Superconducting magnet apparatus with a magnetic shield

A superconducting magnet apparatus with a magnetic shield comprising:

• a superconducting field coil divided into two or more superconducting coils which are connected in series and arranged sequentially, said superconducting coils forming symmetric pairs such that the superconducting coils corresponding to respective symmetric pairs are positioned on opposite sides of a center point of said superconducting field coil at equal distances from said center point, said superconducting field coil further including connection points disposed between each of said superconducting coils;
• a permanent current switch connected between both ends of said superconducting field coil;
• a plurality of protective circuits connected respectively between both ends of the superconducting field coil and between each pair of the connection points positioned symmetrically with respect to said center of the superconducting field coil such that said superconducting coils are arranged in symmetrical pairs with respect to the center of the superconducting field coil when connected to said protective circuits, each of said protective circuits having a predetermined turn-on voltage for protecting the superconducting coils against an overvoltage;
• a cryostat for housing said superconducting coil;
• and
• a magnetic shield for enclosing said cryostat.