Experimental Results of Simplified Balance Bridges for the KSTAR Quench Detection System

The primary quench detection system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device has been operated in technical and plasma experiments for eight years. Cowound-type quench detectors have exhibited distinct performance of compensation for both self-induction and mutual induction; on the other hand, some cowound strips tended to break in the long-term operation. In contrast, Wheatstone bridge (WB)-type quench detectors had no wire breakage, and their signal wires are still accessible and repairable. Therefore, WB-type quench detectors are very important to be a backup method of quench detection for the coils. New WBs using a half-bridge at a fixed ratio of resistances of 1:1 were tested in the KSTAR operation. Upper-lower comparison of the new WBs performed good compensation for induced voltage. The new WBs clearly demonstrated that the bridge circuits may become very simple, and in situ calibration may be unnecessary if the arrangement of voltage taps and quench detectors is optimized with respect to the magnetic field of the tokamak device.