Excitation and Propagation of Alfven Waves in a Helicon Discharge
International Nuclear Information System (INIS)
Grulke, Olaf; Klinger, Thomas; Franck, Christian M.
2003-01-01
An experimental study of shear Alfven waves in a linearly magnetized plasma is presented. Shear Alfven waves are electromagnetic waves propagating parallel to the background magnetic field without compression of the plasma at a frequency well below the ion cyclotron frequency and a wavelength inversely proportional to the square root of the plasma density. A basic condition on laboratory investigations is that the Alfven wavelength must be significantly smaller than the device dimension. This makes Alfven waves difficult to investigate in laboratory experiments and most studies are performed in space, where typical Alfven wavelengths of several kilometers are observed. The results of these studies are often ambiguous due to difficulties concerning the measurements of plasma parameters and the magnetic field geometry. The primary motivation for the present paper is the investigation of Alfven wave propagation in a well defined laboratory situation. The experiments are conducted in the linear VINETA device. The necessary operational regime is achieved by the large axial device length of 4.5m and the use of a helicon plasma source providing high density plasmas with ionization degrees of up to 100%. The Argon plasma is magnetized by a set of 36 magnetic field coils, which produce a maximum magnetic field of 0.1T on the device axis. With this configuration a plasma-β of ≥ 10-4 is achieved, which exceeds the electron to ion mass ration, and the ion cyclotron frequency is ≅ 250kHz. Langmuir probes provide detailed informations on the time-averaged plasma profiles. Magnetic field perturbations for the excitation of Alfven waves are generated by a current loop, which is introduced into the plasma. The surface normal of the current loop is directed perpendicular to the magnetic field. The waves's dispersion relation in dependence of plasma parameters is determined by spatially resolved B probe measurements
Excitation and absorption of electromagnetic waves in helicon discharges by plasma immersed antennas
International Nuclear Information System (INIS)
Cho, S.
1998-01-01
Excitation and absorption of electromagnetic waves are numerically studied for helicon discharges driven by antennas immersed in the plasma. The Maxwell equations are reduced to a set of ordinary differential equations, which are solved for radially inhomogeneous plasmas by using the shooting method. Numerical results show that the plasma resistance is much larger and its peaks due to eigenmode resonance appear at higher densities for the immersed antenna case than for the case of the antenna located outside the plasma under otherwise same conditions. It is also found that the m=-1 mode can be excited in the nonuniform plasma with an inner antenna, while it can be hardly excited when the plasma is driven by an outer antenna. In addition, the fast wave approximation neglecting the electron inertia is discussed. (author)
Plasma production from helicon waves
International Nuclear Information System (INIS)
Degeling, A.W.; Jung, C.O.; Boswell, R.W.; Ellingboe, A.R.
1996-01-01
Experimental measurements taken in a large magnetoplasma show that a simple double half-turn antenna will excite m=1 helicon waves with wavelengths from 10 endash 60 cm. Increased ionization in the center of the downstream plasma is measured when the axial wavelength of the helicon wave becomes less than the characteristic length of the system, typically 50 endash 100 cm. A sharp maximum in the plasma density downstream from the source is measured for a magnetic field of 50 G, where the helicon wave phase velocity is about 3x10 8 cms -1 . Transport of energy away from the source to the downstream region must occur to create the hot electrons needed for the increased ionization. A simple model shows that electrons in a Maxwellian distribution most likely to ionize for these experimental conditions also have a velocity of around 3x10 8 cms -1 . This strong correlation suggests that the helicon wave is trapping electrons in the Maxwellian distribution with velocities somewhat slower than the wave and accelerating them into a quasibeam with velocity somewhat faster than the wave. The nonlinear increase in central density downstream as the power is increased for helicon waves with phase velocities close to the optimum electron velocity for ionization lends support to this idea. copyright 1996 American Institute of Physics
International Nuclear Information System (INIS)
Lorenz, B; Kraemer, M; Selenin, V L; Aliev, Yu M
2005-01-01
The helicon wave field and the excitation of short-scale electrostatic fluctuations in a helicon-produced plasma are closely related as both the helicon wave damping and the fluctuation level are shown to increase with the launched rf power. Correlation methods using electrostatic probes as well as microwave back-scattering at the upper-hybrid resonance are applied to obtain the dispersion relations of the fluctuations in the low-frequency and high-frequency ranges. The frequency and wavenumber spectra measured for all components of the wave vector allow us to identify the fluctuations as ion-sound and Trivelpiece-Gould waves that originate from parametric decay of the helicon pump wave. The growth rates and thresholds inferred from the evolution of the fluctuations in a wide range of helicon plasma parameters are in good agreement with predictions for the parametric decay instability that takes into account realistic damping rates for the decay waves as well as non-vanishing parallel wavenumber of the helicon pump
On helicon wave induced radial plasma transport
International Nuclear Information System (INIS)
Petrzilka, V.
1993-04-01
Estimates of helicon wave induced radial plasma transport are presented. The wave induced transport grows or decreases in dependence on the sign of the azimuthal wave number; these changes in transport may play an important role in helicon wave plasma sources. (author) 5 figs., 18 refs
Helicons in uniform fields. I. Wave diagnostics with hodograms
Urrutia, J. M.; Stenzel, R. L.
2018-03-01
The wave equation for whistler waves is well known and has been solved in Cartesian and cylindrical coordinates, yielding plane waves and cylindrical waves. In space plasmas, waves are usually assumed to be plane waves; in small laboratory plasmas, they are often assumed to be cylindrical "helicon" eigenmodes. Experimental observations fall in between both models. Real waves are usually bounded and may rotate like helicons. Such helicons are studied experimentally in a large laboratory plasma which is essentially a uniform, unbounded plasma. The waves are excited by loop antennas whose properties determine the field rotation and transverse dimensions. Both m = 0 and m = 1 helicon modes are produced and analyzed by measuring the wave magnetic field in three dimensional space and time. From Ampère's law and Ohm's law, the current density and electric field vectors are obtained. Hodograms for these vectors are produced. The sign ambiguity of the hodogram normal with respect to the direction of wave propagation is demonstrated. In general, electric and magnetic hodograms differ but both together yield the wave vector direction unambiguously. Vector fields of the hodogram normal yield the phase flow including phase rotation for helicons. Some helicons can have locally a linear polarization which is identified by the hodogram ellipticity. Alternatively the amplitude oscillation in time yields a measure for the wave polarization. It is shown that wave interference produces linear polarization. These observations emphasize that single point hodogram measurements are inadequate to determine the wave topology unless assuming plane waves. Observations of linear polarization indicate wave packets but not plane waves. A simple qualitative diagnostics for the wave polarization is the measurement of the magnetic field magnitude in time. Circular polarization has a constant amplitude; linear polarization results in amplitude modulations.
Modeling ionization by helicon waves
International Nuclear Information System (INIS)
Degeling, A.W.; Boswell, R.W.
1997-01-01
The response of the electron distribution function in one dimension to a traveling wave electric field is modeled for parameters relevant to a low-pressure helicon wave plasma source, and the resulting change in the ionization rate calculated. This is done by calculating the trajectories of individual electrons in a given wave field and assuming no collisions to build up the distribution function as the distance from the antenna is increased. The ionization rate is calculated for argon by considering the ionization cross section and electron flux at a specified position and time relative to the left-hand boundary, where the distribution function is assumed to be Maxwellian and the wave travels to the right. The simulation shows pulses in the ionization rate that move away from the antenna at the phase velocity of the wave, demonstrating the effect of resonant electrons trapped in the wave close-quote s frame of reference. It is found that the ionization rate is highest when the phase velocity of the wave is between 2 and 3x10 6 m/s, where the electrons interacting strongly with the wave (i.e., electrons with velocities inside the wave close-quote s open-quotes trapping widthclose quotes) have initial energies just below the ionization threshold. Results from the model are compared with experimental data and show reasonable qualitative agreement. copyright 1997 American Institute of Physics
Helicon wave coupling to a chiral-plasma column
International Nuclear Information System (INIS)
Torres-Silva, H.; Reggiani, N.; Sakanaka, P.H.
1995-01-01
Inductive helicon wave coupling to a chiro-plasma column is studied numerically. In our theoretical model, the RF current distribution of the chiro-plasma is taken into account using the constitutive relations of a chiral-plasma. Computational results based on the data of present-day helicon devices are show. In particular, we discuss the role of magnetic-field-aligned electron landau damping for the helicon wave absorption. In many a see, the numerical findings can be understood reasonably in terms of the wavenumber spectra of the helicon wave dispersion relation for slow and fast wave of a chiral-plasma. In general however, the full electromagnetic treatment is necessary in order to describe and to understand the inductive coupling in the helicon wave regime. (author). 9 refs., 1 fig
Variations of helicon wave induced radial plasma transport in different experimental conditions
International Nuclear Information System (INIS)
Petrzilka, V.
1993-08-01
Variations of the helicon wave induced radial plasma transport are presented in dependence on values of the plasma radius, magnetostatic field, plasma density, frequency of the helicon wave and on the ion charge. 22 refs., 14 figs
Wave propagation downstream of a high power helicon in a dipolelike magnetic field
International Nuclear Information System (INIS)
Prager, James; Winglee, Robert; Roberson, B. Race; Ziemba, Timothy
2010-01-01
The wave propagating downstream of a high power helicon source in a diverging magnetic field was investigated experimentally. The magnetic field of the wave has been measured both axially and radially. The three-dimensional structure of the propagating wave is observed and its wavelength and phase velocity are determined. The measurements are compared to predictions from helicon theory and that of a freely propagating whistler wave. The implications of this work on the helicon as a thruster are also discussed.
Using AORSA to simulate helicon waves in DIII-D
International Nuclear Information System (INIS)
Lau, C.; Blazevski, D.; Green, D. L.; Murakami, M.; Park, J. M.; Jaeger, E. F.; Berry, L. A.; Bertelli, N.; Pinsker, R. I.; Prater, R.
2015-01-01
Recent efforts have shown that helicon waves (fast waves at > 20ω ci ) may be an attractive option for driving efficient off-axis current drive during non-inductive tokamak operation for DIII-D, ITER and DEMO. For DIII-D scenarios, the ray tracing code, GENRAY, has been extensively used to study helicon current drive efficiency and location as a function of many plasma parameters. The full wave code, AORSA, which is applicable to arbitrary Larmor radius and can resolve arbitrary ion cyclotron harmonic order, has been recently used to validate the ray tracing technique at these high cyclotron harmonics. If the SOL is ignored, it will be shown that the GENRAY and AORSA calculated current drive profiles are comparable for the envisioned high beta advanced scenarios for DIII-D, where there is high single pass absorption due to electron Landau damping and minimal ion damping. AORSA is also been used to estimate possible SOL effects on helicon current drive coupling and SOL absorption due to collisional and slow wave effects
Using AORSA to simulate helicon waves in DIII-D
Energy Technology Data Exchange (ETDEWEB)
Lau, C., E-mail: lauch@ornl.gov; Blazevski, D.; Green, D. L.; Murakami, M.; Park, J. M. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN (United States); Jaeger, E. F.; Berry, L. A. [XCEL Engineering, Inc., 1066 Commerce Park Dr., Oak Ridge, TN (United States); Bertelli, N. [Princeton Plasma Physics Laboratory, Princeton, NJ (United States); Pinsker, R. I.; Prater, R. [General Atomics, San Diego, CA (United States)
2015-12-10
Recent efforts have shown that helicon waves (fast waves at > 20ω{sub ci}) may be an attractive option for driving efficient off-axis current drive during non-inductive tokamak operation for DIII-D, ITER and DEMO. For DIII-D scenarios, the ray tracing code, GENRAY, has been extensively used to study helicon current drive efficiency and location as a function of many plasma parameters. The full wave code, AORSA, which is applicable to arbitrary Larmor radius and can resolve arbitrary ion cyclotron harmonic order, has been recently used to validate the ray tracing technique at these high cyclotron harmonics. If the SOL is ignored, it will be shown that the GENRAY and AORSA calculated current drive profiles are comparable for the envisioned high beta advanced scenarios for DIII-D, where there is high single pass absorption due to electron Landau damping and minimal ion damping. AORSA is also been used to estimate possible SOL effects on helicon current drive coupling and SOL absorption due to collisional and slow wave effects.
Experimental measurements of Helicon wave coupling in KSTAR plasmas
Energy Technology Data Exchange (ETDEWEB)
Kim, H. J.; Wi, H. H.; Wang, S. J.; Park, S. Y.; Jeong, J. H.; Han, J. W.; Kwak, J. G.; Oh, Y. K. [National Fusion Research Institute, Daejeon (Korea, Republic of); Chun, M. H.; Yu, I. H. [Pohang Accelerator Laboratory, Pohang (Korea, Republic of)
2016-05-15
KSTAR tokamak can be a good platform to test this current drive concept because it has adequate machine parameters. Furthermore, KSTAR will have high electron beta plasmas in near future with additional ECH power. In 2015 KSTAR experiments, low-power traveling wave antenna has been designed, fabricated and installed for helicon wave coupling tests in KSTAT plasmas. In 2016 KSTAR campaign, 200 kW klystron power will be combined using three coaxial hybrid couplers and three dummy loads. High power RF will be fed into the traveling wave antenna with two coaxial feeders through two dual disk windows and 6 inch coaxial transmission line system. Current status and plan for high power helicon wave current drive system in KSTAR will be presented. Mock-up TWA antenna installed at the KSTAR reveals high couplings in both L- and H-mode plasmas. The coupling can be easily controlled by radial outer gap without degradation of plasma confinement or local gas puffing with slight decrease of plasma confinement.
Helicon wave field measurements in Proto-MPEX
Caneses, Juan Francisco; Piotrowicz, Pawel; Goulding, Richard; Caughman, John; Showers, Missy; Kafle, Nischal; Rapp, Juergen; Campbell, Ian; Proto-MPEX Team
2016-10-01
A high density Deuterium discharge (ne 5e19 m-3, Te 4 eV) has been recently observed in ProtoMPEX (Prototype Material Plasma Exposure eXperiment). The discharge (100 kW, 13.56 MHz, D2, 700 G at the source, 1e4 G at the Target) begins with a low density plasma with hollow Te profile and transitions in about 100 ms to a high density mode with flat Te profile. It is believed that the transition to the high density mode is produced by a ``helicon resonance'' as evidenced by the centrally-peaked power deposition profile observed with IR imaging on a 2 mm thick metallic target plate. In this work, we present b-dot probe measurements of the radial helicon wavefields 30 cm downstream of the antenna during both the low and high density modes. In addition, we compare the experimental results with full wave simulations. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.
Vdovin, V.
2014-02-01
The Innovative concept and 3D full wave code modeling Off-axis current drive by RF waves in large scale tokamaks, reactors FNSF-AT, ITER and DEMO for steady state operation with high efficiency was proposed [1] to overcome problems well known for LH method [2]. The scheme uses the helicons radiation (fast magnetosonic waves at high (20-40) IC frequency harmonics) at frequencies of 500-1000 MHz, propagating in the outer regions of the plasmas with a rotational transform. It is expected that the current generated by Helicons will help to have regimes with negative magnetic shear and internal transport barrier to ensure stability at high normalized plasma pressure βN > 3 (the so-called Advanced scenarios) of interest for FNSF and the commercial reactor. Modeling with full wave three-dimensional codes PSTELION and STELEC2 showed flexible control of the current profile in the reactor plasmas of ITER, FNSF-AT and DEMO [2,3], using multiple frequencies, the positions of the antennae and toroidal waves slow down. Also presented are the results of simulations of current generation by helicons in tokamaks DIII-D, T-15MD and JT-60SA [3]. In DEMO and Power Plant antenna is strongly simplified, being some analoge of mirrors based ECRF launcher, as will be shown. For spherical tokamaks the Helicons excitation scheme does not provide efficient Off-axis CD profile flexibility due to strong coupling of helicons with O-mode, also through the boundary conditions in low aspect machines, and intrinsic large amount of trapped electrons, as is shown by STELION modeling for the NSTX tokamak. Brief history of Helicons experimental and modeling exploration in straight plasmas, tokamaks and tokamak based fusion Reactors projects is given, including planned joint DIII-D - Kurchatov Institute experiment on helicons CD [1].
Energy Technology Data Exchange (ETDEWEB)
Vdovin, V. [NRC Kurchatov Institute Tokamak Physics Institute, Moscow (Russian Federation)
2014-02-12
The Innovative concept and 3D full wave code modeling Off-axis current drive by RF waves in large scale tokamaks, reactors FNSF-AT, ITER and DEMO for steady state operation with high efficiency was proposed [1] to overcome problems well known for LH method [2]. The scheme uses the helicons radiation (fast magnetosonic waves at high (20–40) IC frequency harmonics) at frequencies of 500–1000 MHz, propagating in the outer regions of the plasmas with a rotational transform. It is expected that the current generated by Helicons will help to have regimes with negative magnetic shear and internal transport barrier to ensure stability at high normalized plasma pressure β{sub N} > 3 (the so-called Advanced scenarios) of interest for FNSF and the commercial reactor. Modeling with full wave three-dimensional codes PSTELION and STELEC2 showed flexible control of the current profile in the reactor plasmas of ITER, FNSF-AT and DEMO [2,3], using multiple frequencies, the positions of the antennae and toroidal waves slow down. Also presented are the results of simulations of current generation by helicons in tokamaks DIII-D, T-15MD and JT-60SA [3]. In DEMO and Power Plant antenna is strongly simplified, being some analoge of mirrors based ECRF launcher, as will be shown. For spherical tokamaks the Helicons excitation scheme does not provide efficient Off-axis CD profile flexibility due to strong coupling of helicons with O-mode, also through the boundary conditions in low aspect machines, and intrinsic large amount of trapped electrons, as is shown by STELION modeling for the NSTX tokamak. Brief history of Helicons experimental and modeling exploration in straight plasmas, tokamaks and tokamak based fusion Reactors projects is given, including planned joint DIII-D – Kurchatov Institute experiment on helicons CD [1].
Waves generated in the plasma plume of helicon magnetic nozzle
International Nuclear Information System (INIS)
Singh, Nagendra; Rao, Sathyanarayan; Ranganath, Praveen
2013-01-01
Experimental measurements have shown that the plasma plume created in a helicon plasma device contains a conical structure in the plasma density and a U-shaped double layer (US-DL) tightly confined near the throat where plasma begins to expand from the source. Recently reported two-dimensional particle-in-cell simulations verified these density and US-DL features of the plasma plume. Simulations also showed that the plasma in the plume develops non-thermal feature consisting of radial ion beams with large densities near the conical surface of the density structure. The plasma waves that are generated by the radial ion beams affecting the structure of the plasma plume are studied here. We find that most intense waves persist in the high-density regions of the conical density structure, where the transversely accelerated ions in the radial electric fields in the plume are reflected setting up counter-streaming. The waves generated are primarily ion Bernstein modes. The nonlinear evolution of the waves leads to magnetic field-aligned striations in the fields and the plasma near the conical surface of the density structure.
Waves generated in the plasma plume of helicon magnetic nozzle
Energy Technology Data Exchange (ETDEWEB)
Singh, Nagendra; Rao, Sathyanarayan; Ranganath, Praveen [Department of Electrical and Computer Engineering, University of Alabama, Huntsville, Alabama 35899 (United States)
2013-03-15
Experimental measurements have shown that the plasma plume created in a helicon plasma device contains a conical structure in the plasma density and a U-shaped double layer (US-DL) tightly confined near the throat where plasma begins to expand from the source. Recently reported two-dimensional particle-in-cell simulations verified these density and US-DL features of the plasma plume. Simulations also showed that the plasma in the plume develops non-thermal feature consisting of radial ion beams with large densities near the conical surface of the density structure. The plasma waves that are generated by the radial ion beams affecting the structure of the plasma plume are studied here. We find that most intense waves persist in the high-density regions of the conical density structure, where the transversely accelerated ions in the radial electric fields in the plume are reflected setting up counter-streaming. The waves generated are primarily ion Bernstein modes. The nonlinear evolution of the waves leads to magnetic field-aligned striations in the fields and the plasma near the conical surface of the density structure.
AORSA full wave calculations of helicon waves in DIII-D and ITER
Lau, C.; Jaeger, E. F.; Bertelli, N.; Berry, L. A.; Green, D. L.; Murakami, M.; Park, J. M.; Pinsker, R. I.; Prater, R.
2018-06-01
Helicon waves have been recently proposed as an off-axis current drive actuator for DIII-D, FNSF, and DEMO tokamaks. Previous ray tracing modeling using GENRAY predicts strong single pass absorption and current drive in the mid-radius region on DIII-D in high beta tokamak discharges. The full wave code AORSA, which is valid to all order of Larmor radius and can resolve arbitrary ion cyclotron harmonics, has been used to validate the ray tracing technique. If the scrape-off-layer (SOL) is ignored in the modeling, AORSA agrees with GENRAY in both the amplitude and location of driven current for DIII-D and ITER cases. These models also show that helicon current drive can possibly be an efficient current drive actuator for ITER. Previous GENRAY analysis did not include the SOL. AORSA has also been used to extend the simulations to include the SOL and to estimate possible power losses of helicon waves in the SOL. AORSA calculations show that another mode can propagate in the SOL and lead to significant (~10%–20%) SOL losses at high SOL densities. Optimizing the SOL density profile can reduce these SOL losses to a few percent.
Helicon normal modes in Proto-MPEX
Piotrowicz, P. A.; Caneses, J. F.; Green, D. L.; Goulding, R. H.; Lau, C.; Caughman, J. B. O.; Rapp, J.; Ruzic, D. N.
2018-05-01
The Proto-MPEX helicon source has been operating in a high electron density ‘helicon-mode’. Establishing plasma densities and magnetic field strengths under the antenna that allow for the formation of normal modes of the fast-wave are believed to be responsible for the ‘helicon-mode’. A 2D finite-element full-wave model of the helicon antenna on Proto-MPEX is used to identify the fast-wave normal modes responsible for the steady-state electron density profile produced by the source. We also show through the simulation that in the regions of operation in which core power deposition is maximum the slow-wave does not deposit significant power besides directly under the antenna. In the case of a simulation where a normal mode is not excited significant edge power is deposited in the mirror region. ).
Helicon modes in uniform plasmas. III. Angular momentum
International Nuclear Information System (INIS)
Stenzel, R. L.; Urrutia, J. M.
2015-01-01
Helicons are electromagnetic waves with helical phase fronts propagating in the whistler mode in magnetized plasmas and solids. They have similar properties to electromagnetic waves with angular momentum in free space. Helicons are circularly polarized waves carrying spin angular momentum and orbital angular momentum due to their propagation around the ambient magnetic field B 0 . These properties have not been considered in the community of researchers working on helicon plasma sources, but are the topic of the present work. The present work focuses on the field topology of helicons in unbounded plasmas, not on helicon source physics. Helicons are excited in a large uniform laboratory plasma with a magnetic loop antenna whose dipole axis is aligned along or across B 0 . The wave fields are measured in orthogonal planes and extended to three dimensions (3D) by interpolation. Since density and B 0 are uniform, small amplitude waves from loops at different locations can be superimposed to generate complex antenna patterns. With a circular array of phase shifted loops, whistler modes with angular and axial wave propagation, i.e., helicons, are generated. Without boundaries radial propagation also arises. The azimuthal mode number m can be positive or negative while the field polarization remains right-hand circular. The conservation of energy and momentum implies that these field quantities are transferred to matter which causes damping or reflection. Wave-particle interactions with fast electrons are possible by Doppler shifted resonances. The transverse Doppler shift is demonstrated. Wave-wave interactions are also shown by showing collisions between different helicons. Whistler turbulence does not always have to be created by nonlinear wave-interactions but can also be a linear superposition of waves from random sources. In helicon collisions, the linear and/or orbital angular momenta can be canceled, which results in a great variety of field topologies. The work
Spatial mode structures of electrostatic drift waves in a collisional cylindrical helicon plasma
DEFF Research Database (Denmark)
Schröder, C.; Grulke, O.; Klinger, T.
2004-01-01
In a cylindrical helicon plasma, mode structures of coherent drift waves are studied in the poloidal plane, the plane perpendicular to the ambient magnetic field. The mode structures rotate with a constant angular velocity in the direction of the electron diamagnetic drift and show significant...... radial bending. The experimental observations are compared with numerical solutions of a linear nonlocal cylindrical model for drift waves [ Ellis , Plasma Phys. 22, 113 (1980) ]. In the numerical model, a transition to bended mode structures is found if the plasma collisionality is increased....... This finding proves that the experimentally observed bended mode structures are the result of high electron collisionality. (C) 2004 American Institute of Physics....
Gap eigenmode of radially localized helicon waves in a periodic structure
International Nuclear Information System (INIS)
Chang, L; Hole, M J; Breizman, B N
2013-01-01
An ElectroMagnetic Solver (Chen et al 2006 Phys. Plasmas 13 123507) is employed to model a spectral gap and a gap eigenmode in a periodic structure in the whistler frequency range. A radially localized helicon mode (Breizman and Arefiev 2000 Phys. Rev. Lett. 84 3863) is considered. We demonstrate that the computed gap frequency and gap width agree well with a theoretical analysis, and find a discrete eigenmode inside the gap by introducing a defect to the system's periodicity. The axial wavelength of the gap eigenmode is close to twice the system's periodicity, which is consistent with Bragg's law. Such an eigenmode could be excited by energetic electrons, similar to the excitation of toroidal Alfvén eigenmodes by energetic ions in tokamaks. Experimental identification of this mode is conceivable on the large plasma device (Gekelman et al 1991 Rev. Sci. Instrum. 62 2875). (paper)
Inoue, Jun-ichi
2013-09-09
We theoretically explore the electromagnetic modes specific to a topological insulator superlattice in which topological and conventional insulator thin films are stacked periodically. In particular, we obtain analytic formulas for low energy mode that corresponds to a helicon wave, as well as those for photonic bands. We illustrate that the system can be modeled as a stack of quantum Hall layers whose conductivity tensors alternately change signs, and then we analyze the photonic band structures. This subject is a natural extension of a previous study by Tselis et al., which took into consideration a stack of identical quantum Hall layers but their discussion was limited into a low energy mode. Thus we provide analytic formulas for photonic bands and compare their features between the two systems. Our central findings in the topological insulator superlattice are that a low energy mode corresponding to a helicon wave has linear dispersion instead of the conventional quadratic form, and that a robust gapless photonic band appears although the system considered has spacial periodicity. In addition, we demonstrate that the photonic bands agree with the numerically calculated transmission spectra.
Is the bulk mode conversion important in high density helicon plasma?
Energy Technology Data Exchange (ETDEWEB)
Isayama, Shogo; Hada, Tohru [Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-Kohen, Kasuga, Fukuoka 816-8580 (Japan); Shinohara, Shunjiro [Institute of Engineering, Tokyo University of Agriculture and Technology, 2-24-16, Naka-cho, Koganei, Tokyo 184-8588 (Japan); Tanikawa, Takao [Research Institute of Science and Technology, Tokai University 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan)
2016-06-15
In a high-density helicon plasma production process, a contribution of Trivelpiece-Gould (TG) wave for surface power deposition is widely accepted. The TG wave can be excited either due to an abrupt density gradient near the plasma edge (surface conversion) or due to linear mode conversion from the helicon wave in a density gradient in the bulk region (bulk mode conversion). By numerically solving the boundary value problem of linear coupling between the helicon and the TG waves in a background with density gradient, we show that the efficiency of the bulk mode conversion strongly depends on the dissipation included in the plasma, and the bulk mode conversion is important when the dissipation is small. Also, by performing FDTD simulation, we show the time evolution of energy flux associated with the helicon and the TG waves.
Study of density jump in helicon-wave induced H2 plasma
International Nuclear Information System (INIS)
Jiang Fan; Cheng Xinlu; Xiong Zhenwei; Wu Weidong; Wang Yuying; Gao Yingxue; Dai Yang
2012-01-01
Hydrogen plasmas electron density and electron energy distribution function EEDF were studied with Langmuir probe. Two jumps were observed in the variation of the electron density with the radio frequency power. The relative intensity ratio of hydrogen plasmas spectrum line H α , H β and H γ validated this phenomenon. Two density jumps illuminated the transition of discharge mode,which labeled as capacitive, inductive and helicon-wave mode. In this work, the density jumps are explained from two sides, one is the interaction between electrons and hydrogen molecules, the other is Nagoya type III (N-type) antenna-plasma coupling. With the increase of radiofrequency power, the interaction between electron and hydrogen molecule has been enhanced which causes the electron density jumps. The antenna couples well to plasmas when transverse field E y is maximum, and the wave vector of k z locates at π/l a or 3π/l a , corresponding to the first and second density jump. (authors)
Bechert, D. W.
1982-01-01
The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.
Generation of ion-acoustic and magnetoacoustic waves in an RF helicon discharge
International Nuclear Information System (INIS)
Belov, A. S.; Markov, G. A.
2006-01-01
A study is made of the generation of ion-acoustic and magnetoacoustic waves in a discharge excited in an external magnetic field by an electromagnetic wave in the whistler frequency range (ω LH He , where ω LH = √(ω He ω Hi ) and ω He and ω Hi are the electron and ion gyrofrequencies, respectively). The excitation of acoustic waves is attributed to the decay of a high-frequency hybrid mode forming a plasma waveguide into low-frequency acoustic waves and new high-frequency waves that satisfy both the decay conditions and the waveguide dispersion relations. The excitation of acoustic waves is resonant in character because the conditions for the generation of waveguide modes and for the occurrence of the corresponding nonlinear wave processes should be satisfied simultaneously. An unexpected effect is the generation of magnetoacoustic waves by whistlers. A diagnostic technique is proposed that allows one to determine the thermal electron velocity by analyzing decay conditions and dispersion relations for waves in the discharge channel
Springing response due to bidirectional wave excitation
DEFF Research Database (Denmark)
Vidic-Perunovic, Jelena
2005-01-01
theories deal with the unidirectional wave excitation. This is quite standard. The problem is how to include more than one directional wave systems described by a wave spectrum with arbitrary heading. The main objective of the present work has been to account for the additional second-order springing......-linear (second order) high frequency springing analyses with unidirectional wave excitation are much more scattered. Some of the reasons are different level of wave excitation accounted in the different Executive Summary ivtheories, inclusion of additional hydrodynamic phenomena e.g. slamming in the time...... because, to the author's knowledge, this is the first time that the wave data were collected simultaneously with stress records on the deck of the ship. This is highly appreciated because one can use the precise input and not only the most probable sea state statistics. The actual picture of the sea waves...
Energy Technology Data Exchange (ETDEWEB)
Park, S. Y.; Kim, H. J.; Wi, H. H.; Wang, S. J.; Kwak, J. G. [NFRI, Daejeon (Korea, Republic of)
2016-05-15
200 kW RF power will be injected to plasmas through the traveling wave antenna after combining four klystrons output powers using three hybrid combiners. Each klystron produces 60 kW output at the frequency of 500 MHz. RF power combiners commonly used to divide or combine output powers for various rf and microwave applications. It is divided into several types according to the design type such as Wilkinson combiner, radial and quadrature hybrid combiner. We designed high power hybrid combiners using 6-1/8 inch coaxial line. The power combiner has many advantages such as high isolation, low insertion loss and high power handling capability. In this paper design and rf test results of high power combiners will be described. High power combiners using three coaxial hybrid couplers will be utilized for effectively combining of 500 MHz, 200 kW output powers generated by four klystrons. We have designed, fabricated, and tested a 6-1/8 inch coaxial hybrid combiners at 500 MHz for efficiently off-axis Helicon wave current drive in KSTAR. Simulation and test results of high power coaxial hybrid combiners are good agreement.
Resonant power absorption in helicon plasma sources
International Nuclear Information System (INIS)
Chen Guangye; Arefiev, Alexey V.; Bengtson, Roger D.; Breizman, Boris N.; Lee, Charles A.; Raja, Laxminarayan L.
2006-01-01
Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon (RLH) waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two-dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m=1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant power absorption, associated with the RLH eigenmode, accounts for most of the rf power deposited into the plasma in the experiment
Selective Coherent Excitation of Charged Density Waves
Tsvetkov, A.A.; Sagar, D.M.; Loosdrecht, P.H.M. van; Marel, D. van der
2003-01-01
Real time femtosecond pump-probe spectroscopy is used to study collective and single particle excitations in the charge density wave state of the quasi-1D metal, blue bronze. Along with the previously observed collective amplitudon excitation, the spectra show several additional coherent features.
Faraday waves under time-reversed excitation.
Pietschmann, Dirk; Stannarius, Ralf; Wagner, Christian; John, Thomas
2013-03-01
Do parametrically driven systems distinguish periodic excitations that are time mirrors of each other? Faraday waves in a Newtonian fluid are studied under excitation with superimposed harmonic wave forms. We demonstrate that the threshold parameters for the stability of the ground state are insensitive to a time inversion of the driving function. This is a peculiarity of some dynamic systems. The Faraday system shares this property with standard electroconvection in nematic liquid crystals [J. Heuer et al., Phys. Rev. E 78, 036218 (2008)]. In general, time inversion of the excitation affects the asymptotic stability of a parametrically driven system, even when it is described by linear ordinary differential equations. Obviously, the observed symmetry has to be attributed to the particular structure of the underlying differential equation system. The pattern selection of the Faraday waves above threshold, on the other hand, discriminates between time-mirrored excitation functions.
Self-excitation of space charge waves
DEFF Research Database (Denmark)
Lyuksyutov, Sergei; Buchhave, Preben; Vasnetsov, Mikhail
1997-01-01
We report a direct observation of space charge waves in photorefractive crystals with point group 23 (sillenites) based on their penetration into an area with uniform light illumination. It is shown experimentally that the quality factor of the waves increases substantially with respect to what c...... current theory predicts [B. Sturman el al., Appl. Phys. A 55, 235 (1992)]. This results in the appearance of strong spontaneous beams caused by space charge wave self-excitation....
The wave buoy analogy - estimating high-frequency wave excitations
DEFF Research Database (Denmark)
Nielsen, Ulrik Dam
2008-01-01
of sea state parameters — influence of filtering. Ocean Engineering 2007;34:1797–810.], where time series of ship responses were generated from a known wave spectrum for the purpose of the inverse process — the estimation of the underlying wave excitations. Similar response generations and vice versa...
Mexican waves in an excitable medium.
Farkas, I; Helbing, D; Vicsek, T
2002-09-12
The Mexican wave, or La Ola, which rose to fame during the 1986 World Cup in Mexico, surges through the rows of spectators in a stadium as those in one section leap to their feet with their arms up, and then sit down again as the next section rises to repeat the motion. To interpret and quantify this collective human behaviour, we have used a variant of models that were originally developed to describe excitable media such as cardiac tissue. Modelling the reaction of the crowd to attempts to trigger the wave reveals how this phenomenon is stimulated, and may prove useful in controlling events that involve groups of excited people.
Numerical simulations of convectively excited gravity waves
International Nuclear Information System (INIS)
Glatzmaier, G.A.
1983-01-01
Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region
International Nuclear Information System (INIS)
Reichert, T.; Bittner, G.; Heinzelmann, K.G.; Solner, L.; Vetter, J.
1988-01-01
A new superconducting 2 tesla magnet for whole-body magnetic resonance imaging and spectroscopy has been developed as a serial product. The HELICON magnet has the following features: Cryogen losses including ramping losses are eliminated due to helium refrigerator cooling. The magnet size is moderate despite of a large warm bore. The magnet can be ramped in 25 min from zero field to 2 Tesla. The field stability is 5 ppm/hour immediately after ramping and settles to 1 ppm/hour within 1 hour. Shimmed homogeneity band width is less than +- 5 ppm on a 50 cm diameter spherical volume using an 11-plane field plot. The magnet can be combined with a specially designed iron-yoke shield which reduces the extension of the 0.5 tesla stray field line at 2 tesla operating field to 7.4 m axially and 5.6 m radially. Cold shipment of the magnet is possible without special precautions
Hashimoto, Yusuke; Bossini, Davide; Johansen, Tom H.; Saitoh, Eiji; Kirilyuk, Andrei; Rasing, Theo
2017-01-01
Using spin-wave tomography (SWaT), we have investigated the excitation and the propagation dynamics of optically-excited magnetoelastic waves, i.e. hybridized modes of spin waves and elastic waves, in a garnet film. By using time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves through coherent-energy transfer between optically-excited pure-elastic waves and spin waves via magnetoelastic coupling. This process realizes frequency and wavenumber selective excitation of s...
De Haas-Van Alphen affect and helicons in metals
International Nuclear Information System (INIS)
Vol'skij, E.P.
1975-01-01
Specific features of helicon electrodynamics associated with the de Haas-van Alphen effect are considered for an uncompensated metal with the closed Fermi surface of arbitrary shape. The consideration is carried out entirely in the local limit, when the metal may be characterized by a static tensor for the magnetic resistance and by a static tensor for the differential magnetic permeability which describes the anisotropy of the de Haas-van Alphen effect. The amplitude of the effect is assumed to be of an arbitrary value, but in the limits determined by the thermodynamical stability of a uniformly magnetized state. It has been shown that in the general case the de Haas-van Alphen effect may strongly influence not only the phase velocity, but also the damping and polarization of a helicon. A significant effect of nondiagonal components of the differential magnetic permeability tensor that sometimes arise even at very small deviations of the magnetic field from the symmetric direction, is noted. The resonance excitation of waves in a plate is considered. The question of a possible relation between periodic diamagnetic structures in metals and helicons is discussed
A flowing plasma model to describe drift waves in a cylindrical helicon discharge
International Nuclear Information System (INIS)
Chang, L.; Hole, M. J.; Corr, C. S.
2011-01-01
A two-fluid model developed originally to describe wave oscillations in the vacuum arc centrifuge, a cylindrical, rapidly rotating, low temperature, and confined plasma column, is applied to interpret plasma oscillations in a RF generated linear magnetized plasma [WOMBAT (waves on magnetized beams and turbulence)], with similar density and field strength. Compared to typical centrifuge plasmas, WOMBAT plasmas have slower normalized rotation frequency, lower temperature, and lower axial velocity. Despite these differences, the two-fluid model provides a consistent description of the WOMBAT plasma configuration and yields qualitative agreement between measured and predicted wave oscillation frequencies with axial field strength. In addition, the radial profile of the density perturbation predicted by this model is consistent with the data. Parameter scans show that the dispersion curve is sensitive to the axial field strength and the electron temperature, and the dependence of oscillation frequency with electron temperature matches the experiment. These results consolidate earlier claims that the density and floating potential oscillations are a resistive drift mode, driven by the density gradient. To our knowledge, this is the first detailed physics model of flowing plasmas in the diffusion region away from the RF source. Possible extensions to the model, including temperature nonuniformity and magnetic field oscillations, are also discussed.
Controlling nonlinear waves in excitable media
International Nuclear Information System (INIS)
Puebla, Hector; Martin, Roland; Alvarez-Ramirez, Jose; Aguilar-Lopez, Ricardo
2009-01-01
A new feedback control method is proposed to control the spatio-temporal dynamics in excitable media. Applying suitable external forcing to the system's slow variable, successful suppression and control of propagating pulses as well as spiral waves can be obtained. The proposed controller is composed by an observer to infer uncertain terms such as diffusive transport and kinetic rates, and an inverse-dynamics feedback function. Numerical simulations shown the effectiveness of the proposed feedback control approach.
Controlling nonlinear waves in excitable media
Energy Technology Data Exchange (ETDEWEB)
Puebla, Hector [Departamento de Energia, Universidad Autonoma Metropolitana, Av. San Pablo No. 180, Reynosa-Tamaulipas, Azcapotzalco 02200, DF, Mexico (Mexico)], E-mail: hpuebla@correo.azc.uam.mx; Martin, Roland [Laboratoire de Modelisation et d' Imagerie en Geosciences, CNRS UMR and INRIA Futurs Magique-3D, Universite de Pau (France); Alvarez-Ramirez, Jose [Division de Ciencias Basicas e Ingenieria, Universidad Autonoma Metropolitana-Iztapalapa (Mexico); Aguilar-Lopez, Ricardo [Departamento de Biotecnologia y Bioingenieria, CINVESTAV-IPN (Mexico)
2009-01-30
A new feedback control method is proposed to control the spatio-temporal dynamics in excitable media. Applying suitable external forcing to the system's slow variable, successful suppression and control of propagating pulses as well as spiral waves can be obtained. The proposed controller is composed by an observer to infer uncertain terms such as diffusive transport and kinetic rates, and an inverse-dynamics feedback function. Numerical simulations shown the effectiveness of the proposed feedback control approach.
The discharge characteristics in nitrogen helicon plasma
Zhao, Gao; Wang, Huihui; Si, Xinlu; Ouyang, Jiting; Chen, Qiang; Tan, Chang
2017-12-01
Discharge characteristics of helicon plasma in nitrogen and argon-nitrogen mixtures were investigated experimentally by using a Langmuir probe, a B-dot probe, and an optical emission spectrum. Helicon wave discharge is confirmed by the changes of electron density and electromagnetic signal amplitude with the increasing RF power, which shows three discharge stages in nitrogen, corresponding to E-mode, H-mode, and W-mode discharges in helicon plasma, respectively. Discharge images in the radial cross section at different discharge modes through an intensified charge coupled device (ICCD) show a rapid increase in luminous intensity along with the RF power. When the nitrogen discharge is in the W-mode, the images show that the strongest luminance locates near the plasma boundary and no blue core appears in the axial center of tube, which is always observed in argon W-mode discharge. The "big blue" or blue core is a special character in helicon plasma, but it has not been observed in nitrogen helicon plasma. In nitrogen-argon mixtures, a weak blue core is observed in ICCD images since the nitrogen content is increased. The electric field turns to the periphery in the distribution of the radial field and the electron temperature decreases with the increasing nitrogen content, especially when the blue core disappears. The different behaviors of the electron impact and the energy consumption in nitrogen helicon plasma are suggested to be responsible for the decrease in electron energy and the change in the electric field distribution.
Energy Technology Data Exchange (ETDEWEB)
Bertelli, N., E-mail: nbertell@pppl.gov; Gerhardt, S.; Hosea, J. C.; LeBlanc, B.; Perkins, R. J.; Phillips, C. K.; Taylor, G.; Valeo, E. J.; Wilson, J. R. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Jaeger, E. F. [XCEL Engineering Inc., Oak Ridge, TN 37830 (United States); Lau, C.; Blazevski, D.; Green, D. L.; Berry, L.; Ryan, P. M. [Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169 (United States); Bonoli, P. T.; Wright, J. C. [MIT Plasma Science and Fusion Center, Cambridge, MA 02139 (United States); Pinsker, R. I.; Prater, R. [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Qin, C. M. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); and others
2015-12-10
Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves, have found strong interactions between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 3D AORSA results for the National Spherical Torus eXperiment (NSTX), where a full antenna spectrum is reconstructed, are shown, confirming the same behavior found for a single toroidal mode results in Bertelli et al, Nucl. Fusion, 54 083004, 2014, namely, a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is moved away from in front of the antenna by increasing the edge density. Additionally, full wave simulations have been extended to “conventional” tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for Alcator C-Mod and EAST, which operate in the minority heating regime unlike NSTX/NSTX-U and DIII-D, which operate in the mid/high harmonic regime. A substantial discussion of some of the main aspects, such as (i) the pitch angle of the magnetic field; (ii) minority heating vs. mid/high harmonic regimes is presented showing the different behavior of the RF field in the SOL region for NSTX-U scenarios with different plasma current. Finally, the preliminary results of the impact of the SOL region on the evaluation of the helicon current drive efficiency in DIII-D is presented for the first time and briefly compared with the different regimes
Non-Linear Excitation of Ion Acoustic Waves
DEFF Research Database (Denmark)
Michelsen, Poul; Hirsfield, J. L.
1974-01-01
The excitation of ion acoustic waves by nonlinear coupling of two transverse magnetic waves generated in a microwave cavity was investigated. Measurements of the wave amplitude showed good agreement with calculations based on the Vlasov equation.......The excitation of ion acoustic waves by nonlinear coupling of two transverse magnetic waves generated in a microwave cavity was investigated. Measurements of the wave amplitude showed good agreement with calculations based on the Vlasov equation....
Helicons, history, high technology and heliacs
International Nuclear Information System (INIS)
Boswell, R.W.
1999-01-01
A brief introduction to helicon/whistler waves, their discovery, experimental and theoretical investigation, both terrestrial and planetary is presented. The use of wave trapped electrons to increase the ionization rate and eventual development to heat heliacs and in the micro-electronics industry are also discussed and a controversy will be unveiled. For infinite plane waves the inclusion of a magnetic field opens a propagation window below the electron cyclotron frequency which allows whistler or helicon waves to propagate. If electron inertia is ignored then the wave dispersion is dominated by the Hall term (j x B) and the wave is simply electromagnetic. Including the electron inertia via the term dj/dt in Ohm's law brings a severe anisotropy to the dispersion and the wave acquires electrostatic properties (E//K)
Directory of Open Access Journals (Sweden)
Petrov Yuri V.
2017-01-01
Full Text Available The bounce-average (BA finite-difference Fokker-Planck (FP code CQL3D [1,2] now includes the essential physics to describe the RF heating of Finite-Orbit-Width (FOW ions in tokamaks. The FP equation is reformulated in terms of Constants-Of-Motion coordinates, which we select to be particle speed, pitch angle, and major radius on the equatorial plane thus obtaining the distribution function directly at this location. Full-orbit, low collisionality neoclassical radial transport emerges from averaging the local friction and diffusion coefficients along guiding center orbits. Similarly, the BA of local quasilinear RF diffusion terms gives rise to additional radial transport. The local RF electric field components needed for the BA operator are usually obtained by a ray-tracing code, such as GENRAY, or in conjunction with full-wave codes. As a new, practical application, the CQL3D-FOW version is used for simulation of alpha-particle heating by high-harmonic waves in ITER. Coupling of high harmonic or helicon fast waves power to electrons is a promising current drive (CD scenario for high beta plasmas. However, the efficiency of current drive can be diminished by parasitic channeling of RF power into fast ions, such as alphas, through finite Larmor-radius effects. We investigate possibilities to reduce the fast ion heating in CD scenarios.
Ion-Beam-Excited Electrostatic Ion Cyclotron Waves
DEFF Research Database (Denmark)
Michelsen, Poul; Pécseli, Hans; Juul Rasmussen, Jens
1976-01-01
Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field.......Self-excited electrostatic ion cyclotron waves were observed in an ion-beam-plasma system produced in a DP-operated Q-machine. The frequency of the waves showed the theoretically predicted variation with the magnetic field....
Spiral-wave dynamics in excitable medium with excitability modulated by rectangle wave
International Nuclear Information System (INIS)
Yuan Guo-Yong
2011-01-01
We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by the corresponding spectrum analysis. For a large T, the external modulation leads to the occurrence of more frequency peaks and these frequencies change with the modulation period according to their specific rules, respectively. Some of the frequencies and a primary frequency f 1 determine the corresponding curvature periods, which are locked into rational multiplies of the modulation period. These frequency-locking behaviours and the limited life-span of the frequencies in their variations with the modulation period constitute many resonant entrainment bands in the T axis. In the main bands, which follow the relation T/T 12 = m/n, the size variable R x of the tip trajectory is a monotonic increasing function of T. The rest of the frequencies are linear combinations of the two ones. Due to the complex dynamics, many unique tip trajectories appear at some certain T. We find also that spiral waves are eliminated when T is chosen from the end of the main resonant bands. This offers a useful method of controling the spiral wave. (general)
Simple Excitation of Standing Waves in Rubber Bands and Membranes
Cortel, Adolf
2004-04-01
Many methods to excite standing waves in strings, plates, membranes, rods, tubes, and soap bubbles have been described. Usually a loudspeaker or a vibrating reed is driven by the amplified output of an audio oscillator. A novel and simple method consists of using a tuning fork or a singing rod to excite transversal standing waves in stretched rubber membranes sprinkled with fine sand.
Multiple pulse traveling wave excitation of neon-like germanium
International Nuclear Information System (INIS)
Moreno, J. C.; Nilsen, J.; Silva, L. B. da
1995-01-01
Traveling wave excitation has been shown to significantly increase the output intensity of the neon-like germanium x-ray laser. The driving laser pulse consisted of three 100 ps Gaussian laser pulses separated by 400 ps. Traveling wave excitation was employed by tilting the wave front of the driving laser by 45 degrees to match the propagation speed of the x-ray laser photons along the length of the target. We show results of experiments with the traveling wave, with no traveling wave, and against the traveling wave and comparisons to a numerical model. Gain was inferred from line intensity measurements at two lengths
Parametric excitation of drift waves in a sheared slab geometry
International Nuclear Information System (INIS)
Vranjes, J.; Weiland, J.
1992-01-01
The threshold for parametric excitation of drift waves in a sheared slab geometry is calculated for a pump wave that is a standing wave along the magnetic field, using the Hasegawa-Mima nonlinearity. The shear damping is counteracted by the parametric coupling and the eigenvalue problem is solved analytically using Taylor's strong coupling approximation. (au)
Influence of excitability on unpinning and termination of spiral waves.
Luengviriya, Jiraporn; Sutthiopad, Malee; Phantu, Metinee; Porjai, Porramain; Kanchanawarin, Jarin; Müller, Stefan C; Luengviriya, Chaiya
2014-11-01
Application of electrical forcing to release pinned spiral waves from unexcitable obstacles and to terminate the rotation of free spiral waves at the boundary of excitable media has been investigated in thin layers of the Belousov-Zhabotinsky (BZ) reaction, prepared with different initial concentrations of H_{2}SO_{4}. Increasing [H_{2}SO_{4}] raises the excitability of the reaction and reduces the core diameter of free spiral waves as well as the wave period. An electric current with density stronger than a critical value Junpin causes a pinned spiral wave to drift away from the obstacle. For a given obstacle size, Junpin increases with [H_{2}SO_{4}]. Under an applied electrical current, the rotation center of a free spiral wave drifts along a straight path to the boundary. When the current density is stronger than a critical value Jterm, the spiral tip is forced to hit the boundary, where the spiral wave is terminated. Similar to Junpin for releasing a pinned spiral wave, Jterm also increases with [H_{2}SO_{4}]. These experimental findings were confirmed by numerical simulations using the Oregonator model, in which the excitability was adjusted via the ratio of the excitation rate to the recovery rate of the BZ reaction. Therefore, our investigation shows that decreasing the excitability can facilitate elimination of spiral waves by electrical forcing, either in the presence of obstacles or not.
Parasitic excitation of ion Bernstein waves from a Faraday shielded fast wave loop antenna
International Nuclear Information System (INIS)
Skiff, F.; Ono, M.; Colestock, P.; Wong, K.L.
1984-12-01
Parasitic excitation of ion Bernstein waves is observed from a Faraday shielded fast wave loop antenna in the ion cyclotron frequency range. Local analysis of the Vlasov-Maxwell equations demonstrates the role of plasma density gradient in the coupling process. The effects of plasma density and of parallel wave number on the excitation process are investigated
Nonlinear excitation of geodesic acoustic modes by drift waves
International Nuclear Information System (INIS)
Chakrabarti, N.; Singh, R.; Kaw, P. K.; Guzdar, P. N.
2007-01-01
In this paper, two mode-coupling analyses for the nonlinear excitation of the geodesic acoustic modes (GAMs) in tokamak plasmas by drift waves are presented. The first approach is a coherent parametric process, which leads to a three-wave resonant interaction. This investigation allows for the drift waves and the GAMs to have comparable scales. The second approach uses the wave-kinetic equations for the drift waves, which then couples to the GAMs. This requires that the GAM scale length be large compared to the wave packet associated with the drift waves. The resonance conditions for these two cases lead to specific predictions of the radial wave number of the excited GAMs
Excitation of waves in elastic waveguides by piezoelectric patch actuators
CSIR Research Space (South Africa)
Loveday, PW
2006-01-01
Full Text Available for waveguides excited by piezoelectric patch actuators. The waveguide is modelled using specially developed waveguide finite elements. These elements are formulated using a complex exponential to describe the wave propagation along the structure and finite...
Elastic wave excitation in centrosymmetric strontium titanate crystals
International Nuclear Information System (INIS)
Yushin, N.K.; Sotnikov, A.V.
1980-01-01
The main experimental dependencies are measured and the excitation mechanism of elastic waves in centrosymmetric crystals is established. The surface generation of three-dimensional elastic waves of the 30 MHz frequency in strontium titanate crystals is observed and studied. Elastic wave excitation is observed in the 4 350 K temperature range. The efficiency of hysteresis excitation depends on the external electric field. The effect of light irradiation on the amplitude of excited elastic waves is observed. It is shown that escitation is connected with linearization of electrostriction by the constant electric field appearing in a near-surface crystal layer due to phenomena in the Schottky barrier and appearance of electretic near-electrode layers
Control of Spiral Waves and Spatiotemporal Chaos by Exciting Travel Wave Trains
International Nuclear Information System (INIS)
Yuan Guoyong; Wang Guangrui; Chen Shigang
2005-01-01
Spiral waves and spatiotemporal chaos usually are harmful and need to be suppressed. In this paper, a method is proposed to control them. Travel wave trains can be generated by periodic excitations near left boundary, spiral waves and spatiotemporal chaos can be eliminated by the trains for some certain excitation periods. Obvious resonant behavior can be observed from the relation between the periods of the trains and excitation ones. The method is against noise.
Artificial excitation of ELF waves with frequency of Schumann resonance
Streltsov, A. V.; Guido, T.; Tulegenov, B.; Labenski, J.; Chang, C.-L.
2014-11-01
We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8-8.0 Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20-4.57 MHz, and the electric field greater than 5 mV/m is present in the ionosphere.
Slip-stick excitation and travelling waves excite silo honking
Directory of Open Access Journals (Sweden)
Warburton Katarzyna
2017-01-01
Full Text Available Silo honking is the harmonic sound generated by the discharge of a silo filled with a granular material. In industrial storage silos, the acoustic emission during discharge of PET-particles forms a nuisance for the environment and may ultimately result in structural failure. This work investigates the phenomenon experimentally using a laboratory-scale silo, and successfully correlates the frequency of the emitted sound with the periodicity of the mechanical motion of the grains. The key driver is the slip-stick interaction between the wall and the particles, characterized as a wave moving upwards through the silo. A quantitative correlation is established for the first time between the frequency of the sound, measured with an electret microphone, and the slip-frequency, measured with a high-speed camera. In the lower regions of the tube, both the slip-stick motion and the honking sound disappear.
Slip-stick excitation and travelling waves excite silo honking
Warburton, Katarzyna; Porte, Elze; Vriend, Nathalie
2017-06-01
Silo honking is the harmonic sound generated by the discharge of a silo filled with a granular material. In industrial storage silos, the acoustic emission during discharge of PET-particles forms a nuisance for the environment and may ultimately result in structural failure. This work investigates the phenomenon experimentally using a laboratory-scale silo, and successfully correlates the frequency of the emitted sound with the periodicity of the mechanical motion of the grains. The key driver is the slip-stick interaction between the wall and the particles, characterized as a wave moving upwards through the silo. A quantitative correlation is established for the first time between the frequency of the sound, measured with an electret microphone, and the slip-frequency, measured with a high-speed camera. In the lower regions of the tube, both the slip-stick motion and the honking sound disappear.
Active-passive waveguide array for wave excitation in plasmas
International Nuclear Information System (INIS)
Motley, R.W.; Hooke, W.M.
1979-11-01
A modified version of the standard waveguide grill for exciting lower hybrid plasma waves is proposed. This version should reduce both the number of RF drive components and the amplitude of the (undesirable) surface waves. Results from a simple 2-element array are presented
Holograms for power-efficient excitation of optical surface waves
Ignatov, Anton I.; Merzlikin, Alexander M.
2018-02-01
A method for effective excitation of optical surface waves based on holography principles has been proposed. For a particular example of excitation of a plasmonic wave in a dielectric layer on metal the efficiency of proposed volume holograms in the dielectric layer has been analyzed in comparison with optimized periodic gratings in the dielectric layer. Conditions when the holograms are considerably more efficient than the gratings have been found out. In addition, holograms recorded in two iterations have been proposed and studied. Such holograms are substantially more efficient than the optimized periodic gratings for all incidence angles of an exciting Gaussian beam. The proposed method is universal: it can be extended for efficient excitation of different types of optical surface waves and optical waveguide modes.
Springing Response Due to Directional Wave Field Excitation
DEFF Research Database (Denmark)
Vidic-Perunovic, Jelena; Jensen, Jørgen Juncher
2004-01-01
This paper analyses the wave-induced high-frequency bending moment response of ships, denoted springing. The aim is to predict measured severe springing responses in a large bulk carrier. It is shown that the most important springing contribution is due to the resultant second order excitation...... in multidirectional sea. The incident pressure field from the second order bidirectional wave field is derived, including the non-linear cross-coupling terms between the two wave systems (e.g. wind driven waves and swell). The resulting effect of the super-harmonic cross-coupling interaction terms on the springing...... response is discussed. An example with opposing waves is given, representing probably the 'worst' case for energy exchange between the wave systems. Theoretical predictions of standard deviation of wave- and springing-induced stress amidships are compared with full-scale measurements for a bulk carrier....
Geodesic acoustic modes excited by finite beta drift waves
DEFF Research Database (Denmark)
Chakrabarti, Nikhil Kumar; Guzdar, P.N.; Kleva, R.G.
2008-01-01
Presented in this paper is a mode-coupling analysis for the nonlinear excitation of the geodesic acoustic modes (GAMs) in tokamak plasmas by finite beta drift waves. The finite beta effects give rise to a strong stabilizing influence on the parametric excitation process. The dominant finite beta...... effect is the combination of the Maxwell stress, which has a tendency to cancel the primary drive from the Reynolds stress, and the finite beta modification of the drift waves. The zonal magnetic field is also excited at the GAM frequency. However, it does not contribute to the overall stability...... of the three-wave process for parameters of relevance to the edge region of tokamaks....
