About one hundred individually powered low current superconducting quadrupoles will be installed in the LHC insertions. One of the design requirements was to keep the excitation current of the magnet below 6 kA in view of minimizing the costs of the powering circuits. The design of the quadrupole is based on a 8.2 mm NbTi cable, and is designed for a nominal gradient of 200 T/m at 1.9 K. In this paper we present the design of the quadrupole and discuss the construction details of the 1 m single aperture model which has been recently completed

Kirby, G A

Krischel, D

Lucas, J

Ostojic, R

Rodríguez-Mateos, F

Schillo, M

CERN Document Server

150 TREE TRANSACTIONS ON A P P L I B ~  SUPERCONUUCTIVITY, VOL. IO, NO. I ,  MAltCH 2000 Design and Construction of a 1 m Model of the Low Current Superconducting Quadrupole for the LHC Insertions G .  A, Kirby, J .  Liicns, 12. Ostojic, F. Rodrigilea-Mateos CERN , Ge ncva , Srvitzc r 1 and D. Krischcl, M. Schillo RCCEL Instruments, Borgisch- Gladhch  ~ Germany Abstruct-About one hundred individually pow- ered low current supcrconducting quadrupoles will be installed in thc LHC insertions. One of the design requircmcnts was Go keep the excita- tion current of tho magnet below 6 kA in view of minimizing the costs of the powering circuits. The design of tho quadrupole is based on a 8.2 mm NbTi cable, arid i s  designed for a nominal gradi- ent of 200 T/m at 1.9 I(. In this paper wc present  the design of the quadrupoIc and discuss the con- struction details of tkic 1 m single aperture model which has been recently completed. I. INTRUDUCTION In contrast with tho LHC arc quadrupoles which arc powwed in series, t h o  irisortiori quadrupoles are iiidivid- ua.lly powrcd magncts. In view of their specific loca- tioil in tlic twincl, arid in order to reduce the costs of the potvcririg iahastructme, one of the design rcquirc- rneiits is t o  keep the excitaiion currcnt bclow 0 kA. A sinzilar coiistraiiit was assumed in bhc cas[! of the 70 mm qierture quadrupolo dovelopod for the LIIC low-p inser- tions [ I ] ,  The optimal configuration for this inagnet was a coil wound using 8.2 mm NbTi cables. To datc, tbrec 1 111 long 70 r m n  aperture quadrupoles have been built and testcd [a] ,  givirig part’icularly important results for developmcnk of othcr low currcnt quadrupoles using the same cables. A design study of a SG inin npertrire quadrupolc uviiig n 8.2 iiim cable has shown that such a quadrupole could operaw with 3 gradicrit cif 200 T/m at  1.9 K and 160 T/m at 4.5 IC: iit 5200 A mid 4200 A ,  respectively [3]. It bc- carric thcrefore coiiceivfible to introduce tlicsc magnets as pi‘rt of the  IJIC insertions, in particular in the  dispersion slippressors and matching wctions. With the inrliviclual control of cadi niagtgricl nnd of the two riiigs separately, the flexibility and pcrfoorrriaricc of the collider could bo siibst.antially improved. This proposal is  the basis of the current LRC optics version 6. ‘I’hree low currcrit quadruples, with identical cross- section but different: lcrigths, arc foreseen in the LHC iaacrtions: 2.4 m (MQMC), 3.4 ni (MQM) and 4.8 m Subrnittctl 011 tho 21i Hcptcmher IDOD (UQML) magncts. Besides being used as single units, cold masses housing two MQM units, and 5 MQM+M&MC units are also envisagcd. 111 the R.P in- scrtion, thc MQM and MQML collared coils nrc nsed in single aperture yokes to accommodate the 420 mni bcurn separation. The total numbcr of MQM magnets to kic installed is close to onc hundrcd. In this rcport we present the design of thc 56 mm aper- ture low current quadrupnle for the LHC inscrtioris. 