6.7 Guidance forces of HTS bulks over PMG Ë 171Fig. 6.23:Guidance forces vs. lateral displacement in 0.184 T trapped flux [31].
Fig. 6.24:Guidance forces of YBCO bulk arrays above two parallel PMG with different maximum
lateral displacement [31].
Figure 6.24 shows guidance forces on the YBCO bulk arrays above two parallel PMG
when the maximum lateral displacement (MLD) was 5 and 15 mm, respectively. When
MLD was 5 mm, even though guidance forces were small, the place corresponding to
zero guidance force was always the original position, which implied that the YBCO
bulk arrays can return to its original place freely after they have been displaced, i.e.
the center of the PMG. Compared with the guidance force at MLD=5 mm, when MLD
was 15 mm, the guidance forces were larger and increase faster with the increase of
the lateral displacement, but the guidance forces decreased faster to zero before
it returned to its original position. This is not beneficial to lateral stability of the
levitation system. Thus, the effective lateral displacement, which is defined as the
maximum lateral displacement corresponding to the levitation system being able to
return to its original position after being displaced, is very important for the design of
practical levitation systems.