Muon Spectrometer Cooling Means
Research of Additional Cooling Means Efficiency in the Critical Area of ATLAS Facility Muon Spectrometer (CERN)
Tech Area / Field
- PHY-NGD/Fluid Mechanics and Gas Dynamics/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
State Unitary Enterprise STRELA, Russia, Chelyabinsk reg., Snezhinsk
- University of British Columbia / TRIUMF, Canada, BC, Vancouver
Project summaryExperimental facility ATLAS is one of the main detectors of the LHC (Large Hadron Collider) accelerator being under construction at CERN. Its purpose is to support research in the sphere of elementary particle physics. m–mesons are the main particles to be recorded. The facility consists of different types of detectors: calorimeters and muon chambers. To ensure reliable operation of the electronic systems triggering information read-out from those detectors, it is necessary to meet very strict temperature requirements. The calorimeters are cooled down with liquid coolant. As for muon spectrometer located at the periphery of the facility and consisting of the layers of the muon chambers, convection-driven heat exchange plays a significant role in its cooling.
The ATLAS facility (H = 22 m, L = 44 m) is to be located in an underground cavern. The muon spectrometer in its central cylindrical part consists of three two-layered rings of the muon chambers. The chambers in different layers have a bit different design. The chambers release heat at the end-faces and along the perimeter.
It should be noted that space between the chambers is partially occupied with multiple cables and pipes with liquid. In addition, the system incorporates cryogenic magnetic loops. This complicates the convection-driven cooling of the system significantly.
To ensure the convection-driven cooling of the detectors, the ATLAS facility is equipped with air inlets and outlets. There are two inlets located at the cavern bottom, through which 60000 m3/h of air at the temperature of 17 °C will be pumped in. And there are two outlets: one located in the lower part of the cavern, the other – in the upper part. The latter vents about 92% of air.
For the muon chambers to operate normally there should be no large temperature gradients across the chambers (DT < 3 °C) and temperatures should be rather low (17-25 °C). Gradients across the chambers were estimated in ISTC Project #2134. Temperature fields were studied in the vicinity of the typical chambers and estimated in detail with due account of heat conduction and convection- and radiation-driven mass and heat transfer. Chamber design components were studied and accounted for, including heat-generating areas, tube layers, materials of the load-bearing structures, and gas-filled gaps and cavities. To support global simulations of the convection-driven heat extraction, effective thermal and physical parameters of the typical chambers were estimated. Currently this work is under completion in ISTC Project #2134. To do the above simulations, two codes were used: licensed code CFX (ANSYS company) and SINARA code developed at RFNC-VNIITF.
The global simulations were run by a CERN team. Simulations show that convection in the upper part of the muon spectrometer is hampered and some sort of stagnation region is formed. In this region called critical high temperatures are reached which deteriorate normal operation of the muon chambers.
To prevent this, the CERN specialists have proposed that cooling water pipes be added to the system in the vicinity of the muon spectrometer where possible. In the case if these measures are insufficient, forced ventilation of these pipes is proposed in order to increase effectiveness of heat removal. For this purpose, the system is equipped with additional air supply pipes.
The project includes in-depth study of the critical region fragments. The study will consider possible ribbed surfaces of the pipes and their positions. It will use actual directions of the air flows. The simulations will account for volumes and parameters of the liquid flowing in the pipes.
Basic simulations will use the licensed computational fluid dynamics code CFX. In addition, they will also exploit the SINARA code , developed at RFNC-VNIITF.
The proposed project includes the following tasks:
1. Assess heat extraction capabilities of the water pipes with proper account of the actual environment.
2. Study effectiveness of deploying the water pipes in the critical area.
3. Study the convection processes including those forced by additional air supply.
4. Estimate heat extraction due to the water pipes under the condition of increased convection.
5. Evaluate the combined measures taken in the critical region, including all cooling pipes and air supply, and development of recommendations.
Tasks 2 and 5 will be carried out in coordination with the global simulations run at CERN.
Statement of the proposed project tasks are based on the conclusions recorded in the minutes of the meeting between the representatives of RFNC-VNIITF and CERN held during July 7–11, 2003 in Geneva.