Development and Test of the Cooling System for the ATLAS Hadron Tile Calorimeter

The ATLAS detector is a general-purpose experiment for proton-proton collisions designed to investigate the full range of physical processes at the Large Hadron Collider (LHC). The ATLAS Tile Hadron Calorimeter is designed to measure the energies of jets with a resolution of E/E = 50%/pE 3%, for j j<3. This thesis presents the detailed studies which were carried out with prototypes of the Tilecal cooling system during my year as technical student at CERN. The results will be used to validate and to determine the nal design of the cooling system of the ATLAS Tile calorimeter. The performance of the cooling unit built for the calibration of Tilecal modules was evaluated for various parameters like temperature stability and safety conditions during operation. Additionally I contributed to the analysis of the calorimeter response for different cooling temperatures. These results determined the constraints on the operation conditions of the cooling system in terms of temperature stability that will be needed during ATLAS operation. Furthermore I carried out tests to evaluate the effect of ambient temperature on the cooling system and on the foreseen non-isolated cooling pipes. Due to the first test a dependence on ambient temperature was found and could be minimised. The latter test resulted in the nal decision of the type of tube which will be used for the final cooling system. In another test I measured the total power dissipated by the electronics of the Tilecal modules using for the first time final components. I was able to determine the efficiency of the cooling system and the ideal ow rate during real operation conditions. These tests also allowed to better de ne the needs of a cooling system for the ATLAS muon chambers that will be located nearby. For future maintenance purposes of Tilecal I studied the temperature increase inside the Tilecal modules with the cooling disconnected. Additionally I studied the absolute temperatures in the front end electronics of the Tilecal modules during normal operation and without cooling. A special full-scale prototype of the Tilecal cooling system was designed and installed to test the foreseen components, to check the calculations for pressure and ow, to develop the control system and to study the performance stabilitity during several months of operation. I participated in the electrical installation, in the development of the control system and in the analysis of data taken during the operation of the system. Besides I was responsible for the cooling system during the three Tilecal beam calibration periods in 2002. I participated actively in the testbeam program in the form of shifts and helped to implement a monitoring system of the low voltage power supplies and several alarms for the high voltage of the photomultipliers. The results of this thesis are already partially published in an ATLAS internal note [32] and another note will be published in autumn 2002.