Some laser plasma considerations for advanced hohlraums with low plasma fill*

Some laser plasma considerations for advanced hohlraums with low plasma fill are discussed. It is especially important to control backward stimulated Brillouin scattering, which could cause damage to the laser. Several well-known paths to reducing backward scattering; i.e., by enhancing the ion wave damping and the plasma gradients, are reviewed. An important dependence on angle of incidence for irradiation of high Z wall plasma is explored, and some experiments on density profile modification and potential rippling of the reflecting surface are suggested. Some ways to minimize both enhancement of the laser beam intensity via angular scattering of crossing laser beams (CBET) and further amplification of backscattered light by these beams are outlined. Sensitivity of the gains to the plasma conditions and heat transport is discussed, as well as effects due to speckles. Finally, some measurements to better assess sideward and collective scattering are recommended.