Design of inertial fusion implosions reaching the burning plasma regime with the I-Raum*

A burning plasma state [1] has recently been achieved for the first time via indirect-drive inertial confinement fusion (ICF) at the National Ignition Facility (NIF). One of the last remaining milestones in laboratory fusion research before reaching ignition, a burning plasma occurs when energy deposited from alpha particles produced in deuterium-tritium (DT) fusion reactions becomes the dominant source of heating in the plasma. Four NIF experiments recently surpassed the burning plasma threshold, two using traditional cylindrical hohlraums [3] and two using a modified cylindrical geometry with recessed pockets, dubbed the “I-Raum” [2]. Both low gas fill platforms increased hohlraum efficiency while maintaining control over implosion symmetry, enabling larger capsules to be fielded at fixed maximum laser drive energy, resulting in record performance.

 

This presentation describes the simulation design effort for the I-Raum campaign using the radiation-hydrodynamics code HYDRA [3]. The I-Raum hohlraum is engineered to increase late time symmetry control with pockets that radially displace the expanding wall plasma from the outer (44° and 50°) cones of laser beams, delaying interception of the inner (23° and 30°) cones. Further performance gains are achieved by adjusting cross-beam energy transfer (CBET) [4] via wavelength detuning (Δλ) between the inner and outer cones to reduce residual low mode drive asymmetries. These tactics allowed recent I-Raum experiments to reach a burning plasma state, producing up to 161 kJ of fusion yield. We conclude by exploring multiple paths for further performance enhancement in future experiments.

[1] O. A. Hurricane, et al., Plasma Phys. Contr. F. 61, 014033 (2019)

[2] H. F. Robey et al., Phys. Plasmas 25, 012711 (2018)

[3] M. M. Marinak, et al., Phys. Plasmas 8, 2275 (2001)

[4] A. L. Kritcher et al., Phys. Rev. E. 98, 053206 (2018)