Detailed investigations of PMTs in optical sensors for neutrino telescopes such as IceCube Upgrade

TL;DR

This paper provides a detailed analysis of photomultiplier tubes used in neutrino telescopes, focusing on their photocathode and dynode system to improve understanding of their optical and electronic performance.

Contribution

It introduces comprehensive methods including ellipsometry, photocathode scanning, and simulations to analyze PMT properties relevant for neutrino detection.

Findings

Optical properties of photocathodes characterized by ellipsometry.

Performance variations along the photocathode surface identified.

Correlation between electric field, electron trajectories, and amplification deviations.

Abstract

Photomultiplier tubes (PMTs) are a central component of neutrino telescopes such as IceCube and KM3NeT, and an accurate understanding and measurement of their properties is indispensable for improvements of these experiments. In this contribution we focus on a detailed investigation of the photocathode and the dynode system and their influence on the performance of the PMT. Three methods are used for the investigation. Ellipsometry measurements of the photocathode analyze its optical properties in terms of absorption probability and refractive index. Scans of the photocathode in single photon illumination probe performance differences along the photocathode surface. Systematic deviations in the resulting amplifications are compared to electric field and electron tracing simulations through the dynode system to understand the measured values. The goal is an extensive understanding of efficiency, amplification, and timing as functions of wavelength and impact point as well as angle.