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Title: Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering

Abstract

We present a direct measurement of the quenching of nonlocal heat transport in a laser-produced plasma by applying large external magnetic fields (>10 T). The temporally resolved Thomson-scattering measurements of the electron temperature profile show that the heat front propagation transverse to a high-power laser beam is slowed resulting in extremely strong local heating. We find agreement with hydrodynamic modeling when including a magnetic field model that self-consistently evolves the fields in the plasma.

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]
  1. L-399, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
Publication Date:
OSTI Identifier:
20951189
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 13; Other Information: DOI: 10.1103/PhysRevLett.98.135001; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ELECTRON TEMPERATURE; HEAT TRANSFER; LASER-PRODUCED PLASMA; LASERS; MAGNETIC FIELDS; SIMULATION; THOMSON SCATTERING

Citation Formats

Froula, D. H., Ross, J. S., Pollock, B. B., Davis, P., James, A. N., Divol, L., Edwards, M. J., Offenberger, A. A., Price, D., Town, R. P. J., Tynan, G. R., and Glenzer, S. H. Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.135001.
Froula, D. H., Ross, J. S., Pollock, B. B., Davis, P., James, A. N., Divol, L., Edwards, M. J., Offenberger, A. A., Price, D., Town, R. P. J., Tynan, G. R., & Glenzer, S. H. Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering. United States. doi:10.1103/PHYSREVLETT.98.135001.
Froula, D. H., Ross, J. S., Pollock, B. B., Davis, P., James, A. N., Divol, L., Edwards, M. J., Offenberger, A. A., Price, D., Town, R. P. J., Tynan, G. R., and Glenzer, S. H. Fri . "Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering". United States. doi:10.1103/PHYSREVLETT.98.135001.
@article{osti_20951189,
title = {Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering},
author = {Froula, D. H. and Ross, J. S. and Pollock, B. B. and Davis, P. and James, A. N. and Divol, L. and Edwards, M. J. and Offenberger, A. A. and Price, D. and Town, R. P. J. and Tynan, G. R. and Glenzer, S. H.},
abstractNote = {We present a direct measurement of the quenching of nonlocal heat transport in a laser-produced plasma by applying large external magnetic fields (>10 T). The temporally resolved Thomson-scattering measurements of the electron temperature profile show that the heat front propagation transverse to a high-power laser beam is slowed resulting in extremely strong local heating. We find agreement with hydrodynamic modeling when including a magnetic field model that self-consistently evolves the fields in the plasma.},
doi = {10.1103/PHYSREVLETT.98.135001},
journal = {Physical Review Letters},
number = 13,
volume = 98,
place = {United States},
year = {Fri Mar 30 00:00:00 EDT 2007},
month = {Fri Mar 30 00:00:00 EDT 2007}
}
  • We present a direct measurement of the quenching of nonlocal heat transport in a laser produced plasma by high external magnetic fields. Temporally resolved measurements of the electron temperature profile transverse to a high power laser beam were obtained using imaging Thomson scattering. The results are simulated with the 2D hydrodynamic code LASNEX with a recently included magnetic field model that self-consistently evolves the fields in the plasma.
  • The authors propose an experiment in which the collective Thomson scattering lineshape obtained from ion acoustic waves is used to infer the spatial structure of local heat transport parameters and collisionality in a laser-produced plasma. The peak-height asymmetry in the ion acoustic wave spectrum will be used in conjunction with a recently developed model describing the effects of collisional and Landau damping contributions on the low-frequency electron density fluctuation spectrum to extract the relative electron drift velocity. This drift arises from temperature gradients in the plasma. The local heat flux, which is proportional to the drift, can then be estimated,more » and the electron thermal conductivity will be inferred from the relationship between the calculated heat flux and the experimentally determined temperature gradient. Damping of the entropy wave component at zero mode frequency is shown to be an estimate of the ion thermal conductivity, and its visibility is a direct measure of the ion-ion mean free path. The authors also propose to measure thermal transport parameters under dynamic conditions in which the plasma is heated impulsively by a laser beam on a fast ({approximately}50 ps) time scale. This technique will enable the authors to study heat transport in the presence of the large temperature gradients that are generated by this local heating mechanism. Deviations of the inferred local thermal conductivity from its Spitzer-Haerm value can be used to study the transition to the nonlocal heat transport regime. The authors have constructed a simple numerical model of this proposed experiment and present the results of a simulation. 41 refs., 9 figs.« less
  • A nonlocal heat-transport formula for electrons is derived to include the terms associated with the electrostatic potential and [partial derivative]/[partial derivative][ital v]([ital f][sub 0],[ital f][sub 1]) in the Fokker-Planck (FP) equation. Then the FP equation for a strongly inhomogeneous plasma is solved. It is found that the behavior of the electron thermal conductivity at a large temperature gradient is considerably affected by the electrostatic field, and the thermal conductivity [kappa]/[kappa][sub SH] for electrons scales as 1/[ital k] in a large temperature gradient [ital k] when there exists a non-negligible electrostatic field, where [kappa][sub SH] is the Spitzer-Haerm heat coefficient.
  • Scattered light diagnostics offer the attractive possibility of extracting detailed spatial information about the distribution of ions and electrons and associated plasma parameters in high-density plasmas that are relevant to inertial confinement fusion (ICF). Here, temporally integrated ultraviolet collective Thomson scattering measurements were performed with frequency-quadrupled Nd:YAG laser radiation on an underdense long-scale length aluminum plasma (n{sub c} {approximately} 10{sup 21} cm{sup {minus}3}, Z {approx} 7, T{sub e} {approx} T{sub i} {ge} 50 eV, L {ge} 100 {micro}m). The plasma was preformed by an Nd:YAG fundamental beam (1.06 {micro}m) with focusable intensities of 10{sup 11} W/cm{sup 2}. Color images ofmore » two-dimensional (2-D) spatially resolved (30 {micro}m) electron density and electron temperature were obtained. These are the shortest wavelength Thomson scattering measurements on a plasma to date.« less
  • Thomson scattering has been shown to be a valuable technique for measuring the plasma conditions in laser produced plasmas. Measurement techniques that use the ion-acoustic frequency measured from the collective Thomson-scattering spectrum to extract the electron temperature, ion temperature, plasma flow, and electron density in a laser produced plasma are discussed. In a recent study [D. Froula et al., Phys. Rev. Lett. 95, 195005 (2005)], we demonstrated a novel Thomson-scattering technique that employs multiple color Thomson-scattering diagnostics to measure the dispersion of ion-acoustic fluctuations. We obtained frequency-resolved Thomson-scattering spectra of the two separate thermal ion-acoustic fluctuations with significantly different wavemore » vectors. This new technique allows a simultaneous time resolved local measurement of electron density and temperature. The plasma fluctuations are shown to become dispersive with increasing electron temperature. Furthermore, a Thomson-scattering technique to measure the electron temperature profile is presented where recent experiments have measured a large electron temperature gradient (T{sub e}=1.4 keV to T{sub e}=3.2 keV over 1.5 mm) along the axis of a 2 mm long Hohlraum when heated asymmetrically.« less