Improved ion acceleration via laser surface plasma waves excitation
Energy Technology Data Exchange (ETDEWEB)
Bigongiari, A. [CEA/DSM/LSI, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); TIPS/LULI, Université Paris 6, CNRS, CEA, Ecole Polytechnique, 3, rue Galilée, 94200 Ivry-sur-Seine (France); Raynaud, M. [CEA/DSM/LSI, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Riconda, C. [TIPS/LULI, Université Paris 6, CNRS, CEA, Ecole Polytechnique, 3, rue Galilée, 94200 Ivry-sur-Seine (France); Héron, A. [CPHT, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France)
2013-05-15
The possibility of enhancing the emission of the ions accelerated in the interaction of a high intensity ultra-short (<100 fs) laser pulse with a thin target (<10λ{sub 0}), via surface plasma wave excitation is investigated. Two-dimensional particle-in-cell simulations are performed for laser intensities ranging from 10{sup 19} to 10{sup 20} Wcm{sup −2}μm{sup 2}. The surface wave is resonantly excited by the laser via the coupling with a modulation at the target surface. In the cases where the surface wave is excited, we find an enhancement of the maximum ion energy of a factor ∼2 compared to the cases where the target surface is flat.
Direct excitation of a high frequency wave by a low frequency wave in a plasma
International Nuclear Information System (INIS)
Tanaka, Takayasu
1993-01-01
A new mechanism is presented of an excitation of a high frequency wave by a low frequency wave in a plasma. This mechanism works when the low frequency wave varies in time in a manner deviated from a usual periodic motion with a constant amplitude. The conversion rate is usually not large but the conversion is done without time delay after the variation of the low frequency wave. The Manley Rowe relation in the usual sense does not hold in this mechanism. This mechanism can excite also waves with same or lower frequencies. (author)
Shear Alfven wave excitation by direct antenna coupling and fast wave resonant mode conversion
International Nuclear Information System (INIS)
Borg, G.G.
1994-01-01
Antenna coupling to the shear Alfven wave by both direct excitation and fast wave resonant mode conversion is modelled analytically for a plasma with a one dimensional linear density gradient. We demonstrate the existence of a shear Alfven mode excited directly by the antenna. For localised antennas, this mode propagates as a guided beam along the steady magnetic field lines intersecting the antenna. Shear Alfven wave excitation by resonant mode conversion of a fast wave near the Alfven resonance layer is also demonstrated and we prove that energy is conserved in this process. We compare the efficiency of these two mechanisms of shear Alfven wave excitation and present a simple analytical formula giving the ratio of the coupled powers. Finally, we discuss the interpretation of some experimental results. 45 refs., 7 figs
Nonlinear plasma waves excited near resonance
International Nuclear Information System (INIS)
Cohen, B.I.; Kaufman, A.N.
1977-01-01
The nonlinear resonant response of a uniform plasma to an external plane-wave field is formulated in terms of the mismatch Δ/sub n l/ between the driving frequency and the time-dependent, complex, nonlinear normal mode frequency at the driving wavenumber. This formalism is applied to computer simulations of this process, yielding a deduced nonlinear frequency shift. The time dependence of the nonlinear phenomena, at frequency Δ/sub n l/ and at the bounce frequency of the resonant particles, is analyzed. The interdependence of the nonlinear features is described by means of energy and momentum relations
Crowd behaves as excitable media during Mexican wave
Farkas, Illes; Helbing, Dirk; Vicsek, Tamas
2002-01-01
Mexican wave, or La Ola, first widely broadcasted during the 1986 World Cup held in Mexico, is a human wave moving along the stands of stadiums as one section of spectators stands up, arms lifting, then sits down as the next section does the same. Here we use variants of models originally developed for the description of excitable media to demonstrate that this collective human behaviour can be quantitatively interpreted by methods of statistical physics. Adequate modelling of reactions to tr...
Self excitation of second harmonic ion-acoustic waves in a weakly magnetized plasma
International Nuclear Information System (INIS)
Tsukabayashi, I.; Yagishita, T.; Nakamura, Y.
1994-01-01
Electrostatic ion-acoustic waves in a weakly magnetized plasma are investigated experimentally. It is observed that finite amplitudes ion acoustic waves excite a new second harmonic wave train behind the initial ion waves excite a new second harmonic wave train behind the initial ion waves in a parallel magnetic field. The excitation of higher harmonic waves can be explained by non-linearity of finite amplitude ion-acoustic waves. The newly excited second harmonics waves satisfy a dispersion relation of the ion-acoustic waves. (author). 3 refs, 5 figs
Direct excitation of resonant torsional Alfven waves by footpoint motions
Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.
1997-01-01
The present paper studies the heating of coronal loops by linear resonant Alfven waves that are excited by the motions of the photospheric footpoints of the magnetic field lines. The analysis is restricted to torsionally polarised footpoint motions in an axially symmetric system so that only
Delta function excitation of waves in the earth's ionosphere
Vidmar, R. J.; Crawford, F. W.; Harker, K. J.
1983-01-01
Excitation of the earth's ionosphere by delta function current sheets is considered, and the temporal and spatial evolution of wave packets is analyzed for a two-component collisional F2 layer. Approximations of an inverse Fourier-Laplace transform via saddle point methods provide plots of typical wave packets. These illustrate cold plasma wave theory and may be used as a diagnostic tool since it is possible to relate specific features, e.g., the frequency of a modulation envelope, to plasma parameters such as the electron cyclotron frequency. It is also possible to deduce the propagation path length and orientation of a remote radio beacon.
Excitation of seismic waves by a tornado
Valovcin, A.; Tanimoto, T.; Twardzik, C.
2016-12-01
Tornadoes are among the most common natural disasters to occur in the United States. Various methods are currently used in tornado forecasting, including surface weather stations, weather balloons and satellite and Doppler radar. These methods work for detecting possible locations of tornadoes and funnel clouds, but knowing when a tornado has touched down still strongly relies on reports from spotters. Studying tornadoes seismically offers an opportunity to know when a tornado has touched down without requiring an eyewitness report. With the installation of Earthscope's Transportable Array (TA), there have been an increased number of tornadoes that have come within close range of seismometers. We have identified seismic signals corresponding to three tornadoes that occurred in 2011 in the central US. These signals were recorded by the TA station closest to each of the tornado tracks. For each tornado, the amplitudes of the seismic signals increase when the storm is in contact with the ground, and continue until the tornado lifts off some time later. This occurs at both high and low frequencies. In this study we will model the seismic signal generated by a tornado at low frequencies (below 0.1 Hz). We will begin by modeling the signal from the Joplin tornado, an EF5 rated tornado which occurred in Missouri on May 22, 2011. By approximating the tornado as a vertical force, we model the generated signal as the tornado moves along its track and changes in strength. By modeling the seismic waveform generated by a tornado, we can better understand the seismic-excitation process. It could also provide a way to quantitatively compare tornadoes. Additional tornadoes to model include the Calumet-El Reno-Piedmont-Guthrie (CEPG) and Chickasa-Blanchard-Newcastle (CBN) tornadoes, both of which occurred on May 24, 2011 in Oklahoma.
Dynamic response of a riser under excitation of internal waves
Lou, Min; Yu, Chenglong; Chen, Peng
2015-12-01
In this paper, the dynamic response of a marine riser under excitation of internal waves is studied. With the linear approximation, the governing equation of internal waves is given. Based on the rigid-lid boundary condition assumption, the equation is solved by Thompson-Haskell method. Thus the velocity field of internal waves is obtained by the continuity equation. Combined with the modified Morison formula, using finite element method, the motion equation of riser is solved in time domain with Newmark-β method. The computation programs are compiled to solve the differential equations in time domain. Then we get the numerical results, including riser displacement and transfiguration. It is observed that the internal wave will result in circular shear flow, and the first two modes have a dominant effect on dynamic response of the marine riser. In the high mode, the response diminishes rapidly. In different modes of internal waves, the deformation of riser has different shapes, and the location of maximum displacement shifts. Studies on wave parameters indicate that the wave amplitude plays a considerable role in response displacement of riser, while the wave frequency contributes little. Nevertheless, the internal waves of high wave frequency will lead to a high-frequency oscillation of riser; it possibly gives rise to fatigue crack extension and partial fatigue failure.
Ion cyclotron wave excitation by double resonance coupling
International Nuclear Information System (INIS)
Fasoli, A.; Good, T.N.; Paris, P.J.; Skiff, F.; Tran, M.Q.
1990-07-01
A modulated high frequency wave is used to remotely excite low frequency oscillations in a linear, strongly magnetized plasma column. An electromagnetic wave is launched as an extraordinary mode across the plasma by an external waveguide in the Upper Hybrid frequency regime f=f UH =f ce =8 GHz, with P≤2 W. By frequency modulating (at f FM =1-60 kHz, with f ci ≅30 kHz) the pump wave, the resonant layer is swept radially across the profile and perpendicularly to the field lines at f=f FM . The resulting radial oscillation of the electron linear and non linear pressure can be considered to act as a source term for the ion wave. A localized virtual antenna is thereby created inside the plasma. Measurements of the ion dielectric response (interferograms and perturbed distribution functions) via laser induced fluorescence identify the two branches (forward, or ion-acoustic-like, and backward, or Bernstein, modes) of the electrostatic dispersion relation in the ion cyclotron frequency range. By changing the modulation bandwidth, and thus the spatial excursion of the oscillating resonant layer, a control on the perpendicular wavelength of the excited mode can be exerted. In particular, the possibility of selective excitation of the ion Bernstein wave is demonstrated experimentally. (author) 38 refs., 13 figs
Excitation of coherent propagating spin waves by pure spin currents.
Demidov, Vladislav E; Urazhdin, Sergei; Liu, Ronghua; Divinskiy, Boris; Telegin, Andrey; Demokritov, Sergej O
2016-01-28
Utilization of pure spin currents not accompanied by the flow of electrical charge provides unprecedented opportunities for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. It was recently shown that pure spin currents can be used to excite coherent magnetization dynamics in magnetic nanostructures. However, because of the intrinsic nonlinear self-localization effects, magnetic auto-oscillations in the demonstrated devices were spatially confined, preventing their applications as sources of propagating spin waves in magnonic circuits using these waves as signal carriers. Here, we experimentally demonstrate efficient excitation and directional propagation of coherent spin waves generated by pure spin current. We show that this can be achieved by using the nonlocal spin injection mechanism, which enables flexible design of magnetic nanosystems and allows one to efficiently control their dynamic characteristics.
Discharge regimes and density jumps in a helicon plasma source
International Nuclear Information System (INIS)
Shinohara, S.; Yonekura, K.
1999-01-01
A high density plasma source using a helicon wave is becoming very attractive in plasma processing and confinement devices. In the previous work, the characteristics of this wave and plasma performance with diameters of 5 and 45 cm have been studied, and the helicon wave was only observed after the density jump. Recently, density jumps from the low to high electron densities with a level of 10 13 cm -3 were investigated by changing the antenna wavenumber spectrum, and the obtained results were compared with the inductively coupled plasma (ICP). However, the mechanisms of density jumps and plasma production are still open questions to be answered. Here, the authors try to investigate the discharge regimes and density jumps in a helicon plasma source, by changing the antenna wavenumber spectrum. For he case of the parallel current directions in the antenna, where the low wavenumber spectrum part is large, the density jump was observed with the low RF input power of P in < 300 W regardless of the magnetic field. On the other hand, for the case of the opposite directions, where the low wavenumber spectrum part is small, the threshold power to obtain the jump became high with the increase in the magnetic field. This can be understood from the dispersion relation of the helicon wave. The wave structures and the dispersion relations in the discharge modes will be also shown
Parametric excitation of electromagnetic waves by electron Bernstein waves
International Nuclear Information System (INIS)
Kuo, S.P.
1992-01-01
A parametric instability involving the decay of a standing electron Bernstein pump into electromagnetic sidebands and lower-hybrid decay waves is studied. A general dispersion relation is derived and analyzed. Threshold fields and growth rates are obtained for the two cases that the electron Bernstein pump is introduced near the X-mode cutoff layer or introduced in the region between the upper-hybrid resonance layer and the O-mode cutoff layer. Applications of these results to the recent observation [P. Stubbe and H. Kopka, Phys. Rev. Lett. 65, 183 (1990)] of stimulated electromagnetic emission (SEE) with a broad symmetrical structure (BSS) in the ionospheric modifications by powerful high-frequency (HF) wave are discussed
Design of a novel high efficiency antenna for helicon plasma sources
Fazelpour, S.; Chakhmachi, A.; Iraji, D.
2018-06-01
A new configuration for an antenna, which increases the absorption power and plasma density, is proposed for helicon plasma sources. The influence of the electromagnetic wave pattern symmetry on the plasma density and absorption power in a helicon plasma source with a common antenna (Nagoya) is analysed by using the standard COMSOL Multiphysics 5.3 software. In contrast to the theoretical model prediction, the electromagnetic wave does not represent a symmetric pattern for the common Nagoya antenna. In this work, a new configuration for an antenna is proposed which refines the asymmetries of the wave pattern in helicon plasma sources. The plasma parameters such as plasma density and absorption rate for a common Nagoya antenna and our proposed antenna under the same conditions are studied using simulations. In addition, the plasma density of seven operational helicon plasma source devices, having a common Nagoya antenna, is compared with the simulation results of our proposed antenna and the common Nagoya antenna. The simulation results show that the density of the plasma, which is produced by using our proposed antenna, is approximately twice in comparison to the plasma density produced by using the common Nagoya antenna. In fact, the simulation results indicate that the electric and magnetic fields symmetry of the helicon wave plays a vital role in increasing wave-particle coupling. As a result, wave-particle energy exchange and the plasma density of helicon plasma sources will be increased.
International Nuclear Information System (INIS)
Pinsker, R. I.
2015-01-01
This introductory-level tutorial article describes the application of plasma waves in the lower hybrid range of frequencies (LHRF) for current drive in tokamaks. Wave damping mechanisms in a nearly collisionless hot magnetized plasma are briefly described, and the connections between the properties of the damping mechanisms and the optimal choices of wave properties (mode, frequency, wavelength) are explored. The two wave modes available for current drive in the LHRF are described and compared. The terms applied to these waves in different applications of plasma physics are elucidated. The character of the ray paths of these waves in the LHRF is illustrated in slab and toroidal geometries. Applications of these ideas to experiments in the DIII-D tokamak are discussed
Observation of Ion Acoustic Waves Excited by Drift Waves in a Weakly Magnetized Plasma
International Nuclear Information System (INIS)
Tsukabayashi, Isao; Sato, Sugiya; Nakamura, Yoshiharu
2003-01-01
Spontaneous fluctuations excited by drift waves are investigated experimentally in magnetic multi-pole plasma. The magnetic multi-pole has been widely used in DP devices and so on. It was observed that the high level of density fluctuations was generated by the drift instability near a magnetic multi-pole or a dipole magnet. The waves propagate to the middle plasma region forming the envelope train waves
Piezoelectric excitation of elastic waves in centrosymmetrical potassium tantalate crystal
International Nuclear Information System (INIS)
Smolenskij, G.A.; Lemanov, V.V.; Sotnikov, A.V.; Syrnikov, P.P.; Yushin, N.K.
1981-01-01
Experiment results on excitation of elastic oscillations in potassium tantalate crystals are considered. The experiment has been conducted by usual for supersonic measurements technique: an impulse of the variable electric field has been applied to one of plane-parallel sample end-faces, at the same end-face signals corresponding to elastic pulses propagating in the crystal have been detected. Basic radiopulses parameters: basic frequency 30 MHz, duration 1-2 μs, pulse recurrence frequency 500 Hz, power 10 W. The investigation carried out has shown that the application to the sample at T=80 K temperature of constant external electrical field parallel to direction of elastic wave propagation leads to hysteresis dependence of elastic waves amplitude on the external voltage value. With temperature increase the hysteresis loop is deformed. It has been found when investigating temperature dependence of elastic wave amplitude that in the absence of external constant electrical field in short-circuited by constant current samples the oxillation excitation effect disappears at T approximately equal to 200 K. An essential influence on the elastic wave amplitude value is exerted by illumination of the crystal surface by light with 360-630 nm wave length. At T 130 K bacaee of photovoltaic effect in illuminated samples [ru
Collective spin wave and phonon excitations in ferromagnetic organic polymers
International Nuclear Information System (INIS)
Leong, Jit-Liang; Sun, Shih-Jye
2013-01-01
We proposed a model to investigate the properties of a conductive and ferromagnetic organic-polymer (OCP), which contains two collective excitations—spin wave and phonon—competing with each other; namely, the spin wave excitation accompanies the electron–phonon (e–ph) interactions in the conductive and ferromagnetic OCP. The ferromagnetism of the OCP is induced from the conductive carriers which couple with the phonon to become polarons. Due to the competition between both excitations, the Curie temperature (T C ) is sensitively suppressed by the e–ph interaction. In addition, an optimal T C with a small e–ph interaction exists in a specific density of conduction carrier, yet is contrary to the large e–ph interaction case. Furthermore, the dimerization, i.e. the atomic displacement induced from the e–ph interactions, increases with the strength of the e–ph interaction and decreases upon reaching the maximum dimerization. (paper)
Excitation of neutron flux waves in reactor core transients
International Nuclear Information System (INIS)
Carew, J.F.; Neogy, P.
1983-01-01
An analysis of the excitation of neutron flux waves in reactor core transients has been performed. A perturbation theory solution has been developed for the time-dependent thermal diffusion equation in which the absorption cross section undergoes a rapid change, as in a PWR rod ejection accident (REA). In this analysis the unperturbed reactor flux states provide the basis for the spatial representation of the flux solution. Using a simplified space-time representation for the cross section change, the temporal integrations have been carried out and analytic expressions for the modal flux amplitudes determined. The first order modal excitation strength is determined by the spatial overlap between the initial and final flux states, and the cross section perturbation. The flux wave amplitudes are found to be largest for rapid transients involving large reactivity perturbations
Cookbook asymptotics for spiral and scroll waves in excitable media.
Margerit, Daniel; Barkley, Dwight
2002-09-01
Algebraic formulas predicting the frequencies and shapes of waves in a reaction-diffusion model of excitable media are presented in the form of four recipes. The formulas themselves are based on a detailed asymptotic analysis (published elsewhere) of the model equations at leading order and first order in the asymptotic parameter. The importance of the first order contribution is stressed throughout, beginning with a discussion of the Fife limit, Fife scaling, and Fife regime. Recipes are given for spiral waves and detailed comparisons are presented between the asymptotic predictions and the solutions of the full reaction-diffusion equations. Recipes for twisted scroll waves with straight filaments are given and again comparisons are shown. The connection between the asymptotic results and filament dynamics is discussed, and one of the previously unknown coefficients in the theory of filament dynamics is evaluated in terms of its asymptotic expansion. (c) 2002 American Institute of Physics.
Wave speed in excitable random networks with spatially constrained connections.
Directory of Open Access Journals (Sweden)
Nikita Vladimirov
Full Text Available Very fast oscillations (VFO in neocortex are widely observed before epileptic seizures, and there is growing evidence that they are caused by networks of pyramidal neurons connected by gap junctions between their axons. We are motivated by the spatio-temporal waves of activity recorded using electrocorticography (ECoG, and study the speed of activity propagation through a network of neurons axonally coupled by gap junctions. We simulate wave propagation by excitable cellular automata (CA on random (Erdös-Rényi networks of special type, with spatially constrained connections. From the cellular automaton model, we derive a mean field theory to predict wave propagation. The governing equation resolved by the Fisher-Kolmogorov PDE fails to describe wave speed. A new (hyperbolic PDE is suggested, which provides adequate wave speed v( that saturates with network degree , in agreement with intuitive expectations and CA simulations. We further show that the maximum length of connection is a much better predictor of the wave speed than the mean length. When tested in networks with various degree distributions, wave speeds are found to strongly depend on the ratio of network moments / rather than on mean degree , which is explained by general network theory. The wave speeds are strikingly similar in a diverse set of networks, including regular, Poisson, exponential and power law distributions, supporting our theory for various network topologies. Our results suggest practical predictions for networks of electrically coupled neurons, and our mean field method can be readily applied for a wide class of similar problems, such as spread of epidemics through spatial networks.
Simultaneous excitation system for efficient guided wave structural health monitoring
Hua, Jiadong; Michaels, Jennifer E.; Chen, Xin; Lin, Jing
2017-10-01
Many structural health monitoring systems utilize guided wave transducer arrays for defect detection and localization. Signals are usually acquired using the ;pitch-catch; method whereby each transducer is excited in turn and the response is received by the remaining transducers. When extensive signal averaging is performed, the data acquisition process can be quite time-consuming, especially for metallic components that require a low repetition rate to allow signals to die out. Such a long data acquisition time is particularly problematic if environmental and operational conditions are changing while data are being acquired. To reduce the total data acquisition time, proposed here is a methodology whereby multiple transmitters are simultaneously triggered, and each transmitter is driven with a unique excitation. The simultaneously transmitted waves are captured by one or more receivers, and their responses are processed by dispersion-compensated filtering to extract the response from each individual transmitter. The excitation sequences are constructed by concatenating a series of chirps whose start and stop frequencies are randomly selected from a specified range. The process is optimized using a Monte-Carlo approach to select sequences with impulse-like autocorrelations and relatively flat cross-correlations. The efficacy of the proposed methodology is evaluated by several metrics and is experimentally demonstrated with sparse array imaging of simulated damage.
Resonant spin wave excitations in a magnonic crystal cavity
Kumar, N.; Prabhakar, A.
2018-03-01
Spin polarized electric current, injected into permalloy (Py) through a nano contact, exerts a torque on the magnetization. The spin waves (SWs) thus excited propagate radially outward. We propose an antidot magnonic crystal (MC) with a three-hole defect (L3) around the nano contact, designed so that the frequency of the excited SWs, lies in the band gap of the MC. L3 thus acts as a resonant SW cavity. The energy in this magnonic crystal cavity can be tapped by an adjacent MC waveguide (MCW). An analysis of the simulated micromagnetic power spectrum, at the output port of the MCW reveals stable SW oscillations. The quality factor of the device, calculated using the decay method, was estimated as Q > 105 for an injected spin current density of 7 ×1012 A/m2.
Excitation of propagating magnetization waves by microstrip antennas
Dmitriev, V. F.; Kalinikos, B. A.
1988-11-01
We discuss the self-consistent theory of excitation of dipole-exchange magnetization waves by microstrip antennas in a metal-dielectric-ferrite-dielectric-metal stratified structure, magnetized under an arbitrary angle to the surface. Spin-wave Green's functions are derived, describing the response of the spin-system to a spatially inhomogeneous varying magnetic field. The radiative resistance of microstrip antenna is calculated. In this case the distribution of surface current density in the antenna is found on the basis of the analytic solution of a singular integral equation. The nature of the effect of metallic screens and redistributed surface current densities in the antenna on the frequency dependence of the resistive radiation is investigated. Approximate relations are obtained, convenient for practical calculations of radiative resistance of microstrip antennas both in a free and in a screened ferromagnetic film. The theoretical calculations are verified by data of experiments carried out on monocrystalline films of iron-yttrium garnet.
Helicons in uniform fields. II. Poynting vector and angular momenta
Stenzel, R. L.; Urrutia, J. M.
2018-03-01
The orbital and spin angular momenta of helicon modes have been determined quantitatively from laboratory experiments. The current density is obtained unambiguously from three dimensional magnetic field measurements. The only approximation made is to obtain the electric field from Hall Ohm's law which is usually the case for low frequency whistler modes. This allows the evaluation of the Poynting vector from which the angular momentum is obtained. Comparing two helicon modes (m = 0 and m = 1), one can separate the contribution of angular momentum of a rotating and non-rotating wave field. The orbital angular momentum is important to assess the wave-particle interaction by the transverse Doppler shift of rotating waves which has not been considered so far.
Excitation of planetary electromagnetic waves in the inhomogeneous ionosphere
Directory of Open Access Journals (Sweden)
Yu. Rapoport
2014-04-01
Full Text Available In this paper we develop a new method for the analysis of excitation and propagation of planetary electromagnetic waves (PEMW in the ionosphere of the Earth. The nonlinear system of equations for PEMW, valid for any height, from D to F regions, including intermediate altitudes between D and E and between E and F regions, is derived. In particular, we have found the system of nonlinear one-fluid MHD equations in the β-plane approximation valid for the ionospheric F region (Aburjania et al., 2003a, 2005. The series expansion in a "small" (relative to the local geomagnetic field non-stationary magnetic field has been applied only at the last step of the derivation of the equations. The small mechanical vertical displacement of the media is taken into account. We have shown that obtained equations can be reduced to the well-known system with Larichev–Reznik vortex solution in the equatorial region (see e.g. Aburjania et al., 2002. The excitation of planetary electromagnetic waves by different initial perturbations has been investigated numerically. Some means for the PEMW detection and data processing are discussed.
Distributed predictive control of spiral wave in cardiac excitable media
International Nuclear Information System (INIS)
Zheng-Ning, Gan; Xin-Ming, Cheng
2010-01-01
In this paper, we propose the distributed predictive control strategies of spiral wave in cardiac excitable media. The modified FitzHugh–Nagumo model was used to express the cardiac excitable media approximately. Based on the control-Lyapunov theory, we obtained the distributed control equation, which consists of a positive control-Lyapunov function and a positive cost function. Using the equation, we investigate two kinds of robust control strategies: the time-dependent distributed control strategy and the space-time dependent distributed control strategy. The feasibility of the strategies was demonstrated via an illustrative example, in which the spiral wave was prevented to occur, and the possibility for inducing ventricular fibrillation was eliminated. The strategies are helpful in designing various cardiac devices. Since the second strategy is more efficient and robust than the first one, and the response time in the second strategy is far less than that in the first one, the former is suitable for the quick-response control systems. In addition, our spatiotemporal control strategies, especially the second strategy, can be applied to other cardiac models, even to other reaction-diffusion systems. (general)
International Nuclear Information System (INIS)
Arana, J I; Bonilla, L L; Grahn, H T
2011-01-01
Undoped and strongly photoexcited semiconductor superlattices with field-dependent recombination behave as excitable or oscillatory media with spatially discrete nonlinear convection and diffusion. Infinitely long, dc-current-biased superlattices behaving as excitable media exhibit wave fronts with increasing or decreasing profiles, whose velocities can be calculated by means of asymptotic methods. These superlattices can also support pulses of the electric field. Pulses moving downstream with the flux of electrons can be constructed from their component wave fronts, whereas pulses advancing upstream do so slowly and experience saltatory motion: they change slowly in long intervals of time separated by fast transitions during which the pulses jump to the previous superlattice period. Photoexcited superlattices can also behave as oscillatory media and exhibit wave trains. (paper)
Dynamics of Turbulence Suppression in a Helicon Plasma
Hayes, Tiffany; Gilmore, Mark
2012-10-01
Experiments are currently being conducted in the the Helicon-Cathode Device (HelCat) at the University of New Mexico. The goal is to the study in detail the transition from a turbulent to a non-turbulent state in the presence of flow shear. HelCat has intrinsic fluctuations that have been identified as drift-waves. Using simple electrode biasing, it has been found that these fluctuations can be completely suppressed. In some extreme cases, a different instability, possibly the Kelvin-Helmholtz instability, can be excited. Detailed studies are underway in order to understand the characteristics of each mode, and to elucidate the underlying physics that cause the change between an unstable plasma, and an instability-free plasma. Dynamics being observed include changes in flow profiles, both azimuthal and parallel, as well as changes in potential and temperature gradients. Further understanding is being sought using several computer codes developed at EPFL: a linear stability solver (LSS,footnotetextP. Ricci and B.N. Rogers (2009). Phys Plasmas 16, 062303. a one-dimensional PIC code/sheath solver, ODISEE,footnotetextJ. Loizu, P. Ricci, and C. Theiler (2011). Phys Rev E 83, 016406 and a global, 3D Braginski code, GBS.footnotetextRicci, Rogers (2009) A basic overview of results will be presented.
Development and application of helicon plasma sources. Evolution of extensive plasma science
International Nuclear Information System (INIS)
Shinohara, Shunjiro
2009-01-01
Recent advances in plasma science are remarkable, and are deeply indebted to the development of sophisticated plasma sources. While numerous methods have been proposed for producing the plasma, helicon plasma sources, capable of generating high density (>10 13 cm -3 ) plasma with high ionization degree (>several ten percent) over a wide range of external control parameters, have been utilized in such broad areas as fundamental and processing plasmas, nuclear fusion, gas laser, modeling of space plasma, plasma acceleration/propulsion, among others. On the other hand, a number of important issues are left unsolved, in particular, those relevant to the wave phenomena and efficient plasma production. Solution to these issues are expected to play key roles in taking full advantage of the helicon plasma sources in the next generation. In this article, we overview our current understanding of the helicon plasma production and recent development of characteristic helicon plasma sources, and discuss possible future advancement of extensive plasma science utilizing them. (author)
Fast Magnetosonic Waves Observed by Van Allen Probes: Testing Local Wave Excitation Mechanism
Min, Kyungguk; Liu, Kaijun; Wang, Xueyi; Chen, Lunjin; Denton, Richard E.
2018-01-01
Linear Vlasov theory and particle-in-cell (PIC) simulations for electromagnetic fluctuations in a homogeneous, magnetized, and collisionless plasma are used to investigate a fast magnetosonic wave event observed by the Van Allen Probes. The fluctuating magnetic field observed exhibits a series of spectral peaks at harmonics of the proton cyclotron frequency Ωp and has a dominant compressional component, which can be classified as fast magnetosonic waves. Furthermore, the simultaneously observed proton phase space density exhibits positive slopes in the perpendicular velocity space, ∂fp/∂v⊥>0, which can be a source for these waves. Linear theory analyses and PIC simulations use plasma and field parameters measured in situ except that the modeled proton distribution is modified to have larger ∂fp/∂v⊥ under the assumption that the observed distribution corresponds to a marginally stable state when the distribution has already been scattered by the excited waves. The results show that the positive slope is the source of the proton cyclotron harmonic waves at propagation quasi-perpendicular to the background magnetic field, and as a result of interactions with the excited waves the evolving proton distribution progresses approximately toward the observed distribution.
International Nuclear Information System (INIS)
Bell, T.F.; Ngo, H.D.
1990-01-01
Recent satellite observations demonstrate that high amplitude, short wavelength (5 m ≤ λ ≤ 100 m) electrostatic waves are commonly excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and topside ionosphere where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. A new theoretical model of this phenomenon is presented, based upon passive linear scattering in a cold magnetoplasma. In this model the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. The excited short wavelength waves are quasi-electrostatic whistler mode waves, a type of lower hybrid wave, whose wave normal lies near the whistler mode resonance cone where the wave refractive index becomes very large. The amplitude of the excited electrostatic lower hybrid waves is calculated for a wide range of values of input electromagnetic wave frequency, wave normal direction, electron plasma frequency, gyrofrequency, ion composition, and irregularity scale and density enhancement. Results indicate that high amplitude lower hybrid waves can be excited over a wide range of parameters for irregularity density enhancements as low as 5% whenever the scale of the irregularity is of the same order as the lower hybrid wavelength
Multiple sine wave excitation of a hard spring oscillator
International Nuclear Information System (INIS)
Curreri, J.R.; Bezler, P.
1976-06-01
The vibration testing of non-linear systems has not received much attention in the literature. Frequently, linear procedures are used in the hope that large differences between the linear and non-linear responses will not occur. This may be valid for certain small ranges of the non-linearity and for a single harmonic component excitation. However, for multi-component periodic inputs, there is very little guidance in the literature for even a qualitative evaluation of the probable response. With multi-component periodic inputs, it has been shown that sub-combination frequencies can occur in cubic non-linear systems. Under these conditions, large responses can develop. The critical nature of the development of the large response has not been discussed. This is the subject of this paper. The qualitative response of a two component sine wave applied to a hard spring oscillator is shown
Tarvainen, O; Rouleau, G; Keller, R; Geros, E; Stelzer, J; Ferris, J
2008-02-01
The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H(-) ion beams in a filament-driven discharge. In this kind of an ion source the extracted H(-) beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H(-) converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H(-) ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H(-) ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H(-) production (main discharge) in order to further improve the brightness of extracted H(-) ion beams.
Tarvainen, O.; Rouleau, G.; Keller, R.; Geros, E.; Stelzer, J.; Ferris, J.
2008-02-01
The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H- ion beams in a filament-driven discharge. In this kind of an ion source the extracted H- beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H- converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H- ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H- ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H- production (main discharge) in order to further improve the brightness of extracted H- ion beams.
International Nuclear Information System (INIS)
Tarvainen, O.; Rouleau, G.; Keller, R.; Geros, E.; Stelzer, J.; Ferris, J.
2008-01-01
The converter-type negative ion source currently employed at the Los Alamos Neutron Science Center (LANSCE) is based on cesium enhanced surface production of H - ion beams in a filament-driven discharge. In this kind of an ion source the extracted H - beam current is limited by the achievable plasma density which depends primarily on the electron emission current from the filaments. The emission current can be increased by increasing the filament temperature but, unfortunately, this leads not only to shorter filament lifetime but also to an increase in metal evaporation from the filament, which deposits on the H - converter surface and degrades its performance. Therefore, we have started an ion source development project focused on replacing these thermionic cathodes (filaments) of the converter source by a helicon plasma generator capable of producing high-density hydrogen plasmas with low electron energy. In our studies which have so far shown that the plasma density of the surface conversion source can be increased significantly by exciting a helicon wave in the plasma, and we expect to improve the performance of the surface converter H - ion source in terms of beam brightness and time between services. The design of this new source and preliminary results are presented, along with a discussion of physical processes relevant for H - ion beam production with this novel design. Ultimately, we perceive this approach as an interim step towards our long-term goal, combining a helicon plasma generator with an SNS-type main discharge chamber, which will allow us to individually optimize the plasma properties of the plasma cathode (helicon) and H - production (main discharge) in order to further improve the brightness of extracted H - ion beams
International Nuclear Information System (INIS)
Kasahara, H.; Seki, T.; Kumazawa, R.; Saito, K.; Mutoh, T.; Kubo, S.; Shimozuma, T.; Igami, H.; Yoshimura, Y.; Takahashi, H.; Yamada, I.; Tokuzawa, T.; Ohdachi, S.; Morita, S.; Nomura, G.; Shimpo, F.; Komori, A.; Motojima, O.; Oosako, T.; Takase, Y.
2008-01-01
A wave detector, a newly designed magnetic probe, is installed in the large helical device (LHD). This wave detector is a 100-turn loop coil with electrostatic shield. Comparing a one-loop coil to this detector, this detector has roughly constant power coupling in the lower frequency range of 40 MHz, and it can easily detect magnetic wave in the frequency of a few megahertz. During high-harmonic fast wave heating, lower frequency waves (<10 MHz) were observed in the LHD for the first time, and for the power density threshold of lower frequency wave excitation (7.5 MHz) the power density of excited pumped wave (38.47 MHz) was approximately -46 dBm/Hz. These lower frequencies are kept constant for electron density and high energy particle distribution, and these lower frequency waves seem to be ion cyclotron waves caused by nonlinear wave-particle interaction, for example, parametric decay instability.
Magnetic fluctuations due to thermally excited Alfven waves
International Nuclear Information System (INIS)
Agim, Y.Z.; Prager, S.C.
1990-01-01
Magnetic fluctuations due to the thermally excited MHD waves are investigated using fluid and kinetic models to describe a stable, uniform, compressible plasma in the range above the drift wave frequency and below the ion cyclotron frequency. It is shown that the fluid model with resistivity yields spectral densities which are roughly Lorentzian, exhibit equipartition with no apparent cutoff in wavenumber space and a Bohm-type diffusion coefficient. Under certain conditions, the ensuing transport may be comparable to classical values. For a phenomenological cutoff imposed on the spectrum, the typical fluctuating-to-equilibrium magnetic field ratio is found to be of the order of 10 -10 . Physical mechanisms to obtain decay profiles of the spectra with increasing wavenumber due to dispersion and/or different forms of damping are investigated analytically in a cold fluid approximation and numerically, with a kinetic model. The mode dispersion due to the finite ion-gyrofrequency is identified as the leading effect determining the spectral profile shapes. It is found that the amplitude of fluctuations may be within a factor of the value suggested by the cold plasma model. The results from both models are presented and compared in low- and high-β regimes. 21 refs., 6 figs
Thin film characterization by resonantly excited internal standing waves
Energy Technology Data Exchange (ETDEWEB)
Di Fonzio, S [SINCROTRONE TRIESTE, Trieste (Italy)
1996-09-01
This contribution describes how a standing wave excited in a thin film can be used for the characterization of the properties of the film. By means of grazing incidence X-ray reflectometry one can deduce the total film thickness. On the other hand in making use of a strong resonance effect in the electric field intensity distribution inside a thin film on a bulk substrate one can learn more about the internal structure of the film. The profile of the internal standing wave is proven by diffraction experiments. The most appropriate non-destructive technique for the subsequent thin film characterization is angularly dependent X-ray fluorescence analysis. The existence of the resonance makes it a powerful tool for the detection of impurities and of ultra-thin maker layers, for which the position can be determined with very high precision (about 1% of the total film thickness). This latter aspect will be discussed here on samples which had a thin Ti marker layer at different positions in a carbon film. Due to the resonance enhancement it was still possible to perform these experiments with a standard laboratory x-ray tube and with standard laboratory tool for marker or impurity detection in thin films.
Excitation of nonlinear wave patterns in flowing complex plasmas
Jaiswal, S.; Bandyopadhyay, P.; Sen, A.
2018-01-01
We describe experimental observations of nonlinear wave structures excited by a supersonic mass flow of dust particles over an electrostatic potential hill in a dusty plasma medium. The experiments have been carried out in a Π- shaped experimental (DPEx) device in which micron sized Kaolin particles are embedded in a DC glow discharge Argon plasma. An equilibrium dust cloud is formed by maintaining the pumping speed and gas flow rate and the dust flow is induced either by suddenly reducing the height of a potential hill or by suddenly reducing the gas flow rate. For a supersonic flow of the dust fluid precursor solitons are seen to propagate in the upstream direction while wake structures propagate in the downstream direction. For flow speeds with a Mach number greater than 2 the dust particles flowing over the potential hill give rise to dispersive dust acoustic shock waves. The experimental results compare favorably with model theories based on forced K-dV and K-dV Burger's equations.
Development of a helicon ion source: Simulations and preliminary experiments
Afsharmanesh, M.; Habibi, M.
2018-03-01
In the present context, the extraction system of a helicon ion source has been simulated and constructed. Results of the ion source commissioning at up to 20 kV are presented as well as simulations of an ion beam extraction system. Argon current of more than 200 μA at up to 20 kV is extracted and is characterized with a Faraday cup and beam profile monitoring grid. By changing different ion source parameters such as RF power, extraction voltage, and working pressure, an ion beam with current distribution exhibiting a central core has been detected. Jump transition of ion beam current emerges at the RF power near to 700 W, which reveals that the helicon mode excitation has reached this power. Furthermore, measuring the emission line intensity of Ar ii at 434.8 nm is the other way we have used for demonstrating the mode transition from inductively coupled plasma to helicon. Due to asymmetrical longitudinal power absorption of a half-helix helicon antenna, it is used for the ion source development. The modeling of the plasma part of the ion source has been carried out using a code, HELIC. Simulations are carried out by taking into account a Gaussian radial plasma density profile and for plasma densities in range of 1018-1019 m-3. Power absorption spectrum and the excited helicon mode number are obtained. Longitudinal RF power absorption for two different antenna positions is compared. Our results indicate that positioning the antenna near to the plasma electrode is desirable for the ion beam extraction. The simulation of the extraction system was performed with the ion optical code IBSimu, making it the first helicon ion source extraction designed with the code. Ion beam emittance and Twiss parameters of the ellipse emittance are calculated at different iterations and mesh sizes, and the best values of the mesh size and iteration number have been obtained for the calculations. The simulated ion beam extraction system has been evaluated using optimized parameters such
Parametric instability and wave turbulence driven by tidal excitation of internal waves
Le Reun, Thomas; Favier, Benjamin; Le Bars, Michael
2018-04-01
We investigate the stability of stratified fluid layers undergoing homogeneous and periodic tidal deformation. We first introduce a local model which allows to study velocity and buoyancy fluctuations in a Lagrangian domain periodically stretched and sheared by the tidal base flow. While keeping the key physical ingredients only, such a model is efficient to simulate planetary regimes where tidal amplitudes and dissipation are small. With this model, we prove that tidal flows are able to drive parametric subharmonic resonances of internal waves, in a way reminiscent of the elliptical instability in rotating fluids. The growth rates computed via Direct Numerical Simulations (DNS) are in very good agreement with WKB analysis and Floquet theory. We also investigate the turbulence driven by this instability mechanism. With spatio-temporal analysis, we show that it is a weak internal wave turbulence occurring at small Froude and buoyancy Reynolds numbers. When the gap between the excitation and the Brunt-V\\"ais\\"al\\"a frequencies is increased, the frequency spectrum of this wave turbulence displays a -2 power law reminiscent of the high-frequency branch of the Garett and Munk spectrum (Garrett & Munk 1979) which has been measured in the oceans. In addition, we find that the mixing efficiency is altered compared to what is computed in the context of DNS of stratified turbulence excited at small Froude and large buoyancy Reynolds numbers and is consistent with a superposition of waves.
Relativistic shock waves and the excitation of plerions
Energy Technology Data Exchange (ETDEWEB)
Arons, J. (California Univ., Berkeley, CA (USA)); Gallant, Y.A. (California Univ., Berkeley, CA (USA). Dept. of Physics); Hoshino, Masahiro; Max, C.E. (California Univ., Livermore, CA (USA). Inst. of Geophysics and Planetary Physics); Langdon, A.B. (Lawrence Livermore National Lab., CA (USA))
1991-01-07
The shock termination of a relativistic magnetohydrodynamic wind from a pulsar is the most interesting and viable model for the excitation of the synchrotron sources observed in plerionic supernova remnants. We have studied the structure of relativistic magnetosonic shock waves in plasmas composed purely of electrons and positrons, as well as those whose composition includes heavy ions as a minority constituent by number. We find that relativistic shocks in symmetric pair plasmas create fully thermalized distributions of particles and fields downstream. Therefore, such shocks are not good candidates for the mechanism which converts rotational energy lost from a pulsar into the nonthermal synchrotron emission observed in plerions. However, when the upstream wind contains heavy ions which are minority constituent by number density, but carry the bulk of the energy density, much of the energy of the shock goes into a downstream, nonthermal power law distribution of positrons with energy distribution N(E)dE {proportional to}E{sup {minus}s}. In a specific model presented in some detail, s = 3. These characteristics are close to those assumed for the pairs in macroscopic MHD wind models of plerion excitation. The essential mechanism is collective synchrotron emission of left-handed extraordinary modes by the ions in the shock front at high harmonics of the ion cyclotron frequency, with the downstream positrons preferentially absorbing almost all of this radiation, mostly at their fundamental (relativistic) cyclotron frequencies. Possible applications to models of plerions and to constraints on theories of energy loss from pulsars are briefly outlines. 27 refs., 5 figs.
Coupling of RF antennas to large volume helicon plasma
Directory of Open Access Journals (Sweden)
Lei Chang
2018-04-01
Full Text Available Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasma-material interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of 0.5 m, and exploring its frequency dependence in the range of 13.56-70 MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important reference for the experimental design of large volume helicon plasma source with high RF power.
Observation of frequency cutoff for self-excited dust acoustic waves
Nosenko, V.; Zhdanov, S. K.; Morfill, G. E.; Kim, S.-H.; Heinrich, J.; Merlino, R. L.
2009-11-01
Complex (dusty) plasmas consist of fine solid particles suspended in a weakly ionized gas. Complex plasmas are excellent model systems to study wave phenomena down to the level of individual ``atoms''. Spontaneously excited dust acoustic waves were observed with high temporal resolution in a suspension of micron-size kaolin particles in a dc discharge in argon. Wave activity was found at frequencies as high as 400 Hz. At high wave numbers, the wave dispersion relation was acoustic-like (frequency proportional to wave number). At low wave numbers, the wave frequency did not tend to zero, but reached a cutoff frequency fc instead. The value of fc declined with distance from the anode. We propose a simple model that explains the observed cutoff by particle confinement in plasma. The existence of a cutoff frequency is very important for the propagation of waves: the waves excited above fc are propagating, and those below fc are evanescent.
Design of a helicon plasma source for ion–ion plasma production
Energy Technology Data Exchange (ETDEWEB)
Sharma, N., E-mail: narayan.sharma@cppipr.res.in; Chakraborty, M.; Neog, N.K.; Bandyopadhyay, M.
2017-04-15
Highlights: • Development of a helicon plasma system to carry out ion–ion plasma studies in electronegative gases such as Hydrogen, Oxygen and Chlorine. • Determination of initial parameters of helicon plasma source for ion–ion plasma by using dispersion relation of bounded helicon waves. • Design and development of solenoid with magnetic field strength production capability of ∼ 600 G along the axis of the chamber. • Optimization of the chamber parameters using Helic codes and estimation of optimum attainable density. • Estimation of RF power requirements for various gases. - Abstract: A helicon plasma system is being designed and developed at CPP-IPR. The design parameters of the system are deduced from the dispersion relation of bounded helicon waves and the required magnetic fields are simulated by using Poisson Superfish code. The Helic code is used to simulate the power deposition profile for various conditions and to investigate the optimum values of chamber parameters for effective coupling of radio frequency (RF) power to plasma. The helicon source system is aimed at carrying out ion–ion plasma studies in electronegative gases such as Hydrogen, Oxygen and Chlorine. The system mainly consists of a source chamber in which helicon plasma will be produced by injecting RF power at a frequency of 13.56 MHz through a right helical antenna in presence of a DC magnetic field followed by an expansion chamber in which it is expected to produce negative ions along with the positive ions. Installation of the various parts of the system is in progress. The details of the design and development of the system is presented in this article.
Dynamic Excitation of Monopiles by Steep and Breaking Waves: Experimental and Numerical Study
DEFF Research Database (Denmark)
Bredmose, Henrik; Slabiak, Peter; Sahlberg-Nielsen, Lasse
2013-01-01
. Emphasis is given to the observed impulsive excitation of the natural modes by steep and breaking waves. Additionally, springing and ringing-type continuous forcing of the first natural mode is seen for the moderately steep waves. The experiments were carried out at three depths and with two wave climates...
Pandey, Arun; Bandyopadhyay, M.; Sudhir, Dass; Chakraborty, A.
2017-10-01
Helicon wave heated plasmas are much more efficient in terms of ionization per unit power consumed. A permanent magnet based compact helicon wave heated plasma source is developed in the Institute for Plasma Research, after carefully optimizing the geometry, the frequency of the RF power, and the magnetic field conditions. The HELicon Experiment for Negative ion-I source is the single driver helicon plasma source that is being studied for the development of a large sized, multi-driver negative hydrogen ion source. In this paper, the details about the single driver machine and the results from the characterization of the device are presented. A parametric study at different pressures and magnetic field values using a 13.56 MHz RF source has been carried out in argon plasma, as an initial step towards source characterization. A theoretical model is also presented for the particle and power balance in the plasma. The ambipolar diffusion process taking place in a magnetized helicon plasma is also discussed.
Directory of Open Access Journals (Sweden)
Zhong-ye Tian
2014-01-01
Full Text Available The seismic responses of a long-span cable-stayed bridge under uniform excitation and traveling wave excitation in the longitudinal direction are, respectively, computed. The numerical results show that the bridge’s peak seismic responses vary significantly as the apparent wave velocity decreases. Therefore, the traveling wave effect must be considered in the seismic design of long-span bridges. The bridge’s peak seismic responses do not vary monotonously with the apparent wave velocity due to the traveling wave resonance. A new traveling wave excitation method that can simplify the multisupport excitation process into a two-support excitation process is developed.
Excitation of electrostatic ion cyclotron wave in electron beam plasma system
International Nuclear Information System (INIS)
Fukumura, Takashi; Takamoto, Teruo
1984-01-01
The electrostatic ion cyclotron waves excited in an electron beam plasma system was investigated. The excitation condition of the waves was calculated by using Harris type dispersion relation under some assumption, and its comparison with the experimental result was made. Beam plasma discharge is a kind of RF discharge, and it is caused by the waves generated by the interaction of electron beam with plasma. It was shown that electrostatic ion cyclotron waves seemed to be the most probable as excited waves. But the excitation mechanism of these waves has not been concretely investigated. In this study, the excitation condition of electrostatic ion cyclotron waves was calculated as described above. The experimental apparatus and the results of potential, electric field and ion saturation current in beam plasma, electron drift motion in azimuthal direction and the waves excited in beam plasma are reported. The frequency of oscillation observed in beam plasma corresponds to the harmonics or subharmonics of ion cyclotron frequency. The calculation of Harris type dispersion relation, the numerical calculation and the comparison of the experimental result with the calculated result are described. (Kako, I.)
Excitation of the Uller-Zenneck electromagnetic surface waves in the prism-coupled configuration
Rasheed, Mehran; Faryad, Muhammad
2017-08-01
A configuration to excite the Uller-Zenneck surface electromagnetic waves at the planar interfaces of homogeneous and isotropic dielectric materials is proposed and theoretically analyzed. The Uller-Zenneck waves are surface waves that can exist at the planar interface of two dissimilar dielectric materials of which at least one is a lossy dielectric material. In this paper, a slab of a lossy dielectric material was taken with lossless dielectric materials on both sides. A canonical boundary-value problem was set up and solved to find the possible Uller-Zenneck waves and waveguide modes. The Uller-Zenneck waves guided by the slab of the lossy dielectric material were found to be either symmetric or antisymmetric and transmuted into waveguide modes when the thickness of that slab was increased. A prism-coupled configuration was then successfully devised to excite the Uller-Zenneck waves. The results showed that the Uller-Zenneck waves are excited at the same angle of incidence for any thickness of the slab of the lossy dielectric material, whereas the waveguide modes can be excited when the slab is sufficiently thick. The excitation of Uller-Zenneck waves at the planar interfaces with homogeneous and all-dielectric materials can usher in new avenues for the applications for electromagnetic surface waves.
Unusual spiral wave dynamics in the Kessler-Levine model of an excitable medium.
Oikawa, N; Bodenschatz, E; Zykov, V S
2015-05-01
The Kessler-Levine model is a two-component reaction-diffusion system that describes spatiotemporal dynamics of the messenger molecules in a cell-to-cell signaling process during the aggregation of social amoeba cells. An excitation wave arising in the model has a phase wave at the wave back, which simply follows the wave front after a fixed time interval with the same propagation velocity. Generally speaking, the medium excitability and the refractoriness are two important factors which determine the spiral wave dynamics in any excitable media. The model allows us to separate these two factors relatively easily since the medium refractoriness can be changed independently of the medium excitability. For rigidly rotating waves, the universal relationship has been established by using a modified free-boundary approach, which assumes that the front and the back of a propagating wave are thin in comparison to the wave plateau. By taking a finite thickness of the domain boundary into consideration, the validity of the proposed excitability measure has been essentially improved. A novel method of numerical simulation to suppress the spiral wave instabilities is introduced. The trajectories of the spiral tip observed for a long refractory period have been investigated under a systematic variation of the medium refractoriness.
Sound excitation at reflection of two electromagnetic waves from dence semibounded plasma
International Nuclear Information System (INIS)
Livdan, D.O.; Muratov, V.I.; Shuklin, A.P.
1988-01-01
The problem of two electromagnetic waves reflection by semibounded plasma which is nontransparent for each of these waves is solved. The reflection coefficients are obtained for normally incident waves. It is shown that the moduli of the reflection coefficients differ from the unit and this is due to the interaction of the external raiation with the acoustic wave excited in plasma. The energy flux in plasma is calculated
International Nuclear Information System (INIS)
Longinov, A.V.; Lukinov, V.A.
1992-01-01
It is proposed to use a system of auxiliary passive gaps to excite waves in a plasma traveling in one direction parallel to the magnetic field, in order to localize the radiating surface of a surface-wave antenna. Using excitation of ion Bernstein waves in the plasma as an example the main properties of such an antenna system have been studied. It is shown that the use of passive gaps permits high directionality to be achieved for the radiation and allows the size of the radiating surface of the antenna to be controlled. 10 refs., 6 figs
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse
Energy Technology Data Exchange (ETDEWEB)
Grishkov, V. E.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2017-03-15
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.
Theory of spin and lattice wave dynamics excited by focused laser pulses
Shen, Ka; Bauer, Gerrit E. W.
2018-06-01
We develop a theory of spin wave dynamics excited by ultrafast focused laser pulses in a magnetic film. We take into account both the volume and surface spin wave modes in the presence of applied, dipolar and magnetic anisotropy fields and include the dependence on laser spot exposure size and magnetic damping. We show that the sound waves generated by local heating by an ultrafast focused laser pulse can excite a wide spectrum of spin waves (on top of a dominant magnon–phonon contribution). Good agreement with recent experiments supports the validity of the model.
Ignatov, A. I.; Merzlikin, A. M.
2018-03-01
A method for development of gratings for effective excitation of surface plasmonic waves using holography principles has been proposed and theoretically analyzed. For the case of a plasmonic wave in a dielectric layer on metal, the proposed volume hologram is 1.7 times more effective than the simple grating of slits in the dielectric layer with the optimized period and slits' width. The advantage of the hologram over the optimized grating is in the refractive index distribution that accounts phase relationships between an exciting and an excited waves more correctly. The proposed holographic method is universal. As expected, this can be extended for effective excitation of different types of optical surface waves and modes of optical waveguides.
External excitation of ion cyclotron drift waves in a two-ion species plasma
International Nuclear Information System (INIS)
Kando, M.; Ikezawa, S.; Sugai, H.
1984-01-01
Ion cyclotron drift waves propagating across a density gradient and a magnetic field have been excited externally in a two-ion species plasma, with its concentration ratio controlled. The measured dispersion relations agree with the theoretical predictions. (author)
Energy Technology Data Exchange (ETDEWEB)
Matsumoto, H.; Kimura, T.
1986-01-01
Triggered by the experimental results of the MINIX, a computer simulation study was initiated on the nonlinear excitation of electrostatic electron cyclotron waves by a monochromatic electromagnetic wave such as the transmitted microwave in the MINIX. The model used assumes that both of the excited waves and exciting (pumping) electromagnetic wave as well as the idler electromagnetic wave propagate in the direction perpendicular to the external magnetic field. The simulation code used for this study was the one-and-two-half dimensional electromagnetic particle code named KEMPO. The simulation result shows the high power electromagnetic wave produces both the backscattered electromagnetic wave and electrostatic electron cyclotron waves as a result of nonlinear parametric instability. Detailed nonlinear microphysics related to the wave excitation is discussed in terms of the nonlinear wave-wave couplings and associated ponderomotive force produced by the high power electromagnetic waves. 2 references, 4 figures.
International Nuclear Information System (INIS)
Matsumoto, H.; Kimura, T.
1986-01-01
Triggered by the experimental results of the MINIX, a computer simulation study was initiated on the nonlinear excitation of electrostatic electron cyclotron waves by a monochromatic electromagnetic wave such as the transmitted microwave in the MINIX. The model used assumes that both of the excited waves and exciting (pumping) electromagnetic wave as well as the idler electromagnetic wave propagate in the direction perpendicular to the external magnetic field. The simulation code used for this study was the one-and-two-half dimensional electromagnetic particle code named KEMPO. The simulation result shows the high power electromagnetic wave produces both the backscattered electromagnetic wave and electrostatic electron cyclotron waves as a result of nonlinear parametric instability. Detailed nonlinear microphysics related to the wave excitation is discussed in terms of the nonlinear wave-wave couplings and associated ponderomotive force produced by the high power electromagnetic waves. 2 references, 4 figures
International Nuclear Information System (INIS)
Zhang, Y. S.; Cai, F.; Xu, W. M.
2011-01-01
The ship motion equation with a cosine wave excitement force describes the slip moments in regular waves. A new kind of wave excitement force model, with the form as sums of cosine functions was proposed to describe ship rolling in irregular waves. Ship rolling time series were obtained by solving the ship motion equation with the fourth-order-Runger-Kutta method. These rolling time series were synthetically analyzed with methods of phase-space track, power spectrum, primary component analysis, and the largest Lyapunove exponent. Simulation results show that ship rolling presents some chaotic characteristic when the wave excitement force was applied by sums of cosine functions. The result well explains the course of ship rolling's chaotic mechanism and is useful for ship hydrodynamic study.
Self-excited hydrothermal waves in evaporating sessile drops
Sefiane K.; Moffat J.R.; Matar O.K.; Craster R.V.
2008-01-01
Pattern formation driven by the spontaneous evaporation of sessile drops of methanol, ethanol, and FC-72 using infrared thermography is observed and, in certain cases, interpreted in terms of hydrothermal waves. Both methanol and ethanol drops exhibit thermal wave trains, whose wave number depends strongly on the liquid volatililty and substrate thermal conductivity. The FC- 72 drops develop cellular structures whose size is proportional to the local thickness. Prior to this work, hydrotherma...
Thermosonic Testing with Phased Matched Guided Wave Excitation
Markus RAHAMMER, Igor SOLODOV, Wolfgang BISLE, Dieter SCHERLING , Marc KREUTZBRUCK
2016-01-01
Abstract. Vibrothermography, is an established NDT method praised for its full-field and defect-selective imaging. Especially for cracks and similar damage, defect signals are produced within seconds for a wide variety of materials. Usually high power sonotrodes that are applied with kN pressure are employed in order to maximize ultrasonic excitation of the specimens. An increase in excitation power is used for boosting the defect signal strength, i.e. the rise in temperature. Improvements...
Excitation of a plasma wave by a right-handed Gaussian EM beam
International Nuclear Information System (INIS)
Sodha, M.S.; Patheja, B.L.; Sharma, R.P.
