S. Claudet

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>>

Specification of Four New Large 4.5 K Helium Refrigerators for the LHC

The cooling capacity for the superconducting magnets in the Large Hadron Collider (LHC) at the European Laboratory for Particle Physics, CERN will be provided by eight helium refrigerators serving the eight 3.3 km long machine sectors. Of these eight refrigerators, four are already existing and are currently used for the Large Electron Positron Collider (LEP) project. These existing refrigerators have to be modified to fulfil the requirements for the LHC. Four new refrigerators providing cooling capacity down to 4.5 K will be added. All eight 4.5 K refrigerators will be connected to 1.8 K cooling stages. This presentation recalls the cryogenic architecture of the LHC, the constraints in process design resulting from it and from the desired capacity for steady state and transient operation. It then describes how these requirements were expressed in the technical specification for the four new 4.5 K refrigerators to be delivered between the years 2000 and 2002.

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.

Four 12kW/4.5K cryoplants at CERN

Abstract The LEP 2 project at CERN, designed to increase the collision energy in the LEP electron-positron collider from 50 to 90 GeV/beam, involves the installation of 192 superconducting (sc) accelerating cavities in the straight sections of the LEP ring close to the four interaction points. To provide the refrigeration power for the cavities, four 12(18)kW/4.5K cryoplants where ordered in 1991, two from LAir Liquide (France), and two from Sulzer (now Linde; Switzerland/Germany). These plants have been installed in the past years, and two of them have already accumulated a considerable number of operating hours. Processes, construction, commissioning and acceptance tests of the four plants will be described, and their main features will be compared. Performance of the liquid-helium distribution systems delivered by LAir Liquide (France) and Cryogenmash (Russia) will also be given.

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.

Status of cryogenics for the LEP200 energy upgrade project at CERN

Abstract The cryogenics for the LEP200 project covers the liquid helium bath cooling requirements of about 200 superconducting RF acceleration cavities to be installed in the ring tunnel of CERNs electron-positron collider LEP. It includes two cryoplants of 6 kW refrigeration capacity, four of 12 kW, about 2.6 km of transfer lines with actively cooled, flexible screens, and a helium inventory of about 80000 Nm 3 . At present all equipment is ordered; about one quarter is installed and operational. Special design features needed to cope with space problems in the existing pit/tunnel system are presented and first operational experience from running the two 6 kW plants with 550 m of transfer lines and a number of cavities is reported.

Operation of the Cryogenic System for Superconducting Cavities in LEP

Publisher Summary nAt 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.