High-voltage measurement for the BIPM x-ray generators

In an x-ray tube, a spectrum of x-rays is produced when an electron beam hits a target. The electron beam is produced from a filament heated by an electrical current, and the electrons are accelerated by a high voltage (for example up to 250 kV) applied between the cathode and the anode. The intensity of the x-ray beam is determined by the heating current in the filament whereas the x-ray spectrum depends on the high voltage, the material used for the target (tungsten and molybdenum are used at the BIPM) and the target angle. This report describes the arrangement that has been put in place to measure the high voltage for the low- and medium-energy facilities at the BIPM. (author)