Snubbers for Limiting and Mitigating Fault Energy during the Accelerator Grid Breakdown for DNBPS

Abstract

The ITER DNB system is based on the acceleration of negative ions; designed to inject 60A of Neutral beam at (-) 100kV with specified modulation in to the plasma. The acceleration grids operate very close to breakdown. During conditioning and nor- mal operation of the injector, breakdowns can occur frequently and unpredictably. It is important to limit as much as possible the energy owing into the grids. This energy comes from the power supplies and from the electrostatic energy stored in the transmission line and stray capacitances. Core snubbers (annular disc of magnetic material) are considered to be most promising options for limiting the fault energy during the breakdowns in the accelerators. This report presents the study and overview of DNBPS system, design approach for the snubbers- circuit model, simplified model of the grid break down circuit, effect of snubber impedance on the short circuit current. As a prerequisite, simulation software (Pspice) been exposed to have hands-on experience. An experimental setup is been used to study and characterize the actual size CRGO core snubber. Results are discussed to investigate the feasibility of CRGO cores. In order to assess the effectiveness of snubbers, a refined model having frequency dependency should be developed. The model should be able to take in to account the presence of DC component. Reported work presents the development of refined snubber model using PSIM tool.