What are these pages about?

HCAL consists of it's barrel (HB) and endcap (HE) parts, with an outer barrel part (HO) situated outside the cryostat. Forward calorimeter (HF) is outside the main detector volume. There are two different calorimetry technologies involved:

• HB, HE and HO all use CDF design with scintillator tiles read out by embedded wavelength shifting fibers (WLS). Clear fibers are spliced to the WLS fibers and used to guide the captured light to Hybrid Photo Diodes (HPDs), where the light is transformed into electric pulses. Pulses are then amplified and converted into digital signals and sent through optical links to the counting room where eta-phi distribution of energy is derived. The HPD's, preamplifiers and charge integrating ADC's (QIE) are all situated in readout boxes (RBXs) on the detector itself.

• HF is operating in a strong radiation field and in an area with very high occupancy. The chosen technology is detection of Cherenkov light produced by hadron showers in rad. hard silica ("quartz") fibers. The produced light is guided through the same fibers into photomultiplier tubes (PMTs). The readout electronics is this time situated in racks that are positioned next to the detector on its support platform.

Although the technologies are different the control and monitoring tasks are practically the same. We will have to supply, control and monitor high and bias voltage for HPDs and PMTs; low voltages for electronics; laser, LED and charge pulses for the detector monitoring; and we should also monitor temperature in the readout boxes.

All HCAL systems are calibrated by using a radioactive source. The source is mounted on a tip of a (very long!) stainless steel wire that is sent through tubes installed along megatiles or inside spec. channels of HF. The speed of the wire propagation and position of the source have to be controlled and monitored, whereas the recorded response has to be stored in a database of calibration constants.

Given the size of the system, a single source cannot calibrate it completely. Therefore there is a number of separate sources with their drivers permanently installed on the detector, calibrating only selected channels. During long winter shutdowns, it is foreseen to have entire HCAL system calibrated by installing mobile source systems on the detector.

Whereas all other HCAL DCS needs are also present for other detector subsystems (especially ECAL), radioactive source calibration is HCAL specific task. Sharing solutions used for other CMS systems is not possible in this case.

This page will evolve with time and our understanding of problems and possible/chosen solutions.