Superconducting test facility of NIFS for the Large Helical Device

Fusion Engineering and Design 20 (1993) 147-151 North-Holland

147

Superconducting test facility of NIFS for the Large Helical Device J. Y a m a m o t o , T. Mito, K. T a k a h a t a , S. Y a m a d a , N. Yanagi, I. O h t a k e , A. N i s h i m u r a a n d O. M o t o j i m a National Institute for Fusion Science, Chikusa, Nagoya 464-01, Japan

For development of superconducting conductors and coils, the National Institute for Fusion Science prepared a new superconducting test facility which is a combination of an electro-mechanical testing device and a large cryogenic cooling system at the new Cryogenics and Superconductivity Building at the Toki site. The cryogenic cooling system has a capacity of 250 liters of liquid helium per hour or 500 W at 4.5 K, and can also supply supercritical helium up to 50 g/s. A dc power supply generates 75 kA current at 21 V. A split-type superconducting coil generates a magnetic field of 9 T of 100 mm in width. The mechanical testing machine has a capacity of 10MN at liquid-helium temperature. The following R&D experiments for the Large Helical Device have been done using the facility: critical current and stability measurement of helical coil conductors of which the nominal current is 21 kA at 7 T, an elasticity measurement of a helical coil, and stability measurement of a cable-in-conduit conductor.

1. Introduction For development of superconductors and superconducting coils for the Large Helical Device (LHD), the Superconducting Test Facility has been constructed at the new Toki site, using the budget of 1989 and 1990. The construction of the facility started in November of 1990 and was finished at the end of January of 1991 by the main contractor, Kobe Steel Ltd. After initial checks of the system, the facility was used for development of superconductors in the 20 kA class, and superconducting magnets, as an R&D program of LHD [1,2].

2. Cryogenic system 2.1. Design The fundamental design of the system is as follows. (1) The system can produce liquid helium at more than 200 L/h and has a refrigeration power of more

Correspondence to: Dr. J. Yamamoto, National Institute for Fusion Science, Chikusa, Nagoya 464-01, Japan.

than 500 W at 4.5 K with a liquid-helium dewar of 10000 L capacity. (2) The system can supply cooled helium gas and liquid helium to superconducting R&D coils through a distribution box and to a cryogenic 10 MN mechanical testing machine. (3) The system can supply supercritical helium up to 50 g/s at 4.5 K to the distribution box for the coils. (4) The capacity of the circulation compressor should be enough for any cooling mode of the superconducting coils and the mechanical test machine. (5) The capacity for room-temperature gas storage is high enough to store the helium gas when the whole system is at room temperature. (6) To save helium all evaporated gas should be recovered using a gas bag, a recovery compressor, and storage tanks. The high-pressure storage tanks for impure and pure gas have to be separated from each other. (7) The system has to be furnished with a gas purifier. The line pressure is the same as the pressure of the circulation compressor. Output impurity levels should be below 1 ppm for nitrogen or oxygen during a continuous working time of 120h when the input impurity level is 1000 ppm. (8) Operation of the system should be simple, safe, and automatic.

0 9 2 0 - 3 7 9 6 / 9 3 / $ 0 6 . 0 0 © 1 9 9 3 - E l s e v i e r Science Publishers B.V. All rights reserved

148

J. Ya,narnoto et al. / SC test jacility o f NIFS for L H D r-- i0000 ~ DC Current Supply

(DC

30

--~ Gas Warmer -

- Cold BOX

-

~

Cryogenic Mechanical Testing Maehin Recovery

Llle Dewar

kA)

Gas B a g ~

Gas Purifier Supereritical Helium Heat Exchanger Gas Warmer

. . . .

i

9 T Split Coil TOKI-TF,PF Distribution Box

TOEI-}{B

Clean Room ~ Test Stand for Poloidal Coil

DC

Current

Supply

(DC

75

kA)

DC

Current

Supply

(DC

6.fi kA)

Fig. 1. Layout of the superconducting test facility. Table 1 Main parameters of the cryogenic system Cold box capacity 500 W/250 L / h (at 4.4 K) flow rate of SHE 50 g/s n u m b e r of turbines 2 gas bearing Circulation compressor flow rate 2500 N m~/h type oil lubricated two-stage screw input power 450 kW(E) Liquid helium storage tank volume I(I m ' Buffer tank volume 300 m ' pressure 2.0 MPa Helium gas recovery compressor 150 N m ;/h, 2.0 MPa recovery tank 100 m ', 2/0 MPa gas bag I00 m ~, 0.1 MPa Puritier capacity 150 N m3/h, 2.0 MPa input impurity below 1000 ppm output impurity below 1 ppm (N 2, 0 2 ) cycle time 120 h

Transfer

Fig. 2. Flow diagram of the cryogenic system.

