162 Ë 6 First manned HTS Maglev vehicle in the world
Fig. 6.10:Levitation forces vs gap at a
displacement of 5 mm. The top right is the
minor hysteresis loops conducted upon
major loop from gaps of 22–18 mm [29].Fig. 6.11:Schematic drawing of the test device using the GM refrigerator for measurements
of levitation forces at 38–77 K [33].
In order to measure the levitation force between the NdFeB disk and the YBCO bulk,
the permanent magnet NdFeB disk of휙 30 ×15 mm was fixed on the vertical moving
part of the SCML-01, and the YBCO bulk of휙 30 ×14 mm was fixed on the second step
cooling head of the refrigerator. The levitation force between YBCO and NdFeB could
be measured at different gaps and at different temperatures. The maximum magnetic
fields were 0.42, 0.219, and 0.0535 T at the NdFeB surface, 5 mm, and 20 mm above,
respectively. The minimum gap between YBCO and NdFeB was 5 mm.
Figure 6.12 shows the photograph of the test device using the G-M refrigerator at
38–77 K with the SCML-01 platform [32].
After the YBCO bulk was cooled down to 40 K by the refrigerator, the NdFeB
was fixed on the vertical moving part of the SCML-01, which moved down and up.
The gap between YBCO and NdFeB changed from 150 to 5 mm, the levitation force
data were sampled by the computer at the same time, which was used to control
the measurement system and to sample the measurement data. Figure 6.13 shows
one of the measurement results at 38.4 K, which indicates the relationship between
the levitation force and the gap. Table 6.6 shows the measured maximum levitation
force at different temperature. The relationship between the maximum levitation force
at the same (minimal) gap and temperature is shown as Fig. 6.14 [30].