Ph. Gayet

Economics of Large Helium Cryogenic Systems : experience from Recent Projects at CERN

Large projects based on applied superconductivity, such as particle accelerators, tokamaks or SMES, require powerful and complex helium cryogenic systems, the cost of which represents a significant, if not dominant fraction of the total capital and operational expenditure. It is therefore important to establish guidelines and scaling laws for costing such systems, based on synthetic estimators of their size and performance. Although such data has already been published for many years, the experience recently gathered at CERN with the LEP and LHC projects, which have de facto turned the laboratory into a major world cryogenic center, can be exploited to update this information and broaden the range of application of the scaling laws. We report on the economics of 4.5 K and 1.8 K refrigeration, cryogen distribution and storage systems, and indicate paths towards their cost-to-performance optimisation.

Cryogenics for the LEP200 superconducting cavities at CERN

The cryogenics for the LEP200 Project cover the cooling requirements of up to 64 modules containing each four superconducting (SC) cavities at 352 MHz RF. This includes both cooling for the cavities themselves by liquid helium boiling at 4.5 K, and use of cold helium gas for intercepting heat from accessories. Helium refrigeration is provided by separate powerful cryoplants at each of the four interaction points of LEP with 12 kW equivalent refrigeration at 4.5 K and cryogenic distribution lines of up to 810 m length, and by two 6 kW plants for the new test center SM18 where the acceptance tests of both SC cavities and magnets are carried out. Most of the hardware is installed, commissioning of the systems in LEP is progressing and experience in testing the new cavities from industry is accumulating. First conclusions and performance results are reported, and problems listed which require further work.<<ETX>>

Conclusions from Procuring, Installing and Commissioning Six Large-Scale Helium Refrigerators at CERN

Between 1990 and 1994 CERN procured, installed and commissioned six large-scale helium cryoplants for its programme of superconducting acceleration cavities in the electron-positron collider LEP. Two European suppliers were selected to each provide one plant of 6 kW and two plants of 12 kW equivalent cooling power at 4.5 K. All installations are now commissioned and operational, some have been running continuously for several years. The concepts applied to specification, tendering, sharing of responsibilities for infrastructure and controls, installation, and commissioning are presented. Conclusions are drawn from the experiences during the different phases of this project and applied to acquisition of plant upgrades and additional plants required for LHC, CERN’s new project for a proton-proton collider in the LEP tunnel using superconducting magnets.

Architecture of the LEP2 cryogenics control system : Conception, status, and evaluation

Abstract Conception and realisation of the industrial process control system and application programs for the four new 12 kW/4.5K cryoplants, and the 192 superconducting accelerating cavities, were critical activities in the implementation of the cryogenic system for the LEP2 project at CERN. The main objectives like regulation quality, automatic restarts, centralised remote control, homogenisation of the logics for the cryoplants built by different suppliers are exposed as well as the current state of advancement. The modular distributed control system hardware is presented. The architecture of software using an object oriented programming method is described. A tentative evaluation is presented with a general view on work and costs, from which follow conclusions concerning future control systems for similar projects.

Conclusions on 8 years operation of the LEP 4.5K refrigeration system at CERN

After 11 years of operation the Large Electron/Positron collider (LEP) was stopped in November 2000. Since 1993 a cryogenic system has been used to supply up to 72 superconducting (SC) cavity modules, using four large liquid-helium refrigerators at 4.5 K. We review eight years of operation of one of the world’s largest helium cryogenic systems, its evolution and cooling capacity availability correlated to the LEP increasing energy program. Failure statistics, availability, recovery time after breakdowns and reliability are analyzed, and the most relevant problems encountered during the operation and their cure exposed. The operational organization is also briefly described.

CONTROL OPTIMIZATION OF A LHC 18 KW CRYOPLANT WARM COMPRESSION STATION USING DYNAMIC SIMULATIONS

This paper addresses the control optimization of a 4.5 K refrigerator used in the cryogenic system of the Large Hadron Collider (LHC) at CERN. First, the compressor station with the cold‐box have been modeled and simulated under PROCOS (Process and Control Simulator), a simulation environment developed at CERN. Next, an appropriate parameter identification has been performed on the simulator to obtain a simplified model of the system in order to design an Internal Model Control (IMC) enhancing the regulation of the high pressure. Finally, a floating high pressure control is proposed using a cascade control to reduce operational costs.

Operation of the Cryogenic System for Superconducting Cavities in LEP

Publisher Summary At CERN the upgrade of the LEP e+e- collider towards higher beam energies is under way by installing superconducting cavities in the ring. In 1995 superconducting cavity modules have been operated together with ambient temperature copper accelerating cavities allowing for a first step of energy increase. This chapter reports on the experience with the operation of the LEP cryogenic system. Particular attention is given to stability, automatic control, and reliability. It presents the failure analysis and redundancy programs, which should further increase the availability of the cryogenic system in the environment of a large high energy particle collider. Some further work on automatic procedures, redundancies and preventive maintenance, should allow to face successfully the future demands for full capacity and high availability of the cryogenic system as part of the upgraded LEP collider.

Operation of the Four 12 KW at 4.5K Refrigerators for LEP

In 1998 the first energy upgrade of the LEP Electron/Positron collider, LEP2, was completed at CERN. Sixty-eight superconducting modules supplied by four 12 kW @ 4.5 K equivalent power refrigerators have been operated allowing a colliding beam energy of 94.5 GeV. Meanwhile, the operation and maintenance responsibilities were transferred to an industrial firm on the basis of a result-oriented contract. After a short description of the operational organization, we report on the operation of the LEP2 cryogenic system over the past three years. Particular attention is given to power availability, failure statistics and recovery time after interruptions. The most relevant problems and their solutions are exposed. Finally, we review the interactions between the cryogenic system and the particle beams, which are limiting the ultimate performance of the LEP collider.