Nonlinear physics of cross-beam energy transfer relevant to indirect drive ignition inertial confinement fusion experiments*

Cross-beam energy transfer (CBET) allows crossing laser beams to exchange energy. The nonlinear physics of CBET for multi-speckled laser beams is examined using particle-in-cell simulations for a range of plasma conditions, laser intensities, and crossing angles relevant to indirect drive ignition inertial confinement fusion experiments. The growth and saturation of CBET involve complex, nonlinear ion and electron dynamics. It is found that a CBET-amplified seed beam can become unstable to forward stimulated Raman scattering (FSRS) but that FSRS is absent at low densities. Ion trapping induces nonlinear processes such as changes to the ion acoustic wave (IAW) dispersion and IAW nonlinearities (e.g., bowing and self-focusing), which, together with pump depletion and FSRS, determine the time dependent nature and level of CBET gain as the system approaches steady-state. CBET gain figures of merit and energy partitioning among laser beams, plasma waves and particles are discussed.