Development of a Gas-Puff Z-Pinch for the MAIZE Linear Transformer Driver

Abstract

A gas-puff z-pinch experimental platform has been developed for the 0.5–1-MA, 100–250-ns MAIZE pulsed power facility at the University of Michigan. The experiment consists of a nozzle and fast-valve assembly, which is integrated into the pulsed power circuit and forms a gas load in the center of the pulsed power device. The capacitors that form the pulsed power device discharge through the gas, forcing it to pinch on axis. Such a gas-puff z-pinch is afflicted by various instabilities, the mitigation of which is achieved by imploding multiple concentric shells of gas with increasing gas density toward the center of the pinch and imploding high mass number gases onto low mass number gases. These constraints suggested the development of a triple-nozzle system with an outer shell, inner shell, and central jet. A voltage-driven thin-shell model was used to inform the design of the gas-puff nozzles’ radii and gas pressures in the fast valve. The hardware was developed based on this point design. The MAIZE transmission lines were redesigned to accommodate the new hardware. Systems that support the gas-puff experiment include a gas manifold that supplies the nozzles with gas; a driver that pulses the valve to opened and closed states; and a logic circuit that provides a signal if and only if the gas-puff load successfully forms, to trigger MAIZE and the diagnostics. These were all constructed, tested, and integrated into the experiment. Additional diagnostics were also developed and fielded: a 2-D interferometer, a four polycrystalline diamond (PCD) detector array with Ross filter pairs, and neutron bubble detectors. Characteristic results from the first z-pinch experiments conducted with this gas-puff system are presented. The system demonstrates an x-ray energy output of up to $720~\pm ~50$ J per pulse and a neutron output of up to $(4.9 \pm 0.5) \times 10^{8}$ neutrons per pulse. Notably, this system has enabled shot rates of over 30 z-pinch experiments per day on MAIZE.