Thesis defense of Johannes Werthebach

IceCube is the largest neutrino telescope to date and consists of 5160 Digital Optical Modules (DOMs) embedded up to 2450 m deep within the ice at the geographic South Pole. The IceCube Upgrade is scheduled for installation during the 2025/26 field season. During the upgrade, approximately 700 new optical sensor modules, including calibration and test devices, will be installed at the center of the existing IceCube detector to enhance detection capabilities and improve precision measurements. One of these new designs is the Multi-PMT Digital Optical Module (mDOM) combining 24 photomultiplier tubes (PMTs) per module.
As PMTs serve as the primary detection units in IceCube, testing is required to ensure their performance meets specifications. Over 10 000 PMTs were tested at two independent sites during this campaign. A significantly higher dark rate than specified was identified in almost all units during testing. This discrepancy was traced back to elevated contamination levels of radioactive isotopes in the glass envelope of the PMTs.
In this work, a test bench was developed, constructed, and commissioned to facilitate large-scale PMT testing. The design, procedures, challenges, and results are presented.