Mutual induction caused by IVCC currents on quench detection circuits of the KSTAR TF coils

• Published in: IEEE transactions on applied superconductivity 2023-08, Vol.33 (5), p.1-4
• Main Authors: Yonekawa, Hirofumi, Nam, Seokho, Chu, Yong, Lee, Hyunjung, Ahn, Hee-Jae, Kim, Youngok, Kim, Kwangpyo, Park, Kaprai
• Format: Article
• Language: English
• Subjects: Bridge circuits; Circuits; Coils; Coils (windings); Conductors; Electric currents; Error correction; Error correction & detection; Forward error correction; KSTAR; Mutual induction; Plasmas; Quench detection; Superconducting coils; Superconductivity; Tokamaks; Voltage measurement; Wheatstone bridges
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2023.3241267

The Quench Detection System (QDS) for the Toroidal Field (TF) coils and the Poloidal Field (PF) coils made of Nb 3 Sn or NbTi cable-in-conduit conductors is using Wheatstone bridges to compensate induced voltages, which are generated by electrical currents of the superconducting coils and a plasma, on the quench detection circuits of the Korea Superconducting Tokamak Advanced Research (KSTAR) device. On the other hand, the KSTAR device is equipped with In-Vessel Control Coils (IVCCs), which consist of 16 segmented windings made of normal conductors, for fast plasma position control, field error correction, and resistive wall mode stabilization. Electrical currents of the middle Field Error correction Coil (FEC) in a part of the IVCCs have strong mutual induction on the quench detection circuits of the TF coils due to the paths of the FEC's conductors, and the middle FEC currents, which had unusually long and very steep ramps, raised an emergency protection sequence of the TF coils in a KSTAR plasma experiment. Quench detection circuits only using traditional Wheatstone bridges are insufficient to cancel out such a mutual induction; whereas, the mutual induction can be numerically compensated in a theoretically straightforward calculation.