| 摘要 |
PROBLEM TO BE SOLVED: To restrict the increase of a leak magnetic field upon occurrence of quenching concerning an active shield system magnetic field generator.SOLUTION: The magnetic field generator 1 includes a second shield coil 50 and a second shield coil protecting circuit 60. The second shield coil protecting circuit 60 includes a bi-directional diode 61. The ON-voltage Vof the bi-directional diode is set to be larger than electromotive force Vwhich is generated in the second shield coil, by electromagnetic induction caused by magnetic field change in excitation or demagnetization of a main coil protecting circuit 30 and a first shield coil 20 (i), and also is set to be equal to or less than electromotive force Vwhich is generated in the second shield coil 50, by electromagnetic induction caused by the magnetic field change upon occurrence of quenching in the main coil 10 or the first shield coil 20 (ii). |
