Relationship between Electric Field Integral Value and Vacuum Breakdown Characteristics in Small Electrode with Multi-apertures

For the critical plasma test equipment JT-60SA, vacuum electric breakdowns around the apertures are a serious problem for developing the high energy and high power negative ion source accelerator. To improve the high voltage performance of the accelerator, we investigated the relation of a breakdown electric field in vacuum to the electric field integral value of electrode’s surface for the multi-apertures electrode. As the result of breakdown tests for various types of multi aperture electrode, it is found that the electric field integration “ES” has a certain relation with vacuum breakdown field and field emission current characteristic. Reducing the “ES” with the relaxation of electric fields leads the improvement of the breakdown performance. Moreover, the low value of “ES” induced the reductions of field enhance factor “β” and emission area “A” of field electron emission from the electrode. Therefore, we found that reductions of pre-breakdown current that flows before the occurrence of breakdown by reducing the “ES” made the breakdown electric field improved