The Influence on Levitation Force of the Bulk HTSC Above a Permanent Magnet Guideway Operating Dive-Lift Movement with Different Angles

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1 J Supercond Nov Magn (2012) 25: DOI /s ORIGINAL PAPER The Influence on Levitation Force of the Bulk HTSC Above a Permanent Magnet Guideway Operating Dive-Lift Movement with Different Angles Rong Zeng Suyu Wang Xinlin Liao Jiasu Wang Received: 20 April 2012 / Accepted: 8 May 2012 / Published online: 2 June 2012 Springer Science+Business Media, LLC 2012 Abstract In practical applications, the operating of accelerating or decelerating inevitably happens in the high temperature superconducting (HTS) Maglev train. For the further research of the Maglev properties of bulk high temperature superconductor (HTSC) above a permanent magnet guideway (PMG), by moving a fixed vertical distance, this paper studies the influence on levitation force of the bulk HTSC operating dive-lift movement with different angles. Results show that with the angle increasing, the maximal levitation force decreases when the levitation gap is about 10 mm and the hysteresis is increasing. The hysteresis reaches the largest at first time of back and forth movement, and with the operating times increasing; the hysteresis is almost the same case in the following times of back and forth movements. Keywords Maglev Levitation force Dive-lift movement Different angle 1 Introduction Bulk high temperature superconductor (HTSC) with high critical current and high critical magnetic field which can be manufactured by a melt-textured growth technology with R. Zeng ( ) S. Wang X. Liao J. Wang Applied Superconductivity Laboratory, Southwest Jiaotong University (ASCLab), Chengdu , Sichuan, China rzeng@home.swjtu.edu.cn S. Wang asclab@asclab.cn R. Zeng School of Information Science and Technology, Southwest Jiaotong University, Chengdu , Sichuan, China the seeded directional solidification method has unique fluxpinning properties [1 5]. This allows these samples to realize large levitation force and a stable equilibrium between a permanent magnet and bulk HTSC, which makes bulk HTSC show most promising applications in the Maglev vehicle [6 8]. At present, researchers have started to study the high temperature superconducting (HTS) Maglev train in practical operations in Brazil [9], China [10 14], and Germany [15]. When the pull force is applied on the vehicle, the few investigate electromagnetic properties when the bulk HTSC simultaneously moves along longitudinal direction and vertical direction above the permanent magnetic guideway (PMG). When the HTS Maglev train begins to accelerate or decelerate, the tip edges of the train undergo a lifting or diving movement above the PMG, respectively. The diving and lifting movements mean that the bulk HTSC onboard the train moves in a slant-type line. The slant-type line with different angles represents the different moving states, such as slow and softly increasing or decreasing the speed, suddenly increasing or decreasing the speed, and so on. To investigate the levitation force performance of the HTS Maglev system while simultaneously moving along the longitudinal and vertical directions, by moving a fixed vertical distance, this paper gives the experimental results by comparing bulk HTSC operating slant-type line movement with different angles above the PMG with a quasistatic speed in a field-cooling case. This paper also gives the experimental results by comparing bulk HTSC operating slant-type line movement back and forth five times. 2 Experimental Details Figure 1 illustrates the HTS Maglev three-dimensional motion measurement system which combines a vertical step

