Spatiotemporal Characterization of an Electrothermal Arc Plasma Beam

The Electrothermal Arc (ET-Arc) plasma source can provide transiently-relevant particle and heat fluxes (~ 1 GW/m²) to simulate the extreme conditions that occur, for example, during edge localized modes (ELMs) in tokamak divertors. We extend previous studies of a source developed at Oak Ridge National Lab (ORNL) to better characterize the temporal and spatial dependence of the plasma beam parameters using optical emission spectroscopy (OES) and Thomson Scattering (TS). The OES system provides time-resolved measurements of line brightness (for line-ratio measurement of plasma density and electron temperature), line broadening (for plasma density and ion temperature), and line shift (for ion velocity). Emission from hydrogen, helium (the working gas), and boron is analyzed and compared. Simultaneous collection of emission from up to 22 different lines of sight provides information about how the beam parameters vary along the beam trajectory. Shot-to-shot adjustment of the data collection time provides information about the time dependence of the emission (and derived plasma parameters) throughout the 1 ms long plasma discharge. The different atomic species and measurement techniques provide the opportunity to measure some of the same plasma parameters (e.g. plasma density and electron temperature) with two or more independent techniques, allowing underlying assumptions to be evaluated.