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

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