Data Analysis and Tomographic Reconstruction via X-Ray Measurements With a GEM Detector at the High-Voltage Padova Test Facility

In the context of magnetic confinement fusion, the Megavolt ITER Injector and Concept Advancement (MITICA) project is supported by another experiment called High-Voltage Padova Test Facility (HVPTF): a device designed to improve the knowledge of high voltage holding in a vacuum. HVPTF includes a vacuum chamber containing two electrodes separated by an insulator or a vacuum gap, across which electrical discharges can develop. The electrodes are powered by two independent Cockcroft–Walton power supplies, allowing for a total voltage difference up to 800 kV. The current, voltage, and pressure inside the chamber are monitored at a sampling rate of 100 Hz. Studying the physics behind electrical discharges is fundamental to prevent their development in MITICA, where they can lead to structural damage to the experimental components. For this reason, in April 2022, a gas electron multiplier (GEM) detector was installed at HVPTF, allowing to perform X-ray measurements resolved in time, space, and energy at high rates (
$ {>} 1~\text{MHz}$
) without incurring severe pile-up problems. This work describes the analysis of data coming from current, voltage, and pressure sensors, and the X-ray GEM (XR-GEM) detector at HVPTF during two 2022 experimental campaigns. Correlations between sensor signals with the X-ray measurements have been highlighted. Experimental results indicate the presence of characteristic X-ray emissions from anode atoms during electrical discharge events in the needle–plane electrode configuration. An algorithm was developed for generating synthetic detector data based on user-defined X-ray emissions within the vacuum chamber and performing tomographic reconstructions using actual or synthetic detector data. Preliminary results indicate possible gas emissions from the anode’s surface during electrical discharge events.