First inertial confinement fusion implosions using low gas-filled hohlraums on the Laser Mega Joule facility

The Laser Mega Joule (LMJ) facility is now capable of delivering up to 270 kJ of UV energy on target using eighty beams evenly distributed among four rings allowing for a symmetric irradiation inside a hohlraum for the first time. Here, we report on the first indirect-drive implosions performed to achieve an ablative compression regime using this unprecedented irradiation configuration. A relatively long pulse (8 ns) is used to generate X-rays on a plastic capsule filled with deuterium gas in low gas-filled rugby and cylindrical hohlraums. We observed X-ray images of the hot spot emission on LMJ for the first time. Integrated 2D simulations using the radiation hydrodynamics code TROLL are performed to investigate the experimental results including neutron yield, radiation temperature, implosion symmetry and X-ray images. We also report on significantly different levels of backscattered energy measured for rugby and cylindrical hohlraums. Finally, we show how these results will guide the future designs for the inertial confinement fusion campaigns on LMJ in the upcoming years.