Simulation of Secondary Electrons in a Megawatt-Class Gyrotron Collector with Voltage Depression and Magnetic Sweeping

In megawatt-class gyrotrons, the residual energy of the electron beam must be dissipated in the collector without compromising the vacuum integrity of the device, necessitating the use of various methods for lowering the peak power density to acceptable levels. Secondary electron emission from the collector surface can redistribute the power deposition profile of the incident (primary) beam, which can either be beneficial or detrimental. Secondary electrons may also be re-accelerated toward the gyrotron body, and, if not magnetically reflected, may interfere with the operation of the interaction circuit. Here, simulations of a megawatt-class gyrotron collector, including the effects of voltage depression, magnetic sweeping, and secondary/reflected electrons, are presented, to assess the potential impact on gyrotron operation and longevity.