17 May 1994 OCR OutputGeneva, Switzerland

26-28 April 1994, Usti Nad Labem, Czech RepublicInvited paper to Third International Conference KRYOGENIKA’94

Ph. Lebrun on behalf of the CERN Cryogenics Group

Cryogenics in CERN Accelerators

P0002432O

CERN LIBRARIES, GENEVA

Sw ® Ll UZ

/ CERN AT/94-08 (CR)

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

intricate layout of the LEP experimental areas, as well as stringent operational and maintenance requirements OCR Outputluminosity insertions operate with dedicated 400 W @ 4.5 K cryoplants [17]. The deep underground siting andspectrometer magnets. The other detector magnets at L3 and OPAL being normal conducting, their highhelium from the 800 W @ 4.5 K mixed·duty cryoplants serving the ALEPH and DELPHI superconductingdetectors. Although part of the accelerator lattice, two of the LEP high-luminosity insertions are fed in liquidhigh-luminosity insertions [16], based on slim superconducting quadrupoles integrated in the experimentalconducting, the physics yield of the machine, which started to operate in 1989, was strongly enhanced hy fourcircumference of 26.7 km. Although the main magnetic system of LEP is low-field and thus normalThe 1980's were at CERN the years of construction of LEP, a lepton collider unprecendented in size, with a

cryogens in an accelerator with limited access and no cryogenic infrastructure [15].bridged to the upper stage of the cryocoolers. This technique avoided all distribution and handling of liquidGifford-McMahon cryocoolers, while their mobile electrodes were radiatively cooled from a thermal shieldAntiproton Collector (ACOL) had their preamplifiers refrigerated down to 20 K by means of closed—cyclelimitation of thermal noise in wide-band, high-gain power electronics: the stochastic cooling pick-ups of theAlso worth mentioning is an application of cryogenics to accelerators not driven by superconductivity, but by

vacuum behaviour of future fully superconducting accelerators.helium-cooled condensation cryopumps [ll, 12] and tested an experimental cold bore [13, 14] to exploredistribution lines [10]. In the preceding years, the ultra-high vacuum system of the 1SR had operated liquidoperate routinely in an accelerator, fed from a dedicated 270 l/h helium liquefier through 50-in longluminosity insertion [9]. The eight industry-made superconducting quadrupoles were the first of their kind toexcellence, with the installation and operation for physics in the early 1980's of the superconducting highln cryogenics as in other fields, the Intersecting Storage Rings (ISR) showed pioneering spirit and technical

network of lines spanning the site, and purified off·line before reliquefaction.dewars supplied by the CERN Central Liquefier. The vapourized helium was always recovered through a@ 1.8 K cryoplant [8]. In other cases, the moderate thermal budgets permitted intermittent refilling from 500 lSuperconducting RF already appeared as a demanding user, operating in closed cycle with a dedicated 300 Wappeared in isolated devices equipping extracted beam lines, e.g. bending magnets [5, 6] and RF separators [7].not mature enough to equip the kilometer-size accelerators of the early 1970's. Applied superconductivity firstAlthough their potential had been acknowledged in the 1960's, superconducting devices were still considered

HISTORICAL DEVELOPMENT

(LEP2) and tomorrow (LHC). Other applications of cryogenics at CERN have been reported elsewhere [4].the historical development of cryogenics in CERN accelerators, which led to the large-scale projects of todaysuperconducting and thus require large, powerful helium cryogenic systems [2, 3]. In the following, we presentand accelerating RF cavities) in modem machines [1]. Today, almost all new high-energy accelerators aredevelopment of applied superconductivity and the increasing use of superconducting devices (electro-magnetsemergence as a key technology for particle accelerators and colliders is more recent, as it follows thechambers and large spectrometer magnets, to liquid hydrogen targets and liquid argon calorimeters. ltsCryogenics has been for long an ancillary technology to high-energy physics experiments, from bubble

OCR OutputINTRODUCTION

CERN, Geneva, SwitzerlandPh. Lebrun on behalf of the CERN Cryogenics Group

CRYOGENICS IN CERN ACCELERATORS

perform with industrial-class reliability and totalize some 100'00O hours of integrated operation per year [36]. OCR Outputcryogenics (Figure 1), with presently 21 cryoplants covering the whole spectrum of capacity (Figure 2), whichA leading laboratory in high-energy physics, CERN has also become a major center for large-scale helium

