Improvement of potential drop predictions for plasma wind tunnels by cathode sheath

A study was conducted to demonstrate improvement of potential drop predictions for plasma wind tunnels by cathode sheath. The study focused particularly on the sheath phenomena near the cathode wall surface. The electron j_ele and ion j_amb fluxes drifting toward the cathode wall from the plasma region were considered for the electron-generation mechanisms near the cathode surface. It was assumed that no collisions occurred assumed that no collisions in the sheath layer and that the electron flux generated by ionization reactions could be neglected in the proposed model. The test cases used for the investigations were constrictor-type (CAH) and the segmented-type (SAH) arc heaters. It was found that more electrons remained in the sheath, as the magnitude of the potential drop at the cathode surface was small in CAH making the electric field weak. The sheath layer was also filled by ions and most electrons returned return to the plasma in the sheath for SAH, as the potential drop was large.