Two identical single aperture 1-metre superconducting dipoles have been built in collaboration with HMA Power Systems and tested at CERN. The 87.8 mm aperture magnets feature a single layer coil wound using LHC main dipole outer layer cable, phenolic spacer type collars, and a keyed two part structural iron yoke. The magnets are designed as models of the D1 separation dipole in the LHC experimental insertions, whose nominal field is 4.5 T at 4.5 K. In this report we present the test results of the two magnets at 4.3 K and 1.9 K

Boschmann, H

Bottura, L

Dubbeldam, R L

Kirby, G A

Lucas, J

Ostojic, R

Russenschuck, Stephan

Siemko, A

Taylor, T M

Vanenkov, I

Weterings, W

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLarge Hadron Collider ProjectLHC Project Report 238AbstractTwo identical single aperture 1-metre superconducting dipoles have been built in collaborationwith HMA Power Systems and tested at CERN. The 87.8 mm aperture magnets feature a singlelayer coil wound using LHC main dipole outer layer cable, phenolic spacer type collars, and a keyedtwo part structural iron yoke. The magnets are designed as models of the D1 separation dipole in theLHC experimental insertions, whose nominal field is 4.5 T at 4.5 K. In this report we present thetest results of the two magnets at 4.3 K and 1.9 K.*CERN, LHC Division, ** HMA Power Systems, Ridderkerk, The NetherlandsPresented at EPAC’98, 22-26 June 1998, Stockholm, SwedenAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandGeneva, 25 September 1998Testing of the Large Bore Single Aperture 1-metre Superconducting Dipoles Madewith Phenolic Inserts*L. Bottura, G.A. Kirby, J. Lucas, R. Ostojic, S. Russenschuck, A. Siemko, T.M. Taylor, I. Vanenkov, W. Weterings, **H. Boschman, R.L. Dubbeldam2Testing of the Large Bore Single Aperture 1-metre Superconducting DipolesMade with Phenolic InsertsL. Bottura, G.A. Kirby, J. Lucas, R. Ostojic, S. Russenschuck,A. Siemko, T.M. Taylor, I. Vanenkov, W. WeteringsCERN, Geneva, SwitzerlandH. Boschman, R.L. DubbeldamHMA Power Systems, Ridderkerk, The Netherlands.AbstractTwo identical single aperture 1-metre superconductingdipoles have been built in collaboration with HMA PowerSystems and tested at CERN. The 87.8 mm aperturemagnets feature a single layer coil wound using LHCmain dipole outer layer cable, phenolic spacer typecollars, and a keyed two part structural iron yoke. Themagnets are designed as models of the D1 separationdipole in the LHC experimental insertions, whosenominal field is 4.5 T at 4.5 K. In this report we presentthe test results of the two magnets at 4.3 K and 1.9 K.1  INTRODUCTIONIn the present layout of the LHC low-β insertions [1], apair of superconducting dipoles D1 and D2 brings thebeams onto colliding orbits in the ALICE and LHC-Binteraction points. One of the options that has beenconsidered for the single aperture D1 is a magnet with anaperture of 87.8 mm featuring only the outer layerwinding of the LHC main dipole. This type of single layercoil can provide a field of 4.5 T at 4.5 K. An identical coilcould be used in the twin aperture D2, to give a symmetricseparation-recombination dipole pair.As part of the magnet development program for theLHC insertions, two identical 1-meter long 87.8 mmaperture single layer dipoles have been constructed incollaboration with HMA Power Systems (formerlyHOLEC). The first magnet (H1) was completed in August1997 and cold tested in the beginning of October 1997,while the second one (H2) was assembled and testedbeginning of 1998. In this report we present the results ofH1 and H2 training and magnetic field measurements, andreview the performance of phenolic spacers.2  MAGNET DESIGNThe cross section of the MBXSM magnet is shown inFig.1. It consists of a single layer three-block coil woundusing the outer cable of the LHC main dipole. The cableis insulated with an all polyimide tape. The coils aremounted into injection moulded RX613 phenolic spacerswhich hold them in position and serve as ground plaininsulation, similarly as in RHIC magnets [2]. The magnetis protected with two strip quench heaters, placedbetween the coil and the spacers. Gaps are left betweensuccessive 100 mm long spacers to allow radial ventingof helium.Fig. 1: Cross section of MBXSM type model.The yoke has two functions: it provides coil pre-stressby compressing the phenolic spacers, and serves as themagnetic flux return path. It is assembled from a singlelamination. Two such laminations are placed together,one being reversed then fixed with stainless steel