Particle-In-Cell Simulation for Electron Velocity Dispersion in a Vacuum Tube for RF-DC Conversion*

To cause RF-DC conversion with a vacuum tube, an electromagnetic field is applied to the electron beam to induce cyclotron resonance, which accelerates the electrons and extracts energy from the electron beam at a potential depression collector. It has been found that the velocity dispersion of the electrons causes heat loss, which reduces the final energy conversion efficiency. Therefore, it is necessary to analyze the conditions that cause electron acceleration with less velocity dispersion while still producing resonance. In this paper, we used the particle-in-cell (PIC) method, which is the best for analyzing accurate particle behavior and for observing the velocity dispersion and electron acceleration under the interaction of electromagnetic fields. The initial energy of electrons entering the calculation region was assumed to be uniform and 1~2 keV.  The conditions for efficient electron acceleration with low-velocity dispersion were investigated at frequencies from 2.45 GHz to the Ka-band, where the tube is expected to be operated. Preliminary results suggested that velocity dispersion was likely to increase under the same conditions as frequency increased.