1080

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006

New Type Superconducting Bulk Magnet by Pulse
Field Magnetizing With Usable Surface on
Both Sides in Open Space
Hiroyuki Fujishiro, Atsushi Fujiwara, Tatsuya Tateiwa, Tetsuo Oka, and Hidemi Hayashi

Abstract—A new-type of magnet system using high- c superconducting bulks has been developed, in which two aligned bulk disks
are cooled down from the side face by thermal conduction and aremagnetized along the -axis in turn employing a split-type pulse
due to the magnetic flux intrusioncoil. The temperature rise
P is enhanced in comis relatively small and the trapped field T
parison with the conventional bulk magnet system based on a soP
lenoid-type pulse coil. T
on thebulk
4mm
surface at 50 K and T
on the vacuum sheath,
4 mm above the bulk surface, have been attained. This type ofmagnet system, consisting of multi-bulks, with usable surfaces onboth sides in open space, can be realized only by use of a split-type
pulse coil and has a potential for new application fields.

1= 3 20 T= 1 97 T

SmBaCuO

Index Terms—Bulk magnet system, high- c bulk superconductor, pulse field magnetizing, split coil, temperature rise,trapped field.

I. INTRODUCTIONFOR THE PRACTICAL applications of a high- superconducting bulk, a high-strength bulk magnet in a magnetic
separation system for waste water etc. is one of the typical models[1]. On magnetizing the bulk, a field cooled magnetizing (FCM)
has been usually used. Recently, a pulse field magnetizing (PFM)
has been investigated and developed because of a compact andby PFM
inexpensive experimental setup. The trapped field
is, however, generally smaller than that attained by FCM due toduring the PFM process. Several
the large temperature riseandapproaches have been performed in order to reduceenhance[2]–[5]. Very recently, we have attained the trappedby the modified multi-pulse techniquefield ofcombined with stepwise cooling (MMPSC) method, which is thepresent highest value by PFM [6].
To realize a high-strength bulk magnet, a high- bulk is usually cooled down below the superconducting transition temperalong the -axis on the cold stage of the helium reature

Manuscript received September 18, 2005. This work was supported in part by
Grant-in-Aid for Scientific Research 17560001 from the Ministry of the Education, Culture, Sports, Science and Technology, Japan and from Iwate Prefecture,
Japan.
H. Fujishiro, A. Fujiwara, and T. Tateiwa are with the Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, Japan (e-mail:fujishiro@iwate-u.ac.jp; t3204017@iwate-u.ac.jp; t.tatei@ezweb.ne.jp).
T. Oka is with IMRA Material R&D Co., Ltd., 5-50 Hachiken-cho, Kariya
448-0021, Japan (e-mail: toka@ai-i.aisin.co.jp).
H. Hayashi is with Kyushu Electric Power Co., Inc., 2-1-47 Shiobaru,
Fukuoka 815-8520, Japan (e-mail: Hidemi_Hayashi/KYUDEN@kyuden.co.
jp).
Digital Object Identifier 10.1109/TASC.2006.871278

