Space and Time Resolved Ion Doppler Temperature and Velocity Measurements in Z-pinch Plasmas on the ZaP-HD Device

Abstract

The ZaP-HD Flow Z-Pinch device has shown that sheared-flow can stabilize a plasma in a simple Z pinch configuration for times well over that of a static Z pinch. The plasma is stabilized when the shear flow passes the threshold of dVz/dr ≥ 0.1kV_A mitigating the 'kink' instability. The ZaP-HD research project shows promise as both a compact fusion device and as a hypothetical in-space propulsion device. Impurity line radiation from the plasma allows for noninvasive spectroscopic techniques that can provide measurements for various plasma parameters of interest. Time-resolved spectroscopy measurements have been taken on the device in the past, however a new setup with a different high speed camera is used, resulting in measurements with over twice the spatial resolution. Ion Doppler spectroscopy (IDS) is used to measure temperature and velocity of carbon III ions in the plasma. Improved signal due to erosion of the graphite nose cone increases the amount of data collected, allowing for a more complete picture of the pinch behavior over the plasma lifetime. Sheared-flow passing the threshold for stability is found for much of the pulse duration with speeds up to 150 km/s and temperatures up to 500 eV. Time resolved temperature and velocity profiles indicate plasma reflecting off the end wall and propagating upstream as a stagnation wave, causing jump conditions comparable to that of a normal shock in the plasma. An upper limit of thruster performance is found using IDS data in conjunction with typical plasma parameters to yield an effective thrust of 0.216 N and specific impulse of 5.76 x 10^4 s.