The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Development of 7T Superconducting Wiggler Magnet- Manufacture of Reinforced Nb3Sn Coil and Experiment with a Cooling Structure Tsutomu KURUSU, Tsukasa WADA, Koji ITO, Yasutsugu MORII, Hideaki MAEDA,Masami TORIKOSID*, Koji NODA*, Masayuki KUMADA* and Satoru YAMADA*Toshiba Corporation
4-1 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan*National Institute of Radiological Sciences
4-9-1 Anagawa, Inage, Chiba 263-8555, JapanAbstract
A 7T nine-pole wiggler is a key component of thecompact synchrotron light source which National Instituteof Radiological Sciences (NIRS) is planning. In order todevelop the compact wiggler, the authors have developed
an alumina-Cu reinforced Nb3Sn coil whose tensile
strength tolerance is almost double that of conventional
Nb3Sn coils, and a cooling structure which could reduce
refrigerator power to half that required for conventional
cryocooler magnets. In the present paper, we introduce thedesign a manufactured coil and report experimental results
respecting the cooling structure.

buffer cools superconducting coils by heat conduction, is tobe adopted for the wiggler. A schematic diagram of thestructure is shown in Fig. 2. As shown in the diagram,compared with a conventional cryocooler cooled type, thecooling structure has an advantage in terms of powersaving refrigerator because latent heat of helium isavailable for AC loss of coils. In addition, the coil gap canbe shortened because the proposed structure is simpler thanthat of a conventional helium bath filled type.

4K-GM refri2'erator: 2 W

l Introduction

NIRS proposes a compact system for medicaldiagnosis using synchrotron orbital radiation, intravenous
coronary angiography, monochromatic X-ray computer
tomography and so on [I][2][3]. Toshiba is collaboratingwith NIRS on blueprinting of the system and developing
devices for it [4]. A key component of the system is asuperconducting multipole wiggler with nine poles and amaximum field of 7T. Fig. I shows a schematic view of thewiggler. It is compact and a new cooling structure, in which
GM refiigerators cool a liquid helium buffer and then the4K-GM refrigerator

r.imJid helium
conduction"frAC loss of coils: 4 W( Transient load )Sunerconduct.in2' coils

Fig. 2 Schematic diagram of a new cooling structure of 7T ninepole wiggler.
In order to develop the compact 7T nine-polewiggler, the authors developed an alumina-Cu reinforced
Nb3Sn coil whose tensile strength tolerance is almost
double that of conventional Nb3Sn coils, and thenperformed an experiment respecting the cooling structure.

2 Coil Design

2.1 Reinforced Nb3Sn CoilBeam chambec
Fig. I Schematic view of the 7T nine-pole wiggler (a crosssection through the vertical plane along the magnet axis)

Since a wide beam chamber is required for the 7Tnine-pole wiggler, a coil gap is designed in consideration ofa support structure, besides Nb3Sn is adopted as asuperconductor in order to give a compact wiggler design.

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The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

The superconducting coils of the wiggler are required tohave high mechanical strength, since a result of ourpreliminary study indicates that a transient stress would be
too severe for conventional Nb3Sn coils to withstand if thecoils were quenched.
Therefore, the authors developed a Nb3Sn wire
reinforced by alumina-Cu in corporation with The
Furukawa Electric Co., Ltd. The wire's tensile stress at
0.3% strain is 270MPa, a strength almost double that ofconventional Nb3Sn wire. The specification of the wire isgiven in Table 1.
The manufactured coil has a racetrack shape. Its
winding is graded into two sections and impregnated by anepoxy. The specifications of the coil and the wiggler aregiven in Table 2 and Table 3, respectively.
Table 1 Specification of reinforced Nb3Sn wire
Gl~typeG2-typeSuperconductor
Size Thickness
WidthFilament number
Matrix ratio
MatrixCritical current at l2T

We are currently preparing an experiment to demonstrate
the coil's performances. We are also preparing fabricationof the 7T three-pole wiggler as a prototype of a nine-pole
wiggler using the coil.

2.2 AC loss and Quench Simulation
AC loss
AC loss of the coil, charged up to 7T for 20
minutes, is estimated by a model [5][6]. The result isshown in Fig. 3. In the model calculation, the criticalcurrent density; Jc [Nm2], of Nb3Sn is approximated by
the following equation whose coefficients are determinedto fit the actual measurement.
Jc(8)=5.7 X 109(8-0 5 -7.5 X 10"28°·5+1.4 X 10.38u)(1)
Here 8 represents magnetic field in Testa. As shown in thefigure, there is a rapid drop at the beginning and it is foundthat the loss at the end is almost a third of mean value.

