Magnetohydrodynamic Results for Highly Dissociated and Ionized Air Plasma

Abstract

An investigation of air plasma moving through a constant (2300 gauss) transverse magnetic field was conducted in a shock tube. As the plasma traveled through the field, an electromotive force was produced in the plasma. Two diametrically opposite, ½-in. diameter, copper electrodes were used to measure this potential. The shock Mach number varied from 10 to 32 with corresponding equilibrium plasma temperatures from 3600° to 11 000°K. At Mach 30 the observed potential across the electrodes, with a 1-meg external load, was 236 v, which agreed with the theoretical value, but at lower Mach numbers the observed potentials were much lower than theory. By varying the external load for a shock Mach number of 30, the current from the plasma varied from nearly zero to 115 amp. This high current was extracted from the copper electrodes at nearly room temperature. The observed potential decreased linearly with increasing current indicating a nearly constant plasma resistance. For this resistance the electrical conductivity was calculated and was much less than the theoretical prediction. The maximum power extracted from the plasma was 7.8 kw with an external load of 1.85 ohms.