Juengst, K.P.

Krafft, G.

Ries, G.

English

Juengst, K. P.

KITopen

Ma.i 1970Institut für Experim.entelle KernphysikMeasurem.ents on Pulsed Superconducting Magnet.sK. P, J'üng st, G, Kraff't; G. RiesKFK 1217s. H.Mai 1970KERNFORSCHUNGS ZENTRUM KARLSRUHEKFK 1217Institut für Experimentelle KernphysikMeasurements on Pulsed Superconducting Magnets *)K.P. Jüngst, G. Krafft und G. RiesGesellschaft für Kernforschung m.b.H., Karlsruhe*) Paper presented at the Third International Conference onMagnet Technology, 19-22 May 1970 , HamburgAbstractSeveral experiments with superconducting multifilament NbTi wireshave been doneto measure ac losses, degradation effects and reach-•able H, in order to find a suitable conductor for an ac-dipole.Solenoids were built with NbTi multicore wires having the followingparameters: composite diameter 0.04 cm .•. 0.1 cm, Cu and Cu/CuNi(3-component) matrix, twist rate between 0.5 and 2 turns/ern, fila-ment diameter 13/um ••• 48/um. The solenoids typically had aninner diameter of 2.5 cm, an outer diameter of 8.5 cm and a lengthof 5.5 cm, yielding a central field between 40 kG and 72 kG. Thesolenoids were not pot ted and reached 85 % .•• 90 % of short sampIe•critical current. For the chosen cooling conditions a maximum Hwas reached of 95 kG/s with a field amplitude of 52 kG. The measu-red ac losses agree with theoretically predicted ones. Signi-ficant additional self field lasses, as computed by M.N. WILSONet al. 1), could not be confirmed quantitatively.ZusammenfassungSupraleitende Multifilament-NbTi-Drähte wurden auf Wechselstromver-•halten, Degradationseffekte und erreichbares H untersucht, um einengeeigneten Leiter für pulsbare Dipolmagnete zu finden. Die zum Bauvon Testspulen verwendeten Drähte hatten folgende Parameter: Außen-durchmesser 0.04 ••. 0.1 cm, Cu- und Cu/CuNi-(3-Komponenten-)Matrix,Twist mit Ganghöhen zwischen 6 und 25 mm, Filamentdurchmesser 13/um ...48/um. Die Solenoide hatten folgende typische Abmessungen: Innen-durchmesser 2.5 cm, Außendurchmesser 8.5 cm und Länge 5.5 cm. Diedamit erreichten Felder lagen zwischen 40 und 72 kG. Die Spulenwurden nicht vergossen und zeigten eine Degradation von 10 ... 15% .•Bei den gegebenen KÜhlbedingungen wurde ein maximales H von 95 kG/smit einer Feldamplitude von 52 kG erreicht. Die gemessenen Wechsel-stromverluste stimmen mit den theoretisch vorhergesagten überein.Erhebliche zusätzliche "Self-Field"-Verluste, wie sie von M.N. WILSONet al. 1) berechnet worden sind, wurden quantitativ nicht bestätigt.Measurements on Pulsed Superconducting MagnetsK.P. Jüngst, G. Krafft and G. RiesInstitut für Experimentelle KernphysikIIitroductionIn order to check the possibilities of the application of fila-mentary superconducting wires to synchrotron magnets, solenoidshave been tested wound from available conductors.- 2 -The losses were measured usin~ a ealorimetrie method. Themagnets were fixed in a Plexiglass eylinder, whose bottomhas holes in order to allow liquid helium to enter the eylin.der. The eopper eurrent leads (with Nb3 Sn-strips at its ends)were eonneeted outside the eylinder to both ends of the so-lenoid. The evaporating helium gas from the magnet flowsthrough a tube into agas flow meter. Taking into aeeountthe residual gas flow rate for zero eurrent,the aceuracvof the measuring equipment was cheeked using a earbon resistorand determined to 2 - 3 %.All the measurements were earried out with positive triangu-lar eurrent wave forms. The magnets were energized by a 36 kWpower supply, desi~ned for de operation, eontrolled by afunetion generator to give the desired wave form.The tested wires are speeified in table 1.3. AC Losses--~,......._~.,----3.1 Co...pJ?.~_ea~o.