Speaker
Dr
Yongkyoon In
(National Fusion Research Institute)
Description
An extensive study of intrinsic and controlled non-axisymmetric field impacts in KSTAR has enhanced the understanding about non-axisymmetric field physics and its implications, as well as demonstrating the importance of optimal 3-D configurations in resonant magnetic perturbation (RMP)-driven control on edge localized modes (ELMs) in tokamaks. The $n=1$ intrinsic non-axisymmetric field was measured to remain as low as ${\langle\delta B/B_0\rangle}_{m/n=2/1} \sim 4\times 10^{-5}$ at high-beta plasmas ($\beta_N\sim2$), which corresponds to approximately 20% below the targeted ITER tolerance level. A systematic survey of $n=1$ controlled resonant field has revealed that KSTAR has a lower power threshold for L-H transition (at least 10 %) than DIII-D (configured with $n=3$ RMP) with similar plasma densities of $n_e=(2 -2.6)\times 10^{19} m^{-3}$, possibly benefiting from a low level of intrinsic error field and toroidal field ripple. As for the RMP ELM control, a high-quality $n=1$ RMP ELM suppression (duration of $\sim40 \tau_E$) was achieved using an operationally ‘reproducible’ approach. Throughout this investigation, we diagnosed edge activities using 3‐D ECE imaging diagnostics (ECEI) on both high-field-side (HFS) and low-field-side (LFS) simultaneously for the first time. According to ECEIs, the RMP ELM suppression was full of lively edge activities, which appears quite challenging to a prevailing theory that ‘peeling‐ballooning’ stability boundary is crossed from unstable to stable regimes due to RMP. While exploring the most favorable 3-D configuration ($n=1$, +90 deg. phasing), we discovered that midplane IVCC coils played a major role in mitigating the ELMs, while two off-midplane IVCCs ($n=1$ odd-parity) appeared insignificant on ELMy behavior change. In contrast, when the off-midplane IVCCs are configured with n=1 even-parity, strong plasma response was observed, even triggering mode-locking at high RMP currents. Considering that the ITER RMP coils are composed of 3-rows, just like in KSTAR, further 3-D physics study in KSTAR is expected to help us minimize the uncertainties of the ITER RMP coils, as well as establish an optimal 3-D configuration for ITER and beyond.
| Country or International Organization | Korea |
|---|---|
| Paper Number | EX/1-3 |
Primary author
Dr
Yongkyoon In
(National Fusion Research Institute)
