Comparison between the 1st and 3rd order mode temporal characteristics of two-sided multipactor discharge in cavity

Abstract

For investigating the influence of high order two-sided multipactor discharge on the accelerator field-building process, the temporal characteristics of the 3rd order two-sided multipactor discharge in oxygenfree copper cavity are studied numerically. The particle-in-cell and Monte-Carlo methods are used in the simulation and the characteristics of the 1st order mode are also studied for comparison. The numerical results can be concluded as follows. In the multipactor discharge evolution, the electron number, discharge current, deposited and discharge power increase exponentially and tend to be saturated. At the saturation stage of the 3rd order mode, the values of electron number, discharge current, deposited and discharge power are lower than at the saturation stage of the 1st order mode. Meanwhile, the rising time of waveform in the 3rd order mode is longer than in the 1st order mode. There is a time-delay phenomenon in the waveform of discharge current, which results in a partial charging process in multipactor discharge. The average value of the discharge power is equal to the average deposited power. The value of discharge power in the 3rd order mode is about 1% of that in the 1st order mode. Therefore, the 3rd order mode is not significant in accelerator field-building process compared with the 1st order mode. The characteristic of the 1st order two-sided multipactor discharge is the accelerated motion of single electron beam, while that of the 3rd order is the complex accelerated-decelerated-accelerated motion of multi-electron beams. When the multipactor discharge enters into the saturation stage, the space charge effect of the 3rd order mode is not stronger than that of 1st order mode.