Comparison of Diagnostics for Determining Z Pinch Centroid in the ZaP-HD Experiment

Abstract

A Z-pinch configuration plasma has been theoretically shown to be a viable fusion energy source. By applying radially sheared flow, the Z pinch instabilities can be mitigated. In the process of stabilizing the pinch for long pulses, new research opportunities arise in studying this equilibrium plasma. One area of research is attempting to determine the centroid location of the pinch in space. Diagnostic tools are available that can measure various qualities and parameters of the plasma, but no tools are effective in directly measuring the centroid location. Instead, these diagnostics measure the plasma and, using several assumptions, are able to make an inference about the centroid. This paper examines three different diagnostic tools in their accuracy and relevance for determining centroid location. A Kirana fast-framing camera is used to measure visible line emissions from neutral gas in the vacuum chamber. A Helium-Neon laser interferometer is used to measure electron number density along the vertical axis and throughout the pinch. Finally, a set of magnetic field probes are able to measure the magnetic field at the cylinder walls and reduce the raw magnetic field data to centroid location through a simple serious of equations. The Kirana is the most consistent in determining pinch location, but is susceptible to wayward light reflections or over saturation of the detector. The interferometer is roughly accurate during the quiescent period of the plasma. It does however follow the velocity of the centroid as it moves throughout the vacuum chamber. The magnetic field probe data are accurate during the quiescent region because of the current assumptions and equations being used.