1979-01-01
This paper presents an investigation of the excitation of an electron plasma wave in a hot collisionless magnetoplasma by a right-handed Gaussian EM beam (pump wave) when the plasma wave and the pump wave are propagating along the static magnetic field. On account of the Gaussian intensity distribution of the pump wave, pondermotive force becomes finite and the electrons are redistributed. This redistribution is highly dependent on whether ω/sub c/>2ω 0 or ω/sub c/ 0 , where ω/sub c/ is the electron cyclotron frequency and ω 0 is the pump-wave frequency. The modified background electron density leads to coupling between the plasma wave and the pump wave. When the initial power of the pump wave is greater than the critical power for self-focusing, oscillatory self-focusing of the pump wave occurs and the coupling of the two waves are modified. Moreover, the effect of changing the intensity of the magnetic field affects the self-focusing of the pump wave, and the plasma-wave excitation is accordingly affected
Resonance localization in tokamaks excited with ICRF waves
International Nuclear Information System (INIS)
Kerbel, G.D.; McCoy, M.G.
1985-01-01
Advanced wave models used to evaluate ICRH in tokamaks typically use warm plasma theory and allow inhomogeneity in one dimension. The majority of these calculations neglect the fact that gyrocenters experience the inhomogeneity via their motion parallel to the magnetic field. The non-local effects of rotational transform and toroidicity can play a significant role in both the propagation and the absorption physics. In strongly driven systems, wave damping can distort the particle distribution function supporting the wave and this produces changes in the absorption. The most common approach is to use Maxwellian absorption rates. We have developed a bounce-averaged Fokker-Planck quasilinear computational model which evolves the population of particles on more realistic orbits. Each wave-particle resonance has its own specific interaction amplitude within any given volume element; these data need only be generated once, and appropriately stored for efficient retrieval. The wave-particle resonant interaction then serves as a mechanism by which the diffusion of particle populations can proceed among neighboring orbits. The local specific spectral energy absorption rate is directly calculable once the orbit geometry and populations are determined. The code is constructed in such fashion as to accommodate wave propagation models which provide the wave spectral energy density on a poloidal cross-section. Information provided by the calculation includes the local absorption properties of the medium which can then be exploited to evolve the wave field
Excitation of lower hybrid waves by electron beams in finite geometry plasmas
International Nuclear Information System (INIS)
Gagne, R.R.J.; Shoucri, M.M.
1978-01-01
The dispersion relations for the quasi-static lower hybrid surface waves are derived. Conditions for their existence and their linear excitation by a small density electron beam are discussed. Instabilities appearing in low-frequency surface waves are also discussed. (author)
Collision broadened resonance localization in tokamaks excited with ICRF waves
International Nuclear Information System (INIS)
Kerbel, G.D.; McCoy, M.G.
1985-08-01
Advanced wave models used to evaluate ICRH in tokamaks typically use warm plasma theory and allow inhomogeneity in one dimension. The authors have developed a bounce-averaged Fokker-Planck quasilinear computational model which evolves the population of particles on more realistic orbits. Each wave-particle resonance has its own specific interaction amplitude within any given volume element. These data need only be generated once, and appropriately stored for efficient retrieval. The wave-particle resonant interaction then serves as a mechanism by which the diffusion of particle populations can proceed among neighboring orbits. Collisions affect the absorption of rf energy by two quite distinct processes: In addition to the usual relaxation towards the Maxwellian distribution creating velocity gradients which drive quasilinear diffusion, collisions also affect the wave-particle resonance through the mechanism of gyro-phase diffusion. The local specific spectral energy absorption rate is directly calculable once the orbit geometry and populations are determined. The code is constructed in such fashion as to accommodate wave propagation models which provide the wave spectral energy density on a poloidal cross-section. Information provided by the calculation includes the local absorption properties of the medium which can then be exploited to evolve the wave field
Observation and excitation of magnetohydrodynamic waves in numerical models of Earth's core
Teed, R.; Hori, K.; Tobias, S.; Jones, C. A.
2017-12-01
Several types of magnetohydrodynamic waves are theorised to operate in Earth's outer core but their detection is limited by the inability to probe the fluid core directly. Secular variation data and periodic changes in Earth's length-of-day provide evidence for the possible existence of waves. Numerical simulations of core dynamics enable us to search directly for waves and determine their properties. With this information it is possible to consider whether they can be the origin of features observed in observational data. We focus on two types of wave identified in our numerical experiments: i) torsional waves and ii) slow magnetic Rossby waves. Our models display periodic, Earth-like torsional waves that travel outwards from the tangent cylinder circumscribing the inner core. We discuss the properties of these waves and their similarites to observational data. Excitation is via a matching of the Alfvén frequency with that of small modes of convection focused at the tangent cylinder. The slow magnetic Rossby waves observed in our simulations show that these waves may account for some geomagnetic westward drifts observed at mid-latitudes. We present analysis showing excitation of waves by the convective instability and we discuss how the detection of these waves could also provide an estimate of the strength of the toroidal component of the magnetic field within the planetary fluid core.
Excitation of plasma waves by electron guns at the ISEE-1 satellite
International Nuclear Information System (INIS)
Lebreton, Zh.P.; Torbert, R.; Anderson, R.; Kharvi, K.
1985-01-01
Study of the effects resulting from excitation of plasma waves by electron beams injected from JSEE-1 satellite is carried out. Cases of the satellite traversing the magnetosphere magnetosheath and solar wind are considered. 10-60 μA and 0-40 V electron beam injection from the satellite increased electrostatic waves spectral intensity. The waves below ionic plasma frequency are interpreted as ion acoustic waves. To explain the-above-electron-plasma-frequency wave oscillation a communication system between electron plasma mode and electron flux with the velocities above the mean thermal velocity of plasma cold electrons is suggested
International Nuclear Information System (INIS)
Ma Jun; Wang Chunni; Li Yanlong; Pu Zhongsheng; Jin Wuyin
2008-01-01
This paper proposes a scheme of parameter perturbation to suppress the stable rotating spiral wave, meandering spiral wave and turbulence in the excitable media, which is described by the modified Fitzhugh–Nagumo (MFHN) model. The controllable parameter in the MFHN model is perturbed with a weak pulse and the pulse period is decided by the rotating period of the spiral wave approximatively. It is confirmed that the spiral wave and spiral turbulence can be suppressed greatly. Drift and instability of spiral wave can be observed in the numerical simulation tests before the whole media become homogeneous finally. (general)
Nonlocal analysis of the excitation of the geodesic acoustic mode by drift waves
DEFF Research Database (Denmark)
Guzdar, P.N.; Kleva, R.G.; Chakrabarti, N.
2009-01-01
The geodesic acoustic modes (GAMs) are typically observed in the edge region of toroidal plasmas. Drift waves have been identified as a possible cause of excitation of GAMs by a resonant three wave parametric process. A nonlocal theory of excitation of these modes in inhomogeneous plasmas typical...... of the edge region of tokamaks is presented in this paper. The continuum GAM modes with coupling to the drift waves can create discrete "global" unstable eigenmodes localized in the edge "pedestal" region of the plasma. Multiple resonantly driven unstable radial eigenmodes can coexist on the edge pedestal....
Excitation of surface waves of ultracold neutrons on absorbing trap walls as anomalous loss factor
International Nuclear Information System (INIS)
Bokun, R.Ch.
2006-01-01
One analyzed probability of excitation of surface waves of ultracold neutrons in terms of a plane model consisting of three media: vacuum, a finite depth neutron absorbing substance layer and a neutron reflecting substrate. One demonstrated the absence of the mentioned surface waves in terms of the generally accepted model of two media: vacuum contiguous to the plane surface of a substance filled half-space. One pointed out the effect of the excited surface waves of ultracold neutrons on the increase of their anomalous losses in traps [ru
Chaotic wave trains in an oscillatory/excitable medium
International Nuclear Information System (INIS)
Rabinovitch, A.; Gutman, M.; Biton, Y.; Aviram, I.
2006-01-01
We study the chaotic dynamics of a heterogeneous reaction-diffusion medium composed of two uniform regions: one oscillatory, and the other excitable. It is shown that, by altering the diffusion coefficient, local chaotic oscillations can be induced at the interface between regions, which in turn, generate different chaotic sequences of pulses traveling in the excitable region. We analyze the properties of the local chaotic driver, as well as the diffusion-induced transitions. A procedure based on the abnormal frequency-locking phenomenon is proposed for controlling such sequences. Relevance of the obtained results to cardiac dynamics is briefly discussed
Self-excited hydrothermal waves in evaporating sessile drops
Sefiane, K.; Moffat, J. R.; Matar, O. K.; Craster, R. V.
2008-08-01
Pattern formation driven by the spontaneous evaporation of sessile drops of methanol, ethanol, and FC-72 using infrared thermography is observed and, in certain cases, interpreted in terms of hydrothermal waves. Both methanol and ethanol drops exhibit thermal wave trains, whose wave number depends strongly on the liquid volatililty and substrate thermal conductivity. The FC-72 drops develop cellular structures whose size is proportional to the local thickness. Prior to this work, hydrothermal waves have been observed in the absence of evaporation in shallow liquid layers subjected to an imposed temperature gradient. In contrast, here both the temperature gradients and the drop thickness vary spatially and temporally and are a natural consequence of the evaporation process.
International Nuclear Information System (INIS)
Dragila, R.; Vukovic, S.
1988-01-01
The properties of surfave waves that are associated with a boundary between a rare plasma and a dense magnetoactive plasma and that propagate along a dc magnetic field are investigated. It is shown that the presence of the magnetic field introduces symmetry in terms of the polarization of the incident electromagnetic wave that excites the surface waves. A surface wave excited by an incident p-polarized (s-polarized) electromagnetic wave leaks in the form of an s-polarized (p-polarized) electromagnetic wave. The rate of rotation of polarization is independent of the polarization of the incident wave. Because a surface wave can leak in the form of an s-polarized electromagnetic wave, it can also be pumped by such a wave, and conditions were found for excitation of a surface wave by an s-polarized incident electromagnetic wave
Qian, Yu; Zhang, Zhaoyang
2016-01-01
In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects.
Measurements of the power spectrum and dispersion relation of self-excited dust acoustic waves
Nosenko, V.; Zhdanov, S. K.; Kim, S.-H.; Heinrich, J.; Merlino, R. L.; Morfill, G. E.
2009-12-01
The spectrum of spontaneously excited dust acoustic waves was measured. The waves were observed with high temporal resolution using a fast video camera operating at 1000 frames per second. The experimental system was a suspension of micron-size kaolin particles in the anode region of a dc discharge in argon. Wave activity was found at frequencies as high as 450 Hz. At high wave numbers, the wave dispersion relation was acoustic-like (frequency proportional to wave number). At low wave numbers, the wave frequency did not tend to zero, but reached a cutoff frequency instead. The cutoff value declined with distance from the anode. We ascribe the observed cutoff to the particle confinement in this region.
Estimation of excitation forces for wave energy converters control using pressure measurements
Abdelkhalik, O.; Zou, S.; Robinett, R.; Bacelli, G.; Wilson, D.
2017-08-01
Most control algorithms of wave energy converters require prediction of wave elevation or excitation force for a short future horizon, to compute the control in an optimal sense. This paper presents an approach that requires the estimation of the excitation force and its derivatives at present time with no need for prediction. An extended Kalman filter is implemented to estimate the excitation force. The measurements in this approach are selected to be the pressures at discrete points on the buoy surface, in addition to the buoy heave position. The pressures on the buoy surface are more directly related to the excitation force on the buoy as opposed to wave elevation in front of the buoy. These pressure measurements are also more accurate and easier to obtain. A singular arc control is implemented to compute the steady-state control using the estimated excitation force. The estimated excitation force is expressed in the Laplace domain and substituted in the control, before the latter is transformed to the time domain. Numerical simulations are presented for a Bretschneider wave case study.
Spirals in a reaction-diffusion system: Dependence of wave dynamics on excitability
Mahanta, Dhriti; Das, Nirmali Prabha; Dutta, Sumana
2018-02-01
A detailed study of the effects of excitability of the Belousov-Zhabotinsky (BZ) reaction on spiral wave properties has been carried out. Using the Oregonator model, we explore the various regimes of wave activity, from sustained oscillations to wave damping, as the system undergoes a Hopf bifurcation, that is achieved by varying the excitability parameter, ɛ . We also discover a short range of parameter values where random oscillations are observed. With an increase in the value of ɛ , the frequency of the wave decreases exponentially, as the dimension of the spiral core expands. These numerical results are confirmed by carrying out experiments in thin layers of the BZ system, where the excitability is changed by varying the concentrations of the reactant species. Effect of reactant concentrations on wave properties like time period and wavelength are also explored in detail. Drifting and meandering spirals are found in the parameter space under investigation, with the excitability affecting the tip trajectory in a way predicted by the numerical studies. This study acts as a quantitative evidence of the relationship between the excitability parameter, ɛ , and the substrate concentrations.
Spirals in a reaction-diffusion system: Dependence of wave dynamics on excitability.
Mahanta, Dhriti; Das, Nirmali Prabha; Dutta, Sumana
2018-02-01
A detailed study of the effects of excitability of the Belousov-Zhabotinsky (BZ) reaction on spiral wave properties has been carried out. Using the Oregonator model, we explore the various regimes of wave activity, from sustained oscillations to wave damping, as the system undergoes a Hopf bifurcation, that is achieved by varying the excitability parameter, ε. We also discover a short range of parameter values where random oscillations are observed. With an increase in the value of ε, the frequency of the wave decreases exponentially, as the dimension of the spiral core expands. These numerical results are confirmed by carrying out experiments in thin layers of the BZ system, where the excitability is changed by varying the concentrations of the reactant species. Effect of reactant concentrations on wave properties like time period and wavelength are also explored in detail. Drifting and meandering spirals are found in the parameter space under investigation, with the excitability affecting the tip trajectory in a way predicted by the numerical studies. This study acts as a quantitative evidence of the relationship between the excitability parameter, ε, and the substrate concentrations.
Energy Technology Data Exchange (ETDEWEB)
Higashi, Yoichi, E-mail: higashiyoichi@ms.osakafu-u.ac.jp [Department of Mathematical Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531 (Japan); Nagai, Yuki [CCSE, Japan Atomic Energy Agency, 178-4-4, Wakashiba, Kashiwa, Chiba 277-0871 (Japan); Yoshida, Tomohiro [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Kato, Masaru [Department of Mathematical Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531 (Japan); Yanase, Youichi [Department of Physics, Niigata University, Niigata 950-2181 (Japan)
2015-11-15
Highlights: • We focus on the pair-density wave state in bilayer Rashba superconductors. • The zero energy Bogoliubov wave functions are localized at the edge and vortex core. • We investigate the excitation spectra of edge and vortex bound states. - Abstract: We study the excitation spectra and the wave functions of quasiparticle bound states at a vortex and an edge in bilayer Rashba superconductors under a magnetic field. In particular, we focus on the quasiparticle states at the zero energy in the pair-density wave state in a topologically non-trivial phase. We numerically demonstrate that the quasiparticle wave functions with zero energy are localized at both the edge and the vortex core if the magnetic field exceeds the critical value.
Skirting terahertz waves in a photo-excited nanoslit structure
Energy Technology Data Exchange (ETDEWEB)
Shalaby, Mostafa, E-mail: mostafa.shalaby@psi.ch, E-mail: thomas.feurer@iap.unibe.ch [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); SwissFEL, Paul Scherrer Institut, Villigen 5232 (Switzerland); Fabiańska, Justyna; Feurer, Thomas, E-mail: mostafa.shalaby@psi.ch, E-mail: thomas.feurer@iap.unibe.ch [Institute of Applied Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Peccianti, Marco [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Department of Physics and Astronomy, University of Sussex, Pevensey Building II, 3A8, Falmer, Brighton BN1 9QH (United Kingdom); Ozturk, Yavuz; Vidal, Francois; Morandotti, Roberto [INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Sigg, Hans [LMN, Paul Scherrer Institut, Villigen 5232 (Switzerland)
2014-04-28
Terahertz fields can be dramatically enhanced as they propagate through nanometer-sized slits. The enhancement is mediated by a significant accumulation of the induced surface charges on the surrounding metal. This enhancement is shown here to be dynamically modulated while the nanoslits are gradually shunted using a copropagating optical beam. The terahertz fields are found to skirt the nanoscale photo-excited region underneath the slits, scattering to the far field and rigorously mapping the near field.
On the excitation of ULF waves by solar wind pressure enhancements
Directory of Open Access Journals (Sweden)
P. T. I. Eriksson
2006-11-01
Full Text Available We study the onset and development of an ultra low frequency (ULF pulsation excited by a storm sudden commencement. On 30 August 2001, 14:10 UT, the Cluster spacecraft are located in the dayside magnetosphere and observe the excitation of a ULF pulsation by a threefold enhancement in the solar wind dynamic pressure. Two different harmonics are observed by Cluster, one at 6.8 mHz and another at 27 mHz. We observe a compressional wave and the development of a toroidal and poloidal standing wave mode. The toroidal mode is observed over a narrow range of L-shells whereas the poloidal mode is observed to have a much larger radial extent. By looking at the phase difference between the electric and magnetic fields we see that for the first two wave periods both the poloidal and toroidal mode are travelling waves and then suddenly change into standing waves. We estimate the azimuthal wave number for the 6.8 mHz to be m=10±3. For the 27 mHz wave, m seems to be several times larger and we discuss the implications of this. We conclude that the enhancement in solar wind pressure excites eigenmodes of the geomagnetic cavity/waveguide that propagate tailward and that these eigenmodes in turn couple to toroidal and poloidal mode waves. Thus our observations give firm support to the magnetospheric waveguide theory.
Ionic wave propagation and collision in an excitable circuit model of microtubules
Guemkam Ghomsi, P.; Tameh Berinyoh, J. T.; Moukam Kakmeni, F. M.
2018-02-01
In this paper, we report the propensity to excitability of the internal structure of cellular microtubules, modelled as a relatively large one-dimensional spatial array of electrical units with nonlinear resistive features. We propose a model mimicking the dynamics of a large set of such intracellular dynamical entities as an excitable medium. We show that the behavior of such lattices can be described by a complex Ginzburg-Landau equation, which admits several wave solutions, including the plane waves paradigm. A stability analysis of the plane waves solutions of our dynamical system is conducted both analytically and numerically. It is observed that perturbed plane waves will always evolve toward promoting the generation of localized periodic waves trains. These modes include both stationary and travelling spatial excitations. They encompass, on one hand, localized structures such as solitary waves embracing bright solitons, dark solitons, and bisolitonic impulses with head-on collisions phenomena, and on the other hand, the appearance of both spatially homogeneous and spatially inhomogeneous stationary patterns. This ability exhibited by our array of proteinic elements to display several states of excitability exposes their stunning biological and physical complexity and is of high relevance in the description of the developmental and informative processes occurring on the subcellular scale.
International Nuclear Information System (INIS)
Gutierrez Tapia, C.
1990-01-01
It is shown in a one-dimensional model that when a current in a plasma sheath is present, the excitation of surface waves and electrostatic fields by a RF wave is possible in the sheath. This phenomena depends strongly on the joint action of Miller's and driven forces. It is also shown that the action of these forces are carried out at different characteristic times when the wave front travels through the plasma sheath. The influence of the current, in the steady limit, is taken into account by a small functional variation of the density perturbations and generated electrostatic field. (Author)
Suppression of beam-excited electron waves by an externally applied RF signal
International Nuclear Information System (INIS)
Fukumasa, Osamu; Itatani, Ryohei
1980-11-01
Suppression of the beam-excited electron wave in a bounded system is investigated in connection with the beam distribution function. Wave suppression has two different processes depending on whether injected beams are reflected at the other end or not. In the absence of reflected beam electrons, deformation of the beam distribution function is observed in relation to the suppression of the electron wave. However, when beam electrons are reflected, the external wave suppresses the electron wave but distribution function shows no appreciable change. These experimental results show that nonlinear behaviors of beam electrons, namely behaviors of reflected beams, are quite important for wave suppression. By using the method of partial simulation, interaction between two waves in the bounded system including nonlinear motions of beam electrons is studied numerically. Qualitative agreement between experimental and numerical results is obtained. (author)
Nardi, Damiano; Travagliati, Marco; Siemens, Mark E; Li, Qing; Murnane, Margaret M; Kapteyn, Henry C; Ferrini, Gabriele; Parmigiani, Fulvio; Banfi, Francesco
2011-10-12
High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system's excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths.
Excitation of intense shock waves by soft X-radiation
International Nuclear Information System (INIS)
Branitskij, A.V.; Fortov, V.E.; Danilenko, K.N.; Dyabilin, K.S.; Grabovskij, E.V.; Vorobev, O. Yu.; Lebedev, M.E.; Smirnov, V.P.; Zakharov, A.E.; Persyantsev, I.V.
1996-01-01
Investigation of the shock waves generated by soft x radiation in Al, Sn, Fe, and Pb targets is reported. The soft x radiation was induced by the dynamic compression and heating of the cylindrical z-pinch plasma generated in the ANGARA-5-1 pulsed power machine. The temperature of the z-pinch plasma was as high as 60 - 120 eV, and the duration of the x-ray pulse reached 30 ns FWHM. Thick stepped Al/Pb, Sn/Pb, and pure Pb targets were used. The results of experiments show that uniform intense shock waves can be generated by z-pinch plasma soft x-ray radiation. The uniformity of the shock is very high. At a flux power of the order of several TW/cm 2 , a shock pressure of some hundreds of GPa was achieved. (J.U.). 3 figs., 11 refs
Excitation of intense shock waves by soft X-radiation
Energy Technology Data Exchange (ETDEWEB)
Branitskij, A V; Fortov, V E; Danilenko, K N; Dyabilin, K S; Grabovskij, E V; Vorobev, O Yu; Lebedev, M E; Smirnov, V P; Zakharov, A E; Persyantsev, I V [Troitsk Inst. of Innovative and Fusion Research, Troitsk (Russian Federation)
1997-12-31
Investigation of the shock waves generated by soft x radiation in Al, Sn, Fe, and Pb targets is reported. The soft x radiation was induced by the dynamic compression and heating of the cylindrical z-pinch plasma generated in the ANGARA-5-1 pulsed power machine. The temperature of the z-pinch plasma was as high as 60 - 120 eV, and the duration of the x-ray pulse reached 30 ns FWHM. Thick stepped Al/Pb, Sn/Pb, and pure Pb targets were used. The results of experiments show that uniform intense shock waves can be generated by z-pinch plasma soft x-ray radiation. The uniformity of the shock is very high. At a flux power of the order of several TW/cm{sup 2}, a shock pressure of some hundreds of GPa was achieved. (J.U.). 3 figs., 11 refs.
Nonlinear beat excitation of low frequency wave in degenerate plasmas
Mir, Zahid; Shahid, M.; Jamil, M.; Rasheed, A.; Shahbaz, A.
2018-03-01
The beat phenomenon due to the coupling of two signals at slightly different frequencies that generates the low frequency signal is studied. The linear dispersive properties of the pump and sideband are analyzed. The modified nonlinear dispersion relation through the field coupling of linear modes against the beat frequency is derived in the homogeneous quantum dusty magnetoplasmas. The dispersion relation is used to derive the modified growth rate of three wave parametric instability. Moreover, significant quantum effects of electrons through the exchange-correlation potential, the Bohm potential, and the Fermi pressure evolved in macroscopic three wave interaction are presented. The analytical results are interpreted graphically describing the significance of the work. The applications of this study are pointed out at the end of introduction.
International Nuclear Information System (INIS)
Zhang Hai-Yan; Yu Jian-Bo
2011-01-01
Excitation and propagation of Lamb waves by using rectangular and circular piezoelectric transducers surface-bonded to an isotropic plate are investigated in this work. Analytical stain wave solutions are derived for the two transducer shapes, giving the responses of these transducers in Lamb wave fields. The analytical study is supported by a numerical simulation using the finite element method. Symmetric and antisymmetric components in the wave propagation responses are inspected in detail with respect to test parameters such as the transducer geometry, the length and the excitation frequency. By placing only one piezoelectric transducer on the top or the bottom surface of the plate and weakening the strength of one mode while enhancing the strength of the other modes to find the centre frequency, with which the peak wave amplitude ratio between the S0 and A0 modes is maximum, a single mode excitation from the multiple modes of the Lamb waves can be achieved approximately. Experimental data are presented to show the validity of the analyses. The results are used to optimize the Lamb wave detection system. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Wave excitation in electron beam experiment on Japanese satellite JIKIKEN (EXOS-B)
International Nuclear Information System (INIS)
Kawashima, N.
1982-01-01
This chapter reports on a beam-plasma interaction experiment conducted in the magnetosphere by emitting an electron beam (100-200 eV, 0.25-1.0 mA) from the JIKIKEN satellite. Topics considered include instrumentation, wave excitation, and the charging of the satellite. Various types of wave emission are detected by low frequency and high frequency wave detectors. Waves near upper-hybrid frequency and at electron cyclotron frequency are detected in a low L-value region, which will be useful diagnostic means for plasma density and magnetic field. Vehicle charging up to the beam energy is observed outside the plasmapause. The main objectives of the Controlled Beam Experiment (CBE) are to control the satellite potential by an electron beam emission, and to study the wave excitation (linear and non-linear wave phenomena due to the beam-plasma interaction). It is concluded that waves excited in the beamplasma interaction are strongly dependent on plasma and other parameters in the magnetosphere so that it will provide important knowledge of the magnetosphere plasma processes
Bartlett, Philip L.; Stelbovics, Andris T.
2010-02-01
The propagating exterior complex scaling (PECS) method is extended to all four-body processes in electron impact on helium in an S-wave model. Total and energy-differential cross sections are presented with benchmark accuracy for double ionization, single ionization with excitation, and double excitation (to autoionizing states) for incident-electron energies from threshold to 500 eV. While the PECS three-body cross sections for this model given in the preceding article [Phys. Rev. A 81, 022715 (2010)] are in good agreement with other methods, there are considerable discrepancies for these four-body processes. With this model we demonstrate the suitability of the PECS method for the complete solution of the electron-helium system.
Excitation of multiphase waves of the nonlinear Schroedinger equation by capture into resonances
International Nuclear Information System (INIS)
Friedland, L.; Shagalov, A.G.
2005-01-01
A method for adiabatic excitation and control of multiphase (N-band) waves of the periodic nonlinear Schroedinger (NLS) equation is developed. The approach is based on capturing the system into successive resonances with external, small amplitude plane waves having slowly varying frequencies. The excitation proceeds from zero and develops in stages, as an (N+1)-band (N=0,1,2,...), growing amplitude wave is formed in the (N+1)th stage from an N-band solution excited in the preceding stage. The method is illustrated in simulations, where the excited multiphase waves are analyzed via the spectral approach of the inverse scattering transform method. The theory of excitation of 0- and 1-band NLS solutions by capture into resonances is developed on the basis of a weakly nonlinear version of Whitham's averaged variational principle. The phenomenon of thresholds on the driving amplitudes for capture into successive resonances and the stability of driven, phase-locked solutions in these cases are discussed
Plastic deformation of solids viewed as a self-excited wave process
International Nuclear Information System (INIS)
Zuev, L.B.; Danilov, V.I.
1998-01-01
A self-excited wave model of plastic flow in crystalline solids is proposed. Experimental data on plastic flow in single crystals and polycrystalline solids involving different mechanisms have been correlated. The main types of strain localization in the materials investigated have been established and correlated with the respective stages of plastic flow curves. The best observing conditions have been defined for the major types of autowaves emerging by plastic deformation. The synergetic concepts of self-organization are shown to apply to description of plastic deformation. Suggested is a self-excited wave model of plastic flow in materials with different mechanisms of deformation. (orig.)
Numerical simulation of seismic wave propagation from land-excited large volume air-gun source
Cao, W.; Zhang, W.
2017-12-01
The land-excited large volume air-gun source can be used to study regional underground structures and to detect temporal velocity changes. The air-gun source is characterized by rich low frequency energy (from bubble oscillation, 2-8Hz) and high repeatability. It can be excited in rivers, reservoirs or man-made pool. Numerical simulation of the seismic wave propagation from the air-gun source helps to understand the energy partitioning and characteristics of the waveform records at stations. However, the effective energy recorded at a distance station is from the process of bubble oscillation, which can not be approximated by a single point source. We propose a method to simulate the seismic wave propagation from the land-excited large volume air-gun source by finite difference method. The process can be divided into three parts: bubble oscillation and source coupling, solid-fluid coupling and the propagation in the solid medium. For the first part, the wavelet of the bubble oscillation can be simulated by bubble model. We use wave injection method combining the bubble wavelet with elastic wave equation to achieve the source coupling. Then, the solid-fluid boundary condition is implemented along the water bottom. And the last part is the seismic wave propagation in the solid medium, which can be readily implemented by the finite difference method. Our method can get accuracy waveform of land-excited large volume air-gun source. Based on the above forward modeling technology, we analysis the effect of the excited P wave and the energy of converted S wave due to different water shapes. We study two land-excited large volume air-gun fields, one is Binchuan in Yunnan, and the other is Hutubi in Xinjiang. The station in Binchuan, Yunnan is located in a large irregular reservoir, the waveform records have a clear S wave. Nevertheless, the station in Hutubi, Xinjiang is located in a small man-made pool, the waveform records have very weak S wave. Better understanding of
Observation of self-excited acoustic vortices in defect-mediated dust acoustic wave turbulence.
Tsai, Ya-Yi; I, Lin
2014-07-01
Using the self-excited dust acoustic wave as a platform, we demonstrate experimental observation of self-excited fluctuating acoustic vortex pairs with ± 1 topological charges through spontaneous waveform undulation in defect-mediated turbulence for three-dimensional traveling nonlinear longitudinal waves. The acoustic vortex pair has helical waveforms with opposite chirality around the low-density hole filament pair in xyt space (the xy plane is the plane normal to the wave propagation direction). It is generated through ruptures of sequential crest surfaces and reconnections with their trailing ruptured crest surfaces. The initial rupture is originated from the amplitude reduction induced by the formation of the kinked wave crest strip with strong stretching through the undulation instability. Increasing rupture causes the separation of the acoustic vortex pair after generation. A similar reverse process is followed for the acoustic vortex annihilating with the opposite-charged acoustic vortex from the same or another pair generation.
Modeling the Excitation of Seismic Waves by the Joplin Tornado
Valovcin, Anne; Tanimoto, Toshiro
2017-10-01
Tornadoes generate seismic signals when they contact the ground. Here we examine the signals excited by the Joplin tornado, which passed within 2 km of a station in the Earthscope Transportable Array. We model the tornado-generated vertical seismic signal at low frequencies (0.01-0.03 Hz) and solve for the strength of the seismic source. The resulting source amplitude is largest when the tornado was reported to be strongest (EF 4-5), and the amplitude is smallest when the tornado was weak (EF 0-2). A further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground.
A Model for Lower Hybrid Wave Excitation Compared with Observations by Viking
Khazanov, G. V.; Liemohn, M. W.; Krivorutsky, E. N.; Horwitz, J. L.
1997-01-01
The mechanism of lower hybrid wave (LHW) excitation due to the O+ relative drift in a plasma subjected to low-frequency waves (LFWs) is used for analysis of Viking satellite data for events in the cusp/cleft region. In some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed, suggesting the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in space plasmas.
Wake-Field Wave Resonant Excitation in Magnetized Plasmas by Electromagnetic Pulse
International Nuclear Information System (INIS)
Milant'ev, V.P.; Turikov, V.A.
2006-01-01
In this paper the space charge wave excitation process at electromagnetic pulse propagation along external magnetic field in vicinity of electron cyclotron resonance. In hydrodynamic approach it is obtained an equation for plasma density under ponderomotive force action. With help of this equation we investigated a wake-field wave amplitude dependence from resonance detuning. The numerical simulation using a PIC method electromagnetic pulse propagation process in the resonant conditions was done
Katsumata, Hisatoshi; Konishi, Keiji; Hara, Naoyuki
2018-04-01
The present paper proposes a scheme for controlling wave segments in excitable media. This scheme consists of two phases: in the first phase, a simple mathematical model for wave segments is derived using only the time series data of input and output signals for the media; in the second phase, the model derived in the first phase is used in an advanced control technique. We demonstrate with numerical simulations of the Oregonator model that this scheme performs better than a conventional control scheme.
Attractive target wave patterns in complex networks consisting of excitable nodes
International Nuclear Information System (INIS)
Zhang Li-Sheng; Mi Yuan-Yuan; Liao Xu-Hong; Qian Yu; Hu Gang
2014-01-01
This review describes the investigations of oscillatory complex networks consisting of excitable nodes, focusing on the target wave patterns or say the target wave attractors. A method of dominant phase advanced driving (DPAD) is introduced to reveal the dynamic structures in the networks supporting oscillations, such as the oscillation sources and the main excitation propagation paths from the sources to the whole networks. The target center nodes and their drivers are regarded as the key nodes which can completely determine the corresponding target wave patterns. Therefore, the center (say node A) and its driver (say node B) of a target wave can be used as a label, (A,B), of the given target pattern. The label can give a clue to conveniently retrieve, suppress, and control the target waves. Statistical investigations, both theoretically from the label analysis and numerically from direct simulations of network dynamics, show that there exist huge numbers of target wave attractors in excitable complex networks if the system size is large, and all these attractors can be labeled and easily controlled based on the information given by the labels. The possible applications of the physical ideas and the mathematical methods about multiplicity and labelability of attractors to memory problems of neural networks are briefly discussed. (topical review - statistical physics and complex systems)
International Nuclear Information System (INIS)
Kamal, A; Giurgiutiu, V
2014-01-01
This article discusses shear horizontal (SH) guided-waves that can be excited with shear type piezoelectric wafer active sensor (SH-PWAS). The paper starts with a review of state of the art SH waves modelling and their importance in non-destructive evaluation (NDE) and structural health monitoring (SHM). The basic piezoelectric sensing and actuation equations for the case of shear horizontal piezoelectric wafer active sensor (SH-PWAS) with electro-mechanical coupling coefficient d 35 are reviewed. Multiphysics finite element modelling (MP-FEM) was performed on a free SH-PWAS to show its resonance modeshapes. The actuation mechanism of the SH-PWAS is predicted by MP-FEM, and modeshapes of excited structure are presented. The structural resonances are compared with experimental measurements and showed good agreement. Analytical prediction of SH waves was performed. SH wave propagation experimental study was conducted between different combinations of SH-PWAS and regular in-plane PWAS transducers. Experimental results were compared with analytical predictions for aluminium plates and showed good agreement. 2D wave propagation effects were studied by MP-FEM. An analytical model was developed for SH wave power and energy. The normal mode expansion (NME) method was used to account for superpositioning multimodal SH waves. Modal participation factors were presented to show the contribution of every mode. Power and energy transfer between SH-PWAS and the structure was analyzed. Finally, we present simulations of our developed wave power and energy analytical models. (paper)
Energy Technology Data Exchange (ETDEWEB)
Pereyra, Brandon; Wendt, Fabian; Robertson, Amy; Jonkman, Jason
2017-03-09
The hydrodynamic loads on an offshore wind turbine's support structure present unique engineering challenges for offshore wind. Two typical approaches used for modeling these hydrodynamic loads are potential flow (PF) and strip theory (ST), the latter via Morison's equation. This study examines the first- and second-order wave-excitation surge forces on a fixed cylinder in regular waves computed by the PF and ST approaches to (1) verify their numerical implementations in HydroDyn and (2) understand when the ST approach breaks down. The numerical implementation of PF and ST in HydroDyn, a hydrodynamic time-domain solver implemented as a module in the FAST wind turbine engineering tool, was verified by showing the consistency in the first- and second-order force output between the two methods across a range of wave frequencies. ST is known to be invalid at high frequencies, and this study investigates where the ST solution diverges from the PF solution. Regular waves across a range of frequencies were run in HydroDyn for a monopile substructure. As expected, the solutions for the first-order (linear) wave-excitation loads resulting from these regular waves are similar for PF and ST when the diameter of the cylinder is small compared to the length of the waves (generally when the diameter-to-wavelength ratio is less than 0.2). The same finding applies to the solutions for second-order wave-excitation loads, but for much smaller diameter-to-wavelength ratios (based on wavelengths of first-order waves).
CSIR Research Space (South Africa)
Loveday, PW
2007-03-01
Full Text Available Piezoelectric transducers are commonly used to excite waves in elastic waveguides such as pipes, rock bolts and rails. While it is possible to simulate the operation of these transducers attached to the waveguide, in the time domain, using...
Imaging of propagation dynamics of optically-excited spin waves in a garnet film
International Nuclear Information System (INIS)
Hashimoto, Yusuke; Saitoh, Eiji
2016-01-01
We demonstrate the direct imaging of the propagation dynamics of the optically-excited spin waves in a garnet film observed with an all-optical pump-and-probe magneto-optical imaging technique having sub-pico second time-resolution, sub-micrometer spatial resolution, and milli-degrees of accuracy in the rotation angle of the light polarization. (author)
Theory of magnetospheric hydromagnetic waves excited by energetic ring-current protons
International Nuclear Information System (INIS)
Chen, Liu; Hasegawa, Akira.
1987-06-01
A general theoretical formulation, allowing finite ion Larmor radii, general magnetic field geometries and plasma equilibria, has been developed to investigate excitations of magnetohydrodynamic (MHD) Alfven waves within the earth's magnetosphere by the storm-time energetic ring-current protons. In particular, it is found that for adiabatically injected protons, various predicted instability properties are consistent with satellite observations. 8 refs
Helicon plasma with additional immersed antenna
International Nuclear Information System (INIS)
Aanesland, A; Charles, C; Boswell, R W; Fredriksen, A
2004-01-01
A 'primary' RF power (H-power) at 13.56 MHz is coupled to a plasma source excited by an external double saddle field Helicon antenna. A 'secondary' RF power (S-power), also at 13.56 MHz but with variable phase, is additionally coupled by inserting a second antenna in contact with the plasma through one end of the source. The immersed antenna can be grounded or floating, allowing a self-bias to form in the latter case. Changes in the plasma density and electron temperature are measured in both cases with varying power on the immersed antenna. The plasma potential increases dramatically with S-power in the grounded case, and is found to be similar in size to the sum of the plasma potential and the self-bias formed in the floating case for all powers. Hence, the sheath between the immersed antenna and the plasma is shown to be equal in both the grounded and floating cases. Although the power efficiency does not vary significantly as a function of the S-power, it is consistently lower for the grounded case possibly as a result of a dc current to ground. The plasma parameters are drastically changed as the phase between the two antennae are varied (floating case), and a sinusoidal function was fitted to the plasma parameters as a function of the phase shift. The calculated power loss to the antenna indicates that the power efficiency of the immersed antenna, as the phase is changed, is altered from 80% to 10%
The instability of the spiral wave induced by the deformation of elastic excitable media
International Nuclear Information System (INIS)
Ma Jun; Jia Ya; Wang Chunni; Li Shirong
2008-01-01
There are some similarities between the spiral wave in excitable media and in cardiac tissue. Much evidence shows that the appearance and instability of the spiral wave in cardiac tissue can be linked to one kind of heart disease. There are many models that can be used to investigate the formation and instability of the spiral wave. Cardiac tissue is excitable and elastic, and it is interesting to simulate the transition and instability of the spiral wave induced by media deformation. For simplicity, a class of the modified Fitzhugh-Nagumo (MFHN) model, which can generate a stable rotating spiral wave, meandering spiral wave and turbulence within appropriate parameter regions, will be used to simulate the instability of the spiral wave induced by the periodical deformation of media. In the two-dimensional case, the total acreage of elastic media is supposed to be invariable in the presence of deformation, and the problem is described with L x x L y = N x ΔxN x Δy = L' x L' y = N x Δx'N x Δy'. In our studies, elastic media are decentralized into N x N sites and the space of the adjacent sites is changed to simulate the deformation of elastic media. Based on the nonlinear dynamics theory, the deformation effect on media is simplified and simulated by perturbing the diffusion coefficients D x and D y with different periodical signals, but the perturbed diffusion coefficients are compensatory. The snapshots of our numerical results find that the spiral wave can coexist with the spiral turbulence, instability of the spiral wave and weak deformation of the spiral wave in different conditions. The ratio parameter ε and the frequency of deformation forcing play a deterministic role in inducing instability of the spiral wave. Extensive studies confirm that the instability of the spiral wave can be induced and developed only if an appropriate frequency for deformation is used. We analyze the power spectrum for the time series of the mean activator of four sampled sites
The instability of the spiral wave induced by the deformation of elastic excitable media
Ma, Jun; Jia, Ya; Wang, Chun-Ni; Li, Shi-Rong
2008-09-01
There are some similarities between the spiral wave in excitable media and in cardiac tissue. Much evidence shows that the appearance and instability of the spiral wave in cardiac tissue can be linked to one kind of heart disease. There are many models that can be used to investigate the formation and instability of the spiral wave. Cardiac tissue is excitable and elastic, and it is interesting to simulate the transition and instability of the spiral wave induced by media deformation. For simplicity, a class of the modified Fitzhugh-Nagumo (MFHN) model, which can generate a stable rotating spiral wave, meandering spiral wave and turbulence within appropriate parameter regions, will be used to simulate the instability of the spiral wave induced by the periodical deformation of media. In the two-dimensional case, the total acreage of elastic media is supposed to be invariable in the presence of deformation, and the problem is described with Lx × Ly = N × ΔxN × Δy = L'xL'y = N × Δx'N × Δy'. In our studies, elastic media are decentralized into N × N sites and the space of the adjacent sites is changed to simulate the deformation of elastic media. Based on the nonlinear dynamics theory, the deformation effect on media is simplified and simulated by perturbing the diffusion coefficients Dx and Dy with different periodical signals, but the perturbed diffusion coefficients are compensatory. The snapshots of our numerical results find that the spiral wave can coexist with the spiral turbulence, instability of the spiral wave and weak deformation of the spiral wave in different conditions. The ratio parameter ɛ and the frequency of deformation forcing play a deterministic role in inducing instability of the spiral wave. Extensive studies confirm that the instability of the spiral wave can be induced and developed only if an appropriate frequency for deformation is used. We analyze the power spectrum for the time series of the mean activator of four sampled sites
Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids
Energy Technology Data Exchange (ETDEWEB)
Kalaydzhyan, Tigran, E-mail: tigran@caltech.edu [Department of Physics, University of Illinois, 845 W Taylor Street, Chicago, IL 60607 (United States); Jet Propulsion Laboratory, 4800 Oak Grove Dr, M/S 298, Pasadena, CA 91109 (United States); Murchikova, Elena [TAPIR, California Institute of Technology, MC 350-17, Pasadena, CA 91125 (United States)
2017-06-15
In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium {sup 3}He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves) and transverse velocity (chiral Alfvén wave). We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.
Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids
International Nuclear Information System (INIS)
Kalaydzhyan, Tigran; Murchikova, Elena
2017-01-01
In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium "3He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves) and transverse velocity (chiral Alfvén wave). We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.
Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids
Directory of Open Access Journals (Sweden)
Tigran Kalaydzhyan
2017-06-01
Full Text Available In certain circumstances, chiral (parity-violating medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium 3He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves and transverse velocity (chiral Alfvén wave. We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.
Using PVDF for wavenumber-frequency analysis and excitation of guided waves
Ren, Baiyang; Cho, Hwanjeong; Lissenden, Cliff J.
2018-04-01
The role of transducers in nondestructive evaluation using ultrasonic guided waves cannot be overstated. Energy conversion from electrical to mechanical for actuation and then back to electrical for signal processing broadly describes transduction, but there are many other aspects of transducers that determine their effectiveness. Recently we have reported on polyvinylidene difluoride (PVDF) array sensors that enable determination of the wavenumber spectrum, which enables modal content in the received signal to be characterized. Modal content is an important damage indicator because, for example, mode conversion is a frequent consequence of wave interaction with defects. Some of the positive attributes of PVDF sensors are: broad frequency bandwidth, compliance for use on curved surfaces, limited influence on the passing wave, minimal cross-talk between elements, low profile, low mass, and inexpensive. The anisotropy of PVDF films also enables them to receive either Lamb waves or shear horizontal waves by proper alignment of the material principal coordinate axes. Placing a patterned set of electrodes on the PVDF film provides data from an array of elements. A linear array of elements is used to enable a 2D fast Fourier transform to determine the wavenumber spectrum of both Lamb waves and shear horizontal waves in an aluminum plate. Moreover, since PVDF film can sustain high voltage excitation, high power pulsers can be used to improve the signal-to-noise ratio. The capability of PVDF as a transmitter has been demonstrated with high voltage excitation.
Ren, Baiyang; Lissenden, Cliff J.
2018-04-01
Guided waves have been extensively studied and widely used for structural health monitoring because of their large volumetric coverage and good sensitivity to defects. Effectively and preferentially exciting a desired wave mode having good sensitivity to a certain defect is of great practical importance. Piezoelectric discs and plates are the most common types of surface-mounted transducers for guided wave excitation and reception. Their geometry strongly influences the proportioning between excited modes as well as the total power of the excited modes. It is highly desirable to predominantly excite the selected mode while the total transduction power is maximized. In this work, a fully coupled multi-physics finite element analysis, which incorporates the driving circuit, the piezoelectric element and the wave guide, is combined with the normal mode expansion method to study both the mode tuning and total wave power. The excitation of circular crested waves in an aluminum plate with circular piezoelectric discs is numerically studied for different disc and adhesive thicknesses. Additionally, the excitation of plane waves in an aluminum plate, using a stripe piezoelectric element is studied both numerically and experimentally. It is difficult to achieve predominant single mode excitation as well as maximum power transmission simultaneously, especially for higher order modes. However, guidelines for designing the geometry of piezoelectric elements for optimal mode excitation are recommended.
Formation of virtual isthmus: A new scenario of spiral wave death after a decrease in excitability
Erofeev, I. S.; Agladze, K. I.
2015-11-01
Termination of rotating (spiral) waves or reentry is crucial when fighting with the most dangerous cardiac tachyarrhythmia. To increase the efficiency of the antiarrhythmic drugs as well as finding new prospective ones it is decisive to know the mechanisms how they act and influence the reentry dynamics. The most popular view on the mode of action of the contemporary antiarrhythmic drugs is that they increase the core of the rotating wave (reentry) to that extent that it is not enough space in the real heart for the reentry to exist. Since the excitation in cardiac cells is essentially change of the membrane potential, it relies on the functioning of the membrane ion channels. Thus, membrane ion channels serve as primary targets for the substances, which may serve as antiarrhythmics. At least, the entire group of antiarrhythmics class I (modulating activity of sodium channels) and partially class IV (modulating activity of calcium channels) are believed to destabilize and terminate reentry by decreasing the excitability of cardiac tissue. We developed an experimental model employing cardiac tissue culture and photosensitizer (AzoTAB) to study the process of the rotating wave termination while decreasing the excitability of the tissue. A new scenario of spiral wave cessation was observed: an asymmetric growth of the rotating wave core and subsequent formation of a virtual isthmus, which eventually caused a conduction block and the termination of the reentry.
Perturbed soliton excitations of Rao-dust Alfvén waves in magnetized dusty plasmas
Energy Technology Data Exchange (ETDEWEB)
Kavitha, L., E-mail: louiskavitha@yahoo.co.in [Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610 101 (India); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Lavanya, C.; Senthil Kumar, V. [Department of Physics, Periyar University, Salem, Tamil Nadu 636 011 (India); Gopi, D. [Department of Chemistry, Periyar University, Salem 636 011 (India); Center for Nanoscience and Nanotechnology, Periyar University, Salem, Tamil Nadu 636 011 (India); Pasqua, A. [Department of Physics, University of Trieste, Trieste (Italy)
2016-04-15
We investigate the propagation dynamics of the perturbed soliton excitations in a three component fully ionized dusty magnetoplasma consisting of electrons, ions, and heavy charged dust particulates. We derive the governing equation of motion for the two dimensional Rao-dust magnetohydrodynamic (R-D-MHD) wave by employing the inertialess electron equation of motion, inertial ion equation of motion, the continuity equations in a plasma with immobile charged dust grains, together with the Maxwell's equations, by assuming quasi neutrality and neglecting the displacement current in Ampere's law. Furthermore, we assume the massive dust particles are practically immobile since we are interested in timescales much shorter than the dusty plasma period, thereby neglecting any damping of the modes due to the grain charge fluctuations. We invoke the reductive perturbation method to represent the governing dynamics by a perturbed cubic nonlinear Schrödinger (pCNLS) equation. We solve the pCNLS, along the lines of Kodama-Ablowitz multiple scale nonlinear perturbation technique and explored the R-D-MHD waves as solitary wave excitations in a magnetized dusty plasma. Since Alfvén waves play an important role in energy transport in driving field-aligned currents, particle acceleration and heating, solar flares, and the solar wind, this representation of R-D-MHD waves as soliton excitations may have extensive applications to study the lower part of the earth's ionosphere.
Excitation of upper-hybrid waves by a thermal parametric instability
International Nuclear Information System (INIS)
Lee, M.C.; Kuo, S.P.
1983-01-01
A purely growing instability characterized by a four-wave interaction is analysed in a uniform, magnetized plasma. Up-shifted and down-shifted upper-hybrid waves and a non-oscillatory mode can be excited by a pump wave of ordinary rather than extraordinary polarization in the case of ionospheric heating. The differential Ohmic heating force dominates over the ponderomotive force as the wave-wave coupling mechanism. The beating current at zero frequency produces a significant stabilizing effect on the excitation of short-scale modes by counterbalancing the destabilizing effect of the differential Ohmic heating. The effect of ionospheric inhomogeneity is estimated, showing a tendency to raise the thresholds of the instability. When applied to ionospheric heating experiments, the present theory can explain the excitation of field-aligned plasma lines and ionospheric irregularities with a continuous spectrum ranging from metre-scale to hundreds of metre-scale. Further, the proposed mechanism may become a competitive process to the parametric decay instability and be responsible for the overshoot phenomena of the plasma line enhancement at Arecibo. (author)
Plasma wave excitation by intense microwave transmission from a space vehicle
Kimura, I.; Matsumoto, H.; Kaya, N.; Miyatake, S.
An impact of intense microwave upon the ionospheric plasma was empirically investigated by an active rocket experiment (MINIX). The rocket carried two high-power (830W) transmitters of 2.45 GHz microwave on the mother section of the rocket. The ionospheric plasma response to the intense microwave was measured by a diagnostic package installed on both mother and daughter sections. The daughter section was separated from the mother with a slow speed of 15 cm/sec. The plasma wave analyzers revealed that various plasma waves are nonlinearly excited by the microwave. Among them, the most intense are electron cyclotron waves, followed by electron plasma waves. Extremely low frequency waves (several tens of Hz) are also found. The results of the data analysis as well as comparative computer simulations are given in this paper.
Relativistic corrections to the form factors of Bc into P-wave orbitally excited charmonium
Zhu, Ruilin
2018-06-01
We investigated the form factors of the Bc meson into P-wave orbitally excited charmonium using the nonrelativistic QCD effective theory. Through the analytic computation, the next-to-leading order relativistic corrections to the form factors were obtained, and the asymptotic expressions were studied in the infinite bottom quark mass limit. Employing the general form factors, we discussed the exclusive decays of the Bc meson into P-wave orbitally excited charmonium and a light meson. We found that the relativistic corrections lead to a large correction for the form factors, which makes the branching ratios of the decay channels B (Bc ± →χcJ (hc) +π± (K±)) larger. These results are useful for the phenomenological analysis of the Bc meson decays into P-wave charmonium, which shall be tested in the LHCb experiments.
Excitation of compressional waves and the formation of shocklets in the earth's foreshock
International Nuclear Information System (INIS)
Hada, T.; Kennel, C.F.; Teresawa, T.
1987-01-01
Large-amplitude waves with typical frequencies of 0.01--0.05 Hz are often observed in the foreshocks of earth and other planets. Large-amplitude waves in the earth's foreshock are sometimes (but not always) observed in a highly time-developed form, either as steepened pulses or as discrete oscillatory wave packets of finite length. This implies that nonlinearities are strong enough to modify their waveforms before the solar wind carries them out the foreshock. The instabilities and steepening of upstream waves in the earth's foreshock caused by backstreaming ions are discussed in the first part of the paper. For typical foreshock ''diffuse'' ion distributions, right and left-hand polarized(RHP and LHP) waves propagating parallel to the local magnetic field are preferentially excited. Such noncompressional waves neither steepen nor grow fast enough to account for the amplitude polarizations and waveforms observed in the diffuse ion foreshock. Oblique waves develop a density compression and their magnetic field polarization is elliptical. Although these characteristics match the observations of the steepened waves in the diffuse ion zone, the growth rates of those waves oblique enough to steepen are too small to account for observed amplitudes
Alfven wave excitation in a cavity with a transverse magnetic field
International Nuclear Information System (INIS)
Bures, M.
1982-12-01
A transversely magnetized cylindrical plasma model with an internal rod conductor is used to approximate the FIVA internal ring device of Spherator type with a purely poloidal magnetic field. It is shown that an excitation asymmetry along the plasma column, i.e. with a wave number k sub (z) does not equal 0, introduces a coupling between the magnetoacoustic and shear Alfven waves in the frequency range #betta#<<#betta# sub (ci). The introduction of an equilibrium mass motion along the plasma cylinder introduces a flow continuum. Simultaneously the Alfven resonance frequency becomes Doppler shifted. The experimental observations indicate that cavity modes do not build up in the FIVA device in the case of nonsymmetric excitation. If on the other hand the exciting structure becomes symmetric, i.e. with k sub (z) equals 0, the magnetoacoustic resonance become excited. The resulting Q values are rather low which indicates that the coupling to the shear wave through the Hall electric field cannot be neglected. (Author)
Coupled hydromagnetic wave excitation and ion acceleration upstream of the earth's bow shock
International Nuclear Information System (INIS)
Lee, M.A.
1982-01-01
A self-consistent theory is presented for the excitation of hydromagnetic waves and the acceleration of diffuse ions upstream of the earth's bow shock in the quasi-equilibrium that results when the solar wind velocity and the interplanetary magnetic field are nearly parallel. For the waves the quasi-equilibrium results from a balance between excitation by the ions, which stream relative to the solar wind plasma, and convective loss to the magnetosheath. For the diffuse ions the quasi-equilibrium results from a balance between injection at the shock front, confinement to the foreshock by pitch angle scattering on the waves, acceleration by compression at the shock front, loss to the magnetosheath, loss due to escape upstream of the foreshock, and loss via diffusion perpendicular to the average magnetic field onto field lines that do not connect to the shock front. Diffusion equations describing the ion transport and wave kinetic equations describing the hydromagnetic wave transport are solved self-consistently to yield analytical expressions for the differential wave intensity spectrum as a function of frequency and distance from the bow shock z and for the ion omnidirectional distribution functions and anisotropies as functions of energy and z, In quantitative agreement with observations, the theory predicts (1) exponential spectra at the bow shock in energy per charge, (2) a decrease in intensity and hardening of the ion spectra with increasing z, (3) a 30-keV proton anisotropy parallel to z increasing from -0.28 at the bow shock to +0.51 as z→infinity (4) a linearly polarized wave intensity spectrum with a minimum at approx.6 x 10 -3 Hz and a maximum at approx.2--3 x 10 -2 Hz, (5) a decrease in the wave intensity spectrum with increasing z, (6) a total energy density in protons with energies >15 keV about eight times that in the hydromagnetic waves
Energy Technology Data Exchange (ETDEWEB)
Kumar, Ashok; Tripathi, V K [Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016 (India)
2007-06-07
A high power radio wave, launched into the polar ionosphere at angle {theta} with the earth's magnetic field from a ground-based transmitter in the vicinity of twice the electron cyclotron frequency (2.75 MHz), is reported to create an airglow at an effective radiated power (ERP) = 10 MW. We interpret this result as a consequence of parametric decay of the radio wave into an electron Bernstein wave (EBW) and an ion acoustic wave (IAW). The oscillatory velocity of electrons due to the pump couples with the density perturbation due to the IAW to produce a current, driving the Bernstein mode. The latter, in connection with the pump, exerts a ponderomotive force on electrons, driving the IAW. The growth rate of the parametric instability is maximum for {theta} = 0. At the same time, for any given value of {theta}, the growth rate increases with b(=k{sub 1}{sup 2}v{sub th}{sup 2}/2{omega}{sub c}{sup 2}) and attains a maximum around b {approx} 2, then falls gradually. The EBW produces energetic electrons via cyclotron damping. These electrons collide with the neutral atoms of the plasma to excite them to higher energy states. As the excited atoms return to lower energy states, they radiate in the visible.
International Nuclear Information System (INIS)
Kumar, Ashok; Tripathi, V K
2007-01-01
A high power radio wave, launched into the polar ionosphere at angle θ with the earth's magnetic field from a ground-based transmitter in the vicinity of twice the electron cyclotron frequency (2.75 MHz), is reported to create an airglow at an effective radiated power (ERP) = 10 MW. We interpret this result as a consequence of parametric decay of the radio wave into an electron Bernstein wave (EBW) and an ion acoustic wave (IAW). The oscillatory velocity of electrons due to the pump couples with the density perturbation due to the IAW to produce a current, driving the Bernstein mode. The latter, in connection with the pump, exerts a ponderomotive force on electrons, driving the IAW. The growth rate of the parametric instability is maximum for θ = 0. At the same time, for any given value of θ, the growth rate increases with b(=k 1 2 v th 2 /2ω c 2 ) and attains a maximum around b ∼ 2, then falls gradually. The EBW produces energetic electrons via cyclotron damping. These electrons collide with the neutral atoms of the plasma to excite them to higher energy states. As the excited atoms return to lower energy states, they radiate in the visible
Excitation of plane Lamb wave in plate-like structures under applied surface loading
Zhou, Kai; Xu, Xinsheng; Zhao, Zhen; Yang, Zhengyan; Zhou, Zhenhuan; Wu, Zhanjun
2018-02-01
Lamb waves play an important role in structure health monitoring (SHM) systems. The excitation of Lamb waves has been discussed for a long time with absorbing results. However, little effort has been made towards the precise characterization of Lamb wave excitation by various transducer models with mathematical foundation. In this paper, the excitation of plane Lamb waves with plane strain assumption in isotropic plate structures under applied surface loading is solved with the Hamiltonian system. The response of the Lamb modes excited by applied loading is expressed analytically. The effect of applied loading is divided into the product of two parts as the effect of direction and the effect of distribution, which can be changed by selecting different types of transducer and the corresponding transducer configurations. The direction of loading determines the corresponding displacement of each mode. The effect of applied loading on the in-plane and normal directions depends on the in-plane and normal displacements at the surface respectively. The effect of the surface loading distribution on the Lamb mode amplitudes is mainly reflected by amplitude versus frequency or wavenumber. The frequencies at which the maxima and minima of the S0 or A0 mode response occur depend on the distribution of surface loading. The numerical results of simulations conducted on an infinite aluminum plate verify the theoretical prediction of not only the direction but also the distribution of applied loading. A pure S0 or A0 mode can be excited by selecting the appropriate direction and distribution at the corresponding frequency.
