Prediction of mechanical behavior of the KSTAR CS magnet based on PF coil currents

Abstract

The KSTAR includes seven pairs of ring-shaped poloidal field (PF) superconducting coils with rectangular cross section. The central solenoid (CS) is a vertical stack of four pairs of PF coils compressed axially by preloading structures. The axial compression (remaining preload) on the CS coils is monitored by strain measurement, one of the important monitoring parameters for safe operation of KSTAR. The preload variation during plasma discharge can be predicted based on the PF coils and plasma currents without complicated structural analysis. The calculation of equivalent vertical EM force was proposed to estimate the bottom displacement of the CS magnet with the assistance of the joint diagram for bolted joints. The predicted vertical displacements according to the proposed methodology were reasonably well in agreement with the displacement measured during long pulse discharge #18437. The predicted displacement was used to quickly calculate the preloading reduction of the CS magnet structure. This approach will contribute to the development of operation scenarios for long pulse and large plasma current discharges. During plasma discharge, our algorithm can be applied to a real-time plasma control system.