Eddy current heating and thermo-mechanical response of the in-vessel control coil in the Korea Superconducting Tokamak Advanced Research

Accurate control of high-temperature plasma is essential for realizing fusion energy. The in-vessel control coil (IVCC) of the Korea Superconducting Tokamak Advanced Research (KSTAR) plays a key role in plasma stabilization, yet its coil case exhibits a pronounced temperature rise during operation, raising concerns about insulation integrity and mechanical reliability. To address these issues, this study combines full-scale experiments (high vacuum, <10−3 Torr; 0.5–1.0 kA, 60 Hz) with a coupled electromagnetic (EM)–thermal–structural model to quantify eddy current heating and the resulting thermo-mechanical response. Despite larger EM losses in unpowered conductors, the coil case experiences a temperature rise due to the absence of direct cooling. As the input increased from 0.5 kA–60 Hz to 1.8 kA–160 Hz, coil case eddy current loss rose from 1.2 W to 72.6 W and temperature from 37.4°C to 139.0°C, following a scaling (∝I2fn,n≈ 1.6), indicating that the thermal response is governed by eddy current heating. Design variations revealed a trade-off between heat spreading and EM susceptibility: a copper cap intensified eddy currents and raised the temperature to 270°C, whereas a stainless-steel cooling pipe provided convective removal and reduced it to 122°C. These results indicate that, to utilize high-σe materials effectively, design strategies that interrupt eddy current loops are required. Localized eddy current heating induces steep temperature gradients across the epoxy-glass insulation amplified local shear stress. Collectively, these results show that conventional hotspot strategies using high-conductivity masses can exacerbate heating in strong magnetic fields; robust IVCC performance therefore requires integrated EM–thermal co-design, particularly for long-pulse fusion devices. © 2025 Elsevier Ltd.
1.6), indicating that the thermal response is governed by eddy current heating. Design variations revealed a trade-off between heat spreading and EM susceptibility: a copper cap intensified eddy currents and raised the temperature to 270°C, whereas a stainless-steel cooling pipe provided convective removal and reduced it to 122°C. These results indicate that, to utilize high-σe materials effectively, design strategies that interrupt eddy current loops are required. Localized eddy current heating induces steep temperature gradients across the epoxy-glass insulation amplified local shear stress. Collectively, these results show that conventional hotspot strategies using high-conductivity masses can exacerbate heating in strong magnetic fields; robust IVCC performance therefore requires integrated EM–thermal co-design, particularly for long-pulse fusion devices.