~i.te:s:SPURWAY et al. 1) derived a formula for loss eomputation ineoils(1 )avera~eover eoilwhere Hi(Gauss) is a lower limit for the field (typieally1 kG), H~ the maximum local field in the windings, Ho andJ o (A/em ) eonstants, V (em3) the volume of supereonduetor,and d (ern) the filament diameter. For equ. (1) the Je(H)-eurve is supposed to be a hyperbolie funetion. As we have foundlinear andexponential dependences, too, the loss formula 1swritten asW [WATT] ~ V d--'~-.-""---2 • 108avera~e( 2 )- 3 -At first, for simplification, we took for the aver-age the in-tegration from zero or H1 to nM = ~ Hmax(Hmax is the maximum fieldof the coil). The results showed a good agreement with the linearparts of the W(v)-curves. For example the measured losses ofcoils no. 20, 1, and 32 are shown in fig. 1,2, and 3 respective-ly . Nevertheless, a computer calculation, taking into accountthe spatial variation of the field, resulted in smaller lossesthan measured (or computed from equ.(2)). But if we add the lossesfrom transverse currents in the matrix, computed by program,too, a good agreement with the measurements can be observed inthose cases, where no significant self field losses should be ex-pected. M.N. WILSON et al. 1) noted a formula for the ratio of selffield losses Qs to filament losses Qf0.2 • }... J • a 2cHM • dwhere a 15 the composite radius, Aaspace factar equal to theratiO of (filament area)/(compos1te area over filaments), ahd dthe filament diameter.Goil no.3 should show the biggest self f1eld effect: Qs/Qf -' 0.6.Coil 3 is geometrically equal to coil 1 and the wires are thesame except for composite and filament diameters. Therefore thelosses of coil 3 should be twice the los ses of coil 1 in the line-ar part of the W(u)-curves not taking into account the self fieldlosses. But the experiments (fig~4) give a factor of 2.5. Thatcould be a hint for self field losses existing beside the trans-verse current losses, but they will be smaller by at least a fac-tor of 3 than predicted by equ. (3).w+dw-The region, where the additionallosses resulting fromtwisting become significant, can be calculated from2 2.108 ' J .,,1/2. d'.• ~ c )H --"c lr _.-12insufficient(4)1)(c •f. WILSON and v.JALTERS '), where 21 is half the twist pi t ch , ~the resistivity of the matrix, and w the width of matrix between- 4 -filaments. For average va lues of H, J , and p (measured va-2) clues ) the critica1 region shou1d be near 0.03 Hz and 0.14 Hzfor coi1s nOt 20 and 2 respective1y, in agreement with theexperimental resu1ts.Looking on1y at the twist pitches for wire nOt 32 and 1 (6 and8 mm pitch) one cou1d expect a simi1ar non-linear W = W (v) -curve for coi1 32 as for nOt 1.Fig.3 shows the measured va1ues. There is no departure from 1i-•nearity up to a Hr i s e of about 70 kG/sec. (at this fie1d sweep1imitations of the avai1ab1e power supp1y give current wave formsas indicated at the top of fig.3).This 1inearity is due to the fact of the high critica1 currentdensity in the superconductor (2.5 • 10 5 A/em2 at 50 kG) andthe three tirnes 1arger filament diameter. Together with the•shorter twist 1ength the resu1t aceording to equ.(lt) is a He of15 times the value far wire no.1eFor examp1ethe resu1ts for two wires (No.r and 9) are diseussed.Coi1 no.7 had an inner and outer diameter of 2 cm and 8.6 and a1ength of 11 cm; whi1e coi1 9 had the dimensions of 2.4 cm, 8.5emand 5.3 cm respective1y.The observed losses are shown in fig.5. It is to be seen, thatthe 10ss/eyc1e for wire no.T is about four times the loss cf coi19, although the filament diameter i8 only doubled. But normal-izing, to unit superconductor co1ume (120 cm3 for eoi1 no.7 and51 cm3 for no.9) and to unit superconductor critiea1 currentdensity (1.4 • 10 5 A/cm2 and 2.1 • 10 5 A/em2) shows that the 10ss/cyele is doub1ed for a twice 1arger filament diameter. Signi-ficant se1f-field losses cou1d not be confirmed quantitative1y.