Saturation of Cross-Beam Energy Transfer for Multi-Speckled Laser Beams

Cross-beam energy transfer (CBET) is the process by which two crossing laser beams transfer energy between one another through stimulated Brillouin scattering (SBS). Understanding the nonlinear saturation of CBET, including the effects of wave-particle interaction, the excitation of secondary instabilities such as forward stimulated Raman scattering (FSRS), and speckle geometry, is important to controlling low-mode asymmetry in ICF implosions. In this work, VPIC simulations of the nonlinear saturation of CBET for multi-speckled laser beams crossing at arbitrary angles are discussed. In contrast to the CBET saturation dynamics by stochastic ion heating examined previously [1] (a process occurring on ~ns-time scales), these simulations show CBET saturating on a faster (~10s ps) time scale. The nonlinear saturation dynamics, including the excitation of FSRS, may limit the efficacy of CBET for symmetry control and contribute to capsule preheat from FSRS hot electrons. [1] P. Michel, et al., Phys. Plasmas 20, 056308 (2013).