The Large Hadron Collider (LHC) is presently under construction at CERN. Its main components are superconducting magnets which will operate in superfluid helium requiring cryogenics on a length of about 24 km around the machine ring with a total helium inventory of about 100 tonnes. As no permanent liquid helium storage is foreseen and for reasons of investment costs, only half of the total helium content can be stored in gaseous form in medium pressure vessels. During the LHC operation part of these vessels will be used as helium buffer in the case of multiple magnet quenches. This paper describes the storage, distribution and management of the helium, the layout and the connection to the surface and underground equipment of the cryogenic system

Barranco-Luque, M

Tavian, L

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsGASEOUS HELIUM STORAGE AND MANAGEMENTIN THE CRYOGENIC SYSTEM FOR THE LHCM. Barranco-Luque, L. TavianThe Large Hadron Collider (LHC) is presently under construction at CERN. Its main components aresuperconducting magnets which will operate in superfluid helium requiring cryogenics on a length ofabout 24 km around the machine ring with a total helium inventory of about 100 tonnes. As nopermanent liquid helium storage is foreseen and for reasons of investment costs, only half of the totalhelium content can be stored in gaseous form in medium pressure vessels. During the LHC operationpart of these vessels will be used as helium buffer in the case of multiple magnet quenches. This paperdescribes the storage, distribution and management of the helium, the layout and the connection to thesurface and underground equipment of the cryogenic system.LHC DivisionPresented at the Eighteenth International Cryogenic Engineering Conference (ICEC 18)21-25 February 2000, Bombay Mumbai, IndiaGeneva, Large Hadron Collider ProjectAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandLHC Project Report 383Abstract26 July 2000Gaseous Helium Storage and Management in the Cryogenic System for the LHCManuel Barranco-Luque, Laurent TavianLHC Division, CERN, 1211 Geneva 23, SwitzerlandThe Large Hadron Collider (LHC) is presently under construction at CERN. Itsmain components are superconducting magnets which will operate in superfluidhelium requiring cryogenics on a length of about 24 km around the machine ringwith a total helium inventory of about 100 tonnes. As no permanent liquid heliumstorage is foreseen and for reasons of investment costs, only half of the totalhelium content can be stored in gaseous form in medium pressure vessels. Duringthe LHC operation part of these vessels will be used as helium buffer in the caseof multiple magnet quenches. This paper describes the storage, distribution andmanagement of the helium, the layout and the connection to the surface andunderground equipment of the cryogenic system.1 INTRODUCTIONCryogenic systems require storage facilities for the helium inventory. Medium-pressure storage isgenerally preferred to high-pressure storage which needs gas bags and recovery compressors with costlymaintenance and also to liquid storage demanding a permanent re-liquefaction of losses. The LHC willmake use of a large amount of medium pressure storage vessels distributed over the different sites,requiring a precise management of their interconnections.2 HELIUM INVENTORY OF THE LHCThe LHC machine [1] is composed of eight sectors of 3.3 km length. Helium is mainly contained in themagnet cold masses which require a filling rate of 15l/m of superfluid helium for enthalpy buffering aswell as in one of the headers of the cryogenic distribution line [2] (header C) which requires aDN100 diameter for cool down and warm-up operation and which is filled with dense supercriticalhelium in normal operation. Figure 1 shows the helium inventory per sector. The total helium inventoryof the whole machine is about 100 tonnes. The complete storage of this inventory would cost about20 MCHF [3] and would require large facilities. For reasons of investment cost limitation and ofenvironmental impact, it was decided to store only half of the inventory.60%28%7%5%Cold massesHeader COther headersCryoplantsTotal inventory:12 tonnes of He per sectorFigure 1  Helium inventory per sector3 DISTRIBUTION OF THE HELIUM STORAGEThe cryogenic system of LHC has to re-use the existing LEP infrastructure which is constituted of fortyvessels with a capacity of 75m3 each. These vessels with a diameter of 3 m and a length of 12 m havebeen installed in vertical position in the shadow of the buildings. To complete this storage, additionalvessels have been ordered in two steps from European industry on the basis of competitive tendering.12 vessels were delivered by Ferox(Czech Republic) and 38 vessels were contracted to Silva Matos(Portugal). These additional vessels of 250 m3 capacity each, a length of 28 m and a diameter of 3.5 m,will be installed in horizontal position. All vessels are in carbon steel. The gaseous helium will be storedat a maxium working pressure of 2 MPa and ambient temperature. Table 1 shows the type and number ofvessels distributed on the eight sites around the LHC ring.At each point, four 250 m3 vessels will be used as quench buffer in case of resistive transition ofmultiple magnets during LHC operation. These vessels must remain empty during normal operation andmay only be used as storage capacity during shutdown. The remain vessels will be used as make-up gasstorage for the cryogenic system. Helium at a temperature down to 10 K may be discharged into thequench buffer. In order to avoid cold spots on the carbon steel surface, the cold helium is diffused via a26 m long stainless steel inlet pipe perforated with 41 holes of 5mm diameter ; this diffuser is connectedto the quench buffer wall via a stainless steel cold finger. The lowest possible temperature of the bufferwalls during a total LHC sector quench is estimated [4] to -35 oC. The design temperature of the vesselsmade of fine grain carbon steel is -40 oC. Before manufacturing started, a Charpy impact test