Inverse Bremsstrahlung Modeling in Hybrid-Drive ICF Simulations Using Adaptive Paraxial Complex Geometrical Optics

We introduce an implementation of an advanced inverse bremsstrahlung absorption model [1] in hybrid-drive inertial confinement fusion (ICF) [2] simulations developed at Xcimer Energy. These simulations are used to accurately predict laser energy deposition designed to preserve implosion symmetry and mitigate hydrodynamic instabilities. To model laser propagation through the underdense and near-critical plasma surrounding the target, we deploy a form of the Paraxial Complex Geometrical Optics (PCGO) method, where the beam is decomposed into a sum of local Gaussian beamlets. Our approach tracks cumulative energy absorption along the ray-traced beam trajectories of the beamlets to generate physically accurate intensity profiles for ICF-relevant conditions. We present a novel algorithm for adaptive beam refinement near the critical surface to improve resolution in regions with steep density gradients and strong refractive effects. Integration with radiation-hydrodynamics code will enable simulations of beam transport and target evolution in hybrid-drive configurations.

[1] D. Turnbull, et al., Inverse Bremsstrahlung absorption. Phys. Rev. Lett. 14 April 2023; 130 (14): 145103. https://doi.org/10.1103/PhysRevLett.130.145103

[2] C. A. Thomas, et al., 2024. Hybrid direct drive with a two-sided ultraviolet laser. Physics of Plasmas 31, 11 (November 2024). DOI:https://doi.org/10.1063/5.0221201