Yukikazu Iwasa, Juan Bascuñán, Seungyong Hahn, John Voccio, Youngjae Kim, Thibault Lècrevisse, Jungbin Song, and Kazuhiro Kajikawa

October, 2014

Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center

Massachusetts Institute of Technology Cambridge MA 02139 USA

This work was supported by the National Institute of Biomedical Imaging and Bioengineering and National Institute of General Medical Sciences of the National Institutes of Health under Award Number 4R01 EB017097-10. Reproduction, translation, publication, use and disposal, in whole or in part, by or for the United States government is permitted. Submitted to IEEE Trans. Appl. Supercond.

PSFC/JA-15-35

A High-Resolution 1.3-GHz/54-mm LTS/HTS NMR Magnet

http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217http://dx.doi.org/10.1063/1.4826217

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A High-Resolution 1.3-GHz/54-mm LTS/HTS NMRMagnet

Yukikazu Iwasa, Juan Bascuñán, Seungyong Hahn, John Voccio,Youngjae Kim, Thibault Lécrevisse, Jungbin Song, and Kazuhiro Kajikawa

Abstract—A high-resolution 1.3-GHz/54-mm LTS/HTS NMRmagnet (1.3G) is currently in the final stage at the MIT FrancisBitter Magnet Laboratory. Its key component is a 3-coil (Coils 1–3) 800-MHz HTS insert comprising 96 NI (no insulation) DP coils,each wound with 6-mm wide GdBCO tape. In this paper, afterdescribing the overall 1.3G system, we present innovative designfeatures incorporated in 1.3G: 1) NI winding technique appliedto Coils 1–3 and its adverse effect in the form of charging timedelay; 2) persistent-mode HTS shims; 3) a “shaking” magnet;and 4) preliminary results of Coil 1 operated at 4.2K.

Index Terms—HTS shim coils, inside-notch double-pancake coil,LTS/HTS NMR magnet, SCF shaking magnet

I. INTRODUCTION

IN NMR, the well-known advantages of higher magneticfield are improved resolution and higher sensitivity.This enables the examination of complex molecular sys-tems like proteins in a much shorter time frame, or withsmaller quantities of material. Most solution NMR experi-ments utilize the TROSY e↵ect to optimize the resolutionof the experiments. Initially it was predicted that TROSYexperiments would be optimal at ⇠900MHz. However,more recent experimental data on several proteins indi-cate that the resolution is optimized in the range 1200–1400MHz [1]. In magic-angle-spinning solid-state NMR,the optimal field is simply the highest field available [2].This 1.3-GHz NMR magnet is expected to become asignificant resource for the entire NMR community.

From the outset in 1999 when we proposed a 3-phaseproject to build a high-resolution 1-GHz NMR LTS/HTSmagnet (1G) to NIH [3], our design philosophy for a � 1-GHz NMR magnet is based on the following key decisions:1) a combination of an LTS magnet and an HTS insert; and2) all HTS inserts to be assemblies of double-pancake (DP)coils: a 50-MHz (Phase 1) [4], [5], and 100-MHz (Phase 2)[6]–[9], both of Bi2223 tape. At the beginning of Phase 3of this 1G project, when, upon recommendation by NIH,the frequency goal was raised to 1.3GHz, we decided ona combination of a 700-MHz LTS NMR magnet and a600-MHz HTS insert (H600), 2-nested coils of REBCO

Manuscript received August 12, 2014. This work was supported by theNational Institute of Biomedical Imaging and Bioengineering (NIBIB), andthe National Institute of General Medical Sciences (NIGMS).Y. Iwasa (corresponding author), J. Bascuñán, S. Hahn, J. Voccio, Y. Kim,

T. Lécrevisse, and J. Song are with the MIT Francis Bitter Magnet Laboratory(FBML) of the Plasma Science and Fusion Center (PSFC), 170 Albany Street,Cambridge, MA 02139, USA (email: iwasa@jokaku.mit.edu)K. Kajikawa was a visiting scientist at FBML, 4/2013–3/2014. Currently,

he is at the Kyushu University, Fukuoka, Japan.

