Thermonuclear Neutron Emission Profiles of Sheared-Flow Stabilized Z-pinch Plasmas in the Fusion Z-Pinch Experiment

Since its inception in the late 60’s, great progress has been made on the flow Z-pinch concept for a fusion reactor, and the most success in obtaining fusion-relevant plasmas has come from approaches using sheared-flow stabilization, such as in the Fusion Z-Pinch Experiment (FuZE). Recently, FuZE used Thomson scattering measurements to confirm electron temperatures of 1-3 keV, and from ion Doppler spectroscopy measurements, T_e ≤ T_i, demonstrate thermal equilibrium. These plasma conditions are worthy of thermonuclear neutron emissions, and indeed, neutrons have been observed to emit from the plasma at a rate of 3x10⁷ n/μs. However, not all neutrons can be considered thermonuclear due to the likely presence of unsuppressed instabilities during repeated shots in FuZE. In order to gain confidence in reporting neutronics, it is recommended to set-up instrumentation carefully, and planning of this nature requires simulating the expected response of the detectors. In these simulations, the neutron emitting volume can be approximated as a degenerate line source, but with plasma density and temperature profiles from measurements made on FuZE, more realistic profiles of the thermonuclear neutron emissions can be generated. A study was conducted to look into the neutronics on past FuZE experiments using said profiles in the neutron transport code, MCNP. With further development of the approach in this study, it is possible that plasma simulations could make more robust predictions and even suggest new diagnostics.