Patent ID: 7492556

Claim:
A quench protection circuit for a superconducting magnet, said quench protection circuit comprising: at least one heater associated with a corresponding coil of the superconducting magnet; an inductor which is inductively coupled to derive a voltage from variation in a magnetic field of the superconducting magnet, and is connected in series with the at least one heater for driving the at least one heater in response to variation in said magnetic field of the superconducting magnet; and; overcurrent protection means for limiting current which flows through said at least one heater in response to heating of said overcurrent protection means by said current; wherein said overcurrent protection means comprises a self-heating current limiting element that is arranged in a series circuit with said at least one heater and said inductor; and wherein said self heating current limiting element comprises a non-linear positive temperature coefficient resistor.