Investigation of gas discharges with a rotational component

The presence of circulating currents in a plasma, i.e. currents that close back on themselves entirely within the plasma, has been demonstrated experimentally and a theory evolved to explain this. The apparatus, which behaves as a plasma gun, produces a discharge in hydrogen at 4¿19 ¿mHg in an axial magnetic field of 480Gs and in the radial electric field set up by six anodes and one central cathode. Twelve 1 ¿F capacitors, charged to 4.4kV, supply 12kA. The oscillograms of the voltage induced in a small search coil, inside the discharge tube, show that the magnetic field on the axis is reduced by 2100Gs (about 4.4 times the applied field). This can only be due to a circulating current of the order of 5kA which always opposes the applied magnetic field. This was observed below 14 ¿mHg, and when an electromagnetic valve was used to admit hydrogen into the evacuated tube. Currents in the plasma were detected at least 8 cm above the electrodes. The plasma was expelled at 1.1 × 107cm/s and filled a tube 60cm high. It was not always possible to explain the sign of the circulating current in terms of an axially symmetric plasma. It was therefore assumed that the discharge occurred in well defined channels, which permit azimuthal electric fields in the discharge. An expression for the curvature of the channel and the equation of its path were found. The axial magnetic field and the circulating current were calculated. In one case the correct magnitude was obtained for both. With the electric field reversed, both were too low by a factor of 2¿3. The sign was correct in all cases.