Combined sextupole-dipole corrector magnets (MSCB) will be mounted in each half cell of the new Large Hadron Collider (LHC) being built at CERN. The dipole part, used for particle orbit corrections, will be powered individually and is designed for low current, originally 30 A but now 55 A. The sextupole part, used for chromaticity corrections, is connected via cold busbars in families of 12 or 13 magnets and is powered with 550 A. Several versions of this corrector magnet were tested as model magnets in order to develop the final design for the series. In the first design the coils are nested, with the dipole coil wound around the sextupole coil to obtain as short a magnet as possible, accepting the slight cross-talk between the coils due to persistent currents, and increased saturation effects. The design has evolved and an alternative design, in which the dipole and sextupole coils are separated, is now favored. Tests at 4.5 K and at 1.9 K were conducted to determine the training behavior, the field quality, and the cross-talk between the windings. This paper discusses the results for the different configurations

Ang, Z

Arshad, S A

Bajko, M

Bottura, L

Coxill, D

Giloux, C

Ijspeert, Albert

Karppinen, M

Landgrebe, D

Walckiers, L

CERN Document Server

158 lEBE TRANSACTIONS ON APPIJGD SUPERCONDUCTIVITY, VOI.. 10, NO. 1, MARC11 ZROO Further Development of the Sextupole Dipole Corrector (MSCB) Magnet for the LHC Z. Ang, S. Arshad, M. h jko ,  L. Bottura, C. Giloux, A. Ijspeert, M. Karppinen, I,. Walckiers CERN LHC-Division, Geneva, Switzerland D. Coxill, D, Landgrcbc Tesla Engineering Ltd, Storrington, Uiiitcd Kingdom Absiraci - Oniiihiiicd scxtupolc-dipole corrector magnets (MSCB) will be mounted in each half cell of the new Large I-Iadrnii Cdlidcr (LIIC) heing built at CERN. Thc dipolc part, used for particlc orbit corrcctions, will be powered individually and is designed for low currenl, originally 30 A but now 55 A. The scxtupolc part, uscd for chromaticity corrections, is conncctcd via cold busbars in families of 12 or '13 magnets and is powered with 550 A. Several versions of this corrector magnet were tested as niodel mngnets iii order to devclop tiit final design for the seriw. In the first dcsign the coils arc nested, with the dipole coil wound sroiind the scxtiipulc coil to  rrlltnin as short a magnct as possible, ncccytiiig thc slight cross-talk between the coils due to pcrsistenl currcnts, and increased saturation effects. The dcsign has cvolved snd an altcrnativc design, in which the dipolc and scxtupole coils arc scparafed, is now favored. Tests at 4.5 I< and at 1.9 K were conducted to determine the trtiiiiing behavior, thc ficld quality, and the cross-talk between the windings. This papcr discusses the resuIls for the different ConKgnrations. I. INTROWJCTION The LIIC Shorl Straight Scctions (SSS) [ l ]  will be eqiiippcd with 1260 niin long combined dipole and sextupole cnrrcctor magnet assemblies, MSCB [23. The dipole and sextupole magnets of the two LHC rings are mounted in pairs in n common support structure and housed in  the same cold mass and cryostat as ofthc Main Quadrupoles (MQ) [3]. The sextupole is used to correct the natural chromaticity produccd by the focussing elements. Each dipolc pair includes a horizontal orbit correclion for one aperture and a vertical orbit correction for the other. Two complete MSCB asscmblics with the scxtupole coils riestcd inside the dipole coils have been designed by CERN and built in industry, and will be installed in the 3rd and 4th LHC prototype Short Straight Section ( S S S ) .  The magnet asscmblics wcrc first mounted in a dedicated single aperture ynkc and trained at 4.3 K by the magnet manufacturer before being integrated into a common yoke structure. To study an ahernathe of separate magnets, one 0.69 m long sextupole und onc 0.75 in long dipole were built in industry. Both ncstcd MSCB models and the sepnrate dipole-sextupole units wcrc tested at CRKN including magnet training and magnctic ineasiirements at 4.3K and 1.9K. The main design features and thc results of the cold tests amdiscussed below Manuscript rcccivcd 26 Scptmbcr, 1999. 