Development of a data analysis software for the XR-GEM installed at HVPTF and preliminary results

The MITICA experiment, under construction at Consorzio RFX (Padova, Italy), is the full-scale prototype for the Neutral Beam Injector (NBI) of the ITER tokamak. One of the critical aspects for the ion beam accelerator is high voltage holding over long vacuum gaps (up to 1 MV from the ion source to the enclosing vessel), with the main issue being the occurrence of discharge events, which could severely damage the machine. To study this phenomenology, with the aim of prevention of discharges, the High Voltage Padova Test Facility (HVPTF) experiment is in operation. The setup of HVPTF consists in a cylindrical vacuum vessel, with stable pressure control, in which two replaceable electrodes are mounted with an adjustable gap width. The electrodes are powered by independent power supplies, allowing for a total voltage difference up to 800kV. Current and voltage of the power supplies, as well as the pressure and the gas composition inside the chamber are monitored at a sampling rate of 100 Hz. Additionally, the bremsstrahlung X-ray emission produced by the accelerated electrons during discharges is monitored by means of scintillators at higher rates (up to 1 MHz). Data from past experimental campaigns have been analyzed and correlations between the current/voltage signals and the X-ray emission have been highlighted. Recently, a new detector, based on the Gas Electron Multiplier (GEM) and optimized for X-ray detection, has been installed at HVPTF. The detector acts as a very fast single photon counting system (with rates up to about 125 MHz), allowing for real-time measurement of the X-ray emission rate, which could be used as basis for the development of a feedback control system for the prevention of discharges. The aim of this work is to illustrate the development of a new data analysis software, tailored on the data read by the GEM detector, displaying some of the first results obtained from the recent experimental campaigns. Future perspectives will also be drawn, for the next steps to take towards the realization of the breakdown prevention system.