(Coil 1) and Bi2223 (Coil 2) [10], [11]. In 2012, after a theft,in late 2011, of a nearly completed H600, two versionswere considered, first a 700-MHz GdBCO-Bi2223 insert(H700 [12] and later the H800) [13]. In December 2012, weadopted a combination of a 500-MHz LTS NMR magnet(L500), already available at FBML, and H800 to completea high-resolution 1.3-GHz LTS/HTS NMR magnet (1.3G).Note that our 1.3G relies on a greater field contribution ofan HTS insert than an LTS magnet: 18.79T vs. 11.74T

II. INNOVATIVE DESIGNS IN H800The following innovative designs are embodied in H800.

NI Winding Technique No-insulation (NI) windingtechnique [14]–[18] is applied to all DP coils in H800. Itse↵ect on Coils 1–3 are discussed later.

Inside-Notch Pancake Coil Generally, the longer theoverall height of a magnet, the better its inherent fieldhomogeneity [19]. Therefore, to compensate H800 which isshorter than the original H600, those DP coils in the H800located at the center region are “inside-notched”—the veryfirst this classic field-homogeneity-enhancing technique isdeployed to HTS DP coils.

Persistent-Mode HTS Shim Coils (Shims) Theroom-temperature bore of a superconducting magnet ismagnetically shielded by the “diamagnetic walls” of itsown coils. To ameliorate field shimming in our 1.3G, wehave been developing a new shimming technique that relieson wide YBCO tape. Specifically, persistent-mode HTSshims [20] will be placed in a narrow annular space betweenthe liquid helium (LHe) bore tube and Coil 1 innermostwinding diameter. This will be discussed later.

“Shaking” Magnet A “shaking magnet” [21]– [28] toreduce the error fields generated by screening-current field(SCF) [29]– [34] will be installed in the 1.3G. A design forour 1.3G based on the performance of a shaking magnet[34] will be presented later.

LHe Re-Condensation To mitigate the rising cost ofLHe, expected to continue for the unforeseeable future, the1.3G, operated at 4.2K in a bath of LHe, will be equippedwith an LHe re-condenser [35].

III. OVERALL SYSTEMThe 1.3G comprises the L500 and H800; its overall to-scale schematic drawing is shown in Fig. 1. The keycomponents of the 1.3G are indicated in the figure: L500;H800; HTS shims, Z1, Z2, X, Y; Bi2223-wound SCF shak-ing magnet. Before discussing NI technique, presenting

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designs of HTS shims, adesign of shaking mag-net, and 4.2-K resultsof Coil 1, we present be-low key parameters ofL500, H800, and Gb-BCO tape, including itsproperties.

Fig. 1. Cross section of 1.3G.

L500 This persistent-mode 500-MHz MRImagnet can be oper-ated in the tempera-ture range 4.2–6K [36].It consists chiefly ofNb3Sn coils. The keyparameters are listed inTable I. In the previousruns, it never quenched.

H800 Table II lists itskey parameters.

GdBCO Each coil iswound with SuperPower GdBCO coated tape: 6-mm wideand 75-µm thick, of which the Hastelloy substrate is 50-

TABLE IL500 (11.74 T)

Operating temperature [K] 4.2–6.0Cold bore for H800 [mm] 237Overall diameter; height [mm] 780; 1422Magnet mass [kg] 1200Magnetic energy @Iop = 246A [MJ] 4.6Temporal stability [ppm/hr] < 0.01Measured field homogeneity [ppm] 0.45**17-mm diameter⇥ 30-mm length.

TABLE IIH800 (18.79 T) IN L500 AT 4.2 K

Parameter Coil 1 Coil 2 Coil 3Frequency/field [MHz/[T]] 369/8.66 242/5.68 189/4.44Ic @77K, self field (sf) [A] > 160B? [T] 4.8 4.6 3.7Ic(B?,4.2K)/Ic(77K,sf) > 2.3 > 2.3 > 2.7Operating current/density [A]/[MA/m2] 251.3/546.9Total # DP coils (notched) 26 (6) 32 (8) 36 (8)# turns/pancake 185.1 121 95# turns/notched pancake 176.6 118 93Winding i.d. [mm] 91.0 150.7 195.9Winding i.d. (notch) [mm] 92.4 151.2 197.2Winding o.d. [mm] 117.6 167.9 210.1Windingn overall height [mm] 323.7 392.1 465.7Notched section height [mm] 74.7 122.5 98.0SS overband radial build [mm] 7 5 3GdBCO length/DP [m] 121.9 121.5 121.8GdBCO length/notch DP [m] 116.7 118.7 119.3Total length/Coil [km] 3.14 3.84 4.61Inductance [H] 2.43 3.08 3.71Peak bending strain [%] 0.060 0.036 0.028Peak magnetic hoop strain [%] 0.41 0.35 0.32Peak total hoop strain [%] 0.47 0.39 0.35Radial strain [%]