frigerator and then magnetized also along the -axis using a solenoid-type coil. In this setup, only one bulk can be utilized for
one refrigerator, and only the upper surface of the bulk can beutilized as a magnetic pole in open space. Oka et al. constructeda multi-bulk magnet system consisting of 7 bulks and attained
1.4 T at the center of pole surface in open space [7]. The bulks
were mounted on the stainless steel disk 150 mm in diameter
and were cooled down to 67 K using a Stirling pulse tube cooler.
The bulks were simultaneously magnetized by FCM from 5 T
using a cryocooled superconducting magnet with bore 300 mm
in diameter. In a similar setup, it is very difficult to magnetize
the multi-bulks by PFM at a time because of the problems ofthe mechanical strength of the supporting parts and capacity ofthe power supply. If a magnet system consisting of multi-bulks
could be easily realized by successive PFM, a new field of industrial application should develop.
In this paper, we propose and test a new-type of the highbulk magnet system, in which two bulk disks are mounted andcooled down from the side face along the -plane, and are magnetized in turn by PFM along the -axis using a split-type pulse
coil. We can effectively use both surfaces of each bulk as magnetic poles in open space, which may be a great merit. We compare with the results of a conventional-type bulk magnet system,
where the bulk is cooled down along the -axis and magnetizedby PFM using a solenoid-type pulse coil.
II. EXPERIMENTAL PROCEDURE
andbulk disks
Highly -axis oriented(by Dowa Mining Co., Ltd.) 46 mm in diameter and 15 mm inthickness were used in this study [5]. The c-axis was perpendicular to the disk surface. The bulk was uniformly impregnatedwith epoxy resin in vacuum, and the epoxy resin layers on thebulk surface were removed in order to promote the thermal response. Fig. 1 shows the experimental setup around the bulks.
Two bulk disks were tightly fastened with the brass-metal bulk
holder from the side face and the brass holder was attached tothe cold stage of a Gifford McMahon (GM) cycle helium refrigerator (AISIN, GR103). This cooling procedure is expected
to reduce the cooling time and the recovering time of temperature after the heat generation by PFM, because the -plane
thermal conductivity
is much higher than the -axis [8].
The adiabatic vacuum cell was of sheath shape with two parallel surfaces situated 4 mm above each bulk surface. The initial
temperature of the cold stage was fixed at 50 K before every
pulse application. The time evolution of temperatures
and the local fieldon thebulk andon1051-8223/$20.00 © 2006 IEEE

FUJISHIRO et al.: NEW TYPE SUPERCONDUCTING BULK MAGNET

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Fig. 1. The experimental setup around the SmBaCuO and YBaCuO bulks
and the split-type coil (“parallel-sheath-type” system). The positions for thetemperature (T 1 T 4) and trapped field (B (C)) measurements on the surfaceof the bulks are shown.

0

thebulk were monitored using the fine chromel-constantan thermocouples and the Hall sensor (F.W.Bell, Model
BHA921) adhered in the respective places. The bulks were mag.A
netized using the split-type pulse coil dipped in liquid
set of soft iron yokes was located at the center of the split-type
coil. The rise time of the pulse field was about 20 ms. The
was determined from the curstrength of the applied field
rent flowing through the coil, which ranged from 3.83 T to 6.41
, 4 mm above the bulk
T. The trapped field distribution
surface, was monitored using an axial-type Hall sensor, which
was scanned on the vacuum sheath stepwise with a pitch of 1.0
bulk, the split-type coilmm. After magnetizing thewas moved parallel and thebulk was magnetized.
Hereafter, we abbreviate this type of new magnet system as a“parallel-sheath-type”. For comparison, we also magnetized thefor various
using a soleSmBaCuO bulk at
noid-type pulse coil, as shown in the inset of Fig. 3, and mea,
and the trapped field. We abbreviate
sured
the magnet system employing the solenoid coil as a “conventional-type”.

0Fig. 2. The time evolution of temperatures T 1 T 4 and the local field B (C)after applying the pulse field of (a) 4.70 T and (b) 6.09 T to the SmBaCuO
bulk using the “parallel-sheath-type” system. The inset shows the trapped field.
distribution B

III. RESULTS AND DISCUSSION

Fig. 3. The time evolutions of temperatures T 1 and T 2 of the SmBaCuO bulk
after applying the pulse field of 4.70 T and 6.09 T using the “conventional-type”
bulk magnet system. The experimental setup around the bulk and the arrangement of the solenoid-type magnet are shown in the inset.

Figs. 2(a) and 2(b) show the time evolutions of temperaturesand local field
after applying thepulse field of 4.57 T and 6.09 T to thebulk, respec.
tively. The inset of each figure shows the distribution of, the
It can be seen that the maximum temperature riseprofile change detime evolution of temperature, and thepending on thevalue. In Fig. 2(a) for,andrise up sharply with a characteristic peak atand then rapidly decrease to finally return toin 10
increases moderately. The rapid
min. On the other hand,rise and sharp peak inandsuggest that the intense
and the viscous loss
heat generation due to the pining loss
takes place in the vicinity of these positions and that there
exists an easy path for the flux motion due to relatively weakerpinning force . The
quickly saturates within 0.2 s,