(Nb,Ti)3Sn
l.15mm
0.8mm
L68mm
l.25mm
19,000--o-- hysteresis loss

0.90.8----&--coupling loss

0.7l.O[-<>--total AC loss

0.6.,

Alumina-Cu, OFC
430A
240A

..9 0.5- - - - - - - mean value of total loss~ 0.4
0.3
0.2

..

'l.l'';t';$.'\l''.t.l'1.'~·:a.•••.:•u.•v•IJ.•v•.u•:a.•u:..e.·~·.,•u.•"~:•.u•\.•·~·&.•'\U.•~o.".at'&.'I.&.''''Y-'~·u.•v•

0.1

Table 2 Specification of the reinforced Nb3Sn coil
Inner radius at round portion
28mm
Outer radius at round portion
96mm
Length of straight portion
150mm
Width195mm
Height157mm
Rated current
208A
Maximum field
9.5T
Inductance
5.4H/coil

Table 3 Specification of the 7T nine-pole wiggler
Designed field on beam line
7.0T
Period length21 OmmCoil gap
Field integral S B dz
Relative field error
Beam stay clear aperture verticalhorizontal

66mm<lmTm<0.5%±5mm±IOmm

0050100Current [A)

150200Fig. 3 Estimated AC loss of the reinforced Nb3Sn coil

Quench Simulation
In order to investigate behavior of coil quenching,a numerical analysis of quench in the 7T nine-pole wiggler
has been carried out. The results are shown in Fig. 4. The
figure shows transition of coil current when a CoilA_upper
is quenched. Here CoilA_upper represents the upper coil ofthe center pole and it consists of a pole with CoilA_lower.
Coil8_upper/lower is the next pole to CoilA_upper/lower
and
CoilC_upper/lower isthenextpoletoCoil8_upper/lower. As shown in the figure, it is estimatedthat only the coil opposite the quenched coiL CoilA_lower,
would be quenched by magnetic induction. Then themaximum temperature of the quenched coil is estimated to
be about 95K. Moreover, employing the time constant of
current decay for the post-analysis, the internal voltage
inside the quenched coil is estimated to be about 1.8kV-332-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999
250
7250

200200~150.....c:~

6 100-o-coiiB_uppor-CoilB_Iowcr

5050-.fr-CoiiC_uppor-.fr-CoiiC_Iowet

000

0.1

0.3

0.2

0.4Fig. 4 Transition of coil current when CoilA_upper quenched.

3000

04000

5 SummaryWe have developed an alumina-Cu reinforced
Nb3Sn coil and examined a new cooling structure in orderto develop a 7T nine-pole wiggler. Details will be presented
at the conference.
Acknowledgement
The authors are grateful to the staff of The
Furukawa Electric Co., Ltd for their work in developing thereinforced Nb3Sn wire.

4K-GM refrigerator

Fig.5 Experimental apparatus

2000

Fig. 6 Transition of coil temperature dwing charge of the coil

3 Cooling Structure
Fig. 5 shows the experimental apparatus which
was prepared in order to demonstrate the cooling structure
and obtain data. The experiment was carried out using aNb3Sn coil whose shape is as same as that of the reinforced
coil. The experimental result is shown in Fig. 6. The figure
shows that temperature rise of the coil is suppressed byLHe buffer when the coil is charged or discharged. In otherwords, the effect of the power saving respecting therefrigerator has been confirmed.

Nb3Sncoil

1000

Time [s]Time after CoilA_upper quenched [s]LHebuffer"----~---~----"-----'

0References[1] M.Torikoshi et ai.,"Design of a Compact SynchrotronLight Source for Medical Applications at NIRS", J.
Synchrotron Rad. (1998) 5(2] M.Torikoshi et ai.,"A Plan of Synchrotron LightSource Dedicated to Medical Applications at NIRS",
Proc. of the 1st Asian Particle Accel. Conf, Tsukuba,Japan (1998)(3] M.Torikoshi et ai.,"Conceptual Design of aSynchrotoron Light Source Used for Medical
Diagnoses at NIRS",The Int. Symp. on Optical Sci.,
Eng., and Inst., Denver, USA (1999)[4] ToshibaReview(inJapanese),( l999) I[5] L.T.Summers, "A Model for the Prediction ofNb3Sn
Critical Current as a Funchtion of Field, Temperature,
Strain, and Radiation Damage "IEEE Trans. Magn.,
vol27, No2 (1991)[6] M.N.Wilson, "Superconducting Magnets", Oxford,(1983)-333-