Multipactor Breakdown Threshold Reduction Due to Magnetic Confinement in Parallel Fields

In certain high-power RF devices, such as isolators and circulators, a static magnetic field is present in parallel with the oscillating RF electric field. This parallel magnetic field imposes electron Larmor motion, which restricts the trajectories of electrons accelerated by the RF field. In open geometries, magnetic confinement reduces electron losses in the multipactor region and can reduce the breakdown threshold. In this paper, the effect of magnetic confinement on multipactor breakdown threshold was measured experimentally using a stripline fixture with an externally applied uniform magnetic field. Multipactor threshold power was reduced from the unmagnetized case by as much as 3 dB at magnetic fields of about 0.5 kG. Multipactor gap aspect ratio has a significant impact on the degree of threshold reduction.