) emission/hopping-dominant regime (high ΔET). Moreover, our results suggest that the cross-over ΔET point originates from the complicated temperature-dependent competition between the capture rate and the emission rate. The PBTS bias dependence of the relationship between Ea and ΔET suggests that the electric field dependence of the PF emission-based electron hopping is stronger than that of the thermionic field emission-based electron trapping.

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....

A small electron beam ion trap/source facility for electron/neutral–ion collisional spectroscopy in astrophysical plasmas

Science.gov (United States)

Liang, Gui-Yun; Wei, Hui-Gang; Yuan, Da-Wei; Wang, Fei-Lu; Peng, Ji-Min; Zhong, Jia-Yong; Zhu, Xiao-Long; Schmidt, Mike; Zschornack, Günter; Ma, Xin-Wen; Zhao, Gang

2018-01-01

Spectra are fundamental observation data used for astronomical research, but understanding them strongly depends on theoretical models with many fundamental parameters from theoretical calculations. Different models give different insights for understanding a specific object. Hence, laboratory benchmarks for these theoretical models become necessary. An electron beam ion trap is an ideal facility for spectroscopic benchmarks due to its similar conditions of electron density and temperature compared to astrophysical plasmas in stellar coronae, supernova remnants and so on. In this paper, we will describe the performance of a small electron beam ion trap/source facility installed at National Astronomical Observatories, Chinese Academy of Sciences.We present some preliminary experimental results on X-ray emission, ion production, the ionization process of trapped ions as well as the effects of charge exchange on the ionization.

Electron cooling of highly charged ions in penning traps; Elektronenkuehlung hochgeladener Ionen in Penningfallen

Energy Technology Data Exchange (ETDEWEB)

Moellers, B.

2007-02-08

For many high precision experiments with highly charged ions in ion traps it is necessary to work with low energy ions. One possibility to slow ions down to a very low energy in a trap is electron cooling, a method, which is already successfully used in storage rings to produce ion beams with high phase space density. Fast ions and a cold electron plasma are inserted into a Penning trap. The ions lose their energy due to Coulomb interaction with the electrons while they cross the plasma, the electrons are heated. The cooling time is the time, which is needed to cool an ion from a given initial energy to a low final energy. To calculate cooling times it is necessary to solve coupled differential equations for the ion energy and electron temperature. In a Penning trap the strong external magnetic field constitutes a theoretical challenge, as it influences the energy loss of the ions in an electron plasma, which can no longer be calculated analytically. In former estimates of cooling times this influence is neglected. But simulations show a dramatic decrease of the energy loss in the presence of a strong magnetic field, so it is necessary to investigate the effect of the magnetic field on the cooling times. This work presents a model to calculate cooling times, which includes both the magnetic field and the trap geometry. In a first step a simplified model without the external trap potential is developed. The energy loss of the ions in the magnetized electron plasma is calculated by an analytic approximation, which requires a numerical solution of integrals. With this model the dependence of the cooling time on different parameters like electron and ion density, magnetic field and the angle between ion velocity and magnetic field is studied for fully ionized uranium. In addition the influence of the electron heating is discussed. Another important topic in this context is the recombination between ions and electrons. The simplified model for cooling times allows to

Collisionless kinetic-fluid model of zonal flows in toroidal plasmas

International Nuclear Information System (INIS)

Sugama, H.; Watanabe, T.-H.; Horton, W.

2006-12-01

A novel kinetic-fluid model is presented, which describes collisionless time evolution of zonal flows in tokamaks. In the new zonal-flow closure relations, the parallel heat fluxes are written by the sum of short- and long-time-evolution parts. The former part is given in the dissipative form of the parallel heat diffusion and relates to collisionless damping processes. The latter is derived from the long-time-averaged gyrocenter distribution and plays a major role in describing low-frequency or stationary zonal flows, for which the parallel heat fluxes are expressed in terms of the parallel flow as well as the nonlinear-source and initial-condition terms. It is shown analytically and numerically that, when applied to the zonal flow driven by either ion or electron temperature gradient turbulence, the kinetic-fluid equations including the new closure relations can reproduce the same long-time zonal-flow responses to the initial condition and to the turbulence source as those obtained from the gyrokinetic model. (author)

Equilibrium distribution function in collisionless systems

International Nuclear Information System (INIS)

Pergamenshchik, V.M.

1988-01-01

Collisionless systems of a large number of N particles interacting by Coulomb forces are widely spread in cosmic and laboratory plasma. A statistical theory of equilibrium state of collisionless Coulomb systems which evolution obeys Vlasov equation is proposed. The developed formalism permits a sequential consideration of such distributed in one-particle six-dimensional phase space of a system and to obtain a simple result: equilibrium distribution function has the form of Fermi-Dirac distribution and doesn't depend on initial state factors

Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron-hole recombination

International Nuclear Information System (INIS)

Carpene, E; Mancini, E; Dallera, C; Schwen, D; Ronning, C; Silvestri, S De

2007-01-01

We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electron-phonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electron-hole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electron-hole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors

Electronic circuit provides automatic level control for liquid nitrogen traps

Science.gov (United States)

Turvy, R. R.

1968-01-01

Electronic circuit, based on the principle of increased thermistor resistance corresponding to decreases in temperature provides an automatic level control for liquid nitrogen cold traps. The electronically controlled apparatus is practically service-free, requiring only occasional reliability checks.

Phase-Space Density Analyses of the AE-8 Trapped Electron and the AP-8 Trapped Proton Model Environments

Energy Technology Data Exchange (ETDEWEB)

T.E. Cayton

2005-08-12

The AE-8 trapped electron and the AP-8 trapped proton models are used to examine the L-shell variation of phase-space densities for sets of transverse (or 1st) invariants, {mu}, and geometrical invariants, K (related to the first two adiabatic invariants). The motivation for this study is twofold: first, to discover the functional dependence of the phase-space density upon the invariants; and, second, to explore the global structure of the radiation belts within this context. Variation due to particle rest mass is considered as well. The overall goal of this work is to provide a framework for analyzing energetic particle data collected by instruments on Global Positioning System (GPS) spacecraft that fly through the most intense region of the radiation belt. For all considered values of {mu} and K, and for 3.5 R{sub E} < L < 6.5 R{sub E}, the AE-8 electron phase-space density increases with increasing L; this trend--the expected one for a population diffusing inward from an external source--continues to L = 7.5 R{sub E} for both small and large values of K but reverses slightly for intermediate values of K. The AP-8 proton phase-space density exhibits {mu}-dependent local minima around L = 5 R{sub E}. Both AE-8 and AP-8 exhibit critical or cutoff values for the invariants beyond which the flux and therefore the phase-space density vanish. For both electrons and protons, these cutoff values vary systematically with magnetic moment and L-shell and are smaller than those estimated for the atmospheric loss cone. For large magnetic moments, for both electrons and protons, the K-dependence of the phase-space density is exponential, with maxima at the magnetic equator (K = 0) and vanishing beyond a cutoff value, K{sub c}. Such features suggest that momentum-dependent trapping boundaries, perhaps drift-type loss cones, serve as boundary conditions for trapped electrons as well as trapped protons.

Phase-Space Density Analyses of the AE-8 Trapped Electron and the AP-8 Trapped Proton Model Environments

International Nuclear Information System (INIS)

Cayton, Thomas E.

2005-01-01

The AE-8 trapped electron and the AP-8 trapped proton models are used to examine the L-shell variation of phase-space densities for sets of transverse (or 1st) invariants, μ, and geometrical invariants, K (related to the first two adiabatic invariants). The motivation for this study is twofold: first, to discover the functional dependence of the phase-space density upon the invariants; and, second, to explore the global structure of the radiation belts within this context. Variation due to particle rest mass is considered as well. The overall goal of this work is to provide a framework for analyzing energetic particle data collected by instruments on Global Positioning System (GPS) spacecraft that fly through the most intense region of the radiation belt. For all considered values of μ and K, and for 3.5 R E E , the AE-8 electron phase-space density increases with increasing L; this trend--the expected one for a population diffusing inward from an external source--continues to L = 7.5 R E for both small and large values of K but reverses slightly for intermediate values of K. The AP-8 proton phase-space density exhibits μ-dependent local minima around L = 5 R E . Both AE-8 and AP-8 exhibit critical or cutoff values for the invariants beyond which the flux and therefore the phase-space density vanish. For both electrons and protons, these cutoff values vary systematically with magnetic moment and L-shell and are smaller than those estimated for the atmospheric loss cone. For large magnetic moments, for both electrons and protons, the K-dependence of the phase-space density is exponential, with maxima at the magnetic equator (K = 0) and vanishing beyond a cutoff value, K c . Such features suggest that momentum-dependent trapping boundaries, perhaps drift-type loss cones, serve as boundary conditions for trapped electrons as well as trapped protons

Reduction of charge trapping and electron tunneling in SIMOX by supplemental implantation of oxygen

International Nuclear Information System (INIS)

Stahlbush, R.E.; Hughes, H.L.; Krull, W.A.

1993-01-01

Silicon-on-insulator, SOI, technologies are being aggressively pursued to produce high density, high speed, radiation tolerant electronics. The dielectric isolation of the buried oxide makes it possible to design integrated circuits that greatly minimize single event upset and eliminate dose-rate induced latchup and upset. The reduction of excess-silicon related defects in SIMOX by the supplemental implantation of oxygen has been examined. The supplemental implant is 6% of the oxygen dose used to form the buried oxide, and is followed by a 1,000 C anneal, in contrast to the >1,300 C anneal used to form the buried oxide layer of SIMOX. The defects examined include shallow electron traps, deep hole traps, and silicon clusters. The radiation-induced shallow electron and deep hole trapping are measured by cryogenic detrapping and isothermal annealing techniques. The low-field (3 to 6 MV/cm) electron tunneling is interpreted as due to a two phase mixture of stoichiometric SiO 2 and Si clusters a few nm in size. Single and triple SIMOS samples have been examined. All of the defects are reduced by the supplemental oxygen processing. Shallow electron trapping is reduced by an order of magnitude. Because of the larger capture cross section for hole trapping, hole trapping is not reduced as much. The low-field electron tunneling due to Si clusters is also significantly reduced. Both uniform and nonuniform electron tunneling have been observed in SIMOX samples without supplement processing. In samples exhibiting only uniform tunneling, electron capture at holes has been observed. The nonuniform tunneling is superimposed upon the uniform tunneling and is characterized by current spiking

Photoconductivity and bleaching of trapped electrons at 770C in irradiated methylcyclohexane

International Nuclear Information System (INIS)

Dolivo, G.; Gaeumann, T.

1977-01-01

The influence of the wavelength and intensity of the bleaching radiation on the thermoluminescence, thermoconductivity, optical absorption and photoconductivity of the methylcyclohexane, protonated and deuterated, was studied. The energy level scheme of the trapped electron in this alkane is very similar to that found in MTHF and 3-MP. The rate of bleaching of the trapped electrons is less in the deuterated product. (U.K.)

Asymptotic theory of dissipative trapped electron mode overlapping many rational surfaces

International Nuclear Information System (INIS)

Rogister, A.; Hasselberg, G.

1978-01-01

The two dimensional eigenvalue equation describing the dissipative trapped electron mode is solved exactly in the limit of the mode overlapping many rational surfaces using the Pogutse model for the magnetic field and the pitch angle collision operator. The trapped electron contribution to the growth rate decreases, with respect to the standard theory, by a factor of order Δ/chi sub(T) << 1 where chi sub(T) is the position of the turning point and Δ the distance between rational surfaces

Dependence of the confinement time of an electron plasma on the magnetic field in a quadrupole Penning trap

Energy Technology Data Exchange (ETDEWEB)

Dyavappa, B.M.; Datar, Durgesh; Prakash; Ananthamurthy, Sharath [Bangalore University, Department of Physics, Bangalore (India)

2017-12-15

A quadrupole Penning trap is used to confine electrons in weak magnetic fields. Perturbations due to space charge and imperfections in the trap geometry, as well as collisions with the background gas molecules, lead to loss of the electrons from the trap. We present in this work the results on measurements of the electron confinement time and its dependence on the magnetic field in a quadrupolar Penning trap. We describe a method to measure the confinement time of an electron cloud under weak magnetic fields (0.01 T - 0.1 T). This time is found to scale as τ ∝ B{sup 1.41} in variance with the theoretically expected confinement time that scales as τ ∝ B{sup 2} for trapped electrons that are lost through collisions with the neutrals present in the trap. A measurement of the expansion rate of the electron plasma in the trap through controlled variation of the trap voltage, yields expansion times that depend on the energy of escaping electrons. This is found to vary in our case in the scaling range B{sup 0.32} to B{sup 0.43}. Distorting the geometry of the trap, results in a marked change in the confinement time's dependence on the magnetic field. The results indicate that the confinement time of the electron cloud in the trap is limited by both, effects of collisions and perturbations that result in the plasma loss through expansion in the trap. (orig.)

Tuning the Electronic and Dynamical Properties of a Molecule by Atom Trapping Chemistry.

Science.gov (United States)

Pham, Van Dong; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Abad, Enrique; Dappe, Yannick J; Smogunov, Alexander; Lagoute, Jérôme

2017-11-28

The ability to trap adatoms with an organic molecule on a surface has been used to obtain a range of molecular functionalities controlled by the choice of the molecular trapping site and local deprotonation. The tetraphenylporphyrin molecule used in this study contains three types of trapping sites: two carbon rings (phenyl and pyrrole) and the center of a macrocycle. Catching a gold adatom on the carbon rings leads to an electronic doping of the molecule, whereas trapping the adatom at the macrocycle center with single deprotonation leads to a molecular rotor and a second deprotonation leads to a molecular jumper. We call "atom trapping chemistry" the control of the structure, electronic, and dynamical properties of a molecule achieved by trapping metallic atoms with a molecule on a surface. In addition to the examples previously described, we show that more complex structures can be envisaged.

Excitation of THz hybrid modes in an elliptical dielectric rod waveguide with a cold collisionless unmagnetized plasma column by an annular electron beam

Energy Technology Data Exchange (ETDEWEB)

Rahmani, Z., E-mail: z.rahmani@kashanu.ac.ir; Safari, S. [Department of Laser and Photonics, Faculty of Physics, University of Kashan, Kashan, Islamic Republic of Iran (Iran, Islamic Republic of); Heidari-Semiromi, E. [Department of Condense Matter, Faculty of Physics, University of Kashan, Kashan, Islamic Republic of Iran (Iran, Islamic Republic of)

2016-06-15

The dispersion relation of electromagnetic waves propagating in an elliptical plasma waveguide with a cold collisionless unmagnetized plasma column and a dielectric rod is studied analytically. The frequency spectrum of the hybrid waves and the growth rate for excitation of the waves by a thin annular relativistic elliptical electron beam (TAREEB) is obtained. The effects of relative permittivity constant of dielectric rod, geometrical dimensions, plasma frequency, accelerating voltage, and current density of TAREEB on the growth rate and frequency spectra of the waveguide will be investigated.

Dielectronic recombination measurements using the Electron Beam Ion Trap

International Nuclear Information System (INIS)

Knapp, D.A.

1991-01-01

We have used the Electron Beam Ion Trap at LLNL to study dielectronic recombination in highly charged ions. Our technique is unique because we observe the x-rays from dielectronic recombination at the same time we see x-rays from all other electron-ion interactions. We have recently taken high-resolution, state-selective data that resolves individual resonances

Proposed LLNL electron beam ion trap

International Nuclear Information System (INIS)

Marrs, R.E.; Egan, P.O.; Proctor, I.; Levine, M.A.; Hansen, L.; Kajiyama, Y.; Wolgast, R.

1985-01-01

The interaction of energetic electrons with highly charged ions is of great importance to several research fields such as astrophysics, laser fusion and magnetic fusion. In spite of this importance there are almost no measurements of electron interaction cross sections for ions more than a few times ionized. To address this problem an electron beam ion trap (EBIT) is being developed at LLNL. The device is essentially an EBIS except that it is not intended as a source of extracted ions. Instead the (variable energy) electron beam interacting with the confined ions will be used to obtain measurements of ionization cross sections, dielectronic recombination cross sections, radiative recombination cross sections, energy levels and oscillator strengths. Charge-exchange recombinaion cross sections with neutral gasses could also be measured. The goal is to produce and study elements in many different charge states up to He-like xenon and Ne-like uranium. 5 refs., 2 figs

Identification of electron and hole traps in KH2PO4 crystals

International Nuclear Information System (INIS)

Garces, N. Y.; Stevens, K. T.; Halliburton, L. E.; Demos, S. G.; Radousky, H. B.; Zaitseva, N. P.

2001-01-01

Electron paramagnetic resonance (EPR) has been used to characterize a hole trap and several electron traps in single crystals of potassium dihydrogen phosphate (KH 2 PO 4 or KDP). The paramagnetic charge states of these centers are produced by ionizing radiation (e.g., x rays or a 266 nm beam from a pulsed Nd:YAG laser) and are stable for days and even weeks at room temperature. One center consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. This defect has a small, but easily observed, hyperfine interaction with the adjacent substitutional proton. The other centers are formed when an electron is trapped at an oxygen vacancy. These latter defects are best described as (PO 3 ) 2- molecular ions, where the primary phosphorus nucleus is responsible for a large hyperfine splitting (500--800 G in magnitude). Five EPR spectra representing variations of these oxygen vacancy centers are observed, with the differences being attributed to the relative position of a nearby cation vacancy, either a missing proton or potassium. An angular study of the EPR spectra, conducted at room temperature, provided principal values and principal directions for the g matrices and hyperfine matrices for the hole center and two of the electron centers

The Role of Electron Transport and Trapping in MOS Total-Dose Modeling

International Nuclear Information System (INIS)

Flament, O.; Fleetwood, D.M.; Leray, J.L.; Paillet, P.; Riewe, L.C.; Winokur, P.S.

1999-01-01

Deep and shallow electron traps form in irradiated thermal SiO 2 as a natural response to hole transport and trapping. The density and stability of these defects are discussed, as are their implications for total-dose modeling

A way for evaluating parameters of electron transport in non-polar molecular liquids derived from analysis of the trapped electron recombination kinetics

International Nuclear Information System (INIS)

Lukin, L.V.

2012-01-01

The geminate recombination kinetics of electron-ion pairs produced by high energy radiation in liquid hydrocarbons is considered in the two state model of electron transport. The purpose of the study is to relate the trapped electron transient optical absorption, observed in the pulse radiolysis experiments, to fundamental parameters of electron transport in liquid. It is shown that measurements of the half-life time and amplitude of the trapped electron decay curve allow one to find the electron life time in a localized state. - Highlights: ► A two state electron model is applied to geminate charge recombination. ► Time dependence of trapped electrons is computed for liquid isooctane and squalane. ► Electron decay kinetics depends on electron life time in a localized state. ► Key parameters of electron transport are found from the pulse radiolysis studies.

Atomic physics of highly charged ions in an electron beam ion trap

International Nuclear Information System (INIS)

Marrs, R.E.

1990-07-01

Two electron beam ion traps are in use at LLNL for the purpose of studying the properties of very highly charged ions and their interactions with electrons. This paper reviews the operation of the traps and discusses recent experiments in three areas: precision transition energy measurements in the limit of very high ion charge, dielectronic recombination measurements for the He-like isoelectronic sequence, and measurements of x-ray polarization. 22 refs., 11 figs., 1 tab

Coupling of ion temperature gradient and trapped electron modes in the presence of impurities in tokamak plasmas

Science.gov (United States)

Du, Huarong; Wang, Zheng-Xiong; Dong, J. Q.; Liu, S. F.

2014-05-01

The coupling of ion temperature gradient (ITG or ηi) mode and trapped electron mode (TEM) in the presence of impurity ions is numerically investigated in toroidal collisionless plasmas, using the gyrokinetic integral eigenmode equation. A framework for excitations of the ITG modes and TEMs with respect to their driving sources is formulated first, and then the roles of impurity ions played in are analyzed comprehensively. In particular, the characteristics of the ITG and TEM instabilities in the presence of impurity ions are emphasized for both strong and weak coupling (hybrid and coexistent) cases. It is found that the impurity ions with inwardly (outwardly) peaked density profiles have stabilizing (destabilizing) effects on the hybrid (namely the TE-ITG) modes in consistence with previous works. A new finding of this work is that the impurity ions have stabilizing effects on TEMs in small ηi (ηi≤1) regime regardless of peaking directions of their density profiles whereas the impurity ions with density gradient Lez=Lne/Lnz>1 (LezTEMs in large ηi (ηi≥1) regime. In addition, the dependences of the growth rate, real frequency, eigenmode structure, and wave spectrum on charge concentration, charge number, and mass of impurity ions are analyzed in detail. The necessity for taking impurity ion effects on the features of turbulence into account in future transport experimental data analyses is also discussed.

A multidimensional theory for electron trapping by a plasma wake generated in the bubble regime

International Nuclear Information System (INIS)

Kostyukov, I; Nerush, E; Pukhov, A; Seredov, V

2010-01-01

We present a theory for electron self-injection in nonlinear, multidimensional plasma waves excited by a short laser pulse in the bubble regime or by a short electron beam in the blowout regime. In these regimes, which are typical for electron acceleration in the last impressive experiments, the laser radiation pressure or the electron beam charge pushes out plasma electrons from some region, forming a plasma cavity or a bubble with a huge ion charge. The plasma electrons can be trapped in the bubble and accelerated by the plasma wakefields up to a very high energy. We derive the condition of the electron trapping in the bubble. The developed theory predicts the trapping cross section in terms of the bubble radius and the bubble velocity. It is found that the dynamic bubble deformations observed in the three-dimensional (3D) particle-in-cell (PIC) simulations influence the trapping process significantly. The bubble elongation reduces the gamma-factor of the bubble, thereby strongly enhancing self-injection. The obtained analytical results are in good agreement with the 3D PIC simulations.

Shearing Box Simulations of the MRI in a Collisionless Plasma

International Nuclear Information System (INIS)

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

2005-01-01

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

Self-Consistent System of Equations for a Kinetic Description of the Low-Pressure Discharges Accounting for the Nonlocal and Collisionless Electron Dynamics

International Nuclear Information System (INIS)

Kaganovich, Igor D.; Polomarov, Oleg

2003-01-01

In low-pressure discharges, when the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially non-local. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the non-local conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, non-uniform, nearly collisionless plasmas of low-pressure discharges is derived. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. The importance of accounting for the non-uniform plasma density profile on both the current density profile and the EEDF is demonstrated

X-ray spectroscopy of highly-ionized atoms in an electron beam ion trap (EBIT)

International Nuclear Information System (INIS)

Marrs, R.E.; Bennett, C.; Chen, M.H.

1988-01-01

An Electron Beam Ion Trap at Lawrence Livermore National Laboratory is being used to produce and trap very-highly-charged-ions (q /le/ 70+) for x-ray spectroscopy measurements. Recent measurements of dielectronic recombination, electron impact excitation and transition energies are presented. 15 refs., 12 figs., 1 tab

Twisted electron-acoustic waves in plasmas

International Nuclear Information System (INIS)

Aman-ur-Rehman; Ali, S.; Khan, S. A.; Shahzad, K.

2016-01-01

In the paraxial limit, a twisted electron-acoustic (EA) wave is studied in a collisionless unmagnetized plasma, whose constituents are the dynamical cold electrons and Boltzmannian hot electrons in the background of static positive ions. The analytical and numerical solutions of the plasma kinetic equation suggest that EA waves with finite amount of orbital angular momentum exhibit a twist in its behavior. The twisted wave particle resonance is also taken into consideration that has been appeared through the effective wave number q_e_f_f accounting for Laguerre-Gaussian mode profiles attributed to helical phase structures. Consequently, the dispersion relation and the damping rate of the EA waves are significantly modified with the twisted parameter η, and for η → ∞, the results coincide with the straight propagating plane EA waves. Numerically, new features of twisted EA waves are identified by considering various regimes of wavelength and the results might be useful for transport and trapping of plasma particles in a two-electron component plasma.

Direct probing of electron and hole trapping into nano-floating-gate in organic field-effect transistor nonvolatile memories

Energy Technology Data Exchange (ETDEWEB)

Cui, Ze-Qun; Wang, Shun; Chen, Jian-Mei; Gao, Xu; Dong, Bin, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn; Chi, Li-Feng, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn; Wang, Sui-Dong, E-mail: wangsd@suda.edu.cn, E-mail: chilf@suda.edu.cn, E-mail: bdong@suda.edu.cn [Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 (China)

2015-03-23

Electron and hole trapping into the nano-floating-gate of a pentacene-based organic field-effect transistor nonvolatile memory is directly probed by Kelvin probe force microscopy. The probing is straightforward and non-destructive. The measured surface potential change can quantitatively profile the charge trapping, and the surface characterization results are in good accord with the corresponding device behavior. Both electrons and holes can be trapped into the nano-floating-gate, with a preference of electron trapping than hole trapping. The trapped charge quantity has an approximately linear relation with the programming/erasing gate bias, indicating that the charge trapping in the device is a field-controlled process.

Direct probing of electron and hole trapping into nano-floating-gate in organic field-effect transistor nonvolatile memories

International Nuclear Information System (INIS)

Cui, Ze-Qun; Wang, Shun; Chen, Jian-Mei; Gao, Xu; Dong, Bin; Chi, Li-Feng; Wang, Sui-Dong

2015-01-01

Electron and hole trapping into the nano-floating-gate of a pentacene-based organic field-effect transistor nonvolatile memory is directly probed by Kelvin probe force microscopy. The probing is straightforward and non-destructive. The measured surface potential change can quantitatively profile the charge trapping, and the surface characterization results are in good accord with the corresponding device behavior. Both electrons and holes can be trapped into the nano-floating-gate, with a preference of electron trapping than hole trapping. The trapped charge quantity has an approximately linear relation with the programming/erasing gate bias, indicating that the charge trapping in the device is a field-controlled process

Electron heat transport in shaped TCV L-mode plasmas

International Nuclear Information System (INIS)

Camenen, Y; Pochelon, A; Bottino, A; Coda, S; Ryter, F; Sauter, O; Behn, R; Goodman, T P; Henderson, M A; Karpushov, A; Porte, L; Zhuang, G

2005-01-01

Electron heat transport experiments are performed in L-mode discharges at various plasma triangularities, using radially localized electron cyclotron heating to vary independently both the electron temperature T e and the normalized electron temperature gradient R/L T e over a large range. Local gyro-fluid (GLF23) and global collisionless gyro-kinetic (LORB5) linear simulations show that, in the present experiments, trapped electron mode (TEM) is the most unstable mode. Experimentally, the electron heat diffusivity χ e is shown to decrease with increasing collisionality, and no dependence of χ e on R/L T e is observed at high R/L T e values. These two observations are consistent with the predictions of TEM simulations, which supports the fact that TEM plays a crucial role in electron heat transport. In addition, over the broad range of positive and negative triangularities investigated, the electron heat diffusivity is observed to decrease with decreasing plasma triangularity, leading to a strong increase of plasma confinement at negative triangularity

Deep electron traps in HfO_2-based metal-oxide-semiconductor capacitors

International Nuclear Information System (INIS)

Salomone, L. Sambuco; Lipovetzky, J.; Carbonetto, S.H.; García Inza, M.A.; Redin, E.G.; Campabadal, F.

2016-01-01

Hafnium oxide (HfO_2) is currently considered to be a good candidate to take part as a component in charge-trapping nonvolatile memories. In this work, the electric field and time dependences of the electron trapping/detrapping processes are studied through a constant capacitance voltage transient technique on metal-oxide-semiconductor capacitors with atomic layer deposited HfO_2 as insulating layer. A tunneling-based model is proposed to reproduce the experimental results, obtaining fair agreement between experiments and simulations. From the fitting procedure, a band of defects is identified, located in the first 1.7 nm from the Si/HfO_2 interface at an energy level E_t = 1.59 eV below the HfO_2 conduction band edge with density N_t = 1.36 × 10"1"9 cm"−"3. A simplified analytical version of the model is proposed in order to ease the fitting procedure for the low applied voltage case considered in this work. - Highlights: • We characterized deep electron trapping/detrapping in HfO_2 structures. • We modeled the experimental results through a tunneling-based model. • We obtained an electron trap energy level of 1.59 eV below conduction band edge. • We obtained a spatial trap distribution extending 1.7 nm within the insulator. • A simplified tunneling front model is able to reproduce the experimental results.

Instabilities of collisionless current sheets revisited: The role of anisotropic heating

International Nuclear Information System (INIS)

Muñoz, P. A.; Kilian, P.; Büchner, J.

2014-01-01

In this work, we investigate the influence of the anisotropic heating on the spontaneous instability and evolution of thin Harris-type collisionless current sheets, embedded in antiparallel magnetic fields. In particular, we explore the influence of the macroparticle shape-function using a 2D version of the PIC code ACRONYM. We also investigate the role of the numerical collisionality due to the finite number of macroparticles in PIC codes. It is shown that it is appropriate to choose higher order shape functions of the macroparticles compared to a larger number of macroparticles per cell. This allows to estimate better the anisotropic electron heating due to the collisions of macroparticles in a PIC code. Temperature anisotropies can stabilize the tearing mode instability and trigger additional current sheet instabilities. We found a good agreement between the analytically derived threshold for the stabilization of the anisotropic tearing mode and other instabilities, either spontaneously developing or initially triggered ones. Numerical effects causing anisotropic heating at electron time scales become especially important for higher mass ratios (above m i /m e =180). If numerical effects are carefully taken into account, one can recover the theoretical estimated linear growth rates of the tearing instability of thin isotropic collisionless current sheets, also for higher mass ratios

A study of the profile of the E3 electron trap in GaAs

Energy Technology Data Exchange (ETDEWEB)

Kourkoutas, C.D. (TEI Athens (Greece). Dept. of Physics Chemistry and Material Technology); Kovacs, B.; Szentpali, B.; Somogyi, K. (Research Inst. for Technical Physics, Budapest (Hungary)); Euthymiou, P.C. (Athens Univ. (Greece)); Giakoumakis, G.E. (Ioannina Univ. (Greece). Dept. of Physics)

1994-01-01

Electron irradiation at room temperature introduces in GaAs a donor type electronic state Tx at 0.18 eV, which is associated with the E3 electron trap. The presence of Tx is observed at depths d > 1.5 [mu]m, which correspond to the limits of the depletion region under the highest applied reverse bias voltage, while the E3 trap concentration drops off into the same region. (author).

A study of the profile of the E3 electron trap in GaAs

International Nuclear Information System (INIS)

Kourkoutas, C.D.; Euthymiou, P.C.; Giakoumakis, G.E.

1994-01-01

Electron irradiation at room temperature introduces in GaAs a donor type electronic state Tx at 0.18 eV, which is associated with the E3 electron trap. The presence of Tx is observed at depths d > 1.5 μm, which correspond to the limits of the depletion region under the highest applied reverse bias voltage, while the E3 trap concentration drops off into the same region. (author)

Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

Science.gov (United States)

Takahashi, Kazunori; Charles, Christine; Boswell, Rod; Ando, Akira

2018-01-01

A specially constructed experiment shows the near perfect adiabatic expansion of an ideal electron gas resulting in a polytropic index greater than 1.4, approaching the adiabatic value of 5 /3 , when removing electric fields from the system, while the polytropic index close to unity is observed when the electrons are trapped by the electric fields. The measurements were made on collisionless electrons in an argon plasma expanding in a magnetic nozzle. The collision lengths of all electron collision processes are greater than the scale length of the expansion, meaning the system cannot be in thermodynamic equilibrium, yet thermodynamic concepts can be used, with caution, in explaining the results. In particular, a Lorentz force, created by inhomogeneities in the radial plasma density, does work on the expanding magnetic field, reducing the internal energy of the electron gas that behaves as an adiabatically expanding ideal gas.

Ion production and trapping in electron rings

International Nuclear Information System (INIS)

Gluckstern, R.C.; Ruggiero, A.G.

1979-08-01

The electron beam in the VUV and X-ray rings of NSLS will ionize residual gas by collisions. Positive ions will be produced with low velocity, and will be attracted by the electron beam to the beam axis. If they are trapped in stable (transverse) orbits, they may accumulate, thereby increasing the ν/sub x,z/ of the individual electrons. Since the accumulated ions are unlikely to be of uniform density, a spread in ν/sub x,z/ will also occur. Should these effects be serious, it may be necessary to introduce clearing electrodes, although this may increase Z/n in the rings, thereby adding to longitudinal instability problems. The seriousness of the above effect for the VUV and X-ray rings is estimated

Self-trapping and self-focusing of an elliptical laser beam in a collisionless magnetoplasma

Energy Technology Data Exchange (ETDEWEB)

Soni, V S; Nayyar, V P [Punjabi Univ., Patiala (India). Dept. of Physics

1980-03-14

The authors have studied the self-trapping and self-focusing-defocusing of an elliptically shaped laser beam in a magnetoplasma. The critical self-trapping power of the beam for the ordinary mode is twice the critical power for the extraordinary mode. On both sides of the critical power required for self-trapping, there are separate values of the critical power for the x-dimension as well as for the y-dimension of the beam. At and above the critical value for the x-dimension, the beam defocuses in both directions while at and below the critical value for the y-dimension, it self-focuses in both directions. Self-trapping is also observed in the case of the ordinary mode at a critical value of the external magnetic field for any power value.

Electronic properties of hafnium oxide: A contribution from defects and traps

Energy Technology Data Exchange (ETDEWEB)

Gritsenko, Vladimir A., E-mail: grits@isp.nsc.ru; Perevalov, Timofey V.; Islamov, Damir R., E-mail: damir@isp.nsc.ru

2016-02-15

In the present article, we give a review of modern data and latest achievements pertaining to the study of electronic properties of oxygen vacancies in hafnium oxide. Hafnium oxide is a key dielectric for use in many advanced silicon devices. Oxygen vacancies in hafnium oxide largely determine the electronic properties of the material. We show that the electronic transitions between the states due to oxygen vacancies largely determine the optical absorption and luminescent properties of hafnium oxide. We discuss the role of oxygen vacancies as traps that facilitate charge transport in hafnium oxide films. Also, we demonstrate the fact that the electrical conductivity in hafnium oxide is controlled by the phonon-assisted tunnelling of charge carriers between traps that were identified as oxygen vacancies.

