Magnetic fields in vacuum insulated high voltage power apparatus

Magnetic fields in high voltage vacuum insulation are of interest because they may produce cross-field discharges and propel vacuum arcs. This paper shows that the coaxial cable geometry with elbows and high voltage terminations permits neither the gyration of electrons nor the sufficient elongation of electron trajectories to produce a noticeable number of ionizing collisions with residual gas molecules. Experiments with a 10 toot long, 5.75 inch diameter coaxial line did not reveal the theoretically expected are motion away from the current source nor any tendency towards retrograde motion. In a butt-gap geometry, however, the kink instability of the plasma column was found to drive the are rapidly to the electrode edge. A radial magnetic field in the butt-gap enhanced are diffusion and cathode spot tracks indicated a tendency of the plasma to rotate in accordance with the Lorentz force. The beginnings of the new concept of self-sustained ion pumping are outlined. Apparatus for demonstrating this effect utilized permanent bar magnets, titanium cathodes and 60 Hz high voltage.