Multipactor discharges in magnetic fields

In the high frequency electric field in vacuum, discharge occurs at a small electric field which does not cause discharge in the case of DC. This is because the number of electrons is doubled due to the emission of secondary electrons from an electrode synchronizing with the high frequency electric field, and it is called multipactor discharge. The multipactor discharge occurs also in nuclear fusion experimental apparatuses, and has drawn attention. The research on the multipactor discharge when a magnetic field exists is few. The authors carried out the experiment on the multipactor discharge in 100 MHz zone in the statical magnetic field up to about 0.08 T, and the theoretical analysis on the voltage at which discharge begins in a vertical magnetic field corresponding to [Angular frequency of electron cyclotron ω(c)]/(Angular frequency of high frequency field ω) < 1. The experimental result and the theoretical analysis result agreed qualitatively. Moreover, the simple theoretical analysis on the monopole multipactor discharge in a vertical magnetic field was carried out. Accompanying the application of a vertical magnetic field, the region where both-pole multipactor discharge is possible moved in the direction of large voltage and f1(f: frequency, 1: distance between electrodes). Both-pole multipactor discharge is cut off at a certain magnetic flux density of a vertical magnetic field. (Kako, I.)