Spiral waves are stable in discrete element models of two-dimensional homogeneous excitable media
Feldman, A. B.; Chernyak, Y. B.; Cohen, R. J.
1998-01-01
The spontaneous breakup of a single spiral wave of excitation into a turbulent wave pattern has been observed in both discrete element models and continuous reaction-diffusion models of spatially homogeneous 2D excitable media. These results have attracted considerable interest, since spiral breakup is thought to be an important mechanism of transition from the heart rhythm disturbance ventricular tachycardia to the fatal arrhythmia ventricular fibrillation. It is not known whether this process can occur in the absence of disease-induced spatial heterogeneity of the electrical properties of the ventricular tissue. Candidate mechanisms for spiral breakup in uniform 2D media have emerged, but the physical validity of the mechanisms and their applicability to myocardium require further scrutiny. In this letter, we examine the computer simulation results obtained in two discrete element models and show that the instability of each spiral is an artifact resulting from an unphysical dependence of wave speed on wave front curvature in the medium. We conclude that spiral breakup does not occur in these two models at the specified parameter values and that great care must be exercised in the representation of a continuous excitable medium via discrete elements.
Excitation of density waves at the Lindblad and corotation resonances by an external potential
International Nuclear Information System (INIS)
Goldreich, P.; Tremaine, S.
1979-01-01
We calculate the linear response of a differentially rotating two-dimensional gas disk to a rigidly rotating external potential. The main assumptions are that the sound speed is much smaller than the orbital velocity and that the external potential varies on the scale of the disk radius. We investigate disks both with and without self-gravity.The external potential exerts torques on the disk only at the Lindblad and corotation resonances. The torque is positive at the outer Lindblad resonance and negative at the inner Lindblad resonance; at corotation the torque has the sign of the radial gradient of vorticity per unit surface density. The torques are of the same order of magnitude at both types of resonance and are independent of the sound speed in the disk.The external potential also excites density waves in the vicinity of the Lindblad and corotation resonances. The long trailing wave is excited at a Lindblad resonance. It transports away from the resonance all of the angular momentum which is deposited there by the external torque. Short trailing waves are excited at the corotation resonance. The amplitudes of the excited waves are the same on both sides of the resonance and are small unless the disk is almost gravitationally unstable. No net angular momentum is transported away from the corotation region by the waves. Thus the angular momentum deposited there by the external torque accumulates in the gas.We briefly discuss the behavior of particle disks and prove that the external torques on particle disks are identical to those on gas disks
Excitation of Accelerating Plasma Waves by Counter-propagating Laser Beams
International Nuclear Information System (INIS)
Gennady Shvets; Nathaniel J. Fisch; Alexander Pukhov
2001-01-01
Generation of accelerating plasma waves using two counter-propagating laser beams is considered. Colliding-beam accelerator requires two laser pulses: the long pump and the short timing beam. We emphasize the similarities and differences between the conventional laser wakefield accelerator and the colliding-beam accelerator (CBA). The highly nonlinear nature of the wake excitation is explained using both nonlinear optics and plasma physics concepts. Two regimes of CBA are considered: (i) the short-pulse regime, where the timing beam is shorter than the plasma period, and (ii) the parametric excitation regime, where the timing beam is longer than the plasma period. Possible future experiments are also outlined
Selective Excitation of Lamb-Waves for Damage Detection in Composites
Petculescu, G.; Krishnaswamy, S.; Achenbach, J. D.
2006-03-01
Sensors based on periodic arrays of coherent piezoelectric sources (comb design) are used to selectively excite and detect Lamb waves in aluminum and AS4/3601 unidirectional carbon-epoxy plates. 110 μm PVDF film poled in the thickness direction is used as piezoelectric material. An algorithm to eliminate the effect of coupling in amplitude measurements, using individual Lamb modes excited/detected by the same transducer pair, is described. A multiple-impact test showing a decrease in amplitude and group velocity as damage progresses is used as an example.
Generation of spiral waves pinned to obstacles in a simulated excitable system
Phantu, Metinee; Kumchaiseemak, Nakorn; Porjai, Porramain; Sutthiopad, Malee; Müller, Stefan C.; Luengviriya, Chaiya; Luengviriya, Jiraporn
2017-09-01
Pinning phenomena emerge in many dynamical systems. They are found to stabilize extreme conditions such as superconductivity and super fluidity. The dynamics of pinned spiral waves, whose tips trace the boundary of obstacles, also play an important role in the human health. In heart, such pinned waves cause longer tachycardia. In this article, we present two methods for generating pinned spiral waves in a simulated excitable system. In method A, an obstacle is set in the system prior to an ignition of a spiral wave. This method may be suitable only for the case of large obstacles since it often fails when used for small obstacles. In method B, a spiral wave is generated before an obstacle is placed at the spiral tip. With this method, a pinned spiral wave is always obtained, regardless the obstacle size. We demonstrate that after a transient interval the dynamics of the pinned spiral waves generated by the methods A and B are identical. The initiation of pinned spiral waves in both two- and three-dimensional systems is illustrated.
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)
Modeling of microwave applicators with an excitation through the wave guide using TLM method
Directory of Open Access Journals (Sweden)
Ranđelović Tijana
2005-01-01
Full Text Available In this paper, a real microwave applicator with a wave guide used to launch the energy from the source into the cavity is analyzed using 3D TLM method. In order to investigate the influence of the positions and number of feed wave guides to the number of the resonant modes inside the cavity, obtained results are compared with analytical results and results obtained by using TLM software with an impulse excitation as well. TLM method is applied to the both empty and loaded rectangular metallic cavity, and a very good agreement between simulated and experimental results is achieved.
Features of Chaotic Transients in Excitable Media Governed by Spiral and Scroll Waves
Lilienkamp, Thomas; Christoph, Jan; Parlitz, Ulrich
2017-08-01
In excitable media, chaotic dynamics governed by spiral or scroll waves is often not persistent but transient. Using extensive simulations employing different mathematical models we identify a specific type-II supertransient by an exponential increase of transient lifetimes with the system size in 2D and an investigation of the dynamics (number and lifetime of spiral waves, Kaplan-Yorke dimension). In 3D, simulations exhibit an increase of transient lifetimes and filament lengths only above a critical thickness. Finally, potential implications for understanding cardiac arrhythmias are discussed.
Sotnikov, V.; Kim, T.; Caplinger, J.; Main, D.; Mishin, E.; Gershenzon, N.; Genoni, T.; Paraschiv, I.; Rose, D.
2018-04-01
The concept of a parametric antenna in ionospheric plasma is analyzed. Such antennas are capable of exciting electromagnetic radiation fields, specifically the creation of whistler waves generated at the very low frequency (VLF) range, which are also capable of propagating large distances away from the source region. The mechanism of whistler wave generation is considered a parametric interaction of quasi-electrostatic whistler waves (also known as low oblique resonance (LOR) oscillations) excited by a conventional loop antenna. The interaction of LOR waves with quasi-neutral density perturbations in the near field of an antenna gives rise to electromagnetic whistler waves on combination frequencies. It is shown in this work that the amplitude of these waves can considerably exceed the amplitude of whistler waves directly excited by a loop. Additionally, particle-in-cell simulations, which demonstrate the excitation and spatial structure of VLF waves excited by a loop antenna, are presented. Possible applications including the wave-particle interactions to mitigate performance anomalies of low Earth orbit satellites, active space experiments, communication via VLF waves, and modification experiments in the ionosphere will be discussed.
A study on an object transport system using ultrasonic wave excitation
International Nuclear Information System (INIS)
Jeong, Sang Hwa; Kim, Gwang Ho; Choi, Suk Bong; Park, Jun Ho; Cha, Kyoung Rae
2007-01-01
The development of information and telecommunication industries leads to the development of semiconductor and optical industries. In recent years, the demand of optical components is growing due to the demand of faster network. On the other hand, conventional transport systems are not adequate for transporting precision optical components and semiconductors. Because the conveyor belt can damage precision optical components with contact force and a magnetic system would destroy the inner structure of semiconductor with magnetic field, a new system for transporting optical components and semiconductors is required. One of the alternatives to the existing systems is a transport system using ultrasonic wave excitation since it can transport precision components such as semiconductors and optical components without damage. In this paper, a transport system using 2-mode ultrasonic wave excitation was developed for transporting optical components and semiconductor, and its performance was evaluated. The relationship between transporting characteristics and flexural beam shapes were evaluated
Excitation of accelerating plasma waves by counter-propagating laser beams
International Nuclear Information System (INIS)
Shvets, Gennady; Fisch, Nathaniel J.; Pukhov, Alexander
2002-01-01
The conventional approach to exciting high phase velocity waves in plasmas is to employ a laser pulse moving in the direction of the desired particle acceleration. Photon downshifting then causes momentum transfer to the plasma and wave excitation. Novel approaches to plasma wake excitation, colliding-beam accelerator (CBA), which involve photon exchange between the long and short counter-propagating laser beams, are described. Depending on the frequency detuning Δω between beams and duration τ L of the short pulse, there are two approaches to CBA. First approach assumes (τ L ≅2/ω p ). Photons exchanged between the beams deposit their recoil momentum in the plasma driving the plasma wake. Frequency detuning between the beams determines the direction of the photon exchange, thereby controlling the phase of the plasma wake. This phase control can be used for reversing the slippage of the accelerated particles with respect to the wake. A variation on the same theme, super-beatwave accelerator, is also described. In the second approach, a short pulse with τ L >>ω p -1 detuned by Δω∼2ω p from the counter-propagating beam is employed. While parametric excitation of plasma waves by the electromagnetic beatwave at 2ω p of two co-propagating lasers was first predicted by Rosenbluth and Liu [M. N. Rosenbluth and C. S. Liu, Phys. Rev. Lett. 29, 701 (1972)], it is demonstrated that the two excitation beams can be counter-propagating. The advantages of using this geometry (higher instability growth rate, insensitivity to plasma inhomogeneity) are explained, and supporting numerical simulations presented
Spin-wave excitations and magnetism of sputtered Fe/Au multilayers
Indian Academy of Sciences (India)
2LMPG, Ecole supérieure de technologie, Université Hassan II de Casablanca, B.P. 5366 Mâarif, Morocco. 3LPMMAT, Faculté des Sciences Ain Chock, Université Hassan II de Casablanca, B.P. 5366 Mâarif, Morocco. MS received 15 September 2015; accepted 15 February 2016. Abstract. The spin-wave excitations and ...
Non linear excitation of waves at the vicinity of plasma resonance
International Nuclear Information System (INIS)
Chiron, Arnaud
1992-01-01
This research thesis reports the study of the non linear evolution of ionic acoustic and plasma waves excited by resonant absorption of an electromagnetic wave, in a non collisional plasma, without external magnetic field, and with a parabolic density profile. The plasma resonance occurs about the density profile peak. The numerical resolution of the Zakharov equation system is performed to describe the coupled evolution of the plasma wave electric field envelope, and low frequency density disturbances. Experiments performed in the microwave domain show the existence of a new effect related to the modification of the electromagnetic wave propagation under the influence of plasma density disturbances created by the ponderomotive force. This effect which results in a collisional relaxation of plasma waves trapped in the cavity formed at resonance, cannot be taken into account by a numerical simulation using a capacitive pump field. Measurements showed that plasma waves were trapped and relaxing in a cavity with characteristic dimensions of some thousands of Debye lengths, and that the plasma wave in the cavity was stationary. A new turbulence regime is thus highlighted [fr
Directory of Open Access Journals (Sweden)
Yu Tong
2016-02-01
Full Text Available Photoacoustic Doppler (PAD power spectra showing an evident Doppler shift represent the major characteristics of the continuous wave-excited or burst wave-excited versions of PAD flow measurements. In this paper, the flow angle dependences of the PAD power spectra are investigated using an experiment setup that was established based on intensity-modulated continuous wave laser excitation. The setup has an overall configuration that is similar to a previously reported configuration, but is more sophisticated in that it accurately aligns the laser illumination with the ultrasound detection process, and in that it picks up the correct sample position. In the analysis of the power spectra data, we find that the background power spectra can be extracted by combining the output signals from the two channels of the lock-in amplifier, which is very useful for identification of the PAD power spectra. The power spectra are presented and analyzed in opposite flow directions, at different flow speeds, and at different flow angles. The power spectra at a 90° flow angle show the unique properties of symmetrical shapes due to PAD broadening. For the other flow angles, the smoothed power spectra clearly show a flow angle cosine relationship.
Electron Bernstein wave excitation by counterpropagating electromagnetic waves in a plasma
International Nuclear Information System (INIS)
Kumar, Asheel; Tripathi, V.K.
2005-01-01
Two high-power counterpropagating electromagnetic waves (ω 1 ,k 1 x) and (ω 2 ,-k 2 x) in a low-density plasma in the presence of a static magnetic field B s z, drive an electron Bernstein wave at the beat frequency ω=ω 1 -ω 2 and k=(k 1 +k 2 )x, when ω∼ω c 1 ,ω 2 and kρ≥1, where ω c is the electron cyclotron frequency and ρ is the Larmor radius. The electromagnetic waves exert a ponderomotive force on the electrons and resonantly drive the Bernstein mode(ω,k). When the pump waves have finite z extent, the Bernstein wave has an effective k z and a component of group velocity in the direction of the magnetic field, leaking it out of the interaction region, limiting the level of the Bernstein mode. Plasma inhomogeneity also introduces convection losses. However, the electron Bernstein mode potential could still be significantly greater than the ponderomotive potential
Directory of Open Access Journals (Sweden)
Wenbo Duan
2017-12-01
Full Text Available Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank floors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine blades and aeroplane wings. In these applications, the strength of the sound source must be high for scanning a large area, or to break the bond between ice, fouling and plate substrate. More than one transducer may be used to achieve maximum sound power output. However, multiple sources can interact with each other, and form a sound field in the structure with local constructive and destructive regions. Destructive regions are weak regions and shall be avoided. When multiple transducers are used it is important that they are arranged in a particular way so that the desired wave modes can be excited to cover the whole structure. The objective of this paper is to provide a theoretical basis for generating particular wave mode patterns in finite-width rectangular plates whose length is assumed to be infinitely long with respect to its width and thickness. The wave modes have displacements in both width and thickness directions, and are thus different from the classical Lamb-type wave modes. A two-dimensional semi-analytical finite element (SAFE method was used to study dispersion characteristics and mode shapes in the plate up to ultrasonic frequencies. The modal analysis provided information on the generation of modes suitable for a particular application. The number of point sources and direction of loading for the excitation of a few representative modes was investigated. Based on the SAFE analysis, a standard finite element modelling package, Abaqus, was used to excite the designed modes in a three-dimensional plate. The generated wave patterns in Abaqus were then compared with mode shapes predicted in the SAFE model. Good agreement was observed between the
Properties, propagation, and excitation of EMIC waves observed by MMS: A case study
Zhang, J.; Boardsen, S. A.; Coffey, V. N.; Chandler, M. O.; Saikin, A.; Mello, E. M.; Russell, C. T.; Torbert, R. B.; Fuselier, S. A.; Giles, B. L.; Gershman, D. J.
2017-12-01
Electromagnetic ion cyclotron (EMIC) waves (0.1-5 Hz) play an important role in particle dynamics in the Earth's magnetosphere. EMIC waves are preferentially excited in regions where hot anisotropic ions and cold dense plasma populations spatially overlap. While the generation region of EMIC waves is usually on or near the magnetic equatorial plane in the inner magnetosphere, EMIC waves have both equatorial and off-equator source regions on the dayside in the compressed outer magnetosphere. Using field and plasma measurements from the Magnetospheric Multiscale (MMS) mission, we perform a case study of EMIC waves and associated local plasma conditions observed on 19 October 2015. From 0315 to 0810 UT, before crossing the magnetopause into the magnetosheath, all four MMS spacecraft detected long-lasting He+-band EMIC wave emissions around local noon (MLT = 12.7 - 14.0) at high L-shells (L = 8.8 - 15.2) and low magnetic latitudes (MLAT = -21.8º - -30.3º). Energetic (> 1 keV) and anisotropic ions were present throughout this event that was in the recovery phase of a weak geomagnetic storm (min. Dst = -48 nT at 1000 UT on 18 October 2015). The testing of linear theory suggests that the EMIC waves were excited locally. Although the wave event is dominated by small normal angles, its polarization is mixed with right- and left-handedness and its propagation is bi-directional with regard to the background magnetic field. The short inter-spacecraft distances (as low as 15 km) of the MMS mission make it possible to accurately determine the k vector of the waves using the phase difference technique. Preliminary analysis finds that the k vector magnitude, phase speed, and wavelength of the 0.3-Hz wave packet at 0453:55 UT are 0.005 km-1, 372.9 km/s, and 1242.9 km, respectively. We will discuss the characteristics of the wave and particle measurements and their significance in this locale.
Spiral waves in excitable media due to noise and periodic forcing
Energy Technology Data Exchange (ETDEWEB)
Yuan Guoyong, E-mail: g-y-yuan@sohu.com [Department of Physics, Hebei Normal University, Shijiazhuang 050016 (China); Hebei Advanced Thin Films Laboratory, Shijiazhuang 050016 (China); Xu Lin [Department of Physics, Hebei Normal University, Shijiazhuang 050016 (China); Xu Aiguo; Wang Guangrui [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Yang Shiping [Department of Physics, Hebei Normal University, Shijiazhuang 050016 (China); Hebei Advanced Thin Films Laboratory, Shijiazhuang 050016 (China)
2011-09-15
Highlights: > Excitable media jointly driven by periodic forcing and Gaussian white noise. > The joint driving leads to many unique tip motions. > New type of spiral wave breakup occurs between entrainment bands with 1:1 and 2:1. > Arnold tongues for different noise intensities exhibit stochastic resonance. > Fourier spectrum analysis can interpret tip motions and formation of entrainments. - Abstract: We investigate the jointly driven effects of external periodic forcing and Gaussian white noise on meandering spiral waves in excitable media with FitzHugh-Nagumo local dynamics. Interesting phenomena resulted from various forcing periods are found, for example, piece-wise line drift, intermittent straight-line drift and so on. We also observe new type of breakup of spiral wave between entrainment bands with 1:1 and 2:1. It is believed that the occurrence of the new type is relevant to the appearance of local bidirectional propagation window. There exist optimized noise intensities which can induce the broadest entrainments and Arnold tongues. Such a phenomenon is referred to as stochastic resonance. It is also observed that the noise makes significant effects on the spiral wave with straight-line drift. Via the tip Fourier spectrum, the varying of tip motion with external periods on the resonance band is interpreted.
International Nuclear Information System (INIS)
Tournat, V.; Gusev, V.E.; Castagnede, B.
2004-01-01
First laboratory-scale experimental observation of both subharmonics excitation and significant increase in noise level caused by propagation of the acoustic wave in unconsolidated granular material is reported. The bifurcation phenomenon, taking place above a critical level of acoustic excitation (and opening the subharmonics route to chaos) is attributed to the interaction of acoustic wave with distributed system of highly nonlinear inter-grain contacts. The estimates demonstrated that these are weak contacts (loaded at least two orders of magnitude weaker than in average) that might be responsible for the observed nonlinear effects. The additional intermittent contacts created by the acoustic wave (which are open in the absence of acoustic loading) can also contribute. In the clapping (tapping) regime, each of these contacts individually is similar to an impact oscillator, for which the scenario of period doubling cascade and the transition to chaotic behavior has been predicted theoretically and observed experimentally earlier. The experiments confirm that the nonlinear interactions of acoustic waves in granular assemblages are highly sensitive to the fraction of weakly loaded (and unloaded) contacts, information on which is difficult to access by any other experimental methods
Excitation of surface electromagnetic waves in a graphene-based Bragg grating.
Sreekanth, Kandammathe Valiyaveedu; Zeng, Shuwen; Shang, Jingzhi; Yong, Ken-Tye; Yu, Ting
2012-01-01
Here, we report the fabrication of a graphene-based Bragg grating (one-dimensional photonic crystal) and experimentally demonstrate the excitation of surface electromagnetic waves in the periodic structure using prism coupling technique. Surface electromagnetic waves are non-radiative electromagnetic modes that appear on the surface of semi-infinite 1D photonic crystal. In order to fabricate the graphene-based Bragg grating, alternating layers of high (graphene) and low (PMMA) refractive index materials have been used. The reflectivity plot shows a deepest, narrow dip after total internal reflection angle corresponds to the surface electromagnetic mode propagating at the Bragg grating/air boundary. The proposed graphene based Bragg grating can find a variety of potential surface electromagnetic wave applications such as sensors, fluorescence emission enhancement, modulators, etc.
Excitation of electrostatic wave instability by dc electric field in earth's magnetoplasma
International Nuclear Information System (INIS)
Mishra, S.P.; Misra, K.D.; Pandey, R.P.; Singh, K.M.
1992-01-01
The dispersion relation for electrostatic wave propagation in an anisotropic warm collisionless magnetoplasma, in the presence of weak parallel (d c) electric field, has been derived analytically. An expression for the growth rate of the electrostatic wave and the marginal stability condition are also derived. The modifications introduced in the growth rate by the electric field and the temperature anisotropy are discussed using plasma parameters observed in the magnetospheric region (4 < L < 10). The effect of the electric field is to increase the growth rate of electrostatic waves at different electron cyclotron harmonics, whereas the effect of the temperature anisotropy is to decrease the growth rate. The presence of parallel electric field may excite the electrostatic emissions at different electron cyclotron harmonics. The most unstable band of wave frequencies obtained with the aid of computations lies between 5 kHz and 10 kHz. These wave frequencies are well within the experimentally observed frequencies of electrostatic emissions. Therefore such a study would not only explain the observed satellite features of the electrostatic wave emissions but would also account for the diagnostics of the magnetospheric plasma parameters
Ion energy characteristics downstream of a high power helicon
International Nuclear Information System (INIS)
Prager, James; Winglee, Robert; Ziemba, Tim; Roberson, B Race; Quetin, Gregory
2008-01-01
The High Power Helicon eXperiment operates at higher powers (37 kW) and lower background neutral pressure than other helicon experiments. The ion velocity distribution function (IVDF) has been measured at multiple locations downstream of the helicon source and a mach 3-6 flowing plasma was observed. The helicon antenna has a direct effect in accelerating the plasma downstream of the source. Also, the IVDF is affected by the cloud of neutrals from the initial gas puff, which keeps the plasma speed low at early times near the source.
Ion energy characteristics downstream of a high power helicon
Energy Technology Data Exchange (ETDEWEB)
Prager, James; Winglee, Robert; Ziemba, Tim; Roberson, B Race; Quetin, Gregory [University of Washington, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, WA 98195-1310 (United States)], E-mail: jprager@u.washington.edu
2008-05-01
The High Power Helicon eXperiment operates at higher powers (37 kW) and lower background neutral pressure than other helicon experiments. The ion velocity distribution function (IVDF) has been measured at multiple locations downstream of the helicon source and a mach 3-6 flowing plasma was observed. The helicon antenna has a direct effect in accelerating the plasma downstream of the source. Also, the IVDF is affected by the cloud of neutrals from the initial gas puff, which keeps the plasma speed low at early times near the source.
International Nuclear Information System (INIS)
Parchevsky, K. V.; Kosovichev, A. G.
2009-01-01
Investigation of propagation, conversion, and scattering of MHD waves in the Sun is very important for understanding the mechanisms of observed oscillations and waves in sunspots and active regions. We have developed a three-dimensional linear MHD numerical model to investigate the influence of the magnetic field on excitation and properties of the MHD waves. The results show that surface gravity waves (f-modes) are affected by the background magnetic field more than acoustic-type waves (p-modes). Comparison of our simulations with the time-distance helioseismology results from Solar and Heliospheric Observatory/MDI shows that the amplitude of travel time variations with azimuth around sunspots caused by the inclined magnetic field does not exceed 25% of the observed amplitude even for strong fields of 1400-1900 G. This can be an indication that other effects (e.g., background flows and nonuniform distribution of the magnetic field) can contribute to the observed azimuthal travel time variations. The azimuthal travel time variations caused by the wave interaction with the magnetic field are similar for simulated and observed travel times for strong fields of 1400-1900 G if Doppler velocities are taken at the height of 300 km above the photosphere where the plasma parameter β << 1. For the photospheric level the travel times are systematically smaller by approximately 0.12 minutes than for the height of 300 km above the photosphere for all studied ranges of the magnetic field strength and inclination angles. Numerical MHD wave modeling and new data from the HMI instrument of the Solar Dynamics Observatory will substantially advance our knowledge of the wave interaction with strong magnetic fields on the Sun and improve the local helioseismology diagnostics.
DENSITY WAVES EXCITED BY LOW-MASS PLANETS IN PROTOPLANETARY DISKS. I. LINEAR REGIME
International Nuclear Information System (INIS)
Dong, Ruobing; Stone, James M.; Petrovich, Cristobal; Rafikov, Roman R.
2011-01-01
Density waves excited by planets embedded in protoplanetary disks play a central role in planetary migration and gap opening processes. We carry out two-dimensional shearing sheet simulations to study the linear regime of wave evolution with the grid-based code Athena and provide detailed comparisons with theoretical predictions. Low-mass planets (down to ∼0.03 M ⊕ at 1 AU) and high spatial resolution (256 grid points per scale height) are chosen to mitigate the effects of wave nonlinearity. To complement the existing numerical studies, we focus on the primary physical variables such as the spatial profile of the wave, torque density, and the angular momentum flux carried by the wave, instead of secondary quantities such as the planetary migration rate. Our results show percent level agreement with theory in both physical and Fourier spaces. New phenomena such as the change of the toque density sign far from the planet are discovered and discussed. Also, we explore the effect of the numerical algorithms and find that a high order of accuracy, high resolution, and an accurate planetary potential are crucial to achieve good agreement with the theory. We find that the use of a too large time step without properly resolving the dynamical timescale around the planet produces incorrect results and may lead to spurious gap opening. Global simulations of planet migration and gap opening violating this requirement may be affected by spurious effects resulting in, e.g., the incorrect planetary migration rate and gap opening mass.
Characteristics of the self-excited ionization waves in a magnetized positive column
International Nuclear Information System (INIS)
Maruyama, Takeo; Yamamura, Yasuhiro; Takano, Saburo; Miura, Kosuke; Imazu, Shingo.
1979-01-01
In the past, metastable atoms were not considered in the investigations of ionization waves generated in a positive column weakly ionized. However, metastable atoms seem to be important for the generation of ionization waves, and there are many unknown factors. In this paper, the fundamental equations and dispersion relation are explained under the assumption of axi-symmetrical positive column plasma placed in a uniform magnetic field, and the direct ionization frequency and excitation frequency, cumulative ionization coefficient, electron density and metastable atom density, the energy loss factor for electrons, the dependence of plasma quantities on magnetic field and dispersion characteristics are calculated. Experiments have been conducted using Ne gas in a discharge tube of 80 cm long and 1 cm radius with heated oxide cathode. Magnetic field was obtained with a solenoid coil of 75 cm long, 9 cm I.D. and 27 cm O.D. The axially uniform magnetic field was in the range of 35 to 40 cm. As the results, the following points have become clear. (1) The number of waves, angular frequency and phase velocity of ionization waves decrease with the increase of magnetic field. (2) By the consideration of the presence of metastable atoms, the theoretical values were improved pretty well and agreed with the experimental values qualitatively and quantitatively. (3) Longitudinal magnetic field has the effect of suppressing the growth of ionization waves because of the reduction of time and spatial growth rates with the increase of magnetic field. (Wakatsuki, Y.)
The millimeter-wave spectrum of highly vibrationally excited SiO
International Nuclear Information System (INIS)
Mollaaghababa, R.; Gottlieb, C.A.; Vrtilek, J.M.; Thaddeus, P.
1991-01-01
The millimeter-wave rotational spectra of SiO in high vibrational states (v = 0-40) in its electronic ground state were measured between 228 and 347 GHz in a laboratory discharge through SiH4 and CO. On ascending the vibrational ladder, populations decline precipitously for the first few levels, with a vibrational temperature of about 1000 K; at v of roughly 3, however, they markedly flatten out, and from there to v of roughly 40 the temperature is of the order of 10,000 K. With the Dunham coefficients determined here, the rotational spectrum of highly vibrationally excited SiO can now be calculated into the far-infrared to accuracies required for radioastronomy. Possible astronomical sources of highly vibrationally excited SiO are certain stellar atmospheres, ultracompact H II regions, very young supernova ejecta, and dense interstellar shocks. 16 refs
Wave Packet Simulation of Nonadiabatic Dynamics in Highly Excited 1,3-Dibromopropane
DEFF Research Database (Denmark)
Brogaard, Rasmus Y.; Møller, Klaus Braagaard; Sølling, Theis Ivan
2008-01-01
]. In the experiment. DBP is excited to a Rydberg state 8 eV above the ground state. The interpretation of the results is that a torsional motion of the bromomethylene groups with a vibrational period of 680 is is activated upon excitation. The Rydberg state decays to a valence state, causing a dissociation of one...... of the carbon bromine bonds oil a time scale of 2.5 ps. Building the theoretical framework for the wave packet propagation around this model of the reaction dynamics, the Simulations reproduce, to a good extent, the time scales observed in the experiment. Furthermore. the Simulations provide insight into how...... the torsion motion influences the bond breakage, and C we can conclude that the mechanism that delays the dissociation is solely the electronic transition from the Rydberg state to the valence state and does not involve, for example, intramolecular vibrational energy redistribution (IVR)....
Nonlinear response to the multiple sine wave excitation of a softening--hardening system
International Nuclear Information System (INIS)
Koplik, B.; Subudhi, M.; Curreri, J.
1979-01-01
In studying the earthquake response of the HTGR core, it was observed that the system can display softening--hardening characteristics. This is of great consequence in evaluating the structural safety aspects of the core. In order to obtain a better understanding of the governing parameters, an investigation was undertaken with a single-degree-of-freedom system having a softening--hardening spring characteristic and excited by multiple sine waves. A parametric study varying the input amplitudes and the spring characteristic was performed. Transients were introduced into the system, and the jump phenomena between the lower softening characteristics to the higher hardening curve was studied
Statistical mechanics of magnetic excitations from spin waves to stripes and checkerboards
Rastelli, Enrico
2013-01-01
The aim of this advanced textbook is to provide the reader with a comprehensive explanation of the ground state configurations, the spin wave excitations and the equilibrium properties of spin lattices described by the Ising-Heisenberg Hamiltonians in the presence of short (exchange) and long range (dipole) interactions.The arguments are presented in such detail so as to enable advanced undergraduate and graduate students to cross the threshold of active research in magnetism by using both analytic calculations and Monte Carlo simulations.Recent results about unorthodox spin configurations suc
Study of self-excited ion acoustic waves in a plasma
International Nuclear Information System (INIS)
Ghoranneviss, M.H.; Agashe, V.V.
1985-01-01
Plasma oscillation were studied in spherical discharge system of different sizes: with diameters of 10, 20 and 40 cm. The self-excited ion-acoustic waves were observed, and the oscillation amplitudes were measured at different radial distances. If the discharge conditions were varied, the oscillation frequency was found varying discontinuously from mode to mode. The method used is suggested for application in plasma diagnostics as a very reliable tool for the investigation of stationary dc. low pressure plasma in the absence of external magnetic fields. (D.Gy.)
Doubly excited P-wave resonance states of H− in Debye plasmas
International Nuclear Information System (INIS)
Jiao, L. G.; Ho, Y. K.
2013-01-01
We investigate the doubly excited P-wave resonance states of H − system in Debye plasmas modeled by static screened Coulomb potentials. The screening effects of the plasma environment on resonance parameters (energy and width) are investigated by employing the complex-scaling method with Hylleraas-type wave functions for both the shape and Feshbach resonances associated with the H(N = 2 to 6) thresholds. Under the screening conditions, the H(N) threshold states are no longer l degenerate, and all the H − resonance energy levels are shifted away from their unscreened values toward the continuum. The influence of Debye plasmas on resonance widths has also been investigated. The shape resonance widths are broadened with increasing plasma screening strength, whereas the Feshbach resonance widths would generally decrease. Our results associated with the H(N = 2) and H(N = 3) thresholds are compared with others in the literature
International Nuclear Information System (INIS)
Ma Hongcai; Ge Dongjie; Yu Yaodong
2008-01-01
Based on the Bäcklund method and the multilinear variable separation approach (MLVSA), this paper nds a general solution including two arbitrary functions for the (2+1)-dimensional Burgers equations. Then a class of new doubly periodic wave solutions for (2+1)-dimensional Burgers equations is obtained by introducing appropriate Jacobi elliptic functions, Weierstrass elliptic functions and their combination in the general solutions (which contains two arbitrary functions). Two types of limit cases are considered. Firstly, taking one of the moduli to be unity and the other zero, it obtains particular wave (called semi-localized) patterns, which is periodic in one direction, but localized in the other direction. Secondly, if both moduli are tending to 1 as a limit, it derives some novel localized excitations (two-dromion solution). (general)
SELF-EXCITED WAVE PROCESSES IN CHAINS OF UNIDIRECTIONALLY COUPLED IMPULSE NEURONS
Directory of Open Access Journals (Sweden)
S. D. Glyzin
2015-01-01
Full Text Available The article is devoted to the mathematical modeling of neural activity. We propose new classes of singularly perturbed differential-difference equations with delay of Volterra type. With these systems, the models as a single neuron or neural networks are described. We study attractors of ring systems of unidirectionally coupled impulse neurons in the case where the number of links in the system increases indefinitely. In order to study periodic solutions of travelling wave type of this system, some special tricks are used which reduce the existence and stability problems for cycles to the investigation of auxiliary system with impulse actions. Using this approach, we establish that the number of stable self-excited waves simultaneously existing in the chain increases unboundedly as the number of links of the chain increases, that is, the well-known buffer phenomenon occurs.
Excitation of spin waves in BiFeO3 multiferroic film by the slot line transducer
Korneev, V. I.; Popkov, A. F.; Solov'yov, S. V.
2018-01-01
Analysis of the efficiency of magnetoelectric excitation of spin-waves in BiFeO3 multiferroic films by a slot line is performed based on the solution of dynamic Ginzburg-Landau equations for the antiferromagnetic vector. The excitation efficiency is determined by the magnitude of the conversion coefficient of the electromagnetic wave to the spin wave by the slot line transducer or in other words, losses on conversion in the slot line. Calculations are made for a homogeneous antiferromagnetic state of the multiferroic in the presence of a sufficiently large magnetic field and for a spatially modulated spin state (SMSS) at zero magnetic field. It is shown that in the case of a homogeneous antiferromagnetic state, the losses on the excitation of spin waves exceed the excitation efficiency in the SMSS state; however, as the frequency approaches the spin excitation gap, it falls and becomes lower than in the SMSS state. Spin wave excitation in the presence of antiferromagnetic cycloid strongly depends on the relation of the slot width of the transducer to the cycloid periodicity and on the magnitude of the shift of the position of the transducer along the cycloid on its period. The usage of multiferroics for delay lines in the considered frequency range from 100 to 600 GHz requires significant reduction in conversion and propagation losses. More promising seems multiferroic usage in phase shifters and switches for this range.
Convective excitation of quasistatic waves in an inhomogeneous anisothermic plasma. II
International Nuclear Information System (INIS)
Jungwirth, K.; Sizonenko, V.L.
1977-01-01
Nonlinear effects stabilizing the convective instabilities excited in an anisothermic plasma (Tsub(e)>>Tsub(i)) at the plasma boundary (a >ωsub(Bi)) saturate at first. Being excited by a small part of slow plasma electrons (vsub(z)<< vsub(Te)) only, they saturate at a relatively low level. Further, surface waves with lower frequencies and higher phase velocities (vsub(ph)=ω/ksub(z)) become dominant and a broadening of the plasma boundary occurs. For their saturation nonlinear interaction is more important than the quasilinear effects. During the time interval of several ωsub(Bi)sup(-1) the longest surface waves with ksub(y) approximately ωsub(Bi)/Vsub(s), γ approximately ω approximately ωsub(Bi) approximately ksub(y)Vsub(s) and vsub(ph) approximately vsub(Te) saturate at the absolutely highest level. The plasma boundary broadens in the meanwhile up to a approximately Vsub(s)/ωsub(Bi). The wave energy is comparable to the total energy connected with the longitudinal motion of the initially thermal electrons inside this boundary layer. The wave amplitude is large enough to trap the initially cold ions belonging to this layer and 'heat' them up to energies comparable to those of the electron component. The heating process again occurs within several ωsub(Bi)sup(-1) and the Larmor radius of the ions is then comparable to Vsub(s)/ωsub(Bi). Further evolution of the system is governed by the unstable local perturbations. (author)
International Nuclear Information System (INIS)
Choi, M.S.; Yang, M.S.; Kim, H.C.
1992-01-01
A new ultrasonic technique for detecting the infiltrated water in leaked fuel rods is developed. Propagation characteristics of the circumferential Lamb waves in the cladding tubes are estimated by the resonance scattering theory. The Lamb waves are excited by the resonance backscattering of ultrasonic pulses. In sound fuel rods, the existence of the Lamb waves is revealed by a series of periodic echoes. In leaked fuel rods, however, the Lamb waves are perturbed strongly by the scattered waves from the surface of fuel pellets, thus the periodic echoes are not observed. (author)
Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach
International Nuclear Information System (INIS)
Unn-Toc, W.; Meier, C.; Halberstadt, N.; Uranga-Piña, Ll.; Rubayo-Soneira, J.
2012-01-01
A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.
Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach
Energy Technology Data Exchange (ETDEWEB)
Unn-Toc, W.; Meier, C.; Halberstadt, N. [Laboratoire Collisions Agregats et Reactivite, IRSAMC, UMR CNRS 5589, Universite Paul Sabatier, 31062 Toulouse (France); Uranga-Pina, Ll. [Laboratoire Collisions Agregats et Reactivite, IRSAMC, UMR CNRS 5589, Universite Paul Sabatier, 31062 Toulouse (France); Facultad de Fisica, Universidad de la Habana, San Lazaro y L, Vedado, 10400 La Habana (Cuba); Rubayo-Soneira, J. [Instituto Superior de Tecnologias y Ciencias Aplicadas (InSTEC), Ave. Salvador Allende y Luaces, Habana 10600, AP 6163 La Habana (Cuba)
2012-08-07
A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.
Coronal Seismology of Flare-Excited Standing Slow-Mode Waves Observed by SDO/AIA
Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2016-05-01
Flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Å bandpasses. Based on the interpretation in terms of a slow-mode wave, quantitative evidence of thermal conduction suppression in hot (>9 MK) loops has been obtained for the first time from measurements of the polytropic index and phase shift between the temperature and density perturbations (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. One is that the thermal conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The other is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the thermal plasma is sustained well beyond the duration of impulsive hard X-ray bursts in many flares, for a time much longer than expected by the classical Spitzer conductive cooling. In this study, we model the observed standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD code. With the seismology-derived transport coefficients for thermal conduction and compressive viscosity, we successfully simulate the oscillation period and damping time of the observed waves. Based on the parametric study of the effect of thermal conduction suppression and viscosity enhancement on the observables, we discuss the inversion scheme for determining the energy transport coefficients by coronal seismology.
Oscillations in sunspot umbras due to trapped Alfven waves excited by overstability
International Nuclear Information System (INIS)
Uchida, Yutaka; Sakurai, Takashi.
1975-01-01
Oscillations observed in sunspot umbras are interpreted as a vertical motion in the atmosphere induced by a standing Alfven wave trapped in the region between the overstable layer under the photosphere and the chromosphere-corona transition layer. The Alfven wave motion is considered to be excited by the overstable convection occurring at the bottom of the abovementioned oscillating layer, and waves with special frequencies are selected as eigen-mode waves standing in the ''cavity,'' while other waves which are out of phase with themselves after reflections will disappear. It is shown by solving the eigen-value problem that the fundamental eigen frequency falls in a range around 0.04 rad s -1 (corresponding to 140-180 s) for the condition in the umbra of a typical spot, and also that the eigen frequencies do not depend greatly on the circumstantial physical or geometric parameters of the model atmosphere, such as the temperature in the layer, or the height of the transition layer, etc. The eigen frequencies, however, depend on the Alfven velocity at the base of the oscillating layer (or at the top of the overstable layer), but the latter quantity, which represents the stiffness of the magnetic tube of force against the overturning motion, takes roughly a common value for different sunspots according to SAVAGE's (1969) stability analysis of the umbral atmosphere against thermal convection, and thus gives a comparatively narrow range of resonant frequencies. In addition to the selection mechanism for oscillations of 140-180-s period, some other aspects of the oscillation, such as the relation to the running penumbral waves, are discussed. (auth.)
A new traveling wave ultrasonic motor using thick ring stator with nested PZT excitation.
Chen, Weishan; Shi, Shengjun; Liu, Yingxiang; Li, Pei
2010-05-01
To avoid the disadvantages of conventional traveling wave ultrasonic motors--lower efficiency PZT working mode of d(31), fragility of the PZT element under strong excitation, fatigue of the adhesive layer under harsh environmental conditions, and low volume of the PZT material in the stator--a new type of traveling wave ultrasonic motor is presented in this paper. Here we implement the stator by nesting 64 PZT stacks in 64 slots specifically cut in a thick metal ring and 64 block springs nested within another 64 slots to produce preloading on the PZT stacks. In this new design, the d33 mode of the PZT is used to excite the flexural vibrations of the stator, and fragility of the PZT ceramics and fatigue of the adhesive layer are no longer an issue. The working principle, FEM simulation, fabrication, and performance measurements of a prototype motor were demonstrated to validate the proposed ideas. Typical output of the prototype motor is no-load speed of 15 rpm and maximum torque of 7.96 N x m. Further improvement will potentially enhance its features by increasing the accuracy in fabrication and adopting appropriate frictional material into the interface between the stator and the rotor.
About of the Electrostatic fields excitation theory by a RF wave in a plasma
International Nuclear Information System (INIS)
Gutierrez T, C.R.
1991-01-01
In an unidimensional model is shown in the cases of a semi limited plasma and a layer of plasma the excitement mechanism of electrostatic fields for a radiofrequency wave (RF) polarized lineally. This phenomenon depends strongly on the combined action of the Miller force and that of impulsion. It is shown that the action of these forces is carried out in different characteristic times when the front of wave crosses through the plasma. The cases of a semi limited plasma and of a layer of plasma without and with current are analyzed. It is shown that near the frontiers of the plasma where the field is sufficiently big arise oscillations of the width of the field that are slowly muffled in the space in an exponential way. In the cases of a plasma layer its are shown that the processes that arise near the frontier x = L are similar to the processes that arise near the frontier x = 0. The existence of current in the plasma layer leads to the blockade of the excited perturbations in the frontier x = L. (Author)
Tonegawa, T.; Fukao, Y.; Shiobara, H.; Sugioka, H.; Ito, A.; Yamashita, M.
2018-01-01
An array of 10 absolute pressure gauges (APGs) deployed in deep water 50 km east of Aogashima, an island in southern Japan, observed several isolated signals in the infragravity wave (IGW) frequency band (0.002-0.03 Hz) during boreal summer, whereas relatively high IGW energy persisted during boreal winter. The isolated IGW shows dispersion with a delay time of 4-5 days as a function of frequency. Here we estimate the excitation locations of IGWs for the two seasons with estimated incoming direction of IGW, calculation of transoceanic IGW trajectories and propagation times, and spatiotemporal variations of significant wave heights from WAVEWATCH III. In boreal summer, the isolated IGWs are primarily caused by IGW energies excited at the shoreline of South America, based on the following three observations: IGWs observed at the array originated from the east: the easterly ray path from the array reaches South America: and an event-like IGWs were observed at the array when a storm approaches eastward to the shoreline of South America, in which the observed delay time of 4-5 days was also supported by the frequency-dependent calculation of IGW propagation times. In boreal winter, the incessant IGWs consist of transoceanic IGW energies leaked from the shoreline, primarily from North America, and secondly from South America and the western Aleutian Islands.
Impulses and pressure waves cause excitement and conduction in the nervous system.
Barz, Helmut; Schreiber, Almut; Barz, Ulrich
2013-11-01
It is general accepted, that nerval excitement and conduction is caused by voltage changes. However, the influx of fluid into an elastical tube releases impulses or pressure waves. Therefore an influx of ion currents, respectively fluid motions into the elastic neuronal cells and fibres also induce impulses. This motion of charge carriers are measured by voltage devices as oscillations or action potentials, but the voltage changes may be an epiphenomenon of the (mechanical) impulses. Impulse waves can have a high speed. As stiffer or inelastic a tube wall, the greater is the speed of the impulse. Myelin sheaths cause a significant stiffening of the nerve fibre wall and myelinated fibres have a conduction velocity up to 120 m/s. The influx of fluid at the nodes of Ranvier intensifies periodically the impulse wave in the nerve fibres. The authors suggest that also the muscle end-plate acts as a conductor of axonal impulses to the inner of the muscle fibres and that the exocytosis of acetylcholine into the synaptic cleft may be an amplifier of the axonal impulse. It is discussed that intracellular actin filaments may also influence motions at the neuronal membrane. Many sensory nerve cells are excited due to exogenous or endogenous mechanical impulses. It may plausible that such impulses are conducted directly to the sensory nerve cell bodies in the dorsal root ganglia without the transformation in electric energy. Excitation conduction happens without noteworthy energy consumption because the flow of ion currents through the membranes takes place equivalent to the concentration gradient. Impulse waves cause short extensions of the lipid membranes of the cell- and fibres walls and therefore they can induce opening and closing of the included ion channels. This mechanism acts to "voltage gated" and "ligand-gated" channels likewise. The concept of neuronal impulses can be helpful to the understanding of other points of neurophysiology or neuronal diseases. This includes
3D elastic full waveform inversion using P-wave excitation amplitude: Application to OBC field data
Oh, Juwon; Kalita, Mahesh; Alkhalifah, Tariq Ali
2017-01-01
We propose an efficient elastic full waveform inversion (FWI) based on the P-wave excitation amplitude (maximum energy arrival) approximation in the source wavefields. Because, based on the P-wave excitation approximation (ExA), the gradient direction is approximated by the cross-correlation of source and receiver wavefields at only excitation time, it estimates the gradient direction faster than its conventional counterpart. In addition to this computational speedup, the P-wave excitation approximation automatically ignores SP and SS correlations in the approximated gradient direction. In elastic FWI for ocean bottom cable (OBC) data, the descent direction for the S-wave velocity is often degraded by undesired long-wavelength features from the SS correlation. For this reason, the P-wave excitation approach increases the convergence rate of multi-parameter FWI compared to the conventional approach. The modified 2D Marmousi model with OBC acquisition is used to verify the differences between the conventional method and ExA. Finally, the feasibility of the proposed method is demonstrated on a real OBC data from North Sea.
3D elastic full waveform inversion using P-wave excitation amplitude: Application to OBC field data
Oh, Juwon
2017-12-05
We propose an efficient elastic full waveform inversion (FWI) based on the P-wave excitation amplitude (maximum energy arrival) approximation in the source wavefields. Because, based on the P-wave excitation approximation (ExA), the gradient direction is approximated by the cross-correlation of source and receiver wavefields at only excitation time, it estimates the gradient direction faster than its conventional counterpart. In addition to this computational speedup, the P-wave excitation approximation automatically ignores SP and SS correlations in the approximated gradient direction. In elastic FWI for ocean bottom cable (OBC) data, the descent direction for the S-wave velocity is often degraded by undesired long-wavelength features from the SS correlation. For this reason, the P-wave excitation approach increases the convergence rate of multi-parameter FWI compared to the conventional approach. The modified 2D Marmousi model with OBC acquisition is used to verify the differences between the conventional method and ExA. Finally, the feasibility of the proposed method is demonstrated on a real OBC data from North Sea.
Direct measurement of the transition from edge to core power coupling in a light-ion helicon source
Piotrowicz, P. A.; Caneses, J. F.; Showers, M. A.; Green, D. L.; Goulding, R. H.; Caughman, J. B. O.; Biewer, T. M.; Rapp, J.; Ruzic, D. N.
2018-05-01
We present time-resolved measurements of an edge-to-core power transition in a light-ion (deuterium) helicon discharge in the form of infra-red camera imaging of a thin stainless steel target plate on the Proto-Material Exposure eXperiment device. The time-resolved images measure the two-dimensional distribution of power deposition in the helicon discharge. The discharge displays a mode transition characterized by a significant increase in the on-axis electron density and core power coupling, suppression of edge power coupling, and the formation of a fast-wave radial eigenmode. Although the self-consistent mechanism that drives this transition is not yet understood, the edge-to-core power transition displays characteristics that are consistent with the discharge entering a slow-wave anti-resonant regime. RF magnetic field measurements made across the plasma column, together with the power deposition results, provide direct evidence to support the suppression of the slow-wave in favor of core plasma production by the fast-wave in a light-ion helicon source.
Ang, Kar M; Yeo, Leslie Y; Hung, Yew M; Tan, Ming K
2016-09-21
The deposition of a thin graphene film atop a chip scale piezoelectric substrate on which surface acoustic waves are excited is observed to enhance its performance for fluid transport and manipulation considerably, which can be exploited to achieve further efficiency gains in these devices. Such gains can then enable complete integration and miniaturization for true portability for a variety of microfluidic applications across drug delivery, biosensing and point-of-care diagnostics, among others, where field-use, point-of-collection or point-of-care functionality is desired. In addition to a first demonstration of vibration-induced molecular transport in graphene films, we show that the coupling of the surface acoustic wave gives rise to antisymmetric Lamb waves in the film which enhance molecular diffusion and hence the flow through the interstitial layers that make up the film. Above a critical input power, the strong substrate vibration displacement can also force the molecules out of the graphene film to form a thin fluid layer, which subsequently destabilizes and breaks up to form a mist of micron dimension aerosol droplets. We provide physical insight into this coupling through a simple numerical model, verified through experiments, and show several-fold improvement in the rate of fluid transport through the film, and up to 55% enhancement in the rate of fluid atomization from the film using this simple method.
Radio-frequency wave excitation and damping on a high β plasma column
International Nuclear Information System (INIS)
Meuth, H.
1984-01-01
Azimuthally symmetric (m = 0) radio-frequency (RF) waves for zero and for finite axial wave number k/sub z/ are investigated on the High BETA Q Machine, a two-meter, 20 cm-diameter, low-compression linear theta pinch (T greater than or equal to 200 eV, n approx. = 10 15 cm -3 ) fast rising (0.4 μs) compression field. The (k/sub z/ = 0) modes occur spontaneously following the implosion phase of the discharge. A novel 100-MW 1 to 1.3 MHz, short wavelength current drive excites the plasma column in the vicinity of the lowest fast magnetoacoustic mode at various filling pressures. This current drive is designed as an integral part of the compression coil, which is segmented with a 20-cm axial wavelength (k/sub z/ = 0.314 cm -1 ). The electron density oscillations along major and minor chords at various positions are measured by interferometry perpendicular to the pinch axis. The oscillatory radial magnetic field component between pinch wall and hot plasma edge is measured by probes. Phases, amplitudes and radial mode structure are studied for the free (k = 0) modes and the externally driven (k does not equal 0) modes for various filling pressures of deuterium. The energy deposition from the externally driven RF wave leads to a radial expansion of the plasma column, as observed by axial interferometry and by excluded flux measurements
Directory of Open Access Journals (Sweden)
A. S. Leonovich
1996-05-01
Full Text Available The problem of boundary conditions for monochromatic Alfvén waves, excited in the magnetosphere by external currents in the ionospheric E-layer, is solved analytically. Waves with large azimuthal wave numbers m»1 are considered. In our calculations, we used a model for the horizontally homogeneous ionosphere with an arbitrary inclination of geomagnetic field lines and a realistic height disribution of Alfvén velocity and conductivity tensor components. A relationship between such Alfvén waves on the upper ionospheric boundary with electromagnetic oscillations on the ground was detected, and the spatial structure of these oscillations determined.
International Nuclear Information System (INIS)
Saitou, Y.; Yonesu, A.; Shinohara, S.; Ignatenko, M. V.; Kasuya, N.; Kawaguchi, M.; Terasaka, K.; Nishijima, T.; Nagashima, Y.; Kawai, Y.; Yagi, M.; Itoh, S.-I.; Azumi, M.; Itoh, K.
2007-01-01
The importance of reducing the neutral density to reach strong drift wave turbulence is clarified from the results of the extended magnetohydrodynamics and Monte Carlo simulations in a linear magnetized plasma. An upper bound of the neutral density relating to the ion-neutral collision frequency for the excitation of drift wave instability is shown, and the necessary flow velocity to excite this instability is also estimated from the neutral distributions. Measurements of the Mach number and the electron density distributions using Mach probe in the large mirror device (LMD) of Kyushu University [S. Shinohara et al., Plasma Phys. Control. Fusion 37, 1015 (1995)] are reported as well. The obtained results show a controllability of the neutral density and provide the basis for neutral density reduction and a possibility to excite strong drift wave turbulence in the LMD
Evolution of spiral and scroll waves of excitation in a mathematical model of ischaemic border zone.
Directory of Open Access Journals (Sweden)
Vadim N Biktashev
Full Text Available Abnormal electrical activity from the boundaries of ischemic cardiac tissue is recognized as one of the major causes in generation of ischemia-reperfusion arrhythmias. Here we present theoretical analysis of the waves of electrical activity that can rise on the boundary of cardiac cell network upon its recovery from ischaemia-like conditions. The main factors included in our analysis are macroscopic gradients of the cell-to-cell coupling and cell excitability and microscopic heterogeneity of individual cells. The interplay between these factors allows one to explain how spirals form, drift together with the moving boundary, get transiently pinned to local inhomogeneities, and finally penetrate into the bulk of the well-coupled tissue where they reach macroscopic scale. The asymptotic theory of the drift of spiral and scroll waves based on response functions provides explanation of the drifts involved in this mechanism, with the exception of effects due to the discreteness of cardiac tissue. In particular, this asymptotic theory allows an extrapolation of 2D events into 3D, which has shown that cells within the border zone can give rise to 3D analogues of spirals, the scroll waves. When and if such scroll waves escape into a better coupled tissue, they are likely to collapse due to the positive filament tension. However, our simulations have shown that such collapse of newly generated scrolls is not inevitable and that under certain conditions filament tension becomes negative, leading to scroll filaments to expand and multiply leading to a fibrillation-like state within small areas of cardiac tissue.
P-wave excited {B}_{c}^{* * } meson photoproduction at the LHeC
Kai, He; Huan-Yu, Bi; Ren-You, Zhang; Xiao-Zhou, Li; Wen-Gan, Ma
2018-05-01
As an important sequential work of the S-wave {B}c(* ) ({}1{S}0({}3{S}1) ) meson production at the large hadron electron collider (LHeC), we investigate the production of the P-wave excited {B}c* * states (1 P 1 and 3 P J with J = 0, 1, 2) via photoproduction mechanism within the framework of nonrelativistic QCD at the LHeC. Generally, the {e}-+P\\to γ +g\\to {B}c* * +b+\\bar{c} process is considered as the main production mechanism at an electron–proton collider due to the large luminosity of the gluon. However, according to our experience on the S-wave {B}c(* ) meson production at the LHeC, the extrinsic production mechanism, i.e., {e}-+P\\to γ +c\\to {B}c* * +b and {e}-+P\\to γ +\\bar{b} \\to {B}c* * +\\bar{c}, could also provide dominating contributions at low p T region. A careful treatment between these channels is performed and the results on total and differential cross sections, together with main uncertainties are discussed. Taking the quark masses m b = 4.90 ± 0.40 GeV and m c = 1.50 ± 0.20 GeV into account and summing up all the production channels, we expect to accumulate ({2.48}-1.75+3.55)× {10}4 {B}c* * ({}1{P}1), ({1.14}-0.82+1.49)× {10}4 {B}c* * ({}3{P}0),({2.38}-1.74+3.39)× {10}4 {B}c* * ({}3{P}1) and ({5.59}-3.93+7.84)× {10}4 {B}c* * ({}3{P}2) events at the \\sqrt{S}=1.30 {{T}}{{e}}{{V}} LHeC in one operation year with luminosity { \\mathcal L }={10}33 cm‑2 s‑1. With such sizable events, it is worth studying the properties of excited P-wave {B}c* * states at the LHeC.
International Nuclear Information System (INIS)
Kumar, D.; Barman, A.; Kłos, J. W.; Krawczyk, M.
