AbstractThe high field superconducting toroidal field (TF) coils in TRIAM-1M have been successfully operated for more than 10 years. The effect of the plasma disruption on the superconducting TF coils has been studied, since the plasma disruption can give a serious effect such as coil quench. In the actual plasma disruption, the alternative current (AC) loss of the superconducting TF coils increased in proportion to the square of the plasma current just before the disruption. The dependence of the AC loss on the plasma current is in good agreement with the calculation. The AC loss of the TF coil was also measured using external pulse coils with three kinds of characteristic times of variation in the coil current (0.06, 0.5 and 6 ms). The AC loss increased in proportion to the square of the total current of the external pulse coil. The increase in the AC loss depends on the characteristic time of the magnetic field variation. It means that the AC loss due to the disruption can be reduced using the dependence of the AC loss on the characteristic time of the magnetic field variation.