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Self-Protecting When a normal zone appears in anNI coil, the azimuthal current in the coil quickly switchesto the adjacent turns to keep the hot spot from overheat-ing: the NI coil is self-protecting. In an L500 quench, whenits current decays over a few minutes, H800 is globallydriven normal by its induced radial current. Even if theH800 absorbs the entire 1.3G magnetic energy of 6.4MJ—highly unlikely—it will be heated only to ⇠280K. Here,this radial current heats the built-in resistive elements dis-tributed throughout the NI winding: it benefits protection.

Charging Delay & Circuit Model When an NI DPcoil is energized, because current also flows radially, thecoil field trails its supply current, characterized by a charg-ing delay time constant, ⌧d, estimable by an equivalentcircuit model. Each jth pancake coil of a DP coil is modeledby a parallel LjRj circuit [14]– [16]. A circuit model for anNI DP coil comprising 2np turns is a 2np-series-connectedLjRj circuit. Lj and Rj may be lumped into inductanceLdp and resistance Rdp, where Ldp is the coil inductanceand Rdp the sum of 2np Rj [14]– [16]. For an NI magnetof Nm DP coils, its Lm is the magnet inductance and Rmthe sum of Nm Rdp. Thus:

Rm =Nm(2np)Rc

[`mw/Nm(2np)]=

4N2mn2pRc`mw

(1) ⌧d =LmRm

(2)

In Eq. 1, Rc is the turn-to-turn contact resistivity [⌦m2].Figure 3 shows measured ⌧d for 26 DP coils in Coil 1,extracted from the V (I) trace of each DP coil; Coil 1DP coils have an average ⌧d of 31 s. With an averageself inductance of 21mH for these DP coils, we com-pute Rm =26⇥(21mH/31 s)=17.6m⌦, or from Eq. 1Rc =35µ⌦ cm2, agreeing with those of other GdBCOpancakes [13], and ⌧m =138 s (Eq. 2) for Coil 1. For Coils 2and 3, we use the sameRc =35µ⌦ cm2 and applyEqs. 1 and 2 to computeRm and ⌧m—see Table IIIfor Nm, np, `m. ComputedRm and ⌧m for Coils 2 and3 are respectively, 9.1m⌦and 6.1m⌦, and 624 s and603 s. We estimate that itwill take ⇠1 hr to energizeH800 to 251.3A.

Fig. 3. ⌧d for Coil 1 26DP coils.

V. HTS SHIMS: Z1, Z2, X, Y FOR 1.3GFor a shim placed outside of an HTS magnet, besides beingat a great distance from the magnet center, more cruciallyits field is attenuated and distorted by the diamagnetic wallof the magnet [20]. Because H800 represents a diamagneticwall, superconducting shims must be placed in an annularspace inside its Coil 1 bore, where the field is 30.5T: onlyshims of HTS and a thin radial build are viable. We havedeveloped such HTS shims cut from a wide (currently46mm, and later 100mm for 1.3G) YBCO tape, 80-µmthick overall with a 1-µm thick YBCO film.

Primarily due to a very limited space available to thesethin HTS shims (each ⇠1-mm overall thick), they are not

expected to be the only field shimming technique to makethis 1.3G high-resolution. The HTS shims, instead, areto complement conventional RT and ferromagnetic shims.Also, because they themselves generate error fields, theymust be optimized to enhance its benefits and minimizetheir error field. Fig-ure 4 shows drawingsof ideal (zero thick-ness) Z1 (a) and X (b)shims, possible withwide YBCO tape. Thedrawings show properdimensions in termsof the shim radius, a.The 1.3G will haveZ1, Z2, X, Y shims inthe radius range 41–43mm, i.e., each witha 1-mm radial build.

(a) (b)

Fig. 4. Ideal (a) Z1; (b) X shims.