2014-01-01
We present the observation of a complete bandgap and collective spin wave excitation in two-dimensional magnonic crystals comprised of arrays of nanoscale antidots and nanodots, respectively. Considering that the frequencies dealt with here fall in the microwave band, these findings can be used for the development of suitable magnonic metamaterials and spin wave based signal processing. We also present the application of a numerical procedure, to compute the dispersion relations of spin waves for any high symmetry direction in the first Brillouin zone. The results obtained from this procedure have been reproduced and verified by the well established plane wave method for an antidot lattice, when magnetization dynamics at antidot boundaries are pinned. The micromagnetic simulation based method can also be used to obtain iso–frequency contours of spin waves. Iso–frequency contours are analogous of the Fermi surfaces and hence, they have the potential to radicalize our understanding of spin wave dynamics. The physical origin of bands, partial and full magnonic bandgaps have been explained by plotting the spatial distribution of spin wave energy spectral density. Although, unfettered by rigid assumptions and approximations, which afflict most analytical methods used in the study of spin wave dynamics, micromagnetic simulations tend to be computationally demanding. Thus, the observation of collective spin wave excitation in the case of nanodot arrays, which can obviate the need to perform simulations, may also prove to be valuable
Czech Academy of Sciences Publication Activity Database
Chum, Jaroslav; Hruška, František; Zedník, Jan; Laštovička, Jan
2012-01-01
Roč. 117, A8 (2012), A08319/1-A08319/13 ISSN 0148-0227 R&D Projects: GA ČR GA205/09/1253; GA ČR(CZ) GAP209/12/2440; GA MŠk LM2010008 Institutional support: RVO:68378289 ; RVO:67985530 Keywords : Infrasound excited by seismic waves is observed in the ionosphere * Observation is about 9000 km from the epicenter * High cross-correlation, and Doppler shift measurements are presented Subject RIV: BL - Plasma and Gas Discharge Physics; DE - Earth Magnetism, Geodesy, Geography (GFU-E) Impact factor: 3.174, year: 2012 http://onlinelibrary.wiley.com/doi/10.1029/2012JA017767/abstract
Excitable waves at the margin of the contact area between a cell and a substrate
International Nuclear Information System (INIS)
Ali, O; Albigès-Rizo, C; Block, M R; Fourcade, B
2009-01-01
In this paper, we study a new physical mechanism to generate an activator field which signals the extreme margin of the contact area between an adherent cell and the substrate. This mechanism is based on the coupling between the adhesive bridges connecting the substrate to the cytoskeleton and a cytosolic activator. Once activated by adhesion on the adhesive bridges, this activator is free to diffuse on the membrane. We propose that this activator is part of the mecano-transduction pathway which links adhesion to actin polymerization and, thus, to cellular motility. The consequences of our model are as follows: (a) the activator is localized at the rim of the contact area, (b) the adhesion is reinforced at the margin of the contact area between the cell and the substrate, (c) excitable waves of the activator can propagate along the adhesion rim
Plasma simulation in space propulsion : the helicon plasma thruster
Navarro Cavallé, Jaume
2017-01-01
The Helicon Plasma Thruster (HPT) is an electrodynamic rocket proposed in the early 2000s. It matches an Helicon Plasma Source (HPS), which ionizes the neutral gas and heats up the plasma, with aMagneticNozzle (MN),where the plasma is supersonically accelerated resulting in thrust. Although the core of this thruster inherits the knowledge on Helicon Plasma sources, dated from the seventies, the HPT technology is still not developed and remains below TRL 4. A deep review of the HPT State-of-ar...
Enhancement of Lamb Wave Imaging Resolution by Step Pulse Excitation and Prewarping
Directory of Open Access Journals (Sweden)
Shangchen Fu
2015-01-01
Full Text Available For the purpose of improving the damage localization accuracy, a prewarping technology is combined with step pulse excitation and this method is used in Lamb wave imaging of plate structures with adjacent damages. Based on the step pulse excitation, various narrowband or burst response can be derived by signal processing technology and this method provides flexibility for further prewarping approach. A narrowband signal warped with a preselected distance is then designed, and the dispersion in the response of this prewarping signal will be greatly reduced. However, in order to calculate the distance for prewarping, the first arrival needs to be estimated from the burst response. From the step-pulse response, narrowband responses at different central frequencies can be obtained, and by averaging peak-value time of their first arrivals, a more accurate estimation can be calculated. By using the prewarping method to the damage scattering signals before imaging, the imaging resolution of the delay-and-sum method can be highly enhanced. The experiment carried out in an aluminum plate with adjacent damages proves the efficiency of this method.
Electron-helium S-wave model benchmark calculations. I. Single ionization and single excitation
Bartlett, Philip L.; Stelbovics, Andris T.
2010-02-01
A full four-body implementation of the propagating exterior complex scaling (PECS) method [J. Phys. B 37, L69 (2004)] is developed and applied to the electron-impact of helium in an S-wave model. Time-independent solutions to the Schrödinger equation are found numerically in coordinate space over a wide range of energies and used to evaluate total and differential cross sections for a complete set of three- and four-body processes with benchmark precision. With this model we demonstrate the suitability of the PECS method for the complete solution of the full electron-helium system. Here we detail the theoretical and computational development of the four-body PECS method and present results for three-body channels: single excitation and single ionization. Four-body cross sections are presented in the sequel to this article [Phys. Rev. A 81, 022716 (2010)]. The calculations reveal structure in the total and energy-differential single-ionization cross sections for excited-state targets that is due to interference from autoionization channels and is evident over a wide range of incident electron energies.
Resonant Tidal Excitation of Internal Waves in the Earth's Fluid Core
Tyler, Robert H.; Kuang, Weijia
2014-01-01
It has long been speculated that there is a stably stratified layer below the core-mantle boundary, and two recent studies have improved the constraints on the parameters describing this stratification. Here we consider the dynamical implications of this layer using a simplified model. We first show that the stratification in this surface layer has sensitive control over the rate at which tidal energy is transferred to the core. We then show that when the stratification parameters from the recent studies are used in this model, a resonant configuration arrives whereby tidal forces perform elevated rates of work in exciting core flow. Specifically, the internal wave speed derived from the two independent studies (150 and 155 m/s) are in remarkable agreement with the speed (152 m/s) required for excitation of the primary normal mode of oscillation as calculated from full solutions of the Laplace Tidal Equations applied to a reduced-gravity idealized model representing the stratified layer. In evaluating this agreement it is noteworthy that the idealized model assumed may be regarded as the most reduced representation of the stratified dynamics of the layer, in that there are no non-essential dynamical terms in the governing equations assumed. While it is certainly possible that a more realistic treatment may require additional dynamical terms or coupling, it is also clear that this reduced representation includes no freedom for coercing the correlation described. This suggests that one must accept either (1) that tidal forces resonantly excite core flow and this is predicted by a simple model or (2) that either the independent estimates or the dynamical model does not accurately portray the core surface layer and there has simply been an unlikely coincidence between three estimates of a stratification parameter which would otherwise have a broad plausible range.
International Nuclear Information System (INIS)
Takase, Y.; Fiore, C.L.; McDermott, F.S.; Moody, J.D.; Porkolab, M.; Shepard, T.; Squire, J.
1987-01-01
Mode-converted and directly excited ion Bernstein waves (IBW) were studied using CO 2 laser scattering in the Alcator C tokamak. During the ICRF fast wave heating experiments, mode-converted IBW was observed on the high-field side of the resonance in both second harmonic and minority heating regimes. By comparing the relative scattered powers from the two antennas separated by 180 0 toroidally, an increased toroidal wave damping with increasing density was inferred. In the IBW heating experiments, optimum direct excitation is obtained when an ion-cyclotron harmonic layer is located just behind the antenna. Wave absorption at the ω = 3Ω/sub D/ = 1.5Ω/sub H/ layer was directly observed. Edge ion heating was inferred from the IBW dispersion when this absorption layer was located in the plasma periphery, which may be responsible for the observed improvement in particle confinement
Directory of Open Access Journals (Sweden)
Victor M. García-Chocano
2011-12-01
Full Text Available Transmission of ultrasonic waves through a slit between two water immersed brass plates is studied for sub-wavelength plate thicknesses and slit apertures. Extraordinary high absorption is observed at discrete frequencies corresponding to resonant excitation of Rayleigh waves on the both sides of the channel. The coupling of the Rayleigh waves occurs through the fluid and the corresponding contribution to the dispersion has been theoretically derived and also experimentally confirmed. Symmetric and anti-symmetric modes are predicted but only the symmetric mode resonances have been observed. It follows from the dispersion equation that the coupled Rayleigh waves cannot be excited in a channel with apertures less than the critical one. The calculated critical aperture is in a good agreement with the measured acoustic spectra. These findings could be applied to design a broadband absorptive metamaterial.
Nonlinear plasma waves excitation by intense ion beams in background plasma
International Nuclear Information System (INIS)
Kaganovich, Igor D.; Startsev, Edward A.; Davidson, Ronald C.
2004-01-01
Plasma neutralization of an intense ion pulse is of interest for many applications, including plasma lenses, heavy ion fusion, cosmic ray propagation, etc. An analytical electron fluid model has been developed to describe the plasma response to a propagating ion beam. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration τ b is much longer than the electron plasma period 2π/ω p , where ω p =(4πe 2 n p /m) 1/2 is the electron plasma frequency, and n p is the background plasma density. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break. Theoretical predictions are compared with the results of calculations utilizing a particle-in-cell (PIC) code. The cold electron fluid results agree well with the PIC simulations for ion beam propagation through a background plasma. The reduced fluid description derived in this paper can provide an important benchmark for numerical codes and yield scaling relations for different beam and plasma parameters. The visualization of numerical simulation data shows complex collective phenomena during beam entry and exit from the plasma
Nonlinear Plasma Waves Excitation by Intense Ion Beams in Background Plasma
International Nuclear Information System (INIS)
Kaganovich, Igor D.; Startsev, Edward A.; Davidson, Ronald C.
2004-01-01
Plasma neutralization of an intense ion pulse is of interest for many applications, including plasma lenses, heavy ion fusion, cosmic ray propagation, etc. An analytical electron fluid model has been developed to describe the plasma response to a propagating ion beam. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration τ b is much longer than the electron plasma period 2π/ω p , where ω p = (4πe 2 n p /m) 1/2 is the electron plasma frequency and n p is the background plasma density. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break. Theoretical predictions are compared with the results of calculations utilizing a particle-in-cell (PIC) code. The cold electron fluid results agree well with the PIC simulations for ion beam propagation through a background plasma. The reduced fluid description derived in this paper can provide an important benchmark for numerical codes and yield scaling relations for different beam and plasma parameters. The visualization of numerical simulation data shows complex collective phenomena during beam entry and exit from the plasma
Directory of Open Access Journals (Sweden)
Stewart Heitmann
2017-01-01
Full Text Available Constant optogenetic stimulation targeting both pyramidal cells and inhibitory interneurons has recently been shown to elicit propagating waves of gamma-band (40-80 Hz oscillations in the local field potential of non-human primate motor cortex. The oscillations emerge with non-zero frequency and small amplitude-the hallmark of a type II excitable medium-yet they also propagate far beyond the stimulation site in the manner of a type I excitable medium. How can neural tissue exhibit both type I and type II excitability? We investigated the apparent contradiction by modeling the cortex as a Wilson-Cowan neural field in which optogenetic stimulation was represented by an external current source. In the absence of any external current, the model operated as a type I excitable medium that supported propagating waves of gamma oscillations similar to those observed in vivo. Applying an external current to the population of inhibitory neurons transformed the model into a type II excitable medium. The findings suggest that cortical tissue normally operates as a type I excitable medium but it is locally transformed into a type II medium by optogenetic stimulation which predominantly targets inhibitory neurons. The proposed mechanism accounts for the graded emergence of gamma oscillations at the stimulation site while retaining propagating waves of gamma oscillations in the non-stimulated tissue. It also predicts that gamma waves can be emitted on every second cycle of a 100 Hz oscillation. That prediction was subsequently confirmed by re-analysis of the neurophysiological data. The model thus offers a theoretical account of how optogenetic stimulation alters the excitability of cortical neural fields.
Directory of Open Access Journals (Sweden)
Amir Rabani
2016-10-01
Full Text Available The market for process instruments generally requires low cost devices that are robust, small in size, portable, and usable in-plant. Ultrasonic torsional guided wave sensors have received much attention by researchers for measurement of viscosity and/or density of fluids in recent years. The supporting electronic systems for these sensors providing many different settings of sine-wave signals are bulky and expensive. In contrast, a system based on bursts of square waves instead of sine waves would have a considerable advantage in that respect and could be built using simple integrated circuits at a cost that is orders of magnitude lower than for a windowed sine wave device. This paper explores the possibility of using square wave bursts as the driving signal source for the ultrasonic torsional guided wave viscosity sensor. A simple design of a compact and fully automatic analogue square wave front-end for the sensor is also proposed. The successful operation of the system is demonstrated by using the sensor for measuring the viscosity in a representative fluid. This work provides the basis for design and manufacture of low cost compact standalone ultrasonic guided wave sensors and enlightens the possibility of using coded excitation techniques utilising square wave sequences in such applications.
Hybrid excitations due to crystal field, spin-orbit coupling, and spin waves in LiFePO4
Yiu, Yuen; Le, Manh Duc; Toft-Peterson, Rasmus; Ehlers, Georg; McQueeney, Robert J.; Vaknin, David
2017-03-01
We report on the spin waves and crystal field excitations in single crystal LiFePO4 by inelastic neutron scattering over a wide range of temperatures, below and above the antiferromagnetic transition of this system. In particular, we find extra excitations below TN=50 K that are nearly dispersionless and are most intense around magnetic zone centers. We show that these excitations correspond to transitions between thermally occupied excited states of Fe2 + due to splitting of the S =2 levels that arise from the crystal field and spin-orbit interactions. These excitations are further amplified by the highly distorted nature of the oxygen octahedron surrounding the iron atoms. Above TN, magnetic fluctuations are observed up to at least 720 K, with an additional inelastic excitation around 4 meV, which we attribute to single-ion effects, as its intensity weakens slightly at 720 K compared to 100 K, which is consistent with the calculated cross sections using a single-ion model. Our theoretical analysis, using the MF-RPA model, provides both detailed spectra of the Fe d shell and estimates of the average ordered magnetic moment and TN. By applying the MF-RPA model to a number of existing spin-wave results from other Li M PO4 (M =Mn , Co, and Ni), we are able to obtain reasonable predictions for the moment sizes and transition temperatures.
Excitation of Ion Cyclotron Waves by Ion and Electron Beams in Compensated-current System
Xiang, L.; Wu, D. J.; Chen, L.
2018-04-01
Ion cyclotron waves (ICWs) can play important roles in the energization of plasma particles. Charged particle beams are ubiquitous in space, and astrophysical plasmas and can effectively lead to the generation of ICWs. Based on linear kinetic theory, we consider the excitation of ICWs by ion and electron beams in a compensated-current system. We also investigate the competition between reactive and kinetic instabilities. The results show that ion and electron beams both are capable of generating ICWs. For ICWs driven by ion beams, there is a critical beam velocity, v bi c , and critical wavenumber, k z c , for a fixed beam density; the reactive instability dominates the growth of ICWs when the ion-beam velocity {v}{bi}> {v}{bi}c and the wavenumber {k}zz≃ 2{k}zc/3 for a given {v}{bi}> {v}{bi}c. For the slow ion beams with {v}{bi}< {v}{bi}c, the kinetic instability can provide important growth rates of ICWs. On the other hand, ICWs driven by electron beams are excited only by the reactive instability, but require a critical velocity, {v}{be}c\\gg {v}{{A}} (the Alfvén velocity). In addition, the comparison between the approximate analytical results based on the kinetic theory and the exact numerical calculation based on the fluid model demonstrates that the reactive instabilities can well agree quantitatively with the numerical results by the fluid model. Finally, some possible applications of the present results to ICWs observed in the solar wind are briefly discussed.
Pasqualini, Davide; Neto, Andrea; Wyss, Rolf A.
2001-01-01
In this work an electromagnetic model and subsequent design is presented for a traveling-wave, coplanar waveguide (CPW) based source that will operate in the THz frequency regime. The radio frequency (RF) driving current is a result of photoexcitation of a thin GaAs membrane using two frequency-offset lasers. The GaAs film is grown by molecular-beam-epitaxy (MBE) and displays sub-ps carrier lifetimes which enable the material conductivity to be modulated at a very high rate. The RF current flows between electrodes deposited on the GaAs membrane which are biased with a DC voltage source. The electrodes form a CPW and are terminated with a double slot antenna that couples the power to a quasi-optical system. The membrane is suspended above a metallic reflector to launch all radiation in one direction. The theoretical investigation and consequent design is performed in two steps. The first step consists of a direct evaluation of the magnetic current distribution on an infinitely extended coplanar waveguide excited by an impressed electric current distributed over a finite area. The result of the analysis is the difference between the incident angle of the laser beams and the length of the excited area that maximizes the RF power coupled to the CPW. The optimal values for both parameters are found as functions of the CPW and membrane dimensions as well as the dielectric constants of the layers. In the second step, a design is presented of a double slot antenna that matches the CPW characteristic impedance and gives good overall performance. The design is presently being implemented and measurements will soon be available.
Electron temperature measurement by a helium line intensity ratio method in helicon plasmas
International Nuclear Information System (INIS)
Boivin, R.F.; Kline, J.L.; Scime, E.E.
2001-01-01
Electron temperature measurements in helicon plasmas are difficult. The presence of intense rf fields in the plasma complicates the interpretation of Langmuir probe measurements. Furthermore, the non-negligible ion temperature in the plasma considerably shortens the lifetime of conventional Langmuir probes. A spectroscopic technique based on the relative intensities of neutral helium lines is used to measure the electron temperature in the HELIX (Hot hELicon eXperiment) plasma [P. A. Keiter et al., Phys. Plasmas 4, 2741 (1997)]. This nonintrusive diagnostic is based on the fact that electron impact excitation rate coefficients for helium singlet and triplet states differ as a function of the electron temperature. The different aspects related to the validity of this technique to measure the electron temperature in rf generated plasmas are discussed in this paper. At low plasma density (n e ≤10 11 cm -3 ), this diagnostic is believed to be very reliable since the population of the emitting level can be easily estimated with reasonable accuracy by assuming that all excitation originates from the ground state (steady-state corona model). At higher density, secondary processes (excitation transfer, excitation from metastable, cascading) become more important and a more complex collisional radiative model must be used to predict the electron temperature. In this work, different helium transitions are examined and a suitable transition pair is identified. For an electron temperature of 10 eV, the line ratio is measured as a function of plasma density and compared to values predicted by models. The measured line ratio function is in good agreement with theory and the data suggest that the excitation transfer is the dominant secondary process in high-density plasmas
Joo, Taiha; Albrecht, A. C.
1993-06-01
Time-resolved degenerate four-wave mixing (TRDFWM) for an electronically resonant system in a phase-matching configuration that measures population decay is reported. Because the spectral width of input light exceeds the vibrational Bohr frequency of a strong Raman active mode, the vibrational coherence produces strong oscillations in the TRDFWM signal together with the usual population decay from the excited electronic state. The data are analyzed in terms of a four-level system: ground and excited electronic states each split by a vibrational quantum of a Raman active mode. Absolute frequencies and their dephasing times of the vibrational modes at ≈590 cm -1 are obtained for the excited as well as the ground electronic state. The vibrational dephasing rate in the excited electronic state is about an order of magnitude faster than that in the ground state, the origin of which is speculated upon.
Gravitational Waves from F-modes Excited by the Inspiral of Highly Eccentric Neutron Star Binaries
International Nuclear Information System (INIS)
Chirenti, Cecilia; Gold, Roman; Miller, M. Coleman
2017-01-01
As gravitational wave instrumentation becomes more sensitive, it is interesting to speculate about subtle effects that could be analyzed using upcoming generations of detectors. One such effect that has great potential for revealing the properties of very dense matter is fluid oscillations of neutron stars. These have been found in numerical simulations of the hypermassive remnants of double neutron star mergers and of highly eccentric neutron star orbits. Here we focus on the latter and sketch out some ideas for the production, gravitational-wave detection, and analysis of neutron star oscillations. These events will be rare (perhaps up to several tens per year could be detected using third-generation detectors such as the Einstein Telescope or the Cosmic Explorer), but they would have unique diagnostic power for the analysis of cold, catalyzed, dense matter. Furthermore, these systems are unusual in that analysis of the tidally excited f-modes of the stars could yield simultaneous measurements of their masses, moments of inertia, and tidal Love numbers, using the frequency, damping time, and amplitude of the modes. They would thus present a nearly unique opportunity to test the I-Love-Q relation observationally. The analysis of such events will require significant further work in nuclear physics and general relativistic nonlinear mode coupling, and thus we discuss further directions that will need to be pursued. For example, we note that for nearly grazing encounters, numerical simulations show that the energy delivered to the f-modes may be up to two orders of magnitude greater than predicted in the linear theory.
Gravitational Waves from F-modes Excited by the Inspiral of Highly Eccentric Neutron Star Binaries
Energy Technology Data Exchange (ETDEWEB)
Chirenti, Cecilia [Centro de Matemática, Computação e Cognição, UFABC, 09210-170 Santo André-SP (Brazil); Gold, Roman [Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L 2Y5 (Canada); Miller, M. Coleman [Department of Astronomy and Joint Space-Science Institute, University of Maryland, College Park, MD 20742-2421 (United States)
2017-03-01
As gravitational wave instrumentation becomes more sensitive, it is interesting to speculate about subtle effects that could be analyzed using upcoming generations of detectors. One such effect that has great potential for revealing the properties of very dense matter is fluid oscillations of neutron stars. These have been found in numerical simulations of the hypermassive remnants of double neutron star mergers and of highly eccentric neutron star orbits. Here we focus on the latter and sketch out some ideas for the production, gravitational-wave detection, and analysis of neutron star oscillations. These events will be rare (perhaps up to several tens per year could be detected using third-generation detectors such as the Einstein Telescope or the Cosmic Explorer), but they would have unique diagnostic power for the analysis of cold, catalyzed, dense matter. Furthermore, these systems are unusual in that analysis of the tidally excited f-modes of the stars could yield simultaneous measurements of their masses, moments of inertia, and tidal Love numbers, using the frequency, damping time, and amplitude of the modes. They would thus present a nearly unique opportunity to test the I-Love-Q relation observationally. The analysis of such events will require significant further work in nuclear physics and general relativistic nonlinear mode coupling, and thus we discuss further directions that will need to be pursued. For example, we note that for nearly grazing encounters, numerical simulations show that the energy delivered to the f-modes may be up to two orders of magnitude greater than predicted in the linear theory.
Development of very large helicon plasma source
International Nuclear Information System (INIS)
Shinohara, Shunjiro; Tanikawa, Takao
2004-01-01
We have developed a very large volume, high-density helicon plasma source, 75 cm in diameter and 486 cm in axial length; full width at half maximum of the plasma density is up to ∼42 cm with good plasma uniformity along the z axis. By the use of a spiral antenna located just outside the end of the vacuum chamber through a quartz-glass window, plasma can be initiated with a very low value of radio frequency (rf) power ( 12 cm -3 is successfully produced with less than several hundred Watt; achieving excellent discharge efficiency. It is possible to control the radial density profile in this device by changing the magnetic field configurations near the antenna and/or the antenna radiation-field patterns
Directory of Open Access Journals (Sweden)
Borodulin Vladimir
2017-01-01
Full Text Available The present work is a continuation of previous experiments (carried out in the Blasius boundary layer and devoted to quantitative investigation of influence of an adverse pressure gradient on two efficient mechanisms of excitation of 3D TS instability waves due to a distributed boundary layer receptivity to free-stream vortices. These mechanisms are associated with distributed scattering of 3D amplified free-stream vortices both on the natural boundary-layer nonuniformity (on smooth surface and on 2D surface nonuniformities (waviness. The corresponding detailed hotwire measurements were carried out in a self-similar boundary layer with Hartree parameter βH = –0.115 in a wide range of the problem parameters. Complex values of quantitative characteristics of the physical phenomenon under study (the distributed receptivity coefficients are evaluated by based on the obtained experimental data. It is found that the adverse pressure gradient leads to reduction of efficiency of the investigated vortexroughness receptivity mechanism.
International Nuclear Information System (INIS)
Xia, Yang; Liu, Dongping; Bi, Zhenhua; Wang, Xueyang; Niu, Jinhai; Ji, Longfei; Song, Ying; Qi, Zhihua; Wang, Wenchun
2016-01-01
In this paper, by using a high precision synchronization system, the ignition time, velocity, and propagation properties of the ionization waves (IWs) have been investigated in detail from the 1st high voltage (HV) pulse to the sequential ones over a large range of the pulse-off time. In order to clarify the effects of previous ionization and excitation on the IW propagation, the density of the residual charges are controlled by varying the pulse-off time from 199 μs to 15 μs. The results show that the formation and propagation of IWs can be strongly affected by previous discharge. For a longer pulse-off time (100 μs–190 μs), the propagation velocity of plasma bullets are decreased from the 1st to the 10th HV pulse, then increased after the 10th pulse, and finally become stable after about 500 pulses. When the pulse-off time is reduced to 15 μs, the propagation velocity of plasma bullets will rapidly increase and become stable after the 1st HV pulse. The ignition voltage is significantly reduced after the 1st HV pulse with the decrease in pulse-off time. Consequently, the generation and propagation of IWs in the tube are strongly affected by the accumulation of long-lived metastable helium (He) species and residual charges from previous discharges, which is important for understanding the plasma bullet behavior. (paper)
Moessbauer spectra studied of spin-wave excitation for amorphous alloys
International Nuclear Information System (INIS)
Huang Zhigao
1992-01-01
The average hyperfine fields of amorphous Fe 70 Co 20 Zr 10 , Fe 80 Co 10 Zr 10 and Fe 86 Co 4 -Zr 10 alloys at different temperature were measured by the Moessbauer technique. According to Bloch's T 3/2 relation, spin-wave excitations of above amorphous alloys were studied and their B 3/2 values were found to be 0.40 +- 0.02, 0.45 +- 0.02 and 0.88 +- 0.04, respectively. Comparing the B 3/2 values of crystals, a-Fe-(Co, Ni)-ME, a-Fe-(Cr, Mn, W)-ME and a-Fe-B or TM-Zr invar alloys, the obvious difference among them was observed. Above results can be explained well by the exchange coupling fluctuation and the disorder of spatial arrangement. In this work, the difference between the stiffness coefficients obtained from the inelastic neutron scattering and the magnetization measurements for amorphous Invar alloys was also explained
Nonlinear rolling of a biased ship in a regular beam wave under external and parametric excitations
Energy Technology Data Exchange (ETDEWEB)
El-Bassiouny, A.F. [Mathematics Dept., Benha Univ., Benha (Egypt)
2007-10-15
We consider a nonlinear oscillator simultaneously excited by external and parametric functions. The oscillator has a bias parameter that breaks the symmetry of the motion. The example that we use to illustrate the problem is the rolling oscillation of a biased ship in longitudinal waves, but many mechanical systems display similar features. The analysis took into consideration linear, quadratic, cubic, quintic, and seven terms in the polynomial expansion of the relative roll angle. The damping moment consists of the linear term associated with radiation and viscous damping and a cubic term due to frictional resistance and eddies behind bilge keels and hard bilge corners. Two methods (the averaging and the multiple time scales) are used to investigate the first-order approximate analytical solution. The modulation equations of the amplitudes and phases are obtained. These equations are used to obtain the stationary state. The stability of the proposed solution is determined applying Liapunov's first method. Effects of different parameters on the system behaviour are investigated numerically. Results are presented graphically and discussed. The results obtained by two methods are in excellent agreement. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Goulding, Richard Howell [ORNL; Caughman, John B. [ORNL; Rapp, Juergen [ORNL; Biewer, Theodore M. [ORNL; Bigelow, Tim S. [ORNL; Campbell, Ian H. [ORNL; Caneses Marin, Juan F. [ORNL; Donovan, David C. [ORNL; Kafle, Nischal [ORNL; Martin, Elijah H. [ORNL; Ray, Holly B. [ORNL; Shaw, Guinevere C. [ORNL; Showers, Melissa A. [ORNL
2017-09-01
Proto-MPEX is a linear plasma device being used to study a novel RF source concept for the planned Material Plasma Exposure eXperiment (MPEX), which will address plasma-materials interaction (PMI) for nuclear fusion reactors. Plasmas are produced using a large diameter helicon source operating at a frequency of 13.56 MHz at power levels up to 120 kW. In recent experiments the helicon source has produced deuterium plasmas with densities up to ~6 × 1019 m–3 measured at a location 2 m downstream from the antenna and 0.4 m from the target. Previous plasma production experiments on Proto-MPEX have generated lower density plasmas with hollow electron temperature profiles and target power deposition peaked far off axis. The latest experiments have produced flat Te profiles with a large portion of the power deposited on the target near the axis. This and other evidence points to the excitation of a helicon mode in this case.
Wang, Lei-Ming; Zhang, Lingxiao; Seideman, Tamar; Petek, Hrvoje
2012-10-01
We study by numerical simulations the excitation and propagation dynamics of coupled surface plasmon polariton (SPP) wave packets (WPs) in optically thin Ag films and a bulk Ag/vacuum interface under the illumination of a subwavelength slit by 400 nm continuous wave (cw) and femtosecond pulsed light. The generated surface fields include contributions from both SPPs and quasicylindrical waves, which dominate in different regimes. We explore aspects of the coupled SPP modes in Ag thin films, including symmetry, propagation, attenuation, and the variation of coupling with incident angle and film thickness. Simulations of the electromagnetic transients initiated with femtosecond pulses reveal new features of coupled SPP WP generation and propagation in thin Ag films. Our results show that, under pulsed excitation, the SPP modes in an Ag thin film break up into two distinct bound surface wave packets characterized by marked differences in symmetries, group velocities, attenuation lengths, and dispersion properties. The nanometer spatial and femtosecond temporal scale excitation and propagation dynamics of the coupled SPP WPs are revealed in detail by movies recording the evolution of their transient field distributions.
Directory of Open Access Journals (Sweden)
N. Borisov
2005-06-01
Full Text Available It is argued that anisotropic electron pitch angle distributions in the closed magnetic field regions of the Martian ionosphere gives rise to excitation of plasma instabilities. We discuss two types of instabilities that are excited by two different populations of electrons. First, the generation of Langmuir waves by photoelectrons with energies of the order of 10eV is investigated. It is predicted that the measured anisotropy of their pitch angle distribution at the heights z≈400km causes excitation of waves with frequencies f~30kHz and wavelengths λ~30m. Near the terminators the instability of the electrostatic waves with frequencies of the order of or less than the electron gyrofrequency exited by thermal electrons is predicted. The typical frequencies of these waves depend on the local magnitude of the magnetic field and can achieve values f~3-5kHz above strong crustal magnetic fields.
Zhu, Junxiao; Parvasi, Seyed Mohammad; Ho, Siu Chun Michael; Patil, Devendra; Ge, Maochen; Li, Hongnan; Song, Gangbing
2017-05-01
Lamb waves have great potential as a diagnostic tool in the application of structural health monitoring. Propagation properties of Lamb waves are affected by the state of the structure that the waves are traveling upon. Thus Lamb waves can carry information about the structure as they travel across a structure. However, the dispersive, multimodal and attenuation characteristics of Lamb waves make it difficult to determine the time of arrival of Lamb waves. To deal with these characteristics, an innovative method to automatically determine the time of arrival for impact-induced Lamb waves without human intervention is proposed in this paper. Lead zirconate titanate sensors mounted on the surface of an aluminum plate were used to measure the Lamb waves excited by an impact. The time of arrival was determined based on wavelet decomposition, Hilbert transform and statistics (Grubbs’ test and maximum likelihood estimation). Both of numerical analysis and physical measurements have verified the accuracy of this method for impacts on an aluminum plate.
International Nuclear Information System (INIS)
Kousaka, Hiroyuki; Ono, Kouichi
2003-01-01
The electromagnetic fields and plasma parameters have been studied in an azimuthally symmetric surface wave-excited plasma (SWP) source, by using a two-dimensional numerical analysis based on the finite-difference time-domain (FDTD) approximation to Maxwell's equations self-consistently coupled with a fluid model for plasma evolution. The FDTD/fluid hybrid simulation was performed for different gas pressures in Ar and different microwave powers at 2.45 GHz, showing that the surface waves (SWs) occur along the plasma-dielectric interfaces to sustain overdense plasmas. The numerical results indicated that the electromagnetic SWs consist of two different waves, Wave-1 and Wave-2, having relatively shorter and longer wavelengths. The Wave-1 was seen to fade away with increasing pressure and increasing power, while the Wave-2 remained relatively unchanged over the range of pressure and power investigated. The numerical results revealed that the Wave-1 propagates as backward SWs whose phase velocity and group velocity point in the opposite directions. In contrast, the Wave-2 appeared to form standing waves, being ascribed to a superposition of forward SWs whose phase and group velocities point in the same direction. The fadeaway of the Wave-1 or backward SWs at increased pressures and increased powers was seen with the damping rate increasing in the axial direction, being related to the increased plasma electron densities. A comparison with the conventional FDTD simulation indicated that such fine structure of the electromagnetic fields of SWs is not observed in the FDTD simulation with spatially uniform and time-independent plasma distributions; thus, the FDTD/fluid hybrid model should be employed in simulating the electromagnetic fields and plasma parameters in SWPs with high accuracy
3D elastic full-waveform inversion for OBC data using the P-wave excitation amplitude
Oh, Juwon
2017-08-17
We suggest a fast and efficient 3D elastic full waveform inversion (FWI) algorithm based on the excitation amplitude (maximum energy arrival) of the P-wave in the source wavefield. It evaluates the gradient direction significantly faster than its conventional counterpart. In addition, it removes the long-wavelength artifacts from the gradient, which are often originated from SS correlation process. From these advantages, the excitation approach offers faster convergence not only for the S wave velocity, but also for the entire process of multi-parameter inversion, compared to the conventional FWI. The feasibility of the proposed method is demonstrated through the synthetic Marmousi and a real OBC data from North Sea.
3D elastic full-waveform inversion for OBC data using the P-wave excitation amplitude
Oh, Juwon; Kalita, Mahesh; Alkhalifah, Tariq Ali
2017-01-01
We suggest a fast and efficient 3D elastic full waveform inversion (FWI) algorithm based on the excitation amplitude (maximum energy arrival) of the P-wave in the source wavefield. It evaluates the gradient direction significantly faster than its conventional counterpart. In addition, it removes the long-wavelength artifacts from the gradient, which are often originated from SS correlation process. From these advantages, the excitation approach offers faster convergence not only for the S wave velocity, but also for the entire process of multi-parameter inversion, compared to the conventional FWI. The feasibility of the proposed method is demonstrated through the synthetic Marmousi and a real OBC data from North Sea.
Plasma characteristics of a high power helicon discharge
International Nuclear Information System (INIS)
Ziemba, T; Euripides, P; Slough, J; Winglee, R; Giersch, L; Carscadden, J; Schnackenberg, T; Isley, S
2006-01-01
A new high power helicon (HPH) plasma system has been designed to provide input powers of several tens of kilowatts to produce a large area (0.5 m 2 ) of uniform high-density, of at least 5 x 10 17 m -3 , plasma downstream from the helicon coil. Axial and radial plasma characteristics show that the plasma is to a lesser extent created in and near the helicon coil and then is accelerated into the axial and equatorial regions. The bulk acceleration of the plasma is believed to be due to a coupling of the bulk of the electrons to the helicon field, which in turn transfers energy to the ions via ambipolar diffusion. The plasma beta is near unity a few centimetres away from the HPH system and Bdot measurements show ΔB perturbations in the order of the vacuum magnetic field magnitude. In the equatorial region, a magnetic separatrix is seen to develop roughly at the mid-point between the helicon and chamber wall. The magnetic perturbation develops on the time scale of the plasma flow speed and upon the plasma reaching the chamber wall decays to the vacuum magnetic field configuration within 200 μs
Plasma characteristics of a high power helicon discharge
Energy Technology Data Exchange (ETDEWEB)
Ziemba, T; Euripides, P; Slough, J; Winglee, R; Giersch, L; Carscadden, J; Schnackenberg, T; Isley, S [Box 351310, University of Washington, Seattle WA, 98195 (United States)
2006-08-01
A new high power helicon (HPH) plasma system has been designed to provide input powers of several tens of kilowatts to produce a large area (0.5 m{sup 2}) of uniform high-density, of at least 5 x 10{sup 17} m{sup -3}, plasma downstream from the helicon coil. Axial and radial plasma characteristics show that the plasma is to a lesser extent created in and near the helicon coil and then is accelerated into the axial and equatorial regions. The bulk acceleration of the plasma is believed to be due to a coupling of the bulk of the electrons to the helicon field, which in turn transfers energy to the ions via ambipolar diffusion. The plasma beta is near unity a few centimetres away from the HPH system and Bdot measurements show {delta}B perturbations in the order of the vacuum magnetic field magnitude. In the equatorial region, a magnetic separatrix is seen to develop roughly at the mid-point between the helicon and chamber wall. The magnetic perturbation develops on the time scale of the plasma flow speed and upon the plasma reaching the chamber wall decays to the vacuum magnetic field configuration within 200 {mu}s.
Balmashnov, A. A.; Kalashnikov, A. V.; Kalashnikov, V. V.; Stepina, S. P.; Umnov, A. M.
2018-01-01
The formation of a spatially localized plasma with a high brightness has been experimentally observed in a dielectric plasma guide under the electron cyclotron resonance discharge at the excitation of a standing ion-acoustic wave. The results obtained show the possibility of designing compact high-intensity radiation sources with a spectrum determined by the working gas or gas mixture type, high-intensity chemically active particle flow sources, and plasma thrusters for correcting orbits of light spacecraft.
Laser Induced Fluorescence of Helium Ions in a Helicon Plasma
Compton, C. S.; Biloui, C.; Hardin, R. A.; Keesee, A. M.; Scime, E. E.; Boivin, R.
2003-10-01
The lack of a suitable Laser Induced Fluorescence (LIF) scheme for helium ions at visible wavelengths has prevented LIF from being employed in helium plasmas for measurements of ion temperature and bulk ion flow speeds. In this work, we will discuss our attempts to perform LIF of helium ions in a helicon source plasma using an infrared, tunable diode laser operating at 1012.36 nm. The infrared transition corresponds to excitation from the n = 4 level (4f ^2F) to the n = 5 (5g ^2G) level of singly ionized helium and therefore requires substantial electron temperatures (> 10 eV) to maintain an adequate ion population in the n = 4 state. Calculations using a steady state coronal model predict that the n = 4 state population will be 25% larger than the n = 5 population for our experimental conditions. The fluorescence decay from the n = 5 (5f ^2F) level of singly ionized helium level to the n = 3 (3d ^2D) level at 320.31 nm is monitored as the diode laser is swept through 10 GHz around the 1012.36 nm line. Note that the fluorescence emission requires a collisionally coupled transition between two different n = 5 quantum states. We will also present measurements of the emission intensities of both the 1012.36 nm and the 320.31 nm lines as a function of source neutral pressure, rf power, and plasma density. This work supported by the U.S. DoE EPSCoR Lab Partnership Program.
Ding, Feng; Wan, Weixing; Mao, Tian; Wang, Min; Ning, Baiqi; Zhao, Biqiang; Xiong, Bo
2014-05-01
We used a dense GPS network in China to track the ionospheric response to waves excited by the launch of the rocket that carried Shenzhou 10 spacecraft on 11 June 2013. The long-distance propagation of shock and acoustic waves were observed on both sides of the rocket's trajectory. On the southern side, the wave structures (characterized by a horizontal extension of ~1400 km and initial amplitudes of 0.3 total electron content unit (TECU) and 0.1 TECU for the shock and acoustic waves, respectively), traveled southwestward a distance of ~1500 km at mean velocities of 1011 m s-1 and 709 m s-1, respectively. On the northern side, northward propagating waves were seen to travel a distance of ~600 km with much smaller amplitudes of less than 0.05 TECU. Subsequent waves with amplitudes of less than 0.02 TECU could also be seen. Clear wave structures were found at a distance of ~600-2000 km from launch site.
Cherry, M.; Dierken, J.; Boehnlein, T.; Pilchak, A.; Sathish, S.; Grandhi, R.
2018-01-01
A new technique for performing quantitative scanning acoustic microscopy imaging of Rayleigh surface wave (RSW) velocity was developed based on b-scan processing. In this technique, the focused acoustic beam is moved through many defocus distances over the sample and excited with an impulse excitation, and advanced algorithms based on frequency filtering and the Hilbert transform are used to post-process the b-scans to estimate the Rayleigh surface wave velocity. The new method was used to estimate the RSW velocity on an optically flat E6 glass sample, and the velocity was measured at ±2 m/s and the scanning time per point was on the order of 1.0 s, which are both improvement from the previous two-point defocus method. The new method was also applied to the analysis of two titanium samples, and the velocity was estimated with very low standard deviation in certain large grains on the sample. A new behavior was observed with the b-scan analysis technique where the amplitude of the surface wave decayed dramatically on certain crystallographic orientations. The new technique was also compared with previous results, and the new technique has been found to be much more reliable and to have higher contrast than previously possible with impulse excitation.
Kilcrease, D. P.; Brookes, S.
2013-12-01
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. A simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert-Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. We also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.
Zhang, Bei; Sodickson, Daniel K; Lattanzi, Riccardo; Duan, Qi; Stoeckel, Bernd; Wiggins, Graham C
2012-04-01
In 7 T traveling wave imaging, waveguide modes supported by the scanner radiofrequency shield are used to excite an MR signal in samples or tissue which may be several meters away from the antenna used to drive radiofrequency power into the system. To explore the potential merits of traveling wave excitation for whole-body imaging at 7 T, we compare numerical simulations of traveling wave and TEM systems, and juxtapose full-wave electrodynamic simulations using a human body model with in vivo human traveling wave imaging at multiple stations covering the entire body. The simulated and in vivo traveling wave results correspond well, with strong signal at the periphery of the body and weak signal deep in the torso. These numerical results also illustrate the complicated wave behavior that emerges when a body is present. The TEM resonator simulation allowed comparison of traveling wave excitation with standard quadrature excitation, showing that while the traveling wave B +1 per unit drive voltage is much less than that of the TEM system, the square of the average B +1 compared to peak specific absorption rate (SAR) values can be comparable in certain imaging planes. Both systems produce highly inhomogeneous excitation of MR signal in the torso, suggesting that B(1) shimming or other parallel transmission methods are necessary for 7 T whole body imaging. Copyright © 2011 Wiley-Liss, Inc.
Beat-wave excitation and current driven in tokamak plasma. Vol. 2
Energy Technology Data Exchange (ETDEWEB)
Mohamed, B F [Plasma physics Department, Nuclear Research Center, Atomic Energy Authority, Cairo (Egypt)
1996-03-01
Wave heating current drive in tokamaks is a growing subject in the plasma physics literature. For current drive in tokamaks by electromagnetic waves, different methods have been proposed recently. One of the promising schemes for current drive remains the beat wave scheme. This technique employs two CO- or counterpropagating monochromatic laser beams (or microwaves) whose frequency difference matches the plasma frequency, while the wave number difference (or sum, in the case of counterpropagating) determine the wave number of the resulting plasma beat wave. In this work, the basic analysis of a beat wave current drive scheme in which collinear waves are used is discussed. by assuming a Gaussian profile for the amplitude of these pump waves, the amplitudes of the longitudinal and radial fields of the beat wave due to the nonlinear wave interactions have been calculated. Besides, the transfer of momentum flux that accompanies the transfer of wave action in beat-wave scattering will be used to drive the toroidal radial currents in tokamaks. self-generated magnetic fields due to those currents were also calculated. 1 fig.
Wang, Lin; Chen, Xiaoshuang; Hu, Yibin; Wang, Shao-Wei; Lu, Wei
2015-04-28
Plasma waves in graphene field-effect transistors (FETs) and nano-patterned graphene sheets have emerged as very promising candidates for potential terahertz and infrared applications in myriad areas including remote sensing, biomedical science, military, and many other fields with their electrical tunability and strong interaction with light. In this work, we study the excitations and propagation properties of plasma waves in nanometric graphene FETs down to the scaling limit. Due to the quantum-capacitance effect, the plasma wave exhibits strong correlation with the distribution of density of states (DOS). It is indicated that the electrically tunable plasma resonance has a power-dependent V0.8 TG relation on the gate voltage, which originates from the linear dependence of density of states (DOS) on the energy in pristine graphene, in striking difference to those dominated by classical capacitance with only V0.5 TG dependence. The results of different transistor sizes indicate the potential application of nanometric graphene FETs in highly-efficient electro-optic modulation or detection of terahertz or infrared radiation. In addition, we highlight the perspectives of plasma resonance excitation in probing the many-body interaction and quantum matter state in strong correlation electron systems. This study reveals the key feature of plasma waves in decorated/nanometric graphene FETs, and paves the way to tailor plasma band-engineering and expand its application in both terahertz and mid-infrared regions.
Directory of Open Access Journals (Sweden)
M. Jäckl
2017-04-01
Full Text Available Optical tools are promising for spin-wave generation because of the possibilities of ultrafast manipulation and local excitation. However, a single laser pulse can inject spin waves (SWs only with a broad frequency spectrum, resulting in short propagation distances and low wave amplitudes. Here, we excite a magnetic garnet film by a train of fs-laser pulses with a 1-GHz repetition rate so that the pulse separation is shorter than the decay time of magnetic modes, which allows us to achieve a collective impact on the magnetization and establish a quasistationary source of spin waves, namely, a coherent accumulation of magnons (“magnon cloud”. This approach has several appealing features: (i The magnon source is tunable, (ii the SW amplitude can be significantly enhanced, (iii the SW spectrum is quite narrow, providing long-distance propagation, (iv the periodic pumping results in an almost constant-in-time SW amplitude for the distances larger than 20 μm away from the source, and (v the SW emission shows pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave the way for applications in data processing, including the quantum regime. The quasistationary magnon accumulation might also be of interest for applications in magnon Bose-Einstein condensates.
Parallel ferromagnetic resonance and spin-wave excitation in exchange-biased NiFe/IrMn bilayers
Energy Technology Data Exchange (ETDEWEB)
Sousa, Marcos Antonio de, E-mail: marcossharp@gmail.com [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Pelegrini, Fernando [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Alayo, Willian [Departamento de Física, Universidade Federal de Pelotas, Pelotas, 96010-900 (Brazil); Quispe-Marcatoma, Justiniano; Baggio-Saitovitch, Elisa [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, 22290-180 (Brazil)
2014-10-01
Ferromagnetic Resonance study of sputtered Ru(7 nm)/NiFe(t{sub FM})/IrMn(6 nm)/Ru(5 nm) exchange-biased bilayers at X and Q-band microwave frequencies reveals the excitation of spin-wave and NiFe resonance modes. Angular variations of the in-plane resonance fields of spin-wave and NiFe resonance modes show the effect of the unidirectional anisotropy, which is about twice larger for the spin-wave mode due to spin pinning at the NiFe/IrMn interface. At Q-band frequency the angular variations of in-plane resonance fields also reveal the symmetry of a uniaxial anisotropy. A modified theoretical model which also includes the contribution of a rotatable anisotropy provides a good description of the experimental results.
Parametric Excitations of Fast Plasma Waves by Counter-propagating Laser Beams
International Nuclear Information System (INIS)
Shvets, G.; Fisch, N.J.
2001-01-01
Short- and long-wavelength plasma waves can become strongly coupled in the presence of two counter-propagating laser pump pulses detuned by twice the cold plasma frequency. What makes this four-wave interaction important is that the growth rate of the plasma waves occurs much faster than in the more obvious co-propagating geometry
Li, Ping; Jiang, Li Jun; Bagci, Hakan
2016-01-01
A discontinuous Galerkin time-domain (DGTD) method analyzing signal/power integrity on multilayered power-ground parallel plate pairs is proposed. The excitation is realized by introducing wave ports on the antipads where electric/magnetic current
Directory of Open Access Journals (Sweden)
J. Y. Jia
2014-11-01
Full Text Available Absolute values of gravity wave momentum flux (GWMF deduced from satellite measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER instrument and the High Resolution Dynamics Limb Sounder (HIRDLS are correlated with sea surface temperature (SST with the aim of identifying those oceanic regions for which convection is a major source of gravity waves (GWs. Our study identifies those latitude bands where high correlation coefficients indicate convective excitation with confidence. This is based on a global ray-tracing simulation, which is used to delineate the source and wind-filtering effects. Convective GWs are identified at the eastern coasts of the continents and over the warm water regions formed by the warm ocean currents, in particular the Gulf Stream and the Kuroshio. Potential contributions of tropical cyclones to the excitation of the GWs are discussed. Convective excitation can be identified well into the mid-mesosphere. In propagating upward, the centers of GWMF formed by convection shift poleward. Some indications of the main forcing regions are even shown for the upper mesosphere/lower thermosphere (MLT.
Erratum: The Growth Rate of Tidally Excited Waves in Accretion Disks
Vishniac, Ethan T.; Zhang, Changsong
1997-03-01
In the paper ``The Growth Rate of Tidally Excited Waves in Accretion Disks'' by Ethan T. Vishniac and Changsong Zhang (ApJ, 461, 307 [1996]), the original formulae for the Eulerian velocities in terms of the Lagrangian displacements were in error. The correct formulae are (equation numbers here match those in the original paper) Δvr=-2ω¯ξr sin (2ω¯t+2θ) (33)and Δvθ=(3/2Ωξr+2ω¯ξθ) cos (2ω¯t+2θ) . (34) This changes the matrix elements used in calculating the wave growth rates to =sin (2ψ)/8 -∞∞ṽr[vr(-(∂rΔvr)/2-(Δvθ)/r)-Δvz∂zvr-((2Δvθ)/r-(2Δvr)/r)vθ-χkr Δρ/ρ S]dz=sin (2ψ)/8 -∞∞ṽr{vr(ω¯∂rξr-2ω¯ (ξθ)/r-3Ω (ξr)/r)+∂zvr2ω¯ξz-(2vθ)/r [ξr(3Ω/2+2ω¯)+2ω¯ξθ]+χkrS[(ξr)/r+∂rξr+2/r ξθ+∂zξz(1+z∂zlnρ)]}dz ,=sin (2ψ)/8 -∞∞ṽθ[vr(∂rΔvθ+(Δvθ)/r)+vθ(-1/2 ∂rΔvr+(Δvr)/r-(Δvθ)/r)+Δvz∂zvθ]dz=sin (2ψ)/8 -∞∞ṽθ{vr[3Ω/2 ∂rξr+2ω¯∂rξθ-3Ω/4 (ξr)/r+(2ω¯-3Ω) (ξθ)/r]+vθ[ω¯∂rξr-2ω¯ (ξθ)/r-(3Ω+2ω¯) (ξr)/r]-2ω¯ξz∂zvθ}dz ,=(sin(2ψ))/8-∞∞ṽz[vz(-∂zΔvz+1/2∂rΔvr-(Δvθ)/r)-Δvz∂zvz-Δρ/ρS(-(zΩ2)/(c2s)+∂z)χ-δ(1/ρ∂zΔP+2Δρ/ρzΩ2)]dz=sin (2ψ)/8 -∞∞ṽz{vz(-ω¯∂rξr-2ω¯ (ξθ)/r+2ω¯∂zξz)+2ω¯ξz∂zvz-Δρ/ρ S(-(zΩ2)/(c2s)+∂z)χ+zΩ2[(γ-2) Δρ/ρ+γ ΔS/S-∂zξz(2+z∂zlnρ+(γz2Ω2)/(c2s))]δ}dz , (44) (46) (48)=sin (2ψ)/8 -∞∞χ˜[[-(c2s)/S ΔP/P krvr+(c2s)/S ((∂zΔP)/γP+ΔP/P ∂z)vz×{(γ-1/2)[(∂r(rΔvr))/r-(2Δvθ)/r]+Δvz(-(zΩ2)/(c2s)+∂z)+γ∂z(Δvz)}χ
Edge waves excited by underwater landslides : scenarios in the sea of Marmara
Sinan Özeren, Mehmet; Postacioglu, Nazmi; Canlı, Umut; Gasperini, Luca
2014-05-01
In this work we quantify the travel distance of edge waves created by submarine landslide over slopes of finite length. Edge waves, if generated, can constitute severe coastal hazard because they can travel long distances along the shores. In the Sea of Marmara there are several submarine masses susceptible to slide in case of a big earthquake on the Main Marmara Fault and some damage scenarios might involve edge waves. The edge waves generated by landslide Tsunamis over slopes of infinite lenghts are recently studied by Sammarco and Renzi (Landslide tsunamis propagating along a plane beach, 2008, Journal of Fluid Mech.). However the infinite slope length assumption causes a perfect confinement of the waves over the coastal slope, thereby overestimating the edge wave damage. Because of this, in their work there is no alongshore length scale over which these waves can lose their energy. In the real worls, the off-shore limiting depth will be finite and the off-shore direction wave vector will not be completely complex, pointing to radiation damping of these edge waves. In this work we analytically quantify the amount of this damping and we estimate the travel distance of the edge waves along the shoreline as a function of the limiting depth. We examine some some scenarios in the north coast of the Sea of Marmara and the northern shelf to quantify the edge waves. Since the method does not require high-resolution numerical computing, it can be used to calculate the edge-wave related risk factor anywhere with submarine landslide risk.
Fast calcium wave propagation mediated by electrically conducted excitation and boosted by CICR.
Kusters, J.M.A.M.; Meerwijk, W.P. van; Ypey, D.L.; Theuvenet, A.P.R.; Gielen, C.C.A.M.
2008-01-01
We have investigated synchronization and propagation of calcium oscillations, mediated by gap junctional excitation transmission. For that purpose we used an experimentally based model of normal rat kidney (NRK) cells, electrically coupled in a one-dimensional configuration (linear strand).
Wave excited motion of a body floating on water confined between two semi-infinite ice sheets
Ren, K.; Wu, G. X.; Thomas, G. A.
2016-12-01
The wave excited motion of a body floating on water confined between two semi-infinite ice sheets is investigated. The ice sheet is treated as an elastic thin plate and water is treated as an ideal and incompressible fluid. The linearized velocity potential theory is adopted in the frequency domain and problems are solved by the method of matched eigenfunctions expansion. The fluid domain is divided into sub-regions and in each sub-region the velocity potential is expanded into a series of eigenfunctions satisfying the governing equation and the boundary conditions on horizontal planes including the free surface and ice sheets. Matching is conducted at the interfaces of two neighbouring regions to ensure the continuity of the pressure and velocity, and the unknown coefficients in the expressions are obtained as a result. The behaviour of the added mass and damping coefficients of the floating body with the effect of the ice sheets and the excitation force are analysed. They are found to vary oscillatorily with the wave number, which is different from that for a floating body in the open sea. The motion of the body confined between ice sheets is investigated, in particular its resonant behaviour with extremely large motion found to be possible under certain conditions. Standing waves within the polynya are also observed.
Jia, Heping; Yang, Rongcao; Tian, Jinping; Zhang, Wenmei
2018-05-01
The nonautonomous nonlinear Schrödinger (NLS) equation with both varying linear and harmonic external potentials is investigated and the semirational rogue wave (RW) solution is presented by similarity transformation. Based on the solution, the interactions between Peregrine soliton and breathers, and the controllability of the semirational RWs in periodic distribution and exponential decreasing nonautonomous systems with both linear and harmonic potentials are studied. It is found that the harmonic potential only influences the constraint condition of the semirational solution, the linear potential is related to the trajectory of the semirational RWs, while dispersion and nonlinearity determine the excitation position of the higher-order RWs. The higher-order RWs can be partly, completely and biperiodically excited in periodic distribution system and the diverse excited patterns can be generated for different parameter relations in exponential decreasing system. The results reveal that the excitation of the higher-order RWs can be controlled in the nonautonomous system by choosing dispersion, nonlinearity and external potentials.
Propagation and Breaking at High Altitudes of Gravity Waves Excited by Tropospheric Forcing
Prusa, Joseph M.; Smolarkiewicz, Piotr K.; Garcia, Rolando R.
1996-01-01
An anelastic approximation is used with a time-variable coordinate transformation to formulate a two-dimensional numerical model that describes the evolution of gravity waves. The model is solved using a semi-Lagrangian method with monotone (nonoscillatory) interpolation of all advected fields. The time-variable transformation is used to generate disturbances at the lower boundary that approximate the effect of a traveling line of thunderstorms (a squall line) or of flow over a broad topographic obstacle. The vertical propagation and breaking of the gravity wave field (under conditions typical of summer solstice) is illustrated for each of these cases. It is shown that the wave field at high altitudes is dominated by a single horizontal wavelength; which is not always related simply to the horizontal dimension of the source. The morphology of wave breaking depends on the horizontal wavelength; for sufficiently short waves, breaking involves roughly one half of the wavelength. In common with other studies, it is found that the breaking waves undergo "self-acceleration," such that the zonal-mean intrinsic frequency remains approximately constant in spite of large changes in the background wind. It is also shown that many of the features obtained in the calculations can be understood in terms of linear wave theory. In particular, linear theory provides insights into the wavelength of the waves that break at high altitudes, the onset and evolution of breaking. the horizontal extent of the breaking region and its position relative to the forcing, and the minimum and maximum altitudes where breaking occurs. Wave breaking ceases at the altitude where the background dissipation rate (which in our model is a proxy for molecular diffusion) becomes greater than the rate of dissipation due to wave breaking, This altitude, in effect, the model turbopause, is shown to depend on a relatively small number of parameters that characterize the waves and the background state.
On the self-focusing of electric helicons
International Nuclear Information System (INIS)
Tsintadze, N.L.; El-Ashry, M.Y.; Garuchava, D.P.
1987-07-01
The present work is devoted to the investigation of the stationary self-focusing of circularly polarized helicons in a magnetized plasma in the case of ultra-relativistic intensities. It is shown that the larger intensity and effective width at the boundary is the much faster growing self-focusing. (author). 8 refs
CSIR Research Space (South Africa)
von Bergmann, HM
2008-08-01
Full Text Available Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform discharges, resulting in a deterioration...
International Nuclear Information System (INIS)
Anisimov, I.O.; Kelnyk, O.I.; Soroka, S.V.; Siversky, T.V.
2005-01-01
Nonlinear deformation of the initially linear plasma density profile due to the modulated electron beam is studied via computer simulation. In the initial time period the field slaves to the instantaneous profile of the plasma density. Langmuir waves excitation is suppressed by the density profile deformation. The character of the plasma density profile deformation for the late time period depends significantly on the plasma properties. Particularly, for plasma with hot electrons quasi-periodic generation of ion-acoustic pulses takes place in the vicinity of the initial point of plasma resonance
Magnani, N; Caciuffo, R; Lander, G H; Hiess, A; Regnault, L-P
2010-03-24
The anisotropy of magnetic fluctuations propagating along the [1 1 0] direction in the ordered phase of uranium antimonide has been studied using polarized inelastic neutron scattering. The observed polarization behavior of the spin waves is a natural consequence of the longitudinal 3-k magnetic structure; together with recent results on the 3-k-transverse uranium dioxide, these findings establish this technique as an important tool to study complex magnetic arrangements. Selected details of the magnon excitation spectra of USb have also been reinvestigated, indicating the need to revise the currently accepted theoretical picture for this material.