and the trapped fieldat the bulk center,,andis 2.75 T. In Fig. 2(b) for
all rise up faster with a clear peak and the temperature
increases with increasing
and therise increases.
spatial distribution of the heat generation and thedis.
is 3.10 T.
on thetribution change depending on
bulk increases very slowly.
inis about 1
and slightly increases with increasing.
K for
A part of the heat generated in thebulk transfers tothrough the brass-metal holder.
the neighboring
Using the “conventional-type” bulk magnet system, we measured the time evolution of temperatures and trapped field of thebulk atfor various. Fig. 3
present

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006

T t

T t 0T t
:
:
B

B

t
B

(C)( ) on
4( ) on the YBaCuO bulk and 1( )3( ) and= 5 42 T to the YBaCuO bulk. The
SmBaCuO bulk after applying= 6 09 T and the=
SmBaCuO bulk has already been magnetized by
2 90 T has been trapped at the bulk center.

Fig. 5.

:

B

B

1T

Fig. 4. (a) The trapped fieldand (b) the maximum temperature riseat the center of the SmBaCuO bulk as a function of the applied fieldusing
the “parallel-sheath-type” and the “conventional-type” bulk magnet systems.

Bshows the results for,andafter applying
and 6.09 T. It should be noticed that the time evo,
are quite different for the
lutions of temperature“parallel-sheath-type” system; after rising up to the maximum
isvalue, the decay of temperature is more moderate andlarger. These results may mainly come from the difference in thecooling direction for the bulk; the propagating speed of the generated heat in the -plane is much higher than that toward the-axis [8]. The generated heat spreads in the high-thermal-diffusive -plane and more rapidly transfers to the brass holder
in the “parallel-sheath-type” system. On the other hand, in the“conventional-type” system, the generated heat flows out along
the low-thermal-diffusive (c-axis) direction. We reported the effect of the stainless steel ring setting onto the high- bulk diskandduring PFM [4]. The ring acts as a heat reseron
voir and a part of generated heat in the bulk transfers to the ring.
in the bulk decreased andwas enhanced. In
As a result,the “parallel-sheath-type” system, as shown in Fig. 1, the brassbulk holder also acts as an effective heat reservoir.
and the maxFigs. 4(a) and 4(b) compare the trapped fieldat the center of the SmBaCuO
imum temperature risebulk as a function of the applied field
for the “parallelsheath-type” and the “conventional-type” bulk magnet system.
increases
In Fig. 4(a), for the “parallel-sheath-type” system,
up to 6.09 T and then decreases forwith increasing. On the other hand, in the “conventional-type” systems,
takes a maximum atand then decreases with.
for the “parallel-sheath-type”
the further increase of
system is always larger than that for the “conventional-type” one.
and does not show a saturation tendency up to
increases with increasing
for both sysIn Fig. 4(b),value for the “parallel-sheath-type”
tems. However, thesystem is always smaller than that for the “conventional-type”

B

Fig. 6. The trapped field distribution
obtained by the “parallel-sheath= 6 09 T to the SmBaCuO
type” bulk magnet system. After applying the= 5 42 T
bulk, the split-type coil was moved parallel and the pulse field of
was applied to the YBaCuO bulk at= 50 K.

T

B

:

B

:

system. These results suggest that the effect of the heat reservoir of the brass holder is significant and, resultantly,
decreases andincreases, in comparison with the “conventional-type” system.
By use of the “parallel-sheath-type” system, we performed
the PFM procedures for two bulks sequentially; at first, thebulk was magnetized by
at 50
K and then the split-type coil was moved parallel towardbulk and the magnetic field of
thewas applied to thebulk. Fig. 5 presentsonbulk andandon thethebulk after applying the pulse field.
sharply, takes a maximum atandincreases
then decreases.
gradually increase by 2 3 K.
of thebulk
It should be noted that theslightly decreases after applying the pulse field to thebulk due to the small temperature rise in thebulk.
These results suggest that there is almost no deterioration oftrapped on the neighboring bulk in the present case withthe 61 mm distance between the centers of two bulks. Fig. 6
in this case. We
shows the trapped field distribution of

