The conceptual design study of a high gradient super conducting insertion quadrupole magnet has been carried out in collaboration between KEK and CERN for the Large Hadron Collider (LHC) to be built at CERN. A model magnet design has been optimized to provide a nominal design field gradient of 240 T/m with a bore aperture of 70 mm and an operational field gradient of 225 T/m at 1.9 K under radiation environment with a beam energy deposit of several watts per meter in the superconducting coils. The design and its optimization process are discussed

Higashi, N

Kirby, G A

Nakamoto, T

Ogitsu, T

Ohuchi, N

Ostojic, R

Shintomi, T

Taylor, T M

Terashima, A

Tsuchiya, K

Yamamoto, A

CERN Document Server

Design study of a superconducting insertion quadrupole magnet for the Large Hadron Collider

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLarge Hadron Collider Project LHC Project Report 75DESIGN STUDY OF A SUPERCONDUCTING INSERTION QUADRUPOLE MAGNETFOR THE LARGE HADRON COLLIDERG. Kirby, R. Ostojic, and T. M. TaylorA. Yamamoto*, K. Tsuchiya*, N. Higashi*, T. Nakamoto*, T. Ogitsu*, N. Ohuchi*, T. Shintomi*, and A. Terashima*AbstractThe conceptual design study of a high gradient superconducting insertion quadrupole magnet has beencarried out in collaboration between KEK and CERN for the Large Hadron Collider (LHC) to be built atCERN. A model magnet design has been optimized to provide a nominal design field gradient of 240 T/mwith a bore aperture of 70 mm and an operational field gradient of 225 T/m at 1.9 K under radiationenvironment with a beam energy deposit of several watts per meter in the superconducting coils. The designand its optimization process are discussed.LHC Division*National Laboratory for High Energy Physics (KEK), Tsukuba, Ibaraki, 305, JapanASC Pittsburg ‘96Administrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandGeneva, 12 November 1996Design Study of a Superconducting Insertion Quadrupole Magnetfor The Large Hadron ColliderA. Yamamoto, K. Tsuchiya, N. Higashi, T. Nakamoto T. Ogitsu, N. Ohuchi, T. Shintomi, and A. TerashimaNational Laboratory [or High Energy Physics (KEK), Tsukuba, Ibaraki, 305, JapanG. Kirby*, R. Ostojic, and T. M. TaylorEuropean Laboratory for Particle Physics (CERN), 23 Geneva, CH-1211, SwitzerlandAbstract---The conceptual design study of ahigh gradient superconducting insertionquadrupole magnet has been carried out i ncollaboration between KEK and CERN for theLarge Hadron Collider (LHC) to be built at CERN.A model magnet design has been optimized t oprovide a nominal design field gradient of 2 4 0T/m with a bore aperture of 70 mm and anoperational field gradient of 225 T/m at 1.9 Kunder radiation environment with a beam energydeposit of several watts per meter in thesuperconducting coils. The design and i t soptimization process are discussed.1. INTRODUCTIONA cooperative program to develop low-b  insertionquadrupole magnets has been established between KEK andCERN as part of the Japanese contribution to the LHCaccelerator project being carried out at CERN [1]. KEK willprovide half of 32 quadrupole magnets required for the innertriplets. These quadrupoles are key components to providestrongly focused high energy proton beams and to realize highluminosity beam collisions for physics experiments. Themain design goal for the magnet is to provide a design fieldgradient of 240 T/m in a coil aperture of 70 mm diameter andthe nominal operational field gradient of 225 T/m at 1.9 Kwith a superconductor load line ratio of 85 % to the criticalcurrent. The lost particles and showers from the collidingbeams will deposit a power of several watts per meter into thecoil windings. The design optimization has been made basedon the use of NbTi superconductor cooled with pressurizedsuperfluid helium at 1.9 K. In this paper, we describe theconceptual design of the magnet, including the designoptimization process and the proposed model magnetdevelopment program.II. DEVELOPMENT PLAN OF MODEL MAGNETSIn the R&D program following previous studies [2-3], 3-4short insertion quadrupole model magnets will be developed toestablish necessary technology especially in the straightsection and the coil end design. Based on this experience, twofull length (about 6 m) prototype magnets are to be developedto establish the production technology. The short modelmagnets are being developed in the period of 1995 - 97, andthe full size prototypes from 1998 to 99. Series productionwill start in 2,000.Manuscript received Aug 26, 1996.Visiting Scientist at KEK supported by Japan Soc. for the Promotion of Science.111. MODEL MAGNET DESIGNA. General design approachTo realize the field gradient of 225 T/m reliably in a longterm operation under high beam spray loss level of severalwatts per meter (or a few mW/cm3), the following designguide lines are incorporated.