- 5 -4. Final RemarksAeeording to different eooling eonditions a variation in reach-•able maximum Hand critieal eurrent I e is expeeted. For coilno.7 with only one 0.1 em thiek eooling channel in the middle of•the windings the maximum H was limited to about 20 leG/Se Animprovement of the coo l.ä ng conditions to 3 channels di::;tributed•nearer to the inner windings results in an inerease of the H upto 90 kG/s and 95 kG/s with a field amplitude of 52 kG for eoilsno.9 and 32, respectively. For the latter eoils no additionaldeerease of the eritieal current was measured with rising fre-queney (besides the 10 %.•. 15 %degradation observed for deoperation). Wire no.32 shows the highest eurrent density of thetested wires, i.e. 2.5 .105 A/cm2 in the superconductor at 50 kGor 5.3 . 10 4 A/em20ver the windings (filling faetor ~ 0.6).Based on the tested wires, a rough estimation shows that for aneeonomieal ae dipole further improvements are neeessary, e.g.higher twist rate and/or higher eurrent density for wire no.1or a decrease in filament diameter for wire no.32.References1} LEWI~JJ.D., P.F. SMITH, A. H. SPURWAY, C.R. WALTERS, andM.N. WILSON, Rutherford Lab., RPP/A732) FESSLER, N., G. HARTWIG, K.P. JÜNGST, and G. KRAFFT,Gesellseh. f. Kernforschung, Externer Bericht Nr. 3/69/23Table 1Coil + Wire MatrixReference No.Twist"pitch"(mm)(approx.)compC>.sited Lame't er-(cm)Ratiomatrix/s-cNo.offilamentsFilamentdiameter( um)',------~,. .,---------- .,.20 *) Cu 253 **) Cu 51 **) Cu 832 .***) Cu 69 **) Cu,CuNi 67 **) Cu,CuNi 130.050.10.050.040.050.11.35:13:13:11.4:12.7:12.7:1613613616111911942261335. 24480'"'111 ....__:__,,__,,_____ --....~._.'.~, •*) Manuf. by Imperial Metal Industries, Kynoch, Great Britain**) Manuf. by Airco, Murray HilI, USA***) Manuf. by VAC, Vacuumschmelze GmbH, Hanau, GermanyLoss[Watt]1.61.2.',- 5.6cm lIiH :: 42 kG peak•./ .,/ """". .,"L//.~//•0·80.4oo 0.02 r • ---,----'.- ..0.04 0.06 0.08" [Hz]Coi l confi 9uration :2990 turns of 0.05 cm diam.composite (61 x42 urn filaments)Twist: 1 turn/inchIquench =101 A = Hquench ... 40 kG( Ref. No.: 20)Fig. 1: AC -losses vs frequency for twisted copper composite8.4cm-·-·_· - ·-·-2.4cmLc:>=c:r-I-. 5.3cm ~Coil configuration:5650 turns of 0.05 cm diam.composite (361 x13 urn filaments)Twist: 3 turns/inchIquench = 52 A :: Hq uench = 50 k G(Ref. No. 1 )H: 36kG peak, i i ._.,........0.08 0.12 0.16 0.20- ...... \1 [Hz]I•/•./0 ~;L-,"","'-..,.-,-'..-.~0.04o0.2o0.40.8Loss[Watt]f 0.6Fig: 2: AC -losses vs. frequency for twisted copper composite~ 5.3cm ..6.5cm-· - . _. -. -'- 2.4cm~-L(Ref. Nc.: 32 )Coil confi 9uration :6125 turns of 0.04 cm diam.composite (61 x35 um filaments)Twist: 4 turnslinchIquench = 65 A =Hquench = 72 kG•,/'. ...Hrise =H =52 k<3 peak-t•. . I .,-.-, -0.08 0.12 0.16 0.20 -o [Hz]•/'••0.04I0.20" , , , i -o0.62.21.01.81.4Loss[WattJ2.6Fig. 3: AC-losses vs. frequency for copper composite/•I I - • I T~~' -0.10 '\J [HzJ• .>""",",,",,'",,",;".'•/COil No. 1. ",,-./ 13 J,Jm fi laments• H :: 39 kG..Coil No. 326 um filamentsH = 39 kG, . . ,um OßSo pe • , , • • j0.10.20.3Loss[Watt1Fig. 4: Variation of ac-lasses with filornent diameter for twisted copper composites2.5Lass[Watt]2.0/•48 JJm filamentsH = 52 kG•1.S // /'•I 0cL1.0•24 JJm fi lamentsH = 52 kG0.5i i ...0.1 0.2" [Hz]Fig. 5: Variation of ae -losses with filamentdiameter for twisted Cu/CuNi camposites

Measurements on Pulsed Superconducting Magnets

https://publikationen.bibliothek.kit.edu/270004251/3810512

Measurements on Pulsed Superconducting Magnets

Abstract

Similar works

Full text

Available Versions

KITopen