Experimental Study of Shock Wave Dynamics in Magnetized Plasmas

Abstract

In this four-year project (including one-year extension), the project director and his research team built a shock-wave−plasma apparatus to study shock wave dynamics in glow discharge plasmas in nitrogen and argon at medium pressure (1-20 Torr), carried out various plasma and shock diagnostics and measurements that lead to significant progress in understanding shock wave acceleration phenomena in plasmas. Specifically, the team has• completed the construction of spark-discharge shock tube in the first year;• optimized the shock tube over low Mack numbers (Mach 1-4);• built a microwave target plasma and optimized the steady-state plasma condition;• carried out various probe and spectroscopic diagnostics for the dc glow plasma;• launched acoustic shock waves in three different plasma conditions: (i) steady-state, (ii) pulsed or transient, (iii) afterglow plasma;• studied turbulence and the shock wave behaviors in the glow discharge plasmas;• performed a comprehensive set of measurements and computations to increase our understanding of shock-plasma correlation behaviors and improve our understanding of shock acceleration mechanisms in discharge plasmas.The measurements clearly show that in the steady-state dc glow discharge plasma, at fixed gas pressure the shock wave velocity increases, its amplitude decreases, and the shock wave disperses non-linearly as a function of the plasma current. In the pulsed discharge plasma, at fixed gas pressure the shock wave dispersion width and velocity increase as a function of the delay between the switch-on of the plasma and shock-launch. In the afterglow plasma, at fixed gas pressure the shock wave dispersion width and velocity decrease as a function of the delay between the plasma switch-off and shock-launch. These changes are found to be opposite and reversing towards the room temperature value which is the initial condition for plasma ignition case. The observed shock wave properties in both igniting and afterglow plasmas correlate well with the inferred temperature changes in the two plasmas.