Thermally excited capillary waves at vapor/liquid interfaces of water-alcohol mixtures
International Nuclear Information System (INIS)
Vaknin, David; Bu Wei; Sung, Jaeho; Jeon, Yoonnam; Kim, Doseok
2009-01-01
The density profiles of liquid/vapor interfaces of water-alcohol (methanol, ethanol and propanol) mixtures were studied by surface-sensitive synchrotron x-ray scattering techniques. X-ray reflectivity and diffuse scattering measurements, from the pure and mixed liquids, were analyzed in the framework of capillary wave theory to address the characteristic length scales of the intrinsic roughness and the shortest capillary wavelength (alternatively, the upper wavevector cutoff in capillary wave theory). Our results establish that the intrinsic roughness is dominated by average interatomic distances. The extracted effective upper wavevector cutoff indicates capillary wave theory breaks down at distances of the order of bulk correlation lengths.
Wave excitation in electron beam experiment on Japanese satellite JIKIKEN (EXOS-B)
International Nuclear Information System (INIS)
Kawashima, N.
1982-01-01
Beam-plasma interaction experiment has been made in the magnetosphere by emitting an electron beam (100-200 eV, 0.25-1.0 mA) from the satellite JIKIKEN (EXOS-B). Various types of wave emission are detected by LF and HF wave detectors. Waves near at upper-hybrid frequency and at electron cyclotron frequency are detected in a low L-value region, which will be useful diagnostic means for plasma density and magnetic field. Vehicle charging up to the beam energy is also observed outside the plasmapause
International Nuclear Information System (INIS)
Takahashi, Toshio; Granzer, E.; Kikuta, Seishi; Tomimitsu, Hiroshi; Doi, Kenji.
1985-01-01
High frequency time modulation of neutrons was investigated by using Y-cut LiNbO 3 crystals with surface acoustic waves excited. A double crystal arrangement of (+, -) parallel setting was used for 030 symmetric Bragg-case reflections. Synchronized standing waves with a resonance frequency of 14.26 MHz were excited on the both crystals. Variation of the diffracted intensity with phase difference between two standing waves was studied. The result showed an intensity change of diffracted neutrons with twice the resonance frequency. (author)
Discontinuous Galerkin time-domain analysis of power/ground plate pairs with wave port excitation
Li, Ping; Jiang, Li Jun; Bagci, Hakan
2018-01-01
In this work, a discontinuous Galerkin time-domain method is developed to analyze the power/ground plate pairs taking into account arbitrarily shaped antipads. To implement proper source excitations over the antipads, the magnetic surface current expanded by the electric eigen-modes supported by the corresponding antipad is employed as the excitation. For irregularly shaped antipads, the eigen-modes are obtained by numerical approach. Accordingly, the methodology for the S-parameter extraction is derived based on the orthogonal properties of the different modes. Based on the approach, the transformation between different modes can be readily evaluated.
Strongly gapped spin-wave excitation in the insulating phase of NaOsO3
International Nuclear Information System (INIS)
Calder, S.; Vale, J. G.; Bogdanov, N.; Donnerer, C.
2017-01-01
NaOsO_3 hosts a rare manifestation of a metal-insulator transition driven by magnetic correlations, placing the magnetic exchange interactions in a central role. We use resonant inelastic x-ray scattering to directly probe these magnetic exchange interactions. A dispersive and strongly gapped (58 meV) excitation is observed indicating appreciable spin-orbit coupling in this 5d"3 system. The excitation is well described within a minimal model Hamiltonian with strong anisotropy and Heisenberg exchange (J_1 = J_2 = 13.9 meV). As a result, the observed behavior places NaOsO_3 on the boundary between localized and itinerant magnetism.
Discontinuous Galerkin time-domain analysis of power/ground plate pairs with wave port excitation
Li, Ping
2018-04-06
In this work, a discontinuous Galerkin time-domain method is developed to analyze the power/ground plate pairs taking into account arbitrarily shaped antipads. To implement proper source excitations over the antipads, the magnetic surface current expanded by the electric eigen-modes supported by the corresponding antipad is employed as the excitation. For irregularly shaped antipads, the eigen-modes are obtained by numerical approach. Accordingly, the methodology for the S-parameter extraction is derived based on the orthogonal properties of the different modes. Based on the approach, the transformation between different modes can be readily evaluated.
International Nuclear Information System (INIS)
Karfidov, D.M.; Alves, M.V.; Prado, F. do; Ueda, M.
1993-01-01
The results obtained in a beam plasma interaction experiment are reported. The experiment and the wave energy growth and saturation are governed by kinetic effects. The estimation of the maximum wave energy due to the warm beam quasi-linear diffusion process gives W r ≥ (κ o λ D ) 2 , indicating that the modulational instability can be the responsible mechanism for the suppression of the beam plasma instability observed in the experiment. (author)
Nonlinear saturation of wave packets excited by low-energy electron horseshoe distributions.
Krafft, C; Volokitin, A
2013-05-01
Horseshoe distributions are shell-like particle distributions that can arise in space and laboratory plasmas when particle beams propagate into increasing magnetic fields. The present paper studies the stability and the dynamics of wave packets interacting resonantly with electrons presenting low-energy horseshoe or shell-type velocity distributions in a magnetized plasma. The linear instability growth rates are determined as a function of the ratio of the plasma to the cyclotron frequencies, of the velocity and the opening angle of the horseshoe, and of the relative thickness of the shell. The nonlinear stage of the instability is investigated numerically using a symplectic code based on a three-dimensional Hamiltonian model. Simulation results show that the dynamics of the system is mainly governed by wave-particle interactions at Landau and normal cyclotron resonances and that the high-order normal cyclotron resonances play an essential role. Specific features of the dynamics of particles interacting simultaneously with two or more waves at resonances of different natures and orders are discussed, showing that such complex processes determine the main characteristics of the wave spectrum's evolution. Simulations with wave packets presenting quasicontinuous spectra provide a full picture of the relaxation of the horseshoe distribution, revealing two main phases of the evolution: an initial stage of wave energy growth, characterized by a fast filling of the shell, and a second phase of slow damping of the wave energy, accompanied by final adjustments of the electron distribution. The influence of the density inhomogeneity along the horseshoe on the wave-particle dynamics is also discussed.
Owen, L. W.; Rapp, J.; Canik, J.; Lore, J. D.
2017-11-01
Data-constrained interpretative analyses of plasma transport in convection dominated helicon discharges in the Proto-MPEX linear device, and predictive calculations with additional Electron Cyclotron Heating/Electron Bernstein Wave (ECH/EBW) heating, are reported. The B2.5-Eirene code, in which the multi-fluid plasma code B2.5 is coupled to the kinetic Monte Carlo neutrals code Eirene, is used to fit double Langmuir probe measurements and fast camera data in front of a stainless-steel target. The absorbed helicon and ECH power (11 kW) and spatially constant anomalous transport coefficients that are deduced from fitting of the probe and optical data are additionally used for predictive simulations of complete axial distributions of the densities, temperatures, plasma flow velocities, particle and energy fluxes, and possible effects of alternate fueling and pumping scenarios. The somewhat hollow electron density and temperature radial profiles from the probe data suggest that Trivelpiece-Gould wave absorption is the dominant helicon electron heating source in the discharges analyzed here. There is no external ion heating, but the corresponding calculated ion temperature radial profile is not hollow. Rather it reflects ion heating by the electron-ion equilibration terms in the energy balance equations and ion radial transport resulting from the hollow density profile. With the absorbed power and the transport model deduced from fitting the sheath limited discharge data, calculated conduction limited higher recycling conditions were produced by reducing the pumping and increasing the gas fueling rate, resulting in an approximate doubling of the target ion flux and reduction of the target heat flux.
Combined Raman and continuous-wave-excited two-photon fluorescence cell imaging
Uzunbajakava, N.; Otto, Cornelis
2003-01-01
We demonstrate a confocal optical microscope that combines cw two-photon-excited fluorescence microscopy with confocal Raman microscopy. With this microscope fast image acquisition with fluorescence imaging can be used to select areas of interest for subsequent chemical analysis with spontaneous
Excitation spectra of an effective d-wave model for cuprate superconductivity
Yamaguchi, M; Ohta, Y; Eder, R
An exact-diagonalization technique on finite-size clusters is used to study the ground states and some excitation spectra of the two-dimensional effective Fermi-liquid model derived from numerical studies of the t-J model. We show that there is actually a reasonable range of parameter values where
Dc to ac field conversion due to leaky-wave excitation in a plasma slab behind an ionization front
International Nuclear Information System (INIS)
Kostin, V A; Vvedenskii, N V
2015-01-01
We present a way for generating coherent tunable electromagnetic radiation through dc to ac field conversion by an ionization front. The conversion is caused by the excitation of leaky waves behind the transversely limited ionization front propagating in a uniform electrostatic field. This differs significantly from the well-known dc-to-ac-radiation-converter models which consider Doppler-like frequency conversion by a transversely unlimited ionization front propagating in a spatially periodic electric field. We explore the dispersion properties and excitation of these leaky waves radiated through the transverse plasma boundary at the Cherenkov angle to the direction of propagation of a superluminal ionization front as dependent on the parameters of the plasma produced and on the speed of the ionization front. It is shown that not only the center frequency but also the duration and waveform of the generated pulse may significantly depend on the speed of the ionization front. The results indicate the possibility of using such converters based on planar photoconductive antennas to create sources of microwave and terahertz radiation with controllable waveforms that are transformed from video to radio pulse when the angle of incident ionizing radiation is tuned. (paper)
Directory of Open Access Journals (Sweden)
Lei Huang
2013-01-01
Full Text Available Linear generators have the advantage of a simple structure of the secondary, which is suitable for the application of wave energy conversion. Based on the vernier hybrid machines (VHMs, widely used for direct drive wave energy converters, this paper proposes a novel hybrid excitation flux-switching generator (LHEFSG, which can effectively improve the performance of this kind of generators. DC hybrid excitation windings and multitooth structure were used in the proposed generator to increase the magnetic energy and overcome the disadvantages of easily irreversible demagnetization of VHMs. Firstly, the operation principle and structure of the proposed generator are introduced. Secondly, by using the finite element method, the no-load performance of the proposed generator is analyzed and composed with ones of conventional VHM. In addition, the on-load performance of the proposed generator is obtained by finite element analysis (FEA. A dislocation of pole alignments method is implemented to reduce the cogging force. Lastly, a prototype of the linear flux-switching generator is used to verify the correctness of FEA results. All the results validate that the proposed generator has better performance than its counterparts.
Moilanen, Petro; Salmi, Ari; Kilappa, Vantte; Zhao, Zuomin; Timonen, Jussi; Hæggström, Edward
2017-10-01
This paper validates simulation predictions, which state that specific modes could be enhanced in quantitative ultrasonic bone testing. Tunable selection of ultrasonic guided wave excitation is useful in non-destructive testing since it permits the mediation of energy into diagnostically useful modes while reducing the energy mediated into disturbing contributions. For instance, it is often challenging to distinguish and extract the useful modes from ultrasound signals measured in bone covered by a soft tissue. We show that a laser diode array can selectively excite ultrasound in bone mimicking phantoms. A fiber-coupled diode array (4 elements) illuminated two solid tubes (2-3 mm wall thickness) embraced by an opaque soft-tissue mimicking elastomer coating (5 mm thick). A predetermined time delay matching the selected mode and frequency was employed between the outputs of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results suggest that this array reduces the disturbances caused by the elastomer cover and so pave way to permit non-contacting in vivo guided wave ultrasound assessment of human bones. The implementation is small, inexpensive, and robust in comparison with the conventional pulsed lasers.
Energy Technology Data Exchange (ETDEWEB)
Esposti, Claudio Degli; Dore, Luca; Melosso, Mattia [Dipartimento di Chimica “Giacomo Ciamician”, Università di Bologna, via Selmi 2, I-40126 Bologna (Italy); Kobayashi, Kaori [Department of Physics, Faculty of Science, University of Toyama, 3190 Gofuku, Toyama 930-8555 (Japan); Fujita, Chiho; Ozeki, Hiroyuki, E-mail: ozeki@env.sci.toho-u.ac.jp [Department of Environmental Science, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, 274-8510 (Japan)
2017-06-01
It is important to study possible precursors of amino acids such as glycine to enable future searches in interstellar space. Aminoacetonitrile (NH{sub 2}CH{sub 2}CN) is one of the most feasible molecules for this purpose. This molecule was already detected toward Sgr B2(N). Aminoacetonitrile has a few low-lying vibrational excited states, and transitions within these states may be found in space. In this study, the pure-rotational transitions in the three lowest vibrational states in the 80–450 GHz range have been assigned and analyzed. It was found to be very important to include Coriolis coupling between the two lowest vibrational fundamentals, while the third one was unperturbed. The partition function was evaluated considering these new results.
Frequency-tunable terahertz wave generation via excitation of phonon-polaritons in GaP
Tanabé, T; Nishizawa, J I; Saitô, K; Kimura, T
2003-01-01
High-power, wide-frequency-tunable terahertz waves were generated based on difference-frequency generation in GaP crystals with small-angle noncollinear phase matching. The tunable frequency range was as wide as 0.5-7 THz, and the peak power remained high, near 100 mW, over most of the frequency region. The tuning properties were well described by the dispersion relationship for the phonon-polariton mode of GaP up to 6 THz. We measured the spectra of crystal polyethylene and crystal quartz with high resolution using this THz-wave source.
Frequency-tunable terahertz wave generation via excitation of phonon-polaritons in GaP
International Nuclear Information System (INIS)
Tanabe, Tadao; Suto, Ken; Nishizawa, Jun-ichi; Saito, Kyosuke; Kimura, Tomoyuki
2003-01-01
High-power, wide-frequency-tunable terahertz waves were generated based on difference-frequency generation in GaP crystals with small-angle noncollinear phase matching. The tunable frequency range was as wide as 0.5-7 THz, and the peak power remained high, near 100 mW, over most of the frequency region. The tuning properties were well described by the dispersion relationship for the phonon-polariton mode of GaP up to 6 THz. We measured the spectra of crystal polyethylene and crystal quartz with high resolution using this THz-wave source
Excitation of lower hybrid waves by electron beams in finite geometry plasmas
International Nuclear Information System (INIS)
Shoucri, M.m.; Gagne, R.R.J.
1978-01-01
The quasi-static lower hybrid eigenmodes of a plasma column in a cylindrical waveguide are determined, and their linear excitation by a small density electron beam is discussed for the cases of a hot electron beam as well as for a cold electron beam. It is shown that under certain conditions, finite geometry effects introduce important quantitative and qualitative differences with respect to the results obtained in an infinite geometry. (author)
Girka, Igor O.; Pavlenko, Ivan V.; Thumm, Manfred
2018-05-01
Azimuthal surface waves are electromagnetic eigenwaves of cylindrical plasma-dielectric waveguides which propagate azimuthally nearby the plasma-dielectric interface across an axial external stationary magnetic field. Their eigenfrequency in particular can belong to the electron cyclotron frequency range. Excitation of azimuthal surface waves by rotating relativistic electron flows was studied in detail recently in the case of the zeroth radial mode for which the waves' radial phase change within the layer where the electrons gyrate is small. In this case, just the plasma parameters cause the main influence on the waves' dispersion properties. In the case of the first and higher radial modes, the wave eigenfrequency is higher and the wavelength is shorter than in the case of the zeroth radial mode. This gain being of interest for practical applications can be achieved without any change in the device design. The possibility of effective excitation of the higher order radial modes of azimuthal surface waves is demonstrated here. Getting shorter wavelengths of the excited waves in the case of higher radial modes is shown to be accompanied by decreasing growth rates of the waves. The results obtained here are of interest for developing new sources of electromagnetic radiation, in nano-physics and in medical physics.
Pushkin, A. V.; Bychkov, A. S.; Karabutov, A. A.; Potemkin, F. V.
2018-06-01
The processes of conversion of light energy into mechanical energy under mid-IR nanosecond laser excitation on a rigid boundary of water are investigated. Strong water absorption of Q-switched Cr:Yb:Ho:YSGG (2.85 µm, 6 mJ, 45 ns) laser radiation provides rapid energy deposition of ~8 kJ cm‑3 accompanied with strong mechanical transients. The evolution of shock waves and cavitation bubbles is studied using the technique of shadowgraphy and acoustic measurements, and the conversion efficiency into these energy channels for various laser fluence (0.75–2.0 J cm‑2) is calculated. For 6 mJ laser pulse with fluence of 2.0 J cm‑2, the conversion into shock wave energy reaches 67%. The major part of the shock wave energy (92%) is dissipated when the shock front travels the first 250 µm, and the remaining 8% is transferred to the acoustic far field. The calculated pressure in the vicinity of water-silicon interface is 0.9 GPa. Cavitation efficiency is significantly less and reaches up to 5% of the light energy. The results of the current study could be used in laser parameters optimization for micromachining and biological tissue ablation.
Probability density of wave function of excited photoelectron: understanding XANES features
Czech Academy of Sciences Publication Activity Database
Šipr, Ondřej
2001-01-01
Roč. 8, - (2001), s. 232-234 ISSN 0909-0495 R&D Projects: GA ČR GA202/99/0404 Institutional research plan: CEZ:A02/98:Z1-010-914 Keywords : XANES * PED - probability density of wave function Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.519, year: 2001
On the excited state wave functions of Dirac fermions in the random ...
Indian Academy of Sciences (India)
wave functions in FRGP can be written in terms of descendents of the Liouville vertex operator. In the ... that the localization length ξ scales with the energy E as ξ ∼ E−b2/(1+b2)2. , where b is .... Let us write the Hamiltonian of the. FRGP model ...
International Nuclear Information System (INIS)
Cros, Brigitte
1989-01-01
This research thesis reports the study of the non linear evolution of plasma waves excited by mode conversion in a non homogeneous, non collisional, and free-of-external-magnetic-field plasma. Experiments performed in the microwave domain in a plasma created by means of a multi-polar device show that the evolution of plasma waves displays a transition between a non linear quasi-steady regime and a stochastic regime when the power of incident electromagnetic waves or plasma gradient length is increased. These regimes are characterized through a numerical resolution of Zakharov equations which describe the coupled evolution of plasma wave envelope and low frequency density perturbations [fr
High power light gas helicon plasma source for VASIMR
International Nuclear Information System (INIS)
Squire, Jared P.; Chang-Diaz, Franklin R.; Glover, Timothy W.; Jacobson, Verlin T.; McCaskill, Greg E.; Winter, D. Scott; Baity, F. Wally; Carter, Mark D.; Goulding, Richard H.
2006-01-01
In the Advanced Space Propulsion Laboratory (ASPL) helicon experiment (VX-10) we have measured a plasma flux to input gas rate ratio near 100% for both helium and deuterium at power levels up to 10 kW. Recent results at Oak Ridge National Laboratory (ORNL) show enhanced efficiency operation with a high power density, over 5 kW in a 5 cm diameter tube. Our helicon is presently 9 cm in diameter and operates up to 10 kW of input power. The data here uses a Boswell double-saddle antenna design with a magnetic cusp just upstream of the antenna. Similar to ORNL, for deuterium at near 10 kW, we find an enhanced performance of operation at magnetic fields above the lower hybrid matching condition
Excitation and propagation of the fast wave in a two component non uniform plasma
International Nuclear Information System (INIS)
Lapierre, Y.
1980-09-01
The purpose of this study is to compute the coupling of antennas in presence of plasma, and to derive the electric field distribution taking into account inhomogeneity in the magnetic field and in the density. The only calculations which have been down, up to now, were made under two kinds of assumptions: very low damping or very strong radial damping. Our calculation takes into account the mode conversion as it affects wave propagation. This might be of great importance for large machines
Polarization dependence of the spin-density-wave excitations in single-domain chromium
Energy Technology Data Exchange (ETDEWEB)
Boeni, P. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Roessli, B. [Institut Max von Laue - Paul Langevin, 75 - Paris (France); Sternlieb, B.J. [Brookhaven (United States); Lorenzo, E. [Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France); Werner, S.A. [Missouri (United States)
1997-09-01
A polarized neutron scattering experiment has been performed with a single-Q, single domain sample of chromium in a magnetic field of 4 T. It is confirmed that the longitudinal fluctuations are enhanced for small energy transfers and that the spin wave modes with {delta}S parallel to Q and {delta}S perpendicular to Q are similar. (author) 2 figs., 1 tab., 2 refs.
Convective cell excitation by inertial Alfven waves in a low density plasma
International Nuclear Information System (INIS)
Pokhotelov, O.A.; Onishchenko, O.G.; Sagdeev, R.Z.; Srenflo, L.; Balikhin, M.A.
2005-01-01
The parametric interaction of inertial Alfven waves with large-scale convective cells in a low-density plasma is investigated. It is shown that, in plasmas where the Alfven velocity is comparable to or exceeds the speed of light, the parametric interaction is substantially suppressed. A compact expression for the optimal scale and instability growth rate of the fastest growing mode is obtained [ru
Magnetic studies of spin wave excitations in Fe/Mn multilayers
Energy Technology Data Exchange (ETDEWEB)
Salhi, H. [LPMMAT, Faculté des Sciences Ain Chock, Université Hassan II de Casablanca, B.P. 5366 Mâarif, Casablanca (Morocco); LMPG, Ecole supérieure de technologie, Université Hassan de Casablanca, Casablanca (Morocco); Moubah, R.; El Bahoui, A.; Lassri, H. [LPMMAT, Faculté des Sciences Ain Chock, Université Hassan II de Casablanca, B.P. 5366 Mâarif, Casablanca (Morocco)
2017-04-15
The structural and magnetic properties of Fe/Mn multilayers grown by thermal evaporation technique were investigated by transmission electron microscopy, vibrating sample magnetometer and spin wave theory. Transmission electron microscopy shows that the Fe and Mn layers are continuous with a significant interfacial roughness. The magnetic properties of Fe/Mn multilayers were studied for various Fe thicknesses (t{sub Fe}). The change of magnetization as a function of temperature is well depicted by a T{sup 3/2} law. The Fe spin-wave constant was extracted and found to be larger than that reported for bulk Fe, which we attribute to the fluctuation of magnetic moments at the interface, due to the interfacial roughness. The experimental M (T) data were satisfactory fitted for multilayers with different Fe thicknesses; and several exchange interactions were extracted. - Highlights: • The structural and magnetic properties of Fe/Mn multilayers were studied. • Fe and Mn layers are continuous with an important interfacial roughness. • The Fe spin-wave constant is larger than that reported for bulk Fe due to the fluctuation of the interfacial magnetic moments.
Spin correlations and spin-wave excitations in Dirac-Weyl semimetals
Araki, Yasufumi; Nomura, Kentaro
We study correlations among magnetic dopants in three-dimensional Dirac and Weyl semimetals. Effective field theory for localized magnetic moments is derived by integrating out the itinerant electron degrees of freedom. We find that spin correlation in the spatial direction parallel to local magnetization is more rigid than that in the perpendicular direction, reflecting spin-momentum locking nature of the Dirac Hamiltonian. Such an anisotropy becomes stronger for Fermi level close to the Dirac points, due to Van Vleck paramagnetism triggered by spin-orbit coupling. One can expect topologically nontrivial spin textures under this anisotropy, such as a hedgehog around a single point, or a radial vortex around an axis, as well as a uniform ferromagnetic order. We further investigate the characteristics of spin waves in the ferromagnetic state. Spin-wave dispersion also shows a spatial anisotropy, which is less dispersed in the direction transverse to the magnetization than that in the longitudinal direction. The spin-wave dispersion anisotropy can be traced back to the rigidity and flexibility of spin correlations discussed above. This work was supported by Grant-in-Aid for Scientific Research (Grants No.15H05854, No.26107505, and No.26400308) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
Magnetic studies of spin wave excitations in Fe/Mn multilayers
International Nuclear Information System (INIS)
Salhi, H.; Moubah, R.; El Bahoui, A.; Lassri, H.
2017-01-01
The structural and magnetic properties of Fe/Mn multilayers grown by thermal evaporation technique were investigated by transmission electron microscopy, vibrating sample magnetometer and spin wave theory. Transmission electron microscopy shows that the Fe and Mn layers are continuous with a significant interfacial roughness. The magnetic properties of Fe/Mn multilayers were studied for various Fe thicknesses (t Fe ). The change of magnetization as a function of temperature is well depicted by a T 3/2 law. The Fe spin-wave constant was extracted and found to be larger than that reported for bulk Fe, which we attribute to the fluctuation of magnetic moments at the interface, due to the interfacial roughness. The experimental M (T) data were satisfactory fitted for multilayers with different Fe thicknesses; and several exchange interactions were extracted. - Highlights: • The structural and magnetic properties of Fe/Mn multilayers were studied. • Fe and Mn layers are continuous with an important interfacial roughness. • The Fe spin-wave constant is larger than that reported for bulk Fe due to the fluctuation of the interfacial magnetic moments.
Time-domain analytic solutions of two-wire transmission line excited by a plane-wave field
International Nuclear Information System (INIS)
Ni Guyan; Yan Li; Yuan Naichang
2008-01-01
This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum–Liu–Tesche (BLT) equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent. (the physics of elementary particles and fields)
Time-domain analytic Solutions of two-wire transmission line excited by a plane-wave field
Institute of Scientific and Technical Information of China (English)
Ni Gu-Yan; Yan Li; Yuan Nai-Chang
2008-01-01
This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain.By the frequency-domain Baum-Liu-Tesche(BLT)equation,the time-domain analytic solutions are obtained and expressed in an infinite geometric series.Moreover,it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval.In other word.the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval.The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform,and the agreement is excellent.
Excitation of Structures Near Railway Tracks-Analysis of the Wave Propagation Path
DEFF Research Database (Denmark)
Bucinskas, Paulius; Andersen, Lars Vabbersgaard
2017-01-01
High-speed rails are an attractive alternative to other forms of intercity transportation. It is a fast, cost-efficient and environmentally friendly solution, which is being developed in various countries across the world. However, in order to be successful, high-speed rails need to transport...... trains. Unfortunately, the prediction of vibrations in nearby structures is difficult, as wave propagation from the vibration source to the structure is a complex phenomenon. The behaviour of the structure is highly dependent on the path along which the vibrations travel between their source...
Spin-wave excitation and Moessbauer spectrometry of amorphous interface in Tb/Fe multilayer
International Nuclear Information System (INIS)
El Khiraoui, S.; Sajieddine, M.; Lassri, H.; Sahlaoui, M.
2009-01-01
Magnetic properties of Tb(48 A)/Fe(26 A) multilayer were studied with Moessbauer spectrometry at different temperatures before and after isothermal annealing at 673 K. For this last case, a significant perpendicular magnetic anisotropy is induced. This phenomenon is related to the existence of an amorphous and homogenous Tb-Fe alloy, located at the interfaces, which is produced by interdiffusion during the heat processing. The thermal evolution of hyperfine field deduced for interfacial Tb-Fe alloy is found to obey the Bloch law. The spin-wave stiffness constant, the distance between nearest magnetic atoms and the exchange parameter A were calculated from the experimental results
Localized excitations in a nonlinearly coupled magnetic drift wave-zonal flow system
International Nuclear Information System (INIS)
Shukla, Nitin; Shukla, P.K.
2010-01-01
We consider the amplitude modulation of the magnetic drift wave (MDW) by zonal flows (ZFs) in a nonuniform magnetoplasma. For this purpose, we use the two-fluid model to derive a nonlinear Schroedinger equation for the amplitude modulated MDWs in the presence of the ZF potential, and an evolution equation for the ZF potential which is reinforced by the nonlinear Lorentz force of the MDWs. Our nonlinearly coupled MDW-ZFs system of equations admits stationary solutions in the form of a localized MDW envelope and a shock-like ZF potential profile.
Bhatti, Abdul Qadir
2017-12-01
To demonstrate the characteristics of the nonlinear response of steel frames, an elastic dynamic response analysis of the semi-rigid frame is performed under the harmonic wave. The semi-rigid contact is represented by the alternating spring which is given stiffness by a three-parameter energy model which approaches the hysterical curve by hardening model. The properties of spectra and hysteric curves are presented. This study shows that (1) the greater the acceleration input capacitance the smaller the instant connection capability and the smaller is the response. (2) However, by allowing an extreme increase in capacitance input acceleration, response spectra can be increased as the contact stiffness results near zero.
Hama, Noriyuki; Kawai, Minako; Ito, Shin-Ichi; Hirota, Akihiko
2018-02-14
Multisite optical recording has revealed that the neural excitation wave induced by a sensory stimulation begins at a focus and propagates on the cortex. This wave is considered to be important for computation in the sensory cortex, particularly the integration of sensory information; however, the nature of this wave remains largely unknown. In the present study, we examined the interaction between two waves in the rat sensory cortex induced by hindlimb and forelimb stimuli with different inter-stimulus intervals. We classified the resultant patterns as follows: 1) the collision of two waves; 2) the hindlimb response being evoked while the forelimb-induced wave is passing the hindlimb focus; and 3) the hindlimb response being evoked after the forelimb-induced wave has passed the hindlimb focus. In pattern 1, the two waves fused into a single wave, but the propagation pattern differed from that predicted by the superimposition of two solely induced propagation courses. In pattern 2, the state of the interaction between the two waves varied depending on the phase of optical signals constituting the forelimb-induced wave around the hindlimb focus. Although no hindlimb-induced wave was observed in the rising phase, the propagating velocity of the forelimb-induced wave increased. At the peak, neither the hindlimb-induced response nor a modulatory effect on the forelimb-induced wave was detected. In pattern 3, the hindlimb-induced wave showed a reduced amplitude and spatial extent. These results indicate that the state of the interaction between waves was strongly influenced by the relative timing of sensory inputs.
Ji, Hongli; Luo, Jing; Qiu, Jinhao; Cheng, Li
2018-05-01
Acoustic Black Holes (ABHs), as a new type of passive structure for vibration damping enhancement and noise attenuation, have been drawing increasing attentions of many researchers. Due to the difficulty in manufacturing the sharp edges required by the ABH structures, it is important to understand the wave propagation and attenuation process in the presence of damping layers in non-ideal ABHs with a truncated edge. In this paper, an analytical expression of the wave reflection coefficient in a modified one-dimensional ABH is derived and a time-domain experimental method based on a laser excitation technique is used to visualize the wave propagation. In the experimental studies, the flexural waves in the ABH were excited by a scanning pulse laser and measured by a Laser Doppler Vibrometer (LDV). The incident wave and reflected wave were separated from the measured original wave field and the decrease of the wave velocity in the ABH was exhibited. The reflection coefficient was calculated from the ratio of the amplitude of the reflected wave to that of the incident wave for different ABH parameters and different thicknesses of the damping layer. The measured reflection coefficients were used to identify the unknown coefficients in the theoretical formula. The results confirm that there exists an optimal thickness for the damping layer, which leads to the minimum wave reflection. Based on the laser-induced visualization technique and various signal processing and feature extraction methods, the entire process of the wave propagation in a non-ideal one-dimensional ABH structure can be visualized and scrutinized.
Theory and Observations of Plasma Waves Excited Space Shuttle OMS Burns in the Ionosphere
Bernhardt, P. A.; Pfaff, R. F.; Schuck, P. W.; Hunton, D. E.; Hairston, M. R.
2010-12-01
Measurements of artificial plasma turbulence were obtained during two Shuttle Exhaust Ionospheric Turbulence Experiments (SEITE) conducted during the flights of the Space Shuttle (STS-127 and STS-129). Based on computer modeling at the NRL PPD and Laboratory for Computational Physics & Fluid Dynamics (LCP), two dedicated burns of the Space Shuttle Orbital Maneuver Subsystem (OMS) engines were scheduled to produce 200 to 240 kg exhaust clouds that passed over the Air Force Research Laboratory (AFRL) Communications, Navigation, and Outage Forecast System (C/NOFS) satellite. This operation required the coordination by the DoD Space Test Program (STP), the NASA Flight Dynamics Officer (FDO), the C/NOFS payload operations, and the C/NOFS instrument principal investigators. The first SEITE mission used exhaust from a 12 Second OMS burn to deposit 1 Giga-Joules of energy into the upper atmosphere at a range of 230 km from C/NOFS. The burn was timed so C/NOFS could fly though the center of the exhaust cloud at a range of 87 km above the orbit of the Space Shuttle. The first SEITE experiment is important because is provided plume detection by ionospheric plasma and electric field probes for direct sampling of irregularities that can scatter radar signals. Three types of waves were detected by C/NOFS during and after the first SEITE burn. With the ignition and termination of the pair of OMS engines, whistler mode signals were recorded at C/NOFS. Six seconds after ignition, a large amplitude electromagnetic pulse reached the satellite. This has been identified as a fast magnetosonic wave propagating across magnetic field lines to reach the electric field (VEFI) sensors on the satellite. Thirty seconds after the burn, the exhaust cloud reach C/NOFS and engulfed the satellite providing very strong electric field turbulence along with enhancements in electron and ion densities. Kinetic modeling has been used to track the electric field turbulence to an unstable velocity
Probing a dusty magnetized plasma with self-excited dust-density waves
Tadsen, Benjamin; Greiner, Franko; Piel, Alexander
2018-03-01
A cloud of nanodust particles is created in a reactive argon-acetylene plasma. It is then transformed into a dusty magnetized argon plasma. Plasma parameters are obtained with the dust-density wave diagnostic introduced by Tadsen et al. [Phys. Plasmas 22, 113701 (2015), 10.1063/1.4934927]. A change from an open to a cylindrically enclosed nanodust cloud, which was observed earlier, can now be explained by a stronger electric confinement if a vertical magnetic field is present. Using two-dimensional extinction measurements and the inverse Abel transform to determine the dust density, a redistribution of the dust with increasing magnetic induction is found. The dust-density profile changes from being peaked around the central void to being peaked at an outer torus ring resulting in a hollow profile. As the plasma parameters cannot explain this behavior, we propose a rotation of the nanodust cloud in the magnetized plasma as the origin of the modified profile.
Magnetic studies of spin wave excitations in Ni/Au multilayers
International Nuclear Information System (INIS)
Salhi, H.; Chafai, K.; Benkirane, K.; Lassri, H.; Abid, M.; Hlil, E.K.
2010-01-01
Ni/Au multilayers were prepared by the electron beam evaporation method under ultra high vacuum conditions. The multilayer films have a coherent structure with (1 1 1) texture. The magnetic properties of Ni/Au multilayers are examined as a function of Ni layer thickness t Ni . The temperature dependence of the spontaneous magnetization M(T) is well described by a T 3/2 law in all multilayers. A spin wave theory has been used to explain the magnetization versus temperature. Based on this theory, the approximate values for the bulk exchange interaction J b , surface exchange interaction J S and the interlayer coupling strength J I have been obtained for various Ni layer thicknesses.
New method for measuring time-resolved spectra of lanthanide emission using square-wave excitation
International Nuclear Information System (INIS)
Qin, Feng; Zhao, Hua; Cai, Wei; Duan, Qianqian; Zhang, Zhiguo; Cao, Wenwu
2013-01-01
A method using modulated continuous wave (CW) visible laser to measure time-resolved fluorescence spectra of trivalent rare-earth ions has been developed. Electro-optic modulator was used to modulate the CW pumping laser with a rise time of 2 μs. CW Nd 3+ lasers were used as examples to present the method. Upconversion dynamic process of Ho 3+ was studied utilizing a 532 nm CW laser. Quantum cutting dynamic process from Tb 3+ to Yb 3+ was analyzed by a 473 nm CW laser. This method can be applied to any CW laser such as He-Ne laser, Ar + laser, Kr + laser, Ti:sapphire laser, etc
Magnetized Langmuir wave packets excited by a strong beam-plasma interaction
International Nuclear Information System (INIS)
Pelletier, G.; Sol, H.; Asseo, E.
1988-01-01
The physics of beam-plasma interaction, which has been investigated for a long time mostly in relation with solar bursts, is now more widely invoked in various astrophysical contexts such as pulsars, active galactic nuclei, close binaries, cataclysmic variables, γ bursters, and so on. In these situations the interaction is more likely in the spirit of strong Langmuir turbulence rather than in the spirit of quasilinear theory. Many investigations have been done for two opposite extremes, namely, in very weak and in very strong magnetic fields. Very few properties of the strong Langmuir turbulence are known in the most usual astrophysical situation where the magnetic field plays a significant role but is not strong enough to force the electrons into one-dimensional motion. For this case, we analyze the dynamics of Langmuir wave packets and provide new results about the stability of the solitons against transverse perturbations. It turns out that both the averaged Lagrangian method and the adiabatic perturbation method derived from the inverse scattering transform give exactly the same results (which is not obvious in soliton perturbation theory). In particular, they predict the stability of the solitons as long as the electron gyrofrequency is greater than the plasma frequency (strong magnetic field) and their instability against transverse self-modulation in the opposite case (weak magnetic field); moreover, they allow one to deduce the self-similar collapsing oblate cavitons in the latter case. The laws governing the collapse of the wave packets determine the relaxation of the beam in the surrounding medium and we derive a useful formula giving the power loss of the beam. We outline the astrophysical consequences of this investigation
Balasis, G.; Daglis, I. A.; Mann, I. R.; Papadimitriou, C.; Zesta, E.; Georgiou, M.; Haagmans, R.; Tsinganos, K.
2015-10-01
We use multi-satellite and ground-based magnetic data to investigate the concurrent characteristics of Pc3 (22-100 mHz) and Pc4-5 (1-22 mHz) ultra-low-frequency (ULF) waves on the 31 October 2003 during the Halloween magnetic superstorm. ULF waves are seen in the Earth's magnetosphere, topside ionosphere, and Earth's surface, enabling an examination of their propagation characteristics. We employ a time-frequency analysis technique and examine data from when the Cluster and CHAMP spacecraft were in good local time (LT) conjunction near the dayside noon-midnight meridian. We find clear evidence of the excitation of both Pc3 and Pc4-5 waves, but more significantly we find a clear separation in the L shell of occurrence of the Pc4-5 and Pc3 waves in the equatorial inner magnetosphere, separated by the density gradients at the plasmapause boundary layer. A key finding of the wavelet spectral analysis of data collected from the Geotail, Cluster, and CHAMP spacecraft and the CARISMA and GIMA magnetometer networks was a remarkably clear transition of the waves' frequency into dominance in a higher-frequency regime within the Pc3 range. Analysis of the local field line resonance frequency suggests that the separation of the Pc4-5 and Pc3 emissions across the plasmapause is consistent with the structure of the inhomogeneous field line resonance Alfvén continuum. The Pc4-5 waves are consistent with direct excitation by the solar wind in the plasma trough, as well as Pc3 wave absorption in the plasmasphere following excitation by upstream waves originating at the bow shock in the local noon sector. However, despite good solar wind coverage, our study was not able to unambiguously identify a clear explanation for the sharp universal time (UT) onset of the discrete frequency and large-amplitude Pc3 wave power.
Directory of Open Access Journals (Sweden)
G. Balasis
2015-10-01
Full Text Available We use multi-satellite and ground-based magnetic data to investigate the concurrent characteristics of Pc3 (22–100 mHz and Pc4-5 (1–22 mHz ultra-low-frequency (ULF waves on the 31 October 2003 during the Halloween magnetic superstorm. ULF waves are seen in the Earth's magnetosphere, topside ionosphere, and Earth's surface, enabling an examination of their propagation characteristics. We employ a time–frequency analysis technique and examine data from when the Cluster and CHAMP spacecraft were in good local time (LT conjunction near the dayside noon–midnight meridian. We find clear evidence of the excitation of both Pc3 and Pc4-5 waves, but more significantly we find a clear separation in the L shell of occurrence of the Pc4-5 and Pc3 waves in the equatorial inner magnetosphere, separated by the density gradients at the plasmapause boundary layer. A key finding of the wavelet spectral analysis of data collected from the Geotail, Cluster, and CHAMP spacecraft and the CARISMA and GIMA magnetometer networks was a remarkably clear transition of the waves' frequency into dominance in a higher-frequency regime within the Pc3 range. Analysis of the local field line resonance frequency suggests that the separation of the Pc4-5 and Pc3 emissions across the plasmapause is consistent with the structure of the inhomogeneous field line resonance Alfvén continuum. The Pc4-5 waves are consistent with direct excitation by the solar wind in the plasma trough, as well as Pc3 wave absorption in the plasmasphere following excitation by upstream waves originating at the bow shock in the local noon sector. However, despite good solar wind coverage, our study was not able to unambiguously identify a clear explanation for the sharp universal time (UT onset of the discrete frequency and large-amplitude Pc3 wave power.
Directory of Open Access Journals (Sweden)
M.R. Mofakhami
2008-01-01
Full Text Available In this paper sound transmission through the multilayered viscoelastic air filled cylinders subjected to the incident acoustic wave is studied using the technique of separation of variables on the basis of linear three dimensional theory of elasticity. The effect of interior acoustic medium on the mode maps (frequency vs geometry and noise reduction is investigated. The effects of internal absorption and external moving medium on noise reduction are also evaluated. The dynamic viscoelastic properties of the structure are rigorously taken into account with a power law technique that models the viscoelastic damping of the cylinder. A parametric study is also performed for the two layered infinite cylinders to obtain the effect of viscoelastic layer characteristics such as thickness, material type and frequency dependency of viscoelastic properties on the noise reduction. It is shown that using constant and frequency dependent viscoelastic material with high loss factor leads to the uniform noise reduction in the frequency domain. It is also shown that the noise reduction obtained for constant viscoelastic material property is subjected to some errors in the low frequency range with respect to those obtained for the frequency dependent viscoelastic material.
Stochastic flow modeling : Quasi-Geostrophy, Taylor state and torsional wave excitation
DEFF Research Database (Denmark)
Gillet, Nicolas; Jault, D.; Finlay, Chris
We reconstruct the core flow evolution over the period 1840-2010 under the quasi-geostrophic assumption, from the stochastic magnetic field model COV-OBS and its full model error covariance matrix. We make use of a prior information on the flow temporal power spectrum compatible with that of obse......We reconstruct the core flow evolution over the period 1840-2010 under the quasi-geostrophic assumption, from the stochastic magnetic field model COV-OBS and its full model error covariance matrix. We make use of a prior information on the flow temporal power spectrum compatible....... Large length-scales flow features are naturally dominated by their equatorially symmetric component from about 1900 when the symmetry constraint is relaxed. Equipartition of the kinetic energy in both symmetries coincides with the poor prediction of decadal length-of-day changes in the XIXth century. We...... interpret this as an evidence for quasi-geostrophic rapid flow changes, and the consequence of a too loose data constraint during the oldest period. We manage to retrieve rapid flow changes over the past 60 yrs, and in particular modulated torsional waves predicting correctly interannual length-of day...
Spin-Wave Excitations Evidencing the Kitaev Interaction in Single Crystalline α -RuCl3
Ran, Kejing; Wang, Jinghui; Wang, Wei; Dong, Zhao-Yang; Ren, Xiao; Bao, Song; Li, Shichao; Ma, Zhen; Gan, Yuan; Zhang, Youtian; Park, J. T.; Deng, Guochu; Danilkin, S.; Yu, Shun-Li; Li, Jian-Xin; Wen, Jinsheng
2017-03-01
Kitaev interactions underlying a quantum spin liquid have long been sought, but experimental data from which their strengths can be determined directly, are still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α -RuCl3 , we observe spin-wave spectra with a gap of ˜2 meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principles calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagnetic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term. Our experimental data can be well fit using an effective-spin model with K =-6.8 meV and Γ =9.5 meV . These results demonstrate explicitly that Kitaev physics is realized in real materials.
Directory of Open Access Journals (Sweden)
M. Ali Asgarian
2018-04-01
Full Text Available Electron Bernstein waves (EBW consist of promising tools in driving localized off-axis current needed for sustained operation as well as effective selective heating scenarios in advanced over dense fusion plasmas like spherical tori and stellarators by applying high power radio frequency waves within the range of Megawatts. Here some serious non-linear effects like parametric decay modes are highly expect-able which have been extensively studied theoretically and experimentally. In general, the decay of an EBW depends on the ratio of the incident frequency and electron cyclotron frequency. At ratios less than two, parametric decay leads to a lower hybrid wave (or an ion Bernstein wave and EBWs at a lower frequency. For ratios more than two, the daughter waves constitute either an electron cyclotron quasi-mode and another EBW or an ion wave and EBW. However, in contrast with these decay patterns, the excitation of an unusual up-shifted frequency decay channel for the ratio less than two is demonstrated in this study which is totally different as to its generation and persistence. It is shown that this mode varies from the conventional parametric decay channels which necessarily satisfy the matching conditions in frequency and wave-vector. Moreover, the excitation of some less-known local non-propagating quasi-modes (virtual modes through weak-turbulence theory and their contributions to energy leakage from conversion process leading the reduction in conversion efficiency is assessed.
Ali Asgarian, M.; Abbasi, M.
2018-04-01
Electron Bernstein waves (EBW) consist of promising tools in driving localized off-axis current needed for sustained operation as well as effective selective heating scenarios in advanced over dense fusion plasmas like spherical tori and stellarators by applying high power radio frequency waves within the range of Megawatts. Here some serious non-linear effects like parametric decay modes are highly expect-able which have been extensively studied theoretically and experimentally. In general, the decay of an EBW depends on the ratio of the incident frequency and electron cyclotron frequency. At ratios less than two, parametric decay leads to a lower hybrid wave (or an ion Bernstein wave) and EBWs at a lower frequency. For ratios more than two, the daughter waves constitute either an electron cyclotron quasi-mode and another EBW or an ion wave and EBW. However, in contrast with these decay patterns, the excitation of an unusual up-shifted frequency decay channel for the ratio less than two is demonstrated in this study which is totally different as to its generation and persistence. It is shown that this mode varies from the conventional parametric decay channels which necessarily satisfy the matching conditions in frequency and wave-vector. Moreover, the excitation of some less-known local non-propagating quasi-modes (virtual modes) through weak-turbulence theory and their contributions to energy leakage from conversion process leading the reduction in conversion efficiency is assessed.
Jing, Qingli; Bello, Roger Y.; Martín, Fernando; Palacios, Alicia; Madsen, Lars Bojer
2018-04-01
Recent research interests have been raised in uncovering and controlling ultrafast dynamics in excited neutral molecules. In this work we generalize the Monte Carlo wave packet (MCWP) approach to XUV-pump-IR-probe schemes to simulate the process of dissociative double ionization of H2 where singly excited states in H2 are involved. The XUV pulse is chosen to resonantly excite the initial ground state of H2 to the lowest excited electronic state of 1Σu + symmetry in H2 within the Franck-Condon region. The delayed intense IR pulse couples the excited states of 1Σu + symmetry with the nearby excited states of 1Σg + symmetry. It also induces the first ionization from H2 to H2 + and the second ionization from H2 + to H++H+. To reduce the computational costs in the MCWP approach, a sampling method is proposed to determine in time the dominant ionization events from H2 to H2+. By conducting a trajectory analysis, which is a unique possibility within the MCWP approach, the origins of the characteristic features in the nuclear kinetic energy release spectra are identified for delays ranging from 0 to 140 fs and the nuclear dynamics in the singly excited states in H2 is mapped out.
Mruczkiewicz, M.; Gruszecki, P.; Krawczyk, M.; Guslienko, K. Y.
2018-02-01
We study azimuthal spin-wave (SW) excitations in a circular ferromagnetic nanodot in different inhomogeneous, topologically nontrivial magnetization states, specifically, vortex, Bloch-type skyrmion, and Néel-type skyrmion states. A continuous transition between these states is realized by gradually changing the out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange interaction (DMI), and the corresponding SW spectra are calculated for each state. We observe the lifting of degeneracy of SW mode frequencies and a change in the systematics of frequency levels. The latter effect is induced by the geometric Berry phase, which occurs in SWs localized at the edge of the dot in the vortex state, and vanishes in the skyrmion states. Furthermore, channeling of edge-localized azimuthal SWs and a related large frequency splitting are observed in the skyrmion states. This is attributed to DMI-induced nonreciprocity, while the coupling of the breathing and gyrotropic modes is related to the skyrmion motion. Finally, we demonstrate efficient coupling of the dynamic magnetization to a uniform magnetic field in nanodots of noncircular symmetry in the skyrmion states.
Energy Technology Data Exchange (ETDEWEB)
Ellison, James A.; Heinemann, Klaus [New Mexico Univ., Albuquerque, NM (United States). Dept. of Mathematics and Statistics; Vogt, Mathias [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany); Gooden, Matthew [North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics
2013-03-15
We present a mathematical analysis of planar motion of energetic electrons moving through a planar dipole undulator, excited by a fixed planar polarized plane wave Maxwell field in the X-Ray FEL regime. Our starting point is the 6D Lorentz system, which allows planar motions, and we examine this dynamical system as the wave length {lambda} of the traveling wave varies. By scalings and transformations the 6D system is reduced, without approximation, to a 2D system in a form for a rigorous asymptotic analysis using the Method of Averaging (MoA), a long time perturbation theory. The two dependent variables are a scaled energy deviation and a generalization of the so- called ponderomotive phase. As {lambda} varies the system passes through resonant and nonresonant (NR) zones and we develop NR and near-to-resonant (NtoR) MoA normal form approximations. The NtoR normal forms contain a parameter which measures the distance from a resonance. For a special initial condition, for the planar motion and on resonance, the NtoR normal form reduces to the well known FEL pendulum system. We then state and prove NR and NtoR first-order averaging theorems which give explicit error bounds for the normal form approximations. We prove the theorems in great detail, giving the interested reader a tutorial on mathematically rigorous perturbation theory in a context where the proofs are easily understood. The proofs are novel in that they do not use a near identity transformation and they use a system of differential inequalities. The NR case is an example of quasiperiodic averaging where the small divisor problem enters in the simplest possible way. To our knowledge the planar prob- lem has not been analyzed with the generality we aspire to here nor has the standard FEL pendulum system been derived with associated error bounds as we do here. We briefly discuss the low gain theory in light of our NtoR normal form. Our mathematical treatment of the noncollective FEL beam dynamics problem in
International Nuclear Information System (INIS)
Ellison, James A.; Heinemann, Klaus; Gooden, Matthew
2013-03-01
We present a mathematical analysis of planar motion of energetic electrons moving through a planar dipole undulator, excited by a fixed planar polarized plane wave Maxwell field in the X-Ray FEL regime. Our starting point is the 6D Lorentz system, which allows planar motions, and we examine this dynamical system as the wave length λ of the traveling wave varies. By scalings and transformations the 6D system is reduced, without approximation, to a 2D system in a form for a rigorous asymptotic analysis using the Method of Averaging (MoA), a long time perturbation theory. The two dependent variables are a scaled energy deviation and a generalization of the so- called ponderomotive phase. As λ varies the system passes through resonant and nonresonant (NR) zones and we develop NR and near-to-resonant (NtoR) MoA normal form approximations. The NtoR normal forms contain a parameter which measures the distance from a resonance. For a special initial condition, for the planar motion and on resonance, the NtoR normal form reduces to the well known FEL pendulum system. We then state and prove NR and NtoR first-order averaging theorems which give explicit error bounds for the normal form approximations. We prove the theorems in great detail, giving the interested reader a tutorial on mathematically rigorous perturbation theory in a context where the proofs are easily understood. The proofs are novel in that they do not use a near identity transformation and they use a system of differential inequalities. The NR case is an example of quasiperiodic averaging where the small divisor problem enters in the simplest possible way. To our knowledge the planar prob- lem has not been analyzed with the generality we aspire to here nor has the standard FEL pendulum system been derived with associated error bounds as we do here. We briefly discuss the low gain theory in light of our NtoR normal form. Our mathematical treatment of the noncollective FEL beam dynamics problem in the
Energy Technology Data Exchange (ETDEWEB)
Cho, H.; Takemoto, M. [Aoyama Gakuin University, Tokyo (Japan). College of Science and Engineering
1994-07-20
A bulk wave is generated when a pulse laser is irradiated to the material, and the characteristics of a Young`s modulus and Poisson`s ratio can be nondestructively estimated from the bulk wave. The generation mechanism of laser ultrasonic waves must be first clarified for such application. In this paper, fundamental research was conducted to study the generation mechanism of the elastic waves excited by a Q-switched Nd-YAG laser, and the generation method and characteristics of Rayleigh waves. The following result was obtained. A bulk wave is generated by the disk-like adiabatic expansion near the surface if the laser power is small when a spot-shape pulse laser was irradiated. A bulk wave is generated by the thin disk-like adiabatic expansion beneath the surface due to the thermal diffusion in the depth direction of a base material when the laser power becomes large. Moreover, a bulk wave is generated by the impact force due to abrasion and plasma when the power becomes still larger. The information on the bulk wave characteristics and Rayleigh wave was also obtained. 25 refs., 15 figs., 1 tab.
Sandri, Eva; Davies, Richard; Azzari, Phil; Frank, John; Frank, Jackson; James, Royce; Hopson, Jordon; Duke-Tinson, Omar; Paolino, Richard; Sherman, Justin; Wright, Erin; Turk, Jeremy
2016-10-01
Now that reproducible plasmas have been created on the Helicon Plasma Experiment (HPX) at the Coast Guard Academy Plasma Laboratory (CGAPL), a high-performance spectrometer utilizing volume-phase-holographic (VPH) grating and a charge coupled device (CCD) camera with a range of 380-1090 nm and resolution of 1024x1024 is being assembled. This spectrometer will collect doppler shifted photons created by exciting the plasma with the first harmonic of a 2.5 J Nd:YAG laser at a wavelength of 1064 nm. Direct measurements of the plasma's temperature and density will be determined using HPX's Thomson Scattering (TS) system as a single spatial point diagnostic. TS has the capability of determining plasma properties on short time scales and will be used to create a robust picture of the internal plasma parameters. A prototype spectrometer has been constructed to explore the Andor CCD camera's resolution and sensitivity. Concurrently, through intensive study of the high energy TS system, safety protocols and standard operation procedures (SOP) for the Coast Guard's largest and most powerful Laser have been developed. The current status of the TS SOP, diagnostic development, and the collection optic's spectrometer will be reported. Supported by U.S. DEPS Grant [HEL-JTO] PRWJFY15-16.
Operation of the ORNL High Particle Flux Helicon Plasma Source
International Nuclear Information System (INIS)
Goulding, Richard Howell; Biewer, Theodore M.; Caughman, John B.; Chen, Guangye; Owen, Larry W.; Sparks, Dennis O.
2011-01-01
A high power, high particle flux rf-based helicon plasma source has been constructed at ORNL and operated at power levels up to 30 kW. High-density hydrogen and helium plasmas have been produced. The source has been designed as the basis for a linear plasma materials interaction (PMI) test facility that will generate particle fluxes Gamma(p) > 10(23) M-3 s(-1), and utilize additional ion and electron cyclotron heating to produce high parallel (to the magnetic field) heat fluxes of similar to 10 MW/m(2). An rf-based source for PMI research is of interest because high plasma densities are generated with no internal electrodes, allowing true steady state operation with minimal impurity generation. The ORNL helicon source has a diameter of 15 cm and to-date has operated at a frequency f = 13.56 MHz, with magnetic field strength vertical bar B vertical bar in the antenna region up to similar to 0.15 T. Maximum densities of 3 x 10(19) M-3 in He and 2.5 x 10(19) m(-3) in H have been achieved. Radial density profiles have been seen to be dependent on the axial vertical bar B vertical bar profile.
Operation of the ORNL High Particle Flux Helicon Plasma Source
International Nuclear Information System (INIS)
Goulding, R. H.; Biewer, T. M.; Caughman, J. B. O.; Chen, G. C.; Owen, L. W.; Sparks, D. O.
2011-01-01
A high power, high particle flux rf-based helicon plasma source has been constructed at ORNL and operated at power levels up to 30 kW. High-density hydrogen and helium plasmas have been produced. The source has been designed as the basis for a linear plasma materials interaction (PMI) test facility that will generate particle fluxes Γ p 10 23 m -3 s -1 , and utilize additional ion and electron cyclotron heating to produce high parallel (to the magnetic field) heat fluxes of ∼10 MW/m 2 . An rf-based source for PMI research is of interest because high plasma densities are generated with no internal electrodes, allowing true steady state operation with minimal impurity generation. The ORNL helicon source has a diameter of 15 cm and to-date has operated at a frequency f = 13.56 MHz, with magnetic field strength |B| in the antenna region up to ∼0.15 T. Maximum densities of 3x10 19 m -3 in He and 2.5x10 19 m -3 in H have been achieved. Radial density profiles have been seen to be dependent on the axial |B| profile.
Facility Effects on a Helicon Plasma Source with a Magnetic Nozzle
National Aeronautics and Space Administration — Proposed here is an analysis of facility effects on a small helicon plasma source with a magnetic nozzle. Backpressure effects will first be recorded and analyzed....
Characteristics of a High Current Helicon Ion Source With High Monatomic Fraction
International Nuclear Information System (INIS)
Jung, Hwa-Dong; Chung, Kyoung-Jae; Hwang, Yong-Seok
2006-01-01
Applications of neutron need compact and high yield neutron sources as well as very intense neutron sources from giant devices such as accelerators. Ion source based neutron sources using nuclear fusion reactions such as D(d, 3He)n, D(t, 4He)n can meet the requirements. This type of neutron generators can be simply composed of an ion source and a target. High-performance neutron generators with high yield require ion sources with high beam current, high monatomic fraction and long lifetime. Helicon ion source can meet these requirements. To make high current ion source, characteristics of helicon plasma such as high plasma density can be utilized. Moreover, efficient plasma heating with RF power lead high fraction of monatomic ion beam. Here, Characteristics of helicon plasma sources are described. Design and its performances of a helicon ion source are presented
Hutter, Jürg
2003-03-01
An efficient formulation of time-dependent linear response density functional theory for the use within the plane wave basis set framework is presented. The method avoids the transformation of the Kohn-Sham matrix into the canonical basis and references virtual orbitals only through a projection operator. Using a Lagrangian formulation nuclear derivatives of excited state energies within the Tamm-Dancoff approximation are derived. The algorithms were implemented into a pseudo potential/plane wave code and applied to the calculation of adiabatic excitation energies, optimized geometries and vibrational frequencies of three low lying states of formaldehyde. An overall good agreement with other time-dependent density functional calculations, multireference configuration interaction calculations and experimental data was found.
