High performance Ti-alloyed internal-Sn superconductors have been selected for use in the Proof of Principles (PoP) coil, and a 1.0 m o.d., 0.4 m i.d., solenoid designed to produce fields up to 15 T. The PoP coil, which will use forced-flow Cable-In-Conduit Conductors (CICC), will operate at 4.2 K and moderate levels of conductor strain. Here we report the results of detailed characterizations of two proposed PoP coil Nb{sub 3}Sn 19 subelement superconductor wires of different topology. We have investigated the critical current as a function of applied field, and applied strain. The wires were found to have excellent high field properties, providing a high performance margin for the proposed PoP coil. The field and strain dependence of J{sub c} have been found to compare favorably with predictions from a wire performance model recently developed for Nb{sub 3}Sn superconductors. 5 refs., 6 figs., 2 tabs

Duenas, A. R.

Gregory, E.

Karlsen, C. E.

Ozeryansky, G. M.

Summers, L. T.

UNT Digital Library

UCRL-JC-103491PREPRINTA CHARACTERIZATIONOFINTERNAL-SNNB3SNSUPERCONDUCTORSFORUSE INTHE PROOFOF PRINCIPLES (POP) COILL. T. SummersA. R. DuenasC. E. Karl senG. 1.1.OzeryanskyE. GregoryThis paper was prepared for submittal to the1990 Applied Superconductivity Conference,SnowmassVillage, CO 9/24-28/90 __""':-'!..,i :./t-' :';''-'Lt i;_( f'_ ,":.. . !NOV05 190September 21, 1990I '',, ,...This is a preprint oi a paper intended for publication in a journal or proceedings. Sincechanges may be made before publication, this preprint is made available with theunderstanding that it will not be cited or reproduced without the permission of theauthor.DISCI.AIMERThis document was prepared as an account of work sponsored by an agent.', of theUnited States Government. Neither the [ Inited States Government nor the Universityttf ('alifornia nor an) of their employees, makes an)' _arrant)', express or implied, orassumes an) lettal liabilit) or reswmsibilit ) for the accuracy, completeness, (pr useful-ness ttf an) in|ormation, appar.,tlus, pr(Kluct, or process dist,lo_ed, oi' represenl._ that.its u_t, _ould nnt infringe privately (tuned rights. Reference herein to an) specificcommercial product_, process, or service by trade name, trademark, manufacturer, orotherwise, dt_,s not necessarily constitute ttr imply its endorsement, recommendation,ttr favorinK h_ the L!nited States (,overnment or the L;niversit_ of ('alifornia. Thevie_s and opinions ttf authors exprt'ssed herein do not nt,ces_aril.v state or reflectthose of the I.Inited Staten Government ttr the University of California, and shall notbi., used for advertising (tr pr(KiUCt endorsement purpose_.[[I _1 , i i,,A CHARACTERIZATION OF INTERNAL-SN NB3SN SUPERCONDUCTORSFOR USE IN THE PROOF OF PRINCIPLES (POP) COILL.T. Summers, A.R. Duenas, and C.E. KarlsenLawrence Livermore National LaboratoryP.O. Box 5511, L-643Livermore,CA 94550 UCRL-JC-- i0 3491_| G.M. Ozeryansky and E. Gregory DE9 1 00 17 43| Intermagnetics General Corporation| ' 1875 Thomaston AveWaterbury, CT 06704Abstract _Experimental procedure• High performance TJ-alloyed internal-Sn The wire selected for the PoP conductor is an 19superconductors have been selected for use in the the Proof subelement, internal-tin, Nb3Sn superconducting wireof Principles (POP) coil, a 1.0 m o.d., 0.4 m i.d., solenoid produced by Intermagnetics General Corporation. Thisdesigned to produce fields up to 15 T. The PoP coil, which wire was produced in two variants with slightly differentwill use forced-flow Cable-In-Conduit Conductors (CiCC), topologies. The first variant contains a copper layerwill operate at 4.2 K and moderate levels of conductor ,ueasuring approximately 25 _ thick immediately understrain. Here we report the results of detailed characteriza- the diffusion barrier. This layer, referred to as under-barriertions of two proposed PoP coil Nb3Sn 19 subelement copper, is beneficial in increasing transverse resistivity,superconducting wires of differing topology. We have increasing subelement uniformity, and possibly increasinginvestigated the critical current as a function of applied drawability. The second variant of this wire was producedfield, and applied strain. The wires were found to have without under-barrier copper to achieve higher criticalexcellent high field properties, providing a high currents. The details of the wire construction ar_pear inperformance margin for the proposed PoP coil. The field Table 1. For simplicity the wires with and without under-and strain dependence of Jc have been found to compare barrier are referred to as "with UBC" and "w/o UBC"favorably with predictions from a wire performance model respectively. Note