High voltage system for the CMS forward calorimeter

The power supply system developed for the photomultipliers (PMTs) of the forward calorimeter (HF) of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider is described. The 1728 PMTs of the HF are divided into 24 clusters of 72 with similar gain value. All of the PMTs within each cluster are powered by the same three high voltage (HV) power supplies, making a total of only 72 power supplies in the entire system. In this so-called parallel dynode voltage distribution, the three HV power supplies can be adjusted from 0 to −2000, −800, and −400 V, respectively. All output voltages are floating to facilitate a single-point ground configuration. The system is computer controlled and integrated into the CMS detector slow control facility.