Bauschlicher, C. W., Jr.; Yarkony, D. R.
1980-01-01
A previously reported multi-configuration self-consistent field (MCSCF) algorithm based on the generalized Brillouin theorem is extended in order to treat the excited states of polar molecules. In particular, the algorithm takes into account the proper treatment of nonorthogonality in the space of single excitations and invokes, when necessary, a constrained optimization procedure to prevent the variational collapse of excited states. In addition, a configuration selection scheme (suitable for use in conjunction with extended configuration interaction methods) is proposed for the MCSCF procedure. The algorithm is used to study the low-lying singlet states of BeO, a system which has not previously been studied using an MCSCF procedure. MCSCF wave functions are obtained for three 1 Sigma + and two 1 Pi states. The 1 Sigma + results are juxtaposed with comparable results for MgO in order to assess the generality of the description presented here.
International Nuclear Information System (INIS)
Ganic, D.; Day, D.; Gu, M.
1999-01-01
Full text: Two-photon excitation has been employed in three-dimensional optical data storage by many researchers in an attempt to increase the storage density of a given material. The probability of two-photon excitation is proportional to the squared intensity of the incident light; this effect produces excitation only within a small region of the focus spot. Another advantage of two-photon excitation is the use of infrared illumination, which results in the reduction of scattering and enables the recording of layers at a deep depth in a thick material. The storage density thus obtained using multi-layered bit optical recording can be as high as Tbit/cm 3 . To increase this storage density even further, grey level recording can be employed. This method utilises variable exposure times of a laser beam focused into a photobleaching sample. As a result, the bleached area possesses a certain pixel value which depends upon the exposure time; this can increase the storage density many times depending upon the number of grey levels used. Our experiment shows that it is possible to attain grey level recording using both ultrashort pulsed and continuous-wave illumination. Although continuous wave illumination requires an average power of approximately 2 orders of magnitude higher than that for ultrashort pulsed illumination, it is a preferred method of recording due to its relatively low system cost and compactness. Copyright (1999) Australian Optical Society
Energy Technology Data Exchange (ETDEWEB)
Rolland, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1969-05-01
The character, stable or unstable, of a medium can be deduced from the behavior of an ideal model of a semi-infinite medium which is subjected to an excitation only at the boundary. A new analytic method is used to solve this problem. The results obtained show a connection between the character of the medium and certain properties of the dispersion equation, and agree with those derived from other methods. Then, the energy exchange between a medium and a source of excitation is investigated. In order to include the case of growing waves associated with convective instabilities, this problem is treated in the context of the wave packet theory. We find that - even in the absence of collisions - there still is a power exchange. Thus a connexion can be established with the kinematic theories of growing waves and the modes generating power can be found. Moreover, the power absorbed by spatial dispersion is found to be identical with that due to Landau's effect for long waves. This confirms the kinematic character of the latter and bridges a gap between macroscopic and microscopic theories. (author) [French] Le caractere, stable ou instable, d'un milieu peut etre deduit du comportement d'un milieu semi-indefini soumis a une excitation a la frontiere. Une nouvelle methode analytique est developpee pour resoudre ce probleme. Les resultats obtenus montrent une connexion entre le comportement du milieu et certaines proprietes de l'equation de dispersion, et generalisent les resultats obtenus par d'autres methodes. On etudie ensuite les echanges d'energie entre un milieu et une source d'excitation. Pour inclure le cas des ondes croissantes associees aux instabilites convectives, on traite ce probleme dans le cadre de la theorie du paquet d'ondes. On trouve que meme en l'absence de collisions, la puissance echangee n'est pas nulle. Ceci permet d'etablir une connexion avec les theories cinematiques des ondes croissantes, tout en precisant quels sont les modes generateurs d
Stefan, V. Alexander; IAPS-team Team
2017-10-01
The novel study of the laser excitation-suppression of the brain waves is proposed. It is based on the pulsed-operated multi-photon fiber-laser interaction with the brain parvalbumin (PV) neurons. The repetition frequency matches the low frequency brain waves (5-100 Hz); enabling the resonance-scanning of the wide range of the PV neurons (the generators of the brain wave activity). The tunable fiber laser frequencies are in the ultraviolet frequency range, thus enabling the monitoring of the PV neuron-DNA, within the 10s of milliseconds. In medicine, the method can be used as an ``instantaneous-on-off anesthetic.'' Supported by Nikola Tesla Labs, Stefan University.
Directory of Open Access Journals (Sweden)
Shao Yan-Lin
2014-12-01
Full Text Available This paper presents some of the efforts by the authors towards numerical prediction of springing of ships. A time-domain Higher Order Boundary Element Method (HOBEM based on cubic shape function is first presented to solve a complete second-order problem in terms of wave steepness and ship motions in a consistent manner. In order to avoid high order derivatives on the body surfaces, e.g. mj-terms, a new formulation of the Boundary Value Problem in a body-fixed coordinate system has been proposed instead of traditional formulation in inertial coordinate system. The local steady flow effects on the unsteady waves are taken into account. Double-body flow is used as the basis flow which is an appropriate approximation for ships with moderate forward speed. This numerical model was used to estimate the complete second order wave excitation of springing of a displacement ship at constant forward speeds.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yijing, E-mail: yzhng123@illinois.edu; Moore, Keegan J.; Vakakis, Alexander F. [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); McFarland, D. Michael [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
2015-12-21
We study passive pulse redirection and nonlinear targeted energy transfer in a granular network composed of two semi-infinite, ordered homogeneous granular chains mounted on linear elastic foundations and coupled by weak linear stiffnesses. Periodic excitation in the form of repetitive half-sine pulses is applied to one of the chains, designated as the “excited chain,” whereas the other chain is initially at rest and is regarded as the “absorbing chain.” We show that passive pulse redirection and targeted energy transfer from the excited to the absorbing chain can be achieved by macro-scale realization of the spatial analog of the Landau-Zener quantum tunneling effect. This is realized by finite stratification of the elastic foundation of the excited chain and depends on the system parameters (e.g., the percentage of stratification) and on the parameters of the periodic excitation. Utilizing empirical mode decomposition and numerical Hilbert transforms, we detect the existence of two distinct nonlinear phenomena in the periodically forced network; namely, (i) energy localization in the absorbing chain due to sustained 1:1 resonance capture leading to irreversible pulse redirection from the excited chain, and (ii) continuous energy exchanges in the form of nonlinear beats between the two chains in the absence of resonance capture. Our results extend previous findings of transient passive energy redirection in impulsively excited granular networks and demonstrate that steady state passive pulse redirection in these networks can be robustly achieved under periodic excitation.
International Nuclear Information System (INIS)
Soh, Wee Tee; Ong, C. K.; Peng, Bin
2015-01-01
We demonstrate the localized excitation and dc electrical detection of magnetostatic surface spin waves (MSSWs) in yttrium iron garnet (YIG) by a shorted coaxial probe. Thin films of NiFe and Pt are patterned at different regions onto a common bulk YIG substrate. A shorted coaxial probe is used to excite spin precession locally near various patterned regions. The dc voltages across the corresponding regions are recorded. For excitation of the Pt regions, the dc voltage spectra are dominated by the spin pumping of MSSWs from YIG, where various modes can be clearly distinguished. For the NiFe region, it is also found that spin pumping from MSSWs generated in YIG dominated the spectra, indicating that the spin pumped currents are dissipated into charge currents via the inverse Spin Hall effect (ISHE) in NiFe. For all regions, dc signals from YIG MSSWs are observed to be much stronger than the ferromagnetic resonance (FMR) uniform mode, likely due to the nature of the microwave excitation. The results indicate the potential of this probe for microwave imaging via dc detection of spin dynamics in continuous and patterned films
Bliokh, Yu. P.; Nusinovich, G. S.; Shkvarunets, A. G.; Carmel, Y.
2004-10-01
Plasma-assisted slow-wave oscillators (pasotrons) operate without external magnetic fields, which makes these devices quite compact and lightweight. Beam focusing in pasotrons is provided by ions, which appear in the device due to the impact ionization of a neutral gas by beam electrons. Typically, the ionization time is on the order of the rise time of the beam current. This means that, during the rise of the current, beam focusing by ions becomes stronger. Correspondingly, a beam of electrons, which was initially diverging radially due to the self-electric field, starts to be focused by ions, and this focus moves towards the gun as the ion density increases. This feature makes the self-excitation of electromagnetic (em) oscillations in pasotrons quite different from practically all other microwave sources where em oscillations are excited by a stationary electron beam. The process of self-excitation of em oscillations has been studied both theoretically and experimentally. It is shown that in pasotrons, during the beam current rise the amount of current entering the interaction space and the beam coupling to the em field vary. As a result, the self-excitation can proceed faster than in conventional microwave sources with similar operating parameters such as the operating frequency, cavity quality-factor and the beam current and voltage.
Energy Technology Data Exchange (ETDEWEB)
Liu, Xiumei; Jin, Zuanming; Lin, Xian; Ma, Guohong [Department of Physics, Shanghai University (China); Cheng, Zhenxiang [Institute for Superconducting and Electronic Materials, University of Wollongong, NSW (Australia); Balakrishnan, Geetha [Department of Physics, University of Warwick, Coventry (United Kingdom)
2017-09-15
A low-energy collective excitation mode in charge-ordered multiferroic LuFe{sub 2}O{sub 4} is reported via terahertz time-domain spectroscopy. Upon cooling from 300 to 40 K, the central resonance frequency showed a pronounced hardening from 0.85 to 1.15 THz. In analogy to the well-known low-energy optical properties of LuFe{sub 2}O{sub 4}, this emerging resonance was attributed to the charge-density-wave (CDW) collective excitations. By using the Drude-Lorentz model fitting, the CDW collective mode becomes increasingly damped with the increasing temperature. Furthermore, the kinks of the CDW collective mode at the magnetic transition temperature are analyzed, which indicate the coupling of spin order with electric polarization. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Tietze, Sabrina; Singer, Ferdinand; Lasota, Sandra; Ebert, Sandra; Landskron, Johannes; Schwuchow, Katrin; Drese, Klaus Stefan; Lindner, Gerhard
2018-02-09
The monitoring of liquid-filled tubes with respect to the formation of soft deposition layers such as biofilms on the inner walls calls for non-invasive and long-term stable sensors, which can be attached to existing pipe structures. For this task a method is developed, which uses an ultrasonic clamp-on device. This method is based on the impact of such deposition layers on the propagation of circumferential guided waves on the pipe wall. Such waves are partly converted into longitudinal compressional waves in the liquid, which are back-converted to guided waves in a circular cross section of the pipe. Validating this approach, laboratory experiments with gelatin deposition layers on steel tubes exhibited a distinguishable sensitivity of both wave branches with respect to the thickness of such layers. This allows the monitoring of the layer growth.
International Nuclear Information System (INIS)
Ondrej Slezak; Milan Kalal; Hon Jin Kong
2010-01-01
Complete text of publication follows. Analytical description of an experimentally verified scheme leading to a phase-locked stimulated Brillouin scattering (SBS), used in a laser beam combination systems, is presented. The essential condition for the phase-locking effect for SBS is the fixation of the starting position and time of the acoustic Brillouin wave. It is shown that the starting position fixation of this acoustic wave may have its origin in a transient acoustic standing wave initiated by an arising optical interference field produced by the back-seeding concave mirror. This interference field leads to a stationary density modulation of the medium. However, the way to the formation of this density modulation leads via the acoustic standing wave. An appropriate solution, in the form of the standing wave, was obtained from solving the acoustic wave-equation using the electrostriction as a driving force. As a consequence of the damping term included in this equation the acoustic standing wave becomes gradually attenuated and contrary to the undamped solution published earlier, thus constitutes a truly transient phenomenon. Using a mathematical formalism similar to that which is used for the SBS description in the case of a random phase, the coupled equations describing the phase-locked SBS were derived. Contrary to the case without the back-seeding mirror, where the wave chosen from the thermal noise background subsequently plays the role of a trigger of the stimulated process, in this case it is replaced by the transient standing wave produced as a consequence of the presence of an optical interference field arisen in the focal region of the back-seeding concave mirror.
Varin, Christophe; Rancillac, Armelle; Geoffroy, Hélène; Arthaud, Sébastien; Fort, Patrice; Gallopin, Thierry
2015-07-08
Sleep-active neurons located in the ventrolateral preoptic nucleus (VLPO) play a crucial role in the induction and maintenance of slow-wave sleep (SWS). However, the cellular and molecular mechanisms responsible for their activation at sleep onset remain poorly understood. Here, we test the hypothesis that a rise in extracellular glucose concentration in the VLPO can promote sleep by increasing the activity of sleep-promoting VLPO neurons. We find that infusion of a glucose concentration into the VLPO of mice promotes SWS and increases the density of c-Fos-labeled neurons selectively in the VLPO. Moreover, we show in patch-clamp recordings from brain slices that VLPO neurons exhibiting properties of sleep-promoting neurons are selectively excited by glucose within physiological range. This glucose-induced excitation implies the catabolism of glucose, leading to a closure of ATP-sensitive potassium (KATP) channels. The extracellular glucose concentration monitors the gating of KATP channels of sleep-promoting neurons, highlighting that these neurons can adapt their excitability according to the extracellular energy status. Together, these results provide evidence that glucose may participate in the mechanisms of SWS promotion and/or consolidation. Although the brain circuitry underlying vigilance states is well described, the molecular mechanisms responsible for sleep onset remain largely unknown. Combining in vitro and in vivo experiments, we demonstrate that glucose likely contributes to sleep onset facilitation by increasing the excitability of sleep-promoting neurons in the ventrolateral preoptic nucleus (VLPO). We find here that these neurons integrate energetic signals such as ambient glucose directly to regulate vigilance states accordingly. Glucose-induced excitation of sleep-promoting VLPO neurons should therefore be involved in the drowsiness that one feels after a high-sugar meal. This novel mechanism regulating the activity of VLPO neurons reinforces the
International Nuclear Information System (INIS)
Gascoyne, A.; Jain, R.; Hindman, B. W.
2014-01-01
We consider damping and absorption of solar p modes due to their energy loss to magnetic tube waves that can freely carry energy out of the acoustic cavity. The coupling of p modes and sausage tube waves is studied in a model atmosphere composed of a polytropic interior above which lies an isothermal upper atmosphere. The sausage tube waves, excited by p modes, propagate along a magnetic fibril which is assumed to be a vertically aligned, stratified, thin magnetic flux tube. The deficit of p-mode energy is quantified through the damping rate, Γ, and absorption coefficient, α. The variation of Γ and α as a function of frequency and the tube's plasma properties is studied in detail. Previous similar studies have considered only a subphotospheric layer, modeled as a polytrope that has been truncated at the photosphere. Such studies have found that the resulting energy loss by the p modes is very sensitive to the upper boundary condition, which, due to the lack of an upper atmosphere, have been imposed in a somewhat ad hoc manner. The model presented here avoids such problems by using an isothermal layer to model the overlying atmosphere (chromosphere, and, consequently, allows us to analyze the propagation of p-mode-driven sausage waves above the photosphere. In this paper, we restrict our attention to frequencies below the acoustic cut off frequency. We demonstrate the importance of coupling all waves (acoustic, magnetic) in the subsurface solar atmosphere with the overlying atmosphere in order to accurately model the interaction of solar f and p modes with sausage tube waves. In calculating the absorption and damping of p modes, we find that for low frequencies, below ≈3.5 mHz, the isothermal atmosphere, for the two-region model, behaves like a stress-free boundary condition applied at the interface (z = –z 0 ).
Energy Technology Data Exchange (ETDEWEB)
Gascoyne, A.; Jain, R. [Applied Mathematics Department, University of Sheffield, Sheffield S3 7RH (United Kingdom); Hindman, B. W., E-mail: a.d.gascoyne@sheffield.ac.uk, E-mail: r.jain@sheffield.ac.uk [JILA and Department of Astrophysical and Planetary Sciences, University of Colorado at Boulder, Boulder, CO 80309-0440 (United States)
2014-07-10
We consider damping and absorption of solar p modes due to their energy loss to magnetic tube waves that can freely carry energy out of the acoustic cavity. The coupling of p modes and sausage tube waves is studied in a model atmosphere composed of a polytropic interior above which lies an isothermal upper atmosphere. The sausage tube waves, excited by p modes, propagate along a magnetic fibril which is assumed to be a vertically aligned, stratified, thin magnetic flux tube. The deficit of p-mode energy is quantified through the damping rate, Γ, and absorption coefficient, α. The variation of Γ and α as a function of frequency and the tube's plasma properties is studied in detail. Previous similar studies have considered only a subphotospheric layer, modeled as a polytrope that has been truncated at the photosphere. Such studies have found that the resulting energy loss by the p modes is very sensitive to the upper boundary condition, which, due to the lack of an upper atmosphere, have been imposed in a somewhat ad hoc manner. The model presented here avoids such problems by using an isothermal layer to model the overlying atmosphere (chromosphere, and, consequently, allows us to analyze the propagation of p-mode-driven sausage waves above the photosphere. In this paper, we restrict our attention to frequencies below the acoustic cut off frequency. We demonstrate the importance of coupling all waves (acoustic, magnetic) in the subsurface solar atmosphere with the overlying atmosphere in order to accurately model the interaction of solar f and p modes with sausage tube waves. In calculating the absorption and damping of p modes, we find that for low frequencies, below ≈3.5 mHz, the isothermal atmosphere, for the two-region model, behaves like a stress-free boundary condition applied at the interface (z = –z{sub 0}).
Energy Technology Data Exchange (ETDEWEB)
Argall, Matthew R.; Hollick, Sophia J.; Pine, Zackary B., E-mail: Matthew.Argall@unh.edu, E-mail: sjhollick@hotmail.com, E-mail: zbpine@gmail.com [Physics Department and Space Science Center, Morse Hall, University of New Hampshire, Durham, New Hampshire (United States); and others
2017-11-01
We report two observations of magnetic waves due to He{sup +} pickup ions observed by the Voyager 2 spacecraft in mid-1989 to demonstrate that such waves occur as far out as ∼30 au from the Sun. The observations are sufficiently far from planets, interplanetary shocks, and other possible sources of energetic particles to make newborn interstellar He{sup +} the only likely explanation for the source of the waves. Additionally, the low-frequency waves that might be expected for a variety of cometary pickup species are not seen. The events studied here were picked from a preliminary list of ∼300 events that were discovered based on polarization signatures in daily spectrograms of the magnetic field between 1977 and 1990. Analysis of those observations is ongoing. We present an analysis of these two observations using the same techniques we have employed for recently reported observations closer to the Sun.
Bircher, Martin P; Rothlisberger, Ursula
2018-06-12
Linear-response time-dependent density functional theory (LR-TD-DFT) has become a valuable tool in the calculation of excited states of molecules of various sizes. However, standard generalized-gradient approximation and hybrid exchange-correlation (xc) functionals often fail to correctly predict charge-transfer (CT) excitations with low orbital overlap, thus limiting the scope of the method. The Coulomb-attenuation method (CAM) in the form of the CAM-B3LYP functional has been shown to reliably remedy this problem in many CT systems, making accurate predictions possible. However, in spite of a rather consistent performance across different orbital overlap regimes, some pitfalls remain. Here, we present a fully flexible and adaptable implementation of the CAM for Γ-point calculations within the plane-wave pseudopotential molecular dynamics package CPMD and explore how customized xc functionals can improve the optical spectra of some notorious cases. We find that results obtained using plane waves agree well with those from all-electron calculations employing atom-centered bases, and that it is possible to construct a new Coulomb-attenuated xc functional based on simple considerations. We show that such a functional is able to outperform CAM-B3LYP in some cases, while retaining similar accuracy in systems where CAM-B3LYP performs well.
International Nuclear Information System (INIS)
Sauer, F.N.B.
2007-01-01
During my PhD thesis I investigated alkaline dimers with coherent control in a molecular beam as well as with pump-probe spectroscopy in a magneto-optical trap (MOT). The aim of the coherent control experiments were the isotope selective ionization with phase- and amplitude-shaped fs-pulses. Chapter 4 described the gained results of isotope selective ionization of NaK and KRb in a molecular beam by using different pulse formers. For the NaK dimer was the reached optimization factor R Ph and Ampl 770 =R max /R min =25 between maximization and minimization of the isotopomer ratio ( 23 Na 39 K) + /( 23 Na 41 K) + with phase and amplitude modulation of the fs-pulse with a central wavelength of λ=770 nm. From the electronic ground-state X(1) 1 Σ + ;ν''=0 transfers a one-photon-excitation population in the first excited A(2) 1 Σ + state. The coherent control experiment on KRb was used to maximize and minimize the isotopomer ratio ( 124 KRb) + /( 126 KRb) + . It was the first coherent control experiment with a spectral resolution of 1.84 cm -1 /Pixel. For the phase and amplitude optimization was the received optimization factor between minimization and maximization of the isotopomer ratio R Ph and Ampl =R max /R min =7 at a central wavelength of 840 nm. The results showed a stepwise excitation process from the electronic ground-state in the first excited (2) 1 Σ + state with a further excitation, that is possible over three resonant energy potential curves into the ionic ground-state. In the second part of my thesis I realized pump-probe spectroscopy of Rb 2 dimers in a dark SPOT. (orig.)
Estrada, Héctor; Rebling, Johannes; Razansky, Daniel
2017-02-01
The skull bone, a curved solid multilayered plate protecting the brain, constitutes a big challenge for the use of ultrasound-mediated techniques in neuroscience. Ultrasound waves incident from water or soft biological tissue are mostly reflected when impinging on the skull. To this end, skull properties have been characterized for both high-intensity focused ultrasound (HIFU) operating in the narrowband far-field regime and optoacoustic imaging applications. Yet, no study has been conducted to characterize the near-field of water immersed skulls. We used the thermoelastic effect with a 532 nm pulsed laser to trigger a wide range of broad-band ultrasound modes in a mouse skull. In order to capture the waves propagating in the near-field, a thin hydrophone was scanned in close proximity to the skull's surface. While Leaky pseudo-Lamb waves and grazing-angle bulk water waves are clearly visible in the spatio-temporal data, we were only able to identify skull-guided acoustic waves after dispersion analysis in the wavenumber-frequency space. The experimental data was found to be in a reasonable agreement with a flat multilayered plate model.
International Nuclear Information System (INIS)
Fisher, Meghan K.; Argall, Matthew R.; Joyce, Colin J.
2016-01-01
We report observations of low-frequency waves at 1 au by the magnetic field instrument on the Advanced Composition Explorer ( ACE /MAG) and show evidence that they arise due to newborn interstellar pickup He + . Twenty-five events are studied. They possess the generally predicted attributes: spacecraft-frame frequencies slightly greater than the He + cyclotron frequency, left-hand polarization in the spacecraft frame, and transverse fluctuations with minimum variance directions that are quasi-parallel to the mean magnetic field. Their occurrence spans the first 18 years of ACE operations, with no more than 3 such observations in any given year. Thus, the events are relatively rare. As with past observations by the Ulysses and Voyager spacecraft, we argue that the waves are seen only when the background turbulence is sufficiently weak as to allow for the slow accumulation of wave energy over many hours.
Energy Technology Data Exchange (ETDEWEB)
Fisher, Meghan K.; Argall, Matthew R.; Joyce, Colin J., E-mail: mkl54@wildcats.unh.edu, E-mail: Matthew.Argall@unh.edu, E-mail: cjl46@wildcats.unh.edu [Physics Department and Space Science Center, Morse Hall, University of New Hampshire, Durham, NH (United States); and others
2016-10-10
We report observations of low-frequency waves at 1 au by the magnetic field instrument on the Advanced Composition Explorer ( ACE /MAG) and show evidence that they arise due to newborn interstellar pickup He{sup +}. Twenty-five events are studied. They possess the generally predicted attributes: spacecraft-frame frequencies slightly greater than the He{sup +} cyclotron frequency, left-hand polarization in the spacecraft frame, and transverse fluctuations with minimum variance directions that are quasi-parallel to the mean magnetic field. Their occurrence spans the first 18 years of ACE operations, with no more than 3 such observations in any given year. Thus, the events are relatively rare. As with past observations by the Ulysses and Voyager spacecraft, we argue that the waves are seen only when the background turbulence is sufficiently weak as to allow for the slow accumulation of wave energy over many hours.
Wave excitation in the experiment with an electron beam at the Dzhajkiken Exos-B Japanese satellite
International Nuclear Information System (INIS)
Kavashima, N.
1985-01-01
An experiment on investigation of beam-plasma interaction in the magnetosphere is carried out at the ''Dzhajkiken (Exos-B)'' japanese satellite. 100-200 eV and 0.25-1 μA electron beam was injected into the magnetosphere. Using LF and HF detectors in low altitude range waves with the frequencies close to the upper hybrid and electron frequencies are recorded. Beyond the plasmapause the satellite was charged to the potential corresponding to the beam energy
Helicon plasma potential measurements using a heavy ion beam probe
International Nuclear Information System (INIS)
P. Schoch; K. Connor; J. Si
2005-01-01
A Heavy Ion Beam Probe, HIBP, has been installed on a helicon plasma device. The objective was to measure plasma fluctuations at the 13.55MHz RF frequency. This offers a unique challenge for the HIBP, because the transit time of the probing ion is long compared to the fluctuations of interest. For previous HIBPs, the transit time has been short compared to the period of the fluctuations which permits one to assume that the magnetic and electric fields are static. Modeling has shown that the diagnostic will still accurately measure the average potential. The fluctuating potential was to be detected but the absolute magnitude is difficult to determine with signal from a single point. However, modeling indicates multipoint measurements will allow one to resolve the absolute fluctuation magnitude. Work supported by DOE Grant No. DE-FG02-99ER5452985 During the funding of this grant, a helicon plasma discharge device was built and operated. A Heavy Ion Beam Probe primary system was installed and operated. A primary beam detector was installed and primary beam was detected both with and without plasma. Attempts were made to detect secondary ions using the primary beam detector, without success. Given the lack of a detectable signal, the energy analyzer of the HIBP system was never installed. It is available for installation if there is a reason to do so in the future. Analysis of the system indicated that the plasma electron temperature, estimated to be a few eV, was the likely reason for the lack of detectable secondary ions. A change of ion species to either Boron or Magnesium would greatly increase the signal, but neither of these ions have been used in a HIBP system. The ion source used in this system is made by using a charge exchange process to create a zeolite loaded with the desired ion. Attempts were made to use charge exchange to load Magnesium into a zeolite, and were not successful. It is felt that Magnesium and/or Boron zeolite sources could be created, but
Borodulin, V. I.; Ivanov, A. V.; Kachanov, Y. S.; Mischenko, D. A.; Fedenkova, A. A.
2016-10-01
The paper is devoted to quantitative experimental investigation of effective mechanisms of excitation of 3D TS instability waves due to distributed boundary layer receptivity to free-stream vortices. Experiments carried out in a self-similar boundary layer with Hartree parameter βH = -0.115 and concentrated on studying two receptivity mechanisms connected with distributed scattering of 3D unsteady free-stream vortices both on the natural boundary layer nonuniformity (smooth surface) and on 2D surface nonuniformity (waviness). Obtained quantitative characteristics (distributed receptivity coefficients) are compared directly with those obtained in Blasius boundary layer. It is found that the adverse pressure gradient leads to reduction of efficiency of the vortex-roughness receptivity mechanism.
International Nuclear Information System (INIS)
Ohkubo, Makio
2003-01-01
From the requirement of the time periodicity of a (quasi) stable state, frequencies of the normal modes, which compose the state, are commensurable (integer ratios) with each other, and the excitation energies E x are written as a sum of inverse integers. We propose an expression: E x = GΣ1/n, where n = integers and G = 34.5 MeV. Recurrence time is defined as LCM(n j ) x τ o , where τ 0 = 2πℎ/G = 1.20 x 10 -22 s. LCM vs. E x are illustrated for all possible n j of 2 and 3 normal modes. In 16 O +n resonances, integer ratios are found between the recurrence frequencies of 17 O and the de Broglie wave frequencies of incident neutron, meaning time coherency between them. A simple branch pattern is found in 16 O +n resonance levels. (author)
Rendell, Alistair P.; Lee, Timothy J.
1991-01-01
The analytic energy gradient for the single and double excitation coupled-cluster (CCSD) wave function has been reformulated and implemented in a new set of programs. The reformulated set of gradient equations have a smaller computational cost than any previously published. The iterative solution of the linear equations and the construction of the effective density matrices are fully vectorized, being based on matrix multiplications. The new method has been used to investigate the Cl2O2 molecule, which has recently been postulated as an important intermediate in the destruction of ozone in the stratosphere. In addition to reporting computational timings, the CCSD equilibrium geometries, harmonic vibrational frequencies, infrared intensities, and relative energetics of three isomers of Cl2O2 are presented.
National Research Council Canada - National Science Library
Pritchard, David
1999-01-01
Matter wave interferometers, in which de Broglie waves are coherently split and then recombined to produce interference fringes, have opened exciting new possibilities for precision and fundamental...
International Nuclear Information System (INIS)
Zhang, Zhaojun; Zhang, Dong H.
2014-01-01
Seven-dimensional time-dependent wave packet calculations have been carried out for the title reaction to obtain reaction probabilities and cross sections for CHD 3 in J 0 = 1, 2 rotationally excited initial states with k 0 = 0 − J 0 (the projection of CHD 3 rotational angular momentum on its C 3 axis). Under the centrifugal sudden (CS) approximation, the initial states with the projection of the total angular momentum on the body fixed axis (K 0 ) equal to k 0 are found to be much more reactive, indicating strong dependence of reactivity on the orientation of the reagent CHD 3 with respect to the relative velocity between the reagents H and CHD 3 . However, at the coupled-channel (CC) level this dependence becomes much weak although in general the K 0 specified cross sections for the K 0 = k 0 initial states remain primary to the overall cross sections, implying the Coriolis coupling is important to the dynamics of the reaction. The calculated CS and CC integral cross sections obtained after K 0 averaging for the J 0 = 1, 2 initial states with all different k 0 are essentially identical to the corresponding CS and CC results for the J 0 = 0 initial state, meaning that the initial rotational excitation of CHD 3 up to J 0 = 2, regardless of its initial k 0 , does not have any effect on the total cross sections for the title reaction, and the errors introduced by the CS approximation on integral cross sections for the rotationally excited J 0 = 1, 2 initial states are the same as those for the J 0 = 0 initial state
Afraimovich, E.
2009-04-01
Recent investigations have shown that movement of the solar terminator (ST) causes generation of acoustic-gravity waves (AGW), turbulence and instabilities in the ionosphere plasma. Among all the sources of gravity waves, the moving ST has a special status, since it is a predictable phenomenon, whose characteristics are well known. Considering the ST as a stable and repetitive source of AGW, one can derive information about atmospheric conditions from the response of the medium to this input. The great variety of ST-linked phenomena in the atmosphere gave rise to a number of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. However, virtually all experimental data were obtained using indirect methods for analyzing the spectrum of ionosphere parameter variations, which can result from a number of factors. This causes difficulties in the reliable identification of ST-linked AGW, because in general case AGW can be generated by different sources either of natural or of anthropogenic origin. To identify ST-generated wave disturbances it is insufficient to register the time dependence of ionosphere parameters or their spectrum. It is necessary to measure the spatial structure of these disturbances and to compare it with spatial-temporal characteristics of ST. Another important requirement implies the continuous, global character of observations. Using long-term (1998-2007) total electron content (TEC) measurements from the IGS GPS global network and dense networks of GPS sites in USA (CORS) and Japan (GEONET), we have obtained the first evidence for the wave structure excited by the solar terminator (ST). We have found two main types of the observed TEC disturbances: large-scale (LS) 60-min variations with amplitude of about 0.5-1 TECU and medium-scale (MS) 15-min variations with amplitude of about 0.05-0.1 TECU. The first type of disturbances was predicted in theoretical investigations and registered earlier
Li, Ping
2016-09-09
A discontinuous Galerkin time-domain (DGTD) method analyzing signal/power integrity on multilayered power-ground parallel plate pairs is proposed. The excitation is realized by introducing wave ports on the antipads where electric/magnetic current sources are represented in terms of the eigenmodes of the antipads. Since closed-forms solutions do not exist for the eigenmodes of the arbitrarily shaped antipads, they have to be calculated using numerical schemes. Spatial orthogonality of the eigenmodes permits determination of each mode\\'s temporal expansion coefficient by integrating the product of the electric field and the mode over the wave port. The temporal mode coefficients are then Fourier transformed to accurately calculate the S-parameters corresponding to different modes. Additionally, to generalize the DGTD to manipulate dispersive media, the auxiliary differential equation method is employed. This is done by introducing a time-dependent polarization volume current as an auxiliary unknown and the constitutive relation between this current and the electric field as an auxiliary equation. Consequently, computationally expensive temporal convolution is avoided. Various numerical examples, which demonstrate the applicability, robustness, and accuracy of the proposed method, are presented.
Chen, Zhanbin
2018-05-01
The process of excitation of highly charged Fe XXIV ion embedded in weakly coupled plasmas by electron impact is studied, together with the subsequent radiative decay. For the target structure, the calculation is performed using the multiconfiguration Dirac-Hartree-Fock method incorporating the Debye-Hückel potential for the electron-nucleus interaction. Fine-structure levels of the 1s22p and 1s2s2p configurations and the transition properties among these levels are presented over a wide range of screening parameters. For the collision dynamics, the distorted-wave method in the relativistic frame is adopted to include the effect of plasma background, in which the interparticle interactions in the system are described by screened interactions of the Debye-Hückel type. The continuum wave function of the projectile electron is obtained by solving the modified Dirac equations. The influence of plasma strength on the cross section, the linear polarization, and the angular distribution of x-ray photon emission are investigated in detail. Comparison of the present results with experimental data and other theoretical predictions, when available, is made.
Directory of Open Access Journals (Sweden)
J. OLIVER
1977-06-01
Full Text Available SUMMARY. - Seismic activity associated with the collision of the continental
part of the Australian plate with the oceanic Melanesian arcs along Papua New
Guinea and the Banda arc provides an unusual opportunity to study the relative
excitation of the seismic shear waves Sn and Lg. These waves are produced by
earthquakes located along the arcs in the upper 200 km of the earth and are
recorded by the Australian WWSSN Stations at Charters Towers (CTA and Alice
Springs (ASP. The paths to these stations are predominantly continental. The data
clearly show that for events located at crustal depths, Lg is the predominant phase
on the records and Sn is either absent or very weak. For events deeper than about
50-70 km, Sn becomes the predominant phase on the records. These observations
arc in qualitative agreement with the explanations of Sn and Lg as higher
modes of surface waves, for the particle displacement amplitudes are maximum
within the crust for Lg and maximum within the lid of the lithospheric mantle
for Sn. The data suggest that either the crustal wave guide for Lg is more
efficient than that for Sn, or that Lg is more easily excited than Sn. No clear
Lg is observed from shallow earthquakes when the length of the segment of the
path crossing oceanic structure is greater than about 200 km. Also, widespread
Quaternary volcanism within the « stable » area of central Papua New Guinea
to the south of the mobile belt does not seem to affect the efficient transmission
of high-frequency (1 Hz shear energy.
The paths from events located along the New Hebrides, Solomon, and New
Britain arcs to Australia traverse oceanic structure, and no Lg is observed from
these paths. The inefficient propagation of Sn along these paths from both
shallow and intermediate-depth events can be explained as follows: 1 For
the New Hebrides case, the
International Nuclear Information System (INIS)
Zhang, Hao; Qiu, Minghui; Wu, Zhifang; Dong, Hongguang; Liu, Bo; Miao, Yinping
2013-01-01
We have demonstrated the formation of an acoustic grating in a simplified hollow-core photonic crystal fiber, which consists of a hollow hexagonal core and six crown-like air holes, by applying flexural acoustic waves along the fiber axis. The dependence of the resonance wavelength on the applied acoustic frequency has been acquired on the basis of the theoretical calculation of the phase matching curve; it is in good agreement with our experimental observation of the transmission spectral evolution as the applied acoustic frequency varies. Experimental results show that the acoustic grating resonance peak possesses acoustic frequency and strain dependences of 728 nm MHz −1 and −6.98 pm με −1 , respectively, based on which high-performance acousto-optic tunable filters and fiber-optic strain sensors with high sensitivity could be achieved. And furthermore, the research work presented in this paper indicates that microbending rather than physical deformation is the main physical mechanism that leads to the formation of equivalent long-period gratings, which would be of significance for developing related grating devices based on simplified hollow-core photonic crystal fibers. (paper)
DEFF Research Database (Denmark)
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many...... times smaller it remains very high. For example, whilst there is enough potential wave power off the UK to supply the electricity demands several times over, the economically recoverable resource for the UK is estimated at 25% of current demand; a lot less, but a very substantial amount nonetheless....
Jabri, Atef; Motiyenko, R. A.; Margulès, L.; Guillemin, J.-C.; Alekseev, E. A.; Kleiner, Isabelle; Tercero, Belén; Cernicharo, Jose
2017-06-01
Methyl formate CH_{3}OC(O)H is a relatively abundant component of the interstellar medium (ISM). Thus, we decided to study its sulfur derivatives as they can be reasonably proposed for detection in the ISM. In fact there is two relatively stable isomers for methyl thioformate, S-Methyl thioformate CH_{3}SC(O)H and O-Methyl thiofomate CH_{3}OC(S)H. Theoretical investigations on these molecules have been done recently by Senent et al.. Previous experimental investigations were performed only for the S-Methyl thioformate in the 10-41 GHz spectral range by Jones et al. and Caminati et al.. For the present study both isomers were synthesized and the millimeter wave spectrum was then recorded for the first time from 150 to 660 GHz with the Lille's spectrometer based on solid-state sources. The internal rotation effect on the millimeter wave spectra is not the same for these two molecules because the barrier height to internal rotation is relatively low for the S- isomer (V_{3} ≈ 140 \\wn) and rather high for the O- isomer (V_{3} ≈ 700 \\wn). Analysis of the ground and excited torsional states performed with the BELGI-C_{s} code will be presented and discussed. We will provide the search for methyl thioformate in different sources. E. Chruchwell, G. Winnewisser, A&A, 45, 229 (1975) M. L. Senent, C. Puzzarini, M. Hochlaf, R. Dominguez-Gomez, and M. Carvajal, J. Chem. Phys., 141, 104303 (2014) G. I. L. Jones, D. G. Lister, N. L. Owen, J. Mol. Spectrosc., 60, 348 (1976) W. Caminati, B. P. V. Eijck, D. G. Lister, J. Mol. Spectrosc., 90, 15 (1981) J. T. Hougen, I. Kleiner, and M. Godefroid, J. Mol. Spectrosc. 163, 559 (1994)
Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system
International Nuclear Information System (INIS)
Aleksandrov, A. F.; Petrov, A. K.; Vavilin, K. V.; Kralkina, E. A.; Neklyudova, P. A.; Nikonov, A. M.; Pavlov, V. B.; Ayrapetov, A. A.; Odinokov, V. V.; Sologub, V. A.; Pavlov, G. Ya.
2016-01-01
Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.
Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system
Energy Technology Data Exchange (ETDEWEB)
Aleksandrov, A. F.; Petrov, A. K., E-mail: alpetrov57@gmail.com; Vavilin, K. V.; Kralkina, E. A.; Neklyudova, P. A.; Nikonov, A. M.; Pavlov, V. B. [Moscow State University, Faculty of Physics (Russian Federation); Ayrapetov, A. A.; Odinokov, V. V.; Sologub, V. A.; Pavlov, G. Ya. [Research Institute of Precision Engineering (Russian Federation)
2016-03-15
Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.
International Nuclear Information System (INIS)
Yang, S.-H.; Mun, B.S.; Mannella, N.; Sell, B.; Ritchey, S.B.; Fadley, C.S.; Pham, L.; Nambu, A.; Watanabe, M.
2004-01-01
Full text: Buried solid-solid interfaces are becoming increasingly more important in all aspects of nanoscience, and we here dis- cuss the st applications of a new method for selectively studying them with the vuv/soft x-ray spectroscopies. As specific examples, magnetic multilayer structures represent key elements of current developments in spintronics, including giant magnetoresistance, exchange bias, and magnetic tunnel resistance. The buried interfaces in such structures are of key importance to their performance, but have up to now been difficult to study selectively with these spectroscopies. This novel method involves excitation of photoelectrons or fluorescent x-rays with soft x-ray standing waves created by Bragg reflection from a multilayer mirror substrate on which the sample is grown. We will discuss core and valence photoemission, as well soft x-ray emission, results from applying this method to multilayer structures relevant to both giant magnetoresistance (Fe/Cr-[2]) and magnetic tunnel junctions (Al 2 O 3 /FeCo) , including magnetic dichroism measurements. Work supported by the Director, Of e of Science, Of e of Basic Energy Sciences, Materials Science and Engineering Division, U.S. Department of Energy, Contract No. DE-AC03-76SF000
Performance of a permanent-magnet helicon source at 27 and 13 MHz
Energy Technology Data Exchange (ETDEWEB)
Chen, Francis F. [Electrical Engineering Department, University of California, Los Angeles, California 90095 (United States)
2012-09-15
A small helicon source is used to create dense plasma and inject it into a large chamber. A permanent magnet is used for the dc magnetic field (B-field), making the system very simple and compact. Though theory predicts that better antenna coupling will occur at 27.12 MHz, it was found that 13.56 MHz surprisingly gives even higher density due to practical effects not included in theory. Complete density n and electron temperature T{sub e} profiles are measured at three distances below the source. The plasma inside the source is also measured with a special probe, even under the antenna. The density there is lower than expected because the plasma created is immediately ejected, filling the experimental chamber. The advantage of helicons over inductively coupled plasmas (with no B-field) increases with RF power. At high B-fields, edge ionization by the Trivelpiece-Gould mode can be seen. These results are useful for design of multiple-tube, large-area helicon sources for plasma etching and deposition because problems are encountered which cannot be foreseen by theory alone.
Three-dimensional modeling of the neutral gas depletion effect in a helicon discharge plasma
Kollasch, Jeffrey; Schmitz, Oliver; Norval, Ryan; Reiter, Detlev; Sovinec, Carl
2016-10-01
Helicon discharges provide an attractive radio-frequency driven regime for plasma, but neutral-particle dynamics present a challenge to extending performance. A neutral gas depletion effect occurs when neutrals in the plasma core are not replenished at a sufficient rate to sustain a higher plasma density. The Monte Carlo neutral particle tracking code EIRENE was setup for the MARIA helicon experiment at UW Madison to study its neutral particle dynamics. Prescribed plasma temperature and density profiles similar to those in the MARIA device are used in EIRENE to investigate the main causes of the neutral gas depletion effect. The most dominant plasma-neutral interactions are included so far, namely electron impact ionization of neutrals, charge exchange interactions of neutrals with plasma ions, and recycling at the wall. Parameter scans show how the neutral depletion effect depends on parameters such as Knudsen number, plasma density and temperature, and gas-surface interaction accommodation coefficients. Results are compared to similar analytic studies in the low Knudsen number limit. Plans to incorporate a similar Monte Carlo neutral model into a larger helicon modeling framework are discussed. This work is funded by the NSF CAREER Award PHY-1455210.
Helicon plasma ion temperature measurements and observed ion cyclotron heating in proto-MPEX
Beers, C. J.; Goulding, R. H.; Isler, R. C.; Martin, E. H.; Biewer, T. M.; Caneses, J. F.; Caughman, J. B. O.; Kafle, N.; Rapp, J.
2018-01-01
The Prototype-Material Plasma Exposure eXperiment (Proto-MPEX) linear plasma device is a test bed for exploring and developing plasma source concepts to be employed in the future steady-state linear device Material Plasma Exposure eXperiment (MPEX) that will study plasma-material interactions for the nuclear fusion program. The concept foresees using a helicon plasma source supplemented with electron and ion heating systems to reach necessary plasma conditions. In this paper, we discuss ion temperature measurements obtained from Doppler broadening of spectral lines from argon ion test particles. Plasmas produced with helicon heating alone have average ion temperatures downstream of the Helicon antenna in the range of 3 ± 1 eV; ion temperature increases to 10 ± 3 eV are observed with the addition of ion cyclotron heating (ICH). The temperatures are higher at the edge than the center of the plasma either with or without ICH. This type of profile is observed with electrons as well. A one-dimensional RF antenna model is used to show where heating of the plasma is expected.
Modulational instability of electric helicons in a magnetized collisional plasma
International Nuclear Information System (INIS)
El-Ashry, M.Y.; Papuashvili, N.A.
1987-06-01
The interaction of a rf electromagnetic wave with a magnetized collisional plasma in the ultra-relativistic case has been investigated to show the effect of the collisions on the modulational instability growth rate. (author). 5 refs
Hall, Stephen P; Traub, Roger D; Adams, Natalie E; Cunningham, Mark O; Schofield, Ian; Jenkins, Alistair J; Whittington, Miles A
2018-01-01
Acute in vitro models have revealed a great deal of information about mechanisms underlying many types of epileptiform activity. However, few examples exist that shed light on spike-and-wave (SpW) patterns of pathological activity. SpW are seen in many epilepsy syndromes, both generalized and focal, and manifest across the entire age spectrum. They are heterogeneous in terms of their severity, symptom burden, and apparent anatomical origin (thalamic, neocortical, or both), but any relationship between this heterogeneity and underlying pathology remains elusive. In this study we demonstrate that physiological delta-frequency rhythms act as an effective substrate to permit modeling of SpW of cortical origin and may help to address this issue. For a starting point of delta activity, multiple subtypes of SpW could be modeled computationally and experimentally by either enhancing the magnitude of excitatory synaptic events ascending from neocortical layer 5 to layers 2/3 or selectively modifying superficial layer GABAergic inhibition. The former generated SpW containing multiple field spikes with long interspike intervals, whereas the latter generated SpW with short-interval multiple field spikes. Both types had different laminar origins and each disrupted interlaminar cortical dynamics in a different manner. A small number of examples of human recordings from patients with different diagnoses revealed SpW subtypes with the same temporal signatures, suggesting that detailed quantification of the pattern of spikes in SpW discharges may be a useful indicator of disparate underlying epileptogenic pathologies. NEW & NOTEWORTHY Spike-and-wave-type discharges (SpW) are a common feature in many epilepsies. Their electrographic manifestation is highly varied, as are available genetic clues to associated underlying pathology. Using computational and in vitro models, we demonstrate that distinct subtypes of SpW are generated by lamina-selective disinhibition or enhanced
Bray, James William [Niskayuna, NY; Garces, Luis Jose [Niskayuna, NY
2012-03-13
The disclosed technology is a cryogenic static exciter. The cryogenic static exciter is connected to a synchronous electric machine that has a field winding. The synchronous electric machine is cooled via a refrigerator or cryogen like liquid nitrogen. The static exciter is in communication with the field winding and is operating at ambient temperature. The static exciter receives cooling from a refrigerator or cryogen source, which may also service the synchronous machine, to selected areas of the static exciter and the cooling selectively reduces the operating temperature of the selected areas of the static exciter.
Simsic, P. L.
1974-01-01
Excitation of neutral atoms by inelastic scattering of incident electrons in gaseous nebulae were investigated using Slater Wave functions to describe the initial and final states of the atom. Total cross sections using the Born Approximation are calculated for: Li(2s yields 2p), Na(3s yields 4p), k(4s yields 4p). The intensity of emitted radiation from gaseous nebulae is also calculated, and Maxwell distribution is employed to average the kinetic energy of electrons.
Radially sheared azimuthal flows and turbulent transport in a cylindrical helicon plasma device
International Nuclear Information System (INIS)
Tynan, G R; Burin, M J; Holland, C; Antar, G; Diamond, P H
2004-01-01
A radially sheared azimuthal flow is observed in a cylindrical helicon plasma device. The shear flow is roughly azimuthally symmetric and contains both time-stationary and slowly varying components. The turbulent radial particle flux is found to peak near the density gradient maximum and vanishes at the shear layer location. The shape of the radial plasma potential profile associated with the azimuthal E x B flow is predicted accurately by theory. The existence of the mean shear flow in a plasma with finite flow damping from ion-neutral collisions and no external momentum input implies the existence of radial angular momentum transport from the turbulent Reynolds-stress
International Nuclear Information System (INIS)
McGowan, F.K.; Stelson, P.H.
1974-01-01
The theory of Coulomb excitation and a brief review of pertinent treatments of the Coulomb excitation process that are useful for the analysis of experiments are given. Examples demonstrating the scope of nuclear structure information obtainable from gamma spectroscopy are presented. Direct Elambda excitation of 232 Th is discussed in terms of the one phonon octupole vibrational spectrum. B(MI) reduced transition probabilities resulting from Coulomb excitation of odd-A deformed nuclei with heavy ions are presented as a test of the rotational model. The use of gamma ray coincidence and particle-gamma coincidence as tools for investigating Coulomb excitation is discussed. (U.S.)
Development of 2D laser-induced fluorescence (LIF) system in high-density helicon plasma
International Nuclear Information System (INIS)
Teshigahara, Naoto; Shinohara, Shunjiro; Kuwahara, Daisuke; Watanabe, Masaki; Yamagata, Yukihiko
2014-01-01
Lifetimes of most electric propulsion devices are limited owing to electrode erosion and contamination by plasmas. To overcome this problem, a Helicon Electrodeless Advanced Thruster (HEAT) was proposed by our research team. This scheme employs a high-density (∼10 13 cm -3 ) helicon plasma accelerated by the Lorentz force, which is produced by various acceleration methods. For feasibility of this method, a Laser-Induced Fluorescence (LIF) system was developed. The LIF is a powerful tool for plasma diagnostics because it is a non-invasive method that allows high spatial resolution. Using the LIF, it is possible to deduce velocity distribution functions of different particles (ions, atoms, and molecules). In this paper, we report the details of our novel 2D LIF system as well as some preliminary experimental results. Argon ion velocity distributions at different axial and radial locations were obtained using the novel 2D system. Ion velocity was greatest (∼ 2.8 km/s) at z = -24 cm among all the points measured along the z-axis. Velocity values were approximately 2.7 and 3.2 km/s for radial positions of r = 0 and 3 cm, respectively. Ion temperature values were approximately 0.56 and 0.61 eV at r = 0 and 3 cm, respectively. (author)
International Nuclear Information System (INIS)
Cheng Yuguo; Cheng Mousen; Wang Moge; Yang Xiong; Li Xiaokang
2014-01-01
A one-dimensional radial non-uniform fluid model is employed to study plasma behaviors with special emphasis laid on helicon discharges. The plasma density n e , electron temperature T e , electron azimuthal and radial drift velocities are investigated in terms of the plasma radius r p , magnetic field intensity B 0 and gas pressure p 0 , by assuming radial ambipolar diffusion and negligible ion cyclotron movement. The results show that the magnetic confinement plays an important role in the discharge equilibrium, especially at low pressure, which significantly reduces T e compared with the case of a negligible magnetic field effect, and higher B 0 leads to a greater average plasma density. T e shows little variations in the plasma density range of 10 11 cm −3 –10 13 cm −3 for p 0 < 3.0 mTorr. Comparison of the simulation results with experiments suggests that the model can make reasonable predictions of T e in low pressure helicon discharges. (low temperature plasma)
Mcpeak, W. L.
1975-01-01
A new exciter switch assembly has been installed at the three DSN 64-m deep space stations. This assembly provides for switching Block III and Block IV exciters to either the high-power or 20-kW transmitters in either dual-carrier or single-carrier mode. In the dual-carrier mode, it provides for balancing the two drive signals from a single control panel located in the transmitter local control and remote control consoles. In addition to the improved switching capabilities, extensive monitoring of both the exciter switch assembly and Transmitter Subsystem is provided by the exciter switch monitor and display assemblies.
National Research Council Canada - National Science Library
Pritchard, David
2000-01-01
Long-term research objective: Matter wave interferometers, in which de Broglie waves are coherently split and then recombined to produce interference fringes, have opened exciting new possibilities for precision and fundamental...
Mayr, H. G.; Harris, I.; Herrero, F. A.; Varosi, F.
1984-01-01
A transfer function approach is taken in constructing a spectral model of the acoustic-gravity wave response in a multiconstituent thermosphere. The model is then applied to describing the thermospheric response to various sources around the globe. Zonal spherical harmonics serve to model the horizontal variations in propagating waves which, when integrated with respect to height, generate a transfer function for a vertical source distribution in the thermosphere. Four wave components are characterized as resonance phenomena and are associated with magnetic activity and ionospheric disturbances. The waves are either trapped or propagate, the latter becoming significant when possessing frequencies above 3 cycles/day. The energy input is distributed by thermospheric winds. The disturbances decay slowly, mainly due to heat conduction and diffusion. Gravity waves appear abruptly and are connected to a sudden switching on or off of a source. Turn off of a source coincides with a reversal of the local atmospheric circulation.
Hierarchical wave functions revisited
International Nuclear Information System (INIS)
Li Dingping.
1997-11-01
We study the hierarchical wave functions on a sphere and on a torus. We simplify some wave functions on a sphere or a torus using the analytic properties of wave functions. The open question, the construction of the wave function for quasi electron excitation on a torus, is also solved in this paper. (author)
Ion acceleration in a helicon source due to the self-bias effect
Energy Technology Data Exchange (ETDEWEB)
Wiebold, Matt; Sung, Yung-Ta; Scharer, John E. [University of Wisconsin-Madison, Electrical and Computer Engineering, Madison, Wisconsin 53706 (United States)
2012-05-15
Time-averaged plasma potential differences up to 165 V over several hundred Debye lengths are observed in low pressure (p{sub n} < 1 mTorr) expanding argon plasmas in the Madison Helicon eXperiment (MadHeX). The potential gradient leads to ion acceleration greater than that predicted by ambipolar expansion, exceeding E{sub i} Almost-Equal-To 7 kT{sub e} in some cases. RF power up to 500 W at 13.56 MHz is supplied to a half-turn, double-helix antenna in the presence of a nozzle magnetic field, adjustable up to 1 kG. A retarding potential analyzer (RPA) measures the ion energy distribution function (IEDF) and a swept emissive probe measures the plasma potential. Single and double probes measure the electron density and temperature. Two distinct mode hops, the capacitive-inductive (E-H) and inductive-helicon (H-W) transitions, are identified by jumps in density as RF power is increased. In the capacitive (E) mode, large fluctuations of the plasma potential (V{sub p-p} Greater-Than-Or-Equivalent-To 140V, V{sub p-p}/V{sub p} Almost-Equal-To 150%) exist at the RF frequency and its harmonics. The more mobile electrons can easily respond to RF-timescale gradients in the plasma potential whereas the inertially constrained ions cannot, leading to an initial flux imbalance and formation of a self-bias voltage between the source and expansion chambers. In the capacitive mode, the ion acceleration is not well described by an ambipolar relation, while in the inductive and helicon modes the ion acceleration more closely follows an ambipolar relation. The scaling of the potential gradient with the argon flow rate and RF power are investigated, with the largest potential gradients observed for the lowest flow rates in the capacitive mode. The magnitude of the self-bias voltage agrees with that predicted for RF self-bias at a wall. Rapid fluctuations in the plasma potential result in a time-dependent axial electron flux that acts to 'neutralize' the accelerated ion
Energy Technology Data Exchange (ETDEWEB)
Bertel, I.M.; Churakov, V.V.; Petukhov, V.O.; Prokopov, A.P.; Trushin, S.A.; Voitovich, A.P.
1980-01-01
The competition of orthogonally-polarized waves with various differences in the wave Q-factors and active medium pressures is studied. The possibility of controlling the parameters of a pulsed CO/sub 2/ laser by changing the value of the amplitude anisotropy of the cavity is demonstrated. The duration of the emission pulse for one of two orthogonal polarizations was reduced by virtually 50%.
Energy Technology Data Exchange (ETDEWEB)
Gutierrez T, C.R
1991-01-15
In an unidimensional model is shown in the cases of a semi limited plasma and a layer of plasma the excitement mechanism of electrostatic fields for a radiofrequency wave (RF) polarized lineally. This phenomenon depends strongly on the combined action of the Miller force and that of impulsion. It is shown that the action of these forces is carried out in different characteristic times when the front of wave crosses through the plasma. The cases of a semi limited plasma and of a layer of plasma without and with current are analyzed. It is shown that near the frontiers of the plasma where the field is sufficiently big arise oscillations of the width of the field that are slowly muffled in the space in an exponential way. In the cases of a plasma layer its are shown that the processes that arise near the frontier x = L are similar to the processes that arise near the frontier x = 0. The existence of current in the plasma layer leads to the blockade of the excited perturbations in the frontier x = L. (Author)
International Nuclear Information System (INIS)
March, N.H.
2007-08-01
After a brief summary of some basic properties of ideal gases of bosons and of fermions, two many-body Hamiltonians are cited for which ground-state wave functions allow the generation of excited states. But because of the complexity of ground-state many-body wave functions, we then consider properties of reduced density matrices, and in particular, the diagonal element of the second-order density matrix. For both the homogeneous correlated electron liquid and for an assembly of charged bosons, the ground-state pair correlation function g(r) has fingerprints of the zero-point energy of the plasmon modes. These affect crucially the static structure factor S(k), in the long wavelength limit. This is best understood by means of the Ornstein-Zernike direct correlation function c(r), which plays an important role throughout this article. Turning from such charged liquids, both boson and fermion, to superfluid 4 He, the elevated temperature (T) structure factor S(k, T) is related, albeit approximately, to its zero-temperature counterpart, via the velocity of sound, reflecting the collective phonon excitations, and the superfluid density. Finally some future directions are pointed. (author)
National Research Council Canada - National Science Library
Holzricher, John
2004-01-01
To more easily obtain a voiced excitation function for speech characterization, measurements of skin motion, tracheal tube, and vocal fold, motions were made and compared to EM sensor-glottal derived...
