4.7 HTS bulk Maglev train Ë 103levitation forces and the guidance forces are decided by calculation and experiment.
Although the magnetic energy product the HTS bulks is high, it also is certainly
limited. In order to obtain the maximum levitation and guidance forces, we must
complete the optimum design according to the specific application.
The HTS Maglev phenomenon can be very easily demonstrated and its physi-
cal principle is not difficult. However, development of adequate physical models
is difficult because the HTS bulk is a special type II superconductor. It is a quasi-
crystal containing particles and micro-holes and has a strongly irreversible magnetic
behavior, i.e., the magnetization depends on the prehistory of the magnetic field.
In addition, HTSCs are often in a very complex magnetic field. Two- and three-
dimensional modeling and simulation will be introduced in Chapter 7.
The HTS bulk Maglev is discussed above. The HTS bulk Maglev can be widely used
in the construction of practical Maglev trains, Maglev launch systems, frictionless
bearings, Maglev flywheel energy storage devices, etc. In addition to this, the magnetic
levitation of HTS thin films also has been studied.
Epitaxial YBCO films on single crystalline substrates are mainly used for the
superconducting microwave devices. The levitation forces between a permanent
magnet and a superconducting thin film have been investigated [86, 87] experi-
mentally, because of the high current density of YBCO film. It has been found that
thin films produced very high values of the vertical forceFzand magnetic stiffness
휅z=훿Fz/훿zper unit volume of superconducting material. The levitation force of a
three epitaxial YBCO film stack per unit volume is extremely high [86], yielding
100 N/cm^3 , whereas the corresponding levitation force for MTG bulk samples is about
1 N/cm [3]. Experimental studies and theoretical modeling of the levitation force
between a permanent magnet and a superconducting thin film have been reported
[88]. After measurements of the forceFzand magnetic stiffness휅zas functions
of distanceszbetween the magnet and superconductor, the explicit formulas for
bothFzand휅zare derived. An important result is that this has been established
as a basis for usingFz(z) data to infer the critical current density and its field
dependence.
4.7 HTS bulk Maglev train
4.7.1Unique advantages of HTS bulk Maglev
- Magnetic levitation of the HTS bulks is a self-stable levitation system, which does
not require active control. - Energy efficiency: Both levitation and guidance do not require active control or
an on-board power supply system. The total operational cost is almost negligible
due to the affordability of liquid nitrogen (77 K, 78% in air and easy to liquefy). The
price of liquid nitrogen is about 1/100th of that liquid helium (4.2 K). The energy