Induced drift currents in circular planar magnetrons

The circulating E×B drift currents in a circular planar magnetron have been measured as a function of discharge parameters. The drift current was calculated from the magnetic field measured at a probe located over the center of the drift loop. The drift current was found to vary almost linearly with magnetron discharge current over the entire range of the magnetron power capability. The drift current-to-discharge ratio ranged from 2.5–9 and was dependent on gas pressure, and to some extent on gas species and cathode material. This ratio was derived using both classical two-body relations and also Bohm diffusion considerations. The results of the Bohm diffusion calculations are in close agreement with the experimental measurements. An additional feature confirming the Bohm diffusion results is the weak dependence of the observed drift current on gas species. Bohm diffusion is based on turbulent, collective interactions between electrons and the choice of gas species should only have an indirect effect through the electron density and temperature.