Bi Current Sharing among Filaments for Bi-2223 Ag-sheathed Tapes with Inter-filament Barrier

Transcription

1 Bi-2223 Current Sharing among Filaments for Bi-2223 Ag-sheathed Tapes with Inter-filament Barrier Research Institute of Superconductor Science and Systems Kazuhiro Kajikawa, Keiji Enpuku, Kazuo Funaki Department of Electrical and Electronic Systems Engineering Yuki Iiyama Abstract Current distribution in Bi-2223 multifilamentary tapes with inter-filament barrier is numerically evaluated for the application of an alternating transport current. In the case of barrier materials with an infinite resistivity, the current distribution can be determined with a lumped parameter circuit model including the inductances and resistances of all the filaments. The mutual inductance between a pair of filaments is obtained by estimating their geometric mean distance. The power-law model is also assumed to take into account the effect of resistance in each filament. The influences of the silver ratio and filament number in the tape wire on the current distribution are discussed systematically as well as the power index and frequency.. Bi-2223 Bi-2223, 2) 3) NbTi 4 6) 7 6 4) 5)

2 4, 6) Bi Fig. 4, 5) 2 M M = L w µ 2π ln r () 7) L w r 2a 2b ln r = ln[(a + b)/2] /4 Innermost layer Innermost layer Middle layer Middle layer Outermost layer Outermost layer M R M R Alternating current source Alternating current source Fig.. Lumped parameter circuit models for numerical analysis of current sharing among filaments and layers. Only an example for three-layer structure of filament arrangement is shown here.

3 7) n R R = E c I n Ic n (2) E c I c n n (2) R I I m f I t I t = I m cos(2πft) (3) (), (2) Fig. Bi a w 2b w 4.,.225 mm r Ag S s S s = 4a w b w /( + r Ag ) 2a f 2b f 3.6,.8 mm α (= a f /b f ) 2 N Bi-2223 Fig. 3. Fig. 2 Fig. 2 Fig. 2 2 Fig. 2 Fig. 2 E c = µv/cm, J c = 3 ka/cm 2, r Ag = ) I c = NI c i m = I m /I c Fig. 3 n 6 Hz i m.5 Fig. 2 Fig. 3 Figs. 3, (c)

4 2 2 2-layer structure (N = 7) 3-layer structure (N = 9) 4-layer structure (N = 37) 5-layer structure (N = 6) silver ratio:.5 silver ratio: 2. silver ratio: 3. silver ratio: 4. Current sharing Current sharing Layer number 2 3 Layer number Fig. 2. Numerical results of current sharing among coaxial layers for different multifilament configurations. is the case that the silver ratio is fixed at 3. for different numbers of layers, while is for the three-layer structure and different silver ratios. The effect of resistance is ignored. The solid curves are a guide to the eye. Fig. 3(d) Fig. 3 Figs. 4 6 I 2 i m =.5 i m =.7 (c) i m =. (d) i m =. Current, I / Im Fig. 3. Current wave profiles in tape wire with three-layer structure for transport-current amplitudes of i m =.5,.7, (c). and (d).. The silver ratio, n-value and frequency are fixed at 3., and 6 Hz, respectively.

5 Amplitude of fundamental, I / Im 6 Hz. Phase of fundamental (deg.) Hz -8. Fig. 4. Dependence of amplitude and phase of fundamental for current waveforms in tape wire with three-layer structure on amplitude of applied transport current. The n-value is fixed at 5, and the frequency varies from to 6 Hz. Amplitude of fundamental, I / Im 6 Hz. Phase of fundamental (deg.) Hz -8. Fig. 5. Dependence of amplitude and phase of fundamental for current waveforms in tape wire with three-layer structure on amplitude of applied transport current. The n-value is fixed at, and the frequency varies from to 6 Hz. 6 Hz Figs. 4 6 n 5,, 2 Figs. 4 6 n

6 Amplitude of fundamental, I / Im 6 Hz. Phase of fundamental (deg.) Hz -8. Fig. 6. Dependence of amplitude and phase of fundamental for current waveforms in tape wire with three-layer structure on amplitude of applied transport current. The n-value is fixed at 2, and the frequency varies from to 6 Hz. 4. Bi-2223 Bi-2223 Bi th International Symposium on Superconductivity (ISS26) ) M.P. Oomen, J. Rieger, M. Leghissa and H.H.J. ten Kate: Field-angle dependence of alternating current loss in multifilamentary high-t c superconducting tapes, Appl. Phys. Lett., Vol. 7, No. 22 (997) pp ) Y. Fukuda, K. Toyota, K. Kajikawa, M. Iwakuma and K. Funaki: Field angle dependence of ac losses in stacked Bi-2223 Ag-sheathed tapes, IEEE Trans. Appl. Supercond., Vol. 3, No. 2 (23) pp ) N. Ayai, K. Hayashi and K. Yasuda: Development of Bi-2223 superconducting wires

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