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Following completion of the Yamanashi Maglev Test Line, running experiments commenced in the spring of 1997. By utilizing a superconducting magnet loaded on the vehicle, the eddy current flows by being exposed to the fluctuating field from the ground coils. In addition, the field of the superconducting coil influences the eddy current and the magnetic force generates vibration.
A countermeasure against the compounding between this electromagnetic action and the mechanical vibration action is a remarkable and difficult point in the superconducting magnet design. Mechanical vibration in the cryogenic temperature portion generates heat by fretting between the internal structures and by friction. Further, since the eddy current generates heat by joule loss, heat generation at these cryogenic portions leads to the evaporation of liquid helium; the key is whether this amount of heat generation can be compensated by the reliquefying capability of the refrigerator loaded on the vehicle.
Hitachi, Ltd. has achieved, firstly, the suppression of both vibration and the eddy current by structural optimization through numerical analysis, and secondly in accommodating the amount of helium evaporation within the specified value. By developing a peculiar insulating method, which allows excellent mass productivity aiming chiefly at the security of durability and reliability, the ground coil has attained the specified performance.