that the wires are similar in all respectsreceutly developed for Nb3Sn superconductors, except filament size and the inclusion of under-barriercopper. Photomicrographs of the unreacted wires with andIntroduction without under-barrier appear in Figure 1 a and brespectively.The Proof of Principles (POP) coil is designed as a1.0 m o.d., 0.4 m i.d. solenoid for use in demonstrating the Table 1. Construction of Internal-tin wires used in thisengineering design principles assumed for large magnets s_dy.proposed for magnetic fusion energy machines such as thei International Thermonuclear Experimental Reactor (ITER). _ with UBC w/o UBC' The PoP coil is capable of producing a field of 15 T whenoperated in the 8 T backing field provided by the 2.0 m sol- Wire Diameter 0.817 mm 0.817 mmenoid ) coted at the LLNL High Field Test Facility (HFTF). Cu Stabilizer 46.5% _ 5.5%Nb Diffusion BarrierTwo grades of forced-flow conductors will be used for (of non-Cu area) 8.5% 8.5%PoP, the low field grade consisting of a 52 x 3 cable enclosed Non-Cu 53.5% 53.5%in a square stainless steel conduit measuring 7.47 mm flat No. Filaments 4902 4902to flat externally and having a wall thickness of 0.6 m,n. F,_lament Diameter 3.5 _m 3.7 _mThe high field grade will have a 53 cable and be enclosed in Subelement No. 19 19a conduit measuring 9.29 mm externally with a 0.6 mm Ti addition 1.2% 1.2%wall thickness. The operating current of both grades is5 kA. Test specimens measuring 450 mm in length wereheat treated in flowing argon according to the following, Internal-Sn, Ti alloyed multifilamentary schedule; 200°C/24h + 340oc/48h + 660oc/72h + 725oc/12h.superconductors have been selected for use in the PoP coil. No attempt was made to investigate optimal heat treatmentAt the time of their specification the conductors for PoP schedules. The samples were then mounted in a critical_epresented the state-of-the-art of superconductor current vs. strain test apparatus and tested at 4.2 K in a 15 Tmanufacture, a level of technology that is not only suitable split bore solenoid. Details of the test apparatus arefor PoP but possibly also for magnet systerns in ITER. described elsewhere.l,2 The gage length between specimengrips was 307 mm. The force applied to the specimen wasE.xperimental Procedure measured directly with a load cell. Strain in the specimeni_ was calc'-'!atcd from cross head displacement with a.nThe wire selected for the PoP conductor is an 19 accounting for compliance in the load train.subelement, internal-tin, Nb3Sn superconducting wireFor determination of critical current, sample voltageManuscript received September 24, 1990 measured over a 2 cna l ngth of the wire centered at the.... I_ ...... ,, e .... , , , liP' r'Jl'U,lll" II ' II .... rr ', r ,Twhere: t -Teo(e)Bb---Be2(T,e)C = Pinning/geometry factor accounting forfraction of Nb3Sn and effectiveness ofpinning sites,bl;l Iwhere:Be2.0(e)= Bc20m(1 - ale Iu)Te0(e)= TcOm(1 - a lelu) l/wDetails of the model are presented elsewhere. 5Application of the model requires assumptions ofthe critical temperature at zero intrinsic strain and zeroO field (Tc0m) and the upper' critical field al zero intrinsicf_ "_'" C_ strain and zero temperature (Bc20m), For the purposes_ of' O .Q O this calculation the zero temperature critical field at _t._ro"O _ 0 C intrinsic strain was fixed at 18.3 K. This is a reasonableassumption and is close to values used by Ekin to fit I,.. vsstrain data in Nb3Sn wires. 4 Bc20mand the jo UO pinning/geometry factor (C) were varied to obtain th_l.bestO fit tc the data. lt was assumed that Bc20mand Tc0m w_f.st_eO _ q_ same for the two wire topologies and only the /pinning/geometry factor was allowe to vary.ResultsA t:ypical 4 K stress-strain curve is shown in Figure 2.The mechanical properties of both wires (w/ UBC and w/oUBC) are nearly identical. Fhe 0.2% offset yield strengthsFigure 1. Photomicrographs of unreacted PoP coil wires, are approximately 205 MPa and the tensile strengths arewith under-barrier copper (a) and without under-barrier about 640 MPa. Separate mechanical tests have showncopper (b). The under.-barrier copper (photograph a) is the fracture to occur at about 1%.thin layer of copper between the diffusion barrier and theouter row of subelements. 