4
Fig. 1. Screen display of pickup coil readout at full current. * Corresponding author. Fax: #904-644-0867. E-mail address: bird@magnet.fsu.edu (M.D. Bird). Physica B 294}295 (2001) 639}642 The 45 T hybrid insert: recent achievements M.D. Bird*, S. Bole, I. Dixon, Y.M. Eyssa, B.J. Gao, H.J. Schneider-Muntau National High Magnetic Field Laboratory, 1800 E/ Paul Dirac Drive, Tallahassee, FL 32306, USA Abstract The NHMFL hybrid magnet was successfully tested to 45.1 T in an air bore as designed on June 26, 2000. The magnet consists of a cable-in-conduit superconducting outsert producing 14.3 T in a 616 mm bore and a Florida-Bitter resistive insert providing 30.8 T in a 32 mm bore. The insert was tested without the outsert in May 1999. The combined system was tested in December 1999 reaching a peak "eld of 44 T in an air bore. Physics experiments were run in December 1999 at 45 T using dysprosium pole piece #ux concentrators. During the "rst and second quarters of 2000 modi"cations were made to the cryogenic system and the resistive insert. Test results of the resistive insert from December 1999 to June 2000 are presented along with a discussion of the possibilities of upgrading the insert to reach a total "eld of 50 T. Scienti"c experiments are scheduled up to 45 T in a clear bore starting July 3, 2000. A spare set of resistive coils is under construction. 2001 Elsevier Science B.V. All rights reserved. Keywords: Hybrid magnet; Florida-Bitter coils 1. Introduction The hybrid magnet at the NHMFL was tested to full "eld on June 26, 2000 and produced an on-axis "eld of 45.1$0.1 T. Fig. 1 shows the screen dis- playing the output of our pickup coil-based "eld measurement. NMR "eld measurements are plan- ned in the near future. The hybrid magnet will be the centerpiece of the NHMFL high DC "eld user facility located in Tallahassee, FL, USA. The facil- ity houses eight high-"eld resistive magnets, numer- ous superconducting magnets, and a substantial amount of supporting equipment [1]. The world's most intense steady-state magnetic "elds are provided by hybrid (part resistive, part superconducting) magnets. The highest "elds in an 0921-4526/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 0 ) 0 0 7 3 4 - 1

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Page 1: The 45 T hybrid insert: recent achievements

Fig. 1. Screen display of pickup coil readout at full current.*Corresponding author. Fax: #904-644-0867.E-mail address: [email protected] (M.D. Bird).

Physica B 294}295 (2001) 639}642

The 45T hybrid insert: recent achievements

M.D. Bird*, S. Bole, I. Dixon, Y.M. Eyssa, B.J. Gao, H.J. Schneider-Muntau

National High Magnetic Field Laboratory, 1800 E/ Paul Dirac Drive, Tallahassee, FL 32306, USA

Abstract

The NHMFL hybrid magnet was successfully tested to 45.1T in an air bore as designed on June 26, 2000. The magnetconsists of a cable-in-conduit superconducting outsert producing 14.3T in a 616mm bore and a Florida-Bitter resistiveinsert providing 30.8T in a 32mm bore. The insert was tested without the outsert inMay 1999. The combined systemwastested in December 1999 reaching a peak "eld of 44T in an air bore. Physics experiments were run in December 1999 at45T using dysprosium pole piece #ux concentrators. During the "rst and second quarters of 2000 modi"cations weremade to the cryogenic system and the resistive insert. Test results of the resistive insert fromDecember 1999 to June 2000are presented along with a discussion of the possibilities of upgrading the insert to reach a total "eld of 50T. Scienti"cexperiments are scheduled up to 45T in a clear bore starting July 3, 2000. A spare set of resistive coils is underconstruction. � 2001 Elsevier Science B.V. All rights reserved.