11. MAGNETIC I ~ E S I C N  The main paramctecs of tlie two nested versions o T  thc MSCB magnets are presented in Table I togcthcr with those of the separated dipole and sextupole modcls. Thc dipule of the first MSCB was dcsigned to produce a 1.5 T field with the nominal current of' 30 A and the sexlupdc to crcatc a gradient of 1500 Wm2. The coils of Ihc sccoiid ncstcd MSCl3 model were re-optimized to reduce thc quench voltages in the dipole and to opcratc thc scxtupolc with R 66 '%I margin to quench at  1.5, K .  The number of radiitl winding layers of the sextupoIc coils was reduced from 8 to 4 and thc nominal  current was increased from 230 A to 394 A. The dipolc coils were designed tn produce a 16 % highcr field of 1.8 T at the nominal current of 50 A. The separate version of the sextupole had the same coil cross-section as tlic scxtupole of the first nested MSCH. The nominal current was increased to 560 A to produce the required field integral with tlie reduced length. The seperatc dipole was madc strongcr to provide a 3 'I' field at a current of55 A. TAULI! I MAIN PARAMETERS OFMSCB DIPOLE SsxwimE C ~ i t i z t i ~ i n ~  b1oi)iii.s Nestcd Design Scparntc Dcsigrk (3Id sss 14''sss) Nomirial ficld 1.511.8 0.4Y0.43 3.0 1.23 'I' (I= 17") Magnetic feogth 1.03 1.1 0.547 0.525 In Penk fieldincoil 2.7/3.0 3.0/3.3 3.4 4.0 T GEOMETRIC Coil length 1,15 0.655 0.585 in 56156 56.4 5G fnrn Coil ID 80170 Coil OD 96/87 76/66 79.5 66 lnln Yoke ID 1 30/120 85.5 miit Yoke OD 452/452 I74 inin ELBC'l'RICI Tumdcoil 2240i1530 l lU52 1775 112 Stortdenergy 7.W8.2 1.9/1.11 7.4 6.6 k l  Self inductance 21/65 0.072/0.035 4.89 0.042 I3 CONDUCTOR Cross section 0.11/0.14 0.91/0.91 0.14 0.91 mi12 section(mete1) CdSc rntio 4/42 1.711.7 4.2 I .7 MarEin to quench , 59/49 Ovcrnll length 1.26 0.745 . 0.643 Nominal currcnt 30150 230/394 55 560 A cross o.oa/o.ii 0.69/0.69 0.11 o ,w  ll,ml Filament diini. 7/27 717 21 7 pln 77t6G 39 40 5 ---_l_ .-=. _I_l_: .i.<- .1... ^,1* liig. I .  Cruuus-section of ihc scparate dipoie model. Fig, 2. MSCU asscinhly for the 3’SSS 111. &‘kCftANICAL DESIGN AND P A  UHICATION compression in cold conditions. The clcariuicc between these Thc scxlupole coils are wound around a copper central post using a single enamel iosulated, rectangular ‘cross- section superconducting wire. The winding is subdivided at thc ends into seven blocks to house the radial and axial transitions, so-called “joggles”, between the turns. For the first model the 4-block dipole coils are wound with 21 round superconducting wires, prc-assembled as a flat cable. The flat cablc for the second MSCB model was made of 18 wires with a metal section diameter of 0.375 mm instead of the 0.3 I mm uscd for the 30 A design. The coils of the separated version are wound using a cable that is composcd of 25 wires. All dipole and sextupole coils are vacuum imprcgnated, The six sextupolc coils are mounted on an assembly keys and the laminations at room temperature is clioseti such that the inward movement of each lamination phir is blockcd at a pre-defined temperature. The yokc structure OF the MSCB for the SSS3 illustratcd it1 Fig. 2 was made o f  L mnm silicon steel Iaminations glucd together in a precise stacking fixture and secured with four tie-rods. Three sets of keys were located in each apcvlure anrl after inserting thc magnet assemblies with prc-machined keyways on their shrinking cylinders the keys were lockcd in with screws. The yoke structurc of thc sccond piir for thc SSS4 is made in the same way as the Main Quadrupole, i.c. the laminations are assembled with elastic pins aiid aligned with the cxtcmal keys that locate the MSCn asscinhly with respect to the Inwtia Tubc [ 11 of the SSS. mandrel, aligned with dowel pins and then wrapped with dry fiberglass cloth prior to impregnation and curing. The outer IV. Tns’r RESULTS A. TJ’Uhi!tg diameter is then turned to the required dimension. In the nestcd version the dipole coils arc then mounted around thc sextupole coils