Nonlinear cross-beam energy transfer model for ICF/HED design codes

Cross-beam energy transfer (CBET) allows crossing laser beams to exchange energy and is critically important for ICF/HED experiments. 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 ICF experiments.

Ion trapping induces nonlinear processes such as changes to the plasma response function, the IAW dispersion, and nonlinearities (e.g., bowing and self-focusing), which, together with pump depletion, oblique forward stimulated Raman scattering (FSRS), and backward stimulated Brillouin scattering (BSBS), determine the time-dependent nature and level of CBET gain as the system approaches steady state. Using VPIC simulations, we construct a nonlinear CBET model that computes the CBET gain (including effects from ion trapping and secondary instabilities) from local quantities such as plasma density and laser intensity, the IAW wavenumber kλ_D, and the electron-to-ion temperature ratio T_e/T_i.