Available online at ScienceDirect. Physics Procedia 67 (2015 )

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1 Alle onlne t ScenceDrect Pyscs Proced 67 (215 ) t Interntonl Cryogenc Engneerng Conference nd te Interntonl Cryogenc Mterls Conference n 214, ICEC 25 ICMC 214 Het trnsfer smulton to lqud ntrogen from HTS tpes t te oerlod currents V.V. Zuo 1 *, S.M. Ryo 1, S.S. Fetso 1 nd V.S. Vysotsy 1,2 1 Russn Scentfc R&D Cle Insttute, Moscow 11124, Russ 2 Ntonl Nucler Reserc Unsersty MEPI, Moscow, 11549, Russ Astrct Knowledge of HTS mterls eor t oerlod currents s mportnt to desgn fult current lmters or fult protecton systems of electro-tecncl deces. Tere re srp oltge pes nd oltge osclltons durng rectngulr current pulses (DC current) on HTS tpes cooled y lqud ntrogen. It s common nowledge tt omogeneous lqud cn wtstnd certn mount of oeretng efore swtcng to te olng pse. In te lqud ntrogen durng te ncrese of te et flux tere s superetng (temperture oersoot) nd olng ysteress tes plce. We expln oltge pes nd oltge osclltons y te ysteress penomenon n olng ntrogen durng te ncrese nd decrese of te et flux n te ntrogen wc s result of current redstruton n te HTS tpes. Bsed on te mesurements of oltge nd temperture of te HTS tpes durng current oerlod nd numercl nlyss of te process we estmted te et-trnsfer crcterstcs from te HTS tpes to lqud ntrogen. We lso otned te nformton out lmtng superetng of te lqud ntrogen. Te nfluence of coers of te HTS tpes on superetng of te ntrogen s lso dscussed Te Autors. Pulsed y Elseer y Elseer B.V. B.V. Ts s n open ccess rtcle under te CC BY-NC-ND lcense (ttp://cretecommons.org/lcenses/y-nc-nd/4./). Peer-reew under responslty of te orgnzng commttee of ICEC 25-ICMC 214. Peer-reew under responslty of te orgnzng commttee of ICEC 25-ICMC 214 Keywords: g-temperture superconductors, current oerlod, olng ysteress; * Correspondng utor. Tel.: ; fx: E-ml ddress: sly.zuo@gml.com Te Autors. Pulsed y Elseer B.V. Ts s n open ccess rtcle under te CC BY-NC-ND lcense (ttp://cretecommons.org/lcenses/y-nc-nd/4./). Peer-reew under responslty of te orgnzng commttee of ICEC 25-ICMC 214 do:1.116/j.ppro

2 62 V.V. Zuo et l. / Pyscs Proced 67 ( 215 ) Introducton I q o terml quenc current superetng temperture dfference et trnsfer coeffcent It s nown tt HTS wres nd deces cn operte t currents well oe tose we cll te crtcl ones (I c ). Mxmum current I q t wc HTS conductor or dece cn operte stle ws clled s terml quenc current [1] nd could e determned nlytclly for constnt et trnsfer coeffcent s presented n [1]. For prctcl purposes t s necessry to study nd to model processes of et nd oltge deelopment n 1G nd 2G HTS tpes cooled y lqud ntrogen t DC currents oe te crtcl one ut lower tn terml quenc current (oerlod currents) nd to fnd out te terml quenc current for te HTS tpes. Expermentl studes for te HTS tpes t oerlod currents were performed n [2], [3], [4]. In tese wors we lso osered srp pes n te oltge t oerlod currents. Voltge osclltons were osered s well. In ts pper we contnue our study of oerlod eor of dfferent HTS tpes cooled y lqud ntrogen. It s necessry to understnd nd to model processes n te HTS tpes cooled y ntrogen t current oerlods. In spte of DC currents te rel et trnsfer process from te HTS tpes to lqud ntrogen durng current oerlods s complex nture. In te present pper we expln te pes nd te osclltons y nlyzng te olng ysteress n te ntrogen wen te et flux s ncresed nd ten decresed. Hysteress of olng cures under ncresng or decresng trnsport current nd