The EPaX experiment at the University of San Diego (USD), designed to study internal sheaths and ultimately the Bohm Criterion in electronegative, Iodine plasma

There remain open questions regarding the physics of sheath formation in electronegative plasma systems, despite their multifaceted use in plasma processing over the past half-century. While the model of Braithewaite and Allen [J. Phys. D: Appl. Phys. 21 1733 (1988)] is generally assumed to be the case, direct experimental benchmark experiments are still lacking. Further, a focused set of benchmarking experiments directly measuring potential profiles in the neighborhood of sheaths near conducting boundaries, for a variety of electronegativities, is also still lacking. A thermionic emission, DC-discharge device at the University of San Diego (USD), a principally undergraduate institution, called the Electronegative PlAsma Sheath EXperiment, or EPaX, is nearing completion, designed for discharges using corrosive gas feed stocks such as molecular iodine. The plan is to commission the device in Argon, then Argon-Iodine discharges with a view to using the Argon fraction as an experimental knob for electronegativity. The first discharges are now planned for Summer of 2022. Overall design of experiments, progress, and results will be presented.