Characterization of photo-multiplier tubes for the Cryogenic Avalanche Detector

TL;DR

This paper characterizes cryogenic photomultiplier tubes (PMTs) for use in the Cryogenic Avalanche Detector, evaluating their performance in liquid argon, including gain, dark count rate, and operational stability.

Contribution

It provides a detailed performance assessment of two types of cryogenic PMTs for the first time in the context of the CRAD, highlighting their suitability and operational challenges.

Findings

R11065-10 PMTs achieved gain of 10^7 and low dark counts but had stability issues in liquid argon.

R6041-506-MOD PMTs demonstrated high gain and low dark counts with stable operation.

Some R11065-10 PMTs failed after tens of minutes in liquid argon, indicating reliability concerns.

Abstract

New Cryogenic Avalanche Detector (CRAD) with ultimate sensitivity, that will be able to detect one primary electron released in the cryogenic liquid, is under development in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. The CRAD will use two sets of cryogenic PMTs in order to get trigger signal either from primary scintillations in liquid Ar or from secondary scintillations in high field gap above the liquid. Two types of cryogenic PMTs produced by Hamamatsu Photonics were tested and the results are presented in this paper. Low background 3 inch PMT R11065- 10 demonstrated excellent performance according to its specifications provided by the producer. The gain measured with single electron response (SER) in liquid Ar reached 10^7, dark count rate rate did not exceed 300 Hz and pulse height resolution of single electron signals was close to 50%(FWHM). However, two R11065-10 PMTs out of 7 tested stopped functioning after several tens minutes of operation immersed completely into liquid Ar. The remaining 5 devices and one R11065-MOD were operated successfully for several hours each with all the parameters according to the producer specifications. Compact 2 inch PMT R6041-506-MOD with metal-channel dynode structure is a candidate for side wall PMT system that will look at electroluminescence in high field region above liquid. Four of these PMTs were tested in liquid Ar and demonstrated gain up to 2x10^7, dark count rate rate below 100 Hz and pulse height resolution of single electron signals of about 110% (FWHM).