Vacuum High Voltage Holding: DC Experiments and modelling

This report describes the main activities carried out at the High Voltage Padova Test Facility HVPTF in 2018 and the ones related to the installation of a new high voltage test stand at the Consorzio RFX . The activities of the subtask 5.7 have been carried out according with the Work Programme (WP) 2018 between F4E and the Consorzio RFX, agreement on the Neutral Beam Test Facility. The activities mainly consisted in: ? studying of the X-ray spectra to investigate the nature of the physical phenomena which occurs during the high voltage conditioning ? testing instrumentation for precise current measurements and for determining type and position of discharges (visible imaging, IR imaging, RX spectra and Residual Gas Analyzer) ? maintenance of both positive and negative HV power supplies and the refurbishment of high voltage ceramic feedthroughs ? evaluation of other methods for improving voltage holding capabilities: tests of surface treatments on electrodes (e.g. alumina spray) ? testing the behaviour of "transparent anodes", i.e. anodes in which the surface is screened by a thin metallic mesh, aimed at zeroing the electric field at surface behind ? experimental study of two-electrode configurations subjected to a combination of Common-Mode Voltage (CMV) and differential-mode voltage to understand the different contribution of anode and cathode on the discharge initiation ? ordinary maintenance of the vacuum plant and controlling system ? construction of a small experimental set-up to measure with sufficient accuracy the FN emission insulating the electrodes by short vacuum gaps, the experimental set up has been called High Voltage Short Gap Test Facility (HVSGTF) The activity mentioned at the last point is partially reported in sec. 10. The specific technical note T5.7 - P1.4_RFX-IE-TN-59 has been prepared to indicate the data for the radiological safety assessment of the HVSGTF.