Very high QE HPDs with a GaAsP photocathode for the MAGIC telescope project

Hybrid photon detectors are one of the few low light level sensors that can provide an excellent single and multiple photoelectron amplitude resolution. The recently developed hybrid photon detectors for the Major Atmospheric Gamma-Imaging Cherenkov (MAGIC) telescope project with an 18-mm-diameter GaAsP photocathode (the Hamamatsu R9792U-40) have a peak quantum efficiency of more than 50% and a pulse width of ∼ 2.3 ns . In addition, the afterpulsing rate of these tubes is ∼ 300 times lower compared to that of conventional photomultiplier tubes. Photocathode aging measurements showed lifetimes of more than 10 years under standard operating conditions of Cherenkov Telescopes. The temperature dependence of the avalanche gain can be reduced to the same level of a photomultiplier by a simple compensation circuit. Here we report on the recent progress with the above-mentioned hybrid photon detectors.