Summary of 15 Years of HVDC Experiments and Tests in Vacuum at the High-Voltage Padova Test Facilities

Le résumé fourni par la source

This article summarizes 15 years of experimental activity at the High-Voltage Padova Test Facilities in support of the design and commissioning of the ITER neutral beam injector (NBI). High-voltage DC tests up to 800 kV were carried out in high and medium vacuum on electrode gaps ranging from a few millimeters to 150 mm. Systematic experiments on stainless steel electrodes in high vacuum validated a probabilistic model for predicting the maximum hold-off voltage of generic multielectrode systems and confirmed the presence of a significant total-voltage effect for gap lengths above a few centimeters. The spatial distribution of power dissipation during microdischarges in large vacuum gaps suggests charge accumulation points and mutual charged-particle exchange between electrodes to interpret the experimental observations. Time-resolved X-ray measurements indicate that, in a significant fraction of vacuum breakdown events, bursts of electrons impacting the anode act as precursors, with electron-stimulated desorption playing a key role in discharge development and voltage collapse. In medium vacuum, tests in Ar, H2, and N2characterized the dependence of the hold-off voltage with pressure up to the left branch of the Paschen curve and clarified the influence of static magnetic fields on Townsend discharge. Long-duration tests under stationary electric fields up to 60 kV/mm revealed irreversible switch-on phenomena with microampere-level currents on short-gap configurations. Finally, acceptance tests on solid insulators, optical fibers, and spark gaps are reported, and the main lessons learned and open issues are discussed.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.