Lebrun, P

Riddone, G

Tavian, L

Wagner, U

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLHC Project Report 18Large Hadron Collider ProjectDemands in Refrigeration Capacity for the Large Hadron ColliderPh. Lebrun, G. Riddone, L. Tavian and U. WagnerAbstractThe capacity demands on the cryogenic installations for the Large Hadron Collider(LHC) at CERN have been recently updated [1]. Unlike the LEP energy upgradeusing superconducting acceleration cavities LHC will require high powerrefrigeration at 1.9 K, as well as non-isothermal cooling at 4.5 K to 20 K and at 50K to 75 K. This paper presents the assessment of cryogenic capacity that has tobe supplied by the eight refrigerators for LHC in relation with the foreseenoperating modes of the machine.LHC Division, CERN, CH-1211 Geneva 23, SwitzerlandICEC 16/ICMC, Kitakyushu, Japan, 20-24 May 1996Administrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandGeneva, 11 July 1996Demands in Refrigeration Capacity for the Large Hadron ColliderPh. Lebrun, G. Riddone, L. Tavian and U. WagnerLHC Division, CERN, CH-1211 Geneva 23, SwitzerlandThe capacity demands on the cryogenic installations for the Large Hadron Collider(LHC) at CERN have been recently updated [2]. Unlike the LEP energy upgradeusing superconducting acceleration cavities LHC will require high powerrefrigeration at 1.9 K, as well as non-isothermal cooling at 4.5 K to 20 K and at 50K to 75 K. This paper presents the assessment of cryogenic capacity that has tobe supplied by the eight refrigerators for LHC in relation with the foreseenoperating modes of the machine.INTRODUCTIONBased on today’s knowledge the LHC collider will demand a total about 6.6 MW exergetic capacity. Halfof this total capacity is to be supplied at 1.8 K for cooling the cold mass of the superconducting magnets.The rest is distributed mainly for non isothermal loads at 4.5 K to 20 K and 50 K to 75 K as well as forthe cooling of current leads. Due to the exergetic losses which result from refrigeration at 1.8 K, the eightcryogenic plants will have a total equivalent capacity of  150 kW at 4.5 K.The reference design for the current leads is based on the use of high temperature superconductor(HTS) material leaving open the choice of cooling methods [3]. The precise assessment of the heat loads isan important task during the planning phase of the project and has to be kept under tight control.TEMPERATURE LEVELSThe staging of temperature levels envisaged for the LHC cryogenic system are:- thermal shielding between 50 K and 75 K as a first major heat intercept, sheltering the cold mass fromthe bulk of heat inleaks from ambient;- non-isothermal cooling of the beam screens between 4.5 K and 20 K which will shield the cold massfrom synchrotron radiation and image currents produced by the high-energy, high-intensity hadronbeams;- quasi-isothermal superfluid helium cooling the magnet cold mass at a maximum temperature of 1.9 K;- isothermal helium cooling special superconducting magnets in insertion regions, superconductingacceleration cavities, and the lower sections of HTS current leads at a saturation temperature between4.5 K and 4.7 K;- gaseous helium cooling the resistive upper sections of HTS current leads, in forced flow between 20 Kand ambient.STATIC AND DYNAMIC LOADSThe term “static loads” is used for all heat loads which are not dependent on the machine operation. Thiscomprises the heat inleaks due to conduction and radiation to the low temperature part inside thecryostats plus the thermal load by pure conduction in all feedthroughs.The term “dynamic loads” is used for all heat loads which are dependent on the machine operation.This includes loads induced either by the excitation current of the superconducting magnets i.e. in currentleads or residual resistive areas of coil splices, or by the circulating particle beams i.e. synchrotronradiation, resistive heating due to image currents or geometrical singularities in the beam channels andparticle losses. These loads depend strongly on the energy and intensity of the circulating beams and areestimated for the nominal and ultimate operating conditions defined below.MODES OF OPERATIONThe modes of interest for the cryogenic system are:- “nominal operation” at 7 TeV