CONCLUSION

[33], or two-phase flow of superfluid helium [34, 35], is well under way.development of key technologies, e.g. low-pressure cryogenic helium compressors, efficient magnet eryostatsunder minute temperature difference and pressure drop. The main technical issues have been assessed andcryoplants installed around the machine circumference, and the distribution of the cooling power along the arcsof thertnal budgets in 24 km of magnet cryostats, the production of large, variable refrigeration duties in eightwill face considerable challenges, such as the limitation of heat loads, staging of temperature levels and controlunprecedented size, and in view of the specificities of superfluid helium operation, the LHC cryogenic systemadvantage of the high thermal conductivity and low viscosity of superfluid helium for stabilisation. Due to itshelium at 1.9 K [32]. Besides the boosting of current density in NbTi superconductor, this allows to taketwin-aperture superconducting magnets with a bending field of about 9 T, operated in pressurized superfluidissues in the TeV per constituent energy range [30, 31]. For this purpose, the LHC makes use of high-tield,LEP tunnel. lt will accelerate and bring into collision intense beams of protons and ions, to explore physicsThe Large Hadron Collider (LHC) is a high-energy, high-luminosity machine, to be installed in the existing

project, the LHC.large refrigerators of LEP2, after suitable adaptation and upgrade, for the operation of CERN's next largedesigned for high efficiency: they feature power factors as low as 220 W/W [29]. lt is foreseen to reuse the fourin the 50 to 150 m-deep shafts. In view of their large capacity and heavy duty cycle, the cryoplants wereadequately limits the therrrtodynamic cost of transfer line heat loads, while avoiding excessive hydrostatic headtogether by compound lines ntnning vertically along the access shafts. The splitting temperature level of 20 Kdesign, cannot be fully located underground and are thus split in upper and lower cold boxes, connectedlevel [27], and the other in a test hall [28], The final 12 kW @ 4.5 K cryoplants, although also of compactcavities is performed by two compact 6 kW @ 4.5 K cryoplants. one of which is installed underground at tunneleach cryoplant [25, 26]. Cryogenic refrigeration for reception and accelerator testing of the superconducting18 kW), and distributed by cryogenic lines spanning the 250-m length of the cavity strings on either side ofK [24]. They require large refrigeration capacity, supplied by four 12 kW @ 4.5 K cryoplants (upgradeable to352 Ml—Iz cavities, made of niobium sheet or niobium-plated copper, operate in baths of saturated helium at 4.5superconducting acceleration cavities, in four equidistant long straight sections of the machine tunnel [23]. TheThe energy ugrade of LEP in the 90 GeV range and beyond, requires the installation of at least 192

LARGE-SCALE PROJECTS: FROM LEP2 TO LHC

units [22].routinely operates with superconducting cavities, which have progressively replaced the normal conductingdown a shaft, then by a dedicated helium refrigerator installed underground at tunnel level [21]. Today the SPShelium was supplied first from a storage vessel at ground level, through a 100-m long transfer line runningreliably in the SPS accelerator, to gather operating experience in real beam conditions and environment. Liquidsuperconducting acceleration cavities. Prototypes of such cavities were developed in the 1980's and operatedarcs. Exploiting the full energy and luminosity potential of the machine thus requires additional, efficientThe ultimate energy of LEP is limited by the synchrotron power radiated from the circulated beams along the

excellent operational record [20].lines [19]. In spite of their complexity, the LEP superconducting high·luminosity insertions have shown ancontrolled liquid helium transfer across large differences in elevation [18], using high—perforrnance flexibleon the detectors, have imposed technical compromises on the cryogenic systems, in particular long-distzuice

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Magnets, CERN Report 78-03 (1978). OCR Output[5] Ph. Dow & G. Kesseler, Design and Construction of Two 10.8 T.m Superconducting Beam Bending

Albuquerque (1993).J. Schmid & G. Winkler, Application of Liquid—Helium Cryoplants at CERN, paper presented at CEC93,[4] J.P. Dauvergne, D. Delikaris, W.K. Erdt, D. Giisewell, F. Haug, Ph. Lebrun, G. Passardi, J .M. Ricuhlztnd.