at -50 oCwas performed on each shell plate as well as on the welding test plates.Location No. of vessels Volume Mass of helium75 m3 250 m3 [m3] [tonnes]Point 1.8 0 12 3000 9.1Point 2 10 4 1750 5.3Point 3 0 6 1500 4.5Point 4 10 6 2500 6.8Point 5 0 4 1000 3.0Point 6 10 6 2250 6.8Point 7 0 6 1500 4.5Point 8 10 6 2250 6.8Total 40 50 15500 46.9Table 1  Distribution of storage vessels4 STORAGE MANAGEMENT4.1 Interconnection of Storage AerasFigure 2 shows the different interconnections between the storage areasar und the LHC. For reason ofavailable space at the different points, the storage vessels are not equally distributed. The easyaccessibility for helium delivery to some points such as point 1.8 i  also taken into consideration. Ahelium ring line interconnecting the different storage areas will be installed in the tunnel and the accessshafts. Each sector refrigerator is directly connected to its make-up storage. At point3 and 7, where orefrigerator is installed, make-up storage vessels are also available. Make-up storage can beinterconnected by opening the V1valves.During a quench, helium leaves the cold environment via the interconnection box (QUI) and thereturn modules (QRLR) of the cryogenic distribution line ; the quench buffers are filled via the valves V2.The helium then returns to the sector refrigerator via the valves V3 or V4. They are also used during apartial LHC warm-up to store one part of the inventory in the quench buffers. In this case, no electricalpowering of the adjacent sectors is allowed. To minimise the dead volume of the quench buffer, it is alsopossible to complete their emptying by connecting them via the helium ring line and the V5 valves to thelow pressure (LP) of one refrigerator.The hydraulic impedance of the helium ring line must not diminish the liquefaction capacity of therefrigerator during re-cool down of a sector, thus requiring a DN100 diameter pipe.Ref. 1QUIPoint 2V3V2V2V4V1QRLRQRLRPoint 7Ref. 1Ref. 2QUIPoint 6V3V4V1V2V2QRLRQRLRPoint 5CMSRef. 1Ref. 2QUIPoint 4V3V2V2V1V4QRLRQRLRPoint 3Ref. 1QUIPoint 1.8V1V2V4V3Ref. 1Ref. 2QUIPoint 8V3V4V1V2V2QRLRLPV5V5LPLPV5LPV5V5LPV5LPV5LPV5LPV2V2V2V1V4V2 V2V4V1V4V2V2250 m3 vessels (make-up)75 m3 vessels (make-up)250 m3 vessels (quench buffer)He ring lineCryogenic distribution lineFigure 2  Interconnection of storage areas4.2 Protection against Water ContaminationThe compressor stations of the 4.5 K helium refrigerator plants [5] will be equipped with switchable fullflow dryers located after the final oil removal system (ORS). The filling of the storage vessels will bemade with helium taken at the full flow dryer discharge, guaranteeing water and oil-free helium in thestorage. The compressor station of the 1.8 K refrigeration u its [6] are not equipped with dryers. To avoidstorage vessel pollution, the helium make-up discharge of these units is done via the warm compressorstations of the 4.5K refrigerators.Figure 3 shows the interconnection scheme of the compressor stations to the storage vessels. Clean gas isdistributed to the different cryogenic components for circuit and volume purging.LP MPORS4.5 K RefrigeratorHPStorage VesselsDryersVLPORS1.8 K Refrigeration unitHPClean gasdistributionFigure 3  Interconnection of storage vessels to the compressor stations5 PERIODIC CONTROLThe safety code which regulates the pressure vessel construction requires hydraulic pressure tests aftermanufacturing and normally after every 10 years of operation. This retesting is very heavy as it impliessevere risk of contamination. A possible way to seek derogation from safety authorities consists ofmaking use of acoustic emission monitoring during pneumatic tests [7]. A sound cartography isestablished during the first pneumatic test following the installation at CERN. At every retesting p riod, anew cartography is produced and compared to the original one in order to detect any mechanicaldeterioration. This new procedure is developed in collaboration with CETIM (France) who have thetechnical expertise.6 CONCLUSIONFor the LHC cryogenic system, medium-pressure storage will be distributed at the different points aroundthe machine circumference. During normal operation, half of this storage will be dedicated to quenchbuffering. The remaining part will be used as make-up helium gas storage. Interconnection of thedifferent storage areas and protection against contamination will be implemented allowing a flexible andsafe management of the helium distribution. Acoustic emission monitoring of the pressure vessels, whichseems to be promising to obtain derogation for the decennial hydraulic test, will be performed duringpneumatic tests.REFERENCES1. Lebrun, Ph., Cryogenics for the large hadron collider, paper invited at the 16th International Conference on MagnetTechnology, Ponte Vedra Beach, USA2. Erdt, W.K., Riddone, G., Trant, R., The cryogenic distribution line for the LHC: functional specification and conceptualDesign, paper presented at CEC’99, Montréal, Canada3. Claudet, S., Gayet, Ph., Lebrun, Ph., Tavian, L. and Wagner, U. Economics of large helium cryogenic system: experiencefrom recent projects at CERN, paper presented at CEC’99, Montréal, Canada4. Chorowski, M. and Skoczen, B., Thermo-mechanical analysis of cold helium injection into gas storage tanks made ofcarbon steel following resistive transition of the LHC magnets, paper presented at ICEC17, Bournemouth, UK, (14–17 July 1998).5. Claudet, S., Gayet, P. and Wagner, U. Specification of four new large 4.5 K helium refrigerator for the LHC, paperpresented at CEC’99, Montréal, Canada6. Claudet, S., Gayet, P., Jager, B., Millet, F., Roussel, P., Tavian, L. and Wagner, U. Specification of eight 2400 W @ 1.8 Krefrigeration units for the LHC, paper presented at this conference7. Barranco-Luque, M., Cherfaoui, M., Herve, C., Margaroli, C., Sergo, V. Quality Testing of Gaseous Helium PressureVessels by Acoustic Emission, paper presented at ICEC17,

Gaseous Helium storage and management in the cryogenic system for the LHC

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