Superconducting coil protection method and superconducting magnet device

A superconducting magnet device comprising:

• a superconducting coil made by winding superconducting wire;
• a housing for accommodating the superconducting coil in a superconducting state;
• and
• a power supply for energizing the superconducting coil, wherein
• the superconducting magnet device further comprises a controller configured to measure a magnitude of a screening field induced by screening current flowing through the superconducting wire which is in the superconducting state, and to decrease electric current flowing through the superconducting wire based on the measured magnitude of the screening field,
• the controller includes a magnetic sensor which measures a magnetic field in a direction of a thickness of the superconducting wire at a predetermined position, and
• the controller decreases the electric current flowing through the superconducting wire based on the magnitude of the screening field, which is a difference between the magnetic field measured by the magnetic sensor and another magnetic field in the direction of the thickness calculated disregarding an effect of the screening current.