Physics, Dallas 1992, AIP. PP- 2000-2007 (1993).[3] Ph. Lebrun, Large-Scale Cryogenics for Particle Accelerators, Proc. XXVI lnt. Conf. on High-Energy

ICEC14 Kiev, Cryogenics 32, ICEC Supplement, pp. 44-51 (1992).[2] G. Horlitz, Refrigeration of Large—Scale Superconducting Systems for High-Energy Accelerators, Proc.

[1] M. Wilson, Accelerators and Superconductivity: a Marriage of Convenience, CERN Report 87-06 (1987).

REFERENCES

reader is referred to the papers referenced below for more detailed information.Accelerator Technology Division, as well as of our partners in national laboratories and European industry. TheThis brief review is an attempt to reflect the work of many colleagues from the CERN Cryogenics Group and

ACKNOWLEDGEMENTS

Figure 2: Unit size of CERN cryuplzuitsFigure 1: Installed cryogenic capacity at CERN

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1® J·—*‘BEBC \ \x Central Ilsuefler SPS RF\ (BEBC phased out) GMEGA, \ ·.

\ ALEPH. DELPHI19 kw

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E 1000ISR & RF tests

1 993 43 kW

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[kw @ 4.5 K]i~160 kw E '_ z for LHCNeeded 100000

ICEC13, Cryogenics 30, September Supplement, pp. 157-162 (1990). OCR Output[21] G. Passardi, The Cryogenic System for the Superconducting Cavities in the CERN SPS Accelerator, Proc.

Superconducting Quadrupoles, Proc. 3rd EPAC Berlin, 2, pp. 1641-1643 (1992).[20] Ph. Lebrun, O. Pagano, T.M. Taylor & L. Walckiers, Operational Experience with the LEP Low-Beta

Lines, Adv. Cry0. Eng. 35B, pp. 909-916 (1990).[19] H. Blessing, Ph. Lebrun & K. Schippl, Very Low-loss Liquid Helium Transfer with Flexible Cryogenic

(1988).Saturated Liquid Helium Across Large Differences in Elevation, Proc. ICEC12, Butterworth, pp. 222-226[18] H. Blessing, W. Erdt, Ph. Lebrun, L. Walckiers & W. Weingarten, Controlled Downward Transfer of

Experimental Areas, Adv. Cryo. Eng. 35B, pp. 901-908 (1990).[17] J.P. Dauvergne, M. Firth, A. Juillerat, Ph. Lebrun & l.M. Rieubland, Helium Cryogenics at the LEP

Sci. NS·32, 5. PP- 3704-3706 (1985).[16] T.M. Taylor, Technological Aspects of the LEP Low·Beta lnsertions, Proc. PAC'85, IEEE Trans. Nucl.

Antiproton Collector (ACOL), Adv. Cry0. Eng. 31, pp. 543-550 (1986).[15] Ph. Lebrun, S. Milner & A. Poncet, Cryogenic Design of the Stochastic Cooling Pick-Ups for the CERN

Sci. NS-26, 3, pp. 4086-4088 (1979).[14] C. Benvenuti & N. Hilleret, Cold Bore Experiments at the CERN ISR, Proc. PAC'79, IEEE Trans. Nucl.

PAC`77, IEEE Trans. Nucl. Sc. NS-24, 3, PP. 1373-1375 (1977).[13] C. Benvenuti, R. Calder & N. Hilleret, A Vacuum Cold Bore Test Section at the CERN ISR. Proc.

VA/78-27 (1978).[12] C. Benvenuti & M. Firth, Improved Version of the CERN Condensation Cryopump, CERN Repart ISR

J0urn. Vac. Sci. Technol. 11, 3, pp. 591-598 (1974).[11] C. Benvenuti, Characteristics, Advantages and Possible Applications of Condensation Cryopumping,

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lntersecting Storage Rings (ISR), Proc. PAC'79, IEEE Trans. Nucl. Sci. NS·26, 3, pp. 3179-3181 (1979).T. Tortschanoff, A. Verdier, L. Walckiers & R. Wolf, A Superconducting High-Luminosity Insertion in the[9] J. Billan, K.N. Henrichsen, H. Laeger, Ph. Lebrun, R. Perin, S. Pichler, P. Pugin, L. Resegotti, P. Rohmig,

Superconducting RF Particle separator, Proc. ICEC6, IPC Science & Technology Press, pp. 58-61 (1978).[8] AJ. Steel, S. Bmzzi & M.E. Clarke, A 300 W 1.8 K Refrigerator and Distribution System for the CERN

Operation of a Superconducting RF Particle Separator, Nucl. Instr. Meth. 155, pp. 93-96 (1978).[7] A. Citron, G. Dammertz, M. Grundner, L. Husson, R. Lehm, H. Lengeler, D.E. Plane & G. Winkler. First

487-491 (1978).[6] J. Perot & D. Leroy, The Superconducting Bending Magnets CESAR, Proc. MT-6, Bratislava 1977. pp.

