The Karlsruhe Tritium Neutrino Experiment (KATRIN) measures the effective
electron anti-neutrino mass with an unprecedented design sensitivity of 0.2 eV
(90 % C.L.). In this experiment, the energy spectrum of beta electrons near the
tritium decay endpoint is analyzed with a highly accurate spectrometer. To
reach the KATRIN sensitivity target, the retarding voltage of this spectrometer
must be stable to the ppm level and well known on various time scales (μs
up to months), for values around -18.6 kV. A custom-designed high-voltage
regulation system mitigates the impact of interference sources in the absence
of a closed electric shield around the large spectrometer vessel. In this
article, we describe the regulation system and its integration into the KATRIN
setup. Independent monitoring methods demonstrate a stability within 2 ppm,
exceeding KATRIN's specifications.Comment: 28 pages, 17 figures, minor improvement