Optical Emission Spectroscopy of Plasma Formation in a Xenon Theta-Pinch

Analyses of xenon spectral emission data in the IR range from excited neutral xenon transitions and estimations of electron temperature are performed on a theta-pinch test article. Estimations are based on a collisional-radiative model originally written for Hall-effect thrusters utilizing apparent collisional cross-sections. Tests performed on a pulsed xenon plasma at an energy of 80 J, neutral back-fill pressures of 10-100 mtorr, and vacuum discharge frequency of 462 kHz yield time-averaged electron temperatures of 6.4-11.2 eV for spectra integrated over the entire 20 μs. Time-resolved T_e estimations are done using charge coupled device gate widths of 0.25 μs and yield estimates of up to 68 eV during peak spectral activity. Results show that back-fill pressures of 30 and 50 mtorr appear to generate plasma earlier and remain cooler than 10 and 100 mtorr. Poor signal-to-noise ratios produce substantial fluctuation in time-resolved intensities and thus estimation errors, while not quantified here, are assumed high for the time-resolved studies. Additionally, spectra acquired in the UV band verify: 1) the presence of second-order diffraction in the near-IR band from singly ionized xenon transitions and 2) the absence of air (contaminant) spectra.