Multipactor Discharge in a Dielectric-Loaded Accelerating Structure

Summary form only given. This paper presents a Monte-Carlo model to explain the multipactor discharge and its high power absorption in a dielectric-loaded accelerating (DLA) structure reported recently. Kinematic calculation is performed to determine the susceptibility diagram, which is a useful tool in analyzing whether multipactor discharge will take place over a range of RF and DC electric fields for certain material. A resonant condition of a maximum growth region in susceptibility diagram has teen determined numerically and analytically. The constructed susceptibility diagram is compared with the simple dielectric case. Based on the constructed susceptibility diagrams, dynamic calculations for beam loading and its power absorption by the multipactor discharge are performed. It is found that the fraction of power absorbed by multipactor discharge at saturation is much larger than the case of a simple RF window, and it is sensitive to the incident power, which confirms the prior experimental results. This enhanced power absorption is due to the fact that the length of DLA structure is much larger than the radius of the structure. The difference between the resonant condition (due to phase focusing) and saturation (due to team loading) is clarified.