FUJISHIRO et al.: NEW TYPE SUPERCONDUCTING BULK MAGNET

1083

compared with the “conventional-type” bulk magnet systemon thebased on a solenoid-type pulse coil.
bulk surface at 50 K andon thevacuum sheath in open space have been attained. This typeof magnet system consisting of multi-bulks can be realized
only by the PFM technique using a split-type pulse coil andhas a potential for new application fields. The extension of the“parallel-sheath-type” system to more than 3 bulks is possible
without serious difficulty.
ACKNOWLEDGMENT

B

Fig. 7. The line scan profiles of thevalue along the direction throughthe bulk center on both “front” and “back” surfaces.

can confirm the conicalprofiles for both bulks. The
value is 1.97 T and 1.49 T for the
maximumandbulk, respectively. The smallervalue
in thebulk comes from the lower
value of thisbulk [5].
value along
Fig. 7 shows the line scan profiles of thethe direction through the bulk centers on both surfaces of thevacuum sheath. In this figure, “front” means the sample surface
side on which the seed crystal was attached during the crystal
growth and “back” means the opposite side. The very similar
profiles can be seen on both surfaces in open space.
However, thevalue on the “front” surface is a little bit
larger than that on the “back” surface due to the difference of
crystalline property of the superconducting bulk.
IV. CONCLUSION
A new-type of magnet system consisting of two highbulks, named as “parallel-sheath-type”, with usable surface
on both sides in open space, has been realized employing a
split-type pulse magnet. In the “parallel-sheath-type” magnet
due to the magnetic flux insystem, the temperature rise
trusion is relatively small and the trapped field
is enhanced

The authors greatly thank Prof. M. Ikebe for the valuable discussion and M. Kaneyama and K. Kawai of Iwate University forthe technical support.
REFERENCES[1] H. Hayashi, K. Tsutsumi, N. Saho, N. Nishizima, and K. Asano, “Studyon a mobile-type magnetic separator applying highbulk superconductors,” Phys. C, vol. 392–396, pp. 745–748, 2003.
[2] U. Mizutani, T. Oka, Y. Itoh, Y. Yanagi, M. Yoshikawa, and H. Ikuta,“Pulse-field magnetization applied to high- superconductors,” Appl.
Supercond., vol. 6, pp. 235–246, 1998.
[3] M. Sander, U. Sutter, R. Koch, and M. Kläser, “Pulsed magnetizationof HTS bulk at
77 K,” Supercond. Sci. Technol., vol. 13, pp.
841–845, 2000.
[4] H. Fujishiro, K. Yokoyama, M. Kaneyama, T. Oka, and K. Noto, “Effect of metal ring setting outside HTSC bulk disk on trapped field andtemperature rise in pulse field magnetizing,” IEEE Trans. Appl. Supercond., vol. 15, pp. 3762–3765, 2005.
[5] H. Fujishiro, M. Kaneyama, K. Yokoyama, T. Oka, and K. Noto, “Risetime elongation effects on trapped field and temperature rise in pulse
field magnetization for high temperature superconducting bulk,” Jpn.
J. Appl. Phys., vol. 44, pp. 4919–4925, 2005.
[6] H. Fujishiro, M. Kaneyama, T. Tateiwa, and T. Oka, “A record hightrapped magnetic field by pulse field magnetization using GdBaCuO
bulk superconductor,” Jpn. J. Appl. Phys., vol. 44, pp. L1221–L1224,
2005.
[7] T. Oka, K. Yokoyama, and K. Noto, “Construction of strong magnetic
field generators by highbulk superconductors and its applications,”
IEEE Trans. Appl. Supercond., vol. 14, pp. 1058–1061, 2004.
[8] H. Fujishiro and S. Kohayashi, “Thermal conductivity, thermal diffusivity and thermoelectric power in Sm-based bulk superconductors,”
IEEE Trans. Appl. Supercond., vol. 12, pp. 1124–1127, 2002.

T

T

T <

T