beam energy, 2 x 0.536 A beam current and 1 x 1034 cm-2 s-1 luminosity;- “ultimate operation” at 7 TeV beam energy, 2 x 0.848 A beam current and 2.5 x 1034 cm-2 s-1luminosity;- “low beam intensity operation”, still with full beam energy and thus full excitation current in themagnets but negligible beam current;- “injection standby”, characterised by negligible resistive dissipation and beam-induced heat loads in themagnets.THE ARCSThe eight arcs, which form the regular part of the LHC will be composed of 46 half-cells, each consistingof three main dipoles, one main quadrupole plus a number of correction magnets [1]. The expected staticloads of the main elements in the half cells has been assessed with good confidence and experimentallyverified through several independent, yet converging approaches [4-7].Parallel to the magnet cryostats in the arc runs the cryogenic distribution line from which each half-cell is supplied with cryogenic fluids. The heat loads of this line are estimated based on conceptual designdrawings and will have to be validated in future prototype tests. Table 1 shows the total heat loadbudgeted for an LHC arc in the four machine operation modes described above.Table 1  Total heat load for an LHC arc (no contingency included)Operating mode Temperature levels Comments50 - 75 K 4.5 - 20 K 1.9 K[W] [W] [W]Nominal operation 15800 1930 1070 static & dynamic nominalUltimate operation 15800 3630 1040 static & dynamic ultimateLow-beam-intensity 15800 310 920 static & magnet current inducedInjection standby 15700 310 660 pure static loadTHE INSERTIONSThe insertions consist of 0.5 km long sections connecting the arcs. They include dispersion suppressor,beam separation and recombination, RF acceleration and beam focusing sections on each side of thecollision points. Each cryogenic sector includes two half insertions at the both ends of an arc. Since thedetailed design of the superconducting magnets in the insertions has not yet been finalised, their expectedheat loads have been assessed by approximate scaling from the better defined arc magnets. The results,displayed in Table 2, reflect the variations in geometry, layout, functions and operating modes of thedifferent LHC insertions. They also include specific components - for example, superconductingacceleration cavities, which require significant amounts of cryogenic refrigeration as well as referencemagnets for field tracking measurements. Also appearing in these tables are the localised heat loads in thecurrent leads of the different excitation circuits, and based on the use of high-temperaturesuperconductors.Special heat loads have to be accounted for all elements close to the high luminosity physicsexperiments due to absorption of secondary particles in the cold mass of the superconducting magnetslocated close to the experimental areas. The values for the whole machine are:- at the 1.9 K level, from 500 W (nominal) to 1250 W (ultimate) in the inner triplets of low-betaquadrupoles, as well as from 54 W (nominal) to 134 W (ultimate) in the dispersion suppressor- at the 4.7 K level, from 240 W (nominal) to 600 W (ultimate) in the beam separation and recombinationdipoles.Table 2  Total heat loads for the half insertions of the LHC machine at nominal operating conditions (nocontingency included)Half Insertion Temperature Levels Gas heliumconsumption50 - 75 K 4.5 - 20 K 4.7 K 1.9 K 20 - 300 K[W] [W] [W] [W] [g/s]High-luminosity insertion 1300 125 100 300 11Low-luminosity insertion 1350 130 50 150 13Beam-cleaning insertion 800 120 5 80 2RF insertion 1250 130 380 100 13Beam-dump insertion 1150 120 5 120 12DEMANDS ON THE SECTOR CRYOPLANTSThe LHC sectors stretch over 3.3 km between the insertion points. The cryogenic load for each sectorcomprises those a full arc and two half insertions at each end. A special load to be added for each sector isthat resulting from a continuous loss of particles escaping the collimation sections, which may result in alocally deposited heat load estimated at 55 W (nominal) and 92 W (ultimate), over a length of a few tensof metres corresponding to the region of aperture restriction.The total installed cryogenic power to cope with the expected loads for the sectors is determinedusing a contingency calculation to include for uncertainties and overcapacity. For the heat loads at the 50 -75 K and the 20 to 300 K level:Qinstalled = Max [ Fov . Qnominal ; Qultimate];for the heat loads at the 4.5 - 20 K, 4.7 K and 1.9 K level:QInstalled = Max [ Fov .  (Fun .  Qstatic + Qdynamic nominal) ; Fun .  Qstatic + Qdynamic ultimate ].As factor for overcapacity, Fov, 1.5 is used, for uncertainty, Fun, 1.25. Table 3 shows the installedcryogenic power which results for the two types of sectors of the machine. About 250 W of the load at1.9 K listed in Table 3 result from superheating the helium vapour in the 3.3 km long cryogenicdistribution line and do not contribute to the cold compressor flow.Table 3 Installed cryogenic power requirements of the LHCSector Temperature Levels Gas heliumconsumption50 - 75 K 4.5 - 20 K 4.7 K 1.9 K 20 - 300 K[kW] [kW] [kW] [kW] [g/s]High-load sector 31.0 4.30 0.80 2.80 35Low-load sector 30.0 4.30 0.65 2.45 23DAILY LOAD VARIATIONSThe operation phases which the machine will undergo during a 24 hour period will be four hours ofinjection standby, during which the storage ring will be adjusted and filled with particles, half an hour ofcurrent ramping to reach the operating energy, 19 hours of operation at nominal or eventually ultimateconditions, half an hour of current ramp down to prepare for the new injection. Current ramping willgenerate an additional heat load due to resistive dissipation in the superconducting magnet splicesFigure 1 shows the development of the load on the 1.9 K level during the injection and ramp phase leadingfrom the “injection stand-by” to the “nominal” operation mode. Although the rapid changes will bepartially buffered by the heat capacity of the pressurised helium II bath, the variations in demand requireload adaptation of the cryogenic system over a large dynamic range.02 04 06 08 01 0 01 2 01 4 01 6 0- 5 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5Time [mi nHeat Load and Magnet Current [% of nominal]02 0 04 0 06 0 08 0 01 0 0 01 2 0 01 4 0 01 6 0 01 8 0 02 0 0 02 2 0 02 4 0 02 6 0 0Load at 1.9 K [W]CurrentLoad at 1.9 Injection Stan d Injecti Accelerat i Beam Squeeze Nominal Operat iFigure 1  Development of the 1.9 K load of a high luminosity sector from “injection standby” over magnetramping to “nominal” capacity operation (no contingency)CONCLUSIONSThe demands of refrigeration capacity for the LHC machine have been assessed with increasing accuracyduring the recent years. As the project definition is finalised further updates of the heat loads will benecessary. Special attention has to be given to all components which at the moment are still uncertain intheir performance like the insertion magnets or assessed by theoretical calculations like the HTS currentleads.REFERENCES1 The LHC study group, The Large Hadron Collider, Conceptual Design CERN/AC/95-05(LHC)2 The LHC study group, The Large Hadron Collider, Conceptual Design CERN/AC/95-05(LHC)3 Ballarino, A., Ijspeert, A. and Wagner, U., Potential of high-temperature superconducter currentleads for LHC cryogenics, paper presented in this conference4 Jenny, B., Cameron, W., Riddone, G., Rohmig P. and van Weelderen, R., Design and construction ofa prototype superfluid helium cryostat for the short straight sections of the CERN Large HadronCollider, Adv. Cryo. Eng. (1994) 39A 663-6705 Benda, V., Dufay, L., Ferlin, G., Lebrun, Ph., Rieubland, J.M., Riddone, G., Szeless, B., Tavian L.and Williams, L.R., Measurement and analysis of thermal performance of LHC prototype dipolecryostats paper presented at CEC'95 Columbus (1995)6 Bézaguet, A., Casas-Cubillos, J., Flemsaeter, B., Gaillard-Grenadier, B., Goiffon, Th., Guinaudeau,H., Lebrun, Ph., Marquet, M., Serio, L., Suraci, A., Tavian L. and van Weelderen, R., The superfluidhelium cryogenic system for the LHC Test String: design, construction and first operation paperpresented at CEC'95 Columbus (1995)7 Dufay, L., Ferlin, G., Lebrun, Ph., Riddone, G., Rieubland, J.M., Rijllart, A., Szeless B. andWilliams, L.R., A full-scale thermal model of a prototype dipole cryomagnet for the CERN LHCproject Cryogenics 34 ICEC Supplement, (1994),. 693-696

Demands in refrigeration capacity for the Large Hadron Collider

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