Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
At CERN, the European Laboratory for Particle Physics in Geneva, Switzerland, a new modern particle accelerator called the LHC, Large Hadron Collider, is being projected. One of the four large detectors of the LHC, ALICE, consists of many sub-detectors. Temperature stability in ALICE is of great importance for the experiments performed here.
In the ALICE sub-detector TPC, Time Projection Chamber, there is a great risk for thermal instability. This will cause false data in the experiments, and therefore it is imperative to come to terms with the problem. One suggested solution is to install a water-cooled thermal screen around the TPC detector. The task of this thesis work was to design the new thermal screen and to evaluate its thermal abilities by computer simulations. Then, this chosen screen was to be simulated together with the TPC and its drift gas and the results studied. It was also desirable to see what would happen in case of parts of the thermal screen malfunctioning.
Several different designs of the thermal screen have been made and analysed, and the most efficient model has been selected. The chosen model succeeded in keeping a fairly homogenous temperature level and also had good cooling abilities. All simulations were made using the computer software STAR-CD. The next phase of the project involved modelling the thermal screen around the TPC field cage containing drift gas of a certain temperature.
The results of the simulations show that the performance of the cooling thermal screen is unsatisfactory. Although the screen itself seems to work efficiently, it does not succeed in keeping the TPC at an acceptable temperature level. The screen temperature rises more than the desired maximum of 0.5K. The scenario with parts of the thermal screen malfunctioning resulted in temperature peaks of +2K, which is unacceptable.
The conclusions drawn are therefore that the thermal screen must be allowed to be thicker or a new solution must be found. The idea of a thermal screen is a good one, but the limitations in the design of the thermal screen must be redefined if the cooling problem is to be solved.