Keywords: Hybrid magnet; Florida-Bitter coils

1. Introduction

The hybrid magnet at the NHMFL was tested tofull "eld on June 26, 2000 and produced an on-axis"eld of 45.1$0.1T. Fig. 1 shows the screen dis-playing the output of our pickup coil-based "eldmeasurement. NMR "eld measurements are plan-ned in the near future. The hybrid magnet will bethe centerpiece of the NHMFL high DC "eld userfacility located in Tallahassee, FL, USA. The facil-ity houses eight high-"eld resistive magnets, numer-ous superconducting magnets, and a substantialamount of supporting equipment [1].The world's most intense steady-state magnetic"elds are provided by hybrid (part resistive, partsuperconducting) magnets. The highest "elds in an

0921-4526/01/$ - see front matter � 2001 Elsevier Science B.V. All rights reserved.PII: S 0 9 2 1 - 4 5 2 6 ( 0 0 ) 0 0 7 3 4 - 1

Page 2: The 45 T hybrid insert: recent achievements

Fig. 2. Layout of the hybrid insert coils and housing.

air bore reported by other labs include: 37.3TTsukuba, Japan [2]; 35.2T Cambridge, USA [3],31.4T Grenoble, France [4]; and 31.1T Sendai,Japan [5]. The NHMFL hybrid provides 20%greater #ux density than the greatest of these othermagnets and does it with a unique clear top [6].The NHMFL hybrid consists of a 2372mm OD,

616mm ID, 14.3T superconducting outsert [7] anda 610mm OD, 32mm ID, 30.8T resistive insert.The insert consists of "ve concentric Florida-Bittercoils labeled A1, A2, B, C and D from the insideout. Details of the insert design are presented inRef. [6]. Fig. 2 shows the layout of the insert coilsand housing.

2. May 1999 insert testing

Assembly of the NHMFL hybrid insert was ini-tially completed in May 1999 and the insert wastested to full "eld without the outsert. Results arepresented in Ref. [6].

3. December 1999 combined system testing

The outsert coils, cryostat, power supplies, con-trol systems, etc., were completed in December1999 and the combined system was run to a peakon-axis "eld of 44 T in a clear bore on December 11,1999. We compared the resistances of the resistivecoils operating in the presence of the background"eld to those without the background "eld. For theA and B coils there was an increase in resistancethat approaches 2% at high "eld. Coils C and Dexhibit substantially higher deviation, 3% for coilC and 3.5% for coil D. Another run later in the dayshowed a deviation in coil D as high as 6.5%.Users were allowed to run for two days limited to

40.0T from the electromagnet plus 3.0 T from dys-prosium #ux concentrators. One run was made toan applied "eld of 42T (45T with the #ux concen-trators). Physics results from the December 1999operations are reported elsewhere [8] as is theperformance of the superconducting outsert [9].On December 13, 1999 the magnet was shut downto modify the cryogenic system and the resistiveinsert.

4. Modi5cation of resistive insert

When the insert housing was opened, we noticedthe insert coils had undergone a rigid-body rota-tion with respect to the insert housing and the out-sert.When we disassembled coil D, we saw that the

second disk from the top end of the coil had shifted(radially) outward enough to block the coolingholes below it. This caused overheating of neigh-boring conductors and insulators. Also, the tie rodswere bent at the bottom end resulting from thesubstantial magnetic torque about the coil's axis.When we disassembled the C coil, we again dis-covered bent tie rods at the bottom end but bentin the opposite direction. We also directed a high-intensity light through the cooling holes of the

640 M.D. Bird et al. / Physica B 294}295 (2001) 639}642

Page 3: The 45 T hybrid insert: recent achievements

Fig. 3. Coil D original mid-plane cooling hole pattern (left) andnew end turn cooling hole pattern (right).

Fig. 4. Resistance deviation: comparison of resistance with andwithout the background "eld, June 2000.

various coils and discovered that the A1 coil ap-peared to have several blocked cooling passages.To prevent the coils from shifting inside the hous-

ing in the future, a new housing liner was designedand built from glass-epoxy that "ts tighter and issti!er than the previous PVC liner. In addition, theinsulating cylinders between the coils were modi-"ed to have ribs on both the inner and outer dia-meters to help with alignment.To prevent torsion of the coils, the housing and

internal structure were modi"ed such that each endof each coil is connected (pinned) to the housing.Slipping of the end disks of coils has been seen

in many of the hybrid inserts built previously. Thestandard solution is to reduce the current density ofthe end turns [10,11]. We used the ANSYS "nite-element software package to model �

��of a disk

(15 disks per turn in the coil) as being clamped onone end and free on the other and applied theLorenz forces. We computed that the displacementof this cantilevered beam can be several millimeters.By decreasing the current density at the end of thecoil and changing the shape of the cooling holes inthe end turn (double the width while reducing thelength) as shown in Fig. 3, we can obtain greaterthan an order of magnitude decrease in displace-ment in this model.