Impact of Shock Front Rippling and Self-reformation on the Electron Dynamics at Low-Mach-number Shocks

Science.gov (United States)

Yang, Zhongwei; Lu, Quanming; Liu, Ying D.; Wang, Rui

2018-04-01

Electron dynamics at low-Mach-number collisionless shocks are investigated by using two-dimensional electromagnetic particle-in-cell simulations with various shock normal angles. We found: (1) The reflected ions and incident electrons at the shock front provide an effective mechanism for the quasi-electrostatic wave generation due to the charge-separation. A fraction of incident electrons can be effectively trapped and accelerated at the leading edge of the shock foot. (2) At quasi-perpendicular shocks, the electron trapping and reflection is nonuniform due to the shock rippling along the shock surface and is more likely to take place at some locations accompanied by intense reflected ion-beams. The electron trapping process has a periodical evolution over time due to the shock front self-reformation, which is controlled by ion dynamics. Thus, this is a cross-scale coupling phenomenon. (3) At quasi-parallel shocks, reflected ions can travel far back upstream. Consequently, quasi-electrostatic waves can be excited in the shock transition and the foreshock region. The electron trajectory analysis shows these waves can trap electrons at the foot region and reflect a fraction of them far back upstream. Simulation runs in this paper indicate that the micro-turbulence at the shock foot can provide a possible scenario for producing the reflected electron beam, which is a basic condition for the type II radio burst emission at low-Mach-number interplanetary shocks driven by Coronal Mass Ejections (CMEs).

Hydride vapor phase GaN films with reduced density of residual electrons and deep traps

International Nuclear Information System (INIS)

Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Yugova, T. G.; Cox, H.; Helava, H.; Makarov, Yu.; Usikov, A. S.

2014-01-01

Electrical properties and deep electron and hole traps spectra are compared for undoped n-GaN films grown by hydride vapor phase epitaxy (HVPE) in the regular process (standard HVPE samples) and in HVPE process optimized for decreasing the concentration of residual donor impurities (improved HVPE samples). It is shown that the residual donor density can be reduced by optimization from ∼10 17  cm −3 to (2–5) × 10 14  cm −3 . The density of deep hole traps and deep electron traps decreases with decreased donor density, so that the concentration of deep hole traps in the improved samples is reduced to ∼5 × 10 13  cm −3 versus 2.9 × 10 16  cm −3 in the standard samples, with a similar decrease in the electron traps concentration

New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

International Nuclear Information System (INIS)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha

2011-01-01

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.

Electron, hole and exciton self-trapping in germanium doped silica glass from DFT calculations with self-interaction correction

International Nuclear Information System (INIS)

Du Jincheng; Rene Corrales, L.; Tsemekhman, Kiril; Bylaska, Eric J.

2007-01-01

Density functional theory (DFT) calculations were employed to understand the refractive index change in germanium doped silica glasses for the trapped states of electronic excitations induced by UV irradiation. Local structure relaxation and excess electron density distribution were calculated upon self-trapping of an excess electron, hole, and exciton in germanium doped silica glass. The results show that both the trapped exciton and excess electron are highly localized on germanium ion and, to some extent, on its oxygen neighbors. Exciton self-trapping is found to lead to the formation of a Ge E' center and a non-bridging hole center. Electron trapping changes the GeO 4 tetrahedron structure into trigonal bi-pyramid with the majority of the excess electron density located along the equatorial line. The self-trapped hole is localized on bridging oxygen ions that are not coordinated to germanium atoms that lead to elongation of the Si-O bonds and change of the Si-O-Si bond angles. We carried out a comparative study of standard DFT versus DFT with a hybrid PBE0 exchange and correlation functional. The results show that the two methods give qualitatively similar relaxed structure and charge distribution for electron and exciton trapping in germanium doped silica glass; however, only the PBE0 functional produces the self-trapped hole

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.

Trapped electrons as a free energy source for the auroral kilometric radiation

International Nuclear Information System (INIS)

Louarn, P.; Roux, A.; de Feraudy, H.; Le Queau, D.; Andre, M.; Matson, L.

1990-01-01

Simultaneous measurements of electromagnetic fields and particle distributions, measured during the crossing by the Swedish spacecraft Viking of an auroral kilometric radiation (AKR) source, are presented. It is shown that AKR is generated within an acceleration region characterized by an upward directed parallel electric field, as evidenced by its signature on the proton and electron distributions. From particle observations inside the AKR source it is clear that the potential drop below the spacecraft produces upward moving field-aligned ion beams and a depletion in the density of low energy electrons. The potential drop above the spacecraft produces downward accelerated electrons. A large fraction of these electrons have small parallel velocities; they mirror above the ionosphere. These trapped electrons lie in a region of velocity space which should be empty in a simple adiabatic theory. The authors suggest that these electrons get trapped when they experience a time-varying (or space-varying) parallel electric field. This conclusion is supported by the comparison between the observed electron distribution function and a model distribution function built by applying Liouville theorem. Since trapped electrons can cause positive gradients (∂f e /∂V perpendicular > 0) over a broad range of parallel velocities, around v parallel ∼ 0, it is suggested that they are the free energy source for the AKR. This conclusion is substantiated by an evaluation of the convective growth rate, where the various input parameters have been determined by fitting particle data

Fast Transverse Beam Instability Caused by Electron Cloud Trapped in Combined Function Magnets

Energy Technology Data Exchange (ETDEWEB)

Antipov, Sergey [Univ. of Chicago, IL (United States)

2017-03-01

Electron cloud instabilities affect the performance of many circular high-intensity particle accelerators. They usually have a fast growth rate and might lead to an increase of the transverse emittance and beam loss. A peculiar example of such an instability is observed in the Fermilab Recycler proton storage ring. Although this instability might pose a challenge for future intensity upgrades, its nature had not been completely understood. The phenomena has been studied experimentally by comparing the dynamics of stable and unstable beam, numerically by simulating the build-up of the electron cloud and its interaction with the beam, and analytically by constructing a model of an electron cloud driven instability with the electrons trapped in combined function dipoles. Stabilization of the beam by a clearing bunch reveals that the instability is caused by the electron cloud, trapped in beam optics magnets. Measurements of microwave propagation confirm the presence of the cloud in the combined function dipoles. Numerical simulations show that up to 10$^{-2}$ of the particles can be trapped by their magnetic field. Since the process of electron cloud build-up is exponential, once trapped this amount of electrons significantly increases the density of the cloud on the next revolution. In a combined function dipole this multi-turn accumulation allows the electron cloud reaching final intensities orders of magnitude greater than in a pure dipole. The estimated fast instability growth rate of about 30 revolutions and low mode frequency of 0.4 MHz are consistent with experimental observations and agree with the simulations. The created instability model allows investigating the beam stability for the future intensity upgrades.

High-resolution compact Johann crystal spectrometer with the Livermore electron beam ion trap

International Nuclear Information System (INIS)

Robbins, D.L.; Chen, H.; Beiersdorfer, P.; Faenov, A.Ya.; Pikuz, T.A.; May, M.J.; Dunn, J.; Smith, A.J.

2004-01-01

A compact high-resolution (λ/Δλ≅10 000) spherically bent crystal spectrometer in the Johann geometry was recently installed and tested on the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. The curvature of the mica (002) crystal grating allows for higher collection efficiency compared to the flat and cylindrically bent crystal spectrometers commonly used on the Livermore electron beam ion traps. The spectrometer's Johann configuration enables orientation of its dispersion plane to be parallel to the electron beam propagation. Used in concert with a crystal spectrometer, whose dispersion plane is perpendicular to the electron beam propagation, the polarization of x-ray emission lines can be measured

Study of heliumlike neon using an electron beam ion trap

International Nuclear Information System (INIS)

Wargelin, B.J.; Kahn, S.M.; Beiersdorfer, P.

1992-01-01

The 2-to-1 spectra of several astrophysically abundant He-like ions are being studied using the Electron Beam Ion Trap (EBIT) at Lawrence Livermore National Laboratory. Spectra are recorded for a broad range of plasma parameters, including electron density, energy, and ionization balance. We describe the experimental equipment and procedure and present some typical data

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.

Evaluating Origin of Electron Traps in Tris(8-hydroxyquinoline) Aluminum Thin Films using Thermally Stimulated Current Technique

OpenAIRE

Matsushima, Toshinori; Adachi, Chihaya

2008-01-01

We measured the energy distributions and concentrations of electron traps in O_2-unexposed and O_2-exposed tris(8-hydroxyquinoline) aluminum (Alq_3) films using a thermally stimulated current (TSC) technique to investigate how doping O_2 molecules in Alq_3 films affect the films' electron trap and electron transport characteristics. The results of our TSC studies revealed that Alq_3 films have an electron trap distribution with peak depths ranging from 0.075 to 0.1 eV and peak widths ranging ...

EBIT (Electron Beam Ion Trap), N-Division Experimental Physics. Annual report, 1994

International Nuclear Information System (INIS)

Schneider, D.

1995-10-01

The experimental groups in the Electron Beam Ion Trap (EBIT) program continue to perform front-line research with trapped and extracted highly charged ions (HCI) in the areas of ion/surface interactions, atomic spectroscopy, electron-ion interaction and structure measurements, highly charged ion confinement, and EBIT development studies. The ion surface/interaction studies which were initiated five years ago have reached a stage where they an carry out routine investigations, as well as produce breakthrough results towards the development of novel nanotechnology. At EBIT and SuperEBIT studies of the x-ray emission from trapped ions continue to produce significant atomic structure data with high precision for few electron systems of high-Z ions. Furthermore, diagnostics development for magnetic and laser fusion, supporting research for the x-ray laser and weapons programs, and laboratory astrophysics experiments in support of NASA's astrophysics program are a continuing effort. The two-electron contributions to the binding energy of helium like ions were measured for the first time. The results are significant because their precision is an order of magnitude better than those of competing measurements at accelerators, and the novel technique isolates the energy corrections that are the most interesting. The RETRAP project which was initiated three years ago has reached a stage where trapping, confining and electronic cooling of HCI ions up to Th 80+ can be performed routinely. Measurements of the rates and cross sections for electron transfer from H 2 performed to determine the lifetime of HCI up to Xe q+ and Th q+ (35 ≤ q ≤ 80) have been studied at mean energies estimated to be ∼ 5 q eV. This combination of heavy ions with very high charges and very low energies is rare in nature, but may be encountered in planned fusion energy demonstration devices, in highly charged ion sources, or in certain astrophysical events

Trapped Electron Instability of Electron Plasma Waves: Vlasov simulations and theory

Science.gov (United States)

Berger, Richard; Chapman, Thomas; Brunner, Stephan

2013-10-01

The growth of sidebands of a large-amplitude electron plasma wave is studied with Vlasov simulations for a range of amplitudes (. 001 vph = +/-ωbe , where vph =ω0 /k0 and ωbe is the bounce frequency of a deeply trapped electron. In 2D simulations, we find that the instability persists and co-exists with the filamentation instability. 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 funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD.

Experimental demonstration and visual observation of dust trapping in an electron storage ring

Directory of Open Access Journals (Sweden)

Yasunori Tanimoto

2009-11-01

Full Text Available Sudden decreases in the beam lifetime, which are attributed to the dust trappings, sometimes occur at the electron storage ring Photon Factory Advanced Ring (PF-AR. Since these dust events cause difficulties in user operations, we have been carefully observing this phenomenon for many years. Our observations indicated that the dust trappings could be caused by electric discharges in vacuum ducts. In order to demonstrate this hypothesis experimentally, we designed a new vacuum device that intentionally generates electric discharges and installed it in PF-AR. Using this device, we could repeatedly induce sudden decreases in the beam lifetime because of the generated electric discharge. We also detected decreases in the beam lifetime caused by mechanical movement of the electrodes in the device. Moreover, we could visually observe the dust trapping phenomenon; the trapped dust particle was observed by two video cameras and appeared as a luminous body that resembled a shooting star. This was the first direct observation of a luminous dust particle trapped by the electron beam.

Natural variations in the geomagnetically trapped electron population

Science.gov (United States)

Vampola, A. L.

1972-01-01

Temporal variations in the trapped natural electron flux intensities and energy spectra are discussed and demonstrated using recent satellite data. These data are intended to acquaint the space systems engineer with the types of natural variations that may be encountered during a mission and to augment the models of the electron environment currently being used in space system design and orbit selection. An understanding of the temporal variations which may be encountered should prove helpful. Some of the variations demonstrated here which are not widely known include: (1) addition of very energetic electrons to the outer zone during moderate magnetic storms: (2) addition of energetic electrons to the inner zone during major magnetic storms; (3) inversions in the outer zone electron energy spectrum during the decay phase of a storm injection event and (4) occasional formation of multiple maxima in the flux vs altitude profile of moderately energetic electrons.

Spectroscopy of highly charged tungsten ions with Electron Beam Ion Traps

International Nuclear Information System (INIS)

Sakaue, Hiroyuki A.; Kato, Daiji; Morita, Shigeru; Murakami, Izumi; Yamamoto, Norimasa; Ohashi, Hayato; Yatsurugi, Junji; Nakamura, Nobuyuki

2013-01-01

We present spectra of highly charged tungsten ions in the extreme ultra-violet (EUV) by using electron beam ion traps. The electron energy dependence of spectra is investigated of electron energies from 490 to 1440 eV. Previously unreported lines are presented in the EUV range, and some of them are identified by comparing the wavelengths with theoretical calculations. (author)

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.

Nonlinear trapped electron mode and anomalous heat transport in tokamaks

International Nuclear Information System (INIS)

Kaw, P.K.

1982-01-01

We take the phenomenological point of view that the anomalous electron thermal conductivity produced by the non-linear trapped electron mode should also influence the stability properties of the mode itself. Using a model equation, we show that this effect makes the mode self-stabilizing. A simple expression for the anomalous thermal conductivity is derived, and its scaling properties are discussed. (orig.)

Electron self-injection and trapping into an evolving plasma bubble.

Science.gov (United States)

Kalmykov, S; Yi, S A; Khudik, V; Shvets, G

2009-09-25

The blowout (or bubble) regime of laser wakefield acceleration is promising for generating monochromatic high-energy electron beams out of low-density plasmas. It is shown analytically and by particle-in-cell simulations that self-injection of the background plasma electrons into the quasistatic plasma bubble can be caused by slow temporal expansion of the bubble. Sufficient criteria for the electron trapping and bubble's expansion rate are derived using a semianalytic nonstationary Hamiltonian theory. It is further shown that the combination of bubble's expansion and contraction results in monoenergetic electron beams.

A high-energy electron beam ion trap for production of high-charge high-Z ions

International Nuclear Information System (INIS)

Knapp, D.A.; Marrs, R.E.; Elliott, S.R.; Magee, E.W.; Zasadzinski, R.

1993-01-01

We have developed a new high-energy electron beam ion trap, the first laboratory source of low-energy, few-electron, high-Z ions. We describe the device and report measurements of its performance, including the electron beam diameter, current density and energy, and measurements of the ionization balance for several high-Z elements in the trap. This device opens up a wide range of possible experiments in atomic physics, plasma physics, and nuclear physics. (orig.)

Nearly collisionless spherical accretion

International Nuclear Information System (INIS)

Begelman, M.C.

1977-01-01

A fluid-like gas accretes much more efficiently than a collisionless gas. The ability of an accreting gas to behave like a fluid depends on the relationship of the mean free path of a gas particle at r → infinity lambdasub(infinity), to the typical length scales associated with the star-gas system. This relationship is examined in detail. For constant collision cross-section evidence is found for a rapid changeover from collisionless to fluid-like accretion flow when lambdasub(infinity) drops below a certain value, but for hard Coulomb collisions, the transition is more gradual, and is sensitive to the adiabatic index of the gas at r→ infinity. To these results must be added the effects of the substantial cusp of bound particles, which always develops in a system with arbitrarily small but non-zero cross-section. The density run in such a cusp depends on the collision properties of the particles. 'Loss-cone' accretion from the cusp may in some cases exceed the predicted accretion rate. (author)

Origin of the main deep electron trap in electron irradiated InP

International Nuclear Information System (INIS)

Sibille, A.

1986-01-01

The electrical activity and annealing behavior of the main electron trap in electron irradiated InP p + n junctions has been investigated. A very marked depth dependence of the annealing rate has been found. Moreover, this center apparently acts as if it were a deep donor, leading to an increase of carrier concentration on the n side. All these results are coherently interpreted with a model in terms of radiation defect D(P) (phosphorus interstitial or vacancy), residual shallow acceptor complexing, the final annealing resulting from a dissociation of the complex followed by a diffusion and either recapture or annihilation of D(P)

Electron cyclotron current drive predictions for ITER: Comparison of different models

International Nuclear Information System (INIS)

Marushchenko, N.B.; Maassberg, H.; Beidler, C.D.; Turkin, Yu.

2007-01-01

Full text: Due to its high localization and operational flexibility, Electron Cyclotron Current Drive (ECCD) is envisaged for stabilizing the Neoclassical Tearing Mode (NTM) in tokamaks and correcting the rotational transform profile in stellarators. While the spatial location of the electron cyclotron resonant interaction is usually calculated by the ray-tracing technique, numerical tools for calculating the ECCD efficiency are not so common. Two different methods are often applied: i) direct calculation by Fokker-Planck modelling, and ii) by the adjoint approach technique. In the present report we analyze and compare different models used in the adjoint approach technique from the point of view of ITER applications. The numerical tools for calculating the ECCD efficiency developed to date do not completely cover the range of collisional regimes for the electrons involved in the current drive. Only two opposite limits are well developed, collisional and collisionless. Nevertheless, for the densities and temperatures expected for ECCD application in ITER, the collisionless limit model (with trapped particles taken into account) is quite suitable. We analyze the requisite ECCD scenarios with help of the new ray tracing code TRAVIS with the adjoint approach implemented. The (adjoint) Green's function applied for the current drive calculations is formulated with momentum conservation taken into account; this is especially important and even crucial for scenarios, in which mainly bulk electrons are responsible for absorption of the RF power. For comparison, the most common 'high speed limit' model in which the collision operator neglects the integral part and which is approximated by terms valid only for the tail electrons, produces an ECCD efficiency which is an underestimate for some cases by a factor of about 2. In order to select the appropriate model, a rough criterion of 'high speed limit' model applicability is formulated. The results are verified also by

Evaporative cooling of highly charged ions in EBIT [Electron Beam Ion Trap]: An experimental realization

International Nuclear Information System (INIS)

Schneider, M.B.; Levine, M.A.; Bennett, C.L.; Henderson, J.R.; Knapp, D.A.; Marrs, R.E.

1988-01-01

Both the total number and trapping lifetime of near-neon-like gold ions held in an electron beam ion trap have been greatly increased by a process of 'evaporative cooling'. A continuous flow of low-charge-state ions into the trap cools the high-charge-state ions in the trap. Preliminary experimental results using titanium ions as a coolant are presented. 8 refs., 6 figs., 2 tabs

EBIT (Electron Beam Ion Trap), N-Division Experimental Physics. Annual report, 1994

Energy Technology Data Exchange (ETDEWEB)

Schneider, D. [ed.

1995-10-01

The experimental groups in the Electron Beam Ion Trap (EBIT) program continue to perform front-line research with trapped and extracted highly charged ions (HCI) in the areas of ion/surface interactions, atomic spectroscopy, electron-ion interaction and structure measurements, highly charged ion confinement, and EBIT development studies. The ion surface/interaction studies which were initiated five years ago have reached a stage where they an carry out routine investigations, as well as produce breakthrough results towards the development of novel nanotechnology. At EBIT and SuperEBIT studies of the x-ray emission from trapped ions continue to produce significant atomic structure data with high precision for few electron systems of high-Z ions. Furthermore, diagnostics development for magnetic and laser fusion, supporting research for the x-ray laser and weapons programs, and laboratory astrophysics experiments in support of NASA`s astrophysics program are a continuing effort. The two-electron contributions to the binding energy of helium like ions were measured for the first time. The results are significant because their precision is an order of magnitude better than those of competing measurements at accelerators, and the novel technique isolates the energy corrections that are the most interesting. The RETRAP project which was initiated three years ago has reached a stage where trapping, confining and electronic cooling of HCI ions up to Th{sup 80+} can be performed routinely. Measurements of the rates and cross sections for electron transfer from H{sub 2} performed to determine the lifetime of HCI up to Xe{sup q+} and Th{sup q+} (35 {le} q {le} 80) have been studied at mean energies estimated to be {approximately} 5 q eV. This combination of heavy ions with very high charges and very low energies is rare in nature, but may be encountered in planned fusion energy demonstration devices, in highly charged ion sources, or in certain astrophysical events.

Formation of hydrogen-related traps in electron-irradiated n-type silicon by wet chemical etching

International Nuclear Information System (INIS)

Tokuda, Yutaka; Shimada, Hitoshi

1998-01-01

Interaction of hydrogen atoms and vacancy-related defects in 10 MeV electron-irradiated n-type silicon has been studied by deep-level transient spectroscopy. Hydrogen has been incorporated into electron-irradiated n-type silicon by wet chemical etching. The reduction of the concentration of the vacancy-oxygen pair and divacancy occurs by the incorporation of hydrogen, while the formation of the NH1 electron trap (E c - 0.31 eV) is observed. Further decrease of the concentration of the vacancy-oxygen pair and further increase of the concentration of the NH1 trap are observed upon subsequent below-band-gap light illumination. It is suggested that the trap NH1 is tentatively ascribed to the vacancy-oxygen pair which is partly saturated with hydrogen

Measurement of few-electron uranium ions on a high-energy electron beam ion trap

International Nuclear Information System (INIS)

Beiersdorfer, P.

1994-01-01

The high-energy electron beam ion trap, dubbed Super-EBIT, was used to produce, trap, and excite uranium ions as highly charged as fully stripped U 92+ . The production of such highly charged ions was indicated by the x-ray emission observed with high-purity Ge detectors. Moreover, high-resolution Bragg crystal spectromters were used to analyze the x-ray emission, including a detailed measurement of both the 2s 1/2 -2p 3/2 electric dipole and 2p 1/2 -2p 3/2 magnetic dipole transitions. Unlike in ion accelerators, where the uranium ions move at relativistic speeds, the ions in this trap are stationary. Thus very precise measurements of the transition energies could be made, and the QED contribution to the transition energies could be measured within less than 1 %. Details of the production of these highly charged ions and their measurement is given

Atomic origin of high-temperature electron trapping in metal-oxide-semiconductor devices

Energy Technology Data Exchange (ETDEWEB)

Shen, Xiao, E-mail: xiao.shen@vanderbilt.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Dhar, Sarit [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States); Pantelides, Sokrates T. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2015-04-06

MOSFETs based on wide-band-gap semiconductors are suitable for operation at high temperature, at which additional atomic-scale processes that are benign at lower temperatures can get activated, resulting in device degradation. Recently, significant enhancement of electron trapping was observed under positive bias in SiC MOSFETs at temperatures higher than 150 °C. Here, we report first-principles calculations showing that the enhanced electron trapping is associated with thermally activated capturing of a second electron by an oxygen vacancy in SiO{sub 2} by which the vacancy transforms into a structure that comprises one Si dangling bond and a bond between a five-fold and a four-fold Si atoms. The results suggest a key role of oxygen vacancies and their structural reconfigurations in the reliability of high-temperature MOS devices.

EUV spectrum of highly charged tungsten ions in electron beam ion trap

International Nuclear Information System (INIS)

Sakaue, H.A.; Kato, D.; Murakami, I.; Nakamura, N.

2016-01-01

We present spectra of highly charged tungsten ions in the extreme ultra-violet (EUV) by using electron beam ion traps. The electron energy dependence of spectra was investigated for electron energy from 540 to 1370 eV. Previously unreported lines were presented in the EUV range, and comparing the wavelengths with theoretical calculations identified them. (author)

Stratified Simulations of Collisionless Accretion Disks

Energy Technology Data Exchange (ETDEWEB)

Hirabayashi, Kota; Hoshino, Masahiro, E-mail: hirabayashi-k@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Tokyo, 113-0033 (Japan)

2017-06-10

This paper presents a series of stratified-shearing-box simulations of collisionless accretion disks in the recently developed framework of kinetic magnetohydrodynamics (MHD), which can handle finite non-gyrotropy of a pressure tensor. Although a fully kinetic simulation predicted a more efficient angular-momentum transport in collisionless disks than in the standard MHD regime, the enhanced transport has not been observed in past kinetic-MHD approaches to gyrotropic pressure anisotropy. For the purpose of investigating this missing link between the fully kinetic and MHD treatments, this paper explores the role of non-gyrotropic pressure and makes the first attempt to incorporate certain collisionless effects into disk-scale, stratified disk simulations. When the timescale of gyrotropization was longer than, or comparable to, the disk-rotation frequency of the orbit, we found that the finite non-gyrotropy selectively remaining in the vicinity of current sheets contributes to suppressing magnetic reconnection in the shearing-box system. This leads to increases both in the saturated amplitude of the MHD turbulence driven by magnetorotational instabilities and in the resultant efficiency of angular-momentum transport. Our results seem to favor the fast advection of magnetic fields toward the rotation axis of a central object, which is required to launch an ultra-relativistic jet from a black hole accretion system in, for example, a magnetically arrested disk state.

Experimental evaluation of quantum computing elements (qubits) made of electrons trapped over a liquid helium film

International Nuclear Information System (INIS)

Rousseau, E.

2006-12-01

An electron on helium presents a quantized energy spectrum. The interaction with the environment is considered sufficiently weak in order to allow the realization of a quantum bit (qubit) by using the first two energy levels. The first stage in the realization of this qubit was to trap and control a single electron. This is carried out thanks to a set of micro-fabricated electrodes defining a well of potential in which the electron is trapped. We are able with such a sample to trap and detect a variables number of electrons varying between one and around twenty. This then allowed us to study the static behaviour of a small number of electrons in a trap. They are supposed to crystallize and form structures called Wigner molecules. Such molecules have not yet been observed yet with electrons above helium. Our results bring circumstantial evidence for of Wigner crystallization. We then sought to characterize the qubit more precisely. We sought to carry out a projective reading (depending on the state of the qubit) and a measurement of the relaxation time. The results were obtained by exciting the electron with an incoherent electric field. A clean measurement of the relaxation time would require a coherent electric field. The conclusion cannot thus be final but it would seem that the relaxation time is shorter than calculated theoretically. That is perhaps due to a measurement of the relaxation between the oscillating states in the trap and not between the states of the qubit. (author)

Thermal and optical excitation of trapped electrons in high-density polyethylene (HDPE) studied through positron annihilation

International Nuclear Information System (INIS)

Nahid, F.; Zhang, J.D.; Yu, T.F.; Ling, C.C.; Fung, S.; Beling, C.D.

2011-01-01

Positronium (Ps) formation in high-density polyethylene (HDPE) has been studied below the glass transition temperature. The formation probability increases with positron irradiation time due to an increasing number of inter-track trapped electrons becoming available for positron capture. The temperature variation of the saturated Ps level is discussed in different models. The quenching of trapped electrons by light has been studied and the optical de-trapping cross-section for different photon energies has been estimated over the visible region.

Compton harmonic resonances, stochastic instabilities, quasilinear diffusion, and collisionless damping with ultra-high intensity laser waves

International Nuclear Information System (INIS)

Rax, J.M.

1992-04-01

The dynamics of electrons in two-dimensional, linearly or circularly polarized, ultra-high intensity (above 10 18 W/cm 2 ) laser waves, is investigated. The Compton harmonic resonances are identified as the source of various stochastic instabilities. Both Arnold diffusion and resonance overlap are considered. The quasilinear kinetic equation, describing the evolution of the electron distribution function, is derived, and the associated collisionless damping coefficient is calculated. The implications of these new processes are considered and discussed

Electrostatic effect for the collisionless tearing mode

International Nuclear Information System (INIS)

Hoshino, M.

1987-01-01

Electron dynamics has not been self-consistently considered in collisionless tearing mode theories to date because of the mathematical complexity of the Vlasov-Maxwell equations. We have found using computer simulations that electrostatic fields play an important role in the tearing mode. Vlasov theory, including the electrostatic field, is investigated for topologies with both antiparallel and nonantiparallel magnetic field lines. The electrostatic field influences the resonant current in the neutral sheet which is a non-MHD effect, and modifies the linear growth rate. At the magnetopause, where the field lines are not antiparallel, the electrostatic effect acts to raise the linear growth rate of the tearing mode. On the other hand, in the magnetotail, where magnetic field lines are antiparallel, the electrostatic effect reduces the tearing mode growth rate. copyright American Geophysical Union 1987

Effect of Trapped Energetic Ions on MHD Activity in Spherical Tori

International Nuclear Information System (INIS)

White, R.B.; Kolesnichenko, Ya.I.; Lutsenko, V.V.; Marchenko, V.S.

2002-01-01

It is shown that the increase of beta (the ratio of plasma pressure to the magnetic field pressure) may change the character of the influence of trapped energetic ions on MHD stability in spherical tori. Namely, the energetic ions, which stabilize MHD modes (such as the ideal-kink mode, collisionless tearing mode, and semi-collisional tearing mode) at low beta, have a destabilizing influence at high beta unless the radial distribution of the energetic ions is very peaked

Effect of trapped electrons on the transient current density and luminance of organic light-emitting diode

Science.gov (United States)

Lee, Jiun-Haw; Chen, Chia-Hsun; Lin, Bo-Yen; Shih, Yen-Chen; Lin, King-Fu; Wang, Leeyih; Chiu, Tien-Lung; Lin, Chi-Feng

2018-04-01

Transient current density and luminance from an organic light-emitting diode (OLED) driven by voltage pulses were investigated. Waveforms with different repetition rate, duty cycle, off-period, and on-period were used to study the injection and transport characteristics of electron and holes in an OLED under pulse operation. It was found that trapped electrons inside the emitting layer (EML) and the electron transporting layer (ETL) material, tris(8-hydroxyquinolate)aluminum (Alq3) helped for attracting the holes into the EML/ETL and reducing the driving voltage, which was further confirmed from the analysis of capacitance-voltage and displacement current measurement. The relaxation time and trapped filling time of the trapped electrons in Alq3 layer were ~200 µs and ~600 µs with 6 V pulse operation, respectively.

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

International Nuclear Information System (INIS)

Yang Yan; Li Sheng-Tao; Ding Can; Cheng Peng-Fei

2011-01-01

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I—V (current—voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors. (fluids, plasmas and electric discharges)

The Electronic McPhail Trap

Science.gov (United States)

Potamitis, Ilyas; Rigakis, Iraklis; Fysarakis, Konstantinos

2014-01-01

Certain insects affect cultivations in a detrimental way. A notable case is the olive fruit fly (Bactrocera oleae (Rossi)), that in Europe alone causes billions of euros in crop-loss/per year. Pests can be controlled with aerial and ground bait pesticide sprays, the efficiency of which depends on knowing the time and location of insect infestations as early as possible. The inspection of traps is currently carried out manually. Automatic monitoring traps can enhance efficient monitoring of flying pests by identifying and counting targeted pests as they enter the trap. This work deals with the hardware setup of an insect trap with an embedded optoelectronic sensor that automatically records insects as they fly in the trap. The sensor responsible for detecting the insect is an array of phototransistors receiving light from an infrared LED. The wing-beat recording is based on the interruption of the emitted light due to the partial occlusion from insect's wings as they fly in the trap. We show that the recordings are of high quality paving the way for automatic recognition and transmission of insect detections from the field to a smartphone. This work emphasizes the hardware implementation of the sensor and the detection/counting module giving all necessary implementation details needed to construct it. PMID:25429412

Effects of irradiation and isochronal anneal temperature on hole and electron trapping in MOS devices

International Nuclear Information System (INIS)

Fleetwood, D.M.; Winokur, P.S.; Shaneyfelt, M.R.; Riewe, L.C.; Flament, O.; Paillet, P.; Leray, J.L.

1998-02-01

Capacitance-voltage and thermally-stimulated-current techniques are used to estimate trapped hole and electron densities in MOS oxides as functions of irradiation and isochronal anneal temperature. Trapped-charge annealing and compensation effects are discussed

Trapping in GaN-based metal-insulator-semiconductor transistors: Role of high drain bias and hot electrons

Energy Technology Data Exchange (ETDEWEB)

Meneghini, M., E-mail: matteo.meneghini@dei.unipd.it; Bisi, D.; Meneghesso, G.; Zanoni, E. [Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova (Italy); Marcon, D.; Stoffels, S.; Van Hove, M.; Wu, T.-L.; Decoutere, S. [IMEC, Kapeldreef 75, 3001 Heverlee (Belgium)

2014-04-07

This paper describes an extensive analysis of the role of off-state and semi-on state bias in inducing the trapping in GaN-based power High Electron Mobility Transistors. The study is based on combined pulsed characterization and on-resistance transient measurements. We demonstrate that—by changing the quiescent bias point from the off-state to the semi-on state—it is possible to separately analyze two relevant trapping mechanisms: (i) the trapping of electrons in the gate-drain access region, activated by the exposure to high drain bias in the off-state; (ii) the trapping of hot-electrons within the AlGaN barrier or the gate insulator, which occurs when the devices are operated in the semi-on state. The dependence of these two mechanisms on the bias conditions and on temperature, and the properties (activation energy and cross section) of the related traps are described in the text.

Weibel instability mediated collisionless shocks using intense laser-driven plasmas

Science.gov (United States)

Palaniyappan, Sasikumar; Fiuza, Federico; Huang, Chengkun; Gautier, Donald; Ma, Wenjun; Schreiber, Jorg; Raymer, Abel; Fernandez, Juan; Shimada, Tom; Johnson, Randall

2017-10-01

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. A particular type of electromagnetic plasma instability known as Weibel instability is believed to be the dominant mechanism behind the formation of these collisionless shocks in the cosmos. 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 gold foil is used to radiograph the main laser-driven plasma. Work supported by the LDRD program at LANL.

Bifurcation analysis for ion acoustic waves in a strongly coupled plasma including trapped electrons

Science.gov (United States)

El-Labany, S. K.; El-Taibany, W. F.; Atteya, A.

