Dynamic Simulation of a 1.8K Refrigeration Unit for the LHC (original) (raw)
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A Dynamic Simulator for Large Scale Cryogenic Systems
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Modeling, Simulation and Control of Large Scale Cryogenic Systems
Proceedings of the 17th IFAC World Congress, 2008, 2008
This paper presents a dynamic simulator for large scale cryogenic systems using helium refrigerators and controlled by Programmable Logic Controllers (PLC) for the European Organization for Nuclear Research (CERN). The process is modeled by a set of linear differential and algebraic equations and the control policy is based on a hierarchical multilevel and multilayer framework control. First simulation results carried out on the refrigerator used in the Compact Muon Solenoid (CMS) experiment are presented. It is worth to mention that CMS is a particle detector used in the future CERN accelerator (the LHC) where a superconducting magnet of 225 tons, the largest ever built, must be maintained at 4.5K (-268.7 o C). The model of this cryogenic plant is composed of 4126 equations whereof 287 differential-algebraic equations. The work objectives of this simulator are threefold: first, to provide a tool to train the operators, second to validate new control strategies before their implementation and, third, to improve our knowledge about large scale complex cryogenic systems. In order to respect the real system architecture, the simulator is composed of different modules sharing data.
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The Large Hadron Collider (LHC) is a 26.7 km high-energy proton and ion collider based on several thousand high-field superconducting magnets operating in superfluid helium below 2 K, now under commissioning at CERN. After a decade of development of the key technologies, the project was approved for construction in 1994 and the industrial procurement for the cryogenic system launched in 1997, concurrently with the completion of the R&D program. This imposed to base the sizing of the refrigeration plants on estimated and partially measured values of static and dynamic heat loads, with adequate uncertainty and overcapacity coefficients to cope with unknowns in machine configuration and in physical processes at work. With the cryogenic commissioning of the complete machine, full-scale static heat loads could be measured, thus confirming the correctness of the estimates and the validity of the approach, and safeguarding excess refrigeration capacity for absorbing the beam-induced dynamic loads. The methodology is applicable to other large cryogenic projects such as ITER or the International Linear Collider (ILC).
1.8 K Refrigeration Units for the LHCPerformance Assessment of Pre-series Units
Proceedings of the Twentieth International Cryogenic Engineering Conference (ICEC20), 2005
The cooling capacity below 2 K for the superconducting magnets of the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to a 4.5 K refrigerator. The two selected vendors have proposed cycles based on centrifugal cold compressors combined with volumetric screw compressors with sub-atmospheric suction, as previously identified by CERN as "reference cycle". The supply of the series units was linked to successful testing and acceptance of the pre-series temporarily installed in a dedicated test station. The global capacity, the performance of cold compressors and some process specificities have been thoroughly tested and will be presented.
The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to one 18 kW at 4.5 K refrigerator. The supply of the series units was linked to successful testing and acceptance of the pre-series units delivered by the two selected vendors. The two pre-series units were temporarily installed in a dedicated test station to validate the overall capacity and to properly assess the performance of specific components such as cold compressors. Then the cold compressor cartridges to be installed in the six series and associated spare cartridges have been intensively and systematically tested in the test station. After a brief description of the test bench and the main achieved features of the pre-series units, we will present the results of the tests of 35 cold compressor cartridges. These tests show isentropic efficiency in the 75% range, excellent reproducib...
A process and control simulator for large scale cryogenic plants
Control Engineering Practice, 2009
This paper presents a process and control simulator for industrial helium cryogenic plants controlled by Programmable Logic Controllers (PLC). This simulator can be used for different purposes such as operator training, test of the PLC programs or the optimization of the plant. The different component models used in the simulator are detailed and explained. Various large scale cryogenic plants used for the particle accelerator LHC (Large Hadron Collider) at CERN have been modeled and simulated. The good agreement between the simulation results and the dynamic behaviour of real plants is demonstrated with experimental results. Various discussions complete the presentation.
Validation and Performance of the Lhc Cryogenic System Through Commissioning of the First Sector
2008
The cryogenic system [1] for the Large Hadron Collider accelerator is presently in its final phase of commissioning at nominal operating conditions. The refrigeration capacity for the LHC is produced using eight large cryogenic plants and eight 1.8 K refrigeration units installed on five cryogenic islands. Machine cryogenic equipment is installed in a 26.7-km circumference ring deep underground tunnel and are maintained at their nominal operating conditions via a distribution system consisting of transfer lines, cold interconnection boxes at each cryogenic island and a cryogenic distribution line. The functional analysis of the whole system during all operating conditions was established and validated during the first sector commissioning in order to maximize the system availability. Analysis, operating modes, main failure scenarios, results and performance of the cryogenic system are presented.