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A Description of a Shock Wave in Free Particle Hydrodynamics with Internal Magnetic Fields

Description: Abstract: "The structure of an extremely strong magnetohydrodynamic shock is discussed in the limit of no particle collisions. It is tentatively concluded that the shock transition takes place through the mechanism of a strong electric field produced by charge separation. The pressure in the shocked plasma is due primarily to a very high electron temperature. The ions, on the other hand, undergo an irreversible temperature change of only 3."
Date: February 19, 1957
Creator: Colgate, Stirling A.
Partner: UNT Libraries Government Documents Department

Warm wavebreaking of nonlinear plasma waves with arbitrary phase velocities

Description: A warm, relativistic fluid theory of a nonequilibrium, collisionless plasma is developed to analyze nonlinear plasma waves excited by intense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave phase velocities. The maximum amplitude is shown to increase in the presence of a laser field. These results set a limit to the achievable gradient in plasma-based accelerators.
Date: November 12, 2004
Creator: Schroeder, C.B.; Esarey, E. & Shadwick, B.A.
Partner: UNT Libraries Government Documents Department

Role of plasma edge in the direct launch Ion Bernstein Wave experiment in TFTR

Description: Two types of direct IBW launching, EPW {R_arrow} IBW and CESICW {R_arrow} IBW are investigated using two numerical codes, Full Hot Plasma Ray-Tracing Code and SEMAL Full Wave Slab Code, for the TFTR direct launch IBW experimental parameters. The measured density profiles (by microwave reflectometry) in TFTR appear to be satisfactory for IBW launching while the observed stored energy rise compared to the expected value (ray tracing + TRANSP) indicates only up to 50% of launched power is reaching the plasma core. Possible causes of IBW inefficiency are also discussed.
Date: June 1, 1997
Creator: Ono, M.; Cesario, R. & Bush, C.E.
Partner: UNT Libraries Government Documents Department

Observation of Secondary Plasma Waves in Laser-Plasma Interaction Experiments

Description: An experiment is described where the two products of the Langmuir Decay Instability (LDI) of a primary electron plasma wave have been observed and identified without any ambiguity. Primary Langmuir waves are driven by Stimulated Raman Scattering (SRS) of an incident laser which provides well-defined electron plasma waves. Thomson scattering of a short wavelength probe beam yields measurements of the amplitude of the waves resolved in time, space, wavelength and wavevector, that allow identification of the probed waves.
Date: December 8, 1999
Creator: Depierreux, S.; Labaune, C.; Baldis, H.A.; Fuchs, J. & Michard, A.
Partner: UNT Libraries Government Documents Department

The electrostatic wake of a superthermal test electron in a magnetized plasma

Description: The electrostatic potential is determined for a test electron with {upsilon}{sub {parallel}} {much gt} {upsilon}{sub Te}, in a uniform magnetized plasma ({omega}{sub ce} {much gt} {omega}{sub pe}). In the frame of the test electron, part of the spatially oscillatory potential has spherical symmetry over the hemisphere to the rear of the electron and is zero ahead of the electron. A second part of different character, which makes the potential continuous at the plane containing the electron, is oscillatory in the radial direction but decreases almost monotonically in the axial direction.
Date: July 1, 1992
Creator: Ware, A.A. & Wiley, J.C.
Partner: UNT Libraries Government Documents Department

Effects of Hyperbolic Rotation in Minkowski Space on the Modeling of Plasma Accelerators in a Lorentz Boosted Frame

Description: Laser driven plasma accelerators promise much shorter particle accelerators but their development requires detailed simulations that challenge or exceed current capabilities. We report the first direct simulations of stages up to 1 TeV from simulations using a Lorentz boosted calculation frame resulting in a million times speedup, thanks to a frame boost as high as gamma = 1300. Effects of the hyperbolic rotation in Minkowski space resulting from the frame boost on the laser propagation in the plasma is shown to be key in the mitigation of a numerical instability that was limiting previous attempts.
Date: September 21, 2010
Creator: Vay, J.-L.; Geddes, C. G. R.; Cormier-Michel, E. & Grote, D. P.
Partner: UNT Libraries Government Documents Department