2018-02-01

The nonlinear ion acoustic wave propagation in a strongly coupled plasma composed of ions and trapped electrons has been investigated. The reductive perturbation method is employed to derive a modified Korteweg-de Vries-Burgers (mKdV-Burgers) equation. To solve this equation in case of dissipative system, the tangent hyperbolic method is used, and a shock wave solution is obtained. Numerical investigations show that, the ion acoustic waves are significantly modified by the effect of polarization force, the trapped electrons and the viscosity coefficients. Applying the bifurcation theory to the dynamical system of the derived mKdV-Burgers equation, the phase portraits of the traveling wave solutions of both of dissipative and non-dissipative systems are analyzed. The present results could be helpful for a better understanding of the waves nonlinear propagation in a strongly coupled plasma, which can be produced by photoionizing laser-cooled and trapped electrons [1], and also in neutron stars or white dwarfs interior.

Molecular dynamics simulation of electron trapping in the sapphire lattice

International Nuclear Information System (INIS)

Rambaut, C.; Oh, K.H.; Fayeulle, S.; Kohanoff, J.

1995-10-01

Energy storage and release in dielectric materials can be described on the basis of the charge trapping mechanism. Most phenomenological aspects have been recently rationalized in terms of the space charge mode. Dynamical aspects are studied here by performing Molecular Dynamics simulations. We show that an excess electron introduced into the sapphire lattice (α -Al 2 O 3 ) can be trapped only at a limited number of sites. The energy gained by allowing the electron to localize in these sites is of the order of 4-5 eV, in good agreement with the results of the space charge model. Displacements of the neighboring ions due to the implanted charge are shown to be localized in a small region of about 5 A. Detrapping is observed at 250 K. The ionic displacements turn out to play an important role in modifying the potential landscape by lowering, in a dynamical way, the barriers that cause localization at low temperature. (author). 18 refs, 7 figs, 2 tabs

Comparison of multi-fluid moment models with particle-in-cell simulations of collisionless magnetic reconnection

International Nuclear Information System (INIS)

Wang, Liang; Germaschewski, K.; Hakim, Ammar H.; Bhattacharjee, A.

2015-01-01

We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed

Coupled ion temperature gradient and trapped electron mode to electron temperature gradient mode gyrokinetic simulations

International Nuclear Information System (INIS)

Waltz, R. E.; Candy, J.; Fahey, M.

2007-01-01

Electron temperature gradient (ETG) transport is conventionally defined as the electron energy transport at high wave number (high-k) where ions are adiabatic and there can be no ion energy or plasma transport. Previous gyrokinetic simulations have assumed adiabatic ions (ETG-ai) and work on the small electron gyroradius scale. However such ETG-ai simulations with trapped electrons often do not have well behaved nonlinear saturation unless fully kinetic ions (ki) and proper ion scale zonal flow modes are included. Electron energy transport is separated into ETG-ki at high-k and ion temperature gradient-trapped electron mode (ITG/TEM) at low-k. Expensive (more computer-intensive), high-resolution, large-ion-scale flux-tube simulations coupling ITG/TEM and ETG-ki turbulence are presented. These require a high effective Reynolds number R≡[k(max)/k(min)] 2 =μ 2 , where μ=[ρ si /ρ si ] is the ratio of ion to electron gyroradii. Compute times scale faster than μ 3 . By comparing the coupled expensive simulations with (1) much cheaper (less compute-intensive), uncoupled, high-resolution, small, flux-tube ETG-ki and with (2) uncoupled low-resolution, large, flux-tube ITG/TEM simulations, and also by artificially turning ''off'' the low-k or high-k drives, it appears that ITG/TEM and ETG-ki transport are not strongly coupled so long as ETG-ki can access some nonadiabatic ion scale zonal flows and both high-k and low-k are linearly unstable. However expensive coupled simulations are required for physically accurate k-spectra of the transport and turbulence. Simulations with μ≥30 appear to represent the physical range μ>40. ETG-ki transport measured in ion gyro-Bohm units is weakly dependent on μ. For the mid-radius core tokamak plasma parameters studied, ETG-ki is about 10% of the electron energy transport, which in turn is about 30% of the total energy transport (with negligible ExB shear). However at large ExB shear sufficient to quench the low-k ITG

Expansion of a plasma injected from an electrodeless gun along a magnetic field

International Nuclear Information System (INIS)

Raadu, M.A.

1978-04-01

The dynamics of a plasma injected from an electrodeless plasma gun (conical theta pinch) into a longitudinal magnetic field is studied theoretically. For the experiments referred to, conditions are collisionless for the ions and range from collision dominated to collisionless for the electrons. During the expansion of the injected plasma the electrons are trapped by an ambipolar electric field maintaining charge neutrality and a magnetic mirror at the gun. The development of the ion and electron distribution functions for the completely collisionless case is considered in detail. Assuming that the acceleration of the ions is negligible and taking the action integral over an electron oscillation to be an adiabatic invariant self similar solutions are found. The electrons lose energy adiabatically as a result of the plasma expansion and it is suggested that a re-thermalisation process must operate in experimental situations to account for the observed electron energies

The Electronic McPhail Trap

Directory of Open Access Journals (Sweden)

Ilyas Potamitis

2014-11-01

Full Text Available Certain insects affect cultivations in a detrimental way. A notable case is the olive fruit fly (Bactrocera oleae (Rossi, that in Europe alone causes billions of euros in crop-loss/per year. Pests can be controlled with aerial and ground bait pesticide sprays, the efficiency of which depends on knowing the time and location of insect infestations as early as possible. The inspection of traps is currently carried out manually. Automatic monitoring traps can enhance efficient monitoring of flying pests by identifying and counting targeted pests as they enter the trap. This work deals with the hardware setup of an insect trap with an embedded optoelectronic sensor that automatically records insects as they fly in the trap. The sensor responsible for detecting the insect is an array of phototransistors receiving light from an infrared LED. The wing-beat recording is based on the interruption of the emitted light due to the partial occlusion from insect’s wings as they fly in the trap. We show that the recordings are of high quality paving the way for automatic recognition and transmission of insect detections from the field to a smartphone. This work emphasizes the hardware implementation of the sensor and the detection/counting module giving all necessary implementation details needed to construct it.

DC current in the collisionless limit induced by a travelling wave

International Nuclear Information System (INIS)

Midzuno, Yukio; Fukuda, Masaji.

1977-03-01

The DC current induced by a Travelling Wave is calculated on the basis of the assumption that the distribution function of electrons in the collisionless limit should be determined by a condition derived from the nature of the collision operator, as in the case of the calculation of the neoclassical transport in a torus. The resultant net current is found to have the same parameter dependence as the one derived in a previous analysis, in which we assumed the initial distribution of electrons to be uniform and isotropic Maxwellian. The numerical coefficient is found, however, to be a little different from the previous one. The importance of the accurate matching of the distribution function of untrapped particles to the Maxwellian one for large velocity is demonstrated. (auth.)

A tunable electron beam source using trapping of electrons in a density down-ramp in laser wakefield acceleration.

Science.gov (United States)

Ekerfelt, Henrik; Hansson, Martin; Gallardo González, Isabel; Davoine, Xavier; Lundh, Olle

2017-09-25

One challenge in the development of laser wakefield accelerators is to demonstrate sufficient control and reproducibility of the parameters of the generated bunches of accelerated electrons. Here we report on a numerical study, where we demonstrate that trapping using density down-ramps allows for tuning of several electron bunch parameters by varying the properties of the density down-ramp. We show that the electron bunch length is determined by the difference in density before and after the ramp. Furthermore, the transverse emittance of the bunch is controlled by the steepness of the ramp. Finally, the amount of trapped charge depends both on the density difference and on the steepness of the ramp. We emphasize that both parameters of the density ramp are feasible to vary experimentally. We therefore conclude that this tunable electron accelerator makes it suitable for a wide range of applications, from those requiring short pulse length and low emittance, such as the free-electron lasers, to those requiring high-charge, large-emittance bunches to maximize betatron X-ray generation.

Strong ion accelerating by collisionless magnetosonic shock wave propagating perpendicular to a magnetic field

International Nuclear Information System (INIS)

Ohsawa, Yukiharu.

1984-12-01

A 2-1/2 dimensional fully relativistic, fully electromagnetic particle code is used to study a time evolution of nonlinear magnetosonic pulse propagating in the direction perpendicular to a magnetic field. The pulse is excited by an instantaneous piston acceleration, and evolves totally self-consistently. Large amplitude pulse traps some ions and accelerates them parallel to the wave front. They are detrapped when their velocities become of the order of the sum of the ExB drift velocity and the wave phase velocity, where E is the electric field in the direction of wave propagation. The pulse develops into a quasi-shock wave in a collisionless plasma by a dissipation due to the resonant ion acceleration. Simple nonlinear wave theory for a cold plasma well describes the shock properties observed in the simulation except for the effects of resonant ions. In particular, magnitude of an electric potential across the shock region is derived analytically and is found to be in good agreement with our simulations. The potential jump is proportional to B 2 , and hence the ExB drift velocity of the trapped ions is proportional to B. (author)

Plasma confinement in self-consistent, one-dimensional transport equilibria in the collisionless-ion regime of EBT operation

International Nuclear Information System (INIS)

Chang, C.S.; Miller, R.L.

1983-01-01

It has long been recognized that if an EBT-confined plasma could be maintained in the collisionless-ion regime, characterized by positive ambipolar potential and positive radial electric field, the particle loss rates could be reduced by a large factor. The extent to which the loss rate of energy could be reduced has not been as clearly determined, and has been investigated recently using a one-dimensional, time-dependent transport code developed for this purpose. We find that the energy confinement can be improved by roughly an order of magnitude by maintaining a positive radial electric field that increases monotonically with radius, giving a large ExB drift near the outer edge of the core plasma. The radial profiles of heat deposition required to sustain these equilibria will be presented, and scenarios for obtaining dynamical access to the equilibria will be discussed

Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam

CERN Document Server

Lotov, K.V.; Petrenko, A.V.; Amorim, L.D.; Vieira, J.; Fonseca, R.A.; Silva, L.O.; Gschwendtner, E.; Muggli, P.

2014-01-01

It is shown that co-linear injection of electrons or positrons into the wakefield of the self-modulating particle beam is possible and ensures high energy gain. The witness beam must co-propagate with the tail part of the driver, since the plasma wave phase velocity there can exceed the light velocity, which is necessary for efficient acceleration. If the witness beam is many wakefield periods long, then the trapped charge is limited by beam loading effects. The initial trapping is better for positrons, but at the acceleration stage a considerable fraction of positrons is lost from the wave. For efficient trapping of electrons, the plasma boundary must be sharp, with the density transition region shorter than several centimeters. Positrons are not susceptible to the initial plasma density gradient.

Hydrogen treatment as a detergent of electronic trap states in lead chalcogenide nanoparticles

Science.gov (United States)

Voros, Marton; Brawand, Nicholas; Galli, Giulia

Lead chalcogenide (PbX) nanoparticles are promising materials for solar energy conversion. However, the presence of trap states in their electronic gap limits their usability, and developing a universal strategy to remove trap states is a persistent challenge. Using calculations based on density functional theory, we show that hydrogen acts as an amphoteric impurity on PbX nanoparticle surfaces; hydrogen atoms may passivate defects arising from ligand imbalance or off-stoichiometric surface terminations, irrespective of whether they originate from cation or anion excess. In addition, we show, using constrained density functional theory calculations, that hydrogen treatment of defective nanoparticles is also beneficial for charge transport in films. We also find that hydrogen adsorption on stoichiometric nanoparticles leads to electronic doping, preferentially n-type. Our findings suggest that post-synthesis hydrogen treatment of lead chalcogenide nanoparticle films is a viable approach to reduce electronic trap states or to dope well-passivated films. Work supported by the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (NB) and U.S. DOE under Contract No. DE-AC02-06CH11357 (MV).

Direct exchange between silicon nanocrystals and tunnel oxide traps under illumination on single electron photodetector

Energy Technology Data Exchange (ETDEWEB)

Chatbouri, S., E-mail: Samir.chatbouri@yahoo.com; Troudi, M.; Sghaier, N.; Kalboussi, A. [Avenue de I’environnement, Université de Monastir, Laboratoire de Micro électronique et Instrumentation (LR13ES12), Faculté des Sciences de Monastir (Tunisia); Aimez, V. [Université de Sherbrooke, Laboratoire Nanotechnologies et Nanosystémes (UMI-LN2 3463), Université de Sherbrooke—CNRS—INSA de Lyon-ECL-UJF-CPE Lyon, Institut Interdisciplinaire d’Innovation Technologique (Canada); Drouin, D. [Avenue de I’environnement, Université de Monastir, Laboratoire de Micro électronique et Instrumentation (LR13ES12), Faculté des Sciences de Monastir (Tunisia); Souifi, A. [Institut des Nanotechnologies de Lyon—site INSA de Lyon, UMR CNRS 5270 (France)

2016-09-15

In this paper we present the trapping of photogenerated charge carriers for 300 s resulted by their direct exchange under illumination between a few silicon nanocrystals (ncs-Si) embedded in an oxide tunnel layer (SiO{sub x} = 1.5) and the tunnel oxide traps levels for a single electron photodetector (photo-SET or nanopixel). At first place, the presence of a photocurrent limited in the inversion zone under illumination in the I–V curves confirms the creation of a pair electron/hole (e–h) at high energy. This photogenerated charge carriers can be trapped in the oxide. Using the capacitance-voltage under illumination (the photo-CV measurements) we show a hysteresis chargement limited in the inversion area, indicating that the photo-generated charge carriers are stored at traps levels at the interface and within ncs-Si. The direct exchange of the photogenerated charge carriers between the interface traps levels and the ncs-Si contributed on the photomemory effect for 300 s for our nanopixel at room temperature.

Properties and parameters of the electron beam injected into the mirror magnetic trap of a plasma accelerator

Energy Technology Data Exchange (ETDEWEB)

Andreev, V. V., E-mail: temple18@mail.ru; Novitsky, A. A.; Vinnichenko, L. A.; Umnov, A. M.; Ndong, D. O. [Peoples’ Friendship University of Russia (Russian Federation)

2016-03-15

The parameters of the injector of an axial plasma beam injected into a plasma accelerator operating on the basis of gyroresonance acceleration of electrons in the reverse magnetic field are determined. The trapping of the beam electrons into the regime of gyroresonance acceleration is numerically simulated by the particle- in-cell method. The optimal time of axial injection of the beam into a magnetic mirror trap is determined. The beam parameters satisfying the condition of efficient particle trapping into the gyromagnetic autoresonance regime are found.

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

International Nuclear Information System (INIS)

Schaeffer, D. B.; 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.; Winske, D.

2014-01-01

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

Influence of a guide field on collisionless driven reconnection

International Nuclear Information System (INIS)

Horiuchi, Ritoku; Usami, Shunsuke; Ohtani, Hiroaki

2014-01-01

The influence of a guide field on collisionless driven reconnection is investigated by means of two-dimensional electromagnetic particle simulation in an open system. In a quasi-steady state when reconnection electric field evolves fully, a current layer evolves locally in a narrow kinetic region and its scale decreases in proportion to an electron meandering scale as the guide field is intensified. Here, the meandering scale stands for an average spatial scale of nongyrotropic motions in the vicinity of the reconnection point. Force terms associated with off-diagonal components of electron and ion pressure tensors, which are originating from nongyrotropic motions of charged particles, becomes dominant at the reconnection point and sustain the reconnection electric field even when the guide field is strong. It is also found that thermalization of both ions and electrons is suppressed by the guide field. For the weak guide field, an electron nonthermal component is significantly created through a fast outburst from the kinetic region, while for the strong guide field, an ion nonthermal component is generated through the acceleration by an in-plane electric field near the magnetic separatrix. (author)

Kinetic electron model for plasma thruster plumes

Science.gov (United States)

Merino, Mario; Mauriño, Javier; Ahedo, Eduardo

2018-03-01

A paraxial model of an unmagnetized, collisionless plasma plume expanding into vacuum is presented. Electrons are treated kinetically, relying on the adiabatic invariance of their radial action integral for the integration of Vlasov's equation, whereas ions are treated as a cold species. The quasi-2D plasma density, self-consistent electric potential, and electron pressure, temperature, and heat fluxes are analyzed. In particular, the model yields the collisionless cooling of electrons, which differs from the Boltzmann relation and the simple polytropic laws usually employed in fluid and hybrid PIC/fluid plume codes.

A new formulation of theta pinch implosions - a collisionless wave model

International Nuclear Information System (INIS)

Tsui, K.H.

Previous work in theta pinch implosions is characterized by anomalous resistivity owing its origin to plasma instabilities. A diametrically opposite collisionless model is proposed here that consists of an inhomogeneous wave equation. The electron velocities are solved by guiding center approximation. This model offers qualitative explanations to various effects like experimental Alfven scaling law, Alfven penetration time, sheath thickness, shock formation, shock width, piston thickness, Alfven Mach number. Although collision is not essential, the plasma has an apparent resistivity with an effective collision frequency of roughly the same as those anomalous ones used in turbulent model. (Author) [pt

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

Czech Academy of Sciences Publication Activity Database

Burgess, D.; Hellinger, Petr; Gingell, I.; Trávníček, Pavel M.

2016-01-01

Roč. 82, č. 4 (2016), 905820401/1-905820401/23 ISSN 0022-3778 Institutional support: RVO:68378289 Keywords : ion-acceleration * numerical simulations * bow shock * electron acceleration * cluster observations * self-reformation * magnetic-field * whistler waves * injection * nonstationarity Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.160, year: 2016 https://www.cambridge.org/core/ journals /journal-of-plasma-physics/article/microstructure-in-two-and-three-dimensional-hybrid-simulations-of-perpendicular-collisionless-shocks/F964EF89FB14A6504A49CFAD54970E2B

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 ga...

Electron velocity distributions near collisionless shocks

International Nuclear Information System (INIS)

Feldman, W.C.

1984-01-01

Recent studies of the amount of electron heating and of the shapes of electron velocity distributions across shocks near the earth are reviewed. It is found that electron heating increases with increasing shock strength but is always less than the ion heating. The scale length of electron heating is also less than that for the ions. Electron velocity distributions show characteristic shapes which depend on the strength of the shocks. At the weaker shocks, electron heating is mostly perpendicular to the ambient magnetic field, bar B, and results in Gaussian-shaped velocity distributions at low-to-moderate energies. At the stronger shocks, parallel heating predominates resulting in flat-topped velocity distributions. A reasonable interpretation of these results indicates that at the weaker shocks electron heating is dominated by a tendency toward conservation of the magnetic moment. At the stronger fast-mode shocks, this heating is thought to be dominated by an acceleration parallel to bar B produced by the macroscopic shock electric field followed by beam driven plasma instabilities. Some contribution to the heating at the stronger shocks from conservation of the magnetic moment and cross-field current-driven instabilities cannot be ruled out. Although the heating at slow-mode shocks is also dominated by instabilities driven by magnetic field-aligned electron beams, their acceleration mechanism is not yet established

Experimental investigation of the trapping and energy loss mechanisms of intense relativistic electron rings in hydrogen gas and plasma

International Nuclear Information System (INIS)

Smith, A.C. Jr.

1977-01-01

The results of an experimental study on the trapping and energy loss mechanisms of intense, relativistic electron rings confined in Astron-like magnetic field geometries are presented. The work is subdivided into four sections: gas trapping; average ring electron energetics; plasma trapping, and hollow-beam cusp-injection into gas and plasma. The mechanisms by which the injected beam coalesces into a current ring in the existing Cornell RECE-Berta facility are considered. To investigate the nature of ring electron energy loss mechanisms following completion of the trapping process, a diagnostic was developed utilizing multi-foil X-ray absorption spectroscopy to analyze the Bremsstrahlung generated by the electrons as they impinge upon a thin tungsten wire target suspended in the circulating current. Finally, a set of preliminary experimental results is presented in which an annular electron beam was passed through a coaxial, non-adiabatic magnetic cusp located at one end of a magnetic mirror well

Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

Energy Technology Data Exchange (ETDEWEB)

Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-09-15

Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

In situ electromagnetic field diagnostics with an electron plasma in a Penning-Malmberg trap

CERN Document Server

Amole, C; Baquero-Ruiz, M.; Bertsche, W.; Butler, E.; Capra, A.; Cesar, C.L.; Charlton, M.; Deller, A.; Evetts, N.; Eriksson, S.; Fajans, J.; Friesen, T.; Fujiwara, M.C.; Gill, D.R.; Gutierrez, A.; Hangst, J.S.; Hardy, W.N.; Hayden, M.E.; Isaac, C.A.; Jonsell, S.; Kurchaninov, L.; Little, A.; Madsen, N.; McKenna, J.T.K.; Menary, S.; Napoli, S.C.; Olchanski, K.; Olin, A.; Pusa, P.; Rasmussen, C.; Robicheaux, F.; Sarid, E.; Silveira, D.M.; So, C.; Stracka, S.; Tharp, T.; Thompson, R.I.; van der Werf, D.P.; Wurtele, J.S.

2014-01-01

We demonstrate a novel detection method for the cyclotron resonance frequency of an electron plasma in a Penning-Malmberg trap. With this technique, the electron plasma is used as an in situ diagnostic tool for measurement of the static magnetic field and the microwave electric field in the trap. The cyclotron motion of the electron plasma is excited by microwave radiation and the temperature change of the plasma is measured non-destructively by monitoring the plasma's quadrupole mode frequency. The spatially-resolved microwave electric field strength can be inferred from the plasma temperature change and the magnetic field is found through the cyclotron resonance frequency. These measurements were used extensively in the recently reported demonstration of resonant quantum interactions with antihydrogen.

Trap-mediated electronic transport properties of gate-tunable pentacene/MoS2 p-n heterojunction diodes.

Science.gov (United States)

Kim, Jae-Keun; Cho, Kyungjune; Kim, Tae-Young; Pak, Jinsu; Jang, Jingon; Song, Younggul; Kim, Youngrok; Choi, Barbara Yuri; Chung, Seungjun; Hong, Woong-Ki; Lee, Takhee

2016-11-10

We investigated the trap-mediated electronic transport properties of pentacene/molybdenum disulphide (MoS 2 ) p-n heterojunction devices. We observed that the hybrid p-n heterojunctions were gate-tunable and were strongly affected by trap-assisted tunnelling through the van der Waals gap at the heterojunction interfaces between MoS 2 and pentacene. The pentacene/MoS 2 p-n heterojunction diodes had gate-tunable high ideality factor, which resulted from trap-mediated conduction nature of devices. From the temperature-variable current-voltage measurement, a space-charge-limited conduction and a variable range hopping conduction at a low temperature were suggested as the gate-tunable charge transport characteristics of these hybrid p-n heterojunctions. Our study provides a better understanding of the trap-mediated electronic transport properties in organic/2-dimensional material hybrid heterojunction devices.

Dependence of secondary electron emission on surface charging in sapphire and polycrystalline alumina: Evaluation of the effective cross sections for recombination and trapping

International Nuclear Information System (INIS)

Said, K.; Damamme, G.; Si Ahmed, A.; Moya, G.; Kallel, A.

2014-01-01

Highlights: • A novel approach for the analysis of the secondary electron emission in connection with the surface density of trapped charges. • Experimental estimation of the effective cross section for electron–hole recombination and electron trapping in defects. • A simplified charge transport and trapping model which corroborates qualitatively the interpretation of the results. - Abstract: The evolution of the secondary electron emission from sapphire and polycrystalline alumina during electron irradiation, achieved in a scanning electron microscope at room temperature, is derived from the measurement of the induced and the secondary electron currents. The semi-logarithmic plot of the secondary electron emission yield versus the surface density of trapped charges displays a plateau followed by a linear variation. For positive charging, the slope of the linear part, whose value is of about 10 −9 cm 2 , is independent of the primary electron energy, the microstructure and the impurities. It is interpreted as an effective microscopic cross section for electron–hole recombination. For negative charging of sapphire, the slope is associated with an effective electron trapping cross section close to 10 −11 cm 2 , which can be assigned to the dominant impurity trap. These effective values reflect the multiple interactions leading to the accumulation of charges. The yield corresponding to the plateau is controlled by the initial density of impurity traps. A charge transport and trapping >model, based on simplifying assumptions, confirms qualitatively these inferences

Increased electric sail thrust through removal of trapped shielding electrons by orbit chaotisation due to spacecraft body

Directory of Open Access Journals (Sweden)

P. Janhunen

2009-08-01

Full Text Available An electric solar wind sail is a recently introduced propellantless space propulsion method whose technical development has also started. The electric sail consists of a set of long, thin, centrifugally stretched and conducting tethers which are charged positively and kept in a high positive potential of order 20 kV by an onboard electron gun. The positively charged tethers deflect solar wind protons, thus tapping momentum from the solar wind stream and producing thrust. The amount of obtained propulsive thrust depends on how many electrons are trapped by the potential structures of the tethers, because the trapped electrons tend to shield the charged tether and reduce its effect on the solar wind. Here we present physical arguments and test particle calculations indicating that in a realistic three-dimensional electric sail spacecraft there exist a natural mechanism which tends to remove the trapped electrons by chaotising their orbits and causing them to eventually collide with the conducting tethers. We present calculations which indicate that if these mechanisms were able to remove trapped electrons nearly completely, the electric sail performance could be about five times higher than previously estimated, about 500 nN/m, corresponding to 1 N thrust for a baseline construction with 2000 km total tether length.

Real-space Mapping of Surface Trap States in CIGSe Nanocrystals using 4D Electron Microscopy

KAUST Repository

Bose, Riya

2016-05-26

Surface trap states in semiconductor copper indium gallium selenide nanocrystals (NCs) which serve as undesirable channels for non-radiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with sub-picosecond temporal and nanometer spatial resolutions. Here, we precisely map the surface charge carrier dynamics of copper indium gallium selenide NCs before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.

Real-space Mapping of Surface Trap States in CIGSe Nanocrystals using 4D Electron Microscopy

KAUST Repository

Bose, Riya; Bera, Ashok; Parida, Manas R.; Adhikari, Aniruddha; Shaheen, Basamat; Alarousu, Erkki; Sun, Jingya; Wu, Tao; Bakr, Osman; Mohammed, Omar F.

2016-01-01

Surface trap states in semiconductor copper indium gallium selenide nanocrystals (NCs) which serve as undesirable channels for non-radiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with sub-picosecond temporal and nanometer spatial resolutions. Here, we precisely map the surface charge carrier dynamics of copper indium gallium selenide NCs before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.

Kinetic description of quasi-stationary axisymmetric collisionless accretion disk plasmas with arbitrary magnetic field configurations

International Nuclear Information System (INIS)

Cremaschini, Claudio; Miller, John C.; Tessarotto, Massimo

2011-01-01

A kinetic treatment is developed for collisionless magnetized plasmas occurring in high-temperature, low-density astrophysical accretion disks, such as are thought to be present in some radiatively inefficient accretion flows onto black holes. Quasi-stationary configurations are investigated, within the framework of a Vlasov-Maxwell description. The plasma is taken to be axisymmetric and subject to the action of slowly time-varying gravitational and electromagnetic fields. The magnetic field is assumed to be characterized by a family of locally nested but open magnetic surfaces. The slow collisionless dynamics of these plasmas is investigated, yielding a reduced gyrokinetic Vlasov equation for the kinetic distribution function. For doing this, an asymptotic quasi-stationary solution is first determined, represented by a generalized bi-Maxwellian distribution expressed in terms of the relevant adiabatic invariants. The existence of the solution is shown to depend on having suitable kinetic constraints and conditions leading to particle trapping phenomena. With this solution, one can treat temperature anisotropy, toroidal and poloidal flow velocities, and finite Larmor-radius effects. An asymptotic expansion for the distribution function permits analytic evaluation of all the relevant fluid fields. Basic theoretical features of the solution and their astrophysical implications are discussed. As an application, the possibility of describing the dynamics of slowly time-varying accretion flows and the self-generation of magnetic field by means of a ''kinetic dynamo effect'' are discussed. Both effects are shown to be related to intrinsically kinetic physical mechanisms.

Confinement of ripple-trapped slowing-down ions by a radial electric field

International Nuclear Information System (INIS)

Herrmann, W.

1998-03-01

Weakly collisional ions trapped in the toroidal field ripples at the outer plasma edge can be prevented to escape the plasma due to grad B-drift by a counteracting radial electric field. This leads to an increase in the density of ripple-trapped ions, which can be monitored by the analysis of charge exchange neutrals. The minimum radial electric field E r necessary to confine ions with energy E and charge q (q=-1: charge of the electron) is E r = -E/(q * R), where R is the major radius at the measuring point. Slowing-down ions from neutral injection are usually in the right energy range to be sufficiently collisionless in the plasma edge and show the confinement by radial electric fields in the range of tens of kV/m. The density of banana ions is almost unaffected by the radial electric field. Neither in L/H- nor in H/L-transitions does the density of ripple-trapped ions and, hence, the neutral particle fluxes, show jumps in times shorter than 1 ms. According to [1,2] the response time of the density and the fluxes to a sudden jump in the radial electric field is less than 200 μs, if the halfwidth of the electric field is larger or about 2 cm. This would exclude rapid jumps in the radial electric field at the transition. Whether the halfwidth of the electric field is that large during transition cannot be decided from the measurement of the fluxes alone. (orig.)

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.

Formation of Deep Electron Trap by Yb3+ Codoping Leads into Super-Long Persistent Luminescence in Ce3+-doped Yttrium Aluminum Gallium Garnet Phosphors.

Science.gov (United States)

Ueda, Jumpei; Miyano, Shun; Tanabe, Setsuhisa

2018-05-23

The Y 3 Al 2 Ga 3 O 12 :Ce 3+ -Cr 3+ compound is one of the brightest persistent phosphors, but its persistent luminescence (PersL) duration is not so long due to the relatively shallow Cr 3+ electron trap. Comparing the vacuum referred binding energy of the electron trapping state by Cr 3+ and those by lanthanide ions, we selected Yb 3+ as a deeper electron trapping center. The Y 3 Al 2 Ga 3 O 12 :Ce 3+ -Yb 3+ phosphors show Ce 3+ :5d→4f green persistent luminescence after ceasing blue light excitation. The formation of Yb 2+ was confirmed by the increased intensity of absorption at 585 nm during the charging process. This result indicates that the Yb 3+ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found the Yb 3+ trap makes much deeper electron trap with 1.01 eV depth than the Cr 3+ electron trap with 0.81 eV depth. This deeper Yb 3+ trap provides much slower detrapping rate of filled electron traps than the Cr 3+ -codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce 3+ and Yb 3+ concentrations, the Y 3 Al 2 Ga 3 O 12 :Ce 3+ (0.2%)-Yb 3+ (0.1%) as-made transparent ceramic phosphor showed super long persistent luminescence for over 138.8 hours after ceasing blue light charging.

Effects of a Guide Field on the Larmor Electric Field and Upstream Electron Temperature Anisotropy in Collisionless Asymmetric Magnetic Reconnection

Energy Technology Data Exchange (ETDEWEB)

Ek-In, Surapat; Ruffolo, David [Department of Physics, Faculty of Science, Mahidol University, Bangkok (Thailand); Malakit, Kittipat [Department of Physics, Faculty of Science and Techonology, Thammasat University, Pathum Thani (Thailand); Shay, Michael A. [Department of Physics and Astronomy, University of Delaware, Newark, DE (United States); Cassak, Paul A., E-mail: kmalakit@gmail.com [Department of Physics and Astronomy, West Virginia University, Morgantown, WV (United States)

2017-08-20

We perform the first study of the properties of the Larmor electric field (LEF) in collisionless asymmetric magnetic reconnection in the presence of an out-of-plane (guide) magnetic field for different sets of representative upstream parameters at Earth’s dayside magnetopause with an ion temperature greater than the electron temperature (the ion-to-electron temperature ratio fixed at 2) using two-dimensional particle-in-cell simulations. We show that the LEF does persist in the presence of a guide field. We study how the LEF thickness and strength change as a function of guide field and the magnetospheric temperature and reconnecting magnetic field strength. We find that the thickness of the LEF structure decreases, while its magnitude increases when a guide field is added to the reconnecting magnetic field. The added guide field makes the Larmor radius smaller, so the scaling with the magnetospheric ion Larmor radius is similar to that reported for the case without a guide field. Note, however, that the physics causing the LEF is not well understood, so future work in other parameter regimes is needed to fully predict the LEF for arbitrary conditions. We also find that a previously reported upstream electron temperature anisotropy arises in the vicinity of the LEF region both with and without a guide field. We argue that the generation of the anisotropy is linked to the existence of the LEF. The LEF can be used in combination with the electron temperature anisotropy as a signature to effectively identify dayside reconnection sites in observations.

Effects of a Guide Field on the Larmor Electric Field and Upstream Electron Temperature Anisotropy in Collisionless Asymmetric Magnetic Reconnection

International Nuclear Information System (INIS)

Ek-In, Surapat; Ruffolo, David; Malakit, Kittipat; Shay, Michael A.; Cassak, Paul A.

2017-01-01

We perform the first study of the properties of the Larmor electric field (LEF) in collisionless asymmetric magnetic reconnection in the presence of an out-of-plane (guide) magnetic field for different sets of representative upstream parameters at Earth’s dayside magnetopause with an ion temperature greater than the electron temperature (the ion-to-electron temperature ratio fixed at 2) using two-dimensional particle-in-cell simulations. We show that the LEF does persist in the presence of a guide field. We study how the LEF thickness and strength change as a function of guide field and the magnetospheric temperature and reconnecting magnetic field strength. We find that the thickness of the LEF structure decreases, while its magnitude increases when a guide field is added to the reconnecting magnetic field. The added guide field makes the Larmor radius smaller, so the scaling with the magnetospheric ion Larmor radius is similar to that reported for the case without a guide field. Note, however, that the physics causing the LEF is not well understood, so future work in other parameter regimes is needed to fully predict the LEF for arbitrary conditions. We also find that a previously reported upstream electron temperature anisotropy arises in the vicinity of the LEF region both with and without a guide field. We argue that the generation of the anisotropy is linked to the existence of the LEF. The LEF can be used in combination with the electron temperature anisotropy as a signature to effectively identify dayside reconnection sites in observations.

Impact of electron trapping on RF current drive in tokamaks

International Nuclear Information System (INIS)

Giruzzi, G.; Engelmann, F.

