170 Ë 6 First manned HTS Maglev vehicle in the world
In the first FCH case, YBCO bulk was cooled by liquid nitrogen at 50 mm above the
center of the PMG, where the applied field was 0.1575 T. Guidance forces of the single
YBCO bulk were measured at two different heights, i.e. 10 and 20 mm. In the second
FCH case, YBCO bulk was cooled at 8 mm above the center of the PMG, where the
applied field was 0.6874 T, and then the guidance forces of the YBCO bulk were
measured at two different heights mentioned above.
Figure 6.22 shows the guidance forces of a single YBCO bulk above the PMG in
the first FC case, whose trapped flux was 0.092 T. The arrows indicate the moving
direction of the YBCO bulk during the experiments. As shown in Fig. 6.22, the guidance
forces exhibit strong hysteresis; moreover, the hysteresis increases with the decrease
of the measurement height (MH). It is obvious that guidance force at MH 10 mm is
much larger than that at MH 20 mm, especially near the center of the guideway. This is
because guidance forces do not depend only on trapped flux in the YBCO bulk, but also
depend on the applied field. Although the trapped flux was the same, the applied field
at MH 10 mm was stronger than that at MH 20 mm. Another possible reason is that the
strong magnetic field at MH 10 mm increases the amount of trapped flux. Especially
in the center of YBCO bulk, the pinning effect was not strong. In addition, it implied
that YBCO bulk had better lateral stability at a lower position above the PM guideway.
Figure 6.23 shows the guidance forces for the same sample above the same normal
permanent magnet (NPM) guideway in the second FC case, whose trapped flux was
0.184 T. Although its tendency is similar to that in the first FC case, there are also diffe-
rences between them. For example, the change of the guidance forces is monotonous in
Fig. 6.23; however, it is not monotonous in Fig. 6.22, especially at MH 10 mm. There was
nodifferenceexceptforthetrappedfluxinYBCObulkforthetwogroupsofexperimental
results. Thus, trapped flux is very important for investigation of the guidance forces.
The guidance forces of two YBCO bulk arrays above two parallel PMG were mea-
sured. Each array included 9 YBCO bulks arranged in a line. Each sample was 30 mm
in diameter and 17 mm in thickness, and was fixed at the bottom of the rectangular
vessel (Fig. 6.21).
Fig. 6.22:Guidance forces vs. lateral
displacement in 0.092 T trapped flux [31].