RF induced discharges in vacuum in the SPIDER experiment

RF discharges outside the ion source are one of the main issues encountered during SPIDER experimentation limiting the pressure range of operation. Such discharges could be sustained by the power supplies but in many cases cause the plasma pulses to stop and might cause source damages. This work summarizes the experimental evidence obtained by three classes of diagnostics used to classify the type of discharges: electrical measurements from the power supplies, visible cameras and optical fibers collecting lights in the vessel. The comparative analysis of the effects of discharges in these signals improved the understanding of this issue and helped the identifications of different types of discharges that can occur outside the SPIDER Ion Source. An electrical model for the representation of these events is presented, comparing it with the normal operation conditions, and the reasons behind the occurrence of the discharges is discussed.