Developmentandcharacteristicsofpersistentmode inHTSmagnet JungHoKim a ,JunHyungLim a ,JinhoJoo a, * ,SeyongChoi b ,Se-HeeLee b , WansooNah b ,HyoungkuKang c ,TaeKukKo c a School of Metallurgical and Materials Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu Suwon city, Kyunggi-do 440-746, South Korea b School of Information and Communication Engineering, Sungkyunkwan University, Suwon 440-746, South Korea c Department of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, South Korea Received29October2003;accepted13January2004 Availableonline28May2004 Abstract We fabricated a high-temperature superconducting (HTS) magnet with a persistent current switch (PCS) and evaluated the decay characteristics of persistent mode and joint resistance at 77 K. To make the HTS magnet, BSCCO(2223) tapes were wound into a double-pancake coil and connected to the PCS by soldering. Field decay behaviorwasremarkablydependentonoperatingcurrent.Atanoperatingcurrentof50%ofthecriticalcurrent(I c ), decaybehaviorshowedtwodistinctregimes:initialfastdecayandsubsequentlineardecay.Bycontrast,therewasa lineardecayregimeofonly13%of I c .Totalcircuitresistancewasapproximately2.0 · 10 8 X atanoperatingcurrentof 6A.Measureddecaybehaviorwascloselyconsistentwiththecalculateddecaybehaviorobtainedfromboththeindex resistanceandjointresistancecomponents. Ó 2004ElsevierB.V.Allrightsreserved. PACS: 74.72.Hs;85.25.Kx;85.25.Ly Keywords: HTSmagnet;Persistentcurrentswitch;Persistentmode 1. Introduction BSCCO superconductor tape has been widely studiedforuseintheinsertcoilofa1GHznuclear magneticresonance(NMR)magnetbecauseofits highuppercriticalmagneticfieldofmorethan21 Tat4.2K[1].Ingeneral,theinsertcoilisoperated inpersistentmodetomaintainafieldstabilityof 0.01ppm/h.Toimprovefieldstabilityinpersistent mode,thecoilmustminimizedissipation,whichis mainlyduetoindex n andjointresistance. Dissipation from the low index n of BSCCO tape is reported to limit the use of its coil in practical applications for NMR: the index n of BSCCO (10–20 for both 2212 and 2223) is lower thanthatofLTS(40–100forNbTiandNb 3 Sn). Therefore, an HTS must be operated at a lower * Correspondingauthor.Tel.:+82-31-290-7385;fax:+82-31- 290-7371. E-mail address: jinho@skku.ac.kr (J.Joo). 0921-4534/$-seefrontmatter Ó 2004ElsevierB.V.Allrightsreserved. doi:10.1016/j.physc.2004.01.124 www.elsevier.com/locate/physc PhysicaC412–414(2004)1026–1029