Saturation of Cross-Beam Energy Transfer in Conditions Relevant to OMEGA Implosions

In cross-beam energy transfer (CBET), the dynamic interference of two laser beams ponderomotively drives an ion-acoustic wave that coherently scatters light from one beam into the other. This redirection of laser energy can severely inhibit the performance of direct-drive inertial confinement fusion. Recent experiments fielded on the OMEGA laser demonstrated that CBET can saturate through a resonance detuning resulting from ion heating [1,2]. The experiments employed one set of OMEGA laser beams to heat a gas jet plasma and a second set as pump beams for transferring energy to a frequency-detuned seed beam. In contrast, CBET in OMEGA implosions occurs between frequency-degenerate beams in a hotter, denser, inhomogeneous flowing plasma. To determine how CBET saturates in these conditions, we have conducted a series of vector particle-in-cell (VPIC) simulations using plasma profiles from a radiation hydrodynamics simulation of an OMEGA implosion. Results from the VPIC simulations can be used to refine the reduced models for CBET that are implemented in radiation hydrodynamics codes, improving their predictive capability.