Current–voltage relations in magnetrons

The current–voltage relationship in a magnetron plasma appears to be strongly dependent on the dynamics of the sputtered particle–gas atom interaction. Large fluxes of energetic (several eV) sputtered atoms from the cathode heat the gas in the near cathode region, resulting in a significant reduction in the local gas density as a function of discharge current (and hence particle flux). This reduction in gas density results in a lower rate of ion formation, and hence a more resistive plasma. Thus, the rate of voltage increase with current in a magnetron is related to the magnitude of the gas density rarefaction, which is dependent on the cathode sputter yield, sputtered atom energy, the cross section for sputtered atom–gas collisions, the molecular velocity of the gas, and the gas density. A model has been developed which describes the observed rate of voltage increase in a magnetron as a function of this thermalization process.