During more than five years a close collaboration between CERN and CEA-Saclay led to the development and construction of two prototype quadrupole magnets and the integration of one of them into the short straight section of the LHC half-cell test string at CERN. In the frame of the special host country contribution to the LHC project this collaboration has been extended to the CNRS laboratory in Orsay and covers besides the quadrupole magnets the complete cold mass assembly (CEA) and the integration into the short straight section cryostat (CNRS). The short straight sections include not only the main lattice quadrupoles with their protection diodes, they also house different corrector magnets and the beam position monitors. Further, they provide the cryogenic feed units for a half-cell with all the magnet interconnections and the jumper connection to the separate cryo-line. The paper will show the general lay-out of these complex units and elaborate the different aspects of their assembly

Parma, Vittorio

Peyrot, M

Rifflet, J M

Rohmig, P

Tortschanoff, Theodor

Vincent, D

Védrine, P

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLarge Hadron Collider Project LHC Project Report 105THE SHORT STRAIGHT SECTIONS FOR THE LHCT.  Tortschanoff, V. Parma, P. Rohmig*M. Peyrot, J.M. Rifflet, P.Védrine, CEA-Saclay, France and D. VincentAbstractDuring more than five years a close collaboration between CERN and CEA-Saclay led to thedevelopment and construction of two prototype quadrupole magnets and the integration of one of theminto the short straight section of the LHC half-cell test string at CERN. In the frame of the special hostcountry contribution to the LHC project this collaboration has been extended to the CNRS laboratory inOrsay and covers besides the quadrupole magnets the complete cold mass assembly (CEA) and theintegration into the short straight section cryostat (CNRS). The short straight sections include not onlythe main lattice quadrupoles with their protection diodes, they also house different corrector magnetsand the beam position monitors. Further, they provide the cryogenic feed units for a half-cell with all themagnet interconnections and the jumper connection to the separate cryo-line. The paper will show thegeneral lay-out of these complex units and elaborate the different aspects of their assembly.PAC’97, VancouverAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandGeneva, 30 May 1997THE SHORT STRAIGHT SECTIONS FOR THE LHCT.  Tortschanoff, V. Parma, P. Rohmig, CERN, Geneva, Switzerland,M. Peyrot, J.M. Rifflet, P.Védrine, CEA-Saclay, France and D. Vincent CNRS, Orsay, FranceAbstractDuring more than five years a close collaboration betweenCERN and CEA-Saclay led to the development andconstruction of two prototype quadrupole magnets and theintegration of one of them into the short straight sectionof the LHC half-cell test string at CERN. In the frame ofthe special host country contribution to the LHC projectthis collaboration has been extended to the CNRSlaboratory in Orsay and covers besides the quadrupolemagnets the complete cold mass assembly (CEA) and theintegration into the short straight section cryostat(CNRS). The short straight sections include not only themain lattice quadrupoles with their protection diodes, theyalso house different corrector magnets and the beamposition monitors. Further, they provide the cryogenicfeed units for a half-cell with all the magnetinterconnections and the jumper connection to the separatecryo-line. The paper will show the general lay-out ofthese complex units and elaborate the different aspects oftheir assembly.1  INTRODUCTIONThe major effort in the development of the LHCmagnet system has been put into the design andconstruction of the dipole magnets. Since 1989, however,a collaboration with CEA-Saclay in France was started forthe development of the lattice quadrupole magnets for theLHC. This resulted in the successful construction andtesting of two prototype quadrupole magnets [1] of whichone has been integrated into a short straight section unitforming the first cryo-magnet unit in CERN’s test stringoperated since 1994 [2].Following the approval of the LHC project a newcollaboration for the design, prototyping and industrialseries production was concluded between CERN and twoFrench laboratories, CEA-Saclay and CNRS in Orsay.While the CEA is looking after the cold masses of theshort straight sections CNRS has been entrusted with thework for the cryostating of these units.Although much shorter than the 15 m long dipoleunits [3] the short straight sections are of much highercomplexity. As their main magnetic component theycontain the 3.25 m long twin aperture lattice quadrupolemagnets. Further, on one end of the quadrupole thecombined sextupole-dipole corrector magnets for eachbeam are placed, while on the other end a pair of octupolecorrector magnets is mounted or, depending on theirlocation in the arc, a pair of tuning quadrupoles. For theshort straight sections which will be located in thedispersion suppresser regions and near the insertion pointsother types of correctors will be used like long tuningquadrupoles, skew quadrupoles or eventually skewoctupole magnets.2  LAY-OUT OF THE SHORT STRAIGHTSECTIONS FOR LHCThe cold mass of the earlier