The superconducting phenomenon does not occur unconditionally. A superconducting state occurs only under limited temperature, magnetic field, and current density, and the upper limit values are called critical temperature (Tc), critical magnetic field (Hc), and critical current density (Jc), respectively. Until now, these upper limits were the obstacles to industrial applications, and application of superconducting technology was limited to such field as MRI for medical care.
However, development of oxide high-temperature superconductor and improvement in critical current density of superconducting wire materials enhanced the feasibility of practical application of superconductivity in new fields. The possible fields of application include the environment and energy represented by power cables and the transportation and industry represented by linear-motor cars.