Experimental studies of the interpenetration and compression of counter-propagating hypervelocity hot plasma jets

We present experimental observations of counter-propagating interpenetrating hypervelocity plasma jets in the weakly collisional regime (Knudsen numbers, Kn∼0.09–0.27). Two independently operated opposing plasma deflagration accelerators were operated such that the jets they produced collided at a midpoint 68 cm from each device exit plane. Triple Langmuir probe diagnostics of each device's jet at this midpoint prior to collision demonstrated controllable plasma conditions with densities ranging from 1019 to 1020 m−3 and temperatures from 8 to 27 eV across driving capacitor charge voltages of 3–9 kV. Knudsen number analysis confirmed operation in the weakly collisional (Kn∼0.1–10) regime for the parameter space explored. During head-on collisions, we observed significant increases in both density (factors of 1.3–5.3) and temperature (factors of 3.5–19) indicative of stagnation effects, with the magnitude depending strongly on collisionality. High-speed imaging revealed distinct collision dynamics: diffuse interpenetration at lower collisionality transitioning to bright, localized stagnation regions at higher collisionality. At higher voltages (≥5 kV) which corresponded to higher collisionality, measured plasma parameters approached theoretical shock and stagnation predictions from hydrodynamic models, while lower voltage cases showed deviations consistent with kinetic effects. These results provide new experimental benchmarks for validating hybrid plasma simulation codes in the challenging weakly collisional regime relevant to inertial confinement fusion, laser–plasma interactions, and astrophysical jet phenomena.