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

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 custommade 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 83m 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 highvoltage divider K35 is in agreement with the last PTB calibration 4 years ago. This result demonstrates the utility of the calibration method, as well as the long-term stability of the voltage divider.

A novel ppm-precise absolute calibration method for precision high-voltage dividers

“…In order to derive the real scale factor M B from M B we measured the differential scale factor for different voltages up to 35 kV (see figure 10 and 11) and fitted the data * * * according to equation (11) to obtain the coefficients a, b c and d. We also included the low voltage calibration values measured as described in section 2 (see set-up in figure 2) into the analysis. Since in that measurements the real scale factor is determined, we used a combined fit to describe all data points † † †.…”

“…We crosschecked this by comparing the scale factor M B of G35 with the one measured directly with the help of K65 using a set-up as shown in figure 2 two months later. * * * The data was fitted with MINUIT [17] † † †The fit function is a sum of equations (9) for the data point obtained with the low voltage calibration measurement and (11) for the data points of the differential scale factor determination. Thus, we could confirm the result obtained for the linearity measurement with the novel absolute calibration method.…”

First operation of the KATRIN experiment with tritium

“…The alignment of all magnets and the blocking of positive ions were demonstrated [14]. In 2017, the system was further tested with a gaseous and a condensed 83m Kr source, demonstrating the excellent spectroscopic performance of the MAC-E filter technology [15] and verifying the calibration of the high-precision high voltage system at the ppmlevel [16]. The success of these two campaigns was the prerequisite for proceeding with the first tritium injection into the WGTS.…”

High-Precision Atomic Mass Measurements for Fundamental Constants

“…The second row gives the result from the 2006 SMILETRAP measurements [79], and the third gives the more than a factor of 10 more precise result from the FSU group [32]. This result is higher than the SMILETRAP result by 2.2(1.2) eV and its uncertainty is slightly less than that of the absolute calibration of the retarding voltage in KATRIN, which is now 90 meV [70]. Table 6.…”

“…The mass difference between tritium and helium-3 is closely related to the Q-value (available energy) of the beta-decay of tritium. This is an important parameter for testing systematics in precision measurements of the beta-electron energy spectrum of tritium near its endpoint, which set upper limits on the mass of the electron neutrino [69,70]. For this reason, the masses of T + and 3 He + are often measured together so that some systematics cancel in their difference.…”