shearpins. After the top and bottom yoke halves have beenforced together under a press, four keys are inserted tomaintain the stress in the coil. The construction andassembly procedures and the mechanical behaviour of themagnet during assembly and cooldown have beenreported in [3].The phenolic spacers can be fabricated with goodreproducibility and make the assembly of the magnet easyand straightforward. However, due to the elasticproperties of the phenolic material, the coil blocks maynot be sufficiently well defined. Furthermore, the coilposition may change at different stages of magnetoperation, which could lead to geometric field errors that3vary with field. This aspect of phenolic inserts requirescareful study in LHe conditions. Finally, long-term creepeffects need to be checked.3 TRAINING HISTORYThe H1 and H2 magnets were extensively tested atCERN. The training history of the magnets is shown inFig. 2. For H1, the first quench occurred at 5.15 T, 87 %of short sample limit, and after 5 training quenches themagnet reached the short sample current at 4.3 K. Forquench number 13, the energy deposited in the magnetwas increased from 20 % to 65 %, which resulted in areduction in quench field for quench 14. After 16quenches the magnet was cooled to 1.9 K, and the firstquench was at 6 T, 84 % of the estimated short sample.After 7 quenches the magnet trained to above 7 T, veryclose to its short sample limit at 1.9 K. The capacitancegauges showed that the coil poles were unloaded at about5.2 T, which did not seem to harm the performance of themagnet. All quenches were determined to occur in thetransition region between the straight section and coilends, in the peak field area. After training at 1.9 K,another 11 quenches were performed at 4.3 K, some withover 90% of the energy deposited in the magnet. In allcases, the magnet  quenched at its short sample limit.3.54.04.55.05.56.06.57.07.5Quench NumberMagnetic Field at Quench [T]H1 Training history @ 4.3K H2 Training history @ 4.3KH1 Training History @ 1.8K H2 Training history @ 1.8KConductor Limit at 1.9K Conductor Limit at 4.45KBnom@4.3K = 4.5 TeslaTest at 4.3 K Test at 4.3 KTest at 1.8 KFigure 2. Training history of H1 (squares) and H2(triangles)  at 4.3 K and 1.8 K.At 4.3 K, H2 started training at the same field as H1,but reached the short sample limit after 14 quenches. At anumber of intermediate quenches the quench fieldfrequently decreased to the level of the first quench. Thefluctuations of the quench field were even morepronounced as  the energy deposited in the magnet wasincreased; with 90% energy deposited, the quench fielddecreased to 6 % below the short sample. However, thequench field never dropped below the initial quench fieldof 5.15 T.The first quench at 1.8 K was observed at 6 T, slightlyabove that of H1. However, further quenching waserratic, with fluctuations of close to 4 % and with a slowincrease of the moving average. The majority of quenches(18 out of 21) occurred in one of the poles, either in thepole turn, or in the transition region between the ends andthe magnet straight section. This behaviour was traced toa mechanical weak spot in the transition region betweenthe straight section and the coil heads, which was alreadynoticed during magnet assembly. Contrary to H1, thepoles were not unloaded at even the highest quenches.Subsequent test at 4.3 K showed a stabilising effect ofsuperfluid training, as almost all quenches occurred at theshort sample limit.4 MAGNETIC FIELD MEASUREMENTSThe magnetic field was measured in the two dipoles inthe vertical cryostat using radial rotating coils. Fiveadjacent coil sections measured the field dependencealong the magnet bore. Here, the results from thecentremost coil have been used to compute the transferfunction. Higher order harmonics are given as dipole-weighted averages over the straight part (on the threecentral coils). They are quoted in units of 10-4 of the mainfield at the LHC reference radius of 17 mm.Table 2 gives a summary of the field quality asmeasured in the two dipoles at an intermediate field      (5kA, approximately 2.5 T) and 1.8 K after training. Wereport the magnitude of the harmonics up to order 11,compared to the expected values for the allowedharmonics. The transfer function for the dipole fieldcompares well at intermediate fields with the results ofsimulations. Furthermore, the difference in the geometrictransfer function between the two magnets is small,approximately 4 units.The measured sextupole is significantly higher thanexpected, and in addition