Cryogenic R5912-20Mod Photomultiplier Tube Characterization for the ProtoDUNE Dual Phase Detector

TL;DR

This paper characterizes the cryogenic performance of Hamamatsu R5912-20Mod photomultiplier tubes for use in the ProtoDUNE dual phase detector, focusing on their gain, linearity, and fatigue effects at cryogenic temperatures.

Contribution

It provides the first detailed cryogenic performance characterization and validation of R5912-20Mod PMTs for large-scale neutrino detectors like ProtoDUNE.

Findings

PMT gain decreases at cryogenic temperatures with increased output current.

High light intensity or pulse rate causes fatigue effects in the PMTs.

Characterization of 40 PMTs confirms their suitability for ProtoDUNE.

Abstract

The Deep Underground Neutrino Experiment (DUNE) is a dual-site experiment for long baseline neutrino oscillation studies, and for neutrino astrophysics and nucleon decay searches. The far detector is a 40-kton underground liquid argon time-projection-chamber (LAr TPC), in which the photon detector system adds precise timing capabilities. The ProtoDUNE dual phase detector will consist of a 6x6x6 m^3 LAr TPC to be operated at the CERN Neutrino Platform and the photon detection system will be formed by 8-inch cryogenic photomultipliers from Hamamatsu. The PMT model (R5912-20Mod) performance at cryogenic temperature is studied including dark current, gain, and linearity with the light intensity and pulse rate. In addition, the PMT base design is validated. At cold, a decrease of the PMT amplification, or fatigue effect, is measured as the PMT output current increases, either, due to high gain, light intensity or rate. Also, the characterisation results of the 40 photomultipliers to be used in ProtoDUNE dual phase are presented.