The influence of the cathode surface on the movement of magnetically driven electric arcs

The arc movement was examined for tubular copper electrodes using different plasma gases (argon, helium, nitrogen, air, chloride and mixtures of these gases). The normal arc current was 100 A; the arc was moved using an external magnetic field which varied between 10 and 1500 G. The arc velocity followed an aerodynamic type of equation when the cathode surface was contaminated. For clean or heavily contaminated cathode surfaces another opposing force becomes important, the surface drag force. The arc movement was also investigated by using high speed filming and following the arc current fluctuations. The cathode surface was examined using Auger, ESCA and SEM; work function values were obtained using a Kelvin probe. The results were consistent with the model presented for the arc movement.