there is a large differencebetween the two dipoles (2.3 units). The higher orderallowed harmonics (decapole and above) are similar inboth magnets, and close to the expected values.Table 2. Magnitude of the field harmonics measured at5 kA (2.45 T) in the H1 and H2, compared to theexpected allowed harmonics for the nominal coil design.order H1 H2 expected1 0.4888 0.4890 0.4872 1.651 0.7123 10.199 7.707 5.4974 0.200 0.1305 0.734 0.799 0.8086 0.020 0.0517 0.118 0.110 0.0178 0.013 0.0129 0.062 0.063 0.04910 0.004 0.00811 0.044 0.036 0.040The variations of low order harmonics between the twomagnets, and the difference with respect to the expectedvalues, can be explained in terms of minor changes in coil4size between magnets. A symmetric change of theazimuthal pole dimension by 0.1 mm givesapproximately 4 units of dipole and 1.5 units of sextupolefield. Therefore, the sextupole and dipole variationsbetween the two magnets could be ascribed to differencesin coil sizes of the order of 0.1 to 0.15 mm. This iscomparable to coil size variations observed in the LHCmain dipoles.-2-1012345670 1 2 3 4 5 6 7 8Field (T)Normal sextupole (units @ 17 mm)H1H22-D calculationFigure 3. Measured and computed sextupole for H1 andH2 dipoles. Measured values have been shifted by theamount reported in Table 2 to remove the geometricsextupole and ease the comparison.In Fig. 3 we show the high field behaviour of thenormal sextupole for H1 and H2. For ease of comparison,the measured curves were shifted by the value of thegeometric sextupole (Table 2). Both magnets behavesimilarly, but the sextupole increases at high fieldsconsiderably more than expected. We believe that this isdue to an elastic displacement of the coils. The order ofmagnitude of the azimuthal displacement can beestimated to be around 0.3 mm. The small but systematicdifference between the two magnets would correspond toapproximately 30 µm variation in coil displacement.Both magnets were measured at several stages duringtraining at 4.3 and 1.8 K. The main purpose was to detectany change in the coil geometry under the action ofLorentz force and temperature gradients during quench.This is a critical issue as phenolic collars, mechanicallyweaker than metallic collars, could potentially lead tovariations of the field quality in time. Fig. 4 shows themaximum range (max-min) of variations of the fieldharmonics as observed throughout testing. The changesare relatively large for the  sextupole (in the range of 0.5units), and become less significant as the harmonic orderincreases (0.01 units or less for orders higher thanoctupole). These variations correspond to small blockdisplacements, in the range of 35 µm. Furthermore, theyare broadly comparable to the behaviour of the maindipole magnets under similar testing conditions, andtherefore it does not seem that reproducibility of the fieldquality imposes limits on the use of phenolic inserts.0.0010.010.112 3 4 5 6 7 8 9 10 11harmonic order (-)Variation of field harmonics(units @ 17 mm)H1H2Figure 4. Maximum range of variation in the harmonicsthroughout the testing period for the H1 and H2 dipoles.5  CONCLUSIONSTwo identical 1-m superconducting dipoles, featuring asingle layer 87.8 mm aperture coil and phenolic inserts,have been manufactured and cold tested. The magnetstrained to their short sample field of 5.6 T at 4.3 K and to7 T at 1.8 K (90 % of the conductor limit). The quenchesoccurred predominantly in the coil ends and in thetransition region to the straight section. Magnetic fieldmeasurements indicated that although there is evidence ofelastic movement of the coils at high fields, the long termreproducibility is comparable to that of dipoles withmetallic collars.REFERENCES[1] R. Ostojic, T.M. Taylor and S. Weisz, “SystemsLayout of the Low-β Insertions for the LHCExperiments”, PAC’97, Vancouver, May 1997, LHCProject Report 129.[2] P. Wanderer et al. “Construction and Testing of ArcDipoles and Quadrupoles for the Relativistic HeavyIon Collider (RHIC) at BNL”,  Proc. 1995 Part. Acc.Conf., Dallas, USA, May 1995, p. 1393.[3] G. Kirby et al., “Design, Fabrication and InitialTesting of a Large Bore Single Aperture 1 m LongSuperconducting Dipole Made with PhenolicInserts”, MT-15, Beijing,  October 1997, LHCProject Report 160.

Testing of the large bore single aperture 1-meter superconducting dipoles made with phenolic inserts

Testing of the large bore single aperture 1-meter superconducting dipoles made with phenolic inserts

Abstract

Similar works

Full text

Available Versions

CERN Document Server