Origins and scaling of high-energy photon emissions on high-current Z-pinches

Experiments on high current Z-pinch sources, including the Z machine at Sandia National Laboratories, have shown substantial production of hard x-ray and gamma-ray emissions, qualitatively understood to originate from accelerated free electrons in the MITL / pinch region. At Z, these emissions have been inferred to extend well into the MeV energy range, and occur across disparate times of order 10's of nanoseconds before, during and after peak target compression. For Pacific Fusion's Demonstration System, which is planned to operate at ~60+ MA, it is a question how these photon emissions will scale to the higher current machine, with a key concern being the degree to which these emissions will obscure DT fusion gammas at ~16 MeV. The "endpoint" of the machine photon energy emissions could be conjectured to be coincident with the evolved voltage across the machine A-K gap and free electron acceleration, though magnetization and multiple-scattering mechanisms may complicate this picture. We model the MITL free electron population during a high-current Z-pinch discharge using the particle-in-cell code Chicago, obtaining predictions for temporal, spectral, and spatial distributions of the electron population. We model the conversion to gamma emissions and compare to available experimental data, seeking to validate a machine- and load-dependent source term for high energy gamma emissions.