1987-01-01

The impact of the presence of trapped electrons on noninductive current drive by RF waves in tokamak plasmas is investigated. The appropriate response function, allowing to express the current drive efficiency J/P by a simple analytical formula, has been derived. The approach displays the reasons for the degradation of the current drive efficiency away from the plasma axis in the case of methods relying on the diffusion of electrons in the velocity component perpendicular to the confining magnetic field. It is shown that this degradation is appreciable even for large resonant parallel velocities. (author) [pt

Overview of the Livermore electron beam ion trap project

International Nuclear Information System (INIS)

Beiersdorfer, P.; Behar, E.; Boyce, K.R.; Brown, G.V.; Chen, H.; Gendreau, K.C.; Graf, A.; Gu, M.-F.; Harris, C.L.; Kahn, S.M.; Kelley, R.L.; Lepson, J.K.; May, M.J.; Neill, P.A.; Pinnington, E.H.; Porter, F.S.; Smith, A.J.; Stahle, C.K.; Szymkowiak, A.E.; Tillotson, A.; Thorn, D.B.; Traebert, E.; Wargelin, B.J.

2003-01-01

The Livermore electron beam ion trap facility has recently been moved to a new location within LLNL, and new instrumentation was added, including a 32-pixel microcalorimeter. The move was accompanied by a shift of focus toward in situ measurements of highly charged ions, which continue with increased vigor. Overviews of the facility, which includes EBIT-I and SuperEBIT, and the research projects are given, including results from optical spectroscopy, QED, and X-ray line excitation measurements

"Diffusion" region of magnetic reconnection: electron orbits and the phase space mixing

Science.gov (United States)

Kropotkin, Alexey P.

2018-05-01

The nonlinear dynamics of electrons in the vicinity of magnetic field neutral lines during magnetic reconnection, deep inside the diffusion region where the electron motion is nonadiabatic, has been numerically analyzed. Test particle orbits are examined in that vicinity, for a prescribed planar two-dimensional magnetic field configuration and with a prescribed uniform electric field in the neutral line direction. On electron orbits, a strong particle acceleration occurs due to the reconnection electric field. Local instability of orbits in the neighborhood of the neutral line is pointed out. It combines with finiteness of orbits due to particle trapping by the magnetic field, and this should lead to the effect of mixing in the phase space, and the appearance of dynamical chaos. The latter may presumably be viewed as a mechanism producing finite conductivity in collisionless plasma near the neutral line. That conductivity is necessary to provide violation of the magnetic field frozen-in condition, i.e., for magnetic reconnection to occur in that region.

Collisionless two-fluid theory of toroidal ηi stability

International Nuclear Information System (INIS)

Mondt, J.; Weiland, J.

1989-01-01

A collisionless two-fluid theory based on a fourteen-moment generalization of the 'double-adiabatic' equations is developed to lowest order in the Larmor radius parameter, and applied to derive the toroidal η i stability boundary for all values of the ratio of the density gradient scale length divided by the field curvature length. The present model is an improvement over existing collisional two-fluid models in view of the collisionless nature of the η i instability, while retaining the advantage over kinetic theory of the practability of mode-coupling simulations. The linear stability boundary, linear growth rate and real frequency agree fairly accurately with draft-kinetic theory

Collisionless Reconnection in Magnetohydrodynamic and Kinetic Turbulence

Science.gov (United States)

Loureiro, Nuno F.; Boldyrev, Stanislav

2017-12-01

It has recently been proposed that the inertial interval in magnetohydrodynamic (MHD) turbulence is terminated at small scales not by a Kolmogorov-like dissipation region, but rather by a new sub-inertial interval mediated by tearing instability. However, many astrophysical plasmas are nearly collisionless so the MHD approximation is not applicable to turbulence at small scales. In this paper, we propose an extension of the theory of reconnection-mediated turbulence to plasmas which are so weakly collisional that the reconnection occurring in the turbulent eddies is caused by electron inertia rather than by resistivity. We find that the transition scale to reconnection-mediated turbulence depends on the plasma beta and on the assumptions of the plasma turbulence model. However, in all of the cases analyzed, the energy spectra in the reconnection-mediated interval range from E({k}\\perp ){{dk}}\\perp \\propto {k}\\perp -8/3{{dk}}\\perp to E({k}\\perp ){{dk}}\\perp \\propto {k}\\perp -3{{dk}}\\perp .

Plasma heating in collisionless plasma at low plasma density

International Nuclear Information System (INIS)

Wulf, H.O.

1977-01-01

The high frequency heating of a collisionless, fully ionized low density plasma is investigated in the range: 2ωc 2 2 under pumping frequencies. A pulsed 1 MHz transmitter excites a fast standing, magneto-acoustical wave in the plasma, via the high frequency magnetic field of a Stix solenoid. The available modulation degrees are between 0.7 and 7.0%. As power consumption measurements show, there appears at all investigated pumping frequencies an effective energy transfer to the plasma that cannot be explained with the classical MHD models. Measurements with electrostatic probes and further with a miniature counter-field spectrometer yield an electron and ion temperature gain of two to three factors and 15-18, compared to the corresponding values in the initial plasma. (orig./HT) [de

Trapping of self-interstitials at manganese atoms in electron-irradiated dilute AlMn alloys

International Nuclear Information System (INIS)

Bartels, A.; Dworschak, F.

1985-01-01

Dilute AlMn alloys were irradiated isothermally at different temperatures in stage II with 1.8 MeV electrons and the resistivity damage rates were measured as a function of the residual resistivity increase. The results demonstrate that Mn atoms provide deep traps at least up to 150 K for mobile interstitials. A quantitative evaluation of the data with respect to trapping radii is somewhat handicapped by the fact that the resistivity contribution of a Mn-Al interstitial complex was found to be considerably less than the sum of the resistivity contributions of an isolated solute Mn atom and an Al self-interstitial. The results can be explained by a model which assumes that both the trapping radius and the resistivity contribution of solute-self-interstitial complexes increase with the number of trapped interstitials. (author)

METHOD AND APPARATUS FOR INJECTING AND TRAPPING ELECTRONS IN A MAGNETIC FIELD

Science.gov (United States)

Christofilos, N.C.

1962-05-29

An apparatus is designed for the manipulation of electrons in an exially symmetric magnetic field region and may be employed to trap electrons in such a field by directing an electron beam into a gradientially intensified field region therein to form an annular electron moving axially in the field and along a decreasing field gradient. Dissipative loop circuits such as resistive loops are disposed along at least the decreasing field gradient so as to be inductively coupled to the electron bunch so as to extract energy of the electron bunch and provide a braking force effective to reduce the velocity of the bunch. Accordingly, the electron bunch upon entering a lower intensity magnetic field region is retained therein since the electrons no longer possess sufficient energy to escape. (AEC)

Trapped electron decay by the thermally-assisted tunnelling to electron acceptors in glassy matrices. A computer simulation study

International Nuclear Information System (INIS)

Feret, B.; Bartczak, W.M.; Kroh, J.

1991-01-01

The Redi-Hopefield quantum mechanical model of the thermally-assisted electron transfer has been applied to simulate the decay of trapped electrons by tunnelling to electron acceptor molecules added to the glassy matrix. It was assumed that the electron energy levels in donors and acceptors are statistically distributed and the electron excess energy after transfer is dissipated in the medium by the electron-phonon coupling. The electron decay curves were obtained by the method of computer simulation. It was found that for a given medium there exists a certain preferred value of the electronic excess energy which can be effectively converted into the matrix vibrations. If the mismatch of the electron states on the donor and acceptor coincides with the ''resonance'' energy the overall kinetics of electron transfer is accelerated. (author)

Dynamic trapping of electrons in space plasmas

International Nuclear Information System (INIS)

Brenning, N.; Bohm, M.; Faelthammar, C.G.

1989-12-01

The neutralization of positive space charge is studied in a case where heavy positive ions are added to a limited region of length L in a collisionfree magnetized plasma. It is found that electrons which become accelerated towards the positive space charge can only achieve a partial neutralization: they overshoot, and the positive region becomes surrounded by negative space charges which screen the electric field from the surroundings. The process is studied both analytically and by computer simulations with consistent results: large positive potentials (U>>kT e /e) can be built up with respect to the surrounding plasma. In the process of growth, the potential maximum traps electrons in transit so that quasineutrality is maintained. The potential U is proportional to the ambient electron temperature and the square of the plasma density increase, but independent of both the ion injection rate and the length L. The process explains several features of the Porcupinge xenon beam injection experiment. It could also have importance for the electrodynamic coupling between plasmas of different densities, e.g. the injection of neutral clouds in the ionosphere of species that becomes rapidly photoionized, or penetration of dense plasma clouds from the solar wind into the magnetosphere. (31 refs.) (authors)

Electron beam ion trap bi-annual report 1996/1997

International Nuclear Information System (INIS)

Schneider, D.

1999-01-01

The research of the EBIT (Electron Beam Ion Trap) program in N Division of the Physics and Space Technology Directorate at LLNL continues to contribute significantly to the understanding of physical processes with low energy highly charged ions in atomic physics, plasma physics, and material science. Low-energy highly charged ions (up to U 92+ ), provided by the EBIT facilities, provide a unique laboratory opportunity to study high field effects in atomic structures and dynamic interaction processes. The formation, existence, and structure of highly charged ions in astrophysical environments and laboratory plasmas make highly charged ions desirable for diagnosing various plasma conditions. The strong interaction of highly charged ions with matter and the response of solid surfaces make them a sensitive analysis tool and possibly a future capability for materials modifications at the atomic scale (nano technology). These physical applications require a good understanding and careful study of the dynamics of the interactions of the ions with complex systems. The EBIT group hosted an international conference and a workshop on trapped charged particles. The various talks and discussions showed that physics research with trapped charged particles is a very active and attractive area of innovative research, and provides a basis for research efforts in new areas. It also became obvious that the EBIT/RETRAP project has unique capabilities to perform important new experiments with trapped very highly charged ions at rest, which are complementary to and competitive with research at heavy ion storage rings and other trapping facilities planned or in operation in Europe, Japan, and the United States. Atomic structure research at EBIT provides ever better and more experimental complete benchmark data, supplying data needed to improve atomic theories. Research highlights through 1996 and 1997 include hyperfine structure measurements in H-like ions, QED studies, lifetime and

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.

A quasilinear formulation of turbulence driven current

International Nuclear Information System (INIS)

McDevitt, C. J.; Tang, Xian-Zhu; Guo, Zehua

2014-01-01

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

Evolution of velocity dispersion along cold collisionless flows

International Nuclear Information System (INIS)

Banik, Nilanjan; Sikivie, Pierre

2016-01-01

We found that the infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We also discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components

A dominant electron trap in molecular beam epitaxial InAlN lattice-matched to GaN

Science.gov (United States)

Pandey, Ayush; Bhattacharya, Aniruddha; Cheng, Shaobo; Botton, Gianluigi A.; Mi, Zetian; Bhattacharya, Pallab

2018-04-01

Deep levels in lattice-matched undoped and Si-doped InAlN/GaN grown by plasma-assisted molecular beam epitaxy have been identified and characterized by capacitance and photocapacitance measurements. From x-ray diffraction, reflectance measurements, electron energy loss spectroscopy and high-resolution transmission electron microscopy it is evident that the material has two distinct phases with different compositions. These correspond to In compositions of 18.1% and 25.8%, with corresponding bandgaps of 4.6 eV and 4.1 eV, respectively. The lower bandgap material is present as columnar microstructures in the form of quantum wires. A dominant electron trap with an activation energy of 0.293  ±  0.01 eV, a small capture cross-section of (1.54  ±  0.25)  ×  10-18 cm2, and density increasing linearly with Si doping density is identified in all the samples. The characteristics of the electron trap and variation of diode capacitance are discussed in the context of carrier dynamics involving the dominant trap level and the quantum wires.

Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy.

Science.gov (United States)

Akhtar, Parveen; Zhang, Cheng; Liu, Zhengtang; Tan, Howe-Siang; Lambrev, Petar H

2018-03-01

Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P 700 reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

Electron spin-lattice relaxation mechanisms of radiation produced trapped electrons and hydrogen atoms in aqueous and organic glassy matrices. Modulation of electron nuclear dipolar interaction by tunnelling modes in a glassy matrix. [. gamma. rays

Energy Technology Data Exchange (ETDEWEB)

Bowman, M K; Kevan, L [Wayne State Univ., Detroit, Mich. (USA). Dept. of Chemistry

1977-01-01

The spin lattice relaxation of trapped electrons in aqueous and organic glasses and trapped hydrogen atoms in phosphoric acid glass has been directly studied as a function of temperature by the saturation recovery method. Below 50 to 100 K, the major spin lattice relaxation mechanism involves modulation of the electron nuclear dipolar (END) interaction with nuclei in the radical's environment by tunnelling of those nuclei between two or more positions. This relaxation mechanism occurs with high efficiency and has a characteristic linear temperature dependence. The tunnelling nuclei around trapped electrons do not seem to involve the nearest neighbor nuclei which are oriented by the electron in the process of solvation. Instead the tunnelling nuclei typically appear to be next nearest neighbors to the trapped electron. The identities of the tunnelling nuclei have been deduced by isotopic substitution and are attributed to: Na in 10 mol dm/sup -3/ NaOH aqueous glass, ethyl protons in ethanol glass, methyl protons in methanol glass and methyl protons in MTHF glass. For trapped hydrogen atoms in phosphoric acid, the phosphorus nuclei appear to be the effective tunnelling nuclei. Below approximately 10 K the spin lattice relaxation is dominated by a temperature independent cross relaxation term for H atoms in phosphoric acid glass and for electrons in 10 mol dm/sup -3/ NaOH aqueous glass, but not for electrons in organic glasses. This is compared with recent electron-electron double resonance studies of cross relaxation in these glasses. The spin lattice relaxation of O/sup -/ formed in 10 mol dm/sup -3/ NaOH aqueous glass was also studied and found to be mainly dominated by a Raman process with an effective Debye temperature of about 100 K.

Deeply trapped electrons in imaging plates and their utilization for extending the dynamic range

International Nuclear Information System (INIS)

Ohuchi, Hiroko; Kondo, Yasuhiro

2010-01-01

The absorption spectra of deep centers in an imaging plate (IP) made of BaFBr 0:85 I 0:15 :Eu 2+ have been studied in the ultraviolet region. Electrons trapped in deep centers are considered to be the cause of unerasable and reappearing latent images in IPs over-irradiated with X-rays. Deep centers showed a dominant peak at around 320 nm, followed by two small peaks at around 345 and 380 nm. By utilizing deeply trapped electrons, we have attempted to extend the dynamic range of an IP. The IP was irradiated by 150-kV X-rays with doses from 8.07 mGy to 80.7 Gy. Reading out the latent image by the stimulation of Eu 2+ luminescence with a 633-nm He-Ne laser light from a conventional Fuji reader showed a linear relationship with irradiated dose up to 0.8 Gy, but then becoming non-linear. After fully erasing with visible light, unerasable latent images were read out using 635-nm semi-conductor laser light combined with a photon-counting detection system. The dose-response curve so obtained gave a further two orders of magnitude extending the dynamic range up to 80.7 Gy. Comprehensive results indicate that electrons supplied from deep centers to the F centers provided the extended dynamic range after the F centers became saturated. Based on these facts, a model of the excitation of deeply trapped electrons and PSL processes is proposed.

Deuterium trapping at vacancy clusters in electron/neutron-irradiated tungsten studied by positron annihilation spectroscopy

Science.gov (United States)

Toyama, T.; Ami, K.; Inoue, K.; Nagai, Y.; Sato, K.; Xu, Q.; Hatano, Y.

2018-02-01

Deuterium trapping at irradiation-induced defects in tungsten, a candidate material for plasma facing components in fusion reactors, was revealed by positron annihilation spectroscopy. Pure tungsten was electron-irradiated (8.5 MeV at ∼373 K and to a dose of ∼1 × 10-3 dpa) or neutron-irradiated (at 573 K to a dose of ∼0.3 dpa), followed by post-irradiation annealing at 573 K for 100 h in deuterium gas of ∼0.1 MPa. In both cases of electron- or neutron-irradiation, vacancy clusters were found by positron lifetime measurements. In addition, positron annihilation with deuterium electrons was demonstrated by coincidence Doppler broadening measurements, directly indicating deuterium trapping at vacancy-type defects. This is expected to cause significant increase in deuterium retention in irradiated-tungsten.

Ion acoustic eigenmodes in a collisionless bounded plasma:

International Nuclear Information System (INIS)

Kuhn, S.; Schupfer, N.; Santiago, M.A.M.; Assis, A.S. de

1990-01-01

This paper is based on an integral-equation method developed for solving the general linearized perturbation problem for a one-dimensional, uniform collisionless plasma with thin sheats, bounded by two planar electrodes. The underlying system of equations consists of a) the Vlasov equations for all particle species involved; b) Poisson's equation; c) the equation of total-current conservation; d) the particle boundary conditions at the left and right hand electrodes and e) the external-circuit equation. The method allows for very general equilibrium, boundary and external-circuit conditions. Using Laplace transformations in both time and space, it is set up to handle the complete initial value problem but also yields, as a by-product, the solution to the eigenmode problem. The only application to date of this method was to the Pierce Diode with a non-trivial external circuit, in which case the equation determining the complex eigenfrequencies ω n was found in analytic form. The said method is applied to ion-acoustic eigenmodes in a one-dimensional, collisionless bounded plasma consisting of non-drifting thermal electrons and a cold ion beam propagating through them. In this case, which is of relevance in the context of both Q- and DP-machines, the eigenfrequencies can no longer be obtained as solutions of an analytically explicit homogeneous system of linear integral equations. Via appropriate basis- set expansions of all perturbation functions involved, this system is transformed into a system of linear algebraic equations for the ω-dependent expansion coefficients, from which the eigenfrequencies can be obtained as the zeros of the'system determinant'. The results include studies on how the eigenfrequencies depend on plasma, boundary, as well as a comparison between these bounded-system ion-acoustic eigenmodes and their infinite-plasma counter-parts. (Author)

Collisionless sausage instability

International Nuclear Information System (INIS)

Coppins, M.

1989-01-01

The Chew--Goldberger--Low (CGL) double adiabatic model [Proc. R. Soc. London Ser. A 236, 112 (1956)] is used to study the linear m = 0 (sausage) mode in a Z pinch operating in the collisionless, small ion Larmor radius regime. The model is valid in this case since the parallel heat flow is identically zero. A necessary and sufficient condition for stability, applicable to arbitrary (anisotropic) Z-pinch equilibria, is derived and the eigenvalue equation is solved for two classes of isotropic equilibria. Growth rates are shown to be lower than those of ideal magnetohydrodynamics (MHD). It is found that, in contrast to ideal MHD, the CGL eigenfunctions are characterized by an unperturbed inner region

Relaxation oscillations induced by amplitude-dependent frequency in dissipative trapped electron mode turbulence

International Nuclear Information System (INIS)

Terry, P.W.; Ware, A.S.; Newman, D.E.

1994-01-01

A nonlinear frequency shift in dissipative trapped electron mode turbulence is shown to give rise to a relaxation oscillation in the saturated power density spectrum. A simple non-Markovian closure for the coupled evolution of ion momentum and electron density response is developed to describe the oscillations. From solutions of a nonlinear oscillator model based on the closure, it is found that the oscillation is driven by the growth rate, as modified by the amplitude-dependent frequency shift, with inertia provided by the memory of the growth rate of prior amplitudes. This memory arises from time-history integrals common to statistical closures. The memory associated with a finite time of energy transfer between coupled spectrum components does not sustain the oscillation in the simple model. Solutions of the model agree qualitatively with the time-dependent numerical solutions of the original dissipative trapped electron model, yielding oscillations with the proper phase relationship between the fluctuation energy and the frequency shift, the proper evolution of the wave number spectrum shape and particle flux, and a realistic period

Detection of electron and hole traps in CdZnTe radiation detectors by thermoelectric emission spectroscopy and thermally stimulated conductivity

International Nuclear Information System (INIS)

Lee, E.Y.; Brunett, B.A.; Olsen, R.W.; Van Scyoc, J.M. III; Hermon, H.; James, R.B.

1998-01-01

The electrical properties of CdZnTe radiation detectors are largely determined by electron and hole traps in this material. The traps, in addition to degrading the detector performance, can function as dopants and determine the resistivity of the material. Thermoelectric emission spectroscopy and thermally stimulated conductivity are used to detect these traps in a commercially available spectrometer-grade CdZnTe detector, and the electrical resistivity is measured as a function of temperature. A deep electron trap having an energy of 695 meV and cross section of 8 x 10 -16 cm 2 is detected and three hole traps having energies of 70 ± 20 meV, 105 ± 30 meV and 694 ± 162 meV are detected. A simple model based on these traps explains quantitatively all the data, including the electrical properties at room temperature and also their temperature dependence

Adiabatic energy change of plasma electrons and the frame dependence of the cross-shock potential at collisionless magnetosonic shock waves

International Nuclear Information System (INIS)

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

1984-01-01

In collisionless magnetosonic shock waves, ions are commonly thought to be decelerated by dc electrostatic cross-shock electric field along the shock normal n. In a frame where ions are normally incident to the shock the change in the potential energy [qphi/sup N/] in the quasi-perpendicular geommetry is of the order of the change of the energy of normal ion flow: [qphi/sup N/]roughly-equal[1/2m/sub i/(V/sub i//sup N/xn) 2 ], which is approximately 200-500 eV at the earth's bow shock. We show that the electron energy gain, typically 1/10 this number, is consistent with such a large potential jump in this geometry. Key facts are the different paths taken by electrons an ions through the shock wave and the frame dependence of the potential jump in the geometry. In the normal incidence frame, electrons lose energy by doing work against the solar wind motional electric field E/sub M//sup N/, which partially offsets the energy gain from the cross-shock electrostatic potential energy [ephi/sub asterisk//sup N/]. In the de Hoffman-Teller frame the motional electric field vanishes; the elctrons gain the full electrostatic potential energy jump e[phi/sub asterisk//sup H//sup T/] of that frame, which is not, however, equal to the electrostatic potential energy jump e[phi/sub asterisk//sup N/] of that frame, which is not, however, equal to the electrostatic potential energy jump e[phi/sub asterisk//sup N/] in the normal incidence frame

First experiments with the Greifswald electron-beam ion trap

Science.gov (United States)

Schabinger, B.; Biedermann, C.; Gierke, S.; Marx, G.; Radtke, R.; Schweikhard, L.

2013-09-01

The former Berlin electron-beam ion trap (EBIT) was moved to Greifswald. In addition to x-ray studies the setup will be used for the investigation of interaction processes between highly charged ions and atomic clusters such as charge exchange and fragmentation. The EBIT setup has now been reassembled and highly charged ions have been produced from Xe-Ar gas mixtures to study the ‘sawtooth effect’. In addition, the layout of the extraction beamline, the interaction region and product analysis for interaction studies with highly charged ions are presented.

Effects of the radial electric field on confinement and trapping for non collisional electrons in TJ-II

International Nuclear Information System (INIS)

Guasp, J.; Liniers, M.

1998-01-01

The effects of radial electric fields on the non collisional losses, asymmetries at plasma border and on the Vacuum Vessel and trapping fractions for 0.1 1 KeV electrons in TJ-II are analysed. This study complements a series, already published, for ions, therefore only the main differences are stressed. Many of these effect are similar for electrons and ions, mainly the drastic decrease of losses with the electric field, the increasing peripherical loss concentration, the strong accumulation on the Hard Core (HC), the modification in the direction of the induced poloidal rotation, similar angular distributions for trapped particles, etc. Nevertheless, there appear also important differences, that in many cases are originated by the higher electron mobility, in particular a higher sensitivity to the electric field, as well to the intensity as to the sign, producing a faster drop in electron losses for positive potential and a higher asymmetry in the sign dependence. Most of these electron losses exit through the upper side of the plasma, the opposite happens for ions. The strong concentration on the HC appears, many, on the PL-1 plate (the one that is placed upside for toroidal angle φ=0 degree centigree), instead of the opposite PL-2 plate for ions.Finally, for the analysed energy range, there is no variation of electron trapping with the potential nor resonant effect. (Author) 8 refs

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.

Nonlinear electron-acoustic rogue waves in electron-beam plasma system with non-thermal hot electrons

Science.gov (United States)

Elwakil, S. A.; El-hanbaly, A. M.; Elgarayh, A.; El-Shewy, E. K.; Kassem, A. I.

2014-11-01

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, non-thermal hot electrons obeying a non-thermal distribution, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles on the electron beam and energetic population parameter are discussed. The results of the present investigation may be applicable in auroral zone plasma.

Electron trapping in the electrosound solitary wave for propagation of high intensity laser in a relativistic plasma

International Nuclear Information System (INIS)

Heidari, E; Aslaninejad, M; Eshraghi, H

2010-01-01

Using a set of relativistic equations for plasmas with warm electrons and cold ions, we have investigated the effects of trapped electrons in the propagation of an electrosound wave and discussed the possibility of the formation of electromagnetic solitons in a plasma. The effective potential energy and deviations of the electron and ion number densities in this relativistic model have been found. We have obtained the governing equations for the amplitude of the HF field with relativistic corrections. In order to show the destructive impact of the trapped electrons on the solitary wave, a relativistic effective potential and the governing equation have been found. It is shown that for certain values of the parameters the condition of localization of the HF amplitude is violated. In addition, it is shown that as the flow velocity of the plasma changes, the shape of the solitary wave shows two opposing behaviours, depending on whether the solitary wave velocity is larger than the flow velocity or smaller. Also, the existence of stationary solitary waves which are prohibited for nonrelativistic plasma has been predicted. Finally, we have obtained the Korteweg-de Vries equation showing the relativistic, trapping and nonlinearity effects.

Low Mach-number collisionless electrostatic shocks and associated ion acceleration

Science.gov (United States)

Pusztai, I.; TenBarge, J. M.; Csapó, A. N.; Juno, J.; Hakim, A.; Yi, L.; Fülöp, T.

2018-03-01

The existence and properties of low Mach-number (M≳ 1) electrostatic collisionless shocks are investigated with a semi-analytical solution for the shock structure. We show that the properties of the shock obtained in the semi-analytical model can be well reproduced in fully kinetic Eulerian Vlasov-Poisson simulations, where the shock is generated by the decay of an initial density discontinuity. Using this semi-analytical model, we study the effect of the electron-to-ion temperature ratio and the presence of impurities on both the maximum shock potential and the Mach number. We find that even a small amount of impurities can influence the shock properties significantly, including the reflected light ion fraction, which can change several orders of magnitude. Electrostatic shocks in heavy ion plasmas reflect most of the hydrogen impurity ions.

Design and Fabrication of Cryostat Interface and Electronics for High Performance Antimatter Trap (HI-PAT)

Science.gov (United States)

Smith, Gerald A.

1999-01-01

Included in Appendix I to this report is a complete set of design and assembly schematics for the high vacuum inner trap assembly, cryostat interfaces and electronic components for the MSFC HI-PAT. Also included in the final report are summaries of vacuum tests, and electronic tests performed upon completion of the assembly.

Crystal step edges can trap electrons on the surfaces of n-type organic semiconductors.

Science.gov (United States)

He, Tao; Wu, Yanfei; D'Avino, Gabriele; Schmidt, Elliot; Stolte, Matthias; Cornil, Jérôme; Beljonne, David; Ruden, P Paul; Würthner, Frank; Frisbie, C Daniel

2018-05-30

Understanding relationships between microstructure and electrical transport is an important goal for the materials science of organic semiconductors. Combining high-resolution surface potential mapping by scanning Kelvin probe microscopy (SKPM) with systematic field effect transport measurements, we show that step edges can trap electrons on the surfaces of single crystal organic semiconductors. n-type organic semiconductor crystals exhibiting positive step edge surface potentials display threshold voltages that increase and carrier mobilities that decrease with increasing step density, characteristic of trapping, whereas crystals that do not have positive step edge surface potentials do not have strongly step density dependent transport. A device model and microelectrostatics calculations suggest that trapping can be intrinsic to step edges for crystals of molecules with polar substituents. The results provide a unique example of a specific microstructure-charge trapping relationship and highlight the utility of surface potential imaging in combination with transport measurements as a productive strategy for uncovering microscopic structure-property relationships in organic semiconductors.

Extreme ultra-violet emission spectroscopy of highly charged gadolinium ions with an electron beam ion trap

International Nuclear Information System (INIS)

Ohashi, Hayato; Nakamura, Nobuyuki; Sakaue, Hiroyuki A

2013-01-01

We present extreme ultra-violet emission spectra of highly charged gadolinium ions obtained with an electron beam ion trap at electron energies of 0.53–1.51 keV. The electron energy dependence of the spectra in the 5.7–11.3 nm range is compared with calculation with the flexible atomic code. (paper)

Nonextensive statistical mechanics approach to electron trapping in degenerate plasmas

Science.gov (United States)

Mebrouk, Khireddine; Gougam, Leila Ait; Tribeche, Mouloud

2016-06-01

The electron trapping in a weakly nondegenerate plasma is reformulated and re-examined by incorporating the nonextensive entropy prescription. Using the q-deformed Fermi-Dirac distribution function including the quantum as well as the nonextensive statistical effects, we derive a new generalized electron density with a new contribution proportional to the electron temperature T, which may dominate the usual thermal correction (∼T2) at very low temperatures. To make the physics behind the effect of this new contribution more transparent, we analyze the modifications arising in the propagation of ion-acoustic solitary waves. Interestingly, we find that due to the nonextensive correction, our plasma model allows the possibility of existence of quantum ion-acoustic solitons with velocity higher than the Fermi ion-sound velocity. Moreover, as the nonextensive parameter q increases, the critical temperature Tc beyond which coexistence of compressive and rarefactive solitons sets in, is shifted towards higher values.

Two-dimensional spatial structure of the dissipative trapped-electron mode

International Nuclear Information System (INIS)

Rewoldt, G.; Tang, W.M.; Frieman, E.A.

1976-09-01

This paper deals with the complete two-dimensional structure of the dissipative trapped-electron mode over its full width, which may extend over several mode-rational surfaces. The complete integro-differential equation is studied in the limit k/sub r/rho/sub i/ less than 1, where rho/sub i/ is the ion gyroradius, and k/sub r/, the radial wavenumber, is regarded as a differential operator. This is converted into a matrix equation which is then solved by standard numerical methods

Formation and Coalescence of Electron Solitary Holes

DEFF Research Database (Denmark)

Saeki, K.; Michelsen, Poul; Pécseli, H. L.

1979-01-01

Electron solitary holes were observed in a magnetized collisionless plasma. These holes were identified as Bernstein-Green-Kruskal equilibria, thus being purely kinetic phenomena. The electron hole does not damp even though its velocity is close to the electron thermal velocity. Two holes attract...

Electron precipitation in solar flares - Collisionless effects

Science.gov (United States)

Vlahos, L.; Rowland, H. L.

1984-01-01

A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with a set of rate equations that follows, in time, the nonlinearly coupled system of plasma waves-ion fluctuations. As an outcome of the fast transfer of wave energy from the beam to the ambient plasma, nonthermal electron tails are formed which can stabilize the anomalous Doppler resonance instability responsible for the pitch angle scattering of the beam electrons. The non-collisional losses of the precipitating electrons are estimated, and the observational implication of these results are discussed.

Kβ spectra of heliumlike chromium from an electron-beam ion trap

International Nuclear Information System (INIS)

Decaux, V.; Beiersdorfer, P.; Elliott, S.; Osterheld, A.

1993-01-01

Kβ spectra of heliumlike chromium have been recorded using the Livermore electron-beam ion trap (EBIT) with a high-resolution Bragg crystal spectrometer in the von Hamos configuration, in the wavelong range from 1.870 Angstrom. Measurements have been made both for direct excitation at an electron beam energy of 8 k and dielectronic recombination around the KLM resonance energy of 5 keV. In order to evaluate the resonance strength the lithiumlike dielectronic satellites, we used a data routine technique to accumulate spectra at 15 different beam energies between 4.96 and 5.28 keV. Results are compared to theoretical calculations using the multiconfiguration parametric potential method

Computation of transverse muon-spin relaxation functions including trapping-detrapping reactions, with application to electron-irradiated tantalum

International Nuclear Information System (INIS)

Doering, K.P.; Aurenz, T.; Herlach, D.; Schaefer, H.E.; Arnold, K.P.; Jacobs, W.; Orth, H.; Haas, N.; Seeger, A.; Max-Planck-Institut fuer Metallforschung, Stuttgart

1986-01-01

A new technique for the economical evaluation of transverse muon spin relaxation functions in situations involving μ + trapping at and detrapping from crystal defects is applied to electron-irradiated Ta exhibiting relaxation maxima at about 35 K, 100 K, and 250 K. The long-range μ + diffusion is shown to be limted by traps over the entire temperature range investigated. The (static) relaxation rates for several possible configurations of trapped muons are discussed, including the effect of the simultaneous presence of a proton in a vacancy. (orig.)

Electron cooling and finite potential drop in a magnetized plasma expansion

Energy Technology Data Exchange (ETDEWEB)

Martinez-Sanchez, M. [Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Navarro-Cavallé, J. [Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Plaza Cardenal Cisneros 3, Madrid 28040 (Spain); Ahedo, E. [Departamento de Bioingeniería e Ingeniería Aeroespacial, Universidad Carlos III de Madrid, Avda. Universidad 30, Leganés 28911, Madrid (Spain)

2015-05-15

The steady, collisionless, slender flow of a magnetized plasma into a surrounding vacuum is considered. The ion component is modeled as mono-energetic, while electrons are assumed Maxwellian upstream. The magnetic field has a convergent-divergent geometry, and attention is restricted to its paraxial region, so that 2D and drift effects are ignored. By using the conservation of energy and magnetic moment of particles and the quasi-neutrality condition, the ambipolar electric field and the distribution functions of both species are calculated self-consistently, paying attention to the existence of effective potential barriers associated to magnetic mirroring. The solution is used to find the total potential drop for a set of upstream conditions, plus the axial evolution of various moments of interest (density, temperatures, and heat fluxes). The results illuminate the behavior of magnetic nozzles, plasma jets, and other configurations of interest, showing, in particular, in the divergent plasma the collisionless cooling of electrons, and the generation of collisionless electron heat fluxes.

Preferential acceleration in collisionless supernova shocks

International Nuclear Information System (INIS)

Hainebach, K.; Eichler, D.; Schramm, D.