terefore te ncresng nd decresng of te et flux to te lqud ntrogen re presented n [5], [6]. In ts pper we expln et trnsfer process to lqud ntrogen t DC currents wt te ysteress penomenon. In te HTS tpes t current oerlods te ncrese nd decrese of te et flux to te lqud ntrogen tes plce due to current redstruton etween superconductng nd norml-conductng lyers of te HTS tpes. Bsed on mesurements of te oltge nd superet temperture of te HTS tpes durng current oerlod nd numercl nlyss of te process we clculted processes of et nd oltge deelopment. 2. Experment To study HTS tpes t te oerlod currents n lqud ntrogen (pressure 1 tm., mesured temp K) we used tree types of HTS tpes. Te frst one s te 1G HTS tpe from Sumtomo Electrc Industry (SEI): wt szes mm 2 ; n~16; I c.4 K) ~172 A, 68 % of sler mtrx. Te second one s te 2G tpe from Amercn Superconductor corporton (AMSC): wt szes mm 2 ; n~28; I c.4 K) ~86 A. Te trd one s te 2G tpe from Super Power (SP): wt szes 4.1 mm 2 ; n~27; I c.4 K) ~13 A. Te smples were tested n ertcl nd orzontl orenttons n lqud ntrogen twce: non-coered nd coered wt Kpton nsulton (tcness of te nsulton s 1 μm). Lengt of ll smples ws.16 m. Generl expermentl rrngements were te sme s descred n [2]. Two prs of oltge tps nd seerl termocouples (TC) wt 2 cm dstnce etween tem were used. Durng tests DC current ws ppled to te smple wt certn current mgntude nd durton. Te current, oltge nd TC sgnls were recorded y te multcnnel Yoogw DL-85 nlyzng recorder. At ertcl nd orzontl smples orentton we found tt oltge s prctclly unform long te smple, tus we selected one pr of oltge tps to sow te typcl results. It ws found expermentlly tt orentton of te tpes s we nfluence on I q.in olng ntrogen for te SEI tpe I q s out 47 A nd rto I q /I c s 2.76 for non-coered tpe nd for coered tpe I q s out 28 A nd I q /I c s For te AMSC tpe I q s out 21 A nd I q /I c s 2.44 for non-coered tpe nd for coered tpe I q s out 16 A nd I q /I c s 1.8. For te SP tpe I q s out 17 A nd I q /I c s 1.3 for uncoered tpe, for coered tpe I q s out 16 A nd I q /I c s In Fgs. 1-3 seerl oltge recordngs re sown for te HTS tpes tests for ertcl () nd orzontl () smples orentton wtout nd wt nsulton for dfferent oerlod currents up to te terml quenc current I q.

3 V.V. Zuo et l. / Pyscs Proced 67 ( 215 ) In te legend te current mgntudes nd te rto of I/I c re sown. Te results sow te dfferences n te eor of expermentl cures otned for dfferent tpes. Typcl cures t oerlod currents re s follows: for noncoered SEI 1G tpe nd AMSC 2G tpe tere s fst rse of te oltge, ten fst drop wen coolng swtces from conecton to nuclete olng (srp oltge pes), ten oltge ecomes stle untl current stops (Fg. 1). For non-coered SP 2G tpe tere re osclltons of oltge t currents close to I q for ot smple orenttons (Fg. 2). Smlr oltge osclltons were osered for AMSC 2G tpe (Fg. 2) t currents elow te current correspondng to srp oltge pes. For coered tpes tere re smoot cures of te oltge for ot smple orenttons presented for AMSC 2G tpe n Fg. 2 nd for SEI nd SP tpes for ertcl orentton n Fg. 3. Te mesured superetng temperture dfference ersus current for AMSC nd SEI HTS non-coered tpes re sown n Fg (2.71) 4(2.35) 34( 2) 28(1.65) (1.74) 2(2.33) 18(2.1) Fg. 1. Voltge recordngs ersus tme for tests t dfferent currents nd I/I c for non-coered HTS tpes: () 1G SEI; () (1.23) 2G SP 14(1.63) (1.74) 14(1.63) 12(1.4) (1.163) Fg. 2. Voltge recordngs ersus tme for tests t dfferent currents nd I/I c for: () non-coered SP nd AMSC tpes; () AMSC tpe coered wt Kpton.

