Measurement of Ion Heating in Collisional and Semi-Collisional Plasma Shocks

We have measured ion heating via Doppler spectroscopy in collisional and semi-collisional plasma shocks formed by the merging of laboratory plasma jets on the Plasma Liner Experiment (PLX)
¹
. Jets are produced at velocities of 30–50 km/s and initial densities of ~10–
¹⁶
cm-3 using coaxial plasma guns designed and built by HyperJet Fusion Corporation. Collisionality and Mach number of the jet merger are varied by changing the merging incidence angle and the jet species, wi th experimental data obtained using four different gas species. In conditions with negligible ion interpenetration, the observed heating is consistent with collisional plasma shock theory, showing a substantial elevation of ion temperature above electron temperature and subsequent relaxation. In conditions of significant interpenetration, the observed ion heating is much lower than predicted by collisional plasma shock theory, indicating the need for multi-fluid, hybrid, or fully kinetic treatment. Results are compared with modeling performed using the LSP PIC code.