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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

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

Theory of Resonance Influence of Sawtooth Crashes on Ions with Large Orbit Width

Description: The role of resonances in the sawtooth-crash-induced redistribution of fast ions is investigated. In particular, the conditions of wave-particle resonant interaction in the presence of the equilibrium electric field and the mode rotation are obtained, and effects of sawteeth on the resonant particles with arbitrary width of non-perturbed orbits are studied. It is found that resonances play the dominant role in the transport of ions having sufficiently high energy. It is shown that the resonance regions may overlap, in which case the resonant particles may constitute the main fraction of the fast ion population in the sawtooth mixing region. The behavior of the resonant particles is studied both by constructing a Poincaré map and analytically, by means of the adiabatic invariant derived in this paper and calculation of the characteristic frequencies of the particle motion.
Date: February 1, 1998
Creator: White, R.B.; Lutsenko, V.V.; Kolesnichenko, Y.I. & Yakovenko, Y.V.
Partner: UNT Libraries Government Documents Department

Recent results & plans for the future on SLAC Damped Detuned Structures (DDS)

Description: The cells in the SLAC DDS are designed in such a way that the transverse modes excited by the beam are detuned in a Gaussian fashion so that destructive interference causes the wake function to decrease rapidly and smoothly. Moderate damping provided by four waveguide manifolds running along the outer wall of the accelerator is utilized to suppress the reappearance of the wake function at long ranges where the interference becomes constructive again. The newly developed spectral function method, involving a continuum of frequencies, is applied to analyze the wake function of the DDS I design and to study the dependence of the wake function on manifold termination. The wake function obtained with the actually realized manifold terminations is presented and compared to wake function measurements recently carried out at the ASSET facility installed in the SLAC LINAC.
Date: October 1, 1996
Creator: Kroll, N.M.; Jones, R.M. & Adolphsen, C.
Partner: UNT Libraries Government Documents Department

Enhanced discreteness, renormalization, and anomalous transport in turbulent plasma. Final technical report, 15 September 1991--14 September 1992

Description: The Principal Investigator, Professor Shayne Johnston, devoted 25% of his time during the academic year 1991--92 to this grant. The central idea underlying this project was a renormalized vision of a turbulent plasma in which electrons become microclumps, discreteness is thereby enhanced,and transport processes, still essentially classical, become anomalous. After two years of continued investigation, the PI believes strongly that this vision remains viable and compelling as an approach to electron heat conduction in the tokamak core. The simple analysis presented below shows that electrostatic waves can indeed correlate resonant repelling particles on length scales much shorter than a wavelength, thus causing enhanced discreteness within Debye clouds.
Date: May 1, 1997
Creator: Johnston, S.
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas. Revision 1

Description: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been shown that there are at least three ways in which ion waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can Lie excited at the `beat` frequency and wave number of the intersecting beams,, causing the side scatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et. al. Phys. Rev. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: March 3, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department