Tubes

149

J. Yamamoto et al. / SC test facility of NIFS for LHD

start

up of

the

circulating

compressor

1/ m a n u a l l y

3. DC power supply

(*1)

/

I start

3.1. Design

I

up

the

of

purifier

unit

I manually(*l) I

I I tho portlier s operating modo I automatioally

I

leool0 ..... do I ..... lly .,, :Ln2 s u p p l y :supply the temperature

to the cold box cooling helium gas and pressure

at

a controlled

:cool d o w n the e r y o s t a t :start up a n d c o n t r o l l i n g the t u b o e x p a n d e r s : d i s t r i b u t e t h e r e t u r n e d gas l i n e in t h e cold box by the r e t u r n e d g a s t e m p e r a t u r e :LHe's d e l i v e r i n g to the cryostat--manually

In the design, the load of the power supply comprises a short superconductor and superconducting R&D coils having an inductance and nominal current of 54mH at 2 0 k A (TOKI-MC), 4 8 m H at 8 . 9 k A (TOKI-HB), 41 mH at 8 k A (TOKI-TF), and 3.2 mH at 26 k A (TOKI-PF). Short samples of superconductors need the highest current value, up to 75 kA. For precise magnetic field measurements, a transistor power supply which can deliver up to 6 kA is built [4].

I stoa0y state I 3.2. Characteristics

I [ .....

pmode

I

.....

lly(*t)

:stop the t u r b o e x p a n d e r s

:warm u p t h e e r y o s t a t : s t o p LN2 s u p p y - - m a n u a l l y *l)started v i a CRT s c r e e n and a f t e r the program performs automatically

that

Fig. 3. Control system of the cryogenic system using DCS.

2.2. Performance

The layout of the facility is shown in fig. 1. Its cryogenic part [3] includes a helium liquefier/ refrigerator having a capacity of 250 L/h or 500W at 4.5 K, and a distribution box for a superconducting split coil and 3 R&D magnets (TOKI-PF or TF, T O K I - M C , and TOKI-HB), The connections between the distribution box of the facility and two of the four magnets were made by flexible transfer lines and bayonets. The cryogenic mechanical testing machine was directly connected to the cryogenic system. Specification of the cryogenic system are shown in table 1. Figure 2 shows the simplified flow lines of the cryogenic facility. The operating flow chart of the facility is shown in fig. 3 and is realized with a Y E W C O M micro-XL system using the data channels in table 2.

Table 2 Number of input/output data channels analog

input output digital input output control loop

80 50 100 50 50

A thyristor power supply for 75 kA (PS-A) and a transistor power supply for 6 k A (PS-B) are built for conductor and coil tests. PS-A is made from three 25 k A units. Two of the three units have a current breaker to protect the magnets in case of coil quench. Figure 4 shows a schematic drawing of the power supply and the bus lines to the coils. The inductance and resistance of bus lines are about 6 IxH and 66 p,f/, respectively. The typical current drive pattern is shown in fig. 5. The power supply and bus lines are cooled by a pure-water circulation system which has a capacity of 850 kW.

TOKI~MC

TOKI PF,TF

<)

©

Superconducting Split Coil

rJr/l

Alumnlum Bus Lines ( ¢ 180 × t24 )

E II

!

Cooling Ware Unit

75 kA DS Power

Supply (

psg

6 kA DC Power Supply

( PS B ) )

Fig. 4. Layout of the power supply system.

150

J. Yamamoto et al. / SC test facility o f N1FS for L H D

JL ( k A )

5. C r y o g e n i c m e c h a n i c a l testing m a c h i n e

50

/ ~

I

I

I

P

45 A 1 & A-2 U n i t s 40

Kp

35

dI/dt

:

0.4 2000 A/S

30

/

25 20

\

//

,,

\

10

\, \

0 o

5

10

15

20

25

30

Time

35

40

45

50

55

60

{ sec )

Fig. 5. Typical current drive of PS-A. 4. Split-type s u p e r c o n d u c t i n g

coil

A split-type s u p e r c o n d u c t i n g coil having a maxim u m field of 9 T and stored energy of 5.8 MJ is set at the c e n t e r of the facility for the c o n d u c t o r test. The coil is c o m p o s e d of NbTi a n d Nb3Sn s u p e r c o n d u c t o r s a n d is o p e r a t e d at 4.2 K. T h e i n n e r a n d o u t e r diameters of the coil are 248 a n d 907 m m , respectively. T h e h e i g h t of the coil is 139 m m , as s h o w n in table 3. T h e two parts of the coil, since it is a split type, can be set at distances b e t w e e n 10(I a n d 31)0 mm. F o r the conductor tests, the distance was set at 100 mm.

T h e cryogenic m e c h a n i c a l test system consists of a 10 M N cryogenic m a c h i n e for coil-pack elasticity tests a n d real-size c o n d u c t o r critical c u r r e n t m e a s u r e m e n t s u n d e r m e c h a n i c a l stress [5], as described in table 4, a n d a 200 kN l n s t r o n cryogenic m a c h i n e for tests of individual parts. Figure 6 shows an o v e r v i e w of the Ill MN cryogenic m e c h a n i c a l testing m a c h i n e . T h e coil-pack sample is set on a table s u p p o r t e d by four tie rods, and pressurized by a main rod c o n n e c t e d to an a c t u a t o r of oil pressure. Figure 7 shows the pre-cooling curve of the cryostat, the pre-cooling takes a b o u t 4 3 h . S t r e s s strain curves of the m a c h i n e with a stainless steel block sample at r o o m and liquid-helium t e m p e r a t u r e were m e a s u r e d , as s h o w n in fig. 8. T h e facility will bc used for R & D for the L H D a n d for confirmation of m a t e r i a l s and design of the L H D during the construction process.

