Modeling Cross-Beam Energy Transfer for Polar-Drive Experiments

Direct-drive experiments on the National Ignition Facility require use of the nonspherically symmetric, indirect-drive beam layout. In polar-drive (PD), the power and pointing of the cylindrically symmetric NIF beams are optimized to uniformly implode a capsule. As beams refract in the coronal plasma, cross-beam energy transfer (CBET) can cause laser energy to ``bypass'' the high-absorption region of the plasma near the critical surface. The effect of CBET is modeled for PD implosions on OMEGA and the NIF. Three-dimensional paths and crossings of all beams are calculated using \textit{DRACO}-predicted plasma profiles. CBET is modeled for each of the beam rings. The equatorial third ring suffers the most from CBET, but the reduction in total absorption ($\sim $10{\%}) is similar to the 60-beam symmetric illumination case on OMEGA. Scattered-light measurements and predictions from the CBET modeling show good agreement for PD in OMEGA. This work was supported by the U.S. Department of Energy (DOE) Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.