Studies of Flows in Plasmas

Description: Note a pdf document "DOE-flow-final-report' should be attached. If it somehow is not please notify Walter Gekelman (gekelman@physics.ucla.edu) who will e mail it directly
Date: March 7, 2009
Creator: Gekelman, Walter; Morales, George & Maggs, James
Partner: UNT Libraries Government Documents Department

Calculation of Moments from Measurements by the Los Alamos Magnetospheric Plasma Analyzer

Description: The various steps involved in computing the moments (density, velocity, and temperature) of the ion and electron distributions measured with the Los Alamos Magnetospheric Plasma Analyzer (MPA) are described. The assumptions, constants, and algorithms contained in the FORTRAN code are presented, as well as the output parameters produced by the code.
Date: May 1, 1999
Creator: Thomsen, M. F.; Noveroske, E.; Borovsky, J. E. & McComas, D. J.
Partner: UNT Libraries Government Documents Department

Experimental observation of current generation by unidirectional electron plasma waves

Description: A slow wave structure was used to launch electron plasma waves traveling preferentially in one direction. The current generated by the waves was observed. The magnitude of the current can be estimated from momentum conservation in the wave-particle interaction process.
Date: August 1, 1978
Creator: Wong, K.L.
Partner: UNT Libraries Government Documents Department

The dynamics of interacting nonlinearities governing long wavelength driftwave turbulence

Description: Because of the ubiquitous nature of turbulence and the vast array of different systems which have turbulent solutions, the study of turbulence is an area of active research. Much present day understanding of turbulence is rooted in the well established properties of homogeneous Navier-Stokes turbulence, which, due to its relative simplicity, allows for approximate analytic solutions. This work examines a group of turbulent systems with marked differences from Navier-Stokes turbulence, and attempts to quantify some of their properties. This group of systems represents a variety of drift wave fluctuations believed to be of fundamental importance in laboratory fusion devices. From extensive simulation of simple local fluid models of long wavelength drift wave turbulence in tokamaks, a reasonably complete picture of the basic properties of spectral transfer and saturation has emerged. These studies indicate that many conventional notions concerning directions of cascades, locality and isotropy of transfer, frequencies of fluctuations, and stationarity of saturation are not valid for moderate to long wavelengths. In particular, spectral energy transfer at long wavelengths is dominated by the E {times} B nonlinearity, which carries energy to short scale in a manner that is highly nonlocal and anisotropic. In marked contrast to the canonical self-similar cascade dynamics of Kolmogorov, energy is efficiently passed between modes separated by the entire spectrum range in a correlation time. At short wavelengths, transfer is dominated by the polarization drift nonlinearity. While the standard dual cascade applies in this subrange, it is found that finite spectrum size can produce cascades that are reverse directed and are nonconservative in enstrophy and energy similarity ranges. In regions where both nonlinearities are important, cross-coupling between the nolinearities gives rise to large no frequency shifts as well as changes in the spectral dynamics.
Date: September 1, 1993
Creator: Newman, D. E.
Partner: UNT Libraries Government Documents Department

Hot-ion Bernstein wave with large k{sub parallel}

Description: The complex roots of the hot plasma dispersion relation in the ion cyclotron range of frequencies have been surveyed. Progressing from low to high values of perpendicular wave number k{perpendicular} we find first the cold plasma fast wave and then the well-known Bernstein wave, which is characterized by large dispersion, or large changes in k{perpendicular} for small changes in frequency or magnetic field. At still higher k{perpendicular} there can be two hot plasma waves with relatively little dispersion. The latter waves exist only for relatively large k{parallel}, the wave number parallel to the magnetic field, and are strongly damped unless the electron temperature is low compared to the ion temperature. Up to three mode conversions appear to be possible, but two mode conversions are seen consistently.
Date: January 1, 1995
Creator: Ignat, D. W. & Ono, M.
Partner: UNT Libraries Government Documents Department

