Validating cross-beam energy transfer models using indirect-drive ICF experiments at NIF

Cross-beam energy transfer (CBET), a three-wave instability whereby energy is transferred between overlapping laser beams in the presence of a background plasma, is a critical tool to control implosion symmetry in indirect-drive experiments at the National Ignition Facility (NIF). Accurate modeling requires the use of artificial plasma wave amplitude limiters, which are typically varied in an ad-hoc manner between different systems. As part of a larger effort to improve predictive capability in hohlraum modeling, we have developed a new experimental platform to directly quantify total CBET between inner beams and outer beams as a function of time. In this configuration, the bottom half of NIF drives a quartraum (a truncated hohlraum with no capsule). The outer beams strike the interior of the quartraum, while the inner beams exit through the top and hit a titanium plate. The resulting ~5 keV K-shell x-ray emission from the titanium plate is used to infer the laser intensity of each individual inner beam. Here we present simulated predictions of CBET as a function of wavelength detuning (Δλ) at nominal background gas fill density and separately as a function of fill density for a nominal Δλ. Experimental measurements are compared against the predictions.