Signatures of fuel magnetization in reaction-in-flight neutron spectra for pulsed magnetic fusion

Pacific Fusion (PF) is pursuing facility fusion gain via pulser Inertial Fusion Energy (IFE). In this talk, we focus on magnetized liner inertial fusion (MagLIF), where cylindrical metal liners compress DT fuel under strong magnetic fields and pre-heat. The fuel magnetization at peak compression is a key performance metric that needs to be diagnosed. At lower yields, secondary DT neutrons in pure deuterium fuel were used to infer magnetization [P.F. Knapp et. al., PoP (2015)]. At high yields, Reaction-in-Flight (RIF) neutrons are generated with energies up to 30-MeV by knock-on deuterium and tritium ions undergoing DT fusion. RIF neutron yields and spectra depend on the gyro-motion of the charged particles in the fuel. We present calculations using a new Monte-Carlo neutron and charge particle transport code that models RIF production, enabling the first assessment of using RIF neutron measurements for inferring fuel magnetization. The calculations we present utilize the auto-differentiation capabilities of the JAX programming language. This feature unlocks significant speed-ups in relating RIF measurement to higher-level target design choices. In addition, JAX enables a high degree of vectorization on CPUs, GPU and TPUs for efficient Monte-Carlo simulation on any platform. Rapid data assimilation is critical for PF's pursuit of fusion gain via IFE.