IEEE TRANSACTIONS ON MAGNETICS, VOL. 28, NO.l, JANUARY 1992

Test Facility for Investigations of High-Current Supercon&uctor Samples

A.S.BUrsikov, Y.V.Zhelamsky, A.A.Lancetov,A.A.Lebedev, V.V.Mymrlkov, I.Yu.Rodin, G.V.Trokhachev, V.G.Yakubovsky.

D.V Ef'remv Scientfic Research Institute of Electrophysical Apparatus

Leningrad,USSR

Abatract - In this paper the main components of a test facility f o r invest i p t ion of high-current superconductors short samples are described.

1 .Introduction.

The application of high-current superconductors in large-scale msCplet system for fusion machines, makes necessary the construction of the test facility for investigstion of high-current superconductors short samples. This facility, made in Efremov institute,

includes an equipment f o r researching of the main characteristics of superconductors: current carrying ability in high fields ( "11 T ) and A C losses. The parameters of the test facility and the metho& of measurements are given in the paper.

2. Test Facility Enuipanent.

The main components are: - cryostats 1 m and 0,6 m in diameter - laboratory testing magnet system LTS-12 with maxi" field on the winding - 12 T dipole w e t with high field homogeneity - 4 T D C superconducting transformer, current in secondarg winding being up to 40 kA power supply (2*10 M; m e m fo r magnet systems protection data acquisition and processing system

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5 U)

CAMAC HIERA-60 and IBM PC/AT

The magnet system consists of two superconduc t ing magnet 9, each one comprising three coaxial coils. "Fig. 1 " Inner coils are manufactured of NbgSn conductors by the "wind-and-reac t " technology, outer coil of NbTi conductor. W i n d l x q of LTMS-12 was impregnated with epoxy resin.

Fig 1 . Laboratory testing magnet system ( LTSY-12 )

In the middle pert of the superconducting mapet system there is a rectangular hole 25mm*9onan for the samples imerting.

0018-9464/92$03.00 0 1992 IEEE

The main parameters of L T M S - ~ ~ EUW

listed below: number of turna 1 278 induc tance ,H 0,213

11 field on the winding,T 11,8 field in the centre of v e t , T

stored energs,Mj 1.3 maxir" " e n t density,A/sm2 1 o4

2.2 Superconductiag Tmnaforrmer (ST).

Superconducting transformer has NbTi . primary rrinding with 75 turns and two . secondary rrindinga, wound outside the primary one. The first secondarg windizlg bas 1 turn, the second - 1,5 turns. The inductance of the primary rrirrding is 1.6810-38, that of the firat and the second secorrdarg windings 1 ,I*IO* and 2,38810~ respectively. Superconduct~ transformer was tested

in a separate cryostat before its assembly with LTSM-12. Tests were performed to determine the secondary windings critical current abilities and the amplification factors. When charging the primerg winding, one of the secondary windings was quenched by the heater. The current in the other one was measured by a Hall probe, installed on the conductor of the winding. Amplification factors were: k.,=12;k@ 11 I .

Tests of LTSM-12 were performed after the final assembly of the whole Installation. w e t system was charged nith rated m t 1'=5A/s. mining cif the m@et has been performed, the results are &hen in Table 1

TABLE 1 TRdINING RESULTS

--

610

Further, LTSM-12 was operated at the current 1 4 . 3 kA(fie1d in the centre of working volume 1 1 T)

2.3 Inveetmtion of Superconducting Samples Critical Current.

The sample represents non-full scale "react-and-wind" cable for the ITW toroidal field coil. To decrease the joint resistance between the sample and secondary winding, every superconducting strand was soldered with every strand of the transformer. The current in a tested sample was measured by the Hall probe, Installed on the sample. Readings of the Hall probe were controlled by Ro@wskl coil, installed on the secondary winding conductor. To determine the quality of joints between the sample and secondary winding, the time constant of current decay was measured. The joint resistance equaled 3,5*104 n. Results of critical current measurements are given in Pig 2.

36-00 I ,kA 1 32.00 1 \

12.00

charging Quench Field number current

kA T

1 2 9 8 9,35 2 390 10,w

Background Field

11,20 F i g 2. Results of critical current

3 3,3

611

3.2 Method of A C Loeeee Uea”ment 3.1 Inetallation for A C Loeeee

Meamnwnente

The installation is intended A C losses measuremrmts in fields up

for to 4T

end charglng rate up to 0,5T/s. B8cke;rouna - field is created by the aupercoducting . riipole w e t with hlgh field homogeneity.T& main parameters of the dipole are listed below: Length loo0 m Diameter 100 mn Maxi” operating current 6OOOA

2% Field inhomogeneity Maxi” operating charging rate 500 Afs Magnetic constant B/I 0,s T/kA Inductance 6,31 mB

This installation is distinguished by the Ngh field homogeneity and in addition, poasibility for A C losses measurement in large-size samples ( up to 2 d in cmss section ~ i g . 3 .

F i g 3. Installation for A C losses meaaureJnent

The electric method of A C losses measurement was chosen as more simple in comparison with the calorimetric one [21. T h i s circumstance is especially important, because of large volume of work planned to be carried out on the described installation. This method is based on the integration

of the field induction in a sample for the value of the backpound field.

W=J’dV J’B(X,Y,z)dH (1 1 where V is the sample volume

B the induction In the sample Z a coordinate, which coincides

in direction wlth the magnetic field vector H

X,Y the coordinates, laying in the plane, perpendicular to Z axis

In the case, when B doesn’t depend on Z coordinate, the expression (1 ) can be represented as:

where h is the sample size in H vector

Ul is the flux of induction B direct ion

through thesample The expression (2) is sufriclently

correctly fulfilled when h >> ax, where bx is the sample width. For the fulfilment of relationship h >> Ox, several tested samples are stacked together. The measuring coil is wound on the middle plane of the stack and has a mini” h e w t and thickness. Therefore, the A C losses measurement

practically is reduced to that of a flux through the sample in dependence on background field at its cyclic changing. The example of A C losses measurements

in one of the ITW superconducting cable is shown in Fig.4. For the separation of hysteresis and eddy

current losses, the dipole w e t was charged with stops at definite time intervals.

612 :r'- F' - 0.13 T/B /-.

Applied Field

F i g . 4 -le of A c losses measurements in ITER superconducting cable

1. Generated 11,Z T field was achieved using the superconducting split magnet ( working volume 150~111*90nm*Z5m).

2. The superconducting transformer waa successfully used for supply 30 M sample current.

3. Test installation for A C losses measurement allows to examine the losses in high-cirrent full-scale short samples of superconducting cables in the field up to 4T and charging rate of 0,5T/s.

c1 I

12 1

L.shirah0V. and G.gnderlein. iauperoonducting transformer for

superconductors". grperim. Dev. and

8.Foner. and B.Bchnrrtz. The

auperoonaucting Yaohines and Devices. Cambridge, Yaasachusetts: Plenum -8s. 1977

inoeatigation Of high-cufimt

Tech. VOL 2. 1982. p.97-PB