Thresholds of convective Raman backscattering: Effects of deln, Thomson scattering, noise, collisions, and Landau damping

Using kinetic simulations we find that Raman backscattering can exist for laser intensities a factor 2π lower than the density gradient (deln) threshold and that Thomson scattering can account for backscattering signals even lower. In addition, kinetic, collisional simulations show that laser intensities > or approx. =3--10 times the electron-ion collisional threshold are needed for significant Raman absorption. Collisions can also reduce the heat electron temperatures for delnnot =0