Overvoltage protection of the Ion source and extraction power supplies in the SPIDER experiment

The SPIDER (Source for the Production of Ions of Deuterium Extracted from RadioFrequency plasma) experiment will constitute the test bed for developing the ion source of ITER negative ion neutral beam injectors. The beam source of SPIDER will be subjected to breakdowns across the beam extraction and acceleration grids and the protection of the power supply systems from the effects of these events is mandatory. OCEM SpA has been contracted to provide the Ion Source and Extraction Power Supplies (ISEPS) for SPIDER and has developed a design for the Extraction Grid Power Supply, a power supply of -12kV output feeding the beam extractor. This work presents the model used for fast transient simulation of the SPIDER power supply system with particular emphasis on the design solutions against overvoltage across the output poles of the Extraction Grid Power Supply (EGPS).