1979-01-01

The preferential acceleration and resulting cosmic ray abundance enhancements of heavy elements (relative to protons) are calculated in the collisionless supernova shock acceleration model described by Eichler in earlier work. Rapidly increasing enhancements up to several tens times solar ratios are obtained as a function of atomic weight over charge at the time of acceleration. For material typical of hot phase interstellar medium, good agreement is obtained with the observed abundance enhancements

Annual progress report

International Nuclear Information System (INIS)

Simon, A.

1975-01-01

Considerable success has been achieved this year in research aimed at extending the asymptotic threshold nonlinear theory to plasmas governed by the Vlasov equation and in a group of linear studies concerned with drift instabilities in sheared magnetic fields. The nonlinear results are general and have been applied to the bump-on-tail instability and to the collisionless drift and the dissipative trapped electron instability in unsheared fields. The linear studies have dealt with the effects of resonant electrons, finite collisionality, finite-beta, neoclassical modifications and ion gyro-motion on trapped electron instabilities in sheared magnetic fields

Diagnosing collisionless energy transfer using field-particle correlations: Vlasov-Poisson plasmas

Science.gov (United States)

Howes, Gregory G.; Klein, Kristopher G.; Li, Tak Chu

2017-02-01

Turbulence plays a key role in the conversion of the energy of large-scale fields and flows to plasma heat, impacting the macroscopic evolution of the heliosphere and other astrophysical plasma systems. Although we have long been able to make direct spacecraft measurements of all aspects of the electromagnetic field and plasma fluctuations in near-Earth space, our understanding of the physical mechanisms responsible for the damping of the turbulent fluctuations in heliospheric plasmas remains incomplete. Here we propose an innovative field-particle correlation technique that can be used to measure directly the secular energy transfer from fields to particles associated with collisionless damping of the turbulent fluctuations. Furthermore, this novel procedure yields information about the collisionless energy transfer as a function of particle velocity, providing vital new information that can help to identify the dominant collisionless mechanism governing the damping of the turbulent fluctuations. Kinetic plasma theory is used to devise the appropriate correlation to diagnose Landau damping, and the field-particle correlation technique is thoroughly illustrated using the simplified case of the Landau damping of Langmuir waves in a 1D-1V (one dimension in physical space and one dimension in velocity space) Vlasov-Poisson plasma. Generalizations necessary to apply the field-particle correlation technique to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, highlighting several caveats. This novel field-particle correlation technique is intended to be used as a primary analysis tool for measurements from current, upcoming and proposed spacecraft missions that are focused on the kinetic microphysics of weakly collisional heliospheric plasmas, including the Magnetospheric Multiscale (MMS), Solar Probe Plus, Solar Orbiter and Turbulence Heating ObserveR (THOR) missions.

Dissipative dust-acoustic shock waves in a varying charge electronegative magnetized dusty plasma with trapped electrons

Energy Technology Data Exchange (ETDEWEB)

Bacha, Mustapha [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud, E-mail: mouloudtribeche@yahoo.fr, E-mail: mtribeche@usthb.dz [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Algerian Academy of Sciences and Technologies, Algiers (Algeria)

2016-08-15

The combined effects of an oblique magnetic field and electron trapping on dissipative dust-acoustic waves are examined in varying charge electronegative dusty plasmas with application to the Halley Comet plasma (∼10{sup 4} km from the nucleus). A weakly nonlinear analysis is carried out to derive a modified Korteweg-de Vries-Burger-like equation. Making use of the equilibrium current balance equation, the physically admissible values of the electron trapping parameter are first constrained. We then show that the Burger dissipative term is solely due to the dust charge variation process. It is found that an increase of the magnetic field obliqueness or a decrease of its magnitude renders the shock structure more dispersive.

Spectroscopy with trapped highly charged ions

International Nuclear Information System (INIS)

Beiersdorfer, Peter

2009-01-01

We give an overview of atomic spectroscopy performed on electron beam ion traps at various locations throughout the world. Spectroscopy at these facilities contributes to various areas of science and engineering, including but not limited to basic atomic physics, astrophysics, extreme ultraviolet lithography, and the development of density and temperature diagnostics of fusion plasmas. These contributions are accomplished by generating, for example, spectral surveys, making precise radiative lifetime measurements, accounting for radiative power emitted in a given wavelength band, illucidating isotopic effects, and testing collisional-radiative models. While spectroscopy with electron beam ion traps had originally focused on the x-ray emission from highly charged ions interacting with the electron beam, the operating modes of such devices have expanded to study radiation in almost all wavelength bands from the visible to the hard x-ray region; and at several facilities the ions can be studied even in the absence of an electron beam. Photon emission after charge exchange or laser excitation has been observed; and the work is no longer restricted to highly charged ions. Much of the experimental capabilities are unique to electron beam ion traps, and the work performed with these devices cannot be undertaken elsewhere. However, in other areas the work on electron beam ion traps rivals the spectroscopy performed with conventional ion traps or heavy-ion storage rings. The examples we present highlight many of the capabilities of the existing electron beam ion traps and their contributions to physics.

Phase-Space Density Analysis of the AE-8 Traped Electron and the AP-8 Trapped Proton Model Environments

Energy Technology Data Exchange (ETDEWEB)

Thomas E. Cayton

2005-08-01

The AE-8 trapped electron and the AP-8 trapped proton models are used to examine the L-shell variation of phase-space densities for sets of transverse (or 1st) invariants, {mu}, and geometrical invariants, K (related to the first two adiabatic invariants). The motivation for this study is twofold: first, to discover the functional dependence of the phase-space density upon the invariants; and, second, to explore the global structure of the radiation belts within this context. Variation due to particle rest mass is considered as well. The overall goal of this work is to provide a framework for analyzing energetic particle data collected by instruments on Global Positioning System (GPS) spacecraft that fly through the most intense region of the radiation belt. For all considered values of {mu} and K, and for 3.5 R{sub E} < L < 6.5 R{sub E}, the AE-8 electron phase-space density increases with increasing L; this trend--the expected one for a population diffusing inward from an external source--continues to L = 7.5 R{sub E} for both small and large values of K but reverses slightly for intermediate values of K. The AP-8 proton phase-space density exhibits {mu}-dependent local minima around L = 5 R{sub E}. Both AE-8 and AP-8 exhibit critical or cutoff values for the invariants beyond which the flux and therefore the phase-space density vanish. For both electrons and protons, these cutoff values vary systematically with magnetic moment and L-shell and are smaller than those estimated for the atmospheric loss cone. For large magnetic moments, for both electrons and protons, the K-dependence of the phase-space density is exponential, with maxima at the magnetic equator (K = 0) and vanishing beyond a cutoff value, K{sub c}. Such features suggest that momentum-dependent trapping boundaries, perhaps drift-type loss cones, serve as boundary conditions for trapped electrons as well as trapped protons.

EPR study of electron traps in x-ray-irradiated yttria-stabilized zirconia

International Nuclear Information System (INIS)

Azzoni, C.B.; Paleari, A.

1989-01-01

Single crystals of yttria-stabilized zirconia (12 mol % of Y 2 O 3 ) have been x-ray irradiated at room temperature. The electron paramagnetic resonance spectrum of the filled electron traps is analyzed in terms of a single oxygen vacancy type of defect with its symmetry axis along the left-angle 111 right-angle direction. The angular dependence of the linewidth and the asymmetry of the line shape are attributed to the disordered rearrangements of the anion sublattice surrounding the oxygen vacancy. This affects the local crystal fields and the directions of the symmetry axis of the defects

EPR study of electron traps in x-ray-irradiated yttria-stabilized zirconia

Energy Technology Data Exchange (ETDEWEB)

Azzoni, C.B.; Paleari, A. (Dipartimento di Fisica, Alessandro Volta dell' Universita di Pavia, via Bassi 6, 27100 Pavia, Italy (IT))

1989-10-01

Single crystals of yttria-stabilized zirconia (12 mol % of Y{sub 2}O{sub 3}) have been x-ray irradiated at room temperature. The electron paramagnetic resonance spectrum of the filled electron traps is analyzed in terms of a single oxygen vacancy type of defect with its symmetry axis along the {l angle}111{r angle} direction. The angular dependence of the linewidth and the asymmetry of the line shape are attributed to the disordered rearrangements of the anion sublattice surrounding the oxygen vacancy. This affects the local crystal fields and the directions of the symmetry axis of the defects.

Distortions of the distribution function of collisionless particles by high-frequency gravitational waves

International Nuclear Information System (INIS)

Vainer, B.V.; Nasel'skii, P.D.

1983-01-01

Equations for the correlation functions of fluctuations in the spectra of relativistic collisionless particles are obtained from the combined system of Einstein's equations and the Vlasov equation. It is shown that the interaction of high-frequency gravitational waves with collisionless particles leads to diffusion of their spectrum in the momentum space. The distortions in the spectrum of the microwave background radiation in a cosmological model with high-frequency gravitational waves are discussed. Bounds are obtained on the spectral characteristics of background gravitational waves

Electron/electron acoustic instability

International Nuclear Information System (INIS)

Gary, S.P.

1987-01-01

The electron acoustic wave becomes a normal mode of an unmagnetized collisionless plasma in the presence of two electron components with similar densities, but strongly disparate temperatures. The characteristic frequency of this mode is the plasma frequency of the cooler electron component. If these two electron components have a relative drift speed several times the thermal speed of the cooler component, the electron/electron acoustic instability may arise. This paper describes the parametric dependences of the threshold drift speed and maximum growth rate of this instability, and compares these with the same properties of the electron/ion acoustic instability. Under the condition of zero current, the electron/ion acoustic instability typically has the lower threshold drift speed, so that observation of the electron/electron acoustic instability is a strong indication of the presence of an electrical current in the plasma

Trapping and Evolution Dynamics of Ultracold Two-Component Plasmas

International Nuclear Information System (INIS)

Choi, J.-H.; Knuffman, B.; Zhang, X. H.; Povilus, A. P.; Raithel, G.

2008-01-01

We demonstrate the trapping of a strongly magnetized, quasineutral ultracold plasma in a nested Penning trap with a background field of 2.9 T. Electrons remain trapped in this system for several milliseconds. Early in the evolution, the dynamics are driven by a breathing-mode oscillation in the ionic charge distribution, which modulates the electron trap depth. Over longer times scales, the electronic component undergoes cooling. Trap loss resulting from ExB drift is characterized

Kinetic instabilities in plasmas: from electromagnetic fluctuations to collisionless shocks

International Nuclear Information System (INIS)

Ruyer, Charles

2014-01-01

-in-cell (PIC) simulations of the ion Weibel instability in uniform geometries, as well as shock-relevant non-uniform configurations. Moreover, they are found in correct agreement with a recent laser-driven plasma collision experiment. Along with this comparison, we pinpoint the important role of electron screening on the ion-Weibel dynamics, which may affect the results of simulations with artificially high electron mass. We subsequently address the shock propagation resulting from the magnetic Weibel turbulence generated in the upstream region. Generalizing the previous symmetric-beam model to the upstream region of the shock, the role of the magnetic turbulence in the shock-front has been analytically and self-consistently characterized. Comparison with simulations validates the model. The interaction of high-energy, ultra-high intensity lasers with dense plasmas is known to produce copious amounts of suprathermal particles. Their acceleration and subsequent transport trigger a variety of Weibel-like electromagnetic instabilities, acting as additional sources of slowing down and scattering. Their understanding is important for the many applications based upon the energy deposition and/or field generation of laser-driven particles. We investigate the ability of relativistic-intensity laser pulses to induce Weibel instability-mediated shocks in overdense plasma targets, as first proposed by Fiuza in 2012. By means of both linear theory and 2D PIC simulations, we demonstrated that in contrast to the standard astrophysical scenario previously addressed, the early-time magnetic fluctuations (Weibel instability) generated by the suprathermal electrons (and not ions) are strong enough to isotropize the target ions and, therefore, induce a collisionless electromagnetic shock. (author) [fr

Study of the motion of electrons in non polar classical liquids. Measurement of Hall effect and f.i.r. search for low energy traps. Progress report

International Nuclear Information System (INIS)

1981-01-01

Progress is reported on experiments aimed at the measurement of the Hall mobility of injected electrons in classical non polar insulating liquids and the optical absorption associated with electrons captured by shallow traps in the liquefied rare gases. Theoretical work aimed at a better understanding of the trapping kinetics of electrons by SF 6 and O 2 dissolved in rare gas liquids was also carried out. Its conclusion is that the electric field dependence of the trapping probability can be explained, basically without adjustable parameters, by considering the Poole-Frenkel-Schotky ionization of the excited state of the traps. From the analysis of published data on the motion of electrons in liquid ethane it is tentatively concluded that at low temperatures the trapping of electrons in the liquid involves a Jahn-Teller like distortion of a single ethane molecule while at higher temperatures it is necessary to consider a small molecular cluster, possibly made up of 2 molecules

ELECTRON ACCELERATIONS AT HIGH MACH NUMBER SHOCKS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS IN VARIOUS PARAMETER REGIMES

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Yosuke [Department of Physics, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522 (Japan); Amano, Takanobu; Hoshino, Masahiro, E-mail: ymatumot@astro.s.chiba-u.ac.jp [Department of Earth and Planetary Science, University of Tokyo, Hongo 1-33, Bunkyo-ku, Tokyo 113-0033 (Japan)

2012-08-20

Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron {beta}{sub e} (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M{sub A} {approx} 30) with a mass ratio of M/m = 100 and {beta}{sub e} = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

Experimental evaluation of quantum computing elements (qubits) made of electrons trapped over a liquid helium film; Evaluation experimentale d'elements de calcul quantique (qubit) formes d'electrons pieges sur l'helium liquide

Energy Technology Data Exchange (ETDEWEB)

Rousseau, E

2006-12-15

An electron on helium presents a quantized energy spectrum. The interaction with the environment is considered sufficiently weak in order to allow the realization of a quantum bit (qubit) by using the first two energy levels. The first stage in the realization of this qubit was to trap and control a single electron. This is carried out thanks to a set of micro-fabricated electrodes defining a well of potential in which the electron is trapped. We are able with such a sample to trap and detect a variables number of electrons varying between one and around twenty. This then allowed us to study the static behaviour of a small number of electrons in a trap. They are supposed to crystallize and form structures called Wigner molecules. Such molecules have not yet been observed yet with electrons above helium. Our results bring circumstantial evidence for of Wigner crystallization. We then sought to characterize the qubit more precisely. We sought to carry out a projective reading (depending on the state of the qubit) and a measurement of the relaxation time. The results were obtained by exciting the electron with an incoherent electric field. A clean measurement of the relaxation time would require a coherent electric field. The conclusion cannot thus be final but it would seem that the relaxation time is shorter than calculated theoretically. That is perhaps due to a measurement of the relaxation between the oscillating states in the trap and not between the states of the qubit. (author)

Linear spin waves in a trapped Bose gas

International Nuclear Information System (INIS)

Nikuni, T.; Williams, J.E.; Clark, C.W.

2002-01-01

An ultracold Bose gas of two-level atoms can be thought of as a spin-1/2 Bose gas. It supports spin-wave collective modes due to the exchange mean field. Such collective spin oscillations have been observed in recent experiments at JILA with 87 Rb atoms confined in a harmonic trap. We present a theory of the spin-wave collective modes based on the moment method for trapped gases. In the collisionless and hydrodynamic limits, we derive analytic expressions for the frequencies and damping rates of modes with dipole and quadrupole symmetry. We find that the frequency for a given mode is given by a temperature-independent function of the peak density n, and falls off as 1/n. We also find that, to a very good approximation, excitations in the radial and axial directions are decoupled. We compare our model to the numerical integration of a one-dimensional version of the kinetic equation and find very good qualitative agreement. The damping rates, however, show the largest deviation for intermediate densities, where one expects Landau damping--which is unaccounted for in our moment approach--to play a significant role

Superdiffusion revisited in view of collisionless reconnection

Directory of Open Access Journals (Sweden)

R. A. Treumann

2014-06-01

Full Text Available The concept of diffusion in collisionless space plasmas like those near the magnetopause and in the geomagnetic tail during reconnection is reexamined making use of the division of particle orbits into waiting orbits and break-outs into ballistic motion lying at the bottom, for instance, of Lévy flights. The rms average displacement in this case increases with time, describing superdiffusion, though faster than classical, is still a weak process, being however strong enough to support fast reconnection. Referring to two kinds of numerical particle-in-cell simulations we determine the anomalous diffusion coefficient, the anomalous collision frequency on which the diffusion process is based, and construct a relation between the diffusion coefficients and the resistive scale. The anomalous collision frequency from electron pseudo-viscosity in reconnection turns out to be of the order of the lower-hybrid frequency with the latter providing a lower limit, thus making similar assumptions physically meaningful. Tentative though not completely justified use of the κ distribution yields κ ≈ 6 in the reconnection diffusion region and, for the anomalous diffusion coefficient, the order of several times Bohm diffusivity.

ENTROPY PRODUCTION IN COLLISIONLESS SYSTEMS. I. LARGE PHASE-SPACE OCCUPATION NUMBERS

International Nuclear Information System (INIS)

Barnes, Eric I.; Williams, Liliya L. R.

2011-01-01

Certain thermal non-equilibrium situations, outside of the astrophysical realm, suggest that entropy production extrema, instead of entropy extrema, are related to stationary states. In an effort to better understand the evolution of collisionless self-gravitating systems, we investigate the role of entropy production and develop expressions for the entropy production rate in two particular statistical families that describe self-gravitating systems. From these entropy production descriptions, we derive the requirements for extremizing the entropy production rate in terms of specific forms for the relaxation function in the Boltzmann equation. We discuss some implications of these relaxation functions and point to future work that will further test this novel thermodynamic viewpoint of collisionless relaxation.

The effects of electron spiraling on the anisotropy and polarization of photon emission from an electron beam ion trap

International Nuclear Information System (INIS)

Savin, D.W.; Gu, M.F.; Beiersdorfer, P.

1998-01-01

We present a theoretical formalism for calculating the anisotropy and polarization of photon emission due to a spiraling beam of electrons in an electron beam ion trap (EBIT). We present measurements of the polarization for the Fe XXIV 4p 2 P 3/2 → 2s 2 S 1/2 X-ray transition due to electron impact excitation. We discuss these results, together with previously reported EBIT polarization measurements, in the light of electron spiraling. We find that spiraling effects cannot yet be discerned in these measurements. This is important for many EBIT measurements concerned with X-ray line intensity measurements. While the amount of spiraling is not accurately known, neglecting its effects introduces an error typically no larger than that given by counting statistics. (author)

Collisionless shocks and upstream waves and particles: Introductory remarks

International Nuclear Information System (INIS)

Kennel, C.F.

1981-01-01

We discuss more aspects of collisionless shock theory that might be pertinent to the problem of upstream waves and particles. It is hoped that our qualititive remarks may be a useful guide for the general reader as he goes through the detailed papers to come

Towards a Measurement of the n=2 Lamb Shift in Hydrogen-like Nitrogen Using an Electron Beam Ion Trap

International Nuclear Information System (INIS)

Hosaka, K.; Crosby, D. N.; Gaarde-Widdowson, K.; Smith, C. J.; Silver, J. D.; Myers, E. G.; Kinugawa, T.; Ohtani, S.

2003-01-01

Using a 14 C 16 O 2 laser the 2s 1/2 -2p 3/2 (fine structure - Lamb shift) transition has been induced in 14 N 6+ ions trapped in an electron beam ion trap. Prospects for a measurement of the Lamb shift in hydrogen-like nitrogen are discussed.

Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source.

Science.gov (United States)

Izotov, I V; Razin, S V; Sidorov, A V; Skalyga, V A; Zorin, V G; Bagryansky, P A; Beklemishev, A D; Prikhodko, V V

2012-02-01

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap ("vortex" confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of "vortex" confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.

Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source

International Nuclear Information System (INIS)

Izotov, I. V.; Razin, S. V.; Sidorov, A. V.; Skalyga, V. A.; Zorin, V. G.; Bagryansky, P. A.; Beklemishev, A. D.; Prikhodko, V. V.

2012-01-01

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap (''vortex'' confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of ''vortex'' confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.

Bias dependent charge trapping in MOSFETs during 1 and 6 MeV electron irradiation

Energy Technology Data Exchange (ETDEWEB)

Shinde, N.S. [Department of Chemical Engineering, Mie University, 5148507 (Japan); Kulkarni, V.R.; Mathakari, N.L.; Bhoraskar, V.N. [Department of Physics, Univeristy of Pune, Pune 411007 (India); Dhole, S.D. [Department of Physics, Univeristy of Pune, Pune 411007 (India)], E-mail: sanjay@physics.unipune.ernet.in

2008-06-15

To study irradiation-induced charge trapping in SiO{sub 2} and around the SiO{sub 2}-Si interface, depletion n-MOSFETs (metal-oxide-semiconductor field effect transistor) were used. The devices were gate biased during 1 and 6 MeV pulsed electron irradiation. The I{sub D}-V{sub DS} (drain current versus drain voltage) and I{sub D}-V{sub GS} (drain current versus gate voltage) characteristics were measured before and after irradiation. The shift in threshold voltage {delta}V{sub T} (difference in threshold voltage V{sub T} before and after irradiation) exhibited trends depending on the applied gate bias during 1 MeV electron irradiation. This behavior can be associated to the contribution of irradiation-induced negative charge {delta}N{sub IT} buildup around the SiO{sub 2}-Si interface to {delta}V{sub T}, which is sensitive to the electron tunneling from the substrates. However, only weak gate bias dependence was observed in 6 MeV electron irradiated devices. Independent of the energy loss and applied bias, the positive oxide trapped charge {delta}N{sub OT} is marginal and can be associated to thin and good quality of SiO{sub 2}. These results are explained using screening of free and acceptor states by the applied bias during irradiation, thereby reducing the total irradiation-induced charges.

Detection and characterisation of radicals using electron paramagnetic resonance (EPR) spin trapping and related methods

DEFF Research Database (Denmark)

Davies, Michael Jonathan

2016-01-01

Electron paramagnetic resonance (EPR) spectroscopy (also known as electron spin resonance, ESR, or electron magnetic resonance, EMR, spectroscopy) is often described as the “gold standard” for the detection and characterisation of radicals in chemical, biological and medical systems. The article...... reviews aspects of EPR spectroscopy and discusses how this methodology and related techniques can be used to obtain useful information from biological systems. Consideration is given to the direct detection of radicals, the use of spin traps and the detection of nitric oxide, and the advantages...

Modelling of ion thermal transport in ergodic region of collisionless toroidal plasma

International Nuclear Information System (INIS)

Kanno, Ryutaro; Nunami, Masanori; Satake, Shinsuke; Ohyabu, Nobuyoshi; Takamaru, Hisanori; Okamoto, Masao

2009-09-01

In recent tokamak experiments it has been found that so-called diffusion theory based on the 'diffusion of magnetic field lines' overestimates the radial energy transport in the ergodic region of the collisionless plasma affected by resonant magnetic perturbations (RMPs), though the RMPs induce chaotic behavior of the magnetic field lines. The result implies that the modelling of the transport should be reconsidered for low collisionality cases. A computer simulation study of transport in the ergodic region is required for understanding fundamental properties of collisionless ergodized-plasmas, estimating the transport coefficients, and reconstructing the modelling of the transport. In this paper, we report the simulation study of thermal transport in the ergodic region under the assumption of neglecting effects of an electric field, impurities and neutrals. Because of the simulations neglecting interactions with different particle-species and saving the computational time, we treat ions (protons) in our numerical-study of the transport. We find that the thermal diffusivity in the ergodic region is extremely small compared to the one predicted by the theory of field-line diffusion and that the diffusivity depends on both the collision frequency and the strength of RMPs even for the collisionless ergodized-plasma. (author)

Electron collisions in the trapped gyro-Landau fluid transport model

International Nuclear Information System (INIS)

Staebler, G. M.; Kinsey, J. E.

2010-01-01

Accurately modeling electron collisions in the trapped gyro-Landau fluid (TGLF) equations has been a major challenge. Insights gained from numerically solving the gyrokinetic equation have lead to a significant improvement of the low order TGLF model. The theoretical motivation and verification of this model with the velocity-space gyrokinetic code GYRO[J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] will be presented. The improvement in the fidelity of TGLF to GYRO is shown to also lead to better prediction of experimental temperature profiles by TGLF for a dedicated collision frequency scan.

Trapping and dark current in plasma-based accelerators

International Nuclear Information System (INIS)

Schroder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

2004-01-01

The trapping of thermal electrons in a nonlinear plasma wave of arbitrary phase velocity is investigated. The threshold plasma wave amplitude for trapping plasma electrons is calculated, thereby determining the fraction trapped and the expected dark current in a plasma-based accelerator. It is shown that the presence of a laser field (e.g., trapping in the self-modulated regime of the laser wakefield accelerator) increases the trapping threshold. Implications for experimental and numerical laser-plasma studies are discussed

The Current-Driven, Ion-Acoustic Instability in a Collisionless Plasma

DEFF Research Database (Denmark)

Michelsen, Poul; Pécseli, Hans; Juul Rasmussen, Jens

1979-01-01

The current-driven, ion-acoustic instability was investigated by means of an experiment performed in a collisionless plasma produced in a single-ended Q-machine. Reflections at the ends of the plasma column gave rise to a standing wave. Parameters of the instability were investigated, and it was ......, and it was demonstrated that the fluctuations in the plasma column behave as a classical Van der Pol oscillator. Accurate measurements of the growth rate of the instability can be performed by making explicit use of the particular properties of such a system.......The current-driven, ion-acoustic instability was investigated by means of an experiment performed in a collisionless plasma produced in a single-ended Q-machine. Reflections at the ends of the plasma column gave rise to a standing wave. Parameters of the instability were investigated...

Dynamic Trap Formation and Elimination in Colloidal Quantum Dots

KAUST Repository

Voznyy, O.; Thon, S. M.; Ip, A. H.; Sargent, E. H.

2013-01-01

Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping. © 2013 American Chemical Society.

Dynamic Trap Formation and Elimination in Colloidal Quantum Dots

KAUST Repository

Voznyy, O.

2013-03-21

Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers\\' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping. © 2013 American Chemical Society.

Observation of trapped-electron-mode microturbulence in reversed field pinch plasmas

Science.gov (United States)

Duff, J. R.; Williams, Z. R.; Brower, D. L.; Chapman, B. E.; Ding, W. X.; Pueschel, M. J.; Sarff, J. S.; Terry, P. W.

2018-01-01

Density fluctuations in the large-density-gradient region of improved confinement Madison Symmetric Torus reversed field pinch (RFP) plasmas exhibit multiple features that are characteristic of the trapped-electron mode (TEM). Core transport in conventional RFP plasmas is governed by magnetic stochasticity stemming from multiple long-wavelength tearing modes. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasmas. Under these conditions, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at a frequency of f ˜ 50 kHz, which have normalized perpendicular wavenumbers k⊥ρs≲ 0.2 and propagate in the electron diamagnetic drift direction. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with the local electron density gradient. These characteristics are consistent with predictions from gyrokinetic analysis using the Gene code, including increased TEM turbulence and transport from the interaction of remnant tearing magnetic fluctuations and zonal flow.

An application of random field theory to analysis of electron trapping sites in disordered media

International Nuclear Information System (INIS)

Hilczer, M.; Bartczak, W.M.

1993-01-01

The potential energy surface in a disordered medium is considered a random field and described using the concepts of the mathematical theory of random fields. The preexisting traps for excess electrons are identified with certain regions of excursion (extreme regions) of the potential field. The theory provides an analytical method of statistical analysis of these regions. Parameters of the cavity-averaged potential field, which are provided by computer simulation of a given medium, serve as input data for the analysis. The statistics of preexisting traps are obtained for liquid methanol as a numerical example of the random field method. 26 refs., 6 figs

Production of accelerated electrons near an electron source in the plasma resonance region

International Nuclear Information System (INIS)

Fedorov, V.A.

1989-01-01

Conditions of generation of plasma electrons accelerated and their characteristics in the vicinity of an electron source are determined. The electron source isolated electrically with infinitely conducting surface, being in unrestricted collisionless plasma ω 0 >>ν, where ω 0 - plasma frequency of nonperturbated plasma, ν - frequency of plasma electron collisions with other plasma particles, is considered. Spherically symmetric injection of electrons, which rates are simulated by ω frequency, occurs from the source surface. When describing phenomena in the vicinity of the electron source, one proceeds from the quasihydrodynamic equation set

Towards a Measurement of the n=2 Lamb Shift in Hydrogen-like Nitrogen Using an Electron Beam Ion Trap

Energy Technology Data Exchange (ETDEWEB)

Hosaka, K.; Crosby, D. N.; Gaarde-Widdowson, K.; Smith, C. J.; Silver, J. D. [University of Oxford, Department of Physics (United Kingdom); Myers, E. G. [Florida State University (United States); Kinugawa, T.; Ohtani, S. [University of Electro-Communications, Cold Trapped Ions Project, JST (Japan)

2003-03-15

Using a {sup 14}C{sup 16}O{sub 2} laser the 2s{sub 1/2}-2p{sub 3/2} (fine structure - Lamb shift) transition has been induced in {sup 14}N{sup 6+} ions trapped in an electron beam ion trap. Prospects for a measurement of the Lamb shift in hydrogen-like nitrogen are discussed.

Deuterium trapping in carbon fiber composites under high fluence

International Nuclear Information System (INIS)

Airapetov, A.A.; Begrambekov, L.B.; Kuzmin, A.A.; Shigin, P.A.; Zakharov, A.M.

2010-01-01

The paper is devoted to investigation of deuterium trapping in CFC, dance graphite MPG-8 and pyrolytic graphite (PG) under plasma ion- and electron irradiation. Number of specific features of deuterium trapping and retention under plasma ion and electron irradiation is presented and discussed. In particular it is shown that 1) deuterium trapping takes place even when energy of impinging ions approaches zero; 2) deuterium is trapped under irradiation by plasma electrons; 3) under irradiation at equal fluences deuterium trapping is higher, when ion flux is smaller. High energy ion penetrating the surfaces are trapped in the traps created at the expense of their kinetic energy. The process may be named 'kinetic trapping'. Under low energy (smaller than 200 eV) electron and/or ion irradiation the energy of inelastic interaction on the surface provides creation of active centers, which initiate dissociation of deuterium sorbed on the surface, penetration of deuterium atoms into graphite and their trapping in specific low energy traps. The term 'potential trapping' is proposed for this type of trapping. Under high energy irradiation such atoms can fill the traps formed through kinetic mechanism. Origination of moveable deuterium atoms from the layer of surface sorption seems to be time dependent process and it is a reason of increase of trapping along with irradiation time. New features of deuterium trapping and retention in graphite evaluated in this study offer new opportunities for analysis and correct estimation of hydrogen isotope trapping and retention in tokamaks having graphite tiles. (authors)

Effect of electron beam on the properties of electron-acoustic rogue waves

Science.gov (United States)

El-Shewy, E. K.; Elwakil, S. A.; El-Hanbaly, A. M.; Kassem, A. I.

2015-04-01

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, Maxwellian hot electrons, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles and the associated electric field on the carrier wave number, normalized density of hot electron and electron beam, relative cold electron temperature and relative beam temperature are discussed. The results of the present investigation may be applicable in auroral zone plasma.

Precision Measurement of the Electron's Electric Dipole Moment Using Trapped Molecular Ions

Science.gov (United States)

Cairncross, William B.; Gresh, Daniel N.; Grau, Matt; Cossel, Kevin C.; Roussy, Tanya S.; Ni, Yiqi; Zhou, Yan; Ye, Jun; Cornell, Eric A.

2017-10-01

We describe the first precision measurement of the electron's electric dipole moment (de) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on 180Hf 19F+ in its metastable 3Δ1 electronic state, we obtain de=(0.9 ±7. 7stat±1. 7syst)×10-29 e cm , resulting in an upper bound of |de|<1.3 ×10-28 e cm (90% confidence). Our result provides independent confirmation of the current upper bound of |de|<9.4 ×10-29 e cm [J. Baron et al., New J. Phys. 19, 073029 (2017), 10.1088/1367-2630/aa708e], and offers the potential to improve on this limit in the near future.

Species Entropies in the Kinetic Range of Collisionless Plasma Turbulence: Particle-in-cell Simulations

Science.gov (United States)

Gary, S. Peter; Zhao, Yinjian; Hughes, R. Scott; Wang, Joseph; Parashar, Tulasi N.

2018-06-01

Three-dimensional particle-in-cell simulations of the forward cascade of decaying turbulence in the relatively short-wavelength kinetic range have been carried out as initial-value problems on collisionless, homogeneous, magnetized electron-ion plasma models. The simulations have addressed both whistler turbulence at β i = β e = 0.25 and kinetic Alfvén turbulence at β i = β e = 0.50, computing the species energy dissipation rates as well as the increase of the Boltzmann entropies for both ions and electrons as functions of the initial dimensionless fluctuating magnetic field energy density ε o in the range 0 ≤ ε o ≤ 0.50. This study shows that electron and ion entropies display similar rates of increase and that all four entropy rates increase approximately as ε o , consistent with the assumption that the quasilinear premise is valid for the initial conditions assumed for these simulations. The simulations further predict that the time rates of ion entropy increase should be substantially greater for kinetic Alfvén turbulence than for whistler turbulence.

Distinguishing between deep trapping transients of electrons and holes in TiO2 nanotube arrays using planar microwave resonator sensor.

Science.gov (United States)

Zarifi, Mohammad H; Wiltshire, Benjamin Daniel; Mahdi, Najia; Shankar, Karthik; Daneshmand, Mojgan

2018-05-16

A large signal DC bias and a small signal microwave bias were simultaneously applied to TiO2 nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO2 nanotubes, and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel type trap-mediated electrical injection of excess carriers into TiO2 nanotubes which resulted in a near constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then step-wise removed, the resonant frequency shifted due to trapping -mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80 s, 300-800 s and ~3000 s were present regardless of whether light or bias was applied and are also observed in the presence of a hole scavenger, which we attribute to oxygen adsorption and deep electron traps while another characteristic lifetime > 9000 s was only present when illumination was applied, and is attributed to the presence of hole traps.

Proposed demonstration of the Einstein-Poldosky-Rosen paradox using trapped electrons

International Nuclear Information System (INIS)

Martins, Ana M.

