W. Erdt

The Cryogenic Distribution Line for the LHC: Functional Specification and Conceptual Design

The Large Hadron Collider (LHC)1 currently under construction at CERN will make use of superconducting magnets operating in superfluid helium below 2 K. The cryogenic distribution scheme for each of the eight sectors, individually served by a refrigeration plant, is based on a separate Cryogenic Distribution Line (QRL) feeding helium at different temperatures and pressures to the elementary cooling loops. The QRL comprises two supply headers and three return headers including a sub-atmospheric one. Low heat inleak to all temperature levels is essential for the overall LHC cryogenic performance. With an overall length of 25.6 km the QRL has a very critical cost-to-performance ratio. Therefore, following an in-house feasibility study, CERN adjudicated in autumn 1998 three industrial contracts in parallel for the supply of Pre-Series Test Cells (∼ 112 m) of the QRL, which will be tested at CERN in 2000. Installation of the QRL for LHC is scheduled from 2002 to mid 2004. This paper will present the general layout, the functional requirements as well as some aspects of the in-house conceptual design.

A Simplified Cryogenic Distribution Scheme for the Large Hadron Collider

The Large Hadron Collider (LHC), currently under construction at CERN, will make use of superconducting magnets operating in superfluid helium below 2 K. The reference cryogenic distribution scheme was based, in each 3.3 km sector served by a cryogenic plant, on a separate cryogenic distribution line which feeds elementary cooling loops corresponding to the length of a half-cell (53 m). In order to decrease the number of active components, cryogenic modules and jumper connections between distribution line and magnet strings a simplified cryogenic scheme is now implemented, based on cooling loops corresponding to the length of a full-cell (107 m) and compatible with the LHC requirements. Performance and redundancy limitations are discussed with respect to the previous scheme and balanced against potential cost savings.

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.

Mechanical design and layout of the LHC standard half-cell

The LHC Conceptual Design Report issued on 20th October 1995 introduced significant changes to some fundamental features of the LHC standard half-cell, composed of one quadrupole, 3 dipoles and a set of corrector magnets. A separate cryogenic distribution line has been adopted containing most of the distribution lines previously installed inside the main cryostat. The dipole length has been increased from 10 to 15 m and independent powering of the focusing and defocusing quadrupole magnets has been chosen. Individual quench protection diodes were introduced in magnet interconnects and many auxiliary bus bars were added to feed in series the various families of superconducting corrector magnets. The various highly intricate basic systems such as: cryostats and cryogenics feeders, superconducting magnets and their electrical powering and protection, vacuum beam screen and its cooling, support acid alignment devices have been redesigned, taking into account the very tight space available. These space constraints are imposed by the desire to have maximum integral bending field strength for maximum LHC energy, in the existing LEP tunnel. Finally, cryogenic and vacuum sectorisation have been introduced to reduce downtimes and facilitate commissioning.

CONTROLLED DOWNWARD TRANSFER OF SATURATED LIQUID HELIUM ACROSS LARGE DIFFERENCES IN ELEVATION

Superconducting devices, installed in the deep underground tunnels of high-energy accelerators, can be fed with liquid helium from cryogenic plants located in accessible areas at ground surface or at intermediate levels. For this purpose, controlled transfer of liquid helium is required across large differences in elevation. Subsequent to demonstration of feasibility of this technique in a special test across a height of 25 m, a superconducting RF cavity, housed in a bath cryostat fed through a 100 m long transfer line, has been operated success fully in a real accelerator 60 m below ground.