Plasma Experiments with 1.06-µm Lasers at the Lawrence Livermore Laboratory

  • H. G. Ahlstrom
  • J. F. Holzrichter
  • K. R. Manes
  • E. K. Storm
  • M. J. Boyle
  • K. M. Brooks
  • R. A. Haas
  • D. W. Phillion
  • V. C. Rupert
Chapter

Abstract

Recent laser fusion experiments at the Lawrence Livermore Laboratory have provided basic data concerning: laser beam propagation and absorption in high temperature plasmas, electron energy transport processes that transfer the absorbed laser energy to the high-density ablation region, the general fluid dynamic expansion and compression of the heated plasma, and the processes responsible for the production of 14-MeV neutrons during implosion experiments. Irradiation experiments were performed with Nd:YAG glass laser systems: the two-beam Janus (≲40 J/100 ps, ̴0.4 TW) and Argus (≲140 J, 35 ps, ̴4 TW), and the single beam Cyclops (≲70 J/100 ps, ̴0.7 TW). Two classes of targets have been used: glass microshells (̴40 to 120 µm in diameter with ̴0.75-µm-thick walls) filled with an equimolar deuterium-tritium mixture, and disks (̴160 to 600 µm in diameter and ̴10 µm thick) of several compositions. The targets were supported in vacuum (pressure ≲<10-5 Torr) by thin glass stalks.

This paper reports on results related to the propagation, absorption, and scattering of laser light by both spherical and planar targets. Our absorption measurements cannot be explained by inverse bremsstrahlung alone. The scattered light and the plasma energy are polarization dependent, which is evidence of resonance absorption.

The x-ray spectra are characterized by a thermal and a suprathermal distribution. The “temperature” of the hot x-rays is given by θH ̴I0.3-0.4 depending on the target material. Evidence presented indicates that the laser radiation pressure is producing density steepening in the region of the critical density with:
$${\rm n}_{{\rm cr}} \left( {{{\rm \partial n} \over \rm {\partial x}}} \right)_{{\rm cr}}^{ - 1} \, \sim \,{\rm \sigma }\left( {1\,{\rm \mu m}} \right).$$
In some cases, plasma filamentation is observed.

Keywords

Silicate Attenuation Tungsten Manes Hunt 

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Copyright information

© Plenum Press, New York 1977

Authors and Affiliations

  • H. G. Ahlstrom
    • 1
  • J. F. Holzrichter
    • 1
  • K. R. Manes
    • 1
  • E. K. Storm
    • 1
  • M. J. Boyle
    • 1
  • K. M. Brooks
    • 1
  • R. A. Haas
    • 1
  • D. W. Phillion
    • 1
  • V. C. Rupert
    • 1
  1. 1.Lawrence Livermore LaboratoryUniversity of CaliforniaLivermoreUSA

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