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

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Abstract
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.
Funding Information
  • International Thermonuclear Experimental Reactor (ITER) Organization through the ITER-Reverse Field eXperiment (RFX) Neutral Beam Testing Facility (NBTF) Agreement

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