Electron kinetic effects on Raman backscatter in plasmas.
We augment the usual three-wave cold-fluid equations governing Raman backscatter (RBS) with a new kinetic thermal correction, proportional to an average of particle kinetic energy weighted by the ponderomotive phase. From closed-form analysis within a homogeneous kinetic three-wave model and ponderomotively averaged kinetic simulations in a more realistic pulsed case, the magnitude of these new contributions is shown to be a measure of the dynamical detuning between the pump laser, seed laser, and Langmuir wave. Saturation of RBS is analyzed, and the role of trapped particles illuminated. Simple estimates show that a small fraction of trapped particles (approximately 6%) can significantly suppress backscatter. We discuss the best operating regime of the Raman plasma amplifier to reduce these deleterious kinetic effects.
Hur
M S
MS
Center for Advanced Accelerators, KERI, Changwon, Kyongnam 641-120, Korea.
Lindberg
R R
RR
Charman
A E
AE
Wurtele
J S
JS
Suk
H
H