No abstract

We report the characteristics of collisional plasma shocks formed during interactions between low density ([Formula: see text] cm−3), low temperature ([Formula: see text] eV), high velocity (30 km s−1), plasma jets and stagnant plasma of similar parameters. This investigation seeks to probe the structure of shocks in multi-ion-species plasmas, in particular, the presence of gradient-driven ion species separation at the shock front. The railgun-accelerated jets utilized here have previously been shown to exist in a collisional regime with intra-jet collisional mean-free-path substantially smaller than jet size [Schneider et al., Plasma Sources Sci. Technol. 29, 045013 (2020)]. To induce collisions, a dielectric barrier is located downstream of the railgun to stagnate an initially supersonic plasma jet. Around the time of stagnation, the railgun emits a second jet which shortly collides with the stagnant plasma. The presence of a structure emitting in the UV-visible band is evident in high-speed photographs of the moments immediately following the arrival of the second jet at the stagnant plasma. Analysis of interferometric and spectroscopic data suggests that the observed increase in density from the jet to the post-collision plasma is consistent with the formation of a bow shock structure with a multi-millimeter-scale ion shock layer.

This paper reports measured and inferred characteristics of plasma jets produced by a 10 cm plasma-armature railgun designed to provide a platform to study phenomena associated with high-Mach-number plasma flows. This gas-fed accelerator is powered by an underdamped LC pulseforming network operated at charge voltages up to 15 kV and fired into a large cylindrical vacuum chamber, emitting a series of plasma jets which propagate into the chamber. Analysis of data captured by an interferometer and spectrometer at locations 10 and 40 cm away from the railgun's bore suggests jet velocities between 14.5 and -19.7 km s 1 , electron number densities between 3.4×10 14 and 2.5×10 16 cm −3 , a plasma temperature of approximately 2 eV, and Mach number between 5.1 and 7.0. These parameters fall in a parameter space conducive to the study of shock structures in multi-ion-species plasmas, as the ion stopping distances and consequently shock thicknesses are expected to be in the several millimeter to few-centimeter range.