1% also dcscribe the construction proccdures, initial tests per- formed on the prototype coil and on the short mockup, and the final assoinbly of thr: I. i n  single aperture rnoclcl of thc quadrupole which has been rcccritly coniplctcd, 11. QUADRUIWLE I SICN 1 li1.9 I Fig. 1. ‘fianaverse crofis scction of tho MQM q~idr i ipo ln  Thc MQM quadriipole coiisists of two idcntical, indc- pendently gowercd apcrturcs, which are assembled to- gether as shown in Fig. 1. Thc coils are niade using 8.2 inm wide cable wound i l l  lwo laycrs and cured in a single cycle. They are assembled using 21 inin widc col- Inrs, which cover 180 dcgrccs, and are inouiited so that each successive collar is turnod by 90 degrees. ‘J.’ho col- lars give the necessary cornprcssivc strcss in the coils and witlistarid tho magnetic forccs. Thcy arc locked using four fX1 length keys which we wclded oiito the coil erd p l a t q  giving longitudinal stiffness to  the zsembly. The pole leads we joined in the conneckion box inounted on the lend end plate, so thal; cadi nperturc can bc hnnrilcd 88 an iridependctit uiiit. Two collarcd apertures arc asscmbled together in a two- ill-one magiict using single piecc iron laminations, very siinilnr in design to the LEK arc quadrupole. This is an important feature of the dcsigri, fxs the MQM quudrupolcs are part: of the dispcrsion suppressors, wliere t,hc cooling and bushar systcrns hnvc aIready been defined OH thc ba- sis of the LHC arc quadrupole. Besides solving the intc- gr;ltion issiics, this approach decouples t,hc magnetic xnd inechanical dcsign of the niagiiet. A .  Coil The MQM roil is designed 011 the basis of the 8.2 mrn cable of the 70 inm npcrtiirc! quarhupole [l]. The cable i s  irincle nf 34 strancls (fl.48 inin dia.), and its niibthickness arid keystone angle arc 0.845 min and 1.05 degrees. The iilanicnt dinrrieter is 10 pm, and thc cablc critical currelit dcnsity is 2960 A/mma at 4.2 K and 5 T. ‘ I <  :r Fig. 2. Cross snctioii of kllu quadrupole coil The cable insulation consisk of two polyimicle layers. The  first iiisulstion layer is a. 25 pm dry polyimide tape with n 80 % overlap. Tkc oiitcr layer is a 50 pm tape with an iincurcd adhesive layer nn the outer surface, wrapped with a 2 mm gap. The honrling and sizing is achicved hy curing the coil at 185°C. Similarly to the 70 mrri aperture qiindrupolc, we pro- pow a coil design based 011 curirig h t l i  layera in a sin- glc curing cyclt!. This technique requirm thnt  the layfirs we aligned at tho pole. In addition, winding trials have sliown tlmill; for correct positioning of thc pole turn, tlic pole anglc should he greater than 26 degrees. Biurthcr- innrc, the coil design should hc such that llic genmctricnl b~ rnultipolc pa.rtially compcrisstcs the h~ Lcrm duc to persistent currents. Wii;h thc cable parametcru and,thcse xcquiremeiit;s in inirid, t.hc cross-section of the coil wm optimised with IZoric [?I for highest traiisfcr function and opcratinnal margin. The rosulting coil section is shown in 151 Pig. 2, and the operating partrameters uf the magnet listcd in Table I. 1.9 I< 4.5 K Nominal currant 8165 4 4132 A Paak field in coil 6.31 T 5.05 ’L‘ Curreril. donsihy in SC 2349 A/nim2 1851 h/mina Currerib dansity i n  Cn 1350 h/mnia 1089 A/Innia Qocnch field 7.m 1’ 6.13 ‘1.’ Pcrcenhgc of the short silinplc 60.9 % 84.13 % Tcm p emtu re m w g  in Stored anergy 80.63 kJ/in 38.8 kJ/ni IndocLu11ec 4.55 mH/m 4.65 tnH/ni Fy per oclnnt -427 kN/m -273 kN/in E, pcr o c h n t  306 kN/m 196 k N / m  Noinilia1 grd iont  200 T / m  lii0 T f In Porcenhg@ Gf the load line 8U.3 % 82.4 % 1.7 I< 1..1 K The cxpected multipole errnrn due to coil gcometry arid fihmctit magnetisation for the LHC injection gradi- ent (12.5 T/m)  and MQM nominal gradients are given ir i  Tablc 11. The transfer function of the qudrupolc  i s  38.76 {T/in,/kh) at 160 T/m ;uid 38.74 (T/rri/kA) at 200 T,”. \ bn Georrictric Macnetisation Ceo- (l2.5’l1/tn) (le0 Tfni) (200 T,”) 1 112 -10,fi 1 I i:l 1.29 -5.G’J 1.29 1.33 1 -0.17 0.29 -0.17 -0.17 -0.12 -0.031 -0.12 “0.12 13. Design of the  Coil Bnds The coil ends, wore &signed using thc isoperirrietrir: method. The goal wa~3 to keep tlic peak fidd in thc ends helow thnt. in  body of thr! rriagnel while using thc same yolw laminations evcrywhcrc. Also, w e  tricd to kccp trhc ends as ctimpact as possible, to niaxiniisc heir  maglietic Icrigth, mid to d u c e  thc  integrated end harmonics. ‘1Yie resulting peak field is very c lo~e to the 2D vnlue (6.3 T),  and in case non-magncLic lamiriations xe uscd over the cnds, it is lo~ver by 0.4 T. The lead ctid is rriade nf three sections: the layer jump, the  cnd spacm section nnd the corinection box, Fig. 3 .  