Development of high-performance Nb{sub 3}Sn quadrupoles is one of the major goals of the LHC Accelerator Research Program (LARP). As part of this program, long racetrack magnets are being made in order to check that the change in coil length that takes place during reaction is correctly accounted for in the quadrupole design and to check for length effects in implementing the 'shell' method of coil support. To check the racetrack magnet manufacturing plan, a short racetrack magnet is being made. This magnet will be the first to use restack-rod process Nb{sub 3}Sn, making it a 'long sample' test vehicle for this new material. The paper reports the reaction and characterization of the Nb{sub 3}Sn, and construction features and test results from the short racetrack magnet. The paper also reports on the status of the construction of the first long racetrack magnet

Ambrosio, G.

Anerella, M.

Barzi, E.

Bossert, R.

Cheng, D.

Cozzolino, J.

Escallier, J.

Ferracin, P.

Ganetis, G.

Ghosh, A. K.

Gupta, R. C.

Hafalia, A. R.

Hannaford, C. R.

Joshi, P.

Kovach, P.

Lietzke, A. F.

Louie, W.

Marone, A.

McInturff, A. D.

Muratore, J.

Nobrega, F.

Schmalzle, J.

Thomas, R.

Turrioni, D.

Wanderer, P.

UNT Digital Library

LARP Long Nb3Sn Racetrack Coil ProgramP. Wanderer, G. Ambrosio, M. Anerella, E. Barzi, R. Bossert, D. Cheng, J. Cozzolino, J. Escallier, P. Ferracin,G. Ganetis, A. K. Ghosh, R. C. Gupta, A. R. Hafalia, C. R. Hannaford, P. Joshi, P. Kovach, A. F. Lietzke,W. Louie, A. Marone, A. D. McInturff, J. Muratore, F. Nobrega, J. Schmalzle, R. Thomas, and D. TurrioniAbstract—Development of high-performance Nb3Snquadrupoles is one of the major goals of the LHC AcceleratorResearch Program (LARP). As part of this program, longracetrack magnets are being made in order to check that thechange in coil length that takes place during reaction is correctlyaccounted for in the quadrupole design and to check for lengtheffects in implementing the “shell” method of coil support.To check the racetrack magnet manufacturing plan, a shortracetrack magnet is being made. This magnet will be the firstto use restack-rod process Nb3Sn, making it a “long sample”test vehicle for this new material. The paper reports the reactionand characterization of the Nb3Sn, and construction featuresand test results from the short racetrack magnet. The paper alsoreports on the status of the construction of the first long racetrackmagnet.Index Terms—LARP, Nb3Sn, racetrack, superconducting.I. INTRODUCTIONTHIS paper reports work on the development of acceleratormagnets made as part of the LHC Accelerator ResearchProgram (LARP). The goal of LARP is to support the commis-sioning, operation, and eventual upgrade of the LHC at CERN.Brookhaven National Laboratory, Fermi National AcceleratorLaboratory, Lawrence Berkeley National Laboratory, and Stan-ford Linear Accelerator Center are collaborating on LARP ac-tivities. Approximately half of the LARP work is concentratedon the development of high-field magnets for use in a possibleupgrade of the LHC. Work has started in advance of the opera-tion of the LHC because the magnets needed for an upgrade willhave to use a superconductor, such as Nb3Sn, that has a highercritical field than NbTi.Manuscript received August 28, 2006. This work was supported by the USDOE Contract DE-AC02-05CH11231.P. Wanderer, M. Anerella, J. Cozzolino, J. Escallier, G. Ganetis, A.K. Ghosh, R. C. Gupta, P. Joshi, P. Kovach, W. Louie, A. Marone, J.Muratore, J. Schmalzle, and R. Thomas are with the SuperconductingMagnet Division, Brookhaven National Laboratory, Upton, NY 11973 USA(e-mail: wanderer@bnl.gov; mda@bnl.gov; cozz@bnl.gov; escallie@bnl.gov;ganetis1@bnl.gov; ghosh1@bnl.gov; gupta@bnl.gov; joshi@bnl.gov;kovach@bnl.gov; louie@bnl.gov; andym@bnl.gov; muratore@bnl.gov;schmalz1@bnl.gov; thomas1@bnl.gov).G. Ambrosio, E. Barzi, R. Bossert, F. Nobrega, and D. Turrioni are withFermilab, Batavia, IL 60510 USA (e-mail: giorgioa@fnal.gov; barzi@fnal.gov;bossert@fnal.gov; nobrega@fnal.gov; turrioni@fnal.gov).D. Cheng, P. Ferracin, A. R. Hafalia, C. R. Hannaford, A. F. Lietzke, andA. D. McInturff are with Lawrence Berkeley Laboratory, Berkeley, CA 94720USA (e-mail: DWCheng@lbl.gov; PFerracin@lbl.gov; rrhafalia@lbl.gov;RHannaford@lbl.gov; AFLietzke@lbl.gov; ADMcInturff@lbl.gov).Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TASC.2007.899984Fig. 1. Two racetrack coils connected in the common coil configuration.This paper discusses magnets made with short and longracetrack coils supported by a shell-type support structure[1]. The short racetrack magnets, generically denoted SRS,are built to test magnet manufacturing methods before theyare implemented in long magnets. The long racetrack mag-nets, generically denoted LRS, have the goal of checking forlength-dependent effects in coils and in shell-type supportstructures before the construction of the long cos-theta tech-nology quadrupoles (LQ), planned for the LARP program. Thelength of the LRS coils has been chosen to be 4 m so thatthey can be tested in vertical dewars at either BNL or Fermilab.Each magnet consists of two racetrack windings. Coils in SRS(LRS) magnets are 300 mm (3.61 m) long. The magnets arewired in the “common coil” configuration [2] with minimal gapbetween them (Fig. 1). The coils are clamped by an iron yoke,which is held by a thick aluminum shell (Fig. 2). Preload perpen-dicular to the plane of the coils is applied by a system of bladdersand keys. Additional preload is applied during cooldown due tothe differential thermal contractions of the shell and other com-ponents. When powered, the predominant force is in the direc-tion of the preload, with modest forces along the other two axes.II. SRS01 CONSTRUCTION AND TESTA. SuperconductorThe Nb3Sn superconductor used in this magnet was made bythe “restack rod process” (RRP) by Oxford Instruments, Super-conductor Technology [3]. Properties of the strand are given inTable I. These properties are very similar to those of the strandplanned for the LRS magnets, except for the twist pitch, whichis longer than the desired 14 mm. (The strand was made as partof the conductor development program; production strands havethe correct pitch.) Dimensions of the rectangular cable used inWANDERER et al.: LARP LONG RACETRACK COIL PROGRAMFig. 2. Principal components of a magnet with racetrack coils supported by ashell-type structure.TABLE ISTRAND PROPERTIES MEASURED BY OST(1) reaction cycle 210 C (48 h) + 400 C (48 h) + 665 C (48 h)TABLE IIPROPERTIES OF WITNESS SAMPLE OF CABLEthe racetrack coils are given in Table II. The anneal noted in thistable was at 200 C for 4 h. The cable was annealed to reduce thelength change that occurs during reaction.The magnet critical current was determined from tests of ex-tracted strands at BNL and Fermilab is 9.7 kA, with an uncer-tainty of 1% [4]. The uncertainty arises from the strand-to-strand variation in critical current and from uncertainties in themeasurement procedure for these high-current strands, which isstill in development.The stability current, , is an important parameter in magnetperformance, as it would limit the magnet current if it is lowerthan the desired operating current. It is determined by settingthe current in the strand or cable short-sample and ramping thebackground field until the sample quenches [5], [6]. For lowvalues of the background field (0 T–4 T), an unstable conductorwill exhibit flux jump quenches for current levels above . Lowvalues of the reduced resistance ratio (RRR) of the copper inthe strand lower in the conductor. It has been found that RRRgreater than 100 results in strands which have much greaterthan the maximum current