6 0 0- I I 1 _magnet bore. Critical current was measured using a 5 0 0 -resistance criteria of 5 x 10 -13_ °m. For purposes of Jc vs. E a. 4 oo -testing, sample strain was adjusted using displacement _-control. _ 3 0 0 - -03Theoretical calculation of the critical current of the _ 2 00- - ,sample wires was performed using a model developed atLLNL and based on previous work of Hampshire, et al. and 1 00-Ekin.3, 4 The model allows prediction of critical currentdensity in Nb3Sn zuperconductors as a function of field, 0 - I I I -temperature, longitudinal strain, and radiation damage. O,0 0.2 0.4 0.6 0 8Here we have used a simplified version of this equation Engineering Strain, %that assumes a linear fit to the Ginzburg-Landau (_:)coefficient vs temperat,-re and. nPglects the radiation Figure 2. Typical 4 K stress-strain ca_rve for the proposedI dependent terms. PoP coil wires. This data was obtained during j_.vs..' evaluation and the test was terminated at low Ic values and]c(B,T,e) _ C [Be2(T,¢)] "1/2 (1 - t2)2 b-1/2 (1 - b)2 (1) not at specimen fracture. Fracture observed in separatemechanical tests occurs at about 1% strain.1600 , I , I , = • = , = , = , , 1.2 _ I ..., . i , = • = . .i , ,! , J , J%%'_' 1400 "_. 1 15 T0 % 1.0"_l %:= 1200 _ Z_ "'_oc:: 1000 E 0.8800 ",,,,< -_,_,, -._,., o 0.6•E 600 O with UBC _"E" d_ w/o UBC<: 400" 0.4200 i _ Calculated for UBC. Calculated for w/o UBC0' • i • i"' • ...., • I.........• 1 • I • 0.2 • = • i • ' i • . • I " I ' • i -" I9 10 11 12 13 14 15 6 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8B, T Intrinsic Strain, %Figure 3. Jc as a function of B for both wires. Also plottedI are values of Jc vs B calculated using Eq. 1. Figure 4. Critical current as a function of longitudinalstrain for wi es with u der-barrier copper. Da a is shownTable 2. Parameters used with equation 1 to calculate the for two specimens (A&B). The solid line is a fit tocritical current as a function of field and applied calculated values of the strain dependence. The calculatedstrain strain dependence was obtained using the parameters inw / UBC w/o UBC Table 2.Bc20m (T) 27.5 27.5TcOm(K) 18.3 18.3 1.2 ..... , . , . , . , , = , I , _ ,C (AT mm'") 13,500 17,500¢ (for Jc vs B) -0.239 -0.236 1.0 15 Ta (for ¢ < 0) 900 900a Lfor ¢ > 0) 1250 1250 E 0.8u 1.7 1.7 ow 3 3 C 0.6T (K) 4.2 4.2 o0.4The critical current density of both wires as a func- o w/o UBC-Ation of field at zero applied strain are shown in Figure 3. 0.2 m w/o UBC-B °oAlso shown is the predicted critical current density ocalculated using equation l and the input parameters in 0.0 - • , • , .", . , . ', . , • , •Table 2. The transitions observed in these wires are -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8reasonably sharp with n values of approximately 21 at 15 T Intrinsic Strain, %and zero applied strain.The normalized critical current as a function of Figure 5. Critical current as a function of longitudinalintrinsic strain is shown in Figures 4 and 5 for wires with strain for wires without, under-barrier copper. Data isand without UBC respectively. Also shown in these figures shown for two specimens (A&B). The solid line is a fit toare calculated values of the strain dependent normalized calculated values of the strain dependence. The calculatedcritical current. These values were determined using the strain dependence was obtained using the parameters ininput parameters from Table 2. Table 2.The thermal precompression (average of two tests)was -0.239% and -0.236% for with and w/o UBC topology to wire topology, such as available Sn andrespectively. The irreversible strain limit (applied strain) filament diameter, may yield small differences in He20m andwas approximately 0.73% and 0.71%. Tc0m for the two wires. Small changes in these terms will' results in large changes in the calculated fit at highDiscussion compressive or tensile _trains.' An excellent fit of experimental and calculated A reasonable fit of the of experimental Jc vs B data tovalues of normalized critical current vs strain (Figures 4 the calculated values (Figure 3) is also obtained. However,and 5) was obtained. At high positive strains (tension), significant divergence of the experimertal and calculatedcalculation predicts slightly less sensitivity to strain in the values are evident at low fields for both wires. This iswires with UBC than that obtained during testing. This is largely reflected in the choice of Hc20m and Tc0m, whosenot completely unexpected as the choice of parameters, values were constrained to obtain the the best fit to the Ic vs, . .. i ............. 