2002-01-01

Correlations of the type discussed by Einstein, Poldosky, and Rosen in their original 1935 paradox may be generated between the positions and the momenta of two electrons confined in two spatially separated Penning traps when they are allowed to be coupled for a certain time interval. An experimental demonstration of the paradox could be done using the accurate techniques of manipulation and measurement of confined charged particles. The basic ideas presented in this paper might be extended in order to enable quantum information transfer of continuous variables between massive particles

Variations of electron fluxes in the outer radiation belt near the boundary of a trapping region during substorms

International Nuclear Information System (INIS)

Ginzburg, E.A.; Malyshev, A.B.

1979-01-01

Variations of electron fluxes with the energy Esub(e) > 0.7 MeV have been investigated near the high-latitude boundary of electron trapping region in the night and day sections of the magnetosphere. It is found that during substorms the natural changes of the structure of electron fluxes take place. On the night side of the magnetosphere after the flux boundary drift to the equator at the preliminary phase, its sharp drift to the pole at the explosion phase takes place with further slow ( during 1-2 hours) shift to the initial position. The boundary position reconstruction period coincide by duration with the life time of negative bays at magnetograms of the night section stations. On the day side the boundary of electron fluxes recorded drifts to the pole in 30-60 min after the beginning of the substorm exposion phase. The results obtained are interpreted within the framework of the theory of adiabatic drift of trapped electrons and their pitch-angular diffusion under the effect of very low frequency waves

Magnetic field amplification in interstellar collisionless shock waves

International Nuclear Information System (INIS)

Chevalier, R.A.

1977-01-01

It is stated that it is commonly assumed that a simple compression of the magnetic field occurs in interstellar shock waves. Recent space observations of the Earth's bow shock have shown that turbulent amplification of the magnetic field can occur in a collisionless shock. It is shown here that radio observations of Tycho's supernova remnant indicate the presence of a shock wave with such magnetic field amplification. There is at present no theory for the microinstabilities that give rise to turbulent amplification of the magnetic field. Despite the lack of theoretical understanding the possibility of field amplification in interstellar shock waves is here considered. In Tycho's supernova remnant there is evidence for the presence of a collisionless shock, and this is discussed. On the basis of observations of the Earth's bow shock, it is expected that turbulent magnetic field amplification occurs in the shock wave of this remnant, and this is supported by radio observations of the remnant. Consideration is given as to what extent the magnetic field is amplified in the shock wave on the basis of the non-thermal radio flux. (U.K.)

Screening conditions in a magnetized plasma with electron beam, with application to ripple trapped electron losses

Energy Technology Data Exchange (ETDEWEB)

Faudot, E.; Heuraux, S. [Nancy-1 Univ. Henri Poincare, LPMIA, UMR CNRS 7040, 54 (France); Colas, L.; Saint-Laurent, F.; Martin, G.; Basiuk, V. [Association Euratom-CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

2004-07-01

In Tore Supra, electrons are accelerated by lower hybrid waves in the direction parallel to the confinement magnetic field, in order to drive non-inductive current. But electrons have also on increase of their perpendicular velocity, then 10% of the most energetic electrons get trapped in the magnetic ripple between 2 adjacent toroidal coils, thus forming a beam. The electron beam follows a banana trajectory, the 20 mm wide protection represented by a cooled copper tube is assumed to protect the VP entrance from this energetic flux. Nevertheless, this beam is able to go beyond the copper tube and creates a hot spot on the steel panel edge able to melt the metal. Heat fluxes deposition on the vertical port (VP) can be understood with a beam+sheath theory including the fact that the sheaths can be obstructed when their length becomes greater than flux tube length. By this way, we identify 4 deposition regimes: 2 free sheath regimes and 2 obstructed sheath regimes. Beam flux deposits either at the entrance of the VP along first 2 cm behind the copper tube or until the end of the VP when beam flux is high and for free sheath. Obstructed sheaths make the repulsive, potential for electrons decrease and so accelerate the flux deposition. (authors)

A generalized two-fluid picture of non-driven collisionless reconnection and its relation to whistler waves

Science.gov (United States)

Yoon, Young Dae

2017-10-01

A generalized, intuitive two-fluid picture of 2D non-driven collisionless magnetic reconnection is described using results from a full-3D numerical simulation. The relevant two-fluid equations simplify to the condition that the flux associated with canonical circulation Q =me ∇ ×ue +qe B is perfectly frozen into the electron fluid. Q is the curl of P =meue +qe A , which is the electron canonical momenrum. Since ∇ . Q = 0 , the Q flux tubes are incompressible and so have a fixed volume. Because they are perfectly frozen into the electron fluid, the Q flux tubes cannot reconnect. Following the behavior of these Q flux tubes provides an intuitive insight into 2D collisionless reconnection of B . In the reconnection geometry, a small perturbation to the central electron current sheet effectively brings a localized segment of a Q flux tube towards the X-point. This flux tube segment is convected downwards with the central electron current, effectively stretching the flux tube, decreasing its cross-section to maintain a fixed volume and so increasing the magnitude of Q . Also, because Q is the sum of the electron vorticity and the magnetic field, the two terms may change in such a way that one term becomes smaller while the other becomes larger while preserving constant Q flux. This allows magnetic reconnection, which is a conversion of magnetic field into particle velocity, to occur without any dissipation mechanism. The entire process has positive feedback with no restoring mechanism and therefore is an instability. The Q motion provides an interpretation for other phenomena as well, such as spiked central electron current filaments. The simulated reconnection rate was found to agree with a previous analytical calculation having the same geometry. Energy analysis shows that the magnetic energy is converted and propagated mainly in the form of the Poynting flux, while helicity analysis shows that the canonical helicity ∫ P . QdV as a whole must be considered when

New experimental initiatives using very highly charged ions from an 'electron beam ion trap'

International Nuclear Information System (INIS)

Schneider, D.

1996-01-01

A short review of the experimental program in highly-charged heavy ion physics conducted at the Lawrence Livermore National Laboratory Electron Beam Ion Trap (EBIT) facility is presented. The heavy-ion research, involving ions up to fully stripped U 92+ , includes precision x-ray spectroscopy and lifetime studies, electron impact ionization and excitation cross section measurements. The investigations of ion-surface interactions following the impact of high-Z highly charged ions on surfaces are aimed to study the neutralization dynamics effecting the ion and the response of the surface as well. (author)

Experimental evaluation of quantum computing elements (qubits) made of electrons trapped over a liquid helium film; Evaluation experimentale d'elements de calcul quantique (qubit) formes d'electrons pieges sur l'helium liquide

Energy Technology Data Exchange (ETDEWEB)

Rousseau, E

2006-12-15

An electron on helium presents a quantized energy spectrum. The interaction with the environment is considered sufficiently weak in order to allow the realization of a quantum bit (qubit) by using the first two energy levels. The first stage in the realization of this qubit was to trap and control a single electron. This is carried out thanks to a set of micro-fabricated electrodes defining a well of potential in which the electron is trapped. We are able with such a sample to trap and detect a variables number of electrons varying between one and around twenty. This then allowed us to study the static behaviour of a small number of electrons in a trap. They are supposed to crystallize and form structures called Wigner molecules. Such molecules have not yet been observed yet with electrons above helium. Our results bring circumstantial evidence for of Wigner crystallization. We then sought to characterize the qubit more precisely. We sought to carry out a projective reading (depending on the state of the qubit) and a measurement of the relaxation time. The results were obtained by exciting the electron with an incoherent electric field. A clean measurement of the relaxation time would require a coherent electric field. The conclusion cannot thus be final but it would seem that the relaxation time is shorter than calculated theoretically. That is perhaps due to a measurement of the relaxation between the oscillating states in the trap and not between the states of the qubit. (author)

PIC simulations of the trapped electron filamentation instability in finite-width electron plasma waves

Science.gov (United States)

Winjum, B. J.; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Chapman, T.; Hittinger, J. A. F.; Rozmus, W.; Strozzi, D. J.; Brunner, S.

2012-10-01

We present results on the kinetic filamentation of finite-width nonlinear electron plasma waves (EPW). Using 2D simulations with the PIC code BEPS, we excite a traveling EPW with a Gaussian transverse profile and a wavenumber k0λDe= 1/3. The transverse wavenumber spectrum broadens during transverse EPW localization for small width (but sufficiently large amplitude) waves, while the spectrum narrows to a dominant k as the initial EPW width increases to the plane-wave limit. For large EPW widths, filaments can grow and destroy the wave coherence before transverse localization destroys the wave; the filaments in turn evolve individually as self-focusing EPWs. Additionally, a transverse electric field develops that affects trapped electrons, and a beam-like distribution of untrapped electrons develops between filaments and on the sides of a localizing EPW. 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 funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD-061. Supported also under Grants DE-FG52-09NA29552 and NSF-Phy-0904039. Simulations were performed on UCLA's Hoffman2 and NERSC's Hopper.

(Anti)hydrogen recombination studies in a nested Penning trap

International Nuclear Information System (INIS)

Quint, W.; Kaiser, R.; Hall, D.; Gabrielse, G.

1993-01-01

Extremely cold antiprotons, stored in Penning trap at 4 K, open the way toward the production and study of cold antihydrogen. We have begun experimentally investigating the possibility to recombine cold positrons and antiprotons within nested Penning traps. Trap potentials are adjusted to allow cold trapped protons (and positive helium ions) to pass through cold trapped electrons. Electrons, protons and ions are counted by ejecting them to a cold channel plate and by nondestructive radiofrequency techniques. The effect of the space charge of one trapped species upon another trapped species passing through is clearly observed. (orig.)

Electron energy confinement in ELMO Bumpy Torus (EBT)

International Nuclear Information System (INIS)

Hiroe, S.; Haste, G.R.; Dandl, R.A.

1979-06-01

Using a calibrated, solid-state, soft x-ray detector, the electron temperature and density have been measured over a wide range of operating conditions of ELMO Bumpy Torus (EBT). The empirical relations of the temperature or the density to the microwave power and the ambient pressure have been determined. The toroidally stored energy has been observed to increase as the stored energy of the hot electron annulus increases. The energy confinement time has been obtained for various plasma parameters and has been found to agree with the neoclassical theory. The advantages of EBT collisionless scaling for fusion plasma confinement have been noted, i.e., n/sub e/tau/sub E/ increases as T/sub e/ 1 5 in the collisionless regime

Capture, Electron-Cooling and Compression of Antiprotons in a Large Penning-Trap for Physics Experiments with an Ultra-Low Energy Extracted Antiproton Beam

CERN Multimedia

2002-01-01

% PS200 \\\\ \\\\The availability of ultra-low energy antiprotons is a crucial ingredient for the execution of the gravity measurements PS200. We have developed a method to provide such low energy antiprotons based on a large Penning trap (the PS200 catching trap). This system can accept a fast-extracted pulse from LEAR, reduce the energy of the antiprotons in the pulse from 5.9~MeV to several tens of kilovolts using a degrading foil, and then capture the antiprotons in a large Penning trap. These antiprotons are cooled by electrons previously admitted to the trap and are collected in a small region at the center of the trap. We have demonstrated our capability to capture up to 1~million antiprotons from LEAR in a single shot, electron cool these antiprotons, and transfer up to 95\\% of them into the inner, harmonic region. A storage time in excess of 1 hour was observed. These results have been obtained with the cryogenic trap vacuum coupled to a room temperature vacuum at about l0$ ^- ^{1} ^0 $ Torr, which is an...

Limits on the streaming and escape of electrons in thermal models for solar hard X-ray emission

International Nuclear Information System (INIS)

Smith, D.F.; Brown, J.C.

1980-01-01

Upper limits on the number of fast electrons streaming through and escaping from a plasma whose electrons have been heated to approx.10 8 K and confined by a collisionless ion-acoustic thermal conduction front are determined. It is shown that such a front is fairly transparent to fast electrons with velocities much larger than the thermal velocity because the anisotropic ion-acoustic waves cannot scatter them, making them collisionless on a scale much larger than the thickness of the front. The collisionless analog of the collisional thermoelectric field is derived self-consistently and shown to offer a significant impediment to fast electrons because they must climb over a large potential barrier than in the collisional case. The only factors limiting the escape of electrons able to surmount this barrier are their rate of production and the requirement that they carry less heat flux than the maximum heat flux allowable. The rate of production is determined for the case of a Maxwellian whose tail is being filled collisionally. Requirements for the stability of these electrons in the hot source plasma and conduction front are given. Methods of refining these limits are discussed

Collisionless tearing mode reconnection at the dayside magnetopause of the earth's magnetosphere

International Nuclear Information System (INIS)

Quest, K.B.

1982-01-01

The purpose of this thesis was to determine if the collisionless tearing mode, a plasma instability, is a viable mechanism for interconnecting field lines at the dayside magnetopause. More generally, it was wished to test theoretically the assertion that collisionless tearing is a probable first step in cosmical reconnection. The procedure was to model the magnetopause as a local one-dimensional Vlasov equilibrium, and then calculate the linear and nonlinear stability properties of tearing and tearing-like oscillations. Quantitative estimates of the range of plasma parameter space over which significant growth occurs were obtained. Assuming that significant tearing mode growth implies significant reconnection, conditions were determined for which tearing will be important to dayside reconnection. Linearly it was found that the growth rate is relatively insensitive to the temperature of the species, but depends sensitively on (1) the thickness of the magnetopause current, (2) the number density at the location of the singular layer, and (3) the magnitude of the magnetic shear. For significant linear growth the magnetopause half-sheet thickness was required to be on the order of or less than a thermal ion gyroradius, the number density was required to be no more than 100 cm - 3 , and the magnetosheath field was required to be locally antialigned with the magnetospheric field. If the above conditions are met, which are stringent but not impossible, the mode will linearly amplify. Another topic examined is the question of the structure of the tearing eigenmodes at the dayside magnetopause. By considering finite transit time effects on electron Landau resonance it was concluded that magnetopause tearing turbulence probably occurs in spatially bounded wave packets

Stable confinement of toroidal electron plasma in an internal conductor device Prototype-Ring Trap

International Nuclear Information System (INIS)

Saitoh, H.; Yoshida, Z.; Watanabe, S.

2005-01-01

A pure electron plasma has been produced in an internal conductor device Prototype-Ring Trap (Proto-RT). The temporal evolution of the electron plasma was investigated by the measurement of electrostatic fluctuations. Stable confinement was realized when the potential profile adjusted to match the magnetic surfaces. The confinement time varies as a function of the magnetic field strength and the neutral gas pressure, and is comparable to the diffusion time of electrons determined by the classical collisions with neutral gas. Although the addition of a toroidal magnetic field stabilized the electrostatic fluctuation of the plasma, the effects of the magnetic shear shortened the stable confinement time, possibly because of the obstacles of coil support structures

Electron shakeoff following the β+ decay of +19Ne and +35Ar trapped ions

Science.gov (United States)

Fabian, X.; Fléchard, X.; Pons, B.; Liénard, E.; Ban, G.; Breitenfeldt, M.; Couratin, C.; Delahaye, P.; Durand, D.; Finlay, P.; Guillon, B.; Lemière, Y.; Mauger, F.; Méry, A.; Naviliat-Cuncic, O.; Porobic, T.; Quéméner, G.; Severijns, N.; Thomas, J.-C.

2018-02-01

The electron shakeoff of 19F and 35Cl atoms resulting from the β+ decay of +19Ne and +35Ar ions has been investigated using a Paul trap coupled to a time of flight recoil-ion spectrometer. The charge-state distributions of the recoiling daughter nuclei were compared to theoretical calculations based on the sudden approximation and accounting for subsequent Auger processes. The excellent agreement obtained for 35Cl is not reproduced in 19F. The shortcoming is attributed to the inaccuracy of the independent particle model employed to calculate the primary shakeoff probabilities in systems with rather low atomic numbers. This calls for more elaborate calculations, including explicitly the electron-electron correlations.

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.

Excitation of an ion-acoustic wave by two whistlers in a collisionless magnetoplasma

International Nuclear Information System (INIS)

Sodha, M.S.; Singh, T.; Singh, D.P.; Sharma, R.P.

1981-01-01

An investigation is made into the excitation of an ion-acoustic wave in a collisionless hot magnetoplasma by two whistlers. On account of the interaction of the two whistlers, of frequencies ω 1 and ω 2 , ponderomotive force at frequency Δω(=ω 1 -ω 2 ) leads to the generation of an ion-acoustic wave. When the two whistlers have initially Gaussian intensity distributions, a d.c. component of the ponderomotive force leads to the redistribution of the background electron/ion density, and cross-focusing of the whistlers occurs. The power of the generated ion-acoustic wave, being dependent on the background ion density and powers of the whistlers, is further modified. The ion-acoustic wave power also changes drastically with the strength of the static magnetic field. (author)

A (2 d,3 v) cylindrical, kinetic model of a time-independent, collisionless bounded plasma

International Nuclear Information System (INIS)

Pedit, H.; Kuhn, S.

1994-01-01

A (2 d,3 v) cylindrical, electrostatic, collisionless kinetic model for a wide class of negative-bias de states of the single-ended Q machine is developed. Based on the method presented recently by the authors for an analogous cartesian model, the self-consistent plasma state is found by means of an iterative scheme in which the charge-density and potential distributions are alternately advanced. The electron an ion velocity distribution functions are calculated via trajectory integration, which ensures high accuracy and resolution in both configuration and velocity space. The main differences between cartesian and cylindrical geometry are discussed, and typical macroscopic as well as microscopic quantities for an exemplary special case are presented. (author). 3 refs, 5 figs

Particle trapping in stimulated scattering processes

International Nuclear Information System (INIS)

Karttunen, S.J.; Heikkinen, J.A.

1981-01-01

Particle trapping effects on stimulated Brillouin and Raman scattering are investigated. A time and space dependent model assumes a Maxwellian plasma which is taken to be homogeneous in the interaction region. Ion trapping has a rather weak effect on stimulated Brillouin scattering and large reflectivities are obtained even in strong trapping regime. Stimulated Raman scattering is considerably reduced by electron trapping. Typically 15-20 times larger laser intensities are required to obtain same reflectivity levels than without trapping. (author)

Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids

NARCIS (Netherlands)

Boehme, Simon C.; Mikel Azpiroz, Jon; Aulin, Yaroslav V.; Grozema, Ferdinand C.; Vanmaekelbergh, Daniel; Siebbeles, Laurens D. A.; Infante, Ivan; Houtepen, Arjan J.

Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact

Density of trap states and Auger-mediated electron trapping in CdTe quantum-dot solids

NARCIS (Netherlands)

Boehme, Simon C.; Azpiroz, Jon Mikel; Aulin, Yaroslav V.; Grozema, Ferdinand C.; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Infante, Ivan; Houtepen, Arjan J.

2015-01-01

Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact

Dynamic investigation of electron trapping and charge decay in electron-irradiated Al sub 2 O sub 3 in a scanning electron microscope: Methodology and mechanisms

CERN Document Server

Fakhfakh, S; Belhaj, M; Fakhfakh, Z; Kallel, A; Rau, E I

2002-01-01

The charging and discharging of polycrystalline Al sub 2 O sub 3 submitted to electron-irradiation in a scanning electron microscope (SEM) are investigated by means of the displacement current method. To circumvent experimental shortcomings inherent to the use of the basic sample holder, a redesign of the latter is proposed and tests are carried out to verify its operation. The effects of the primary beam accelerating voltage on charging, flashover and discharging phenomena during and after electron-irradiation are studied. The experimental results are then analyzed. In particular, the divergence between the experimental data and those predicted by the total electron emission yield approach (TEEYA) is discussed. A partial discharge was observed immediately after the end of the electron-irradiation exposure. The experimental data suggests, that the discharge is due to the evacuation to the ground, along the insulator surface, of released electrons from shallow traps at (or in the close vicinity of) the insulat...

Structure and dynamics of highly charged heavy ions studied with the electron beam ion trap in Tokyo

International Nuclear Information System (INIS)

Nakamura, Nobuyuki; Hu, Zhimin; Watanabe, Hirofumi; Li, Yueming; Kato, Daiji; Currell, Fred J.; Tong Xiaomin; Watanabe, Tsutomu; Ohtani, Shunsuke

2011-01-01

In this paper, we present the structure and the dynamics of highly charged heavy ions studied through dielectronic recombination (DR) observations performed with the Tokyo electron beam ion trap. By measuring the energy dependence of the ion abundance ratio in the trap at equilibrium, we have observed DR processes for open shell systems very clearly. Remarkable relativistic effects due to the generalized Breit interaction have been clearly shown in DR for highly charged heavy ions. We also present the first result for the coincidence measurement of two photons emitted from a single DR event.

Solar cyclic behavior of trapped energetic electrons in Earth's inner radiation belt

Science.gov (United States)

Abel, Bob; Thorne, Richard M.

1994-10-01

Magnetic electron spectrometer data from six satellites (OV3-3, OV1-14, OGO 5, S3-2, S3-3, and CRRES) have been used to study long-term (1966-1991) behavior of trapped energetic electrons in the inner radiation belt. Comparison of the observed energy spectra at L equal to or greater than 1.35 for different phases of the solar cycle reveals a clear trend toward enhanced fluxes during periods of solar maximum for energies below a few hundred keV; we suggest that this is caused by an increase in the rate of inward radial diffusion from a source at higher L. In contrast, for L less than 1.30, where atmospheric collisions become increasingly important, the electron flux is reduced during solar maximum; we attribute this to the expected increase in upper atmospheric densities. The electron flux above 1 MeV exhibits a systematic decay beyond 1979 to values well below the current NASA AE-8 model. This indicates that the natural background of high-energy electrons has previously been overestimated due to the long lasting presence of electrons produced by nuclear detonations in the upper atmosphere in the late 1950s and early 1960s.

Effect of trapped electron on the dust ion acoustic waves in dusty plasma using time fractional modified Korteweg-de Vries equation

International Nuclear Information System (INIS)

Nazari-Golshan, A.; Nourazar, S. S.

2013-01-01

The time fractional modified Korteweg-de Vries (TFMKdV) equation is solved to study the nonlinear propagation of small but finite amplitude dust ion-acoustic (DIA) solitary waves in un-magnetized dusty plasma with trapped electrons. The plasma is composed of a cold ion fluid, stationary dust grains, and hot electrons obeying a trapped electron distribution. The TFMKdV equation is derived by using the semi-inverse and Agrawal's methods and then solved by the Laplace Adomian decomposition method. Our results show that the amplitude of the DIA solitary waves increases with the increase of time fractional order β, the wave velocity v 0 , and the population of the background free electrons λ. However, it is vice-versa for the deviation from isothermality parameter b, which is in agreement with the result obtained previously

Ion-acoustic solitons in a plasma with electron beam

International Nuclear Information System (INIS)

Esfandyari, A. R.; Khorram, S.

2001-01-01

Ion-acoustic solitons in a collisionless plasma consisting of warm ions, hot isothermal electrons and a electron beam are studied by using the reductive perturbation method. The basic set of fluid equations is reduced to Korteweg-de Vries and modified Korteweg-de Vries temperature and electron beam on ion acoustic equations. The effect of ion solitons are investigated

Instability, Turbulence, and Enhanced Transport in Collisionless Black-Hole Accretion Flows

Science.gov (United States)

Kunz, Matthew

simulation of the magnetorotational dynamo (publication in preparation). For the first time, global kinetic simulations of magnetorotational turbulence will be also performed, spanning more than two orders of magnitude in radius. These simulations will allow the global structure of collisionless accretion flows to be computed from first principles, and compared and contrasted with that found in prior MHD models. Special attention will be paid to whether vertical stratification results in the formation of a hot magnetized corona and to whether significant non-thermal particle acceleration occurs (as implied by non-thermal spectra observed in many systems). Finally, to make comparisons to existing and upcoming submillimeter and X-ray astronomical observations, the electron thermodynamics and emission will be modeled. This work compliments ongoing numerical studies using MHD in strong-field general relativity, which seek to directly connect the properties of simulated black-hole accretion flows in curved spacetime with the observed mm/sub-mm emission. What makes this ambitious proposal tenable is the widespread availability of HPC resources, the vast improvement in numerical algorithms for plasma kinetics, and the emerging consensus that the detailed plasma physics of the Universe must be understood in order to advance research in many frontier areas of theoretical astrophysics. The themes that this proposal tackles are broad and far-reaching: the nature of black-hole accretion, the material properties of high-beta magnetized plasmas, the acceleration of particles by turbulence, the efficiency of magnetic dynamo in a collisionless plasma, the interplay between fluid and kinetic scales, and the impact all of this physics has on the observed emission. But we believe that they are also addressable if a single physical process encapsulating these themes - namely, kinetic magnetorotational turbulence - is considered. This is what we propose to do.

First experiments with the 200 keV electron beam ion trap at LLNL

International Nuclear Information System (INIS)

Marrs, R.E.; Knapp, D.A.; Elliott, S.

1993-01-01

A high-energy electron beam ion trap (Super EBIT) is operating at electron energies up to 200 keV and currents up to 200 mA. Highly charged ions up to Li-like U 89+ and H-like Pb 81+ have been produced and studied. Ionization cross sections for H-like Dy 66+ at E e = 170 keV have been measured with respect to radiative recombination from the observed Dy 66+ /Dy 67+ equilibrium ionization balance. A Bragg crystal spectrometer has been used to measure 2s 1/2 -2p 3/2 transition energies in Li-like U 82+ with respect to the Lymann-series transitions in lower-Z hydrogenic ions

Trapped Electron Mode Turbulence Driven Intrinsic Rotation in Tokamak Plasmas

International Nuclear Information System (INIS)

Wang, W.X.; Hahm, T.S.; Ethier, S.; Zakharov, L.E.

2011-01-01

Recent progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported with emphasis on electron thermal transport dominated regimes. The turbulence driven intrinsic torque associated with nonlinear residual stress generation by the fluctuation intensity and the intensity gradient in the presence of zonal flow shear induced asymmetry in the parallel wavenumber spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current. These results qualitatively reproduce empirical scalings of intrinsic rotation observed in various experiments. The origin of current scaling is found to be due to enhanced kll symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic torque on pressure gradient is that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving residual stress, increase with the strength of turbulence drive, which is R0/LTe and R0/Lne for the trapped electron mode.

Charge generation and trapping in bisphenol-A-polycarbonate/N-isopropylcarbazole mixture: A study by electron bombardment-induced conductivity

International Nuclear Information System (INIS)

Santos, S.; Caraballo, D.

2007-01-01

Electron bombardment-induced conductivity measurements were carried out on cast films of N-isopropylcarbazole (NIPC) dispersed into an amorphous matrix of bisphenol-A-polycarbonate. The charge generation was studied by estimating the hole yield (g), the fraction of charge escaping recombination, as a function of electric field and concentration of NIPC at room temperature. The hole yield, besides increasing by increasing the content of NIPC, was observed to increase with the electric field in the manner predicted by the Onsager theory of geminate recombination. Deep trapping levels were studied by filling under electron bombardment and observing transients. The deep traps were neutral in nature with a concentration on the order of 8.0x10 14 cm -3 , which was low enough not to degrade transport under normal conditions

Hydromagnetic waves, turbulence, and collisionless processes in the interplanetary medium

International Nuclear Information System (INIS)

Barnes, A.

1983-01-01

The solar wind does not flow quietly. It seethes and undulates, fluctuating on time scales that range from the solar rotation period down to fractions of milliseconds. Most of the power in interplanetary waves and turbulence lies at hydromagnetic scales. These fluctuations are normally of large amplitude, containing enough energy to affect solar and galactic cosmic rays, and may be the remnants of a coronal turbulence field powerful enough to play a major role in accelerating the solar wind itself. The origin and evolution of interplanetary hydromagnetic waves and turbulence, and their influence on the large-scale dynamics of the solar wind are among the most fundamental questions of solar-terrestrial physics. First hydrodynamic waves and turbulences in the interplanetary medium are discussed in two sections, respectively. Because the length and time scales for hydromagnetic fluctuations are very much smaller than the corresponding Coulomb collision scales of the plasma ions and electrons, the interplanetary variations are modelled as fluctuations in a magnetohydrodynamic fluid. In the last section, collisionless phenomena are discussed. They are of qualitative significance. (Auth.)

Damping of electron center-of-mass oscillation in ultracold plasmas

International Nuclear Information System (INIS)

Chen, Wei-Ting; Witte, Craig; Roberts, Jacob L.

2016-01-01

Applying a short electric field pulse to an ultracold plasma induces an electron plasma oscillation. This manifests itself as an oscillation of the electron center of mass around the ion center of mass in the ultracold plasma. In general, the oscillation can damp due to either collisionless or collisional mechanisms, or a combination of the both. To investigate the nature of oscillation damping in ultracold plasmas, we developed a molecular dynamics model of the ultracold plasma electrons. Through this model, we found that depending on the neutrality of the ultracold plasma and the size of an applied DC electric field, there are some parameter ranges where the damping is primarily collisional and some primarily collisionless. We conducted experiments to compare the measured damping rate with theory predictions and found them to be in good agreement. Extension of our measurements to different parameter ranges should enable studies for strong-coupling influence on electron-ion collision rates.

The influence of ion temperature on solitary waves in collisionless weak relativistic plasma

International Nuclear Information System (INIS)

Cerepaniuc, Adina

2004-01-01

Korteweg-de Vries equation is used to study the influence of the ion temperature, on the ion acoustic waves in the frame of collisionless plasma's weak relativistic effect. In the literature it is discussed the influence of ion temperature on the ion acoustic wave in a relativistic plasma for a ratio of the ion flow velocity to the light velocity between 0 and 1. In this paper, the dependence of the phase velocity on the relativistic effect for different values of the ratio of the ion temperature to the electron temperature is studied. In case of weak relativistic effect (ratio of the ion flow velocity to the light velocity is 10 -6 and the step of the representation is 10 -6 ) we noticed the occurrence of an antisoliton within soliton amplitude graphical representation as function of the relativistic effect and the temperature ratio. The novelty of this article consists in the fact that a much smaller interval is considered for velocity ratio (size) and we studied the influence of ion temperature on ion acoustic wave in a collisionless relativistic plasma. We performed the numerical calculation of equations and we plotted the phase velocity and the amplitude of soliton wave as a function of velocity ratio and the temperature ratio. We considered the step of velocity ratio variation equal with 10 -6 and the step of temperature ratio variation 10 -2 . The observation made in this paper refines the results of other authors who studied these equations for velocity ratio variation of 10 -1 . In herein chosen interval we observed new phenomena that were not noticed in the case of choosing larger intervals. (author)

Unequilibrium kinetic of collisionless boundary layers in binary plasmas

International Nuclear Information System (INIS)

Kotelnikov, V.A.; Nikolaev, F.A.; Cherepanov, V.V.

1985-01-01

Relaxation processes of kinetic nonequilibrium collisionless boundary layers near spherical charged full absorbing surfaces in binary low-temperature plasmas are investigated. The effect of magnetic field on relaxation processes was neglected. The dynamics of components of the ionized gas was treated near the boundary layer. The potential distribution and the space dependence of concentration were calculated numerically. These results agree well with the experimental data. (D.Gy.)

Theoretical characterization on the size-dependent electron and hole trapping activity of chloride-passivated CdSe nanoclusters

Science.gov (United States)

Cui, Yingqi; Cui, Xianhui; Zhang, Li; Xie, Yujuan; Yang, Mingli

2018-04-01

Ligand passivation is often used to suppress the surface trap states of semiconductor quantum dots (QDs) for their continuous photoluminescence output. The suppression process is related to the electrophilic/nucleophilic activity of surface atoms that varies with the structure and size of QD and the electron donating/accepting nature of ligand. Based on first-principles-based descriptors and cluster models, the electrophilic/nucleophilic activities of bare and chloride-coated CdSe clusters were studied to reveal the suppression mechanism of Cl-passivated QDs and compared to experimental observations. The surface atoms of bare clusters have higher activity than inner atoms and their activity decreases with cluster size. In the ligand-coated clusters, the Cd atom remains as the electrophilic site, while the nucleophilic site of Se atoms is replaced by Cl atoms. The activities of Cd and Cl atoms in the coated clusters are, however, remarkably weaker than those in bare clusters. Cluster size, dangling atoms, ligand coverage, electronegativity of ligand atoms, and solvent (water) were found to have considerable influence on the activity of surface atoms. The suppression of surface trap states in Cl-passivated QDs was attributed to the reduction of electrophilic/nucleophilic activity of Cd/Se/Cl atoms. Both saturation to under-coordinated surface atoms and proper selection for the electron donating/accepting strength of ligands are crucial for eliminating the charge carrier traps. Our calculations predicted a similar suppressing effect of chloride ligands with experiments and provided a simple but effective approach to assess the charge carrier trapping behaviors of semiconductor QDs.

Investigation of diocotron modes in toroidally trapped electron plasmas using non-destructive method

Science.gov (United States)

Lachhvani, Lavkesh; Pahari, Sambaran; Sengupta, Sudip; Yeole, Yogesh G.; Bajpai, Manu; Chattopadhyay, P. K.

2017-10-01

Experiments with trapped electron plasmas in a SMall Aspect Ratio Toroidal device (SMARTEX-C) have demonstrated a flute-like mode represented by oscillations on capacitive (wall) probes. Although analogous to diocotron mode observed in linear electron traps, the mode evolution in toroids can have interesting consequences due to the presence of in-homogeneous magnetic field. In SMARTEX-C, the probe signals are observed to undergo transition from small, near-sinusoidal oscillations to large amplitude, non-linear "double-peaked" oscillations. To interpret the wall probe signal and bring forth the dynamics, an expression for the induced current on the probe for an oscillating charge is derived, utilizing Green's Reciprocation Theorem. Equilibrium position, poloidal velocity of the charge cloud, and charge content of the cloud, required to compute the induced current, are estimated from the experiments. Signal through capacitive probes is thereby computed numerically for possible charge cloud trajectories. In order to correlate with experiments, starting with an intuitive guess of the trajectory, the model is evolved and tweaked to arrive at a signal consistent with experimentally observed probe signals. A possible vortex like dynamics is predicted, hitherto unexplored in toroidal geometries, for a limited set of experimental observations from SMARTEX-C. Though heuristic, a useful interpretation of capacitive probe data in terms of charge cloud dynamics is obtained.

A metastable helium trap for atomic collision physics

International Nuclear Information System (INIS)

Colla, M.; Gulley, R.; Uhlmann, L.; Hoogerland, M.D.; Baldwin, K.G.H.; Buckman, S.J.