in LARP magnets [7], [8]. All strandstested for SRS01 have greater than the strand critical currentin the magnet, 485 A. The cable measurement of yields valuesconsistent with the strand measurements.B. Cold Mass Fabrication and AssemblyThe cable was insulated with a continuous, woven S-glasssleeve. The double-layer, flat racetrack, coil was wound aroundan iron island with the layer-to-layer transition in the pole turn.The island is insulated from the coil by a 0.13 mm-thick coatingof aluminum oxide. The winding tension was 111 N and the coilwas clamped on one side while the opposite side was wound. Alayer contained 21 turns of cable. A double-layer coil required23 m of cable. When winding was complete, two stainless-steelend shoes, one covering the return end and both sides, the othercovering the lead end, were placed around the coil. The facesof the coil were insulated with S-glass and the top and bottomplates of the reaction fixture bolted to the two pieces that cov-ered the sides of the coil. The coils were reacted in a vacuumoven equipped so that a continuous flow of Ar was maintainedduring the heating cycle. The nominal reaction cycle was 72 h at210 , 52 h at 400 and 48 h at 639 . Witness samples wereplaced in the oven during the coil reaction. After reaction, NbTileads were soldered to the coils and the coils were then trans-ferred to other fixtures for vacuum impregnation with CTD101K[9] epoxy. For simplicity, the coils have minimal instrumenta-tion (voltage taps on the leads, a voltage tap on the island turnnear the ramp, and a spot heater with voltage taps on both sidesat the high field point, turn 10).The two coil modules were bolted together in between twoiron pads and then inserted into the support structure. The sup-port structure is composed the yoke (six 50.8 mm-thick steelplates) and a 12.7 mm-thick Al cylindrical shell with 215.1 mminner diameter and 304.8 mm long. Stainless steel bladders wereused to expand the shell, permitting keys to be inserted betweenthe yoke and the coil pack. The bladders were removed, al-lowing the keys to determine the preload, which was estimatedto be 31.5 MPa. Splices between coil modules were then made,external to the magnet. A full description of the magnetic de-sign and support structure is given in a separate paper [10]. ForSRS01, the peak field at the conductor critical current is 12.3 T.C. Test ResultsSRS01 was tested in liquid helium at a nominal temperatureof 4.5 K (Fig. 3). There were two test periods. During the firstperiod, there was a large ripple in the current (e.g., at 6 kA, 25A ripple peak-to-peak at 180 Hz and 50 A ripple peak-to-peakat 60 Hz) due to problems with the firing circuits in the powersupply. The circuits were replaced between the two test periodsand the ripple decreased to negligible values.During the first test period, the quench currents were stronglydependent on ramp rate. Both the current ripple and the larger-than-design pitch length of the strand contributed to eddy cur-rent heating during these tests. After repair of the power supplyand a decrease in ramp rate to 1 A/s, the magnet quickly reached96% of its critical current. The 1 A/s quenches originated nearthe interlayer ramp.III. LRS01 STATUSA. Design and Fabrication FeaturesIt was decided to make LRS01 as much like SRS01 as pos-sible, so that possible effects due to changes in length would notFig. 