Analysis and development of a high performance core snubber based on deltamax

The core snubber is one of the most important devices in the EAST (Experimental Advanced Superconducting Tokamak) with NBI (Neutral Beam Injector) system. This device is designed to protect the NBI system during periods of high voltage breakdown. The theory for the core snubber was developed by Fink, Baker and Owen (the FBO model), who considered only resistance effects which generates a snubber design based on saturation conditions. The paper presents an approach to limit high voltage breakdown effects based on the concepts of the equivalent resistance and inductance implemented on a parallel circuit model with Deltamax cores. The EAST NBI circuit fault simulation code simulates fault conditions using a time-varying resistance and inductance in the parallel circuit model. The code was calibrated with the experimental results. Based on the simulation results an ion source core snubber using Deltamax was designed. This snubber was tested at 50 kV in a real NBI system, which has a large gradient capacitor, and a peak short current less than 400 A. The results show that testing verify the modeling method and two such snubbers can protect ion source reliability at 100 kV.