Progress in the Validation of the Voltage Holding Prediction Model at the High-Voltage Padova Test Facility

In the framework of the program for the construction-in Padova, Italy-of the first prototype of the International Thermonuclear Experimental Reactor 1 MeV-16 MW negative neutral beam injector (NNBI), an R&D activity on voltage holding in vacuum has been initiated since 2009, aimed at supporting the design, construction, and development of the NNBI accelerator. For this purpose, the high-voltage Padova test facility, designed to operate up to 800 kV, has been built, in parallel to the development of a multivoltage multielectrode voltage holding prediction model (VHPM). This paper focuses on the results of the experimental campaign (up to 270 kV) carried out on a number of electrostatic configurations, aimed at validating the VHPM under a well-controlled condition. The prediction capability of the model is partially confirmed. This result makes it worthwhile to review the physical basis of the model-based on the Cranberg-Slivkov clump theory-while also taking into consideration an alternative breakdown initiation mechanism.