PPPS-2013: Optical emission spectroscopy of initial plasma formation in a heavy gas theta pinch coil

Abstract

Summary form only given. Pulsed inductive plasma devices such as the common theta-pinch have become a standard high energy plasma source in research and industry. Recent pulsed inductive plasmas currently being investigated by the fusion and space propulsion communities utilize deuterium and xenon, respectively, and have provided promising new results. However, little has been done to better understand the energy conversion processes during early plasma formation times (i.e., during the initial inductive coupling). The broad efforts of this research are to elucidate the electric-to-particle energy conversion processes during initial plasma formation over time scales of 10-8 to 10-6 seconds. In this work an analysis of spectral emission data is performed on a theta pinch test article intended for use in field reversed configuration (FRC) studies. Testing is performed on a pulsed xenon plasma at energies of around 80 joules, neutral back-fill pressures of 10-2 Torr, and an RLC discharge frequency of 500 kHz. Efforts are paralleled by magnetic field studies (B-dot probes, flux loops) of the same experiment. Using a collisional-radiative model previously developed for analysis on xenon Hall effect thrusters, line emission intensity ratios are used to approximate electron temperatures independent of plasma density. A Princeton Instruments SP2300i spectrometer with PI-MAX 1024×1024 pixel iCCD camera is used with gate times of 10-9 to 10-8 seconds and variable delay to allow for time-resolved spectral data.