Position-sensitive vacuum photon detectors

Thierry Gys,Christian Joram

doi:10.1016/j.nima.2019.163373

Abstract

This article reviews the principles, performance and limitations of position-sensitive vacuum photon detectors which find applications in high-energy physics experiments. Particular emphasis is devoted to multi-anode photo-multiplier tubes, devices based on micro-channel plates and hybrid photon detectors. Over the past 25 years, innovation in industrial environments, research centres and universities has led to the invention and consequent optimization of a number of position-sensitive photon detectors. Miniaturization of known principles and components or the smart combination of established concepts allowed to build new classes of finely-segmented photodetectors which in turn enabled new applications in high-energy physics, but also elsewhere. The imaging of Cherenkov light in hostile hadron environments like at the CERN Large Hadron Collider is perhaps one of the most demanding applications which would not have been possible without this breakthrough.

Highlights

Today, 42 years after the pioneering work by Tom Ypsilantis and Jacques Séguinot [1], the precise and efficient imaging of Cherenkov photons remains challenging, in high rate and high occupancy environments like for instance at modern hadron colliders.The separation of particle species through the combined measurement of their Cherenkov angles θ and their momenta relies on the precise localization of a sufficient number of Cherenkov photons within a short time interval and with little background.This is generally true for classical RICH (Ring Imaging CHerenkov) geometries [5] as well as for DIRC (Detection [of] Internally Reflected Cherenkov [light]) [6]
Operation of the tube for 3000 h under light exposure, very close to the maximum anode current rating of 100 μA, revealed gain variations of |ΔG| ≤ 20%. In the latter two cases the gain can be re-adjusted by adapting the bias voltage
To overcome the low active area of the R7600 MAPMT (48%) LHCb developed a concentrating optics based on a single 24 mm thick plano-convex quartz lens which led to a demagnification factor 1.5 and a 55% increase in the number of detected photoelectrons

Summary

Introduction

42 years after the pioneering work by Tom Ypsilantis and Jacques Séguinot [1], the precise and efficient imaging of Cherenkov photons remains challenging, in high rate and high occupancy environments like for instance at modern hadron colliders. Other characteristics like tolerance to magnetic fields and ionizing radiation, gain uniformity, longevity and cost may be decisive In other applications, such as calorimetry or scintillating fibre tracking, where the same or similar multi-pixel photodetectors are being used, signal linearity and gain uniformity over the tube surface may be key requirements. Multi-pixel Geiger-mode avalanche photodiodes, commonly called Silicon Photo-Multipliers (SiPM), evolved from small laboratory samples, with relatively low sensitivity, high dark noise and some other unwanted features, to a mature, robust and cost-effective single-photon sensitive detector. They are about to replace vacuum photo-tubes in many domains such as scintillating. The process changes which led to this important progress, directly impacting on the performance of a Cherenkov detector, are kept confidential by the company

Multi-anode PMTs

Applications in Cherenkov imaging

Micro-channel plate photo-multiplier tubes

Hybrid photon detectors

Findings

Summary and outlook