Effect of gas configuration and initial conditions on implosion dynamics and neutron production in gas-puff Z-pinches

The gas-puff Z-pinch is a plasma compression scheme in which a high current is driven through a cylindrical gas load, causing it to implode onto its axis via the Lorentz force. Understanding how initial gas conditions affect stability and yield is critical for developing gas-puff Z-pinches as a fusion concept. Experiments investigating the effect of gas configuration, gas injection time, and plenum pressure on neutron production and implosion dynamics in gas-puff Z-pinches have been carried out on the 500-kA, 160-ns rise-time CESZAR linear transformer driver. The gas configurations tested include deuterium target-only, deuterium liner-only, deuterium liner on deuterium target, and krypton liner on deuterium target. Deuterium target-only shots with long injection times that were substantially affected by zippering achieved yields of up to (5.07 ± 0.08) × 108 neutrons. Zippering was effectively mitigated by decreasing the injector delay time; however, neutron yields decreased by an order of magnitude. ANSYS Fluent simulations demonstrate how cathode geometry, along with timing, determines the axial mass distribution. Deuterium liner-only shots produced neutron yields up to (1.8 ± 0.2) × 107 neutrons but were highly susceptible to the Magneto-Rayleigh–Taylor Instability (MRTI). The D2-on-D2 configuration reduced both zippering and MRTI. Measured neutron yields were comparable to the liner-only configuration, reaching (2.0 ± 0.2) × 107. Kr-on-D2 shots produced up to (1.14 ± 0.04) × 108 neutrons and exhibited two different structures: one that had a low-density plasma surrounding a denser imploding core and another demonstrating more standard pinch dynamics.