Diamagnetic flux measurement without a compensation coil in the Hanbit mirror

A diamagnetic loop receives the external magnetic field fluctuations distorted by vacuum vessel eddy currents. Without installing a compensation coil in vacuum, the fluctuation is compensated from the circuit model of the vacuum vessel with only a Rogowski coil measurement of the external magnetic coil current. The vacuum vessel is modeled as a mixture of several inductively linked conductors. By solving the circuit equations, it is shown that the distortion is given as a convolution of exponentially decaying functions and the Rogowski coil signal. The characteristic time is obtained by a least-squares fitting algorithm. The convolution is calculated by using the fast Fourier transform technique. The external magnetic field fluctuations of the diamagnetic loop are reduced to 0.005% of the external magnetic field intensity