4.5 HTS wire Maglev train Ë 99Fig. 4.7:Appearance of HTS magnet using Ag-sheathed Bi2223 coil of the EDS Maglev train in
Japan [65].
in the EDS Maglev vehicle proved the practicability of the HTS magnet using G-M type
two-stage pulse tube cryocoolers.
In addition to the above EDS Maglev, the practicability of the EMS Maglev using
BSCCO HTS wire was studied [76]. The experimental results about the applicability of
HTS coils to Maglev systems were reported. EMS Maglev active control for a copper coil
magnet has been achieved, but the active control of the HTS coil magnet is complex.
This issue should be studied and solved.
The HTS BSCCO wires exhibit a poor pinning performance already at intermediate
temperatures and thus cannot be used for levitation even with liquid nitrogen cooling.
It is for this reason that coated conductors of YBCO are preferred to BSCCO. The corre-
sponding BSCCO, YBCO superconducting wires are referred to as second-generation
(2G) HTS wires. The main advantages of 2G HTS wires are: high critical current density,
large-scale production, lower manufacturing cost, better mechanical properties, and
superior performance under high magnetic fields. The 2G HTS REBCO wires are very
attractive to various Maglev applications (see Section 2.3).
Using 2G wires is especially effective in stability and reliability of Maglev magnets
and in simplification of magnet structure. Figure 4.8 shows the merits of applying HTS
2G wires to a superconducting magnet for the Maglev train. The original figure is a
schematic view of the LTS magnet which used Nb-Ti coils, and the symbol “≫” shows
merits of applying HTS 2G wires. In order to make use of the advantages of 2G wires, the
possibility of Maglev applications of the 2G wire with a high critical current density in
a high magnetic field was examined. Clearly, the weight and the energy consumption
of the on-board HTS 2G magnets and the cryocooler for the Maglev train will decrease.
The optimized operation temperature, 40 to 50 K for commercial 2G wires, used to
minimize the magnet weight has been reported [77].
The 2G wire enables conduction cooling of the magnet and reduction the total
weight of Maglev vehicles. A HTS 2G wire magnet was used to demonstrate [78] that a
magnetic flux density of 5 T can be achieved at 45 K and 6 T can be achieved at 40 K.
The current density of the 2G coil is 130 A/mm^2 , and it is similar to that of the existing
LTS Nb-Ti coil on-board magnet for the Maglev. The results of these studies have
proved that 2G wire can be applied to on-board magnets of the Maglev. The single-stage
cryocooler and radiation shieldless cryogenic structure can meet the requirements of