Shockwave Acceleration and Attenuation in Glow Discharge Argon Plasma

Abstract

Experimental investigations of the shockwave propagation in the direction parallel to the electric field in low-pressure longitudinal glow discharge argon plasmas are performed by the simultaneous multipoint laser deflection technique. In the newly developed shock tube at Troy University, Mach 1.5-2.2 shockwaves are produced by a fast capacitor discharge (quarter period τ 1/4 = 1.4 µs). In this paper, the shock propagation measurements are extended to the low pressure limit down to 3.6 torr while confirming the earlier measurements performed at gas pressures 15 torr and above. The shockwaves are launched through a plasma medium inside the shock tube, where the deflections of the laser beams are recorded on a fast oscilloscope. An average shockwave velocity in the plasma is determined from the time history of the laser deflection signals. The shockwave speed and the broadening of the laser deflection signals in the plasma are found to be dependent on the plasma discharge current. Shockwave speeds increase by 18% for the plasma at 3.6 torr over a range of plasma discharge current I = 0-150 mA and by 46% for the plasma at 15 torr over I = 7-150 mA. In addition, shockwave amplitudes are attenuated in the plasma and show linear dependence on the shockwave speed or Mach number.

Experimental Study of Shock Wave Dynamics in Magnetized Plasmas

“…In addition, PI's group has three more papers have currently been either submitted or being reviewed for publication. 11,12,19 Since the funding of the DOE grant in 2004, a total of eight national-level conference presentations [20][21][22][23][24][25][26][27] -five at the American Physical Society's Division of Plasma Physics (APS-DPP), three at the American Physical Society's Gaseous Electronics Conference (APS-GEC), and one at the IEEE International Pulsed Power and Plasma Science Conference, and eight state-level conference presentations at the Alabama Academy of Science (AAS) meeting have been made.…”

“…3(b) indicate that a shock wave is accelerated, attenuated, and dispersed while traveling in plasma. 9,10 Clear indications of shock wave dispersion as a function of the glow discharge current are shown in Fig. 4: (a) for gas pressure P = 3.6 Torr and (b) for P = 15 Torr at capacitor charging voltage V cap = 12 kV.…”

“…Moreover, the entire spark-gap plus capacitor system are placed inside a light-tight housing. 9,10 Steady-state plasma and electric-field characteristics are diagnosed with various electrical and high voltage probes. A sample measurement of plasma parameters using single Langmuir and floating double probes at a fixed current of 35 mA (and corresponding current density J = 3.6 mA/cm 2 ) in the range of gas pressures from 3-18 Torr yields an electron number density ~ 10 Shock wave profiles in the plasma are measured with the photo acoustic deflection (PAD) technique of laser beams.…”

“…The laser deflection signals at both pressures show attenuation and an increasing widening of the shock-front as the plasma current is increased. 9 Shock wave dynamics are also captured on a high-speed camera that was obtained from Princeton Plasma Physics Laboratory (PPPL) last summer as part of an outreach program to aid in the collaborative research efforts. The high-speed Phantom 4 CMOS camera recorded the events in the glow discharge Ar and N 2 plasmas at a frame rate in access of 43,000 fps.…”

Shock wave interaction with pulsed glow discharge and afterglow plasmas

“…jump connected with the shock wave can result in local neutral gas heating causing the shock dispersion and the shock-speed increase [14][15][16]. Others argued that the thermal non-uniformities and temperature effects are the dominant mechanisms for the observed shock wave broadening and velocity changes in plasmas [17][18][19][20][21][22][23][24]. In a glow discharge plasma column, the temperature gradients (longitudinal and radial) and thermal non-uniformities are always present.…”