Identifying low gas-fill hohlraum designs for high performance implosions on the Laser Mega Joule facility

The final commissioning of the LMJ facility will use 40 laser quads to deliver 1.2 MJ of laser energy and 400 TW of laser power. Because of specific technical constraints, such as lower available energy and power, different laser beam balance and smaller focal spots than on the National Ignition Facility (NIF), a dedicated configuration has to be determined to guide high-performance designs. Integrated 2D simulations of low gas-fill rugby-shaped hohlraum implosions are performed using the TROLL radiation hydrodynamics code. This work presents an overview of these designs described by different case-to-capsule ratios, ablator materials and beam pointings. Key features such as hohlraum shape, inner beam propagation and energy coupled to the implosion are compared to recent NIF campaigns. A trade-off between hohlraum size, late-time inner beam propagation and achievable implosion velocity is defined to maintain implosion symmetry control. The effects of cross-beam energy transfer on low-mode implosion symmetry are also investigated for the first time on LMJ designs.