6. C o n c l u s i o n T h e s u p e r c o n d u c t i n g test facility of NIFS was completed in J a n u a r y 1991 and p r o v i d e d i m p o r t a n t data for c o n d u c t o r and coil d e v e l o p m e n t . This c o m b i n a t i o n of cryogenics, p o w e r supplies for up to 75 k A , coil test

Table 3 Specification of the split superconducting coil

(:oil dimensions (i.d.)

(o.d.) (height) Number of turns Winding Inductance Operating current Current density Central field Max. lield at conductor Ampere-turn Load ratio Stored energy Weight Conductor Cross section Material Filament diameter Copper ratio Critical current

Inner coil

Outer coil

248 mm 486 mm

561) mm 907 mm 139 mm

550 double pancake

920 2.5H 2160 A

72 A/mm 2

82 A / m m ~' 9.0T

I1.0T

6.5T 6.3MA

82%

7(1~/~ 5.8 MJ 2.7t

monolith 2.0 × 12.0 mm e (NbTi)3Sn 4.8 ~m 1.35 3400 A at 12 T, 4.2 K

compacted strands 1.785 x 12 mm ~ NbTi 24 ~m 1.9 4000 A at 9 T, 4.2 K

151

J. Yamamoto et al. / SC test facility o f NIFS for L H D

Table 4 Design conditions of 10MN cryogenic compressive testing machine Maximum load capacity Working load capacity in the cryostat Load range Load accuracy Repeatability Sample Current Magnetic field Temperature

I

z

I

1

f

I

I

I

I

5OO0

1000t (compression)

4000

500 t 1000, 500,200, 100 t + 1% + 1% superconductor and coil pack max. 30 kA max. 8 T 4.2 K (with magnetic field) 4.2-300 K (without magnetic field)

3000

4.2K

/

2000 E o

1000 , e ° I

I

100 200 300 400 500

Strainoutput (X10-6) Fig. 8. Stress-strain curve of the 10 MN machine.

2800

~Actuator

I . ~ H H I---~

~Tierod

II "~..L_.~ Ib

Acknowledgement

..---Mainrod -----Sample Cryostat F.L.

~

Unit:mm I =~7."..----'t 31

The authors wish to acknowledge Professors M. T a k e o , M. Fujiwara and Director General A. Iiyoshi for their efforts to prepare the facility, and members of D e p a r t m e n t of Engineering and Technical Service of NIFS for construction and maintenance of the facility.

~~Lifte7 P4"!

r,

i

l~21o0~J

References

5500

Fig. 6. Layout of the 10MN cryogenic mechanical testing machine.

380 ~ 200

E

o

d

440turnapart from the support bed surface

] ~ " ~ Start up of the turbo expander at thebottc~n of/the support bed ~ ' ~ " ~ ' ~ . . _ I

100

0

at the bottom of the cryostat

i 10

i 20 Time (h)

30

/ "'~,

40

Fig. 7. Cool-down curve of the cryostat for the 10 MN testing system. stands, and a 1 0 M N cryogenic mechanical testing machine makes this the leading test facility for highcurrent superconducting technology. The facility will be used for large-scale conductor and coil developm e n t for the L H D project.

[1] J. Yamamoto, O. Motojima, T. Satow and T. Mito, Superconducting coil design for Large Helical Device, IEEE Trans. Magn. 27 (1991) 2220-2223. [2] J. Yamamoto, T. Mito, O. Motojima, K. Takahata, N. Yanagi, S. Yamada, A. Nishimura, M. Sakamoto, H. Tamura, S. Imagawa, S. Satoh, T. Satow, M. Takeo, M. Fujiwara and A. Iiyoshi, Research and development of superconductors and superconducting coils for Large Helical Device, presented at ITC-3, paper MT-4 (1991). [3] J. Yamamoto, T. Mito, K. Takahata, N. Yanagi, S. Yamada, I. Ohtake, E. Tada, S. Kashihara, K. Shinkai, H. Yamamura, M. Takamatsu and M. Taneda, A cryogenic system for the superconducting magnet testing facility, Adv. Cryogenic Engrg. A 37 (1992) 755-762. [4] S. Yamada, T. Mito, S. Tanahashi, K. Takahata, N. Yanagi, M. Sakamoto, A. Nishimura, J. Yamamoto and O. Motojima, Characteristics of DC 75 kA power supply in the superconducting magnet test facilities, presented at ITC-3, paper PT-13 (1991). [5] A. Nishimura, T. Mito, H. Tamura, K. Takahata, N. Yanagi, M. Sakamoto, S. Yamada, J. Yamamoto and O. Motojima, Rigidity tests of superconducting coil at 4.2 K simulated for helical coil on LHD program, presented at ITC-3, paper PT-14 (1991).