The magnetic levitation performance of YBaCuObulk at different temperature

He Jiang *, Jiasu Wang, Suyu Wang, Zhongyou Ren, Min Zhu,Xiaorong Wang, Xuming Shen

Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031, China

Received 27 September 2001; accepted 15 February 2002

Abstract

The magnetic levitation (maglev) performance of YBaCuO bulk at different temperature is studied. The YBaCuO

bulk is cooled by the G–M refrigerators and its temperature can descend from 100 to 40 K. The maglev performance of

YBaCuO bulk, such as levitation force, can be obtained by the high temperature superconducting maglev measurement

system. The measured results in the different temperature are analyzed and discussed.

� 2002 Published by Elsevier Science B.V.

PACS: 85.25.Ly

Keywords: YBaCuO; NdFeB; G–M refrigerator; Magnetic levitation performance

1. Introduction

The magnetic levitation (maglev) is being stud-ied in hot because of its potential applications [1].The study of the high temperature superconduct-ing (HTS) maglev is very significant [2,3], becausethe melt-textured YBaCuO bulk used in thismaglev not only has high critical current densityand critical magnetic flux but also can make theHTS maglev levitate stably and work at liquidnitrogen (LN2) temperature [4–9].

The levitation force and the guide force areimportant parameters of HTS maglev [10]. Muchwork has been done to study the levitation force

and guide force only at LN2 temperature in cur-rent situation. But the relationship between levi-tation force and temperature is seldom studied[11]. The performance of the YBaCuO is better atlower temperature in theory. So the levitationforce of YBaCuO will be studied from 100 to 40 K.And the measurement results will be analyzed anddiscussed.

2. Measurement conditions

The HTS maglev measurement system is usedto measure the levitation force of YBaCuO bulk(shown as Fig. 1), the measurement process anddata acquisition are fully controlled by a computer[12]. In order to measure the levitation force

Physica C 378–381 (2002) 869–872

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E-mail address: jheriver@sohu.com (H. Jiang).

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between the NdFeB and the YBaCuO bulk, thepermanent magnetic track and the liquid nitrogenvessel are replaced by the G–M refrigerator and adisc-shape NdFeB which is £ 30 mm� 15 mm.The temperature lower than LN2 is obtained bythe refrigerator, which is fixed on the base of theHTS maglev measurement system, the YBaCuO isfixed on the second step cooling head of refriger-ator (shown as Fig. 2). The NdFeB fixed on ver-tical moving part of the HTS maglev measurementsystem can move down and up. So the levitationforce of YBaCuO can be measured at different gapfrom the NdFeB and at different temperature.

The size of the YBaCuO bulk is £ 30 mm� 14mm. The maximal magnetic field is 0.42 T on theNdFeB surface, 0.219 T at 5 mm above it, and0.0535 T at 20 mm. The minimal gap betweenYBaCuO and NdFeB is 5 mm.

3. Measurement results

After the YBaCuO bulk is cooled down to 40 Kby the refrigerator, the NdFeB fixed on verticalmoving part of the HTS maglev measurementsystem moves down and up. The gap betweenYBaCuO and NdFeB changes from 150 to 5 mm,at the same time, the levitation force data aresampled by the computer, which is used to controlthe measurement system and sample measurementdata. Fig. 3 is one of the measurement results at38.4 K, which indicates the relationship betweenthe levitation force and the gap. Fig. 4 shows thetwo curves at 82.0 and 38.4 K, respectively. Table1 is the measured maximum levitation force atdifferent temperature. The relationship betweenthe maximum levitation force at the same (mini-mal) gap and temperature is shown as Fig. 5.

4. Discussion

Fig. 4 gives the measurement results of thelevitation force at 82.0 and 38.4 K, 21.1 and 33.3 Nare the maximum values, respectively. From Figs.4 and 5, we can see that the levitation force islarger at lower temperature than at higher tem-perature when the gap between YBaCuO andNdFeB is the same.

Figs. 3 and 4 show that the levitation forcebegins to increase exponentially when the NdFeBmoves down to 20 mm gap. There is almost nohysteresis at 38.4 K, and slightly hysteresis appearsat 82.0 K. That is to say the magnetic field entersthe HTS bulks at lower temperature hardly.