• NbTi superconductor used at 1.9 K in pressurizedsuperfluid helium,• Io/Ic of 92 % at 240 T/m and 85 % at 225 T/m along theload line in design and in operation, respectively,• Safety design in terms of T-peak «300 K after quench,• 4 layer coils with current grading,• High-Mn steel, 4-split collar for preassembly,• Horizontally split yoke, with its two functions:(i) magnetic return iron yoke, and(ii) coil prestressing and dimensional control.Fig. 1. Cross section of the insertion quadrupole model.B. 2D coil design (straight section)The coil design in the straight section has been optimizedaccording to the following guidelines;• Graded 4 layer coil with a reasonably smaller operationalcurrent (< 10,000 A) resulting in a cable width of 11 mm,• Conductor optimization with Cu/S ratio of 1.2/ 1.9 ininner/outer coil from a view point of MIITs resulting in acoil peak temperature of « 300 K after quench,• Iron yoke as close the coil as possible, resulting in an inneryoke radius of 92 mm with a collar minimum thickness ofapproximately 10 mm.A general cross section of the first model magnet is shownin Fig. 1, and the main design parameters are given inTable 1. The enlarged coil cross section is shown in Fig. 2,and superconductor parameters are given in Table II. The cablewidth of 11 mm has been optimized to realize the fieldgradient of 225 T/m at the load line ratio of approximately 85%, as shown in Fig. 3 and Fig. 4. Higher order harmonicshave been minimized to optimize the coil angle in each layerand grading of the current density in the inner and outer layers.The optimization has been carried out, independently, by usinga program which uses analytic expressions for computing thefield harmonics of sector coils, and also by using the programROXIE [4] developed at CERN, and consistent results havebeen obtained. The effect of iron saturation has been evaluatedby using OPERA-2D program (developed by Vector Fields).C. Coil end designThe coil end design has been optimized with consideration tothe following points: peak fields, integrated harmonicsthrough the end, stress in the cable due to bend radius, andaccess for fixing bolts to hold the end spacers on the windingmandrel during coil winding. The ROXIE program has beenused to design the ends. The full 3D coil can be modeled (seeFig. 5). The ends were optimized to minimize the integratedharmonics by moving the eleven end blocks in the 'Z'direction back and forth, shown in Fig. 6.Fig. 3. Cable width dependence on field gradient at a load linecondition of 85%.Fig. 4. Expected conductor performance along load lines.A limit was placed on this movement to allow space for thefixing bolts. There are many solutions to the shape of curvedsection of coil end. We chose shapes that tried to maximizethe bend radius and conform to a constant perimeter. ROXIEgenerates a Computer Numerical Control (CNC) file that wasread by the CNC machining center and a set of end spacers forwinding test have been machined. The test coil winding willsoon be made to check the fitness of the end spacers.D. Mechanical DesignThe mechanical design of the magnet is based on thefollowing considerations;• Preassembly of the coil by using thin High-Mn steel collars,without high prestress in the coil,• Full prestressing of the coil by using the 2-split iron yokeassembly with keys to fix the yoke assemblies together[5],• Rigid and well fixed structure at room temperature./) Cable rigidity test. In order to optimize the coildimensions and mechanical characteristics, preliminary coilmodulus measurement have been made by using a dummyFig. 5. The coil end view (by ROXIE).Fig. 6. Cross section of the coil end (by ROXIE).Fig. 7. Coil end spacers made by using ROXIE output datatransferred to a CNC machine at KEK.cable. Fig. 8 shows the test results with a schematic sketch ofthe experimental apparatus. A test stack of 16 insulated turnswas prepared. This stack was cured at a pressure of 50 MPa anda temperature of 130 deg. C for more than 2 hours to cure theepoxy coating on the outer layer of insulation. Ten preliminarytest cycles were made to make the system stable up to 100MPa, and then the measurements were carried out, as shown inFig. 