Characteristics of micro-particle phenomena under electron beam bombardment in vacuum pre-breakdown processes

It is well known that there are numerous micro-particles and micro-protrusions on electrodes surface in vacuum gaps. The vacuum breakdown mechanisms initiated by the micro-particles and the micro-protrusions have been studied during the vacuum pre-breakdown processes. However, there is no quantitative research on interaction effect between the micro-particles and the field emission electrons based on the non-ideal micro-protrusions in different vacuum gaps. In this paper, by means of a micro-protrusion model based on the fractal theory and the micro-particle dynamic equations, the anode micro-particle characteristics under the bombardment of the field emission electrons in different vacuum gaps are investigated quantitatively. The results show that the bombardment of the field emission electrons has a significant influence on the dynamic characteristics of the micro-particles. There is a close relationship between the vacuum gap and the dynamic characteristics of the micro-particles. With a vacuum gap less than 1.0 mm, the maximum temperature of the micro-particles would eventually reach the boiling point and the evaporation rate would reach 97 kg-m^-2·s^-1. With a vacuum gap more than 5.0 mm, the maximum temperature would not reach the boiling point and the evaporation rate would decrease to zero. Furthermore, in a vacuum gap more than 5.0 mm, there are more obvious impact phenomena occurred between the cathode and the micro-particle than that in a vacuum gap less than 1.0 mm. The results of this paper may provide some useful information to understand the physical mechanism of vacuum breakdown.