Performance Enhancement of Quench Detection System for the KSTAR Superconducting Pulse Coils

Since the first plasma was achieved in 2008, the quench detection system for the Korea Superconducting Advanced Tokamak Research (KSTAR) coils has been successfully operated. Simple bridge circuits and cowound voltage sensors were used for the first quench detectors. In order to enhance the reliability and stability of the quench detection especially for the pulse coils such as the KSTAR CS coil, a couple of schemes to actively reject inductive voltages have been added and tested. They have focused on rejecting as much inductive voltages as possible and increasing the noise rejection ratio (NRR) because the inductive voltage noise is a main factor to disturb the stable quench detection. One scheme is to use the voltage difference between two balanced bridge voltages or two voltages of cowound voltage sensors, where each voltage is the voltage across each of two coils having the same electrical currents and structurally symmetry. The other is to use the voltage difference between the measured voltage and the calculated voltage. With the additional schemes, inductive voltages were reduced so that the NRR could substantially increase up to 20 000. In this paper, the upgraded quench detection system was described for the KSTAR PF1 coil and the performance results were presented together with experimental data in the 2016 KSTAR campaign.