Propagation direction reversal of ionization zones in the transition between high and low current magnetron sputtering

Past research has revealed the propagation of dense, asymmetric ionization zones in both high and low current magnetron discharges. Here, we report about the direction reversal of ionization zone propagation as observed with fast cameras. At high currents, zones move in the E×B direction with velocities of 103–104 m/s. However, at lower currents, ionization zones are observed to move in the opposite, the −E×B direction, with velocities ∼103 m/s. It is proposed that the direction reversal is associated with the local balance of ionization and supply of neutrals in the ionization zone.