Nonlinear instability and chaos in plasma wave-wave interactions, I., Introduction

Description: Conventional linear stability analyses may fail for fluid systems with an indefinite free energy functional. When such a system is linearly stable, it is said to possess negative energy modes. Instability may then occur either via dissipation of the negative energy modes, or nonlinearly via resonant wave-wave coupling, leading to explosive growth. In the dissipationless case, it is conjectured that intrinsic chaotic behavior may allow initially nonresonant systems to reach resonance by diffusion in phase space. In this and a companion paper [submitted to Physics of Plasmas], this phenomenon is demonstrated for a simple equilibrium involving cold counterstreaming ions. The system is described in the fluid approximation by a Hamiltonian functional and associated noncanonical Poisson bracket. By Fourier decomposition and appropriate coordinate transformations, the Hamiltonian for the perturbed energy is expressed in action-angle form. The normal modes correspond to Doppler-shifted ion-acoustic waves of positive and negative energy. Nonlinear coupling leads to decay instability via two-wave interactions, and to either decay or explosive instability via three-wave interactions. These instabilities are described for various (integrable) systems of waves interacting via single nonlinear terms. This discussion provides the foundation for the treatment of nonintegrable systems in the companion paper.
Date: November 1, 1994
Creator: Kueny, C. S. & Morrison, P. J.
Partner: UNT Libraries Government Documents Department

The generalized accessibility and spectral gap of lower hybrid waves in tokamaks

Description: The generalized accessibility of lower hybrid waves, primarily in the current drive regime of tokamak plasmas, which may include shifting, either upward or downward, of the parallel refractive index (n{sub {parallel}}), is investigated, based upon a cold plasma dispersion relation and various geometrical constraint (G.C.) relations imposed on the behavior of n{sub {parallel}}. It is shown that n{sub {parallel}} upshifting can be bounded and insufficient to bridge a large spectral gap to cause wave damping, depending upon whether the G.C. relation allows the oblique resonance to occur. The traditional n{sub {parallel}} upshifting mechanism caused by the pitch angle of magnetic field lines is shown to lead to contradictions with experimental observations. An upshifting mechanism brought about by the density gradient along field lines is proposed, which is not inconsistent with experimental observations, and provides plausible explanations to some unresolved issues of lower hybrid wave theory, including generation of {open_quote}seed electrons.{close_quote}
Date: March 1, 1994
Creator: Takahashi, Hironori
Partner: UNT Libraries Government Documents Department

Nonlinear pulse propagation and phase velocity of laser-driven plasma waves

Description: Laser evolution and plasma wave excitation by a relativistically-intense short-pulse laser in underdense plasma are investigated in the broad pulse limit, including the effects of pulse steepening, frequency red-shifting, and energy depletion. The nonlinear plasma wave phase velocity is shown to be significantly lower than the laser group velocity and further decreases as the pulse propagates owing to laser evolution. This lowers the thresholds for trapping and wavebreaking, and reduces the energy gain and efficiency of laser-plasma accelerators that use a uniform plasma profile.
Date: March 25, 2011
Creator: Schroeder, Carl B.; Benedetti, Carlo; Esarey, Eric & Leemans, Wim
Partner: UNT Libraries Government Documents Department

On Asymmetric Collisions with Large Disruption Parameters

Description: Collisions between a weak electron bunch and a strong positron bunch are studied within a flat beam model. Electrons are tracked through the transverse space charge field of the positron bunch, and it is shown that positrons in a storage ring may remain stable after asymmetric collisions with a weak electron bunch in spite of large values of the electron disruption parameter. The plasma oscillations that effect collisions with large disruption parameters may be suppressed by properly matching the electrons.
Date: June 1, 1990
Creator: Krafft, Geoffrey; Fripp, Michael & Heifets, Sam
Partner: UNT Libraries Government Documents Department

