Cathode Position Response of Large-Area Photomultipliers Under a Magnetic Field

TL;DR

This study investigates how magnetic fields affect the response of large-area photomultiplier tubes across their photocathodes, revealing position-dependent effects on efficiency and gain crucial for experimental data analysis.

Contribution

It provides detailed measurements of magnetic field effects on PMT response as a function of cathode position, using an automated scanning method.

Findings

Magnetic fields cause position-dependent variations in PMT efficiency and gain.

A pronounced valley in collection efficiency occurs at specific cathode locations.

Response patterns vary with magnetic field magnitude and orientation.

Abstract

With the increasingly common use of large area PMTs (photomultiplier tubes) for nuclear and particle physics experiments, information on the position dependent magnetic field effects across the PMT's photocathode is important to effectively analyze and understand data collected from PMTs. Using an automated two-dimensional scanner, we have measured the PMT response to an external magnetic field as a function of the cathode position impinged by a collimated light source. This study shows a clear dependence on the cathode position in both collection efficiency and gain of the PMT in the presence of a magnetic field. In particular, a pronounced valley in the collection efficiency is observed for certain locations of the cathode when the magnetic field is transverse to the PMT axis. The pattern of the position dependence is presented for several different magnitudes and orientations of the magnetic field relative to the PMT.