Observables of the Electrical Potential of the KATRIN Tritium Source from Calibration with a High-Intensity Krypton-83m Source
Creators: name: Machatschek, Moritz
Publisher: name: Zenodo
Year: 2022

description: Authors: Moritz Machatschek, Matthias Böttcher, Caroline Fengler, Jaroslav Storek, Magnus Schlösser Co-author: KATRIN Collaboration<br> The KArlsruhe TRItium Neutrino experiment currently provides the best neutrino mass upper limit of 0.8 eV/c2 (90% C. L.) in the field of direct neutrino-mass measurements [1]. This result has been obtained with only 5% of the anticipated total measurement time. However, reaching the target sensitivity of 0.2 eV/c2 at 90% C. L. not only requires the full measurement time, but also the detailed study of systematic measurement uncertainties. One major systematic effect is linked to the electrical potential which is formed inside of the tritium source. The β-electrons generated in the source partly ionize the molecular gas and form a plasma inside a source magnetic field of 2.5 T [2]. A spatial inhomogeneity in this plasma and thus in the starting potential of the β-electrons would lead to a distortion of the β-spectrum. This effect needs to be characterized in order to reduce systematic bias in the neutrino mass measurement. To this end we measure the line-profile of mono-energetic conversion electrons from of 83mKr, which serves as an atomic reference standard. By co-circulating trace amounts of 83mKr with tritium inside of the WGTS, spatial distortions can be precisely quantified. Most suitable for the determination of these effects are the electron conversion N-lines, which offer a vanishing intrinsic line width. Any additional broadening would thus be assigned to inhomogeneities in the electric potential of the plasma. In 2021 a three-week measurement of the 83mKr N-line spectrum was performed, using a strong 10 GBq 83Rb [3] source to allow unprecedented precision. In addition, measurements with co-circulating helium and krypton were performed, which has allowed to record a reference spectrum under non-plasma conditions. In this poster we describe the measurements, the analysis and the impact on the neutrino mass result. We acknowledge the support of Helmholtz Association (HGF); Ministry for Education and Research BMBF (05A17PM3, 05A17PX3, 05A17VK2, 05A17PDA, 05A17WO3, 05A20VK3, 05A20PMA and 05A20PX3); Helmholtz Alliance for Astroparticle Physics (HAP); the doctoral school KSETA at KIT; Helmholtz Young Investigator Group (VH-NG-1055); Max Planck Research Group (MaxPlanck@TUM); Deutsche Forschungsgemeinschaft DFG (Research Training Group grant nos. GRK 1694 and GRK 2149); Graduate School grant no. GSC 1085-KSETA, SFB-1258, and Excellence Cluster ORIGINS in Germany; Ministry of Education, Youth and Sport (CANAM-LM2015056, LTT19005) in the Czech Republic; the Department of Energy through grants DE-FG02-97ER41020, DE-FG02-94ER40818, DE-SC0004036, DE-FG02-97ER41033, DE-FG02-97ER41041, DE-SC0011091 and DE-SC0019304; and the Federal Prime Agreement DE-AC02-05CH11231 in the USA. This project has received funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme (grant agreement no. 852845). We thank the computing cluster support at the Institute for Astroparticle Physics at Karlsruhe Institute of Technology, Max Planck Computing and Data Facility (MPCDF), and National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory. [1] M. Aker, et al., Nature Physics 18, 2022, 160-166.<br> [2] M. Aker, et al., Journal of Instrumentation Volume 16, 2021, T08015.<br> [3] O. Lebeda, D. Vénos, J. Ráliš, M. Šefčík, O. Dragoun, Ultra-intense 83Rb/83mKr emanation generator for the source plasma calibration at the KATRIN experiment, this conference