5. May 2000 combined system testing

Modi"cations of the end turns of the C andD coils and installation of the coils back into the

housing was completed on June 5, 2000. Modi"ca-tions to the cryogenic system and cooldown of theoutsert were completed in late June and the com-bined system was run to 45.1T on June 26, 2000.(45.1749T corrected for linear drift of pickup coilintegrator.) Again we can compare the resistance ofthe insert with and without the background "eld.Results are presented in Fig. 4.We see that all four coils behave similarly with

roughly 2% higher resistance at 67.1 kA with thebackground "eld than without. After testing, thecoils were removed, examined and re-installed. Itappears that the modi"cations to the C and D coilswere e!ective.

6. 50T upgrade

Within the next few years, we intend to upgradethe insert to allow operation at 50T. Towards thatend, we have performed "nite-element analyses ofthe mid-plane mechanical behavior at insert cur-rents as high as 77.6 kA. Such a design processrequires bilinear (elastic}plastic) mechanics. Thepeak strains at the mid-planes of the coils accord-ing to our calculations are located at the tie rodholes and are presented in Table 1. We have madetensile fatigue specimens both parallel and perpen-dicular to the rolling direction from the sheet metal

M.D. Bird et al. / Physica B 294}295 (2001) 639}642 641

Page 4: The 45 T hybrid insert: recent achievements

Table 1Peak strain in insert coils at 50T per ANSYS bilinear model& experimental fatigue life at 120% of 50T stress

A1 A2 B C D

Strain (%) 4.4 4.0 2.4 5.1 4.2Cycles 4065 4471 9092

7645 7995 9877

used for coils B, C and D. The samples were fatigueloaded in tension such that the stress near the tierod holes was equal to 120% of what is expectedunder 50 T operation (10% reduction of strengthat operating temperature, 10% safety factor). Themaximum and minimum lifetime of the varioussamples is also reported in Table 1.We have also recently performed bilinear ana-

lysis of the strain in some of our other magnets thathave been operating reliably for years. Both ourfatigue testing and our operating experience in-dicate the stress at the mid plane should accom-modate 50T operation. We have also performedour end turn analyses at 50 T. These calculationsindicate that we may need a few more minor modi-"cations to the ends of the coils to reach 50Treliably. We intend to push our 33T, 17 MW mag-nets toward 36T over the next few years. In theprocess, we will develop the technology to extendour hybrid insert to 50T.

7. Conclusion

The NHMFL hybrid is complete and stable op-eration has been demonstrated at 45T. We arecurrently building a spare set of coils for the resis-tive insert. We intend to allow users unlimited time

at 40T and limited time at 45T until the spare coilsare complete. Once spare coils are available, weintend to provide unlimited time at 45T. Presentlythere are roughly 40h of user time scheduled foreach of the weeks of July 3, July 10, July 31, andAugust 7, 2000. Within the next few years, weintend to increase the operating "eld to 50T.

Acknowledgements

The authors are very indebted to the manypeople at the NHMFL and elsewhere who assistedin design, construction and testing of the hybridinsert magnet, principally S. Gundlach, W. Lo!el-bein, J. O'Reilly, J.F. Payne, G. Tanacs and W.Walker. This work was supported by the State ofFlorida and the National Science Foundationthrough NSF Cooperative Grant No. DMR9016241.

References

[1] www.magnet.fsu.edu/users/facilities/dc"eld.[2] T. Asano et al., in these Proceedings (RHMF 2000),

Physica B 294}295 (2001).[3] Y. Iwasa et al., IEEE Trans. Magn. 30 (1994) 2162.[4] H.-J. Schneider-Muntau, IEEE Trans. Magn. 24 (1988)

1041.[5] Y. Nakagawa et al., J. Phys. Colloq. 45 (1984) C1.[6] M.D. Bird, et al., IEEE Trans. Appl. Supercond. 10 (2000)

439.[7] J.R. Miller, Applied Superconductivity Conference, Sep-

tember 18}22, 2000.[8] Brooks et al., in these Proceedings (RHMF 2000), Physica

B 294}295 (2001).[9] A. Gavrilin, Y.M. Eyssa, J.R. Miller, Applied Supercon-

ductivity Conference, September 18}22, 2000.[10] R.J. Weggel, private communication to M.D. Bird.[11] M. Ohl et al., IEEE Trans. Appl. Supercond. 3 (1993) 66.

642 M.D. Bird et al. / Physica B 294}295 (2001) 639}642