S. Fukui

Y. Hishinuma

National Institute for Fusion Science (NIFS-Repository)

..."" 0 .." " ..o80,--, 22o 0! 20 .."" G.." ".. ""· · i "..,,,,""S-o18Aspect ratio 0.21 0.28 0.55 1.23 1.78No.oftums 11414 9556 7365 6900 7145Inner radius Ql (mm) 25 25 25 25 25Outer radius Q2 (mm) 68 7 80 105 123Hight(mm) 200 160 100 65 55111.....'Fig3. Calculated temperature distribution in coil cross-section.{KIZ .....!Time (sec.)Fig2. Comparison of and calculated coil temperature.Reference[1] Yamaguchi, M., Fukui, S., Presented at EUCAS 2001.[2] Ymaguchi, M., Fukui, S., Presented atASC 2002.24current of the test HTS coil was 35A. Fig. 3 shows thecalculated temperature distribution in the coil cross-sectionat t=60 sec. As shown in Fig. 1, the temperature rise at theedge of the coil is very small after 60 sec. However as seenfrom Fig. 3, the temperature at the center of the coilcross-section is larger than 35K. It is considered that thistemperature rise is due to the Joule heating caused by theconnection resistance. Therefore, depending on theoperating current, the Joule heating caused by theconnection resistance together with the flux flow lossshould be taking into consideration.Tab.I Specification of test HTS coil1. IntroductionThe DC current and voltage (I-V) relation of the hightemperature superconducting (HTS) tape strongly dependson the flux angle to the tape. Therefore, it is necessary toprecisely consider this 1-V relation for the design of theHTS coils. In this study, we numerically investigated thecoil cross-section which enhances the characteristics of thecritical current, the stored energy and reduces the flux flowloss. The FEM analysis was also done to calculate thetemperature distribution in the coil cross-section in the caseof the conduction cooling.2. Relation between Coil Structure and PerformanceNumerical calculation was done for five coils withdifferent cross-sections. The specifications of the coils usedfor the numerical analysis are listed in Tab. 1. The coildimensions shown in Tab. 1 were determined by providingthat the magnetic field intensity at the center of the coilkeeps constant. The specification represented as Case 3 isas same as that of the HTS magnet used for the temperaturemeasurement. The I-V relation of the HTS tape used for theanalysis is based on the measured data of a Bi2223/Ag tapeat 77K. Fig. I(a)--(c) show the dependencies of the criticalcurrent, the stored energy and the flux flow loss on theaia1' From the figures, the critical current and the storedenergy density decrease as a2/a1 increases, although theflux flow loss becomes minimum around a2/a1=3.5.3. FEM Analysis of Temperature Distribution inConduction Cooled HTS CoilThe temperature distribution in the cross-section of theconduction cooled HTS coil was numerically calculated byFEM analysis. The anlysis was done for the Case 3 asshown in Tab. 1. In the analysis, the flux flow loss and theJoule heating caused by the connection resistance betweenthe pancake coils were taking into account. Fig. 2 showsthe numerical results of the temperature rise at the edge ofthe coil when the DC current of 36A continuously flows atthe virgin temperature of 20K. In Fig. 2, the measuredtemperature of the conduction cooled HTS coil wound byBi2223/Ag tape was also shown. The measured critical§ 28. Study on Optimization of HighTemperature Superconducting MagnetFukui, S. (Niigata University)Hishinuma, Y. (NIFS),--,r<l S;::::;"-'€' -oSo ]0 02 3 4 5 6 L..L.......... .....""'-&__1-I3 a fa 4 5 6.s a fa 2 3 a fa 4 5 621 rFJ 21 21(a) Critical current vs. a2/al (b) Stored energy density vs. az/al (c) Flux flow loss vs. a2/alFigl.Critical current, stored energy density and flux flow loss VS. Q1/Q2'1Or-r-"""""'T"'T""I"""Ir-r-r-r-T'""I""T""T"'T'"'I-r-r-r-I$8t=6 I:-"."""""" I ,,.."":!o 4 t--.".."" " " "".., " """."""" , "f "" ..2 2'c 1'-"" " " " ; " " " ;,,, ,,,, ,, ,, ,,,, ..,."."" "" -tUO'-'- """'""" &...&..""""""' -I-I"""""'""'2120

Study on Optimization of High Temperature Superconducting Magnet

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