Influence of an axial magnetic field on the electron temperature in a vacuum arc plasma

The influence of an axial magnetic field on the electron temperature of a vacuum arc plasma has been studied experimentally and theoretically for moderate discharge currents of 400-600 A, magnetic flux densities of 0-50 mT, and different cathode materials such as uranium, titanium, and carbon. Experiments have been performed using the vacuum arc ion source VARIS. An 127° electrostatic cylinder spectrometer has been used to detect the electron energy spectra. The electron temperature has been derived by a Maxwellian approach applied to the experimental data demonstrating a significant temperature and mean energy rise with increasing magnetic flux density consistently with the model calculations. The electron temperature in the inter-electrode gap of a vacuum arc has been calculated from an energy balance equation that was supplemented by an equation for the cross-section of the plasma flow. The plasma flow is constricted by an external axial magnetic field instead of the free spherical plasma flow in its absence. This leads to an increase in the electron temperature. The constriction of the plasma jet is limited by the cathode group spot diameter at a flux density B_max specifying an upper limit of the electron temperature.