The layer junip is dcsigned such to move the c a l h  away from tlic inncr layer, align it to thc outer laycr, and fi- nally hring it in the position of the first turn of tho outer layer. The cable path mid the corriponerits of the laycr jump guaranixe mmhanicd stability of tho cablr! and i t s  electrical inixgrity. is.? C. Quench. Protection, Although the inductancc and stored cnorgy in . the MQM quadrupole arc small, the high current density in copper, 1300 A/mm2, is a major coiicerii for magnet; pro- tection, Assurning a strip hentcr on the outer coil laycr ilnd a. heater clclay of 50 ms, the adiabatic conditions prc- dict, ii pcak temperatiire of 330 K for the noniinal current of 5200 A. As at least 20 ms are required for filtering and detection, tho heater reaction time should be lcss than 30 my. Test rasults of the 70 mm quadrupole [2], which uses tho same cable mid insulation system, Iiave shorun tlint Lhc heater delays for these conditions are typically :I540 ins. The corresponding qiiencli load nurnhcr is 3 MI- ITS, and the expected maxilnum voltage to ground for the longest, magnet chain is bclow 150 V. Fl~ttx:~. protection can hc obtained if both hycw are heatctl sirriultaneously. Iri ordor to do so, a qiicnch licstor has to  bo mounted 011 tho oi.itcr surface of the innw layer during winding, aizd has to suirvivc coil curing without loss of electrical inlcgrity. For tbc rnodcl magnet, wc have dccided to includo both quench hoatcrs, YO AS t.n test Lhc production aspccki of tho inner hcatcr, and to cllcck their relative cflicioncy. Further iinprovcnient , pnrticulnrly in vicw nf relaxing detection tirnes, could be ohtainccl iF the cablc! wcrc modified from 34 to 36 strands. This possibility has bacri studied thoroughly and adopted for the final magnet design. 111. CONSI'RCCTION OF TIIE 1 M MODEL A. Coil winding  Fivc 1 m qiiadrupolo coils were wound iri ACCEL In- strumclits, including a prntcitypo coil which was ueod to test the new winding features, in particular winding over the iunrr quench heater and curing both layers simultane oiisly with the heater in place. Separate teats have shown t h a t  tlic inner heaters, crmsiuting of two 75 pm polyimide sliccts with a 25 pm thick stainless steel strip glucd in between, cnii withstand temperatures of over 185°C with- out, apparent damage. Novortholcsu, the mnin concerii was the integriky of khc insulation under t.he cornbird CITCCC~; of high pressure niid fcmpcraknre during curing. The widkh of the inner heater used in the prototype coil WRS idcntkal to the first layer at nomirial curnpres- sion, and it did not cover it fiilly during winding. AS a result,, thc mi&plarie turns of thc t>wo layers were not sep- arated by t l i ~  heater, and when coniprcsscd in the curing mold, pushcd tho hcater inwards so that it wrinkled in the inter-turn spnccs arid dcvcloped shorts. To rcnicdy this deficiency, a 25 pm polyirliidc h p e  W ~ . Y  added on tach side of tho hcatcr 50 that thc tJapc!s protruded over th(! inner layer by nt)ouk 5 inin. ?,'his prnvcd vcry effective as the electrical integrity of the inner hcator i n  Ihe four production coils wns fully satisfactory. '.L'Iic nvorsixt! of the insulation bet.wcan t h u  layere was removt?d aft.cr curing. The protntypc coil mds were imprcgrintcd in resin a.nrl several sccticjiis were made to iiispcct thc quality of fit of the cablc: t,o thc end spacers. A dctajl of the return end oF thc coil ca.n be scm in Fig. 4. W e  fmmd that. the fit wa.3 very good in $11 sect,iors, so that no further moclificatiolls of tlw end spa.cers were ner:r!ssary for the prodiiction coils. Fig. 4. Detail 01 the return cnd of the inner c d .  