VI. ”SHAKING” MAGNET FOR 1.3GFor a > 1-GHz NMR magnet, like our 1.3G, that mustincorporate an HTS insert, screening-current field (SCF),equivalent to magnetization, is a major error field [29]–[33]. Although SCF error field is much less serious withLTS magnets than with HTS magnets, a remedy to removean SCF error field, proposed in 1982 for LTS magnets[21]– [23], also applies to HTS magnet [24]– [28]. Thelargest SCF error field occurs in the top and bottom endregions of a magnet, where the radial fields, applied andself field, are greatest and the e↵ective superconductorsize approaches the tape width, i.e., 6mm for H800. The± screening currents flow in the ± azimuthal directions,separated by ⇠ the tape width. The basic idea is to apply asmall time-varying ± axial field, and repeatedly (“shake”)force the SC in the ± radial directions, gradually de-pin and wipe out the SCF [26]. Using this shaking fieldtechnique, we performed an experiment [34] to confirmthat the technique would be applicable to reduce SCFerror fields from H800. Figure 5 shows a shaking field timefunction, Bsh(t), which is a series of full triangle waves.

Fig. 5. Time function of shaking magnetic field.

The key important results from our experiment are thatSCF error field at the magnet center decreases with: 1) thenumber of cycles; and 2) Bsh amplitude. Equally impor-tant is that this decrease in SCF error field is not due to AClosses. We demonstrated this important independency onAC losses by varying shaking field frequency and showingthat for a given Bsh amplitude, the error field decreasesonly with number of cycles.

Table IV lists key parameters of a shaking magnet for 1.3G.The shaking magnet will be wound with Bi2223/stainless

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TABLE IVKEY PARAMETERS OF SHAKING MAGNET FOR 1.3G

M C1 C2 C3 C4Winding 2a1 (i.d.) [mm] 600Winding 2a2 (o.d.) [mm] 602.1600.7 603.5 600.7 600.7b1 [mm] �48.348.3 108.2 158.9 320.0b2 [mm] 48.3 108.2 158.9 320.0 407.5# turns/layer; # layers 21; 313; 1 11; 5 35; 1 19; 9Total conductor length [m] 1160Magnet inductance [mH] 126Bsh @Iop = 98 A [mT] 60Bsh field error @Iop [%] < 0.3 (500-mm DSV)One wave cycle period [hr] 4 (= 1" +1# +1" +1#)Shaking period [day] ⇠17 [= (4 hr/cycle)⇥100 cycles]

steel tape, overall 4.3-mm wide and 0.31-mm thick, manu-factured by Sumitomo Electric. Figure 6 shows computedSCF axial field vs. axial distance plots from Coils 1–3at 30.5T, before and after a shaking field of 60mT isapplied. Although an amplitude of 60mT (by Coil 1) is2000 ppm of 30.5T, because the SCF fields are symmetricabout the midplane, their contributions to error fields arezero. However, in reality, a 2000-ppm raw SCF field maygenerate an error field of ⇠200 ppm, which may be wipedout by a shaking field of 60mT, resulting in a total SCF-error field of ⇠20 ppm. For the NI H800, a full triangularwave period will be 4 hr (4 ramps, each 1-hr long). For 100cycles, a shaking period will last 400 hours or ⇠17 days.

Fig. 6. Computed axial Coils 1–3 SCF plots vs. axial distance at30.5 T before and after a ±60mT shaking field (Table IV)

VII. OVERALL FIELD SHIMMING FOR 1.3G

Figure 7 shows a schematic drawing of a field shimmingstrategy to be deployed to 1.3G to make its field suitablefor a high-resolution NMR magnet. The LTS (NbTi) shimsare built into L500 and make L500 by itself high-resolution.The SCF shaking magnet cuts down the H800 SCF errorfields to ⇠20 ppm. Next, the persistent-mode HTS shims(Z1, Z2, X, Y) will bring it to < 10 ppm. Final shimmingwill be achieved with a combination of RT shims andferro shims, making 1.3G high-resolution, i.e., error fields< 0.1 ppm over a 10-mm DSV.

Fig. 7. 1.3G field shimming.

