Study of methods to reduce SRS of inner beams in ICF ignition hohlraums

Laser-plasma interactions (LPI) is very important to the success of indirect-drive inertial confinement fusion on NIF. LPI is related not only to laser intensity or laser quality, but also to the plasma state on laser path. Simulations show that the He plasma near gold wall in inner cone laser path is prone to produce SRS in ignition hohlraums. The plasma state can be optimized by changing hohlraum parameters to depress LPI. Accordingly, two methods (using large hohlraums and high laser energy, changing the filling gases) are proposed to reduce SRS gain at this position. Simulations show the peak SRS gain is reduced by 70% and 63% respectively by these two methods.