The production of radiation tolerant vacuum phototriodes and their HV filters for the Compact Muon Solenoid endcap electromagnetic calorimeter

Abstract

Particle detectors which will operate at the Large Hadron Collider face unprecedented challenges in both the number of active detector elements and in operating without maintenance in a high radiation environment for many years. In the Compact Muon Solenoid (CMS) detector the scintillating crystal electromagnetic calorimeter uses vacuum photodetectors in the endcap where the lifetime neutron and hadron fluence is too high for the silicon avalanche photodiodes used in the barrel. Over 15000 radiation tolerant vacuum phototriodes (VPT) have been now been produced by industry for the endcap calorimeter. The VPT have to operate in an environment which has both a significant lifetime dose (up to 50 kGy) from electrons and gamma rays and a high neutron fluence (up to nearly 10 15 n.cm −2 for E > 100 keV). This paper discusses the steps taken during both the development and production of the VPT to ensure that the response to the scintillation light from the lead tungstate scintillator will not be significantly degraded during the operational lifetime of the experiment. Data from the quality assurance procedures and radiation induced degradation of complete VPT devices is presented. Other components of the endcap calorimeter are also exposed to a similarly intense radiation field. The quality assurance procedure used to select the passive components (resistors and capacitors) used in the high-voltage filter cards is described.