Patent ID: 7990661

Claim:
An active shield superconducting electromagnet apparatus comprising: a main switching circuit including a first main coil, a second main coil, a first shield coil, a second shield coil, and a first superconducting persistent current switch, which are connected in series, the second main coil having the same excitation direction as that of the first main coil, and the first shield coil and the second shield coil having an excitation direction reverse to that of the first main coil; a sub switching circuit including a bypass circuit which is connected to a series circuit of the first main coil and the second main coil, or to a series circuit of the first shield coil and the second shield coil, in parallel, the bypass circuit including: a superconducting fault current limiter for limiting a current flowing therethrough through transition from a superconducting state to a normal conducting state when a value of the current is greater than a pre-determined value, and a second superconducting persistent current switch, connected to the superconducting fault current limiter in series, and a first closed circuit including at least one of the first main coil and the first shield coil, and a first quench protection circuit, which are connected in series, the first quench protection circuit allowing a current not to flow therethrough in the absence of potential difference between both ends thereof, and allowing a current to flow therethrough in the presence of potential difference between both ends thereof; and a second closed circuit including at least one of the second main coil and the second shield coil, and a second quench protection circuit, which are connected in series, each of the first and second quench protection circuits allowing a current not to flow therethrough in the absence of potential difference between both ends thereof, and allowing a current to flow therethrough in the presence of potential difference between both ends thereof, wherein the first main coil, the second main coil, the first shield coil, and the second shield coil have the same axis, and are arranged on the axis in order of the first shield coil, the first main coil, the second main coil, and the second shield coil, and wherein each of the coils are connected in series in order of the first shield coil, the second main coil, the first main coil, and the second shield coil.