Wright, Bradford L.
1975-01-01
Advocates the creation of swimming pool oscillations as part of a general investigation of mechanical oscillations. Presents the equations, procedure for deriving the slosh modes, and methods of period estimation for exciting swimming pool oscillations. (GS)
Lim, Edward C
1974-01-01
Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab
Ion ejection from a permanent-magnet mini-helicon thruster
Energy Technology Data Exchange (ETDEWEB)
Chen, Francis F. [Electrical Engineering Department, University of California, Los Angeles 90095-1594 (United States)
2014-09-15
A small helicon source, 5 cm in diameter and 5 cm long, using a permanent magnet (PM) to create the DC magnetic field B, is investigated for its possible use as an ion spacecraft thruster. Such ambipolar thrusters do not require a separate electron source for neutralization. The discharge is placed in the far-field of the annular PM, where B is fairly uniform. The plasma is ejected into a large chamber, where the ion energy distribution is measured with a retarding-field energy analyzer. The resulting specific impulse is lower than that of Hall thrusters but can easily be increased to relevant values by applying to the endplate of the discharge a small voltage relative to spacecraft ground.
Development of a compact permanent magnet helicon plasma source for ion beam bioengineering
Energy Technology Data Exchange (ETDEWEB)
Kerdtongmee, P.; Srinoum, D.; Nisoa, M. [Plasma Technology for Agricultural Applications Research Laboratory, School of Science, Walailak University, Nakhon Si Thammarat 80161 (Thailand); ThEP Center, CHE, 328 Si Ayutthaya Rd., Bangkok 10400 (Thailand)
2011-10-15
A compact helicon plasma source was developed as a millimeter-sized ion source for ion beam bioengineering. By employing a stacked arrangement of annular-shaped permanent magnets, a uniform axial magnetic flux density up to 2.8 kG was obtained. A cost effective 118 MHz RF generator was built for adjusting forward output power from 0 to 40 W. The load impedance and matching network were then analyzed. A single loop antenna and circuit matching elements were placed on a compact printed circuit board for 50 {Omega} impedance matching. A plasma density up to 1.1 x 10{sup 12} cm{sup -3} in the 10 mm diameter tube under the magnetic flux density was achieved with 35 W applied RF power.
Development of a compact permanent magnet helicon plasma source for ion beam bioengineering.
Kerdtongmee, P; Srinoum, D; Nisoa, M
2011-10-01
A compact helicon plasma source was developed as a millimeter-sized ion source for ion beam bioengineering. By employing a stacked arrangement of annular-shaped permanent magnets, a uniform axial magnetic flux density up to 2.8 kG was obtained. A cost effective 118 MHz RF generator was built for adjusting forward output power from 0 to 40 W. The load impedance and matching network were then analyzed. A single loop antenna and circuit matching elements were placed on a compact printed circuit board for 50 Ω impedance matching. A plasma density up to 1.1 × 10(12) cm(-3) in the 10 mm diameter tube under the magnetic flux density was achieved with 35 W applied RF power.
Neutral-depletion-induced axially asymmetric density in a helicon source and imparted thrust
Takahashi, Kazunori; Takao, Yoshinori; Ando, Akira
2016-02-01
The high plasma density downstream of the source is observed to be sustained only for a few hundreds of microsecond at the initial phase of the discharge, when pulsing the radiofrequency power of a helicon plasma thruster. Measured relative density of argon neutrals inside the source implies that the neutrals are significantly depleted there. A position giving a maximum plasma density temporally moves to the upstream side of the source due to the neutral depletion and then the exhausted plasma density significantly decreases. The direct thrust measurement demonstrates that the higher thrust-to-power ratio is obtained by using only the initial phase of the high density plasma, compared with the steady-state operation.
Atomic and molecular hydrogen gas temperatures in a low-pressure helicon plasma
Samuell, Cameron M.; Corr, Cormac S.
2015-08-01
Neutral gas temperatures in hydrogen plasmas are important for experimental and modelling efforts in fusion technology, plasma processing, and surface modification applications. To provide values relevant to these application areas, neutral gas temperatures were measured in a low pressure (radiofrequency helicon discharge using spectroscopic techniques. The atomic and molecular species were not found to be in thermal equilibrium with the atomic temperature being mostly larger then the molecular temperature. In low power operation (measurements near a graphite target demonstrated localised cooling near the sample surface. The temporal evolution of the molecular gas temperature during a high power 1.1 ms plasma pulse was also investigated and found to vary considerably as a function of pressure.
Backreaction of excitations on a vortex
Arodz, Henryk; Hadasz, Leszek
1996-01-01
Excitations of a vortex are usually considered in a linear approximation neglecting their backreaction on the vortex. In the present paper we investigate backreaction of Proca type excitations on a straightlinear vortex in the Abelian Higgs model. We propose exact Ansatz for fields of the excited vortex. From initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the backreaction corrections. Their approximate solutions are found ...
Energy Technology Data Exchange (ETDEWEB)
Lee, Jin-Won; Lee, Yun-Seong, E-mail: leeeeys@kaist.ac.kr; Chang, Hong-Young [Low-temperature Plasma Laboratory, Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701 (Korea, Republic of); An, Sang-Hyuk [Agency of Defense Development, Yuseong-gu, Daejeon 305-151 (Korea, Republic of)
2014-08-15
In this study, we attempted to determine the possibility of multiple inductively coupled plasma (ICP) and helicon plasma sources for large-area processes. Experiments were performed with the one and two coils to measure plasma and electrical parameters, and a circuit simulation was performed to measure the current at each coil in the 2-coil experiment. Based on the result, we could determine the possibility of multiple ICP sources due to a direct change of impedance due to current and saturation of impedance due to the skin-depth effect. However, a helicon plasma source is difficult to adapt to the multiple sources due to the consistent change of real impedance due to mode transition and the low uniformity of the B-field confinement. As a result, it is expected that ICP can be adapted to multiple sources for large-area processes.
Magnetic excitations in amorphous ferromagnets
International Nuclear Information System (INIS)
Continentino, M.A.
The propagation of magnetic excitations in amorphous ferromagnets is studied from the point of view of the theory of random frequency modulation. It is shown that the spin waves in the hydrodynamic limit are well described by perturbation theory while the roton-like magnetic excitations with wavevector about the peak in the structure factor are not. A criterion of validity of perturbation theory is found which is identical to a narrowing condition in magnetic resonance. (author) [pt
Back reaction of excitations on a vortex
International Nuclear Information System (INIS)
Arodz, H.; Hadasz, L.
1997-01-01
Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component. copyright 1997 The American Physical Society
Back reaction of excitations on a vortex
Arodź, Henryk; Hadasz, Leszek
1997-01-01
Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component.
DEFF Research Database (Denmark)
Ferri, Francesco; Ambühl, Simon; Kofoed, Jens Peter
2015-01-01
A large amount of energy is freely roaming around the world each day, without us being able to exploit it: wave energy is a largely untapped source of renewable energy, which can have a substantial influence in the future energy mix. The reason behind the inability of using this free resource is ...
International Nuclear Information System (INIS)
Payne, M.G.; Miller, J.C.; Hart, R.C.; Garrett, W.R.
1991-01-01
We consider effects which occur when four-wave sum frequency generation and multiphoton ionization are induced by lasers tuned near a three-photon resonance and simultaneously near or at a dipole allowed four-photon resonance. In studies with unfocused laser beams, if the phase mismatch of the generated four-wave-mixing field is large and the related two-photon resonance for the absorption of a four-wave-mixing photon and a laser photon results in strong absorption of the four-wave-mixing field, a coherent cancellation occurs between the pumping of the resonance by two- and four-photon processes. This interference effect occurs when the first laser is tuned on either side of the three-photon resonance and |Δk rL |much-gt 1, where Δk r is the mismatch and L is the length of the path of the laser beams in the gas. With focused laser beams large differences occur between ionization with unidirectional beams and with counterpropagating laser beams when |Δk rb |much-gt 1, where b is the confocal parameter of the focused laser beams. Strong absorption of the four-wave-mixing field is shown not to be necessary for strong destructive interference with focused laser beams when the phase mismatch is large. This work also suggests an explanation for earlier experiments where the presence of a four-photon resonance enabled the generation of third-harmonic light in a positively dispersive wavelength region. We argue that this process can occur when the laser used to achieve the four-photon resonance is focused on the small z (z is the coordinate in the direction of propagation) side of the focal point of the laser responsible for the third-harmonic generation
Wiebold, Matthew D.
Time-averaged plasma potential differences up to ˜ 165 V over several hundred Debye lengths are observed in low pressure (pn floating potential for argon (Vp ≈ 5kTe/e). In the capacitive mode, the ion acceleration is not well described by an ambipolar relation. The accelerated population decay is consistent with that predicted by charge-exchange collisions. Grounding the upstream endplate increases the self-bias voltage compared to a floating endplate. In the inductive and helicon modes, the ion acceleration more closely follows an ambipolar relation, a result of decreased capacitive coupling due to the decreased RF skin depth. The scaling of the potential gradient with the argon flow rate, magnetic field and RF power are investigated, with the highest potential gradients observed for the lowest flow rates in the capacitive mode. The magnitude of the self-bias voltage agrees well with that predicted for RF sheaths. Use of the self-bias effect in a plasma thruster is explored, possibly for a low thrust, high specific impulse mode in a multi-mode helicon thruster. This work could also explain similar potential gradients in expanding helicon plasmas that are ascribed to double layer formation in the literature.
International Nuclear Information System (INIS)
Boudjema, F.; Djouadi, A.; Kneur, J.L.
1992-01-01
The production of excited fermions with mass above 100 GeV is considered. f→Vf (1) decay widths are calculated where V=γ, Z or W. Excited fermion pair production in e + e - annihilation and in γγ collisions, and single production in e + e - annihilation, eγ and γγ collisions is also discussed. Cross sections are calculated for all these cases. The discovery potential of the NLC at 500 GeV is compared with that of other colliders. (K.A.) 15 refs., 5 figs., 2 tabs
Chen, Zhenhua; Chen, Xun; Wu, Wei
2013-04-01
In this series, the n-body reduced density matrix (n-RDM) approach for nonorthogonal orbitals and their applications to ab initio valence bond (VB) methods are presented. As the first paper of this series, Hamiltonian matrix elements between internally contracted VB wave functions are explicitly provided by means of nonorthogonal orbital based RDM approach. To this end, a more generalized Wick's theorem, called enhanced Wick's theorem, is presented both in arithmetical and in graphical forms, by which the deduction of expressions for the matrix elements between internally contracted VB wave functions is dramatically simplified, and the matrix elements are finally expressed in terms of tensor contractions of electronic integrals and n-RDMs of the reference VB self-consistent field wave function. A string-based algorithm is developed for the purpose of evaluating n-RDMs in an efficient way. Using the techniques presented in this paper, one is able to develop new methods and efficient algorithms for nonorthogonal orbital based many-electron theory much easier than by use of the first quantized formulism.
International Nuclear Information System (INIS)
Zhang, Hong Lin; Sampson, D. H.
1989-02-01
Relativistic distorted wave collision strengths are given for the 88 possible transitions between the ground level and the excited levels with n = 3 and n = 4 in the 71 neon-like ions with nuclear charge number Z in the range 22 ≤ Z ≤ 92. The calculations are made for the six final, or scattered, electron energies E' = 0.008, 0.04, 0.10, 0.21, 0.41 and 0.75, where E' is in units of Z/sub eff/ 2 Rydbergs with Z/sub eff/ = Z /minus/ 7.5. In addition, the transition energies and electric dipole oscillator strengths are given. 10 refs., 4 tabs
International Nuclear Information System (INIS)
Krebs, H.; Epelbaum, E.; Meissner, U.G.
2007-01-01
We study the two-nucleon force at next-to-next-to-leading order in a chiral effective field theory with explicit Δ degrees of freedom. Fixing the appearing low-energy constants from a next-to-leading-order calculation of pion-nucleon threshold parameters, we find an improved convergence of most peripheral nucleon-nucleon phases compared to the theory with pions and nucleons only. In the delta-full theory, the next-to-leading-order corrections are dominant in most partial waves considered. (orig.)
Fundamentals of wave phenomena
Hirose, Akira
2010-01-01
This textbook provides a unified treatment of waves that either occur naturally or can be excited and propagated in various media. This includes both longitudinal and transverse waves. The book covers both mechanical and electrical waves, which are normally covered separately due to their differences in physical phenomena.
Ion acceleration in a helicon source due to the self-bias effect
International Nuclear Information System (INIS)
Wiebold, Matt; Sung, Yung-Ta; Scharer, John E.
2012-01-01
Time-averaged plasma potential differences up to 165 V over several hundred Debye lengths are observed in low pressure (p n i ≈ 7 kT e in some cases. RF power up to 500 W at 13.56 MHz is supplied to a half-turn, double-helix antenna in the presence of a nozzle magnetic field, adjustable up to 1 kG. A retarding potential analyzer (RPA) measures the ion energy distribution function (IEDF) and a swept emissive probe measures the plasma potential. Single and double probes measure the electron density and temperature. Two distinct mode hops, the capacitive-inductive (E-H) and inductive-helicon (H-W) transitions, are identified by jumps in density as RF power is increased. In the capacitive (E) mode, large fluctuations of the plasma potential (V p-p ≳140V, V p-p /V p ≈150%) exist at the RF frequency and its harmonics. The more mobile electrons can easily respond to RF-timescale gradients in the plasma potential whereas the inertially constrained ions cannot, leading to an initial flux imbalance and formation of a self-bias voltage between the source and expansion chambers. In the capacitive mode, the ion acceleration is not well described by an ambipolar relation, while in the inductive and helicon modes the ion acceleration more closely follows an ambipolar relation. The scaling of the potential gradient with the argon flow rate and RF power are investigated, with the largest potential gradients observed for the lowest flow rates in the capacitive mode. The magnitude of the self-bias voltage agrees with that predicted for RF self-bias at a wall. Rapid fluctuations in the plasma potential result in a time-dependent axial electron flux that acts to “neutralize” the accelerated ion population, resulting in a zero net time-averaged current through the acceleration region when an insulating upstream boundary condition is enforced. Grounding the upstream endplate increases the self-bias voltage compared to a floating endplate.
International Nuclear Information System (INIS)
Mukhopadhyay, N.C.
1986-01-01
The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested
Energy Technology Data Exchange (ETDEWEB)
Mukhopadhyay, N.C.
1986-01-01
The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested. (LEW)
Fung, Shing F.; Vinas, Adolfo F.
1994-01-01
The electron cyclotron maser instability (CMI) driven by momentum space anisotropy (df/dp (sub perpendicular) greater than 0) has been invoked to explain many aspects, such as the modes of propagation, harmonic emissions, and the source characteristics of the auroral kilometric radiation (AKR). Recent satellite observations of AKR sources indicate that the source regions are often imbedded within the auroral acceleration region characterized by the presence of a field-aligned potential drop. In this paper we investigate the excitation of the fundamental extraordinary mode radiation due to the accelerated electrons. The momentum space distribution of these energetic electrons is modeled by a realistic upward loss cone as modified by the presence of a parallel potential drop below the observation point. On the basis of linear growth rate calculations we present the emission characteristics, such as the frequency spectrum and the emission angular distribution as functions of the plasma parameters. We will discuss the implication of our results on the generation of the AKR from the edges of the auroral density cavities.
Numerical simulation of current-free double layers created in a helicon plasma device
Rao, Sathyanarayan; Singh, Nagendra
2012-09-01
Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E⊥) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E⊥ on the high potential side of the double layer in the CFDL. The accelerated ions are trapped near the conical surface, where E⊥ reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop (φ||o) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.
On-axis parallel ion speeds near mechanical and magnetic apertures in a helicon plasma device
International Nuclear Information System (INIS)
Sun Xuan; Cohen, S.A.; Scime, Earl E.; Miah, Mahmood
2005-01-01
Using laser-induced fluorescence, measurements of parallel ion velocities were made along the axis of a helicon-generated Ar plasma column whose radius was modified by spatially separated mechanical and magnetic apertures. Ion acceleration to supersonic speeds was observed 0.1-5 cm downstream of both aperture types, simultaneously generating two steady-state double layers (DLs) when both apertures were in place. The DL downstream of the mechanical aperture plate had a larger potential drop, Δφ DL =6-9 kT e , compared to the DL downstream of the magnetic aperture, Δφ DL ∼3 kT e . In the presheath region upstream of the mechanical aperture, the convective ion speed increased over a collisional distance; from stagnant at 4 cm from the aperture to the 1.4 times the sound speed at the aperture. The dependence of the free- and trapped-ion-velocity-distribution functions on the magnetic-field strength and mechanical-aperture electrical bias are also presented
High-beta plasma effects in a low-pressure helicon plasma
International Nuclear Information System (INIS)
Corr, C. S.; Boswell, R. W.
2007-01-01
In this work, high-beta plasma effects are investigated in a low-pressure helicon plasma source attached to a large volume diffusion chamber. When operating above an input power of 900 W and a magnetic field of 30 G a narrow column of bright blue light (due to Ar II radiation) is observed along the axis of the diffusion chamber. With this blue mode, the plasma density is axially very uniform in the diffusion chamber; however, the radial profiles are not, suggesting that a large diamagnetic current might be induced. The diamagnetic behavior of the plasma has been investigated by measuring the temporal evolution of the magnetic field (B z ) and the plasma kinetic pressure when operating in a pulsed discharge mode. It is found that although the electron pressure can exceed the magnetic field pressure by a factor of 2, a complete expulsion of the magnetic field from the plasma interior is not observed. In fact, under our operating conditions with magnetized ions, the maximum diamagnetism observed is ∼2%. It is observed that the magnetic field displays the strongest change at the plasma centre, which corresponds to the maximum in the plasma kinetic pressure. These results suggest that the magnetic field diffuses into the plasma sufficiently quickly that on a long time scale only a slight perturbation of the magnetic field is ever observed
Injection of a coaxial-gun-produced magnetized plasma into a background helicon plasma
Zhang, Yue; Lynn, Alan; Gilmore, Mark; Hsu, Scott
2014-10-01
A compact coaxial plasma gun is employed for experimental investigation of plasma bubble relaxation into a lower density background plasma. Experiments are being conducted in the linear device HelCat at UNM. The gun is powered by a 120-uF ignitron-switched capacitor bank, which is operated in a range of 5 to 10 kV and 100 kA. Multiple diagnostics are employed to investigate the plasma relaxation process. Magnetized argon plasma bubbles with velocities 1.2Cs, densities 1020 m-3 and electron temperature 13eV have been achieved. The background helicon plasma has density 1013 m-3, magnetic field from 200 to 500 Gauss and electron temperature 1eV. Several distinct operational regimes with qualitatively different dynamics are identified by fast CCD camera images. Additionally a B-dot probe array has been employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify plasma bubble configurations. Experimental data and analysis will be presented.
Consideration of neutral beam prompt loss in the design of a tokamak helicon antenna
International Nuclear Information System (INIS)
Pace, D.C.; Van Zeeland, M.A.; Fishler, B.; Murphy, C.
2016-01-01
Highlights: • Neutral beam prompt losses place appreciable power on an in-vessel tokamak antenna. • Simulations predict prompt loss power and inform protective tile design. • Experiments confirm the validity of the prompt loss simulations. - Abstract: Neutral beam prompt losses (injected neutrals that ionize such that their first poloidal transit intersects with the wall) can put appreciable power on the outer wall of tokamaks, and this power may damage the wall or other internal components. These prompt losses are simulated including a protruding helicon antenna installation in the DIII-D tokamak and it is determined that 160 kW of power will impact the antenna during the injection of a particular neutral beam. Protective graphite tiles are designed in response to this modeling and the wall shape of the installed antenna is precisely measured to improve the accuracy of these calculations. Initial experiments confirm that the antenna component temperature increases according to the amount of neutral beam energy injected into the plasma. In this case, only injection of beams that are aimed counter to the plasma current produce an appreciable power load on the outer wall, suggesting that the effect is of little concern for tokamaks featuring only co-current neutral beam injection. Incorporating neutral beam prompt loss considerations into the design of this in-vessel component serves to ensure that adequate protection or cooling is provided.
Consideration of neutral beam prompt loss in the design of a tokamak helicon antenna
Energy Technology Data Exchange (ETDEWEB)
Pace, D.C., E-mail: pacedc@fusion.gat.com; Van Zeeland, M.A.; Fishler, B.; Murphy, C.
2016-11-15
Highlights: • Neutral beam prompt losses place appreciable power on an in-vessel tokamak antenna. • Simulations predict prompt loss power and inform protective tile design. • Experiments confirm the validity of the prompt loss simulations. - Abstract: Neutral beam prompt losses (injected neutrals that ionize such that their first poloidal transit intersects with the wall) can put appreciable power on the outer wall of tokamaks, and this power may damage the wall or other internal components. These prompt losses are simulated including a protruding helicon antenna installation in the DIII-D tokamak and it is determined that 160 kW of power will impact the antenna during the injection of a particular neutral beam. Protective graphite tiles are designed in response to this modeling and the wall shape of the installed antenna is precisely measured to improve the accuracy of these calculations. Initial experiments confirm that the antenna component temperature increases according to the amount of neutral beam energy injected into the plasma. In this case, only injection of beams that are aimed counter to the plasma current produce an appreciable power load on the outer wall, suggesting that the effect is of little concern for tokamaks featuring only co-current neutral beam injection. Incorporating neutral beam prompt loss considerations into the design of this in-vessel component serves to ensure that adequate protection or cooling is provided.
Uniform magnetic excitations in nanoparticles
DEFF Research Database (Denmark)
Mørup, Steen; Hansen, Britt Rosendahl
2005-01-01
We have used a spin-wave model to calculate the temperature dependence of the (sublattice) magnetization of magnetic nanoparticles. The uniform precession mode, corresponding to a spin wave with wave vector q=0, is predominant in nanoparticles and gives rise to an approximately linear temperature...... dependence of the (sublattice) magnetization well below the superparamagnetic blocking temperature for both ferro-, ferri-, and antiferromagnetic particles. This is in accordance with the results of a classical model for collective magnetic excitations in nanoparticles. In nanoparticles of antiferromagnetic...... materials, quantum effects give rise to a small deviation from the linear temperature dependence of the (sublattice) magnetization at very low temperatures. The complex nature of the excited precession states of nanoparticles of antiferromagnetic materials, with deviations from antiparallel orientation...
DEFF Research Database (Denmark)
Clausen, Kurt Nørgaard; Lebech, Bente
1980-01-01
Spin wave excitations in a single crystal of Ho2Co17 have been studied at 4.8 and 78 K. The results are discussed in terms of a linear spin wave model. At 78 K both ground state and excited state spin waves are observed.......Spin wave excitations in a single crystal of Ho2Co17 have been studied at 4.8 and 78 K. The results are discussed in terms of a linear spin wave model. At 78 K both ground state and excited state spin waves are observed....
On Emulation of Flueric Devices in Excitable Chemical Medium.
Directory of Open Access Journals (Sweden)
Andrew Adamatzky
Full Text Available Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies.
On Emulation of Flueric Devices in Excitable Chemical Medium.
Adamatzky, Andrew
2016-01-01
Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ) medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies.
Energy Technology Data Exchange (ETDEWEB)
Imai, Y [Hiroshima University, Hiroshima (Japan); Okusu, M [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1997-12-31
A method to predict drift force acting on a floating structure has been developed for a marine structure consisting of a number of floating elements, positioned in a region having a slope at the sea bottom. When a huge marine structure, such as floating air port, is located in a coastal area, scale of the overall structure is very large, of the order of scale of water depth change. The new method assumes that a marine structure consisting of an infinite number of cylindrical floating elements is installed in parallel to the seashore, where symmetrical nature of the configuration allows to predict behavior of the whole system by analyzing one element. Integration of pressures acting on structure surfaces determines the horizontal component of the drift force acting on the structure. Being influenced by topography, drift force predicted peaks at a frequency different from that for the level predicted on the assumption of constant water depth. This indicates the necessity for consideration of seabottom slope and effects of broken waves at the seashore. 6 refs., 12 figs.
Energy Technology Data Exchange (ETDEWEB)
Imai, Y. [Hiroshima University, Hiroshima (Japan); Okusu, M. [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1996-12-31
A method to predict drift force acting on a floating structure has been developed for a marine structure consisting of a number of floating elements, positioned in a region having a slope at the sea bottom. When a huge marine structure, such as floating air port, is located in a coastal area, scale of the overall structure is very large, of the order of scale of water depth change. The new method assumes that a marine structure consisting of an infinite number of cylindrical floating elements is installed in parallel to the seashore, where symmetrical nature of the configuration allows to predict behavior of the whole system by analyzing one element. Integration of pressures acting on structure surfaces determines the horizontal component of the drift force acting on the structure. Being influenced by topography, drift force predicted peaks at a frequency different from that for the level predicted on the assumption of constant water depth. This indicates the necessity for consideration of seabottom slope and effects of broken waves at the seashore. 6 refs., 12 figs.
Seismic excitation by space shuttles
Kanamori, H.; Mori, J.; Sturtevant, B.; Anderson, D.L.; Heaton, T.
1992-01-01
Shock waves generated by the space shuttles Columbia (August 13, 1989), Atlantis (April 11, 1991) and Discovery (September 18, 1991) on their return to Edwards Air Force Base, California, were recorded by TERRAscope (Caltech's broadband seismic network), the Caltech-U.S.G.S Southern California Seismic Network (SCSN), and the University of Southern California (USC) Los Angeles Basin Seismic Network. The spatial pattern of the arrival times exhibits hyperbolic shock fronts from which the path, velocity and altitude of the space shuttle could be determined. The shock wave was acoustically coupled to the ground, converted to a seismic wave, and recorded clearly at the broadband TERRAscope stations. The acoustic coupling occurred very differently depending on the conditions of the Earth's surface surrounding the station. For a seismic station located on hard bedrock, the shock wave (N wave) was clearly recorded with little distortion. Aside from the N wave, very little acoustic coupling of the shock wave energy to the ground occurred at these sites. The observed N wave record was used to estimate the overpressure of the shock wave accurately; a pressure change of 0.5 to 2.2 mbars was obtained. For a seismic station located close to the ocean or soft sedimentary basins, a significant amount of shock wave energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave. A distinct topography such as a mountain range was found effective to couple the shock wave energy to the ground. Shock wave energy was also coupled to the ground very effectively through large man made structures such as high rise buildings and offshore oil drilling platforms. For the space shuttle Columbia, in particular, a distinct pulse having a period of about 2 to 3 seconds was observed, 12.5 s before the shock wave, with a broadband seismograph in Pasadena. This pulse was probably excited by the high rise buildings in downtown Los Angeles which were
Mechanism of spiral formation in heterogeneous discretized excitable media.
Kinoshita, Shu-ichi; Iwamoto, Mayuko; Tateishi, Keita; Suematsu, Nobuhiko J; Ueyama, Daishin
2013-06-01
Spiral waves on excitable media strongly influence the functions of living systems in both a positive and negative way. The spiral formation mechanism has thus been one of the major themes in the field of reaction-diffusion systems. Although the widely believed origin of spiral waves is the interaction of traveling waves, the heterogeneity of an excitable medium has recently been suggested as a probable cause. We suggest one possible origin of spiral waves using a Belousov-Zhabotinsky reaction and a discretized FitzHugh-Nagumo model. The heterogeneity of the reaction field is shown to stochastically generate unidirectional sites, which can induce spiral waves. Furthermore, we found that the spiral wave vanished with only a small reduction in the excitability of the reaction field. These results reveal a gentle approach for controlling the appearance of a spiral wave on an excitable medium.
Energy Technology Data Exchange (ETDEWEB)
Pandey, Arun; Sudhir, Dass; Bandyopadhyay, M., E-mail: mainak@iter-india.org; Chakraborty, A.
2016-02-15
A conceptual design of a permanent magnet based single driver helicon plasma source module along with its design approach is described in this paper. The module unit is intended to be used in a large size ion source. The conceptual design of the helicon source module has been carried out using a computer code, HELIC. The magnetic field topology for the ring magnet is simulated with another code, BFieldM and the magnetic field values obtained from the calculation are further used as input in HELIC calculation for the conceptual design. The module is conceptualized based on a cylindrical glass vessel to produce plasma of diameter ∼50 mm, height ∼50 mm. The inner diameter of the permanent ring magnets is also of the same dimension with thickness ∼10 mm each, placed slightly above the backplate to maintain the required magnetic field. The simulated results show that for hydrogen gas, expected plasma density can be achieved as high as ∼10{sup 12}–10{sup 13} cm{sup −3} in the proposed helicon source configuration using 1 kW 13.56 MHz RF generator. An experimental setup to characterize a Helicon source module unit, consisting of a cylindrical glass (plasma) chamber along with the vacuum system, RF power supplies, probes and data acquisition system is being installed.
Computing correct truncated excited state wavefunctions
Bacalis, N. C.; Xiong, Z.; Zang, J.; Karaoulanis, D.
2016-12-01
We demonstrate that, if a wave function's truncated expansion is small, then the standard excited states computational method, of optimizing one "root" of a secular equation, may lead to an incorrect wave function - despite the correct energy according to the theorem of Hylleraas, Undheim and McDonald - whereas our proposed method [J. Comput. Meth. Sci. Eng. 8, 277 (2008)] (independent of orthogonality to lower lying approximants) leads to correct reliable small truncated wave functions. The demonstration is done in He excited states, using truncated series expansions in Hylleraas coordinates, as well as standard configuration-interaction truncated expansions.
Simulation and laboratory validation of magnetic nozzle effects for the high power helicon thruster
International Nuclear Information System (INIS)
Winglee, R.; Ziemba, T.; Giersch, L.; Prager, J.; Carscadden, J.; Roberson, B. R.
2007-01-01
The efficiency of a plasma thruster can be improved if the plasma stream can be highly focused, so that there is maximum conversion of thermal energy to the directed energy. Such focusing can be potentially achieved through the use of magnetic nozzles, but this introduces the potential problem of detachment of plasma from the magnetic field lines tied to the nozzles. Simulations and laboratory testing are used to investigate these processes for the high power helicon (HPH) thruster, which has the capacity of producing a dense (10 18 -10 20 m -3 ) energetic (tens of eV) plasma stream which can be both supersonic and super-Alfvenic within a few antenna wavelengths. In its standard configuration, the plasma plume generated by this device has a large opening angle, due to relatively high thermal velocity and rapid divergence of the magnetic field. With the addition of a magnetic nozzle system, the plasma can be directed/collimated close to the pole of the nozzle system causing an increase in the axial velocity of the plasma, as well as an increase in the Alfven Mach number. As such the magnetic field of the nozzle is insufficient to pull the plasma back to the spacecraft, i.e., plasma attachment is not a problem for the system. Laboratory results show that the specific impulse (Isp) of the system can be increased by ∼30% by the addition of the nozzle due to the conversion of thermal energy into directed energy in association with a highly collimated profile. An interesting feature of the system is that self-collimation of the beam is expected to occur during continuous operation through plasma currents induced downstream from the magnetic nozzle. These currents lead to magnetic fields that have a smaller divergence than the original vacuum magnetic field so that the following plasma will be more collimated than the proceeding plasma. This self-focusing can lead to beam propagation over extended distances
Energy Technology Data Exchange (ETDEWEB)
Gulbrandsen, N., E-mail: njal.gulbrandsen@uit.no; Fredriksen, Å. [Department of Physics and Technology, UiT The Arctic University of Norway, 9037 Tromsø (Norway); Carr, J. [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States); Department of Physics, Texas Lutheran University, Seguin, Texas 78155 (United States); Scime, E. [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States)
2015-03-15
Both Laser-Induced Fluorescence (LIF) and Retarding Field Energy Analyzers (RFEA) have been applied to the investigation of beams formed in inductively coupled helicon plasmas. While the LIF technique provides a direct measurement of the velocity distribution in the plasma, the RFEA measures ion flux as a function of a retarding potential. In this paper, we present a method to compare the two techniques, by converting the LIF velocity distribution to an equivalent of a RFEA measurement. We applied this method to compare new LIF and RFEA measurements in two different experiments; the Hot Helicon Experiment (HELIX) - Large Experiment on Instabilities and Anisotropies (LEIA) at West Virginia University and Njord at University of Tromsø. We find good agreement between beam energies of the two methods. In agreement with earlier observations, the RFEA is found to measure ion beams with densities too low for the LIF to resolve. In addition, we present measurements of the axial development of the ion beam in both experiments. Beam densities drop exponentially with distance from the source, both in LIF and RFEA measurements. The effective quenching cross section from LIF in LEIA is found to be σ{sub b,*}=4×10{sup −19} m{sup 2}, and the effective beam collisional cross sections by RFEA in Njord to be σ{sub b}=1.7×10{sup −18} m{sup 2}.
Yadav, Sonu; Ghosh, Soumen; Bose, Sayak; Barada, Kshitish K.; Pal, Rabindranath; Chattopadhyay, Prabal K.
2018-04-01
Experimentally, the density profile in the magnetic nozzle of a helicon antenna based plasma device is seen to be modified from being centrally peaked to that of hollow nature as the external magnetic field is increased. It occurs above a characteristic field value when the ions become magnetized in the expansion chamber. The density profile in the source chamber behind the nozzle, however, remains peaked on-axis irrespective of the magnetic field. The electron temperature there is observed to be hollow and this nature is carried to the expansion chamber along the field line. In the electron energy distribution near the off axis peak location, a high energy tail exists. Rotation of these tail electrons in the azimuthal direction due to the gradient-B drift in the expansion chamber leads to an additional off-axis ionization and forms the hollow density profile. It seems that if the ions are not magnetized, then the off-axially produced additional plasma is not confined and the density profile retains the on-axis peak nature. The present experiment successfully demonstrates how the knowledge of the ion magnetization together with tail electrons significantly contributes to the design of an efficient helicon plasma based thruster.
The optical properties and applications of AlN thin films prepared by a helicon sputtering system
Chiu, W Y; Kao, H L; Jeng, E S; Chen, J S; Jaing, C C
2002-01-01
AlN thin films were grown on SiO sub 2 /Si and quartz substrates using a helicon sputtering system. The dependence of film quality on growth parameters, such as total sputtering pressure, substrate temperature, and nitrogen concentration has been studied. There is a good correlation of thin film crystallinity addressed by x-ray diffraction (XRD) and spectroscopic ellipsometer. The optimized films exhibit highly oriented, with only (002) peak shown in a theta-2 theta scan XRD pattern, and extremely smooth surface with rms roughness of 2 Aa. The extinction coefficient of the film was 4x10 sup - sup 4 , which is lower than that of AlN films grown by conventional sputtering. Double-layer antireflection (DLAR) coating using AlN and Al sub 3 O sub 3 grown on quartz has been demonstrated. The transmittance of DLAR was high as 96% compared to 93% of bare substrates with the measurement error less than 0.2%. AlN films prepared by Helicon sputtering thus are potential for optical application.
Vector boson excitations near deconfined quantum critical points.
Huh, Yejin; Strack, Philipp; Sachdev, Subir
2013-10-18
We show that the Néel states of two-dimensional antiferromagnets have low energy vector boson excitations in the vicinity of deconfined quantum critical points. We compute the universal damping of these excitations arising from spin-wave emission. Detection of such a vector boson will demonstrate the existence of emergent topological gauge excitations in a quantum spin system.
Alfven wave propagation in a partially ionized plasma
International Nuclear Information System (INIS)
Watts, Christopher; Hanna, Jeremy
2004-01-01
Results from a laboratory study of the dispersion relation of Alfven waves propagating through a partially ionized plasma are presented. The plasma is generated using a helicon source, creating a high density, current-free discharge, where the source can be adjusted to one of several modes with varying neutral fraction. Depending on the neutral fraction, the measured dispersion curve of shear Alfven waves can change significantly. Measurement results are compared with theoretical predictions of the effect of neutral particles on Alfven wave propagation. In fitting the theory, the neutral fraction is independently estimated using two simple particle transport models, one collisionless, the other collisional. The two models predict comparable neutral fractions, and agree well with the neutral fraction required for the Alfven dispersion theory
More about orbitally excited hadrons from lattice QCD
International Nuclear Information System (INIS)
DeGrand, T.A.; Hecht, M.W.
1992-01-01
This is the second of two papers describing the calculation of spectroscopy for orbitally excited states from lattice simulations of quantum chromodynamics. New features include higher statistics for P-wave systems and first results for the spectroscopy of D-wave mesons and baryons, for relatively heavy-quark masses. We parametrize the Coulomb gauge wave functions for P- and D-wave systems and compare them to those of their corresponding S-wave states
International Nuclear Information System (INIS)
Goree, J.; Ono, M.; Colestock, P.; Horton, R.; McNeill, D.; Park, H.
1985-07-01
Fast wave current drive is demonstrated in the Princeton ACT-I toroidal device. The fast Alfven wave, in the range of high ion-cyclotron harmonics, produced 40 A of current from 1 kW of rf power coupled into the plasma by fast wave loop antenna. This wave excites a steady current by damping on the energetic tail of the electron distribution function in the same way as lower-hybrid current drive, except that fast wave current drive is appropriate for higher plasma densities
RF compensation of single Langmuir probe in low density helicon plasma
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Soumen, E-mail: soumen@ipr.res.in; Chattopadhyay, Prabal K.; Ghosh, Joydeep; Bora, Dhiraj
2016-11-15
Highlights: • Appropriate density and temperature measurement with Langmuir probe in RF Eenvironment. • Necessity of large auxiliary electrode for RF compensation at low densities (∼10{sup 16} m{sup −3}). • Measured two temperature electrons in low pressure helicon antenna produced RF plasma. • Tail electrons are localized only at off-axis in our cylindrical plasma system. - Abstract: Interpretations of Single Langmuir probe measurements in electrode-less radio frequency (RF) plasmas are noteworthy tricky and require adequate compensation of RF. Conventional RF compensation technique is limited only at high density (>10{sup 17} m{sup −3}) RF plasmas. RF compensation of single Langmuir probe at low density RF plasmas (∼10{sup 16} m{sup −3}) is presented in this paper. In RF driven plasmas, where the RF voltage is high (∼50 V) and density is in the range (∼10{sup 16} m{sup −3}), the primary RF compensation condition (Z{sub ck} > >Z{sub sh}) is very difficult to fulfill, because of high sheath impedance (Z{sub sh}) at 13.56 MHz and the construction limitation of a self-resonant tiny chock (Z{sub ck}) with very high impedance. Introducing a large auxiliary electrode (A{sub x}), (A{sub x} >>> A{sub p}), close to the small Langmuir probe (A{sub p}) tip, connected in parallel with probe via a coupling capacitor (C{sub cp}), significantly reduces the effective sheath impedance (Z{sub sh}) and allows probe bias to follow the RF oscillation. Dimensional requirements of the auxiliary electrode and the role of suitable coupling capacitor are discussed in this paper. Observations show proper compensation leads to estimation of more positive floating potentials and lower electron temperatures compared to uncompensated probe. The electron energy probability function (EEPF) is also obtained by double differentiating the collected current with respect to the applied bias voltage using an active analog circuit.
Experimental Uncertainty Associated with Traveling Wave Excitation
2014-09-15
center. The rotor was machined from a 3.24 mm thick, precision ground 4140 steel plate. The disk has a diameter of 300 mm and the blades are 92 mm...bladed disk,” Journal of Engineering for Gas Turbines and Power, vol. 123, pp. 940–950, 2001. [10] 40th AIAA/ASME/ SAE /ASEE Joint Propulsion Conference
Study of Ion Acoustic Wave Damping through Green's Functions
DEFF Research Database (Denmark)
Hsuan, H.C.S.; Jensen, Vagn Orla
1973-01-01
Green's function analyses of ion acoustic waves in streaming plasmas show that, in general, the waves damp algebraically rather than exponentially with distance from exciter.......Green's function analyses of ion acoustic waves in streaming plasmas show that, in general, the waves damp algebraically rather than exponentially with distance from exciter....
Two-photon excitation of argon
International Nuclear Information System (INIS)
Pindzola, P.S.; Payne, M.C.
1982-01-01
The authors calculate two photon excitation parameters for various excited states of argon assuming the absorption of near resonance broad-bandwidth laser radiation. Results are given for the case of two photons absorbed for the same laser beam as well as the case of absorbing photons of different frequency from each of two laser beams. The authors use multiconfiguration Hartree-Fock wave functions to evaluate the second-order sums over matrix elements. Various experimental laser schemes are suggested for the efficient excitation and subsequent ionization of argon
Switchable directional excitation surface plasmon polaritons with dielectric nanoantennas
DEFF Research Database (Denmark)
Sinev, I.; Komissarenko, F.; Bogdanov, A.
We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic and elect......We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic...
Fractal effects on excitations in diluted ferromagnets
International Nuclear Information System (INIS)
Kumar, D.
1981-08-01
The low energy spin-wave like excitations in diluted ferromagnets near percolation threshold are studied. For this purpose an explicit use of the fractal model for the backbone of the infinite percolating cluster due to Kirkpatrick is made. Three physical effects are identified, which cause the softening of spin-waves as the percolation point is approached. The importance of fractal effects in the calculation of density of states and the low temperature thermodynamics is pointed out. (author)
Study on Excitation-triggered Damage Mechanism in Perilous Rock
Chen, Hongkai; Wang, Shengjuan
2017-12-01
Chain collapse is easy to happen for perilous rock aggregate locating on steep high slope, and one of the key scientific problems is the damage mechanism of perilous rock under excitation action at perilous rock rupture. This paper studies excitation-triggered damage mechanism in perilous rock by wave mechanics, which gives three conclusions. Firstly, when only the normal incidence attenuation spread of excitation wave is considered, while the energy loss is ignored for excitation wave to spread in perilous rock aggregate, the paper establishes one method to calculate peak velocity when excitation wave passes through boundary between any two perilous rock blocks in perilous rock aggregate. Secondly, following by Sweden and Canmet criteria, the paper provides one wave velocity criterion for excitation-triggered damage in the aggregate. Thirdly, assuming double parameters of volume strain of cracks or fissures in rock meet the Weibull distribution, one method to estimate micro-fissure in excitation-triggered damage zone in perilous rock aggregate is established. The studies solve the mechanical description problem for excitation-triggered damage in perilous rock, which is valuable in studies on profoundly rupture mechanism.
Magnetic excitations in ferromagnetic semiconductors
International Nuclear Information System (INIS)
Furdyna, J.K.; Liu, X.; Zhou, Y.Y.
2009-01-01
Magnetic excitations in a series of GaMnAs ferromagnetic semiconductor films were studied by ferromagnetic resonance (FMR). Using the FMR approach, multi-mode spin wave resonance spectra have been observed, whose analysis provides information on magnetic anisotropy (including surface anisotropy), distribution of magnetization precession within the GaMnAs film, dynamic surface spin pinning (derived from surface anisotropy), and the value of exchange stiffness constant D. These studies illustrate a combination of magnetism and semiconductor physics that is unique to magnetic semiconductors
Electronic excitation in ion-atom collisions
International Nuclear Information System (INIS)
Rodriguez, V.D.; Miraglia, J.E.
1988-01-01
Theoretical calculations for excitation of hydrogen-like atoms by ion impact at high and intermediate energies, are presented. Impulsive and eikonal wave functions are employed, both normalized. It is studied the dependence on energy and projectil charge (saturation) of cross sections, compared to experimental results. (A.C.A.S.) [pt
Coherent acoustic excitation of cavity polaritons
DEFF Research Database (Denmark)
Poel, Mike van der; de Lima, M. M.; Hey, R.
The study of acoustic excitation of semiconductor based photonic structures is anemerging field with great potential for new types of photonic manipulation1. In this paperwe present results of using a surface acoustic wave (SAW) to modulate a microcavitywith embedded quantum-well (QW) active layer...
Topics in magnetism: magnetic excitations in insulators
International Nuclear Information System (INIS)
Rezende, S.M.
1975-01-01
The concept of spin waves is introduced and green's functions formalism is used in connection with thermodynamic properties of ferromagnets. Simple features of magnons in ferromagnetic insulators are discussed and also of those with dipolar and anisotropic contributions in the hamiltonian. Magnons in more complex systems, e.g. antiferromagnetic crystals, are dealt with. Finally, excitation and detection of magnons are also discussed [pt
Baryon excitations in the bag model
International Nuclear Information System (INIS)
Jaffe, R.L.
1976-07-01
Two recent spectroscopic applications of the bag model are discussed. The first is a study of the place of multiquark states in meson and baryon spectroscopy, and the second is an attempt to sort out the P-wave baryon excitations in a bag model. 33 references
International Nuclear Information System (INIS)
Butler, J.N.; Shukla, S.
1995-05-01
The experimental status of excited charmed mesons is reviewed and is compared to theoretical expectations. Six states have been observed and their properties are consistent with those predicted for excited charmed states with orbital angular momentum equal to one
Beecher, L. C.; Williams, F. T.
1970-01-01
Gas-driven vibration exciter produces a sinusoidal excitation function controllable in frequency and in amplitude. It allows direct vibration testing of components under normal loads, removing the possibility of component damage due to high static pressure.
Younis, Mohammad I.
2016-01-01
Embodiments of multi-frequency excitation are described. In various embodiments, a natural frequency of a device may be determined. In turn, a first voltage amplitude and first fixed frequency of a first source of excitation can be selected
Collective excitations in itinerant spiral magnets
International Nuclear Information System (INIS)
Kampf, A.P.
1996-01-01
We investigate the coupled charge and spin collective excitations in the spiral phases of the two-dimensional Hubbard model using a generalized random-phase approximation. Already for small doping the spin-wave excitations are strongly renormalized due to low-energy particle-hole excitations. Besides the three Goldstone modes of the spiral state the dynamical susceptibility reveals an extra zero mode for low doping and strong coupling values signaling an intrinsic instability of the homogeneous spiral state. In addition, near-zero modes are found in the vicinity of the spiral pitch wave number for out-of-plane spin fluctuations. Their origin is found to be the near degeneracy with staggered noncoplanar spiral states which, however, are not the lowest energy Hartree-Fock solutions among the homogeneous spiral states. copyright 1996 The American Physical Society
Investigation of bulk acoustic microwaves excited by an interdigital transducer
Directory of Open Access Journals (Sweden)
Reshotka O. G.
2015-12-01
Full Text Available Excitation of bulk and surface acoustic waves with the interdigital transducer (IDT, which is deposited on the surface of piezoelectric crystal, is widely used in the development of devices in acoustoelectronics and in the design of the microwave acousto-optic deflectors. Excitation of bulk acoustic waves by IDT in the devices on surface acoustic waves leads to the appearance of spurious signals. At the same time excitation of bulk acoustic waves with IDT from the surface of lithium niobate crystals allows creating high frequency acousto-optic deflectors, which makes possible to significantly simplify the technology of their production. Therefore, significant attention is paid to the task of excitation and distribution of bulk acoustic waves with IDT including recent times by the method of simulation of their excitation and distribution. The obtained theoretical results require experimental verification. This paper documents the visualization of acoustic beams excited with IDT from the XY-surface of lithium niobate crystals. The Bragg cells with LiNbO3 crystals coated with IDT with a different period of electrodes were manufactured for the experimental research of excitation and distribution of bulk acoustic waves. Visualization results have shown that the acoustic waves excited with IDT distribute in both the Fresnel zone and the Fraunhofer zone. The length of these zones is caused by individual elementary emitters of which consists the IDT (by their size. At the same time the far zone for IDT is located at distances much greater than the actual size of the LiNbO3 crystals. This peculiarity is not always taken into account when calculating diffraction. The achieved results can be used to design high-frequency acousto-optic devices, as well as in the development of devices based on surface acoustic waves.
Hydrodynamic Excitation Forces on Floating Structures with Finite Displacements
DEFF Research Database (Denmark)
Andersen, Morten Thøtt; Nielsen, Søren R. K.
2015-01-01
excitation force is solely a function of time, hence the body is fixed in reference to the wave field. In this paper, the instantaneous position of the body is included in the calculation of the excitation force. Even though the displacement of the structure relative to a characteristic wavelength...
Switchable directional excitation surface plasmon polaritons with dielectric nanoantennas
DEFF Research Database (Denmark)
Sinev, I.; Komissarenko, F.; Bogdanov, A.
2017-01-01
We demonstrate directional launching of surface plasmon polaritons on thin goldfilm with a single silicon nanosphere. The directivity pattern of the excited surface waves exhibits rapid switching from forward to backward excitation, which is driven by the mutual interference of magnetic and elect...... and electric dipole moments supported by the dielectric nanoantenna....
The effect of lower-hybrid waves on the propagation of hydromagnetic waves
International Nuclear Information System (INIS)
Hamabata, Hiromitsu; Namikawa, Tomikazu; Mori, Kazuhiro
1988-01-01
Propagation characteristics of hydromagnetic waves in a magnetic plasma are investigated using the two-plasma fluid equations including the effect of lower-hybrid waves propagating perpendicularly to the magnetic field. The effect of lower-hybrid waves on the propagation of hydromagnetic waves is analysed in terms of phase speed, growth rate, refractive index, polarization and the amplitude relation between the density perturbation and the magnetic-field perturbation for the cases when hydromagnetic waves propagate in the plane whose normal is perpendicular to both the magnetic field and the propagation direction of lower-hybrid waves and in the plane perpendicular to the propagation direction of lower-hybrid waves. It is shown that hydromagnetic waves propagating at small angles to the propagation direction of lower-hybrid waves can be excited by the effect of lower-hybrid waves and the energy of excited waves propagates nearly parallel to the propagation direction of lower-hybrid waves. (author)
Elementary excitations in nuclei
International Nuclear Information System (INIS)
Lemmer, R.H.
1987-01-01
The role of elementary quasi-particle and quasi-hole excitations is reviewed in connection with the analysis of data involving high-lying nuclear states. This article includes discussions on: (i) single quasi-hole excitations in pick-up reactions, (ii) the formation of single quasi-hole and quasi-particle excitations (in different nuclei) during transfer reactions, followed by (iii) quasi-particle quasi-hole excitations in the same nucleus that are produced by photon absorption. Finally, the question of photon absorption in the vicinity of the elementary Δ resonance is discussed, where nucleonic as well as nuclear degrees of freedom can be excited
International Nuclear Information System (INIS)
Yan, Zhenya
2011-01-01
The coupled nonlinear volatility and option pricing model presented recently by Ivancevic is investigated, which generates a leverage effect, i.e., stock volatility is (negatively) correlated to stock returns, and can be regarded as a coupled nonlinear wave alternative of the Black–Scholes option pricing model. In this Letter, we analytically propose vector financial rogue waves of the coupled nonlinear volatility and option pricing model without an embedded w-learning. Moreover, we exhibit their dynamical behaviors for chosen different parameters. The vector financial rogue wave (rogon) solutions may be used to describe the possible physical mechanisms for the rogue wave phenomena and to further excite the possibility of relative researches and potential applications of vector rogue waves in the financial markets and other related fields. -- Highlights: ► We investigate the coupled nonlinear volatility and option pricing model. ► We analytically present vector financial rogue waves. ► The vector financial rogue waves may be used to describe the extreme events in financial markets. ► This results may excite the relative researches and potential applications of vector rogue waves.
Younis, Mohammad I.
2016-03-10
Embodiments of multi-frequency excitation are described. In various embodiments, a natural frequency of a device may be determined. In turn, a first voltage amplitude and first fixed frequency of a first source of excitation can be selected for the device based on the natural frequency. Additionally, a second voltage amplitude of a second source of excitation can be selected for the device, and the first and second sources of excitation can be applied to the device. After applying the first and second sources of excitation, a frequency of the second source of excitation can be swept. Using the methods of multi- frequency excitation described herein, new operating frequencies, operating frequency ranges, resonance frequencies, resonance frequency ranges, and/or resonance responses can be achieved for devices and systems.
a simple a simple excitation control excitation control excitation
African Journals Online (AJOL)
eobe
field voltages determined follow a simple quadratic relationship that offer a very simple control scheme, dependent on only the stator current. Keywords: saturated reactances, no-load field voltage, excitation control, synchronous generators. 1. Introduction. Introduction. Introduction. The commonest generator in use today is ...
Takahashi, Kazunori; Ando, Akira
2017-05-01
Individual measurements of forces exerted to an upstream back wall, a radial source wall, and a magnetic field of a helicon plasma thruster, which has two solenoids upstream and downstream of a radiofrequency antenna, are precisely measured. Two different structures of magnetic field lines in the source are tested, where the solenoid current is supplied to either only the downstream solenoid or to both the solenoids. It is observed that the high density plasma exists upstream of the rf antenna when both the solenoids are powered, while the maximum density exists near the rf antenna when only the downstream solenoid is powered. Although the force exerted to the back wall is increased for the two solenoids case, the axial momentum lost to the radial wall is simultaneously enhanced; then the total force exerted to the whole structure of the thruster is found to be very similar for the two magnetic field configurations. It is shown that the individual force measurement provides useful information on the plasma momentum interacting with the physical boundaries and the magnetic fields.
Nonlinear Waves on Stochastic Support: Calcium Waves in Astrocyte Syncytia
Jung, P.; Cornell-Bell, A. H.
Astrocyte-signaling has been observed in cell cultures and brain slices in the form of Calcium waves. Their functional relevance for neuronal communication, brain functions and diseases is, however, not understood. In this paper, the propagation of intercellular calcium waves is modeled in terms of waves in excitable media on a stochastic support. We utilize a novel method to decompose the spatiotemporal patterns into space-time clusters (wave fragments). Based on this cluster decomposition, a statistical description of wave patterns is developed.
Leading edge effect in laminar boundary layer excitation by sound
International Nuclear Information System (INIS)
Leehey, P.; Shapiro, P.
1980-01-01
Essentially plane pure tone sound waves were directed downstream over a heavily damped smooth flat plate installed in a low turbulence (0.04%) subsonic wind tunnel. Laminar boundary layer disturbance growth rates were measured with and without sound excitation and compared with numerical results from spatial stability theory. The data indicate that the sound field and Tollmien-Schlichting (T-S) waves coexist with comparable amplitudes when the latter are damped; moreover, the response is linear. Higher early growth rates occur for excitation by sound than by stream turbulence. Theoretical considerations indicate that the boundary layer is receptive to sound excitation primarily at the test plate leading edge. (orig.)
DEFF Research Database (Denmark)
Hedegård, Erik D.; Jensen, Hans Jørgen Aagaard; Knecht, Stefan
2013-01-01
-MC-srDFT) excitation energies calculated over a larger benchmark set of molecules with predominantly single reference character yield good agreement with their reference values, and are in general comparable to the CAM-B3LYP functional. The SOPPA-srDFT scheme is tested for a subset of molecules used for benchmarking...
Energy Technology Data Exchange (ETDEWEB)
Perez, R. B.; Booth, R. S. [University of Florida, Gainesville, FL (United States)
1965-10-15
Placement of either a sinusoidally modulated or pulsed source of thermal neutrons at one of the boundaries of a nuclear assembly creates a disturbance which can be analysed in terms of wave components, propagating away from the localized source with frequency-dependent attenuation factors and wave velocities. The dispersive properties of the assembly are expressed through the dispersion relation, connecting the inverse complex relaxation length (or complex wave number). {rho}({omega}), to the frequency of the excitation and the nuclear parameters of the system. It will be shown that the dispersion relation is of the form {rho}{sup 2}({omega}) = {Sigma}{sub n(even)} B{sup (n)}{omega}{sup n} + i {Sigma}{sub n(odd}) B{sup (n)} {omega}{sup n} (1) where the coefficients B{sup (n)} are related to matrix elements of the various operators in moderating and multiplicative media. In a neutron wave experiment one measures the attenuation factor {alpha}({omega}) and the phase shift per unit length {delta}({omega}), which satisfy the relationships {alpha}{sup 2}({omega}) - {delta}{sup 2}({omega}) = {Sigma}{sub n(even)} B{sup (n)}{omega}{sup n}. (2) 2{alpha}({omega}){delta}({omega}) = {Sigma}{sub n(odd)} B{sup (n)}{omega}{sup n}. (3) One has then the advantage over the conventional pulsing with fast neutrons of measuring two independent magnitudes (real and imaginary part of the wave number) from which more information can be extracted about the nuclear properties of interest. Experiments were performed using graphite as the moderating material. Two different sources of thermal neutrons were used. In one case 14-MeV neutrons generated by a Cockcroft-Walton machine were thermalized in a tank containing several layers of iron, lead and graphite immersed in water. Lately the University of Florida 4-MeV Van de Graaff accelerator produced 29-keV neutrons from the (Li-p) reaction which were thermalized in a few inches of paraffin. In both instances the ion beams could be modulated
International Nuclear Information System (INIS)
Li Wenfei; Zhang Fengshou; Chen Liewen
2001-01-01
Within the framework of Hartree-Fock theory using the extended Skyrme effective interaction, the isospin excitation energy as a function of relative neutron excess δ was investigated at different temperatures and densities. It was found that the isospin excitation energy decreased with the increment of temperature and/or the decrement of density. The authors pointed out that the decrement of isospin excitation energy was resulted from the weakening of quantum effect with increment of temperature and/or decrement of density. Meanwhile, the relationship between the isospin excitation energy and the symmetry energy was discussed and found that the symmetry energy was just a part of the isospin excitation energy. With increasing temperature and decreasing density, the contribution of the symmetry energy to the isospin excitation energy becomes more and more important. The isospin excitation energy as a function of relative neutron excess was also investigated using different potential parameters. The results shows that the isospin excitation energy is almost independent of the incompressibility and the effective mass, but strongly depends on the symmetry energy strength coefficient, which indicates that it is possible to extract the symmetry energy of the nuclear equation of state by investigating the isospin excitation energy in experiments