Calibration of high voltages at the ppm level by the difference of $^{83\mathrm{m}}$Kr conversion electron lines at the KATRIN experiment

TL;DR

This paper introduces a novel in-situ calibration method for high-voltage dividers in the KATRIN neutrino mass experiment, using $^{83 ext{m}}$Kr electron lines to achieve ppm-level voltage stability verification.

Contribution

The paper presents a new calibration technique based on $^{83 ext{m}}$Kr electron lines, eliminating the need for external metrology lab calibration for high-voltage dividers.

Findings

Calibration method achieves 3 ppm stability verification.

Measured scale factor agrees with PTB calibration after four years.

Demonstrates long-term stability of the high-voltage divider.

Abstract

The neutrino mass experiment KATRIN requires a stability of 3 ppm for the retarding potential at -18.6 kV of the main spectrometer. To monitor the stability, two custom-made ultra-precise high-voltage dividers were developed and built in cooperation with the German national metrology institute Physikalisch-Technische Bundesanstalt (PTB). Until now, regular absolute calibration of the voltage dividers required bringing the equipment to the specialised metrology laboratory. Here we present a new method based on measuring the energy difference of two $^{83\mathrm{m}}$Kr conversion electron lines with the KATRIN setup, which was demonstrated during KATRIN's commissioning measurements in July 2017. The measured scale factor $M=1972.449(10)$ of the high-voltage divider K35 is in agreement with the last PTB calibration four years ago. This result demonstrates the utility of the calibration method, as well as the long-term stability of the voltage divider.