4 622 V.V. Zuo et l. / Pyscs Proced 67 ( 215 ) coered 1G SEI, I=26(1.53) 2G SP, I=16(1.23) Temperture dfference (K) G SEI Current (A) Fg. 3. () Voltge recordngs ersus tme for tests t dfferent currents nd I/I c for coered SEI nd SP tpes; () Mesured superetng temperture dfference o s functon of current for non-coered HTS tpes. 3. Numercl model For smultons of et/oltge deelopment of te HTS tpes t oerlods, we nlyzed te stndrd et lnce equton: N n CS S P T T P T T Q T t x T x, (1) were s te numer of te tpe s lyer; C nd re te effecte olumetrc specfc et nd te terml conductty of te mterls of te tpe s lyer; S s te cross secton of lyer; (P) s te et trnsfer nd permeter of contct etween contctng lyers; s te temperture of coolng t; s te coeffcent of et trnsfer nto ntrogen nd permeter of contct lyer wt ntrogen. Q =E J s te resste et n lyer. Here J s te current densty n te lyer; E s te oltge oer te lyer. E n superconductng lyer s nonlner, we used expresson: E=E c (J/J c ) n for t, were E c J nd J c re trnsport nd crtcl current densty correspondngly, n s te ndex of oltge current crcterstcs. Currents I n lyers of tpe were clculted from te equton set: R I R m I 1 I m 1 I 1 L L 1, ( 1, m 1) 1 totl I t (2) were m numer of lyer, I totl current n te tpe, R s te resstnce of lyer, L, s self nd mutul nductnce of lyers. Te computer code smultneously soles te equtons (1) nd (2) y te fnte dfference metod (mplct dfference sceme). Becuse tere s non-lner eor of te oltge oer superconductng lyer, nd s result of te resste et n te superconductng lyer of te tpe, of et cpcty, of et conductty nd of et flow to ntrogen, n terte lgortm for ec tme step s used. To smulte te rel et/oltge deelopment of te HTS tpe t oerlods one e to elute properly te et trnsfer coeffcent to lqud ntrogen For te stedy-stte et trnsfer tere re two regmes: nturl conecton wen 1 / 3 con con T [7], were C con coeffcent depends on te sze of te smple eng cooled, nd nuclete olng (NB). For cryogenc fluds

5 V.V. Zuo et l. / Pyscs Proced 67 ( 215 ) for olng regme te et-trnsfer coeffcent s proed to depend lso on te mterl of te eter surfce, te est-ft equton to predct te et trnsfer coeffcent s gen y [8]: ol c. 117 C q, (3).624 p were q (g/m 3 ), c p s te specfc et (J/(g K)) nd s te terml conductty (W/(K m)). All te terml pyscl propertes re eluted t te sturton temperture of te olng lqud. Te constnt C depends on te mterl of eter surfce nd propertes of olng lqud [8]. Temperture dely of egnnng of NB c cn e determned from condton of equlty of et trnsfer coeffcents t regmes of conecton nd nuclete olng. In te lqud ntrogen durng te trnsent ncrese of te et flux my occur ddtonl seerl Keln s oeretng (superetng or temperture oersoot) nd totl superetng temperture dfference o my e fe - ten tmes ger tn c, ut temperture dfference of swtc c to conecton c s out c. In te present pper we expln te dfferences n te eor of te oltge t current oerlods y nlyzng te ysteress penomenon n lqud ntrogen. In Fg. 4 te olng cures wt ysteress, o nd c re sown. 4. Clculton To nlyze te eor of te oltge n te 1G SEI nd tpes we used superetng temperture dfference o mesured y termocouples (Fg. 3). Coeffcent ws determned from experment s well. In Fg. 4oltges ersus tme for te 1G SEI nd tpes re sown, clculted y te numercl model for DC currents presented n Fgs. 1 nd 1. Te oltge pes re occurrng wen dfference etween temperture of te tpe nd temperture of te ntrogen exceeds o nd te nuclete