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.