VIII. TEMPORAL FIELD STABILITYThe H800 will be in driven mode, powered by a stable sup-ply. A frequency-locking field-stabilizing technique enableda driven-mode NMR magnet [35] achieve a temporal fieldstability of 1-GHz LTS/HTSNMR magnets now under development takes advantageof the enabling technology of HTS. Its share, by H800,is 61.5% of 30.5T. We believe that this trend of an HTSinsert doing more heavy lifting in the future > 1.3GHzNMR magnets is inevitable. Thus, it is more criticalto further develop innovative field-shimming techniques,some of which, to be applied to 1.3G, were reported here.

ACKNOWLEDGMENTWe thank the NIBIB and NIGMS of the National

Institutes of Health for support of this 1.3G project. Gwen-dolyn V. Gettli↵e (MIT) and FBML visiting scientists,Dr. Yong Chu (National Fusion Research Institute, SouthKorea) and Prof. Daisuke Miyagi (Tohoku University,Japan), contributed to the shaking magnet experiment.We also thank Julio Colque and Peter Allen for theirassistance, and AMSC for supply of wide YBCO tape.

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REFERENCES

[1] Gerhard Wagner (Harvard Medical School; personal communication,2008, 2014)

[2] Robert G. Griffin (MIT; personal communication, 2008).[3] Y. Iwasa, “Low and High Temperature superconducting NMR magnet,”

R01-RR15034-01, NIH (1999).[4] Juan Bascuñán, Emanuel Bobrov, Haigun Lee, and Yukikazu Iwasa, ”A

low- and high-superconducting (LTS/HTS) NMR magnet: design andperformance results,” IEEE Trans. Appl. Superconduc. 13, 1550(4pp) (2003).

[5] Haigun Lee, Juan Bascuñán, and Yukikazu Iwasa, “A high-temperaturesuperconducting (HTS) insert comprised of double pancakes for an NMRmagnet,” IEEE Trans. Appl. Supercond. 13, 1546 (4pp) (2003).

[6] Juan Bascuñán, Wooseok Kim, Seungyong Hahn, Emanuel S. Bobrov,Haigun Lee, and Yukikazu Iwasa, “An LTS/HTS NMR Magnet Operatedin the range 600–700MHz,” IEEE Tran. Appl. Superconduc. 17,1446 (4pp) (2007).

[7] Seung-yong Hahn, Juan Bascuñán, Woo-Seok Kim, Emanuel S. Bobrov,Haigun Lee, and Yukikazu Iwasa, “Field mapping, NMR lineshape, andscreening currents induced field analyses for homogeneity improvementin LTS/HTS NMR magnets,” IEEE Tran. Appl. Superconduc. 18,858 (4pp) (2008).

[8] S. Hahn, J. Bascuñán, H. Lee, E.S. Bobrov, W. Kim, and Y. Iwasa,“Development of a 700MHz low-/high-temperature superconductor fornuclear magnetic resonance magnet: Test results and spatial homogeneityimprovement,” Rev. Sci. Instrum. 79, 026105 (3pp) (2008).

[9] Seung-yong Hahn, Juan Bascuñán, Haigun Lee, Emanuel S. Bobrov,Wooseok Kim, Min Cheol Ahn, and Yukikazu Iwasa, “Operation andperformance analyses of 350 and 700MHz low-/high-temperature su-perconductor nuclear magnetic resonance magnets: A march towardoperating frequencies above 1GHz,” J. Appl. Phys. 105, 024501 (8pp)(2009).

[10] Seungyong Hahn, Juan Bascuñán, Weijun Yao, and Yukikazu Iwasa,“Two HTS Options for a 600 MHz Insert of a 1.3 GHz LTS/HTS NMRMagnet: YBCO and BSCCO,” Physica C: Superconductivity 470,1721 (6pp) (2010).

[11] Juan Bascuñán, Seungyong Hahn, Dong Keun Park, Youngjae Kim,and Yukikazu Iwasa, “On the 600 MHz HTS insert for a 1.3 GHzNMR magnet,” IEEE Trans. Appl. Superconduc. 22, 4302104 (4pp)(2012).

[12] Juan Bascuñán, Seungyong Hahn, Youngjae Kim, and Yukikazu Iwasa,“A new high-temperature superconducting (HTS) 700-MHz insert magnetfor a 1.3-GHz LTS/HTS NMR magnet,” IEEE Trans. Appl. Super-conduc. 23, 4400304 (4pp) (2013).

