Characteristics of Voltage Holding Capability in Multi-stage Large Electrostatic Accelerator for Fusion Application

Voltage holding capability of a 500 kV, 22 A three-stage electrostatic accelerator, where large-area grids of 0.28 m² and large fiberglass reinforced plastic (FRP) insulators of 1.8 m in diameter are used, was examined. High voltage was independently applied to each acceleration stage, where the voltage holding capabilities of 130 kV were obtained. To identify whether the breakdowns occur in the gaps between the grids or the FRP insulators, high voltages were applied to the accelerator with and without the grids. Breakdown voltages without grids, i.e., the FRP insulator itself reached 170 kV of design value for each stage. These results show that the breakdown voltage of the accelerator was mainly determined by the gaps between the large-area grids. In this paper, the influence of non-uniform electric field and multi-stage grids on the voltage holding capabilities was also discussed.