and wrapped with fibreglass before impregnating the whole assembly in vacuum. The separate dipole is assembled like the sextupole. TIic wires of the flat cable in each dipole coil are conncctcd in series by soldering the twisted ends and these cunncctions are then soldered onto a printcd circuit board for mechanical fastening. The series connections of the sextupole coils are madc by soldering in tight-fitting grooves in copper backing pieces. The pre-stress in the nested coils is given by fitting an aluminum shrinking cylindcr, subdivided into 100 mm long segments, around the coiI asscmbIy with a radial interference of 0.10 mm. In the case of the separate dipole and sextupote models the prc-compression is applied to the coils by shrink fitting an aluminum cylinder over the eccentric steel faminations [41 that makes up the yoke, as shown in Fig. 1. In this case each lamination is designed to support the coil asscmbly in one azimuthal direction only and the laminations were assembled in pairs such that each pair compresses the coil assembly from opposite sides. By sequentially stacking these pairs such that the subsequent pair is  turned by 90’ with respect to thc previous one the coil assembly is effectively supported. Four kcys were introduced to limit the coil The training results for thc dipolc and scxhipole in  onc aperture or the 2nd nested model, and Tor tlic separated sextupole and dipole models are shown in Fig. 3 anrl 4 respectively. In the former case the tests included indivitlual and combined powering of the nested coils. The full working space is accessible in both models after training. l’hc ncs&l design showed only slight improvement when conlctl IO 1.9K. No retraining was observed after thermal cycling. In the separated coil version the slow initinl training was caused by too IOW a pre-stress. After re-fitting (he shrinking cylinder with a higher interfcrcnce only LWO quenchcs occurred below the operating current and both the sextupulc and the dipole trained up to their short samplc limits. ‘[’he high quench voltages, up to 760 V observed for the 1st nested model, were reduced to 430 V far the 2nd one. The hot-spot temperature was betow 140 K for all the magnets. An example is given in Fig. 5, showing individual volFge tap measurements along one pole of the dipole cc.)il. The maximum voltage corresponds to thc pcitk of the suni of the individual measurcments. The Fig. 5 dsti shows propagation of the c~ucnch in the coil Over a p c r i d  of -40ms, which is consistent with transverse thermal conduction through the coil. 160 i o0  I -150 -100 -50 0 50 100 150 Dlpole current [A] -- I I Fig, 3. Individual and coinbincd tmining qucnches of the scxriipole and dipolc windings in nnc of the npcrtures of the sccond nesretl MSCB design I Model wlth separated colls :- eo -: -- 0 1 OD0 900 a m  - 700 600 500 m 100 5 360 H 8 200 c U I-zoo 0 Time from stan of quench [SI Pig. S. Voltagcs across individual layers anti currcni during a qucnch in n dipole ol' Ihc first nested dcsign. The inlny shows propngntion o f  the qiicnch across Ihc laycw Second model wlth neated colls -63 -40 -20 0 P 40 60 Dipole current Third model with separated colls 1 ---- - r -7- 0.05 3 2 1 E o  i I -2 -3 -4 0.04 0.03 -0.02 m' -0.03 -0.04 4.05 -60 -40 -20 0 20 40 60 Dipole current [A] Fig. 6. Mcosiired loatlliiics and hystcresir i n  the second nesretl coil rod thc separated coil modclr;. B.Mragrietic Mcusurements The dipole loadlines and hysteresis loops for the 2nd ncsted model and the modcl with separated coils are shown in Fig. 6. The dcviation is calculated as the drflcrcncc betwccn the loadlinc ancl a linear fit to the loadlinc, Tho shortcr lcngth of thc coil in  the niodcl with separated coils implies a higher nominal field (3 T comparcd with 1.8 T in the 2nd nested modcl), which is cvidcnt in the loadlinc. A consequence of this is the much higher degree OC saturation in this magnct . Similar fealures are seen in thc sextupole windings. The levels of hysteresis at m o  current for thc dipoles and scxtupoles of the three modcls are compared in Fig. 7. A significantly lowcr lcvel is found Tor both the dipolc and in particular the sextuple in the separated coil modcl, for most harinonics in the rangc 1 to 9. Pig. 8 shows tho harmonic conicnt of the dipolc and sextupolc in the modcl with separatcd coils. Values are givcn at bcam injection (0.2 Tin for thc dipolc and 0.012 Tm for the sextupole) and at bcam collision (1.65 Tm Tor h e  dipole and 0.48 Tm for the scxtupole). Absolute lcvcls of both normal and skcw components arc shown. 