1999-01-01

Full text: Metastable helium in the 2 3 S state is an important species for atom optics and atomic collision physics. Because of its large internal energy (20eV), long lifetime (∼8000s) and large collision cross section for a range of processes, metastable helium plays an important role in atmospheric physics, plasma discharges and gas laser physics. We have embarked on a program of studies on atom-atom and electron-atom collision processes involving cold metastable helium. We confine metastable helium atoms in a magneto-optic trap (MOT), which is loaded by a transversely collimated, slowed and 2-D focussed atomic beam. We employ diode laser tuned to the 1083 nm (2 3 S 1 - 2 3 P2 1 ) transition to generate laser cooling forces in both the loading beam and the trap. Approximately 10 million helium atoms are trapped at temperatures of ∼ 1mK. We use phase modulation spectroscopy to measure the trapped atomic density. The cold, trapped atoms can collide to produce either atomic He + or molecular He 2 + ions by Penning Ionisation (PI) or Associative Ionisation (AI). The rate of formation of these ions is dependant upon the detuning of the trapping laser from resonance. A further laser can be used to connect the 2 3 S 1 state to another higher lying excited state, and variation of the probe laser detuning used to measure interatomic collision potential. Electron-atom collision processes are studied using a monochromatic electron beam with a well defined spatial current distribution. The total trap loss due to electron collisions is measured as a function of electron energy. Results will be presented for these atomic collision physics measurements involving cold, trapped metastable helium atoms. Copyright (1999) Australian Optical Society

Hermite Polynomials and the Inverse Problem for Collisionless Equilibria

Science.gov (United States)

Allanson, O.; Neukirch, T.; Troscheit, S.; Wilson, F.

2017-12-01

It is long established that Hermite polynomial expansions in either velocity or momentum space can elegantly encode the non-Maxwellian velocity-space structure of a collisionless plasma distribution function (DF). In particular, Hermite polynomials in the canonical momenta naturally arise in the consideration of the 'inverse problem in collisionless equilibria' (IPCE): "for a given macroscopic/fluid equilibrium, what are the self-consistent Vlasov-Maxwell equilibrium DFs?". This question is of particular interest for the equilibrium and stability properties of a given macroscopic configuration, e.g. a current sheet. It can be relatively straightforward to construct a formal solution to IPCE by a Hermite expansion method, but several important questions remain regarding the use of this method. We present recent work that considers the necessary conditions of non-negativity, convergence, and the existence of all moments of an equilibrium DF solution found for IPCE. We also establish meaningful analogies between the equations that link the microscopic and macrosopic descriptions of the Vlasov-Maxwell equilibrium, and those that solve the initial value problem for the heat equation. In the language of the heat equation, IPCE poses the pressure tensor as the 'present' heat distribution over an infinite domain, and the non-Maxwellian features of the DF as the 'past' distribution. We find sufficient conditions for the convergence of the Hermite series representation of the DF, and prove that the non-negativity of the DF can be dependent on the magnetisation of the plasma. For DFs that decay at least as quickly as exp(-v^2/4), we show non-negativity is guaranteed for at least a finite range of magnetisation values, as parameterised by the ratio of the Larmor radius to the gradient length scale. 1. O. Allanson, T. Neukirch, S. Troscheit & F. Wilson: From one-dimensional fields to Vlasov equilibria: theory and application of Hermite polynomials, Journal of Plasma Physics, 82

Mini ion trap mass spectrometer

Science.gov (United States)

Dietrich, D.D.; Keville, R.F.

1995-09-19

An ion trap is described which operates in the regime between research ion traps which can detect ions with a mass resolution of better than 1:10{sup 9} and commercial mass spectrometers requiring 10{sup 4} ions with resolutions of a few hundred. The power consumption is kept to a minimum by the use of permanent magnets and a novel electron gun design. By Fourier analyzing the ion cyclotron resonance signals induced in the trap electrodes, a complete mass spectra in a single combined structure can be detected. An attribute of the ion trap mass spectrometer is that overall system size is drastically reduced due to combining a unique electron source and mass analyzer/detector in a single device. This enables portable low power mass spectrometers for the detection of environmental pollutants or illicit substances, as well as sensors for on board diagnostics to monitor engine performance or for active feedback in any process involving exhausting waste products. 10 figs.

X-ray spectroscopy of hydrogen-like ions in an electron beam ion trap

Energy Technology Data Exchange (ETDEWEB)

Tarbutt, M.R.; Crosby, D.; Silver, J.D. [Univ. of Oxford, Clarendon Lab. (United Kingdom); Myers, E.G. [Dept. of Physics, Florida State Univ., Tallahassee, FL (United States); Nakamura, N.; Ohtani, S. [ICORP, JST, Chofu, Tokyo (Japan)

2001-07-01

The X-ray emission from highly charged hydrogen-like ions in an electron beam ion trap is free from the problems of satellite contamination and Doppler shifts inherent in fast-beam sources. This is a favourable situation for the measurement of ground-state Lamb shifts in these ions. We present recent progress toward this goal, and discuss a method whereby wavelength comparison between transitions in hydrogenlike ions of different nuclear charge Z, enable the measurement of QED effects without requiring an absolute calibration.

Intrinsic charge trapping in amorphous oxide films: status and challenges

Science.gov (United States)

Strand, Jack; Kaviani, Moloud; Gao, David; El-Sayed, Al-Moatasem; Afanas’ev, Valeri V.; Shluger, Alexander L.

2018-06-01

We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO2, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy measurements and theoretical calculations using density functional theory shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO2. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modeling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO2 and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO2, a-Al2O3, a-TiO2. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO2 and a-SiO2 weakens Hf(Si)–O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O2‑ ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection

Quasi-Linear Evolution of Trapped Electron Fluxes Under the Influence of Realistic Whistler-Mode Waves

Science.gov (United States)

Agapitov, O. V.; Mourenas, D.; Artemyev, A.; Krasnoselskikh, V.

2014-12-01

The evolution of fluxes of energetic trapped electrons as a function of geomagnetic activity is investigated using brand new statistical models of chorus waves derived from Cluster observations in the radiation belts. The new wave models provide the distributions of wave power and wave-normal angle with latitude as a function of either Dst or Kp indices. Lifetimes and energization of energetic electrons are examined, as well as the relevant uncertainties related to some of the wave models implicit assumptions.From the presented results, different implications concerning the characterization of relativistic flux enhancements and losses are provided.

Compression of Antiproton Clouds for Antihydrogen Trapping

CERN Document Server

Andresen, G B; Bowe, P D; Bray, C C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Funakoshi, R; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Hydomako, R; Jenkins, M J; Jørgensen, L V; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; Van der Werf, D P; Wurtele, J S; Yamazaki, Y

2008-01-01

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.

Direct observation of 0.57 eV trap-related RF output power reduction in AlGaN/GaN high electron mobility transistors

Science.gov (United States)

Arehart, A. R.; Sasikumar, A.; Rajan, S.; Via, G. D.; Poling, B.; Winningham, B.; Heller, E. R.; Brown, D.; Pei, Y.; Recht, F.; Mishra, U. K.; Ringel, S. A.

2013-02-01

This paper reports direct evidence for trap-related RF output power loss in GaN high electron mobility transistors (HEMTs) grown by metal organic chemical vapor deposition (MOCVD) through increased concentration of a specific electron trap at EC-0.57 eV that is located in the drain access region, as a function of accelerated life testing (ALT). The trap is detected by constant drain current deep level transient spectroscopy (CID-DLTS) and the CID-DLTS thermal emission time constant precisely matches the measured drain lag. Both drain lag and CID-DLTS measurements show this state to already exist in pre-stressed devices, which coupled with its strong increase in concentration as a function of stress in the absence of significant increases in concentrations of other detected traps, imply its role in causing degradation, in particular knee walkout. This study reveals EC-0.57 eV trap concentration tracks degradation induced by ALT for MOCVD-grown HEMTs supplied by several commercial and university sources. The results suggest this defect has a common source and may be a key degradation pathway in AlGaN/GaN HEMTs and/or an indicator to predict device lifetime.

Landau fluid models of collisionless magnetohydrodynamics

International Nuclear Information System (INIS)

Snyder, P.B.; Hammett, G.W.; Dorland, W.

1997-01-01

A closed set of fluid moment equations including models of kinetic Landau damping is developed which describes the evolution of collisionless plasmas in the magnetohydrodynamic parameter regime. The model is fully electromagnetic and describes the dynamics of both compressional and shear Alfven waves, as well as ion acoustic waves. The model allows for separate parallel and perpendicular pressures p parallel and p perpendicular , and, unlike previous models such as Chew-Goldberger-Low theory, correctly predicts the instability threshold for the mirror instability. Both a simple 3 + 1 moment model and a more accurate 4 + 2 moment model are developed, and both could be useful for numerical simulations of astrophysical and fusion plasmas

Correlation of interface states/border traps and threshold voltage shift on AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

Energy Technology Data Exchange (ETDEWEB)

Wu, Tian-Li, E-mail: Tian-Li.Wu@imec.be; Groeseneken, Guido [imec, Kapeldreef 75, 3001 Leuven (Belgium); Department of Electrical Engineering, KU Leuven, Leuven (Belgium); Marcon, Denis; De Jaeger, Brice; Lin, H. C.; Franco, Jacopo; Stoffels, Steve; Van Hove, Marleen; Decoutere, Stefaan [imec, Kapeldreef 75, 3001 Leuven (Belgium); Bakeroot, Benoit [imec, Kapeldreef 75, 3001 Leuven (Belgium); Centre for Microsystems Technology, Ghent University, 9052 Gent (Belgium); Roelofs, Robin [ASM, Kapeldreef 75, 3001 Leuven (Belgium)

2015-08-31

In this paper, three electrical techniques (frequency dependent conductance analysis, AC transconductance (AC-g{sub m}), and positive gate bias stress) were used to evaluate three different gate dielectrics (Plasma-Enhanced Atomic Layer Deposition Si{sub 3}N{sub 4}, Rapid Thermal Chemical Vapor Deposition Si{sub 3}N{sub 4}, and Atomic Layer Deposition (ALD) Al{sub 2}O{sub 3}) for AlGaN/GaN Metal-Insulator-Semiconductor High-Electron-Mobility Transistors. From these measurements, the interface state density (D{sub it}), the amount of border traps, and the threshold voltage (V{sub TH}) shift during a positive gate bias stress can be obtained. The results show that the V{sub TH} shift during a positive gate bias stress is highly correlated to not only interface states but also border traps in the dielectric. A physical model is proposed describing that electrons can be trapped by both interface states and border traps. Therefore, in order to minimize the V{sub TH} shift during a positive gate bias stress, the gate dielectric needs to have a lower interface state density and less border traps. However, the results also show that the commonly used frequency dependent conductance analysis technique to extract D{sub it} needs to be cautiously used since the resulting value might be influenced by the border traps and, vice versa, i.e., the g{sub m} dispersion commonly attributed to border traps might be influenced by interface states.

Electron scavenging in ethylene glycol-water glass at 4 and 77 K: scavenging of trapped vs mobile electrons. [. gamma. -rays, x radiation

Energy Technology Data Exchange (ETDEWEB)

Lin, D P; Kevan, L [Wayne State Univ., Detroit, Mich. (USA). Dept. of Chemistry; Steen, H B

1976-01-01

Electron scavenging efficiencies have been measured at 77 and 4 K in ethylene glycol-water glass for the following scavengers which span a 250-fold range of scavenger efficiencies at 77 K: HCl, NaNO/sub 3/ and K/sub 2/Cr0/sub 4/. The range of scavenging efficiencies decreases to 62 at 4 K with the largest relative change occurring for the less efficient scavengers. These results are suggested to be most consistent with a model in which scavenging occurs by tunneling from shallowly and deeply trapped electrons at 4 and 77 K, respectively.

Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Energy Technology Data Exchange (ETDEWEB)

Higgins, Andrew, E-mail: aehiggin@princeton.edu, E-mail: kahn@princeton.edu; Kahn, Antoine, E-mail: aehiggin@princeton.edu, E-mail: kahn@princeton.edu [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544-5263 (United States); Mohapatra, Swagat K.; Barlow, Stephen; Marder, Seth R. [Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States)

2015-04-20

Charge transport in organic semiconductors is often inhibited by the presence of tail states that extend into the band gap of a material and act as traps for charge carriers. This work demonstrates the passivation of acceptor tail states by solution processing of ultra-low concentrations of a strongly reducing air-stable organometallic dimer, the pentamethylrhodocene dimer, [RhCp*Cp]{sub 2}, into the electron transport polymer poly([N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide) -2,6-diyl]-alt-5,5′-(2,2′-bithiophene)), P(NDI{sub 2}OD-T{sub 2}). Variable-temperature current-voltage measurements of n-doped P(NDI{sub 2}OD-T{sub 2}) are presented with doping concentration varied through two orders of magnitude. Systematic variation of the doping parameter is shown to lower the activation energy for hopping transport and enhance film conductivity and electron mobility.

Trapping, self-trapping and the polaron family

International Nuclear Information System (INIS)

Stoneham, A M; Gavartin, J; Shluger, A L; Kimmel, A V; Ramo, D Munoz; Roennow, H M; Aeppli, G; Renner, C

2007-01-01

The earliest ideas of the polaron recognized that the coupling of an electron to ionic vibrations would affect its apparent mass and could effectively immobilize the carrier (self-trapping). We discuss how these basic ideas have been generalized to recognize new materials and new phenomena. First, there is an interplay between self-trapping and trapping associated with defects or with fluctuations in an amorphous solid. In high dielectric constant oxides, like HfO 2 , this leads to oxygen vacancies having as many as five charge states. In colossal magnetoresistance manganites, this interplay makes possible the scanning tunnelling microscopy (STM) observation of polarons. Second, excitons can self-trap and, by doing so, localize energy in ways that can modify the material properties. Third, new materials introduce new features, with polaron-related ideas emerging for uranium dioxide, gate dielectric oxides, Jahn-Teller systems, semiconducting polymers and biological systems. The phonon modes that initiate self-trapping can be quite different from the longitudinal optic modes usually assumed to dominate. Fourth, there are new phenomena, like possible magnetism in simple oxides, or with the evolution of short-lived polarons, like muons or excitons. The central idea remains that of a particle whose properties are modified by polarizing or deforming its host solid, sometimes profoundly. However, some of the simpler standard assumptions can give a limited, indeed misleading, description of real systems, with qualitative inconsistencies. We discuss representative cases for which theory and experiment can be compared in detail

EBIT trapping program

International Nuclear Information System (INIS)

Elliott, S.R.; Beck, B.; Beiersdorfer, P.; Church, D.; DeWitt, D.; Knapp, D.K.; Marrs, R.E.; Schneider, D.; Schweikhard, L.

1993-01-01

The LLNL electron beam ion trap provides the world's only source of stationary highly charged ions up to bare U. This unique capability makes many new atomic and nuclear physics experiments possible. (orig.)

Numerical treatment of linearized equations describing inhomogeneous collisionless plasmas

International Nuclear Information System (INIS)

Lewis, H.R.

1979-01-01

The equations governing the small-signal response of spatially inhomogeneous collisionless plasmas have practical significance in physics, for example in controlled thermonuclear fusion research. Although the solutions are very complicated and the equations are different to solve numerically, effective methods for them are being developed which are applicable when the equilibrium involves only one nonignorable coordinate. The general theoretical framework probably will provide a basis for progress when there are two or three nonignorable coordinates

Electron self-trapped at molybdenum complex in lead molybdate: An EPRand TSL comparative study

Czech Academy of Sciences Publication Activity Database

Buryi, Maksym; Laguta, Valentyn; Fasoli, M.; Moretti, F.; Trubitsyn, M.; Volnianskii, M.; Vedda, A.; Nikl, Martin

2017-01-01

Roč. 192, Dec (2017), s. 767-774 ISSN 0022-2313 R&D Projects: GA MŠk LO1409; GA MŠk LM2015088; GA ČR GA17-09933S EU Projects: European Commission(XE) 690599 - ASCIMAT Institutional support: RVO:68378271 Keywords : EPR * wavelength resolved TSL * self-trapped electron * lead molybdate * molecular orbitals Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 2.686, year: 2016

Effects of antimony (Sb) on electron trapping near SiO{sub 2}/4H-SiC interfaces

Energy Technology Data Exchange (ETDEWEB)

Mooney, P. M.; Jiang, Zenan; Basile, A. F. [Physics Department, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Zheng, Yongju; Dhar, Sarit [Physics Department, Auburn University, Auburn, Alabama 36849 (United States)

2016-07-21

To investigate the mechanism by which Sb at the SiO{sub 2}/SiC interface improves the channel mobility of 4H-SiC MOSFETs, 1 MHz capacitance measurements and constant capacitance deep level transient spectroscopy (CCDLTS) measurements were performed on Sb-implanted 4H-SiC MOS capacitors. The measurements reveal a significant concentration of Sb donors near the SiO{sub 2}/SiC interface. Two Sb donor related CCDLTS peaks corresponding to shallow energy levels in SiC were observed close to the SiO{sub 2}/SiC interface. Furthermore, CCDLTS measurements show that the same type of near-interface traps found in conventional dry oxide or NO-annealed capacitors are present in the Sb implanted samples. These are O1 traps, suggested to be carbon dimers substituted for O dimers in SiO{sub 2}, and O2 traps, suggested to be interstitial Si in SiO{sub 2}. However, electron trapping is reduced by a factor of ∼2 in Sb-implanted samples compared with samples with no Sb, primarily at energy levels within 0.2 eV of the SiC conduction band edge. This trap passivation effect is relatively small compared with the Sb-induced counter-doping effect on the MOSFET channel surface, which results in improved channel transport.

Disruption of Alfvénic turbulence by magnetic reconnection in a collisionless plasma

Science.gov (United States)

Mallet, Alfred; Schekochihin, Alexander A.; Chandran, Benjamin D. G.

2017-12-01

We calculate the disruption scale \\text{D}$ at which sheet-like structures in dynamically aligned Alfvénic turbulence are destroyed by the onset of magnetic reconnection in a low- collisionless plasma. The scaling of \\text{D}$ depends on the order of the statistics being considered, with more intense structures being disrupted at larger scales. The disruption scale for the structures that dominate the energy spectrum is \\text{D}\\sim L\\bot 1/9(de\\unicode[STIX]{x1D70C}s)4/9$ , where e$ is the electron inertial scale, s$ is the ion sound scale and \\bot $ is the outer scale of the turbulence. When e$ and s/L\\bot $ are sufficiently small, the scale \\text{D}$ is larger than s$ and there is a break in the energy spectrum at \\text{D}$ , rather than at s$ . We propose that the fluctuations produced by the disruption are circularised flux ropes, which may have already been observed in the solar wind. We predict the relationship between the amplitude and radius of these structures and quantify the importance of the disruption process to the cascade in terms of the filling fraction of undisrupted structures and the fractional reduction of the energy contained in them at the ion sound scale s$ . Both of these fractions depend strongly on e$ , with the disrupted structures becoming more important at lower e$ . Finally, we predict that the energy spectrum between \\text{D}$ and s$ is steeper than \\bot -3$ , when this range exists. Such a steep `transition range' is sometimes observed in short intervals of solar-wind turbulence. The onset of collisionless magnetic reconnection may therefore significantly affect the nature of plasma turbulence around the ion gyroscale.

Saturation regime of the collisionless drift instability in a hydrogen plasma column

International Nuclear Information System (INIS)

Boissier, R.

1982-09-01

The saturation regime of the collisionless drift instability is observed in a steady state hydrogen column. The steady state parameters are observed to relax around the average values. A quasilinear model is proposed to describe the dynamics of wave growth and density gradient decay

Ion Thermalization and Electron Heating across Quasi-Perpendicular Shocks Observed by the MMS Mission

Science.gov (United States)

Chen, L. J.; Wilson, L. B., III; Wang, S.; Bessho, N.; Figueroa-Vinas, A.; Lai, H.; Russell, C. T.; Schwartz, S. J.; Hesse, M.; Moore, T. E.; Burch, J.; Gershman, D. J.; Giles, B. L.; Torbert, R. B.; Ergun, R.; Dorelli, J.; Strangeway, R. J.; Paterson, W. R.; Lavraud, B.; Khotyaintsev, Y. V.

2017-12-01

Collisionless shocks often involve intense plasma heating in space and astrophysical systems. Despite decades of research, a number of key questions concerning electron and ion heating across collisionless shocks remain unanswered. We `image' 20 supercritical quasi-perpendicular bow shocks encountered by the Magnetospheric Multiscale (MMS) spacecraft with electron and ion distribution functions to address how ions are thermalized and how electrons are heated. The continuous burst measurements of 3D plasma distribution functions from MMS reveal that the primary thermalization phase of ions occurs concurrently with the main temperature increase of electrons as well as large-amplitude wave fluctuations. Approaching the shock from upstream, the ion temperature (Ti) increases due to the reflected ions joining the incoming solar wind population, as recognized by prior studies, and the increase of Ti precedes that of the electrons. Thermalization in the form of merging between the decelerated solar wind ions and the reflected component often results in a decrease in Ti. In most cases, the Ti decrease is followed by a gradual increase further downstream. Anisotropic, energy-dependent, and/or nongyrotropic electron energization are observed in association with large electric field fluctuations in the main electron temperature (Te) gradient, motivating a renewed scrutiny of the effects from the electrostatic cross-shock potential and wave fluctuations on electron heating. Particle-in-cell (PIC) simulations are carried out to assist interpretations of the MMS observations. We assess the roles of instabilities and the cross-shock potential in thermalizing ions and heating electrons based on the MMS measurements and PIC simulation results. Challenges will be posted for future computational studies and laboratory experiments on collisionless shocks.

The ion polytropic coefficient in a collisionless sheath containing hot ions

Energy Technology Data Exchange (ETDEWEB)

Lin, Binbin; Xiang, Nong, E-mail: xiangn@ipp.ac.cn; Ou, Jing [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei 230031 (China)

2016-08-15

The fluid approach has been widely used to study plasma sheath dynamics. For a sheath containing hot ions whose temperature is greater than the electron's, how to truncate the fluid hierarchy chain equations while retaining to the fullest extent of the kinetic effects is always a difficult problem. In this paper, a one-dimensional, collisionless sheath containing hot ions is studied via particle-in-cell simulations. By analyzing the ion energy equation and taking the kinetic effects into account, we have shown that the ion polytropic coefficient in the vicinity of the sheath edge is approximately constant so that the state equation with the modified polytropic coefficient can be used to close the hierarchy chain of the ion fluid equations. The value of the polytropic coefficient strongly depends on the hot ion temperature and its concentration in the plasma. The semi-analytical model is given to interpret the simulation results. As an application, the kinetic effects on the ion saturation current density in the probe theory are discussed.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

Science.gov (United States)

Anand, M. J.; Ng, G. I.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.; Syamal, B.; Zhou, X.

2015-02-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (ΔVth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 μm), the devices exhibited higher dyn-RDS[ON] degradation but a small ΔVth (˜120 mV). However, at low-EF (Lgd = 5 μm), smaller dyn-RDS[ON] degradation but a larger ΔVth (˜380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔVth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by ID-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

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.

Simulation of perturbation produced by an absorbing spherical body in collisionless plasma

Energy Technology Data Exchange (ETDEWEB)

Krasovsky, V. L., E-mail: vkrasov@iki.rssi.ru; Kiselyov, A. A., E-mail: alexander.kiselyov@stonehenge-3.net.ru; Dolgonosov, M. S. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2017-01-15

A steady plasma state reached in the course of charging of an absorbing spherical body is found using computational methods. Numerical simulations provide complete information on this process, thereby allowing one to find the spatiotemporal dependences of the physical quantities and observe the kinetic phenomena accompanying the formation of stable electron and ion distributions in phase space. The distribution function of trapped ions is obtained, and their contribution to the screening of the charged sphere is determined. The sphere charge and the charge of the trapped-ion cloud are determined as functions of the unperturbed plasma parameters.

Simulation of perturbation produced by an absorbing spherical body in collisionless plasma

International Nuclear Information System (INIS)

Krasovsky, V. L.; Kiselyov, A. A.; Dolgonosov, M. S.

2017-01-01

A steady plasma state reached in the course of charging of an absorbing spherical body is found using computational methods. Numerical simulations provide complete information on this process, thereby allowing one to find the spatiotemporal dependences of the physical quantities and observe the kinetic phenomena accompanying the formation of stable electron and ion distributions in phase space. The distribution function of trapped ions is obtained, and their contribution to the screening of the charged sphere is determined. The sphere charge and the charge of the trapped-ion cloud are determined as functions of the unperturbed plasma parameters.

Variation of carrier concentration and interface trap density in 8MeV electron irradiated c-Si solar cells

Energy Technology Data Exchange (ETDEWEB)

Bhat, Sathyanarayana, E-mail: asharao76@gmail.com; Rao, Asha, E-mail: asharao76@gmail.com [Department of Physics, Mangalore Institute of Technology and Engineering, Moodabidri, Mangalore-574225 (India); Krishnan, Sheeja [Department of Physics, Sri Devi Institute of Technology, Kenjar, Mangalore-574142 (India); Sanjeev, Ganesh [Microtron Centre, Department of Physics, Mangalore University, Mangalagangothri-574199 (India); Suresh, E. P. [Solar Panel Division, ISRO Satellite Centre, Bangalore-560017 (India)

2014-04-24

The capacitance and conductance measurements were carried out for c-Si solar cells, irradiated with 8 MeV electrons with doses ranging from 5kGy – 100kGy in order to investigate the anomalous degradation of the cells in the radiation harsh environments. Capacitance – Voltage measurements indicate that there is a slight reduction in the carrier concentration upon electron irradiation due to the creation of radiation induced defects. The conductance measurement results reveal that the interface state densities and the trap time constant increases with electron dose due to displacement damages in c-Si solar cells.

Progress toward magnetic confinement of a positron-electron plasma: nearly 100% positron injection efficiency into a dipole trap

Science.gov (United States)

Stoneking, Matthew

2017-10-01

The hydrogen atom provides the simplest system and in some cases the most precise one for comparing theory and experiment in atomics physics. The field of plasma physics lacks an experimental counterpart, but there are efforts underway to produce a magnetically confined positron-electron plasma that promises to represent the simplest plasma system. The mass symmetry of positron-electron plasma makes it particularly tractable from a theoretical standpoint and many theory papers have been published predicting modified wave and stability properties in these systems. Our approach is to utilize techniques from the non-neutral plasma community to trap and accumulate electrons and positrons prior to mixing in a magnetic trap with good confinement properties. Ultimately we aim to use a levitated superconducting dipole configuration fueled by positrons from a reactor-based positron source and buffer-gas trap. To date we have conducted experiments to characterize and optimize the positron beam and test strategies for injecting positrons into the field of a supported permanent magnet by use of ExB drifts and tailored static and dynamic potentials applied to boundary electrodes and to the magnet itself. Nearly 100% injection efficiency has been achieved under certain conditions and some fraction of the injected positrons are confined for as long as 400 ms. These results are promising for the next step in the project which is to use an inductively energized high Tc superconducting coil to produce the dipole field, initially in a supported configuration, but ultimately levitated using feedback stabilization. Work performed with the support of the German Research Foundation (DFG), JSPS KAKENHI, NIFS Collaboration Research Program, and the UCSD Foundation.

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.

Nonlinear theory of trapped electron temperature gradient driven turbulence in flat density H-mode plasmas

International Nuclear Information System (INIS)

Hahm, T.S.

1990-12-01

Ion temperature gradient turbulence based transport models have difficulties reconciling the recent DIII-D H-mode results where the density profile is flat, but χ e > χ i in the core region. In this work, a nonlinear theory is developed for recently discovered ion temperature gradient trapped electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for L Ti /R approx-lt κ θ ρ s approx-lt (L Ti /R) 1/4 . They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave-particle-wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity. 17 refs., 3 figs

Status of THe-Trap

Energy Technology Data Exchange (ETDEWEB)

Streubel, Sebastian; Eronen, Tommi; Hoecker, Martin; Ketter, Jochen; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA (United States)

2013-07-01

THe-Trap (short for Tritium-{sup 3}He Trap) is a Penning-trap setup dedicated to measure the {sup 3}H to {sup 3}He mass-ratio with a relative uncertainty of better than 10{sup -11}. The ratio is of relevance for the KArlsruhe TRItium Neutrino experiment (KATRIN), which aims to measure the electron anti-neutrino mass, by measuring the shape of the β-decay energy spectrum close to its endpoint. An independent measurement of the {sup 3}H to {sup 3}He mass-ratio pins down this endpoint, and thus will help to determine the systematics of KATRIN. The trap setup consists of two Penning-traps: One trap for precision measurements, the other trap for ion storage. Ideally, the trap content will be periodically switched, which reduces the time between the measurements of the two ions' motional frequencies. In 2012, a mass ratio measurement of {sup 12}C{sup 4+} to {sup 14}N{sup 5+} was performed to characterize systematic effects of the traps. This measurement yielded a accuracy of 10{sup -9}. Further investigations revealed that a major reason for the modest accuracy is the large axial amplitude of ∼100 μm, compared to a ideal case of 3 μm at 4 K. In addition, relative magnetic fluctuations at a 3 x 10{sup -10} level on a 10 h timescale need to be significantly improved. In this contribution, the aforementioned findings and further systematic studies will be presented.

Entropy in Collisionless Self-gravitating Systems

Science.gov (United States)

Barnes, Eric; Williams, L.

2010-01-01

Collisionless systems, like simulated dark matter halos or gas-less elliptical galaxies, often times have properties suggesting that a common physical principle controls their evolution. For example, N-body simulations of dark matter halos present nearly scale-free density/velocity-cubed profiles. In an attempt to understand the origins of such relationships, we adopt a thermodynamics approach. While it is well-known that self-gravitating systems do not have physically realizable thermal equilibrium configurations, we are interested in the behavior of entropy as mechanical equilibrium is acheived. We will discuss entropy production in these systems from a kinetic theory point of view. This material is based upon work supported by the National Aeronautics and Space Administration under grant NNX07AG86G issued through the Science Mission Directorate.

Status of THe-trap

Energy Technology Data Exchange (ETDEWEB)

Ketter, Jochen; Eronen, Tommi; Hoecker, Martin; Streubel, Sebastian; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA (United States)

2012-07-01

Originally developed at the University of Washington and relocated to the Max-Planck-Institut fuer Kernphysik in 2008, the Penning-trap spectrometer THe-Trap is specially tailored for a {sup 3}H/{sup 3}He mass-ratio measurement, from which the Q-value of the beta-decay of {sup 3}H to {sup 3}He can be derived. Improving the current best value by at least an order of magnitude will provide an important independent test parameter for the determination of the electron-antineutrino's mass by the Karlsruhe Tritium Neutrino Experiment (KATRIN). However, Penning-trap mass spectrometry has to be pushed to its limits in a dedicated experiment for a sufficiently accurate mass-ratio measurement with a relative uncertainty of 10{sup -11}. Unlike the closed-envelope, single-trap predecessor, the new spectrometer features an external ion source, owing to the radioactive nature of tritium, and two traps in order to speed up the measurement cycle. While the double-trap technique holds great promise, it also calls for more intricate procedures, such as ion transfer. Details about the recent progress of the experiment are given.

Spectroscopy of a Synthetic Trapped Ion Qubit

Science.gov (United States)

Hucul, David; Christensen, Justin E.; Hudson, Eric R.; Campbell, Wesley C.

2017-09-01

133Ba+ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1 /2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser cool the synthetic A =133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the 62P1 /2↔62S1 /2 and 62P1 /2↔52D3 /2 electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the 62P1 /2↔52D3 /2 electronic transition isotope shift for the rare A =130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.

Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp

CERN Document Server

Hansson, M.; Ekerfelt, H.; Aurand, B.; Gallardo Ganzalez, I.; Desforges, F. G.; Davoine, X.; Maitrallain, A.; Reymond, S.; Monot, P.; Persson, A.; Dobosz Dufrénoy S.; Wahlström C-G.; Cros, B.; Lundh, O.

2016-01-01

We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.

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.

Collisionless damping of dust-acoustic waves in a charge varying dusty plasma with nonextensive ions

International Nuclear Information System (INIS)

Amour, Rabia; Tribeche, Mouloud

2014-01-01

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

Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds

Science.gov (United States)

Horowitz, Viva R.; Alemán, Benjamín J.; Christle, David J.; Cleland, Andrew N.; Awschalom, David D.

2012-01-01

Using an optical tweezers apparatus, we demonstrate three-dimensional control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy color centers. Despite the motion and random orientation of nitrogen-vacancy centers suspended in the optical trap, we observe distinct peaks in the measured ESR spectra qualitatively similar to the same measurement in bulk. Accounting for the random dynamics, we model the ESR spectra observed in an externally applied magnetic field to enable dc magnetometry in solution. We estimate the dc magnetic field sensitivity based on variations in ESR line shapes to be approximately . This technique may provide a pathway for spin-based magnetic, electric, and thermal sensing in fluidic environments and biophysical systems inaccessible to existing scanning probe techniques. PMID:22869706

Improved theory of collisionless particle motion in stellarators

International Nuclear Information System (INIS)

Mynick, H.E.

1983-01-01

A theory of particle motion in stellarators is developed which, in contrast to previous work, is both realistic enough to account for collisionless detrapping, yet simple enough that most features of the orbits can be expressed in analytic, reasonably simple formulas. From the study of detrapping, a systematic, complete classification of possible orbit types emerges. The theory is valid for a class of stellarator configurations which contains the standard model traditionally envisaged, as well as somewhat more complex configurations recently found to have favorable transport properties. The reasons for the differences in transport between configurations are elucidated

Performance improvement of charge trap flash memory by using a composition-modulated high-k trapping layer

International Nuclear Information System (INIS)

Tang Zhen-Jie; Li Rong; Yin Jiang

2013-01-01

A composition-modulated (HfO 2 ) x (Al 2 O3) 1−x charge trapping layer is proposed for charge trap flash memory by controlling the Al atom content to form a peak and valley shaped band gap. It is found that the memory device using the composition-modulated (HfO 2 ) x (Al 2 O 3 ) 1−x as the charge trapping layer exhibits a larger memory window of 11.5 V, improves data retention even at high temperature, and enhances the program/erase speed. Improvements of the memory characteristics are attributed to the special band-gap structure resulting from the composition-modulated trapping layer. Therefore, the composition-modulated charge trapping layer may be useful in future nonvolatile flash memory device application. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

A fully kinetic, self-consistent particle simulation model of the collisionless plasma--sheath region

International Nuclear Information System (INIS)

Procassini, R.J.; Birdsall, C.K.; Morse, E.C.