2 2310 J Supercond Nov Magn (2012) 25: Fig. 1 Scheme of the HTS Maglev three-dimension motion measurement system. 1 Vertical step motor; 2 Vertical displacement sensor; 3 Longitudinal step motor; 4 Longitudinal displacement sensor; 5 Lateral step motor; 6 Lateral displacement sensor Fig. 2 Scheme of the mechanism of the clamp. 1 The base; 2 Fixed board; 3 Left force sensor; 4 Support pillar; 5 Right force sensor motor and a longitudinal step motor to simulate the slanttype movements back and forth multiple times [16]. As showninfig.2, the direction of the y-axis is parallel to the longitudinal direction of the PMG. The direction of the x-axis is parallel to the lateral direction of the PMG. The direction of the z-axis is parallel to the vertical direction of the PMG. The center axis of the clamp superposes the center line of the symmetry plane of the PMG parallel to the YZ plane at the grid origin (y = 0 mm, z = 0 mm) in Cartesian coordinates. In the following, the vertical displacement is the distance from the surface of the PMG to the appointed position parallel to the Z-axis. The longitudinal displacement is the distance from the bulk HTSC center to the appointed position parallel to the Y -axis. The bulk HTSC is fixed by the clamp. Either repulsive force or attractive force along Z direction is transmitted to the clamp, then to the pillar of the clamp, and finally to the force sensor. The force data can be acquired in the computer. AsshowninFig.3, the levitation gap is defined as the distance from the bottom of the surface of the bulk to the top surface of the PMG. The rectangle-shaped multi-seeds HTSC bulk is 32 mm 13 mm 64 mm. The working height (WH) is 10 mm. The field-cooling height is 30 mm. The bulk HTSC moving route is shown as Fig. 4. The experimental method is as follows. First, the bulk HTSC is cooled by liquid nitrogen at field-cooling height and some flux is trapped. Second, the bulk HTSC with the Dewar is lifted to the appointed position where the distance is 60 mm from the bottom of the surface of the bulk to the top surface of the PMG along Z direction. Third, the bulk HTSC moves along the routes shown in Fig. 5 come and back five times with different angles θ (θ = 30, 40 and 60 ) at a speed of 2.0 mm/s. Figure 5 displays that the h is defined the vertical length, and the l is defined the length of moving route. 3 Results and Discussion Figure 6 displays the distribution of calculated magnetic field of the bulk HTSC moving route above the PMG with different angles along longitudinal direction when x = 0. As shown in Fig. 6, with the angle increasing, the maximum of Bz and By along Y direction decreases. According to the Lorentz equation, the formulation of the magnetic force act-

3 J Supercond Nov Magn (2012) 25: Fig. 3 Schematic diagram of levitation system Fig. 4 The bulk moving route along Y Z plane Figure 7 shows the levitation force performance along vertical direction by operating slant-type line movement with different angles (θ = 30, 40 and 60 ) at a speed of 2.0 mm/s. It shows that the levitation force reaches a maximum when θ = 30 with the levitation gap of 10 mm, however, with the angle increasing, the levitation force decreases when the levitation gap is 10 mm. The maximal levitation force reaches N, N, and N, respectively, when θ = 30, 40, and 60 with the levitation gap of 10 mm. And this result is consonant with the result of calculated magnetic field. The hysteresis is the largest when θ = 60. With the angle decreasing, the hysteresis is getting smaller. From the bulk HTSC moving route on the PMG with different angles, the length along vertical direction is the same distance of 50 mm with different angles. However, because of the different angles, the length of moving route is different. The relationship is l = h/ sin θ (2) Fig. 5 The bulk HTSC moving route above the PMG with different angles ing on the bulk HTSC is given F lev = J B ext dv (1) V J is the current density. The levitation force is related to the external magnetic field of the bulk HTSC. With the external magnetic field increasing, the levitation force will increase. Therefore, with the angle increasing, the moving distance is decreasing. This means that it spends more time when θ = 30 than when θ = 60 to complete the 50 mm vertical distance with the same speed of 2.0 mm/s. According to Maxwell equations, the electric field intensity E should satisfy E dl = l s B t ds (3) This means that with the moving speed increasing along the vertical direction, the electric field intensity E is increasing also. Because the loss power density p l satisfies p l E 2, with E increasing p l increases. Therefore, with the moving speed along the vertical direction increasing, the hysteresis is increasing.

4 2312 J Supercond Nov Magn (2012) 25: Fig. 6 Distribution of calculated magnetic field of the bulk HTSC moving route above the PMG with different angles along longitudinal direction when x = 0. (a) Bz,(b) By Fig. 7 The relationship of levitation force and vertical displacement by operating slant-type line movement with different angles (θ = 30, 40, and 60 ) at a speed of 2.0 mm/s. (a) the levitation force performance by moving slant-type line movement when θ = 60, (b) the levitation force performance by moving slant-type line movement when θ = 40,(c) the levitation force performance by moving slant-type line movement when θ = 30,(d) the levitation force performance with the levitation gap of 10 mm Figure 8 shows that the levitation force performance along longitudinal direction is the same case as along vertical direction by operating slant-type line movement with different angles (θ = 30, 40, and 60 ) at a speed of 2.0 mm/s. AsshowninFig.6, with the angle increasing, the maximum of Bz and By along Y direction decreases. So, the maximal levitation force along Y direction decreases while the angle is increasing. And the moving route along Y direction is increasing with the angle decreasing, the hysteresis is decreasing. Figure 9 is the experimental results of levitation force of the bulk HTSC moving slant-type line movement back and forth five times above the PMG when θ = 30.FromFig.9, the levitation force is the largest at first time when the lev-