[13] Juan Bascuñán, Seungyong Hahn, Youngjae Kim, Jungbin Song, andYukikazu Iwasa, “18.8-T/90-mm All-GdBCO Insert for a 1.3 GHzLTS/HTS NMR Magnet: Design and Double-Pancake Coil Fabrication,”IEEE Trans. Appl. Supercond. 24, 4300904 (4pp) (2014).

[14] Seungyong Hahn, Dong Keun Park, Juan Bascuñán, and Yukikazu Iwasa,“HTS pancake coils without turn-to-turn insulation,” IEEE Trans. Appl.Superconduc. 21, 1592 (4pp) (2011).

[15] S. Hahn, D.K. Park, J. Voccio, J. Bascuñán, and Y. Iwasa, “No-insulation(NI) HTS inserts for >1GHz LTS/HTS NMR magnets,” IEEE Trans.Appl. Superconduc. 22, 4302405 (5pp) (2012).

[16] X. Wang, S. Hahn, Y. Kim, J. Bascuñán, J. Voccio, H. Lee, and Y. Iwasa,“Turn-to-turn contact characteristics for an equivalent circuit model of no-insulation Re[RE]BCO pancake coil,” Supercond. Sci. Technol. 26,035012 (6pp) (2013).

[17] Seungyong Hahn, Youngjae Kim, Jiayin Ling, John Voccio, DongkeunPark, Juan Bascuñán, Hyun-Jin Shin, Haigun Lee, and Yukikazu Iwasa,“No-insulation coil under time-varying conditions: charging delay andmagnetic coupling,” IEEE Trans. Appl. Supercond. 23, 4601705(5pp) (2013).

[18] Seungyong Hahn, Youngjae Kim, Dong Keun Park, Kwangmin Kim,John P. Voccio, Juan Bascu-ñán, and Yukikazu Iwasa, “No-insulationmulti-width winding technique for high temperature superconductingmagnet,” Appl. Phys. Lett. 103, 173511 (3pp) (2013).

[19] Yukikazu Iwasa, Case Studies in Superconducting Magnet2nd Edition (Springer, New York, 2009).

[20] Yukikazu Iwasa, Seungyong Hahn, John Voccio, Dong Keun Park,Youngjae Kim, and Juan Bascuñán, “Persistent-mode high-temperaturesuperconductor shim coils: a design concept and experimental results ofa prototype Z1 high-temperature superconductor shim,” Appl. Phys.Lett. 103, 052607 (3pp) (2013).

[21] Kazuo Funaki and Kaoru Yamafuji, “Abnormal transverse-field effectsin nonideal type II superconductor I. a linear array of monofilamentarywires,” Japanese J. Appl. Phys. 21, 299 (6pp) (1982).

[22] Kazuo Funaki, Teruhide Nidome and Kaoru Yamafuji, “Abnormaltransverse-field effects in nonideal type II superconductor II. influ-ence of dimension ratios in a superconducting ribbon,” Japa- neseJ. Appl. Phys. 21, 1121 (6pp) (1982).

[23] Kazuo Funaki, Minoru Noda and Kaoru Yamafuji, “Abnormaltransverse-field effects in nonideal type II superconductor III. a theory foran AC-induced decrease in the semi-quasistatic magnetization parallel toa DC bias field,” Japanese J. Appl. Phys. 21, 1580 (7pp) (1982).

[24] Ernst Helmut Brandt and Grigorii P. Mikitik, “Why an ac mag-netic field shifts the irreversibility line in type-II superconductors,”Phys. Rev. Lett. 89, 027002 (4pp) (2002).

[25] Grigorii P. Mikitik and Ernst Helmut Brandt, “Theory of the longitudinalvortex-shaking effect in superconducting strips,” Phys. Rev. B67,104511 (8pp) (2003).

[26] Ernst Helmut Brandt and Grigorii P. Mikitik, “Shaking of the criticalstate by a small transverse ac field can cause rapid relaxation in super-conductors,” Supercond. Sci. Technol. 17, S1 (4pp) (2004).

[27] Kazuhiro Kajikawa and Kazuo Funaki, “A simple method to eliminateshielding currents for magnetization perpendicular to superconductingtapes wound into coils,” Supercond. Sci. Technol. 24, 125005 (4pp)(2011).

