Time-dependent physics of single-surface multipactor discharge with two carrier frequencies

This work investigates the time-dependent physics of multipactor discharge on a single dielectric surface with a transverse rf electric field of two carrier frequencies using a multiparticle Monte Carlo simulation model with adaptive time steps. The effects of the relative strength and phase, and the frequency separation between the two carriers are studied. Closed Lissajous curves are obtained to describe the relationship between the rf electric field parallel to the surface and the normal surface charging field in the ac saturation state. It is found that two-frequency operation can reduce the multipactor strength compared to single-frequency operation with the same total rf power, though the effect of the frequency separation is not prominent on multipactor susceptibility. Formation of beat waves is observed in the temporal profiles of the normal electric field due to surface charging with a noninteger frequency ratio between the two carrier modes. Phase space evolution of multipactor electrons is examined, revealing a periodic bunching and debunching of electrons in the surface normal direction, but a gradual debunching effect in the direction tangential to the dielectric surface. Migration of the multipactor trajectory is also demonstrated for different configurations of the two-frequency rf fields.