'l'ho inner he fit^ connections <:tit1 bc won 011 the left. The coils wcrc measured after curing ia order to ohtain their size and rriodulus of elasticity. Tlic measureinents OF the straight section of the coil wcrc made separately for the two arcs in 6t;cp~ of 100 mm. Thr! average size of the coil was 0.33 inm larger than riorriiiid, with a rms of k0.13 mm. The avcragc incremental modulus at 50 MPii was 10 GPa. Thesc values were med to cletermine tho shim size necessary for achieving the target average stress in the coils of GO MPa after assembly. D. Collaring In ordcr to  verify the collar design, the toolirig a.nd pro- ccdurcs, a 200 mxn moclmp of the magrick &might section wns made, Fig 5. For tlic coil arches, wc used sections of thc prototype coil. Very encoiiragiiig results were oh- tained, ns tho collaring procccdcd smoothly, without n~iy  particular problem during assemhly, compression op key- ing. The azimuthal strcvs in thc coils was recorded wiLh capacitivc gaiigca [ 5 ] .  The stross after kcying was 70 MPa, and 50 MPa nftcr cooldown to 77 K ,  iii very good agrcc- nicnt with the design valucs. At subseqiicnt warmup, the stress of BO MPs was recorded, w r y  closc! to the value before cooling. After disassoinbly, the collars and kcys showed no sign of deformatioii. Fig. 6. Short inockrip of the ~ollared coil. Bo t r--y --.... 1 2 3 4 6 B ccllarlng atop F i g  6. Ar,iinuthal Strcss diiriufi collnring: (2) Main press at 40 MPa; (3)  Keya inserted half way, press released; (4) Keys fully insertrd; (5 )  Alter 1 hour; (6) After 1 day. The assambly of the full aperture prococded with fit- ting tlic coils with instrumentation wires (voltage taps and spot heaters), and installing a set, of auter quench protcction heaters. Also, eight capacitance gauges wcrc piacad in tho grooves of the pole fncc shims on tho in- ner arid outer coil layera. A non-collapsible mandrel was uscrl, and after fitting the ground insulation, the coils were lightly compressed with polo sections, which were taken out as the collar stack was built,. In this way, thc two collar arnis were pnrtially locked and held in place by friction. Subscqucntly, thc assembly was compresscd over the full length by pushing bars, and tho 1 m long collaring keys iiiscrted half way. At this point, in ordcr to extract thc as- scrribly mandrel, the collaring prcss was released, a d  the pressiirc droppcd by ahoiii; 30 MPa, Fig. 6. The collaring keys were finally pushcd in the noniinal posifioii by coni- prossing in 100 inin steps in two passes, giving the firial stress in thc coil of 70 MPa. AfLcr one day, tllc pressurc decreased due to creep to  F6 MPn. The assenikdp of thr? collared coil was completed with quadranl jointing, a~id thc magnet, Fig. 7, rrisde ready ~ G Y  testing. Fig. 7. Collared qoadrnpolc ~semblrxl in it singlt! npcrturrr yoke., IV. CONCLUSIONS A 56 inin aperturc low crirrcnt quadrupole for the LHC: insertions has been dcsigned on the hasis of thc cxistiiig 8.2 mm cable for a nominal gradient of 200 T,” ai; 1.9 K. A I m model of the qurtrlrupolc has becri recently com- pleted. During coristriiction, the mechanical design and assembly procedures haw been vcrified, iii particular thc possibility of wioding and curing two coil layers n t  a time with the quench protection heater in bettvcen. In spite of previous concerns, the heaters have kept a high lcvel of dielectric insulation in dl production coils. The magnet;, suitably instrumentcd with spot heatcrv and prcssurc sen- sors, will give valuahlo information for the final design of the qriadrupolc. REFERENCES R. Ostojic, T .M.  Taylor, G.A.  Kirby, lLDcsign and Construction of a OricMetre Model of the 70 mrii Aperture Q u a d r i q ~ ~ l c  forthe LIlC [.ow-p Infiwtions”, M l W ,  IIClcIS ‘ l h n s .  Mngii, Vn1.30, N0.4, July 1994, IIP. 1750-1753 M. Camrri e t  al., “‘l’ests of the 70 inn1 Quadriipdc for til<: LIIC Low-G’ Insertions”, ASC’98, IEIW ‘hnns. Appl, Supermnduc- tivity, Vol. 9, No. 2, pp. 455-458. J. Lucm, R. Ostojic, “Cormptid Dosign of tho Low-Current Quadriipolc for the IJIC Insertions (MQM)”, LRC Project. Note 165 Y.Russenschuck, ”A coinputcr program for the design u f  super- condiictiiig accelerator niagiiets” ~ 1JIC I’rojcct k p n r t  46, 11198. N.Slogc1, 1). Toinwilssirii, I. Vnnenlcov, “Oesign and Use of Capac- itive hutcc Transducers for Superconducting Magnet Models Lor the I,1-IC”,viT-15, Ueijing, LHC ProjecL Report 173. 

Design and construction of a 1 m model of the low current superconducting quadrupole for the LHC insertions

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