3. Quench test history for SRS01. The symbols indicate the ramp rates:20 A/s (diamond), 100 A/s (circle), 4 A/s (asterisk), 2 A/s (triangle), and 1 A/s(square). The vertical line indicates a thermal cycle. The horizontal line indicatesthe estimated critical current. The horizontal bar indicates a ramp at 2 A/s to7718 A, the power supply maximum current at the time, without a quench.be masked by other effects. Thus, the island will be made of iron.Because the coil shrinks due to the reaction, the island must beshorter than the length allowed for it during coil winding. Thegap for the iron island in the 3.6 m LRS coils will be set based onexperience in reacting 0.7 m-long TQ coils [11], [12]. The gapwill be implemented by dividing the island into five equal-lengthsegments, with a gap between each pair of segments.Other length-related changes have been made. Because oftheir greater length, the LRS coils are supported by saddles ateach end and full length stainless steel rails on each side. Thesaddle, coil, and island will be clamped together during the re-action cycle in order to assure that the good fit of these com-ponents after reaction. The electrical integrity will be increasedby adding a 0.13 mm-thick layer of glass cloth between the twolayers of the coil and by doubling the thickness of the aluminumoxide coating on the island to 0.25 mm. During the first phaseof the reaction, when the palmitic acid is vaporized, the flow ofargon will be increased significantly.The coil instrumentation and quench protection heaters willbe printed circuits on a Kapton substrate. Each of the four coilsurfaces will be protected by two redundant heaters. Voltagetaps will be placed at the leads, the coil ends, the layer transition,and the high field point (turn 10 on the inner part of the coil).Voltage taps will also bracket the spot heater, which will be inthe high field region of the coil.Practice winding with a copper cable insulated with an over-wrap of S-glass is now underway. The copper coil will be takenthrough all the production steps except coil reaction. This willallow a partial test of the coil-to-island electrical integrity andfull tests of the fit of the instrumentation trace to the coil, thecompleteness of the vacuum impregnation, and the fit and oper-ation of most of the toolingIt was decided that the maximum strain in the reacted coilshould not exceed 0.05%. This is a factor of four lower than thenominal benchmark for significant ( 10%) effects of strain inthis material. An additional safety factor of five has been appliedto the design of the coil handling tooling; that is, the design max-imum strain is 0.01%. The material to be used for the reactionfixture is 347H stainless steel. Two sets of coil handling toolingFig. 4. Devices to manipulate reacted coil in fixture.Fig. 5. Device to manipulate coil installed in support structure.are needed. One set consists of beams and a spreader that handletwo uses: to transport, flip, and upright the coil in the reactionand impregnation fixtures (Fig. 4), and to upright the completedcold mass for vertical testing. The beams attach to the reactionfixture and cold mass at the two quarter points. In both cases, thecalculated maximum deflection of the coil is less than 0.08 mm.The other set (Fig. 5) of tooling lifts up the reacted coil usingholes in the rails. The tooling is designed so that the maximumdeflection of the coil is less than 0.03 mm.B. Fabrication StatusAs noted above, practice winding with the copper coil is un-derway. Sufficient cable is available to allow for a prac-tice coil. The pacing element in the schedule is the reaction oven,which is to be delivered in September. The support structure isdue to be sent from LBNL to BNL at the end of October. Testsof LRS01 are scheduled for Feb., 2007.IV. FUTURE PLANS: SRS02, LRS02To achieve the uniform coil size needed for the IR quads,the coils for the LQ quadrupoles will be coated with a ceramicbinder that will be cured under pressure to a fixed size beforethe coils are reacted [12]. The reaction fixture will be slightlylarger than the curing fixture, also in order to achieve uniformWANDERER et al.: LARP LONG RACETRACK COIL PROGRAMcoil size. These features will be tried initially in a short racetrackcoil (SRS02) and then in a long racetrack coil (LRS02) beforeconstruction of the LQ coils begins.V. SUMMARYTest results from SRS01 indicate that the technology formaking short racetrack magnets has been successfully trans-ferred from LBNL to BNL. The results also indicate that theconductor is sufficiently stable for use in the LARP program.The first 3.8 m magnet, LRS01, is well underway.ACKNOWLEDGMENTWe acknowledge the careful work of our technical staffs.REFERENCES[1] R. Hafalia, S. Caspi, L. Chiesa, M. Coccoli, D. Dietderich, S. Gourlay,J. O’Neill, G. Sabbi, and R. Scanlan, “An approach for faster high fieldmagnet technology development,” IEEE Trans. Appl. Supercond., vol.13, no. 2, pp. 1258–1261, Jun. 2003.[2] R. C. Gupta, “A common coil design for high field 2-in-1 acceler-ator magnets,” presented at the Proc. Particle Accel. Conf., Vancouver,Canada, 1997.[3] S. Hong, M. Field, J. Parrell, and Y. Zhang, “Latest improvementsof current carrying capability of Niobium Tin and its magnet appli-cations,” Trans. Appl. Supercond., vol. 16, no. 2, pp. 1146–1151, Jun.2006.[4] E. Barzi, D. Dietderich, P. Ferracin, A. Ghosh, and D. Turrioni, Wit-ness Sample Test Results for SRS01 Fermilab Technical Division NoteTD-06-013, Mar. 2006.[5] A. K. Ghosh and L. D. Cooley, “Magnetization, RRR and stabilityof Nb Sn strands,” presented at the 2006 Appl. Supercond. Conf.,Seattle, WA, Aug. 28–Sep. 1 2006, paper 4MW03, unpublished.[6] D. R. Dietderich, S. E. Bartlett, S. Caspi, P. Ferracin, S. A. Gourlay, H.C. Higley, A. F. Lietzke, and S. Mattafirri, “Correlation between strandstability and magnet performance,” IEEE Trans. Appl. Supercond., vol.15, no. 2, pp. 1524–1528, Jun. 2005.[7] A. D. McInturff, G. L. Sabbi, and R. M. Scanlan.[8] E. Barzi, D. Turrioni, D. Dietderich, and A. Ghosh, “RRP Nb Snstrand studies for LARP,” presented at the Appl. Supercond. Conf.,Seattle, WA, Aug. 28–Sep. 1 2006, paper 1MK07, unpublished.[9] D. R. Dietderich, A. Godeke, and H. C. Higley, LBNLE. Barzi,FNALA. K. Ghosh, BNL, “Cable R&D for the LHC acceleratorresearch program magnets,” presented at, 2006 Appl. Supercond.Conf.. Seattle, WA, Aug. 28–Sep. 1 2006, paper 3LB07.[10] P. Fabian, N. Munshi, and R. Denis, “Highly radiation-resistantvacuum impregnation resin systems for fusion magnet insulation,” inProc. Int. Cryogenic Materials Conf. ICMC, vol. 48, pp. 295–302.[11] P. Ferracin, S. Caspi, D. W. Cheng, S. A. Gourlay, C. R. Hannaford,A. R. Hafalia, A. F. Lietzke, G. L. Sabbi, G. Ambrosio, A. R. Nobrega,A. V. Zlobin, M. Anerella, J. Schmalzle, and P. Wanderer, “Fabrica-tion and test of a supporting structure for 4 m Long Nb Sn coils,”presented at the Appl. Supercond. Conf., Seattle, WA, Aug. 28–Sep. 12006, paper 1LK05, unpublished.[12] S. Caspi, D. Dietderich, P. Ferracin, S. A. Gourlay, R. Hafalia, R. Han-naford, A. F. Lietzke, G. L. Sabbi, A. N. Andreev, E. Barzi, R. Bossert,V. V. Kashikhin, I. Novitski, A. Z. Zlobin, and A. Ghosh, “Fabricationand test of TQS01—A 90 mm Nb Sn quadrupole magnet for LARP,”presented at the Appl. Supercond. Conf., Seattle, WA, Aug. 28–Sep. 12006, paper 4LX03, unpublished.[13] R. C. Bossert, N. Andreev, E. Barzi, S. Feher, V. Kashikhin, I. Novitski,Y. Pischalnikov, C. Sylvester, M. Tartaglia, D. Turrioni, R. Yamada,and A. Zlobin, Fermi National Accelerator LaboratoryS. Caspi, D. Di-etderich, and G. Sabbi, Lawrence Berkeley National Laboratory, “De-velopment of LARP technological quadrupole (TQC) magnets,” pre-sented at, 2006 Appl. Supercond. Conf. Seattle, WA, Aug. 28–Sep. 12006, paper 1LK02.[14] J. A. Rice, P. E. Fabian, and C. S. Hazelton, “Wrappable ceramic in-sulation for superconducting magnets,” Advances in Cryogenic Engi-neering (Materials), vol. 46, 2000.

LARP Long Nb3Sn Racetrack Coil Program

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LARP Long Nb3Sn Racetrack Coil Program

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