1..,..... ,.,._-1,, _,..,,I,-4 _c,_-_r_FHc20m and Tc0m, were held constant and only C allowed to strain c=ara. The_¢ v==u¢_ w¢,¢ :,_,_,o=_t_,,_,,,y ...............vary for both wire topologies. The fit to experimental data during calculation of Jc as a function of field and only theis therefore a compromise. Subtle variations from wire pinning/geometry factor (C) was varied.The slight divergence of experimental and calculated internal-Sn Nb3Sn wires, one with and one without under-data does not reduce the usefulness of the equations for barrier copper. Precompression for both wires is similar,predicting Jc vs B as they appear to work well within a approximately -0.24%. The irreversible strain limit (¢irrev)limited range of field. However, it does suggest that the is approximately -.70% for both wires.two tests, Jc vs strain and field, are not yet fully selfconsistent. A more detailed characterization with better The 4 K tensile properties of both wires were nearlycontrol of experimental conditions is required to obtain a identical. The 0.2% offset yield strengths are approximately ,closer fit of the experimental and calculated data. 205 MPa and the tensile strengths are about 640 MPa.Fracture in all specimens occurs at about 1% applied strain.It should be noted that the experimental criticalcurrents presented here are measured using a relatively low An excellent correlation between experimental andresistance criteria of 5 x 10"13 _ .m. This is due to the short calculated Jc vs strain data was obtained. This correlationdistance between sample voltage taps and the need to was obtained with values of Hc20m and Tc0m of 27.5 T and! suppress the effects of spurious noise in the sample voltage 18.3 K respectively. Good agreement between experimentali and curret_t signals. However, the large resistance criteria and calculated values of Jc vs B were obtained for a limitedican lead to a slight over estimation of the critical current range of fields. This fit was obtained using the same valuewhen compared to more sensitive criteria. Figure 6 shows for I-Ic20m and Tc0m with the pinning/geometry ¢6efficientthe critical current of a wire with UBC at 15 T and zero set to 13,500 and 17,500 for wires with and without UBCi applied strain as a function of resistance criteria. This data respectively.may be used to approximately scale the critical currents to acriteria of interest. It is worth noting that a resistance The high field critical current of wires without thecriteria an order of magnitude smaller than those used here under-barrier copper is excellent. The wire is suitable for(5 x 10-14vs 5 x 10"13_"/om) yields critical currents that are the PoP coil and _ppears to meet the critical currentapproximately 15% lower. _ requirements established for FI'ER.._ _ , , ,,,I _ , , , j , ,,I Acknowled_:ments...... _i o This work was performed under the auspices of the-- U.S. Department of Energy by the Lawrence Livermore1 - - National Laboratory under Contract W-7405-Eng-48.ReferencesO7 0. 1. M.J. Strum, L.T. Summers, and J.R. Miller, "Ductilityo_ i enhancement in unreacted internal-Sn Nb3Sn throughJ low-temperature anneals," IEEE Trans. Mag., V. 25,No. 2, 2208, 1989.8. _i " ' _"l '-- -13 ._2 2. L.T. Summers, M.J. Strum, and J.R. Miller, "The1 0 1 0 characterization of Nb3Sr_ superconductors for use inmagnets of 19 T and greater," Adv. Cryo. Eng., V. 36A,Figure 6. Approximate relation between resistance criteria 77, 1990.and measured critical current. Ic has been normalized tothe 115 A, the value obtained at a resistance criteria of 3. D.P. Hampshire, H. Jones, and E.W.J. Mitchell, "An in5 x 10-13 fl.m (used for most of the analyses presented here), depth characterization of (NbTa)3 Sn filamentaryThe best fit to the normalized Ic is given by, superconductor," IEEE Trans. Mag., V. MAG-21,289,Ic (normalized) = 2.1 + 0.09 log (Resistance Criteria) 1985.The overall performance of the wires ,,xamined is 4. J.W. Ekin, "Strain scaling law for flux pinning inencouraging. The high critical current of the w/o UBC wire practical superconductors. Part 1: Basic relationshipsis excellent, providing an ample operating margin for the and application to Nb3Sn conductors," Cryogenics,PoP coil. Perhaps more importantly, the high-field critical V. 20, 611, 1980.currents of the wires without under-barrier copperapproach or exceed (one must account for the selection ofcritical current criteria) the Jc requirements established for 5. L.T. Summers, M.W. Guinan, J.R. Miller, andthe proposed International Thermonuclear Experimental P.A. Hahn, "A Model for the Prediction of Nb3Sn 'Reactor (ITER). Critical Current as a Function of Field, Temperature,Strain, and Radiation Damage," to be presented at theConclusions Applied Superconductivity Conference, Snowrnass,CO, 1990.The critical current as a function of longitudinalstrain and magnetic field has been examined for twoI ' ' " rl]lr!II '

A characterization of internal-Sn Nb sub 3 Sn superconductors for use in the Proof of Principles (PoP) coil

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A characterization of internal-Sn Nb sub 3 Sn superconductors for use in the Proof of Principles (PoP) coil

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