8. Point 'A' is placed at the pressure at which the cabledimensions were originally measured. This gives a startingpoint for coil size estimations. The average rising modulusbetween points A & B is 8,200 MPa. The initial fallingmodulus is 47.900 MPa between points B & C, and theaverage falling modulus between points C & D is17,000 MPa. We repeated the test for a sample with noinsulation so that we could obtain the compressed insulationthickness at the working pressure of 55 MPa. The nominal 0.1mm thick insulation is compressed to 0.096 mm and the 1.470mm thick cable decreases to 1.466 mm.2) Coil Prestress: Fig. 9 shows an expected trend for the coilprestress, based on the cable rigidity measurements. The coilsare collared at low pressure. We expect a maximum pressure of17 MPa reducing to about 5 MPa when the collaring press isreleased. The collared coil assembly is then placed into the twopart iron yoke and the top and bottom yokes are then forcedtogether under the 15 MN/m press. This increases the coilpressure to about 100 MPa. At this point a total of six keysare placed into the yoke key slots to hold the gap between thetwo yoke halves together. When the Yoking press is releasedwe expect to lose some pressure due to relaxing in thestructure. After yoking, the gap in the iron is closed withsome pressure in the mating faces. This places the collaredcoil assembly in a symmetric cavity in the yoke, at a pressureof about 80 to 90 MPa. As the assembly is cooled the ironyoke contracts less than the coil assembly and the resultingloss in pressure is about 35 MPa. As the magnet is energized,the redistribution of forces in the coil reduces the pole stressby a further 35 MPa. The coil position is not affected leaving10 to 20 MPa in the coil at full field.3) 10 cm long 2D cross section test: Prior to the magnetfabrication, a 10 cm long 2D cross sectional model test willbe carried out. We will use a Capacitance Sheet-Pressure-Transducer (CSPT), recently developed at CERN, tomeasure the change in prestress during: collaring, yoking,placing the keys, and cooling. The CSPT’s are 0.5 mm thicksheets that can measure up to 200 MPa and be placed betweenthe coil and collar shims [6].Fig. 8. The coil rigidity measurement.Fig. 9. Expected trend (changes) of the prestress in the coilsaccording to the magnet assembly, cool down and excitation.IV. SUMMARYA conceptual design of an insertion quadrupole modelmagnet has been made with the following design approach,• 225 T/m operating field gradient.• NbTi conductor at 1.9 K, lo/Ic = 85 % in operation,• 4 layer graded coil with 11 mm wide Rutherford cables,• High Mn-steel 4-split collar, 2 part yoke that provides theprestress for the coils.The first 1 m short model magnet is being developed, andwill be tested at KEK. During the next 3 years, the designshould be advanced to a full length prototype.ACKNOWLEDGMENTSThe authors would like to thank Dr. S. Russenschuck for hishelp in using the ROXIE program. The KEK workshop(mechanical engineering center) and cryogenics center are alsoappreciated for their professional support and cooperation.REFERENCES[1] The Large Hadron Collider Conceptual Design Report,CERN/AC/95-05 (LHC), 1995.[2] R. Ostojic and T.M.Taylor, "Conceptual Design of a70 mm Aperture Quadrupole for the LHC Insertions",IEEE Trans. Appl. Superconductivity, 3 (1993) pp761-764.[3]R. Ostojic T.M. Taylor and G.A. Kirby, "Design andConstruction of a One-Metre Model of the 70 mmAperture Quadrupole for the LHC Low-beta Insertions",IEEE Trans. Magn., 30 (l994) pp 1750-1753.[4] S. Russenschuck, "A computer program for the Design ofsuperconducting accelerator magnets" to be published inProc. of ACES'95, CERN LHC Note 354, (1995).[5] P. Wanderer et al., "Construction and Testing of ArcDipoles and Quadrupoles for the Relativistic Heavy IonCollider (RHIC) at BNL", Proc. of the 1995 Int. Conf.Particle Accelerators, Dallas, 1995.[6] I. Vanenkov, A. Ijspeert, and G. Kirby, CERN, privatecommunication, 1996.

Design Study of a Superconducting Insertion Quadrupole Magnet for the Large Hadron Collider

Design Study of a Superconducting Insertion Quadrupole Magnet for the Large Hadron Collider

Abstract

Similar works

Full text

Available Versions

CERN Document Server

CERN Document Server