Development of bases and qualification tests of Photomultiplier Tubes for the AugerPrime scintillation detectors

Abstract

We describe two test benches that were designed and constructed to perform a set of acceptance tests for about 1200 Photomultiplier Tube (PMT) units to be installed in the surface scintillation detectors of AugerPrime. Besides possessing robustness, long-term reliability, and low power consumption, each PMT-unit requires a dynamic range wide enough to cover signals ranging from a single to more than 20,000 minimum ionizing particles with not more than 5 % deviation from linear response. This posed a particular challenge which was met by combining a specially selected 1.5" PMT type with a custom made Cockcroft Walton type base. The characteristics of the PMT units and qualification results obtained for a large quantity of tested units will be presented and discussed. Besides measuring the gain and linearity for each PMT-unit for different supply voltages, in a sub-sample of about 10 %, we also measured the quantum-efficiency of the photocathode as a function of wavelength as well as its homogeneity across the full photocathode area with 1 mm spatial resolution. The latter is of importance because of the fiber-optical readout of the scintillation detectors.