Superconducting magnet, MRI, and NMR

A superconducting magnet comprising:

• a superconducting coil;
• a persistent current switch;
• and
• one of a pulsed power supply or a charge/discharge circuit, wherein
• the one of the pulsed power supply or the charge/discharge circuit is connected to a loop circuit of the superconducting coil and the persistent current switch such that the one of the pulsed power supply or the charge/discharge circuit is in parallel with the persistent current switch,
• the persistent current switch includes a superconducting wire,
• the superconducting wire has disposed on an inner periphery thereof a normal conducting portion and a superconducting filament, and has disposed on an outer periphery thereof a sheath, and
• provided that a fundamental frequency of a waveform of a current supplied by one of the pulsed power supply or the charge/discharge circuit when expanded in a Fourier Series is f, a thickness of the sheath is t, a resistivity of a material of the sheath is ρ, and a permeability of the sheath is μ, t/2√(ρ/πfμ).