[28] Kazuhiro Kajikawa and Kazuo Funaki, “Reduction of magnetizationin windings composed of HTS tapes,” IEEE Trans. Appl. Super-cond. 22, 4400404 (4pp) (2012).

[29] C. Gu, T. Qu, and Z. Han, “Measurement and calculation of residualmagnetic field in a Bi2223/Ag Magnet,” IEEE Trans. Appl. Super-conduct. 17, 2394 (4pp) (2007).

[30] Seungyong Hahn, Juan Bascuñán, Wooseok Kim, Emanuel S. Bobrov,Haigun Lee, and Yukikazu Iwasa, “Field Mapping, NMR lineshape, andscreening currents induced field analyses for homogeneity improvementin LTS/HTS NMR magnets,” IEEE Trans. Appl. Supercond. 18, 856(4pp) (2008).

[31] Naoyuki Amemiya and Ken Akachi, “Magnetic field generated byshielding current in high Tc superconducting coils for NMR magnets,”Supercond. Sci. Technolo. 21, 095001 (7pp) (2008).

[32] Min Cheol Ahn, Tsuyoshi Yagai, Seungyong Hahn, Ryuya Ando, JuanBascuñán, and Yukikazu Iwasa, “Spatial and temporal variations of ascreening current induced magnetic field in a double-pancake HTS insertof an LTS/HTS NMR magnet,” IEEE Tran. Appl. Superconduc. 19,2269 (4pp) (2009).

[33] Yoshinori Yanagisawa, Hideki Nakagome, Davide Uglietti, TsukasaKiyoshi, Ruixin Hu, Takuya Takematsu, Tomoaki Takao, Masato Taka-hashi, and Hideaki Maeda, “Effect of YBCO-Coil Shape on the ScreeningCurrent-Induced Magnetic Field Intensity,” IEEE Trans. Appl. Super-cond. 20, 744 (4pp) (2010).

[34] Kazuhiro Kajikawa, Gwendolyn V. Gettliffe, Seungyong Hahn, YongChu, Daisuke Miyagi, and Yukikazu Iwasa, “Design and tests of com-pensation coils to reduce screening currents induced in HTS coil for NMRmagnet,” In this conference.

[35] Y. Yanagisawa, H. Nakagome, K. Tennmei, M. Hamada, M. Yoshikawa,A. otsuka, M. Hosono, T. Kiyoshi, M. Takahashi, T. Yamazaki andH. Maeda, “Operation of a 500 MHz high temperature superconduct-ing NMR: towards an NMR spectrometer operating beyond 1 GHz,”J. Magn. Reson. 203, 274-282 (8pp) (2010).

[36] J. Bascuñán, S. Hahn, M. Ahn and Y. Iwasa, “Construction and Test of a500MHz/200mm RT Bore Solid Cryogen Cooled Nb3Sn MRI Magnet,”Adv. Cryogenic Tech. 55A, 523 (8pp) (2010)

[37] K. Kasaba, K. Katagiri, Y. Shoji, T. Takahashi, K. Watanabe, K. Noto,K. Goto, T. Saito, and O. Kono, “Stress/strain dependence of crit-ical current in Nb3Sn superconducting wires stabilized with CuNbmicrocomposites—effect of Nb content,” Cryogenics 41, 9 (6pp) (2001).

[38] J. Lu, E.S. Choi, and H.D. Zhou, “Physical properties of Hastelloy�R c-267TM at cryogenic temperatures,” J. Appl. Phys. 103, 064908 (6pp)(2008).

[39] R.P. Reed and A.F. Clark, Materials at Low Temperatures,American Society for Metals (Metals Park, Ohio, 1983).

[40] D. Hazelton, “Application of SuperPower 2G HTS wire to high fielddevices,” 22 nd International Conf. Magnet Tech. (MT-22), (2011).

[41] hhtp:/www.k-mac-plastics.net/data%20sheets/fiberglass technical data.htm.

[42] Thibault Lécrevisse, Juan Bascuñán, Seungyong Hahn, Youngjae Kim,Jungbin Song, and Yukikazu Iwasa, “Pancake-pancake joint resistancesof a magnet assembled from GdBCO double-pancake coils,” In thisconference.

JA15-35-IEEE2015-1.3G-Iwasa-PSFCReport-CoverSheet-151204JA-15-35 4LOr2A03-Iwasa-141013Final