Ion acoustic decay instability in a large scale, hot plasma relevant to direct drive laser fusion -- Application to a critical surface diagnostic. Final report

摘要

The authors have studied the ion acoustic decay instability in a large ((approximately) 1 mm) scale, hot ((approximately) 1 keV) plasma, which is relevant to a laser fusion reactor target. They have shown that the instability threshold is low. They have developed a novel collective Thomson scattering diagnostic at a 90(degree) scattering angle. The scattering is nonetheless coherent, because of the modest ratio of the frequency of the probe laser to that of the pump laser, such that even for such a large angle, (k(lambda)(sub De))(sup 2) is much less than one. With this system they have measured the electron plasma wave excited by the ion acoustic decay instability near the critical density (n(sub e) (approximately) 0.86 n(sub c)). This allows them to use the frequency of the detected wave to measure the electron temperature in the interaction region, obtaining a result reasonably close to that predicted by the SAGE computer code.