The CMS Detector Power System

The power system for the on-detector electronics of the CMS Experiment comprises approximately 12000 low voltage channels, with a total power requirement of 1.1 MVA. The radiation environment inside the CMS experimental cavern combined with an ambient magnetic field (reaching up to 1.3 kGauss at the detector periphery) severely limit the available choices of low voltage supplies, effectively ruling out the use of commercial off-the-shelf DC power supplies. Typical current requirements at the CMS detector front end range from 1A-30A per channel at voltages ranging between 1.25V and 8V. This requires in turn that the final stage of the low voltage power supply be located on the detector periphery. Power to the CMS front-end electronics is stabilized by a 2 MVA uninterruptible power supply (UPS) located in a CMS surface building. This UPS isolates the CMS detector from disturbances on the local power grid and provides for 2 minutes of autonomy following a power failure, allowing for an orderly shutdown of detector electronics and controls. This paper describes the design of the CMS Detector Power System, reviews the process of its installation and commissioning, and discusses issues of power distribution common to current-generation collider detectors.