1990-01-01

A fully kinetic particle-in-cell (PIC) model is used to self-consistently determine the steady-state potential profile in a collisionless plasma that contacts a floating, absorbing boundary. To balance the flow of particles to the wall, a distributed source region is used to inject particles into the one-dimensional system. The effect of the particle source distribution function on the source region and collector sheath potential drops, and particle velocity distributions is investigated. The ion source functions proposed by Emmert et al. [Phys. Fluids 23, 803 (1980)] and Bissell and Johnson [Phys. Fluids 30, 779 (1987)] (and various combinations of these) are used for the injection of both ions and electrons. The values of the potential drops obtained from the PIC simulations are compared to those from the theories of Emmert et al., Bissell and Johnson, and Scheuer and Emmert [Phys. Fluids 31, 3645 (1988)], all of which assume that the electron density is related to the plasma potential via the Boltzmann relation. The values of the source region and total potential drop are found to depend on the choice of the electron source function, as well as the ion source function. The question of an infinite electric field at the plasma--sheath interface, which arises in the analyses of Bissell and Johnson and Scheuer and Emmert, is also addressed

Intensity dependent waiting time for strong electron trapping events in speckle stimulated raman scatter

Energy Technology Data Exchange (ETDEWEB)

Rose, Harvey [Los Alamos National Laboratory; Daughton, W [Los Alamos National Laboratory; Yin, L [Los Alamos National Laboratory

2009-01-01

The onset of Stimulated Raman scatter from an intense laser speckle is the simplest experimentally realizable laser-plasma-interaction environment. Despite this data and recent 3D particle simulations, the controlling mechanism at the onset of backscatter in the kinetic regime when strong electron trapping in the daughter Langmuir wave is a dominant nonlinearity is not understood. This paper explores the consequences of assuming that onset is controlled by large thermal fluctuations. A super exponential dependence of mean reflectivity on speckle intensity in the onset regime is predicted.

Laser induced fluorescence of trapped molecular ions

Energy Technology Data Exchange (ETDEWEB)

Grieman, F.J.

1979-10-01

An experimental apparatus for obtaining the optical spectra of molecular ions is described. The experimental technique includes the use of three dimensional ion trapping, laser induced fluorescence, and gated photon counting methods. The ions, which are produced by electron impact, are confined in a radio-frequency quadrupole ion trap of cylindrical design. Because the quadrupole ion trap allows mass selection of the molecular ion desired for study, the analysis of the spectra obtained is greatly simplified. The ion trap also confines the ions to a region easily probed by a laser beam. 18 references.

Laser induced fluorescence of trapped molecular ions

International Nuclear Information System (INIS)

Grieman, F.J.

1979-10-01

An experimental apparatus for obtaining the optical spectra of molecular ions is described. The experimental technique includes the use of three dimensional ion trapping, laser induced fluorescence, and gated photon counting methods. The ions, which are produced by electron impact, are confined in a radio-frequency quadrupole ion trap of cylindrical design. Because the quadrupole ion trap allows mass selection of the molecular ion desired for study, the analysis of the spectra obtained is greatly simplified. The ion trap also confines the ions to a region easily probed by a laser beam. 18 references

In-trap decay spectroscopy for {beta}{beta} decays

Energy Technology Data Exchange (ETDEWEB)

Brunner, Thomas

2011-01-18

The presented work describes the implementation of a new technique to measure electron-capture (EC) branching ratios (BRs) of intermediate nuclei in {beta}{beta} decays. This technique has been developed at TRIUMF in Vancouver, Canada. It facilitates one of TRIUMF's Ion Traps for Atomic and Nuclear science (TITAN), the Electron Beam Ion Trap (EBIT) that is used as a spectroscopy Penning trap. Radioactive ions, produced at the radioactive isotope facility ISAC, are injected and stored in the spectroscopy Penning trap while their decays are observed. A key feature of this technique is the use of a strong magnetic field, required for trapping. It radially confines electrons from {beta} decays along the trap axis while X-rays, following an EC, are emitted isotropically. This provides spatial separation of X-ray and {beta} detection with almost no {beta}-induced background at the X-ray detector, allowing weak EC branches to be measured. Furthermore, the combination of several traps allows one to isobarically clean the sample prior to the in-trap decay spectroscopy measurement. This technique has been developed to measure ECBRs of transition nuclei in {beta}{beta} decays. Detailed knowledge of these electron capture branches is crucial for a better understanding of the underlying nuclear physics in {beta}{beta} decays. These branches are typically of the order of 10{sup -5} and therefore difficult to measure. Conventional measurements suffer from isobaric contamination and a dominating {beta} background at theX-ray detector. Additionally, X-rays are attenuated by the material where the radioactive sample is implanted. To overcome these limitations, the technique of in-trap decay spectroscopy has been developed. In this work, the EBIT was connected to the TITAN beam line and has been commissioned. Using the developed beam diagnostics, ions were injected into the Penning trap and systematic studies on injection and storage optimization were performed. Furthermore, Ge

In-trap decay spectroscopy for ββ decays

International Nuclear Information System (INIS)

Brunner, Thomas

2011-01-01

The presented work describes the implementation of a new technique to measure electron-capture (EC) branching ratios (BRs) of intermediate nuclei in ββ decays. This technique has been developed at TRIUMF in Vancouver, Canada. It facilitates one of TRIUMF's Ion Traps for Atomic and Nuclear science (TITAN), the Electron Beam Ion Trap (EBIT) that is used as a spectroscopy Penning trap. Radioactive ions, produced at the radioactive isotope facility ISAC, are injected and stored in the spectroscopy Penning trap while their decays are observed. A key feature of this technique is the use of a strong magnetic field, required for trapping. It radially confines electrons from β decays along the trap axis while X-rays, following an EC, are emitted isotropically. This provides spatial separation of X-ray and β detection with almost no β-induced background at the X-ray detector, allowing weak EC branches to be measured. Furthermore, the combination of several traps allows one to isobarically clean the sample prior to the in-trap decay spectroscopy measurement. This technique has been developed to measure ECBRs of transition nuclei in ββ decays. Detailed knowledge of these electron capture branches is crucial for a better understanding of the underlying nuclear physics in ββ decays. These branches are typically of the order of 10 -5 and therefore difficult to measure. Conventional measurements suffer from isobaric contamination and a dominating β background at theX-ray detector. Additionally, X-rays are attenuated by the material where the radioactive sample is implanted. To overcome these limitations, the technique of in-trap decay spectroscopy has been developed. In this work, the EBIT was connected to the TITAN beam line and has been commissioned. Using the developed beam diagnostics, ions were injected into the Penning trap and systematic studies on injection and storage optimization were performed. Furthermore, Ge detectors, for the detection of X-rays, were

Collisionless shock formation and the prompt acceleration of solar flare ions

Science.gov (United States)

Cargill, P. J.; Goodrich, C. C.; Vlahos, L.

1988-01-01

The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.

Time-dependence in relativistic collisionless shocks: theory of the variable

Energy Technology Data Exchange (ETDEWEB)

Spitkovsky, A

2004-02-05

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 Observatory. By selecting the parameters of the ion orbits to fit the spatial separation of the wisps, we predict the period of time variability of the wisps that is consistent with the data. When coupled with a mechanism for non-thermal acceleration of the pairs, the compressions in the magnetic field and plasma density associated with the optical wisp structure naturally account for the location of X-ray features in the Crab. We also discuss the origin of the high energy ions and their acceleration in the equatorial current sheet of the pulsar wind.

Temperature dependence of photoluminescence spectra of bilayer two-dimensional electron gases in LaAlO3/SrTiO3 superlattices: coexistence of Auger recombination and single-carrier trapping

Directory of Open Access Journals (Sweden)

H. J. Harsan Ma

2015-06-01

Full Text Available We report emerging photoluminescence (PL of bilayer two-dimensional electron gases (2DEG in LaAlO3/SrTiO3 (LAO/STO systems. A strong blue PL emerges in bilayer-2DEGs in LAO/STO/LAO/STO which doesn’t show in LAO/STO. PL band in bilayer-2DEGs includes both nearly temperature independent Auger recombination and temperature dependent free electron trapping while it crossovers from Auger recombination to single carrier trapping in LAO/STO. The PL signal of free electron trapping appears at high temperatures and it is much stronger than Auger recombination in the conducting channel in bilayer 2DEGs. This observation shows that high mobility carriers dominate the carrier dynamics in bilayer-2DEGs in LAO/STO superlattices.

Toward Rechargeable Persistent Luminescence for the First and Third Biological Windows via Persistent Energy Transfer and Electron Trap Redistribution.

Science.gov (United States)

Xu, Jian; Murata, Daisuke; Ueda, Jumpei; Viana, Bruno; Tanabe, Setsuhisa

2018-05-07

Persistent luminescence (PersL) imaging without real-time external excitation has been regarded as the next generation of autofluorescence-free optical imaging technology. However, to achieve improved imaging resolution and deep tissue penetration, developing new near-infrared (NIR) persistent phosphors with intense and long duration PersL over 1000 nm is still a challenging but urgent task in this field. Herein, making use of the persistent energy transfer process from Cr 3+ to Er 3+ , we report a novel garnet persistent phosphor of Y 3 Al 2 Ga 3 O 12 codoped with Er 3+ and Cr 3+ (YAG G:Er-Cr), which shows intense Cr 3+ PersL (∼690 nm) in the deep red region matching well with the first biological window (NIR-I, 650-950 nm) and Er 3+ PersL (∼1532 nm) in the NIR region matching well with the third biological window (NIR-III, 1500-1800 nm). The optical imaging through raw-pork tissues (thickness of 1 cm) suggests that the emission band of Er 3+ can achieve higher spatial resolution and more accurate signal location than that of Cr 3+ due to the reduced light scattering at longer wavelengths. Furthermore, by utilizing two independent electron traps with two different trap depths in YAG G:Er-Cr, the Cr 3+ /Er 3+ PersL can even be recharged in situ by photostimulation with 660 nm LED thanks to the redistribution of trapped electrons from the deep trap to the shallow one. Our results serve as a guide in developing promising NIR (>1000 nm) persistent phosphors for long-term optical imaging.

The NSSDC trapped radiation model facility

International Nuclear Information System (INIS)

Gaffey, J.D. Jr.; Bilitza, D.

1990-01-01

The National Space Science Data Center (NSSDC) trapped radiation models calculate the integral and differential electron and proton flux for given values of the particle energy E, drift shell parameter L, and magnetic field strength B for either solar maximum or solar minimum. The most recent versions of the series of models, which have been developed and continuously improved over several decades by Dr. James Vette and coworkers at NSSDC, are AE-8 for electrons and AP-8 for protons. The present status of the NSSDC trapped particle models is discussed. The limits of validity of the models are described. 17 refs

Ion traps fabricated in a CMOS foundry

Energy Technology Data Exchange (ETDEWEB)

Mehta, K. K.; Ram, R. J. [Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Eltony, A. M.; Chuang, I. L. [Center for Ultracold Atoms, Research Laboratory of Electronics and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Bruzewicz, C. D.; Sage, J. M., E-mail: jsage@ll.mit.edu; Chiaverini, J., E-mail: john.chiaverini@ll.mit.edu [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States)

2014-07-28

We demonstrate trapping in a surface-electrode ion trap fabricated in a 90-nm CMOS (complementary metal-oxide-semiconductor) foundry process utilizing the top metal layer of the process for the trap electrodes. The process includes doped active regions and metal interconnect layers, allowing for co-fabrication of standard CMOS circuitry as well as devices for optical control and measurement. With one of the interconnect layers defining a ground plane between the trap electrode layer and the p-type doped silicon substrate, ion loading is robust and trapping is stable. We measure a motional heating rate comparable to those seen in surface-electrode traps of similar size. This demonstration of scalable quantum computing hardware utilizing a commercial CMOS process opens the door to integration and co-fabrication of electronics and photonics for large-scale quantum processing in trapped-ion arrays.

Investigation of trap states in high Al content AlGaN/GaN high electron mobility transistors by frequency dependent capacitance and conductance analysis

International Nuclear Information System (INIS)

Zhu, Jie-Jie; Ma, Xiao-Hua; Hou, Bin; Chen, Wei-Wei; Hao, Yue

2014-01-01

Trap states in Al 0.55 Ga 0.45 N/GaN Schottky-gate high-electron-mobility transistors (S-HEMTs) and Al 2 O 3 /Al 0.55 Ga 0.45 N/GaN metal-oxide-semiconductor HEMTs (MOS-HEMTs) were investigated with conductance method in this paper. Surface states with time constant of (0.09–0.12) μs were found in S-HEMTs, and electron tunneling rather than emission was deemed to be the dominant de-trapping mechanism due to the high electric field in high Al content barrier. The density of surface states evaluated in S-HEMTs was (1.02–4.67)×10 13 eV −1 ·cm −2 . Al 2 O 3 gate insulator slightly reduced the surface states, but introduced low density of new traps with time constant of (0.65–1.29) μs into MOS-HEMTs

A kinetic study of solar wind electrons

International Nuclear Information System (INIS)

Lie-Svendsen, Oeystein; Leer, Egil

1996-01-01

The evolution of the distribution function for a test population of electrons in an isothermal electron-proton corona has been studied using a Fokker-Planck description. The aim is to investigate whether a suprathermal tail forms due to the energy dependence of the Coulomb cross section. We find that a Maxwellian test population, injected into this background close to the coronal base with a temperature equal to that of the background electrons, maintains its shape throughout the transition from collision-dominated to collisionless flow. No significant suprathermal tail in the electron distribution function is seen in the outer corona

MOS Capacitance—Voltage Characteristics III. Trapping Capacitance from 2-Charge-State Impurities

International Nuclear Information System (INIS)

Jie Binbin; Sah Chihtang

2011-01-01

Low-frequency and high-frequency capacitance—voltage curves of Metal—Oxide—Semiconductor Capacitors are presented to illustrate giant electron and hole trapping capacitances at many simultaneously present two-charge-state and one-trapped-carrier, or one-energy-level impurity species. Models described include a donor electron trap and an acceptor hole trap, both donors, both acceptors, both shallow energy levels, both deep, one shallow and one deep, and the identical donor and acceptor. Device and material parameters are selected to simulate chemically and physically realizable capacitors for fundamental trapping parameter characterizations and for electrical and optical signal processing applications. (invited papers)

Self-consistency constraints on turbulent magnetic transport and relaxation in collisionless plasma

International Nuclear Information System (INIS)

Terry, P.W.; Diamond, P.H.; Hahm, T.S.

1985-10-01

Novel constraints on collisionless relaxation and transport in drift-Alfven turbulence are reported. These constraints arise due to the consideration of mode coupling and incoherent fluctuations and the proper application of self-consistency conditions. The result that electrostatic fluctuations alone regulate transport in drift-Alfven turbulence follows directly. Quasilinear transport predictions are discussed in light of these constraints

Theoretical parameters of powerful radio galaxies. II. Generation of MHD turbulence by collisionless shock waves

International Nuclear Information System (INIS)

Baryshev, Yu.V.; Morozov, V.N.

1988-01-01

It is shown that MHD turbulence can be generated by collisionless shock waves due to anisotropy of the pressure behind the front of the reverse sock at the hot spot of a powerful radio galaxy. The energy density of the MHD turbulence generated behind the shock front is estimated. Analysis of the theoretical studies and experimental data on collisionless shock waves in the solar wind indicates that an important part is played by streams of ions reflected by the shock fronts, the streams generating plasma and MHD turbulence in the region ahead of the front. The extension of these ideas to shock waves in powerful radio galaxies must be made with care because of the great difference between the parameters of the shock waves in the two cases

Hybrid (Vlasov-Fluid) simulation of ion-acoustic solitons chain formation including trapped electrons

Energy Technology Data Exchange (ETDEWEB)

Behjat, E.; Aminmansoor, F.; Abbasi, H. [Faculty of Energy Engineering and Physics, Amirkabir University of Technology, P. O. Box 15875-4413, Tehran (Iran, Islamic Republic of)

2015-08-15

Disintegration of a Gaussian profile into ion-acoustic solitons in the presence of trapped electrons [H. Hakimi Pajouh and H. Abbasi, Phys. Plasmas 15, 082105 (2008)] is revisited. Through a hybrid (Vlasov-Fluid) model, the restrictions associated with the simple modified Korteweg de-Vries (mKdV) model are studied. For instance, the lack of vital information in the phase space associated with the evolution of electron velocity distribution, the perturbative nature of mKdV model which limits it to the weak nonlinear cases, and the special spatio-temporal scaling based on which the mKdV is derived. Remarkable differences between the results of the two models lead us to conclude that the mKdV model can only monitor the general aspects of the dynamics, and the precise picture including the correct spatio-temporal scales and the properties of solitons should be studied within the framework of hybrid model.

Overview of the current spectroscopy effort on the Livermore electron beam ion traps

International Nuclear Information System (INIS)

Beiersdorfer, P.; Lopez-Urrutia, J.C.; Brown, G.

1995-01-01

An overview is given of the current spectroscopic effort on the Livermore electron beam ion trap facilities. The effort focuses on four aspects: spectral line position, line intensity, temporal evolution, and line shape. Examples of line position measurements include studies of the K-shell transitions in heliumlike Kr 34+ and the 2s-2p intrashell transitions in lithiumlike Th 87+ and U 89+ , which provide benchmark values for testing the theory of relativistic and quantum electrodynamical contributions in high-Z ions. Examples of line intensity measurements are provided by measurements of the electron-impact excitation and dielectronic recombination cross sections of heliumlike transition-metal ions Ti 20+ through CO 25+ . A discussion of radiative lifetime measurements of metastable levels in heliumlike ions is given to illustrate the time-resolved spectroscopy techniques in the microsecond range. The authors also present a measurement of the spectral lineshape that illustrates the very low ion temperatures that can be achieved in an EBIT

Cooling and trapping neutral atoms with radiative forces

International Nuclear Information System (INIS)

Bagnato, V.S.; Castro, J.C.; Li, M.S.; Zilio, S.C.

1988-01-01

Techniques to slow and trap neutral atoms at high densities with radiative forces are discussed in this review articles. Among several methods of laser cooling, it is emphasized Zeeman Tuning of the electronic levels and frequency-sweeping techniques. Trapping of neutral atoms and recent results obtained in light and magnetic traps are discussed. Techniques to further cool atoms inside traps are presented and the future of laser cooling of neutral atoms by means of radiation pressure is discussed. (A.C.A.S.) [pt

A Solid Trap and Thermal Desorption System with Application to a Medical Electronic Nose

Directory of Open Access Journals (Sweden)

Xuntao Xu

2008-11-01

Full Text Available In this paper, a solid trap/thermal desorption-based odorant gas condensation system has been designed and implemented for measuring low concentration odorant gas. The technique was successfully applied to a medical electronic nose system. The developed system consists of a flow control unit, a temperature control unit and a sorbent tube. The theoretical analysis and experimental results indicate that gas condensation, together with the medical electronic nose system can significantly reduce the detection limit of the nose system and increase the system’s ability to distinguish low concentration gas samples. In addition, the integrated system can remove the influence of background components and fluctuation of operational environment. Even with strong disturbances such as water vapour and ethanol gas, the developed system can classify the test samples accurately.

Pumped helium system for cooling positron and electron traps to 1.2 K

CERN Document Server

Wrubel, J; Kolthammer, W S; Larochelle, P; McConnell, R; Richerme, P; Grzonka, D; Oelert, W; Sefzick, T; Zielinski, M; Borbely, J S; George, M C; Hessels, E A; Storry, C H; Weel, M; Mullers, A; Walz, J; Speck, A

2011-01-01

Extremely precise tests of fundamental particle symmetries should be possible via laser spectroscopy of trapped antihydrogen ((H) over bar) atoms. (H) over bar atoms that can be trapped must have an energy in temperature units that is below 0.5 K-the energy depth of the deepest magnetic traps that can currently be constructed with high currents and superconducting technology. The number of atoms in a Boltzmann distribution with energies lower than this trap depth depends sharply upon the temperature of the thermal distribution. For example, ten times more atoms with energies low enough to be trapped are in a thermal distribution at a temperature of 1.2 K than for a temperature of 4.2 K. To date, (H) over bar atoms have only been produced within traps whose electrode temperature is 4.2 K or higher. A lower temperature apparatus is desirable if usable numbers of atoms that can be trapped are to eventually be produced. This report is about the pumped helium apparatus that cooled the trap electrodes of an (H) ove...

Numerical experiments on charging of a spherical body in a plasma with Maxwellian distributions of charged particles

Science.gov (United States)

Krasovsky, Victor L.; Kiselyov, Alexander A.

2017-12-01

New results of numerical simulation of collisionless plasma perturbation caused by a sphere absorbing electrons and ions are presented. Consideration is given to nonstationary phenomena accompanying the process of charging as well as to plasma steady state reached at long times. Corresponding asymptotic values of charges of the sphere and trapped-ion cloud around it have been found along with self-consistent electric field pattern depending on parameters of the unperturbed plasma. It is established that contribution of the trapped ions to screening of the charged sphere can be quite significant, so that the screening becomes essentially nonlinear in nature. A simple interconnection between the sphere radius, electron and ion Debye lengths has been revealed as the condition for maximum trapped-ion effect. Kinetic structure of the space charge induced in the plasma is discussed with relation to the specific form of the unperturbed charged particle distribution functions.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

International Nuclear Information System (INIS)

Anand, M. J.; Ng, G. I.; Syamal, B.; Zhou, X.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.

2015-01-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-R DS[ON] ) and threshold-voltage shift (ΔV th ) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I DS -V DS ) and drain current (I D ) transients. Different EF was realized with devices of different gate-drain spacing (L gd ) under the same OFF-state stress. Under high-EF (L gd  = 2 μm), the devices exhibited higher dyn-R DS[ON] degradation but a small ΔV th (∼120 mV). However, at low-EF (L gd  = 5 μm), smaller dyn-R DS[ON] degradation but a larger ΔV th (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R DS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔV th . A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I D -transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations

Electron Spin Resonance study of charge trapping in α-ZnMoO.sub.4./sub. single crystal scintillator

Czech Academy of Sciences Publication Activity Database

Buryi, Maksym; Spassky, D.A.; Hybler, Jiří; Laguta, Valentyn; Nikl, Martin

2015-01-01

Roč. 47, Sep (2015), 244-250 ISSN 0925-3467 R&D Projects: GA MŠk LO1409; GA MŠk(CZ) LM2011029; GA ČR GAP204/12/0805 Institutional support: RVO:68378271 Keywords : Electron Spin Resonance * scintillator * charge traps * zinc molybdate Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.183, year: 2015

Trapping processes in CaS:Eu2+,Tm3+

International Nuclear Information System (INIS)

Jia, Dongdong; Jia, Weiyi; Evans, D. R.; Dennis, W. M.; Liu, Huimin; Zhu, Jing; Yen, W. M.

2000-01-01

CaS:Eu 2+ ,Tm 3+ is a persistent red phosphor. Thermoluminescence was measured under different excitation and thermal treatment conditions. The results reveal that the charge defects, created by substituting Tm 3+ for Ca 2+ , serve as hole traps for the afterglow at room temperature. Tm 3+ plays the role of deep electron trapping centers, capturing electrons either through the conduction band or directly from the excited Eu 2+ ions. These two processes, in which two different sites of Tm 3+ are involved, correspond to two traps with different depths. (c) 2000 American Institute of Physics

Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

Science.gov (United States)

Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

2005-01-01

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This

A conservative scheme of drift kinetic electrons for gyrokinetic simulation of kinetic-MHD processes in toroidal plasmas

Science.gov (United States)

Bao, J.; Liu, D.; Lin, Z.

2017-10-01

A conservative scheme of drift kinetic electrons for gyrokinetic simulations of kinetic-magnetohydrodynamic processes in toroidal plasmas has been formulated and verified. Both vector potential and electron perturbed distribution function are decomposed into adiabatic part with analytic solution and non-adiabatic part solved numerically. The adiabatic parallel electric field is solved directly from the electron adiabatic response, resulting in a high degree of accuracy. The consistency between electrostatic potential and parallel vector potential is enforced by using the electron continuity equation. Since particles are only used to calculate the non-adiabatic response, which is used to calculate the non-adiabatic vector potential through Ohm's law, the conservative scheme minimizes the electron particle noise and mitigates the cancellation problem. Linear dispersion relations of the kinetic Alfvén wave and the collisionless tearing mode in cylindrical geometry have been verified in gyrokinetic toroidal code simulations, which show that the perpendicular grid size can be larger than the electron collisionless skin depth when the mode wavelength is longer than the electron skin depth.

Electron Cloud Generation and Trapping in a Quadrupole Magnet at the Los Alamos Proton Storage Ring

International Nuclear Information System (INIS)

Macek, Robert J.; Browman, Andrew A.; Ledford, John E.; TechSource, Santa Fe; Los Alamos; Borden, Michael J.; O'Hara, James F.; McCrady, Rodney C.; Rybarcyk, Lawrence J.; Spickermann, Thomas; Zaugg, Thomas J.; Pivi, Mauro T.F.

2008-01-01

Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the 'prompt' electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the 'swept' electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100 (micro)s. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole

Electron cloud generation and trapping in a quadrupole magnet at the Los Alamos proton storage ring

Directory of Open Access Journals (Sweden)

Robert J. Macek

2008-01-01

Full Text Available Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the “prompt” electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the “swept” electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100  μs. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole.

Noncoplanar magnetic fields at collisionless shocks: A test of a new approach

International Nuclear Information System (INIS)

Gosling, J.T.; Winske, D.; Thomsen, M.F.

1988-01-01

Within the foot and ramp of a fast mode collisionless shock the magnetic field rotates out of the plane of coplanarity defined by the upstream magnetic field and the shock normal. As previously noted (Goodrich and Scudder, 1984), the sense of this rotation is such as to reduce the cross-shock potential drop when measured in the deHoffman-Teller frame relative to that measured in the normal incidence frame. From a consideration of the requirement that there be zero current in the coplanarity plane downstream of the shock, Jones and Ellison (1987) have argued that the field rotation and potential drop difference are a consequence of unequal ion and electron masses, and have derived an expression for the spatial integral of the noncoplanar field component in terms of the electron current within the shock layer. Moreover, by assuming that the ion current within the shock layer is negligible compared to the electron current, they derive equations which predict the magnitude of both the field rotation and the potential drop difference in terms of upstream quantities and the field jump at the shock. We have tested their equations with ISEE 1 and 2 plasma and field measurements at the Earth's bow shock and by means of numerical simulations. We find substantial support for their suggestion that the field rotation and thus also the frame dependence of the potential drop are fundamentally a consequence of unequal ion and electron masses. Further, for subcritical shocks (low Mach number) one can neglect the ion current to predict both the sign and the magnitude of the field rotation and potential drop difference. However, at supercritical shocks (high Mach numbers) the ion current associated with reflected, gyrating ions cannot be neglected, and the final equations of Jones and Ellison seriously underestimate the magnitude of the field rotation and the potential drop difference at these shocks

DICE/ColDICE: 6D collisionless phase space hydrodynamics using a lagrangian tesselation

Science.gov (United States)

Sousbie, Thierry

2018-01-01

DICE is a C++ template library designed to solve collisionless fluid dynamics in 6D phase space using massively parallel supercomputers via an hybrid OpenMP/MPI parallelization. ColDICE, based on DICE, implements a cosmological and physical VLASOV-POISSON solver for cold systems such as dark matter (CDM) dynamics.

Co-existence of free and self-trapped excitons in J-aggregates

International Nuclear Information System (INIS)

Malyukin, Yu.V.; Lebedenko, A.N.; Sorokin, A.V.; Yefimova, S.L.

2005-01-01

Nature of excited electronic states of amphi-PIC J-aggregates, which are the source of the self-trapping states, have been investigated using low-temperature site-selective, time-resolved spectroscopy techniques. The self-trapping states are shown to evolve from the delocalized exciton states within the J-band. The strongly localized electronic states located on the low-frequency edge of the J-band, are not able to form polaronic states and, hence, the polaronic relaxation process is particularly collective one. The exciton self-trapping is more effective in J-aggregates with strong disorder, requires overcoming a self-trapping barrier

Subcritical collisionless shock waves. [in earth space plasma

Science.gov (United States)

Mellott, M. M.

1985-01-01

The development history of theoretical accounts of low Mach number collisionless shock waves is related to recent observational advancements, with attention to weaker shocks in which shock steepening is limited by dispersion and/or anomalous resistivity and whose character is primarily determined by the dispersive properties of the ambient plasma. Attention has focused on nearly perpendicular shocks where dispersive scale lengths become small and the associated cross-field currents become strong enough to generate significant plasma wave turbulence. A number of oblique, low Mach number bow shocks have been studied on the basis of data from the ISEE dual spacecraft pair, allowing an accurate determination of shock scale lengths.

Resonant ion acceleration by collisionless magnetosonic shock waves

International Nuclear Information System (INIS)

Ohsawa, Y.

1985-01-01

Resonant ion acceleration ( the ν/sub rho/xΒ acceleration ) in laminar magnetosonic shock waves is studied by theory and simulation. Theoretical analysis based on a two-fluid model shows that, in laminar shocks, the electric field strength in the direction of the wave normal is about (m/sub i/m/sub e/) 1 2 times large for quasi-perpendicular shocks than that for the quasi-parallel shocks, which is a reflection of the fact that the width of quasi-perpendicular shocks is much smaller than that of the quasi-parallel shocks. Trapped ions can be accelerated up to the speed about ν/sub A/(m/sub i/m/sub e/) 1 2(M/sub A/-1) 3 2 in quasi-perpendicular shocks. Time evolution of self-consistent magnetosonic shock waves is studied by using a 2-12 dimensional fully relativistic, fully electromagnetic particle simulation with full ion and electron dynamics. Even a low-Mach-number shock wave can significantly accelerate trapped ions by the ν/sub rho/xΒ acceleration. The resonant ion acceleration occurs more strongly in quasi-perpendicular shocks, because the magnitude of this acceleration is proportional to the electric field strength

Nested Penning Trap as a Source of Singly Charged Ions

International Nuclear Information System (INIS)

Ordonez, C.A.

2003-01-01

In the work reported, the possibility of using a nested Penning trap as a high purity source of low-charge-state ions is studied. For the configuration considered, a relatively dense ion plasma is confined by a three-dimensional electric potential well. The three-dimensional well is produced by the electric field generated by both the trap electrodes and a trapped electron plasma. The ion and electron plasmas are each considered to have Maxwellian velocity distributions. However, it is shown that the electron plasma must have a temperature that is higher than that of the ion plasma when the ions have low charge states. The work reported includes a self-consistent prediction of a possible plasma equilibrium

An active trap filter for high-power voltage source converters

DEFF Research Database (Denmark)

Bai, Haofeng; Wang, Xiongfei; Loh, Poh Chiang

2015-01-01

This paper proposes a power electronic based device to actively trap the switching current ripples for highpower converters. Control principle and system design of the active trap filter are discussed first. Comparisons of the active trap filter with LCL and LLCL filters are then carried out...

Trapping of deuterium in krypton-implanted nickel

International Nuclear Information System (INIS)

Frank, R.C.; McManus, S.P.; Rehn, L.E.; Baldo, P.

1986-01-01

Krypton ions with energy 600 keV were implanted in nickel to fluences of 2 x 10 16 cm -2 under three different conditions. Deuterium was subsequently introduced into the implanted regions by electrolysis at room temperature. After the diffusible deuterium was permitted to escape, the 2 H( 3 He, 1 H) 4 He nuclear reaction was used to analyze for the trapped deuterium during an isochronal annealing program. The region implanted at 100 0 C with no higher temperature anneal had the largest number of traps; the region implanted at 100 0 C and annealed for 100 min at 500 0 C had considerably less; the region implanted at 500 0 C had the least. Electron diffraction patterns confirmed the existence of solid crystalline krypton in all three regions. Transmission electron microscope studies revealed precipitates with an average diameter of 8 nm in the region implanted at 500 0 C. The two regions implanted at 100 0 C contained smaller precipitates. Trap binding enthalpies were obtained by math modeling. In addition to the traps with binding enthalpy of 0.55 eV reported earlier by other investigators for helium implanted in nickel, a smaller number of traps with binding enthalpies up to 0.83 eV were also found. The trapping of deuterium by various types of imperfections, including the solid krypton precipitates, is discussed

Geometry and electronic structure of an impurity-trapped exciton in the Cs2GeF6 crystal doped with U4+. The 5f17s1 manifold

International Nuclear Information System (INIS)

Ordejon, B.; Seijo, L.; Barandiaran, Z.

2007-01-01

Complete text of publication follows: Excitons trapped at impurity centres in highly ionic crystals were first described by McClure and Pedrini [Phys. Rev. B 32, 8465 (1985)] as excited states consisting of a bound electron-hole pair with the hole localized on the impurity and the electron on nearby lattice sites, and a very short impurity-ligand bond length. In this work we present a detailed microscopic characterization of an impurity - trapped exciton in Cs 2 GeF 6 doped with U 4+ . Its electronic structure has been studied by means of CASSCF/CASPT2/SOCI relativistic ab initio model potential (AIMP) embedded-cluster calculations on (UF 6 ) 2- and (UF 6 Cs 8 ) 6+ clusters embedded in Cs 2 GeF 6 . The local geometry of the impurity-trapped exciton, the potential energy curves, and the multi electronic wavefunctions, have been obtained as direct, non-empirical results of the methods. The calculated excited states appear to be significantly delocalized outside the UF 6 volume and their U-F bond length turns out to be very short, closer to that of a pentavalent uranium defect than to that of a tetravalent uranium defect. The wavefunctions of these excited states show a dominant U 5f 1 7s 1 configuration character. This result has never been anticipated by simpler models and reveals the unprecedented ability of diffuse orbitals of f-element impurities to act as electron traps in ionic crystals

How to Patch Active Plasma and Collisionless Sheath: Practical Guide