Influence of an external magnetic field on the threshold of multipactor onset on a dielectric surface

Abstract

537.521.7+621.385.6 In this paper, we propose a theoretical model of the initial stage of development of a one-sided secondary-emission (multipactor) discharge on a dielectric surface. Consideration is based on a statistical method supported by an exact analytical solution for the transit-time distribution function of secondary electrons. The general integral equation allowing us to determine the stationary emission-phase distribution functions and the threshold of multiplicator onset in the presence of an external magnetic field is formulated. It is shown that the presence of an external magnetic field can significantly change the conditions of multipactor onset. It is found that the discharge-zone boundaries calculated within the framework of a statistical model are in qualitative agreement with the results obtained by the Monte-Carlo method.

Reduction of the Multipactor Threshold Due to Electron Cyclotron Resonance

“…Reduction of the multipactor threshold under the ECR condition was observed in experiments in a microwave cavity [21]. Within this experiment, the microwave field was parallel to the surface of emission and the permanent magnetic field was perpendicular to this surface, a situation which is similar to the case previously considered in [19,20]. However, in contrast to the case of multipactor on dielectric surfaces, the microwave field amplitude was zero at the cavity wall and the dc electric field was zero everywhere inside the cavity.…”

“…As follows from the above analysis (see also [19,20]), a strong ECR effect on the multipactor threshold can be expected only in the case when the electron flight time significantly exceeds the microwave period. Under typical multipactor conditions, the dc electric field pushes the secondary electrons back to the surface of emission.…”

“…More extended studies on the effect of a permanent magnetic field on the multipactor on a dielectric plate was undertaken in papers [19,20] where different orientations of the magnetic field with respect to the dielectric surface and the polarization of the microwave field were considered. Specifically, it was found that under the ECR condition, the multipactor threshold (in terms of the microwave field amplitude) can be significantly reduced if the permanent magnetic field is perpendicular to the microwave electric field and the electron flight time is long enough to satisfy the second equality in (17) 2 .…”

“…But even a weak magnetic field may still have a large effect on the resonance conditions. Situations have also been observed when the presence of a dc magnetic field causes a reduction in the multipactor threshold [10,[17][18][19][20][21]. Thus, there is some uncertainty concerning the effect of a magnetic field on the multipactor threshold and some clarification of the situation seems desirable.…”

Influence of work function on the multipactor threshold

“…The TEEY is highly dependent on the energy and incidence angle of the primary flux [4], the nature and surface condition of the sample [5], the presence of a magnetic field [6]... External magnetic or electric field will also modify the particle trajectories, influencing the RF/electron resonance and thus making the multipactor phenomenon more complex [7]. In tokamaks, RF antennas are used to heat or drive current in fusion plasma, and are subject to a magnetic field so that to ensure the plasma confinement.…”