161 1 .E+OO ?.E-02 -8 c- I! LE-06 @I Y l.E-04 8 3 1.E-08 3 l .E-10 B I  A I  83 A 3  I35 A 5  87 A 7  BO A9 . .  I5O’ 1 Sextupolss Harmonic no. I Sextuple In verslon whh separated coils 61 A1 83 A 3  65 A5 67 A7 B9 A9 Harmonic no. Fig. 7. Compnrison of the tiinximum hysteresis sccn in thc dipole nnd sextupolc coils oflhc three MSCB models at zero current. Bn and An are normnl and skew components rcsptively intcgmled ovcr length, An important requiremcnt for (he operation of the accelerator is that the ficld patterns generated by energising any combination of coils should correspond closely to the linear superposition or their individual loadlines. It might, be expccted that in a iicsted coil system interaction between the individual coils could complicatc the compound ficld pattern giving rise to increascd non-linearity. In prncticc this effect is found to bc small. In the 2nd nested model the compositc ficld deviatcs from the linear superposition of thc loadlines by a maximum of -1 mT for (he dipolc componcnt and -2 mT for thc scxtupole componcnt. All other harmonics deviate by less than 0.5 mT. In the model with separated coils this effect was below 1 mT for both the dipole and scxtupole cumponcnts and below 0.5 - mT for othcr components. Thercfore, from this point of view, the nested models do not appcar to bc very different from the arrangement with sepratcd coils. The nested models testcd were built with twin apertnrcs, and in  the 2nd nestcd version the cross-talk betwccn apertures is found to be a1 a level of 0.5 mT for the dipolc component and hclow 0.1 mT for other compoticnts. V. CONCLUSIONS The expcricncc with scvcral nestcd magnct models has shown wmc magnetic and medinnical coupling between the 1602 4 Harmonic no. o At Injectton o Allowed at iniectbn Q Allowed at collision 1. ’ .- - A d  Rg. 8 .  Mcasured harmonic content of thc dipole and sextupole for thc model with scparnted coils. For each hannonic both the nonnal and skew components nrc fihown and coinpared with thc cstimatcd talernnces [SI. different coils, Short scparated models with incrcased field were succcssfully built and proven to be a vdid alternative to thc nested dcsign, This version is considcrably simplcr to fabricate and thc modular arrangement provides inorc flexibility for asscmbly of thc final units in the machine. On this basis it is the prcfcrred design lor the LHC. RE FER EN c E s [l] J-M. Kifflet, M. Pcyrot, P, Rohmig, T. Tortschnnoff , P. Verlrine, “Status of the Cold Mass of the Short Stixight Section for the LHC“, CERN LfIC Projcct Report 182, May 1998. 121 A. ljspwrt, R. Perin, L. Walckiers, E. Daynham, P. Clee, R. Coombs, M. Bcgg, D. hndgrebc, I‘ Test Results of the combined scxtupole- dipole corrector magnct for LHC“, Applied Superconductivity Conferencc, Cldgago. August 1992 [3] N. Siegel. T. Tortschanoff, J-M Rifflet, P. GiovannonLF. Le Coz. C. Lyizlud, J. Perot, P. Vedrine, “Status of the fabrication and test of  thc prototype LHC lnttice quadrupole mngnets”, 13th lntemationnl Confcrcnce on Magnct Technology, Victoria, BC, Cnnnda, Sep 1993. A. Ijspeert, J .  Salinhen, ”Superconducting Coil Compression by Scissor htninations”, EPAC, Sitgcs, Spsin, lune 1996. A. Vcrdier, “Tolcmncc on the MuItipolc Components in the Closcd Orbit Correctors”, LHC Project Notc S1. CERN, Geneva, Switzerland, August 1996. [4] I S ]  

Further Development of the Sextupole Dipole Corrector (MSCB) Magnet for the LHC

Further Development of the Sextupole Dipole Corrector (MSCB) Magnet for the LHC

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