Laser-driven instabilities in long scalelength plasmas, 2
There is considerable interest in the interaction of intense laser light with plasmas characterized by a long density scale length. Such plasmas are created in laser fusion applications when targets are irradiated by long shaped pulses of intense laser light. The preferred absorption process is inverse bremsstrahlung, which is simply collisional absorption. However, a hot plasma also supports waves, which correspond to density fluctuations and their self-consistent electric fields. Excitation of these waves can lead to scattering of the laser light and/or to absorption into an undesirable component of energetic electrons which preheat the fuel capsule. A variety of plasma instabilities can be driven by intense laser light in long scale-length plasmas. Most of these instabilities can be represented as the resonant decay of the incident light wave into two other waves. If we neglect self-generated magnetic fields, the plasma will support light waves, electron plasma waves, and ion acoustic waves. Various combinations are apparent. Decay into electron and ion waves takes place near the critical density, where the electron plasma frequency equals the laser light frequency. Decay into two electron plasma waves occurs near .25 n{sub cr}. The analogous process involving a scattered light wave plus an ion sound wave can be operative throughout the underdense plasma. Another possible instability is due to long wavelength density modulations which can enhance perturbations in the radial intensity profile of the laser beam. In order to delineate the regimes of efficient coupling, it is important to characterize these various processes. Instabilities which operate in the plasma with density .25 n{sub cr} are a particular concern, since collisional absorption can be quite effective at higher densities. 64 refs., 7 figs.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- DOE/DP
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5437415
- Report Number(s):
- UCRL-99302; CONF-8808203-1; ON: DE90002806
- Resource Relation:
- Conference: 35. Scottish University summer school in physics: laser plasma interactions '88, St. Andrews (UK), 7-20 Aug 1988
- Country of Publication:
- United States
- Language:
- English
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