Thresholds of Convective Raman Backscattering: Effects of∇n, Thomson Scattering, Noise, Collisions, and Landau Damping

Abstract

Using kinetic simulations we find that Raman backscattering can exist for laser intensities a factor $2\ensuremath{\pi}$ lower than the density gradient ($\ensuremath{\nabla}n$) threshold and that Thomson scattering can account for backscattering signals even lower. In addition, kinetic, collisional simulations show that laser intensities \ensuremath{\gtrsim}3-10 times the electron-ion collisional threshold are needed for significant Raman absorption. Collisions can also reduce the heated electron temperatures for $\ensuremath{\nabla}n\ensuremath{\ne}0$.