Saturation of Stimulated Raman Scattering in Inhomogeneous Plasma

Stimulated Raman scattering (SRS) in one of the most important laser-plasma interaction processes for the inertial confinement fusion (ICF) because it determines the balance between scattering and absorption, and also because SRS generates fast electrons that can propagate to the core of ICF target.¹ SRS can grow as an absolute instability and the instability threshold is well exceeded in ICF experiments at the National Ignition Facility (NIF). A crucial question in ICF research has been how much laser light can propagate through the instability region to higher plasma densities. The SRS instability has been simulated in inhomogeneous plasmas with the laser-plasma simulation environment for the parameters relevant to NIF experiments. The SRS absolute instability has been found to undergo the dynamic saturation in which the electrostatic waves with a broad spectrum are coupled to the Raman and laser light waves, thereby increasing their incoherence. This allows a large fraction of the incident laser power to propagate through the SRS instability region to higher plasma densities.

1 J. F. Myatt et al., Phys. Plasmas 21, 055501 (2014).