Patent ID: 7224250

Claim:
A superconducting magnet apparatus comprising: a vacuum container including an inner tank forming therein a low-temperature domain and housing a superconducting coil, a heat shield covering the inner tank and forming therein a mid-temperature domain with a temperature higher than in the low-temperature domain, and an outer tank containing the heat shield so as to separate the heat shield from the ambient air and forming a normal-temperature domain with a temperature higher than in the mid-temperature domain; a current lead connected at one end to the superconducting coil, and connected at the other end to a lead line leading to an external excitation power source provided outside the vacuum container; a switch to be turned on and off in order to shunt or open both ends of the superconducting coil; and a switching device that turns on and off the switch, the superconducting apparatus being switched to a persistent current mode by supplying an electric current to the superconducting coil from the external excitation power source through the current lead under a condition that the switch is off, thereby causing the superconducting coil to generate a necessary magnetic field, arid then shunting both ends of the superconducting coil by turning on the switch, wherein the current lead includes a first current lead connected at one end to one end of the superconducting coil in the low-temperature domain and a second current lead connected at one end to the other end of the first current lead in the mid-temperature domain and connected at the other end to the lead line in the normal-temperature domain, at least the first current lead including the superconducting current lead which becomes a superconducting state in the mid-temperature domain, and wherein the switch includes a thermal superconducting switch connected to the both ends of the superconducting coil to shunt the superconducting coil in the low-temperature domain and a mechanical switch connected to the both ends of the first current lead in parallel to the thermal superconducting switch and able to shunt the superconducting coil in the mid-temperature domain, the mechanical switch being turned on and off through a driving mechanism disposed in the mid-temperature domain and driven by the switching device.