olng strts. Te oltge pes re result of current redstruton from superconductng to norml-conductng lyers of te HTS tpe efore te pes (tere s te conecton) nd from norml-conductng to superconductng lyers fter te pes (tere s NB). Wen te oltge ecomes stle tere s olng et trnsfer. One cn see te good greements etween numercl clculton (Fg. 4) nd mesurement (Fgs. 1 nd 1). Te oltge cures re qute smlr. Te clculted nd mesured I q for ot HTS tpes re well concded s well. Het flux Het flux decresng c Het flux ncresng Temperture dfference Onset of olng o (1.74) 18(2.1) 1G SEI 28(1.65) 34(2) 4(3.25) 46(2.71) Fg. 4. () Bolng cures wt ysteress; () Exmple of clculted oltges ersus tme for dfferent currents nd I/I c for 1G SEI nd 2G AMSC HTS non-coered tpes. For currents presented n Fg. 2 for SP nd AMSC tpes tere re multple temperture oersoot ccompned y swtcng from conecton to NB nd ten c from NB to conecton. Clculted o s out 3K. Osclltons of oltge re te result of multple current redstrutons etween superconductng nd normlconductng lyers n te HTS tpes. Results of clculton te oltge t currents re sown n Fg. 5. One cn see te good qultte greement etween numercl clculton (Fg. 5) nd mesurement (Fg. 2).

6 624 V.V. Zuo et l. / Pyscs Proced 67 ( 215 ) For non-coered tpe tere s swtc to te olng pse wtout temperture oersoot. Results of clculton for te oltge t mesured currents re sown n Fg. 5. One cn see te good greements etween numercl clculton (Fg. 5) nd mesurement (Fg. 2) s well. Te et trnsfer mecnsm n 1G SEI nd 2G SP HTS non-coered tpes (Fg. 3) s nturl conecton. Te deeloped numercl model ges te explnton of te dfferences n te eor of expermentl cures otned for dfferent tpes, ecuse te complex nture of et trnsfer to lqud ntrogen from HTS tpes t current oerlods ws ten nto ccount. Bolng ysteress penomenon requres more understndng (1.63) G SP 16(1.23) (1.16) 12(1.4) 14(1.63) 15(1.74) Fg. 5. Exmple of clculted oltges ersus tme for dfferent currents nd I/I c: () SP nd HTS non-coered; () HTS coered tpes. 4. Concluson We tested 1G nd 2G HTS smples mmersed n lqud ntrogen wt nd wtout nsultng coer t current oerlods wt ertcl nd orzontl orentton. Te numercl model ws deeloped to nlyse te eour of te HTS tpes cooled wt ntrogen t current oerlods. Te numercl nlyss s sown tt tere re temperture oersoot nd ysteress penomenon n te olng ntrogen durng te et trnsfer process from oerlodng 1G nd 2G HTS tpes to ntrogen. Te suggested model proded dt close to te expermentl ones nd cn e used for eluton of te HTS tpes eour t oerlod currents. References [1] Rmno A., Vysotsy V., Ilyn Yu., 2. Unersl sclng low for quenc deelopment n HTSC deces, Cryogencs. 4, [2] Fetso S., Vysotsy V., Zuo V., 211. HTS Tpes Cooled y Lqud Ntrogen t Current Oerlods. IEEE Trns. on Appled Superconductty, 21, 3, [3] Vlo S. et l, 211. Het trnsfer fetures from copper nd HTS tpes to lqud ntrogen y step-wse current pulse. Terml Engneerng, 58, 14, [4] Conec F., Us P., 22. Instltes oe crtcl current regon n B-2223/Ag superconductng cols cooled y lqud ntrogen. Cryogencs, 42, [5] Dee V., Kutseno K. et l, Instlty of et trnsfer from HTSC-smples to lqud ntrogen. Cryogencs, 38, 7, [6] S M. et.l, Anlyss on ysteress n nuclete pool olng et trnsfer. Int. J. Het Mss Trnsfer, 36, 18, [7] Alexee V. et l, Clculton nd modelng of cryogenc pprtus nd deces. Energotomzdt, Russ. [8] Stepn K., Adelslm M., 198. Het-trnsfer correltons for nturl conecton olng. Int. J. Het Mss Trnsfer, 23,