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presented at PAC'93, Washington (1993). OCR OutputTerm Experience with Cryoplant operation for Superconducting Magnets and RF cavities at CERN, paper[36] D. Delikaris, J.P. Dauvergne, P.K. Frandsen, F. Haug, G. Passardi, J.M. Rieubland & J. Schmid, Long

(1993).

Helium Model Cryoloop for the CERN Large Hadron Collider, paper presented at CEC`93, Albuquerque[35] A. Bézaguet, J. Casas-Cubillos, Ph. Lebrun, M. Marquet, L. Tavian & R. van Weelderen, The Supertluid

Proc. ICEC14, Cryogenics 32, ICEC Supplement, pp. 1118-121 (1992).Experimental Validation of the Superfluid Helium System for the Large Hadron Collider Project at CERN.[34] J. Casas, A. Cyvoct, Ph. Lebrun, M. Marquet, L. Tavian & R. van Weelderen, Design Concept and First

Dipole Cryostats, Proc. ICEC 14, Cryogenics 32, ICEC Supplement, pp. 191-194 (1992).[33] J.C. Brunet, J. Kerby, Ph. Lebnin, P. Rohmig, B. Szeless & L.R. Williams, Design ol LllC Prototype

presented at EUCAS'93, Gottingen (1993).[32] R. Perin & J. Vlogaert for the LHC Magnet Team, Magnets for the Large Hadron Collider, paper

Washington (1993).[31] G. Brianti on behalf of the LHC Machine Group, LHC Progress and Status, paper presented at PAC'93,

Tunnel, CERN Report 91-03 (1991).[30] The LHC Study Group, Design Study of the Large Hadron Collider: A Multiparticle Collider in the LEP

PAC'93, Washington (1993).Ch. Titcomb & G. Winkler, Cryogenics for the LEP2OO Superconducting Cavities at CERN, paper presented at[29] D. Giisewell, M. Bananco-Luque, S. Claudet, W.K. Erdt, P. Frandsen, Ph. Gayet, J. Schmid, N. Solheim,

paper presented at CEC'93, Albuquerque (1993).[28] G.M. Gistau & M. Bonneton, A 6kW at 4.5 K Helium refrigerator for CERN's Cryogenic Test Station,

Helium Refrigerator for the LEP2OO Project at CERN, paper presented at CEC'93, Albuquerque (1993).[27] K. Kurtcuoglu, K. Lohlein, U. Wagner & B. Ziegler, Plant Performance of the High Ellicient 6 kW

CERN, Proc. ICEC14, Cryogenics 32, ICEC Supplement, pp. 151-154 (1992).Schmid, N. Solheim, G. Winkler & C. Wyss, Status of Cryogenics t`or the LEP200 Energy Upgrade Project at[26] M. Barranco-Luque, S. Claudet, W.K. Erdt, P.K. Frandsen, Ph. Gayet, D. Gusewell, K.P. Hoffmann. .I.

Cryogenics 30, September Supplement pp. 136-142 (1990).Passardi, J. Schmid & G. Winkler, The Refrigeration System for the LEP Energy Upgrade, Proc. ICECI3.[25] M. Barranco-Luque, J.P. Dauvergne, W. Erdt, P. Frandsen, D. Gusewell, F. Haug, A. Juillerat, G.

PAC'93, Washington (1993).Tuckmantel & W. Weingarten, Superconducting cavities for the LEP Energy Upgrade, paper presented at[24] G. Cavallari, C. Benvenuti, P. Bemard, D. Bloess, E. Chiaveri, F. Genesio, E. Haebel, N. Hilleret, J.

[23] C. Wyss, Progress of the LEP Energy Upgrade Project, paper presented at PAC'93, Washington (1993).

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