Cross-Beam Energy Transfer (CBET) is a laser-plasma instability that redistributes energy from the center of inbound beams to light traveling away from the capsule in direct-drive inertial confinement fusion implosions. In current direct-drive experiments, CBET reduces deposited laser energy by approximately 20% and amplifies beam-mode asymmetries in stagnated hydrodynamic profiles by an order of magnitude [1]. Recent progress in direct-drive research has leveraged statistical modeling to optimize experimental design and identify sources of performance degradation [2,3]. These studies have revealed that experimental fusion yield saturates more rapidly than simulations predict when increasing the beam width relative to the target radius (Rb/Rt), a key parameter governing beam-mode asymmetry [4]. Understanding these discrepancies is essential for accurately scaling direct-drive performance and benchmarking it against indirect-drive implosions on larger facilities.In this study, we provide simulation evidence that this yield saturation is driven by CBET. We present multidimensional simulations of implosions that accurately capture CBET effects and the growth of beam-mode asymmetries using the SOLAS laser model coupled with the CHIMERA radiative-hydrodynamics code. Our results demonstrate that in the presence of CBET, increasing Rb/Rt​ significantly enhances CBET scattering and amplifies beam-mode asymmetries. This behaviour contrasts with CBET-free cases, where increasing Rb/Rt instead reduces perturbation amplitudes due to improved illumination symmetry.

References:
[1] A. Colaïtis et al., Plasma Phys. Control. Fusion 65, 014003 (2023)
[2] V. Gopalaswamy et al., Nature 565, 581–586 (2019)
[3] V. Gopalaswamy et al., Phys. Plasmas 28, 122705 (2021)
[4] A. Lees et al., Phys. Plasmas 30, 012709 (2023)