Fluctuations in an electron-positron plasma: linear theory and implications for turbulence

Description: Linear kinetic theory of electromagnetic fluctuations in a homogeneous, magnetized, collisionless electron-positron plasma predicts two lightly damped modes propagate at relatively long wavelengths: an Alfven-like mode with dispersion {omega}{sub r} = k{sub {parallel}}{bar {nu}}{sub A} and a magnetosonic-like mode with dispersion {omega}{sub r} {approx_equal} k{bar {nu}}{sub A} if {beta}{sub e} << 1. Here {bar {nu}}{sub A} is the Alfven speed in an electron-positron plasma and {parallel} refers to the direction relative to the background magnetic field B{sub 0}. Alfven-like fluctuations are incompressible, but the magnetosoniclike fluctuations become compressible at propagation oblique to B{sub 0}. The onset of cyclotron damping of both modes moves to smaller k{sub {parallel}}c/{omega}{sub e} as {beta}{sub {parallel}e} increases. Using the linear dispersion properties of these modes, scaling relations are derived which predict that turbulence of both modes should be relatively anisotropic, with fluctuating magnetic energy preferentially cascading in directions relatively perpendicular to B{sub 0}. But two-regime turbulence with a distinct breakpoint in wavenumber space observed in the solar wind should not be present in electron-positron plasmas because of the absence of whistler-like dispersion. Linear theory properties of the cyclotron and mirror instabilities driven by either electron or positron temperature anisotropies are generally analogous to the corresponding instabilities in electron-proton plasmas.
Date: January 1, 2009
Creator: Gary, S Peter & Karimabadi, Homa
Partner: UNT Libraries Government Documents Department

Nonlinear laser energy depletion in laser-plasma accelerators

Description: Energy depletion of intense, short-pulse lasers via excitation of plasma waves is investigated numerically and analytically. The evolution of a resonant laser pulse proceeds in two phases. In the first phase, the pulse steepens, compresses, and frequency red-shifts as energy is deposited in the plasma. The second phase of evolution occurs after the pulse reaches a minimum length at which point the pulse rapidly lengthens, losing resonance with the plasma. Expressions for the rate of laser energy loss and rate of laser red-shifting are derived and are found to be in excellent agreement with the direct numerical solution of the laser field evolution coupled to the plasma response. Both processes are shown to have the same characteristic length-scale. In the high intensity limit, for nearly-resonant Gaussian laser pulses, this scale length is shown to be independent of laser intensity.
Date: April 3, 2009
Creator: Shadwick, B.A.; Schroeder, C.B. & Esarey, E.
Partner: UNT Libraries Government Documents Department

Escaping radio emission from pulsars: Possible role of velocity shear

Description: It is demonstrated that the velocity shear, intrinsic to the e{sup +}e{sup {minus}} plasma present in the pulsar magnetosphere, can efficiently convert the nonescaping longitudinal Langmuir waves (produced by some kind of a beam or stream instability) into propagating (escaping) electromagnetic waves. It is suggested that this shear induced transformation may be the basic mechanism needed for the eventual generation of the observed pulsar radio emission.
Date: January 1, 1997
Creator: Mahajan, S.M.; Machabeli, G.Z. & Rogava, A.D.
Partner: UNT Libraries Government Documents Department

Ion-beam Plasma Neutralization Interaction Images

Description: Neutralization of the ion beam charge and current is an important scientific issue for many practical applications. The process of ion beam charge and current neutralization is complex because the excitation of nonlinear plasma waves may occur. Computer simulation images of plasma neutralization of the ion beam pulse are presented.
Date: April 9, 2002
Creator: Kaganovich, Igor D.; Startsev, Edward; Klasky, S. & Davidson, Ronald C.
Partner: UNT Libraries Government Documents Department