6.10 Levitation forces and guidance forces of ring HTS bulks Ë 181Fig. 6.35:Levitation forces of residual
thickness of YBCO sample [43].6.10 Levitation forces and guidance forces of ring HTS bulks [43]
The levitation forces of ring-shaped YBCO bulks above an NPM guideway were studied.
The investigation focused on the influence of the ring HTS YBCO bulk on the levitation
forces. In this experiment, three cylindrical YBCO bulks, one with a hole of 8 mm in
diameter was made in sample BJ214, one with a hole of 12 mm in diameter for sample
BJ215 and one with a hole of 18 mm in diameter for sample BJ216, were used (Fig. 6.36).
The outer diameter was 30 mm, and the thickness was 16 mm. The levitation forces of
each bulk were measured above the PMG at FCH 40 mm.
Figure 6.37 shows the levitation forces comparison for each of these bulk as
shown in Fig. 6.37a and b, when the hole diameter was 8 or 12 mm, there was hardly
any difference in the levitation forces between with or without a hole. As shown in
Fig. 6.37a and b, when the hole diameter was 8 and 12 mm, it hardly had any influence
on the levitation forces in the whole measuring range, i.e. gap from 40 to 3 mm. When
the hole was enlarged to 18 mm in diameter, the levitation forces began to decrease
at a lower levitation gap, but still hardly influenced the levitation forces at a larger
levitation gap. For example, gaps more than 20 mm are shown in Fig. 6.37c. This
proved that the outer part of YBCO bulk contributes more to the levitation forces
Fig. 6.36:Ring-shaped YBCO bulk with different holes [43].