Control system design of the CERN/CMS tracker thermal screen

The Tracker is one of the CMS (Compact Muon Solenoid experiment) subdetectors to be installed at the LHC (Large Hadron Collider) accelerator, scheduled to start data taking in 2007 at CERN (European Organization for Nuclear Research). The tracker will be operated at a temperature of -10 degree C in order to reduce the radiation damage on the silicon detectors; hence, an insulated environment has to be provided by means of a screen that introduces a thermal separation between the Tracker and the neighboring detection systems. The control system design includes a formal description of the process by means of a thermodynamic model; then, the electrical equivalence is derived. The transfer function is inferred by the ratio of the voltage on the outer skin and the voltage input, i.e. the ratio of the temperature outside the tracker and the heat generated (which is the controlled variable). A PID (Proportional Integral Derivative) controller has been designed using MatLab. The results achieved so far prove that this methodology is rigorous, effective and time saving; every step of the procedure is well defined, simplifying the debugging and updating. Besides, the first field tests show a good accordance of the model to the real system. 5 Refs.