short straight sectiondesigned for the LHC test string consisted of two parts.One, the main twin aperture quadrupole magnet with itsstiffening inertia tube, the other with all the correctionelements, placed in a separate inertia tube: The two halveswere aligned and joined together, both mechanically andelectrically to form the cold mass of the prototype straightsection.The new LHC design features now among othermodifications a symmetric arrangement of the quadrupoleswith respect to the dipole magnets. This implies that thecorrector magnets have to be on both sides of thequadrupole. Furthermore, the quadrupoles are poweredindependently from the dipoles thus reducing theintegrated length of the tuning quadrupoles significantly.The inertia tube into which all magnets must be aligned,will no more be made out of two halves but in one singlepiece. It has to be rigid enough to guaranty thegeometrical stiffness under the weight load and in alloperating conditions.The cryostat which has been simplified with respectto earlier versions [4] by the implementation of a separatecryogenic feed line, will be completed on one end by thecryogenic technical service module. The functions of thismodule are multiple. Each module will house the beamposition monitors, the protection diodes of the quadrupolemagnets and the cold mass instrumentation capillaries.Every second will contain in addition the cryogenicinterconnection and the liquid helium separator. On theopposite end of the short straight section theinterconnection is practically identical to those of thestandard dipole magnets.An important feature of the short straight sectiondesign is the sectorisation of the insulation vacuum [5].This implies that the short straight section has a vacuumbarrier which in the present design will be mounted everysecond cell, i.e., every fourth short straight section. Thishelps in the leak testing during installation and makesshort intervention, like the exchange of a diode, possible.It permits in case of a major intervention, like thereplacing of a magnet, to warm up one sector only. Theliquid helium flow in between cold masses is also sectoredby means of pressure plugs placed in the bus-barconnection tubes for every second cell.3  MAIN QUADRUPOLE MAGNETSThe new quadrupole design follows the line of theearlier concept. The main parameters of this twin aperturemagnet are summarised in table 1.   Table 1: LHC Main Quadrupoles ParametersThe super-conducting cable of the quadrupolemagnets will be the same as the key-stoned cable used forthe outer coil layer in the main dipole magnets. By this itis hoped to achieve savings not only because ofstandardisation but especially since the unit cable lengthfor a quadrupole coil is considerably shorter than that forthe dipoles.Fig. 1 shows the cross-section of the quadrupoleinits cryostat. Since the electromagnetic forces in aquadrupole are significantly lower than in a dipole nocontribution of the yoke is needed to pre-stress the coils.This is ensured by the independent stainless steel collarswhich themselves are centred inside the single piece yokelaminations by longitudinal keys. The cut-off on top orbottom of every second yoke laminations allows to pressand key them such that the coil collar units are well fixedand aligned inside the yoke apertures. The centring of theyoke inside the inertia tube is again provided by a seriesof keys which are blocked from the outside of the tube bya series of bolts. Welded covers over these series of boltshave to make sure that the inertia tube is helium leaktight to an operational maximum pressure of 20 bar andfulfils its function as helium vessel. The upper of the two60 mm diameter holes in the yoke will house the heatexchanger tube which runs through all elements of onemachine cell and where the cooling down to 1.9 K takesplace [6]. The lower one will be used for the passage ofcables, especially for instrumentation and eventually forcorrector magnet wiring.Figure 1 - Cross-section of the LHC lattice quadrupole inits short straight section cryostat4  CORRECTOR MAGNETSEach short straight section will have on the end,opposite to the connections, the sextupole- dipolecorrector magnets. While the sextupole coils of thiscombined units will be powered in series to currents up tonominally 500 A the corrector dipole magnets,alternatively either horizontally or vertically deflectingones, will be powered individually which means that theyhave to have their current passage between 1.9 K androom temperature in every short straight section. Theirmaximum operational current will be 32 A. The yokelength of these units will be 1.26 m, the sextupolestrength is 1500 T/m2 over a magnetic length of 1.10 mthe corrector dipole field is 1.5 T over 1.03 m. Thesecoils will be assembled in a common yoke and fixedinside the inertia tube similar to the main quadrupoles.On the connection side of the quadrupole, most shortstraight sections will have two octupole corrector magnetsof 380 mm overall length, including a magnetic shieldaround them. Their strength will be 6.7.104 T/m3 over amagnetic length of 320 mm. Their outer diameter will notbe more than 117 mm and thus they will be mountedseparately and fixed by a pair of plates inside the inertiatube. The nominal current will be 600 A.The short straight sections near the ends of the arcwill have tuning quadrupoles in place of the octupoles.With the same amperage and overall length they will havea larger outer diameter of 170 mm. Their field gradientwill be 120 T/m. In some of the short straight sections inNominal temperature 1.9 KNominal gradient 223T/mMargin on load line . 