Experimental Evaluation of a Mutually Induced Voltage Correction Method to Improve the KSTAR Quench Detection System

The superconducting state of the coils and bus lines of the Korea Superconducting Tokamak Advanced Research is monitored by a quench detection system. The system utilizes co-wound conductive strips and Wheatstone bridges, and in addition compares two quench detection signals for upper and lower coils to reduce induced voltage. The co-wound conductive strips and Wheatstone bridges, however, are very sensitive to mutual induction by neighboring coil currents, and on the other hand the comparison of the quench detection signals is not assured in a vertically asymmetric magnetic field. Thus, a numerical correction method of the inductances and induced voltages on quench detection circuits for the CS and PF coils was evaluated using actual measurements. The inductance on each quench detection circuit had a peculiar profile probably caused by magnetism of the conductors. The amplitudes of the induced voltages certainly reflected the magnitudes of the inductances; however, the correction of the quench detection signals was difficult because the inductances available for the correction were obtained by alternately applying each coil current.