5 J Supercond Nov Magn (2012) 25: Fig. 8 The relationship of levitation force performance and longitudinal direction by operating slant-type line movement with different angles (θ = 30, 40, and 60 )ata speed of 2.0 mm/s. (a) the levitation force performance by moving slant-type line movement when θ = 60, (b) the levitation force performance by moving slant-type line movement when θ = 40,(c) the levitation force performance by moving slant-type line movement when θ = 30 Fig. 9 The levitation force performance by moving slant-type line movement back and forth five times when θ = 30 itation gap is 10 mm, and the levitation force is almost the same case from two to five times when the levitation gap is 10 mm. At first time back and forth movement, the hysteresis reaches the largest, however, the hysteresis is almost the same case from two to five times back and forth movements. The reason is that when the bulk HTSC first declines in the process, the interior of the bulk HTSC produces only one direction of the induced current. However, in the second decline process, with two directions of the induction current in the bulk, the positive induction current is separated by a negative induction current. The positive induction current interacts with the external magnetic field to produce the levitation force, and the negative induction current interacts with the external magnetic field to produce the attractive force. In spite of two parts positive induction current within the bulk HTSC in the second descent, the inside induction current ring is smaller. On the influence of attraction force caused by negative induction current, in the second decline process, the levitation force is smaller than it in the first decline process. In the process of testing, the nuance between the two levitation forces is caused by the superconductor internal magnetic flux peristalsis. With the movement times increasing, the hysteresis goes to saturation, and so the hysteresis curve is the same.

6 2314 J Supercond Nov Magn (2012) 25: Conclusion We have carried out an experimental investigation of divelift movement on HTS electromagnetic properties by considering different angles above the PMG with a fixed vertical distance. Three points are noteworthy: First, with the angle increasing, the levitation force decreases when the levitation gap is 10 mm. Second, with the angle increasing, the hysteresis is increasing. Third, the hysteresis reaches the largest at first time of back and forth movement, and with the increasing operating times, the hysteresis is almost the same case in the following times of back and forth movements. And these results mean that slow and softly accelerating or decelerating will have little effect on the bulk, but suddenly increasing or decreasing the speed will decrease the levitation force of the bulk and increase the hysteresis of the bulk HTSC. Hopefully, the present may stimulate further work to contribute to HTS Maglev application in practical use. Acknowledgements This work was supported by the National High Technology Research and Development Program of China (2007AA03Z210), and the National Natural Science Foundation in China ( ), and the Fundamental Research Funds for the Central Universities (SWJTU09BR114). The authors would like to thank all the persons who contributed to the project. We are also grateful to D.C. Yang and L. Qin for providing technology support. References 1. Lee, D.F., et al.: J. Appl. Phys. 76, 603 (1994) 2. Brant, E.H.: Science 243, 349 (1989) 3. Moon, F.C.: Superconducting Levitation, pp Wiley, Hoboken (1994) 4. Okano, M., Iwamoto, T., Furuse, M., et al.: J. Phys. Conf. Ser. 43, 999 (2006) 5. Murakami, M.: Physica C 341(348), (2000) 6. Wang, S., et al.: In: Proceedings of Fifteenth International Conference on Magnet Technology, Part I, p. 767 (1998) 7. Wang, J., et al.: IEEE Trans. Appl. Supercond. 9(2), 904 (1999) 8. Weh, H.: In: Proceedings of Fifteenth International Conference on Magnet Technology, Part I, p. 383 (1998) 9. Stephan, R., David, E., et al.: In: Proc. 20th Int. Conf. on Magnetically Levitated Systems and Linear Drives (MAGLEV), San Diego (2008) 10. Wang, J., et al.: Physica C (1), (2002) 11. Ren, Z., et al.: Physica C 384(1 2), (2003) 12. He, Q., et al.: J. Supercond. Nov. Magn. 22, (2005) 13. Deng, Z., et al.: Supercond. Sci. Technol. 22(5), (2009) 14. Lu, Y., et al.: J. Supercond. Nov. Magn. 21, (2008) 15. Schultz, L., et al.: IEEE Trans. Appl. Supercond 15(2) (2005) 16. Zeng, R., et al.: IEEE Trans. Appl. Supercond. (2012). doi: /tasc