High Temperature Superconducting Magnetic Levitation

6.20 Long-term stability of YBCO bulks in 2001–2009 Ë 211

Fig. 6.75:Measurement results of YBCO

bulk properties of some samples for A 15

group in 2000 and 2009 [63].

Fig. 6.76:Measurement results of trapped flux

for several YBCO bulks in 2000 and 2009 [63].

In addition, the properties of the YBCO bulks from different periods for some samples
in the A 15 group were compared. Figure 6.75 shows the measurement results of YBCO
bulk properties for some samples from the A 15 group in 2000 and 2009 which were in
close agreement. The figure demonstrates that the difference between levitation forces
for different YBCO bulks was small after long-term use.
In order to confirm the influence of the vehicle operation on pinning in the YBCO
bulk, the trapped flux of both bulk A5 and bulk old-1 was measured using constant
magnetic field magnetization method. The old-2 bulk was another sample from the
same A5 batch purchased, but not used in the loading operation.
The constant magnetic field was provided by an EM4-VC electromagnet from
Lakeshore, duration was 15 minutes, and the magnetic field was 1.16 T at a current
of 60 A. Magnetic field scan at gap of 6 mm above the YBCO bulk seeded surface was
measured with 460 Gaussmeter and Hall probe. Figure 6.76 shows the measurement
results for the trapped flux in several YBCO bulks.
As you can see from Fig. 6.76, the trapped flux in the A5 bulk and the old-2
bulk was close, and both were slightly higher than that with the old-1 bulk. In
addition, the maximum trapped flux of A5, old-1, and old-2 were 2270, 2084, and
2132 mT, respectively. The measurement results showed that the trapped magnetic