Development of X-Ray Collimators to Identify Sources of Radiation in Devices Insulated by Large Vacuum Gaps

The article outlines the development of a diagnostic system designed to pinpoint the origins of X-ray emissions in high-voltage direct current (HVdc) equipment isolated by large vacuum gaps. Electrons extracted from cathodic surfaces through field emission (FE) processes are accelerated to energies below 1 MeV, generating bremsstrahlung radiation upon impact with anodic surfaces. This radiation constitutes one of the main evidence that high-voltage conditioning is taking place on a long gap isolated system and with voltages above 50-100 kV. The development of MITICA, the prototype for ITER's neutral beam injector (NBI), necessitates diagnostic systems capable of monitoring the progression of high-voltage conditioning in the electrostatic accelerator. Detectors can be placed in atmospheric air to monitor the evolution of the high-voltage conditioning of the electrostatic accelerator through the metallic vacuum vessel. The adoption of an X-ray collimator embedding a cerium-doped lutetium-based scintillation crystal has been proposed to cope with this target. A prototype of a single-pixel collimator (SPC) with a lead shield and variable geometry has been produced and tested at the high-voltage Padova test facility (HVPTF). High-voltage assessments, reaching up to 780 kVdc, were conducted to refine the collimator design. A multipixel variable-geometry system, utilizing the same technology, is recommended for monitoring the vacuum high-voltage conditioning of the MITICA electrostatic accelerator.