CMS HCAL High Voltage Power Supply System

L. Dimitrov¹, B. Kunov¹, S. Sergeev², I. Vankov¹

¹ INRNE, BAS, Sofia, Bulgaria
²FERMILAB, USA/JINR, Dubna, Russia

The CMS hadronic calorimeter [1] is the sampling calorimeter. Thin plate plastic scintillators are used as an active media and the light collection is provided by wave length shifting fibers. The light from them is fed by optical links to the Hybrid Photo Diode photodetectors (HPDs), capable of operating in high magnetic field. For the normal operation HPDs need two voltages [96] the acceleration (High) voltage around 10 kV and the bias voltage around 100 V. In total HCAL will have about 500 HPDs. To provide the voltage source for the HCAL subdetector the 500-channel power supply system has been developed. The basic unit of the system is an 19" 6U Eurostandard crate. Each crate holds six HPD Power Supply modules, a Crate Controller and a Crate Power Supply Unit. 4 high voltage and 4 bias voltage channels are housed in each module. The output value of the high voltage channels could be set in range of 0..14 kV and the bias voltage [96] in range of 0..200 V. The HV channels maximum output current is 40 uA, and for the Bias channels [96] 10 uA. The Overvoltage and Overcurrent protection with adjustable thresholds are foreseen. The HV system is computer controlled. The crate controllers operate the channels with a custom protocol. They are grouped to branches and each branch is connected to the host computer by RS485 serial link. Each branch could contain up to 128 crates. The integration of the HCAL HV power supply system in the CMS Detector Control System is realized by a HV server with a DIM-interface. The HV program package contains a set of engineering tools providing debugging and control and monitoring for a stand-alone operation.

[1] CMS Collaboration. The Hadron Calorimeter Technical Design Report. CERN/LHCC, CMS TDR 2, 20.06.2003.