Effect of Metallic Dust on Operation of Repetition-Rate High-Power Microwave Devices

In the circuits of high-power microwave (HPM) devices, such as HPM sources and/or high-gradient accelerating structures, small quantities of metallic dust may exist. These metallic particles of a micrometer size being located in the region of high RF magnetic field can absorb enough energy for significant heating and even melting. The melted clumps can then impinge on structure surface and create nonuniformities, leading to the RF field enhancement and subsequent breakdown events. This heating process in single long-enough RF pulses was analyzed in our previous paper (“Possible role of RF melted microparticles on the operation of high-gradient accelerating structures,” Phys. Rev. ST-Accel. and Beams, 12, 101001, 2009). In this paper, we consider similar processes in HPM devices operating in repetition-rate regimes. The process of particles cooling between RF pulses is first analyzed under an assumption of blackbody radiation. Then, the applicability of this assumption is discussed, and the effect of deviation from it is estimated. It is shown that the melting of metallic particle of a size comparable to the skin depth in HPM devices is possible when the RF magnetic field, microwave pulse duration, and repetition frequency are large enough.