Table 1 and Fig. 5 show that the levitation forceappears when the temperature is 88.0 K becausethe temperature is lower than the Tc of YBaCuO.From 88.0 K down to 82.0 K, the levitation forceincreases rapidly, since F / JcdB=dz, (F indicates

Fig. 2. Cross-section diagram of the G–M refrigerators. (1)

Vacuum cover; (2) second step cooling head; (3) NdFeB; (4)

YBaCuO.

Fig. 1. Schematic diagram of HTS maglev measurement sys-

tem. (1) Servo motor; (2) vertical guided way; (3) vertical col-

umn; (4) cant lever; (5) vertical sensor; (6) fix frame of vessel; (7)

liquid nitrogen vessel; (8) permanent magnetic track; (9) hori-

zontal drive platform; (10) horizontal sensor; (11) base; (12)

drive device of three dimension.

870 H. Jiang et al. / Physica C 378–381 (2002) 869–872

the levitation force, Jc is the critical current den-sity of YBaCuO and dB=dz is the gradient ofmagnetic induction at the direction of z.) and theJc of YBaCuO increases when the temperature

decreases. From 82.0 K down to 70.5 K, the levi-tation force increases slower than before. And therate of the levitation force increase becomes gentlyat the range between 70.5 and 38.4 K.

Fig. 4. Measurement results at 82.0 and 38.4 K.

Fig. 3. Sampled data curve at 38.4 K.

H. Jiang et al. / Physica C 378–381 (2002) 869–872 871

5. Conclusion

Results show that the levitation force is largerobviously at lower temperature than at highertemperature near the critical temperature of theYBaCuO. When the temperature is lower than 70

K, the improvement of the YBaCuO performanceis not notable.

In addition, the guide force of the YBaCuOneeds to be studied at different temperature.

Acknowledgements

The authors gratefully acknowledge the supportof the Hi-Tech Research and Development Pro-gram of China.

References

[1] H. Nakao, T. Yamashita, M. Yamaji, M. Arata, M.

Kawai, S. Nakagaki, T. Shudo, A. Miura, in: Proceedings

of Fifteenth International Conference on Magnet Tech-

nology, 1997, p. 732.

[2] H. Weh, in: Proceedings of Fifteenth International Con-

ference on Magnet Technology, 1997, p. 833.

[3] S. Wang, J. Wang, J. Lian, in: Proceedings of Fifteenth

International Conference on Magnet Technology, 1997,

p. 767.

[4] F. Hellman, E.M. Gyorgy, D.W. Johnson Jr., H.M.

O’Bryan, R.C. Sherwood, J. Appl. Phys. 63 (1988) 447.

[5] R. Williams, J.R. Matey, Appl. Phys. Lett. 63 (1988) 751.

[6] F.C. Moon, M.M. Yanoviak, R. Ware, Appl. Phys. Lett.

52 (1988) 1534.

[7] P.N. Peters, R.C. Sisk, E.W. Urban, C.Y. Huang, M.K.

Wu, Appl. Phys. Lett. 52 (1988) 2066.

[8] H. Weh, H. Pahl, H. Hupe, A. Steingrver, H. May, in: 14th

International Conference on Magnetically Levitated Sys-

tems and Liner Drives (Mag-Lev’95), 1995, p. 217.

[9] M. Komori, T. Hamasaki, IEEE Trans. Appl. Supercond.

11 (2001) 1677.

[10] Y. Zhang, S.G. Xu, in: Proceedings of Fifteenth Interna-

tional Conference on Magnet Technology, 1997, p. 763.

[11] S. Nagaya, N. Kashima, M. Minami, H. Kawashima, S.

Unisuga, IEEE Trans. Appl. Supercond. 11 (2001) 1649.

[12] J. Wang, S. Wang, G. Lin, H. Huang, C. Zhang, Y. Zeng,

S. Wang, C. Deng, Z. Xu, Q. Tang, Z. Ren, H. Jiang, M.

Zhu, High Technol. Lett. 118 (2000) 55.

Fig. 5. Relationship between the levitation force at the minimal

gap and the temperature.

Table 1

The maximum levitation force at different temperature

Temperature (K) Levitation force (N)

38.4 32.5

48.5 33.5

50.0 32.5

54.3 32.5

59.0 30.6

64.5 29.7

67.6 29.6

70.5 28.7

75.5 25.8

82.0 21.1

88.0 9.6

93.0 0

100.0 0

872 H. Jiang et al. / Physica C 378–381 (2002) 869–872