Novel Photo Multiplier Tubes for the Cherenkov Telescope Array Project

TL;DR

This paper discusses the development of advanced photo multiplier tubes with significantly improved quantum efficiency, collection efficiency, and reduced after-pulsing, tailored for the Cherenkov Telescope Array project in gamma astrophysics.

Contribution

It presents the latest advancements in PMT technology, achieving peak QE of around 40% and enhanced collection efficiency, marking a major upgrade over previous generations for Cherenkov telescopes.

Findings

Peak quantum efficiency increased to approximately 40%.

Photoelectron collection efficiency improved to 95-98%.

After-pulsing reduced to 0.02%.

Abstract

Currently the standard light sensors for imaging atmospheric Cherenkov telescopes are the classical photo multiplier tubes that are using bialkali photo cathodes. About eight years ago we initiated an improvement program with the Photo Multiplier Tube (PMT) manufacturers Hamamatsu (Japan), Electron Tubes Enterprises (England) and Photonis (France) for the needs of imaging atmospheric Cherenkov telescopes. As a result, after about 40 years of stagnation of the peak Quantum Efficiency (QE) on the level of 25-27%, new PMTs appeared with a peak QE of 35%. These have got the name super-bialkali. The second significant upgrade has happened very recently, as a result of a dedicated improvement program for the candidate PMT for Cherenkov Telescope Array. The latter is going to be the next generation major instrument in the field of very high energy gamma astrophysics and will consist of over 100 telescopes of three different sizes of 23m, 12m and 4-7m, located both in southern and northern hemispheres. Now PMTs with average peak QE of approximately 40% became available. Also, the photo electron collection efficiency of the previous generation PMTs of 80- 90% has been enhanced towards 95-98% for the new ones. The after-pulsing of novel PMTs has been reduced towards the level of 0.02% for the set threshold of 4 photo electrons. We will report on the PMT development work by the companies Electron Tubes Enterprises and Hamamatsu Photonics K.K. show the achieved results and the current status.