19.7 %Nominal Current 11870 AMagnetic length 3.10 mBeam separation distance (cold) 194.0 mmInner coil aperture diameter (warm) 56mmOuter coil diameter 118.6mmOuter yoke diameter 452 mmCollar material Stainless steelYoke length including end plates 3250 mmthe dispersion suppresser region their yoke length will be1700 mm. Because of their high number and theirsimilitude to the corrector magnets in the dipoles coldmasses a semi-automized coil fabrication is envisaged forall corrector magnet coils.5   C R Y O S T A TThe short straight section cryostat has beenconceived together with the dipole cryostat. With theseparated cryo line in the tunnel its cross-section had beensimplified considerably. As a variation to the dipolecryostat the sectorisation must be mentioned. This itemwill have to take not only differences in pressure andassure leak tightness it must also allow for all thedimensional variations during cool-down and operation.Further, it must be mountable in the short straightsection cryostats where needed and interface well with thecryostat, the cold mass, the tubes and the shielding insidethe cryostat. Two techniques have been pursued, one withan all steel membrane and one with a compositemembrane in collaboration with industry [7].RADIATION SCREENHOUSING FORMQ DIODESMACHINECONNECTION BOX      QRIINTERCONNECTSUPPORT POSTBEAM TUBEVACUUM BARRIERPHASESEPARATORLATTICEQUADRUPOLEINTERCONNECT WITHRING TUNNEL INTER-BPMQUADRUPOLE CRYOSTATTECHNICAL SERVICE MODULEVACUUM VESSELHELIUM VESSEL(INERTIA TUBE)MACHINEINTERCONNECTOCTUPOLEMOCORRECTORMSCV/HBEAM VACUUMPUMPING MANIFOLDQQSFigure 2 - Perspective view of the cold mass in cryostattogether with cryogenic technical service moduleOnly two cryogenic pipes remain inside the cryostatwhich are the one for thermalising the thermal shield at50 K and that for thermalising the upper part of thesupport posts to 5 - 10 K. One of the two support posts,positioning the cold mass inside the cryostat, will befixed, the other one will be allowed to slide to compensatethermal contraction. Fig. 2 shows a perspective view ofthe cold mass in the cryostat.6  CRYOGENIC TECHNICAL SERVICEMODULEThe short straight section is completed by acryogenic technical service module. This will contain thetwo beam position monitors attached to their beamscreens and bolted to the endplate of the cold mass, thequench protection diodes in their container. Every secondmodule will have its cryogenic jumper connection to theseparate cryogenic supply line and a helium phaseseparator. which provides for all cryogenic but alsoelectrical interconnections. This implies that there will betwo major types of these modules.The magnet to magnet linking must provide thecontinuity of the currents and helium flow or of theplugging of the latter one where required. In this area willalso be placed the interconnections for the auxiliary bus-bars and their leads to the corrector magnets of the shortstraight section in question. Further, there must bepassages of the instrumentation wiring from the cold-mass interior to the capillaries which leads them tooutside of the cryostat. All this makes this service modulea very complex unit the study of which is not yetfinalised.7   CONCLUSIONSThe short straight sections of the LHC are vitalunits for the operation of the machine. Their complexityis given by the multitude of magnetic and other machinecomponents. The presence of the cryogenic technicalservice module with its variants and differentcombinations of function complicates the still ongoingdesign even further. CERN is however confident to realisethese units in the great number of their different versionswith the active help of the collaborating laboratories,CEA-Saclay and CNRS in Orsay.REFERENCES[1] K. Henrichsen et al., Cryogenic and mechanicalmeasurements of the first two LHC lattice quadrupoleprototypes, Proc. EPAC 94, London, UK, 27 June to1 June 1994.[2] A. Bézaguet et al., The LHC test string: firstoperational experience, Proc. EPAC 96, Sitges,Barcelona, Spain, 10 to 14 June 1996.[3] R. Perin, Super-conducting magnets for the LargeHadron Collider, Proc. EPS 10, Trends in Physics,Seville, Spain, 3 to 13 Sep. 1996.[4] W. Cameron et al., Design and construction of aprototype super-fluid helium cryostat for the shortstraight section of the CERN Large Hadron Collider(LHC), Proc. Int. Cryogenic Engineering Conf.(CEC), Albuquerque, NM, USA, 12 to 16 July 1993.[5] M. Bona et al., Cryogenic and vacuum sectorisation ofthe LHC arcs, CERN-LHC-Project Report 60.[6] V. Benda et al., Conceptual design of the cryogenicsystem for the Large Hadron Collider (LHC), Proc.EPAC 96, Sitges, Spain, 10 to 14 June 1996.[7] B. Jenny, P. Rohmig, J.-M. Uriarte, A CompositeVacuum Barrier for the LHC Short Straight Section,Proc. Cryogenic Engineering Conf. (CEC),Columbus-Ohio, USA, 17 to 21 July 1995.

The short straight sections for the LHC

Abstract

Similar works

Full text

Available Versions

CERN Document Server