Current Speed in a Magnetic Annular Shock Tube

Abstract

A parametric study of the speeds of the current sheet and center-of-gravity of current in a magnetic annular shock tube has been carried out. The parameters varied include: (1) the drive current, (2) the polarity of the inner electrode, (3) the gas pressure, (4) the nature of the gas, (5) the radius of the inner electrode and (6) the material of the inner electrode. The most interesting result of the investigation was the observation of limiting speeds for the current sheet and center-of-gravity of current of approximately 8 cm/μsec and 3 cm/μsec, respectively. These speeds were not exceeded even under conditions where the magnetic pressure exceeded the dynamic pressure by a factor of 10. The most probable explanation of the limiting speed is that it is due to the inertial drag of material ablated from the insulator at the driver end of the shock tube.

A characteristic velocity for gas-fed PPT performance scaling

“…6. As expected, and found in previous experiments [14,19], as both the energy and current increase, the effective plasma resistance drops. A decreasing value of ψ for the observed increasing performance of PT5 in Mode I operation is the most consistent explanation with all the observed trends presented here and in the literature.…”

“…The discrepancy (the performance improvement was measured to be nearly a factor of 2.5) could be caused by the lower propellant utilization expected with helium. Ion diffusion to the walls has been suspected before as a significant loss mechanism in magnetic shock tubes [14] and plasma guns [15]. In addition, if the current is carried at all by the ions in these discharges, then the cathode surface could also be retarding the bulk motion of the current sheet.…”

Gas-Fed Pulsed Plasma Thrusters: Fundamentals, Characteristics and Scaling Laws

“…5.6. As expected, and found in previous experiments [79,31], as both the energy and current increase, the effective plasma resistance drops. A decreasing value of ip for the observed increasing performance of PT5 in Mode I operation is the most consistent explanation with all the observed trends presented here and in the literature.…”

“…The discrepancy (the performance improvement was measured to be nearly a factor of 2.5) could be caused by the lower propellant utilization expected with helium. Ion diffusion to the walls has been suspected before as a significant loss mechanism in magnetic shock tubes [79] and plasma gvnz [80]. In addition, if the current is carried at all by the ions in these discharges, then the cathode surface could also be retarding the bulk motion of the current sheet.…”

A Phenomenological Study of the Steady-State Current Sheet Speed in a Magnetically Driven Shock Tube

“…Although there is some experimental evidence of electrode erosion, both experimental results and theoretical calculations showed that neither sputtering nor desorption could be of great importance as far as their direct influence on the steady-state speed of the current sheet is concerned 16 . Apart from the effect of increasing the apparent density of the plasma, the introduction of insulator material into the discbarge can also cause the formation of a standing arc near the driving end of the electrodes and thus reduce the effective driving current 12,17,18 . To investigate this effect, as shown in Fig.…”