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# 27th IAEA Fusion Energy Conference - IAEA CN-258

22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
CONFERENCE MATERIAL NOW AVAILABLE!

## Experimental observations of the plasma shape effect on the RMP-ELM coupling for optimization of the KSTAR ELM-crash control

26 Oct 2018, 08:30
4h
Mahatma Mandir Conference Centre

#### Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Poster

### Speaker

Dr YoungMu Jeon (National Fusion Research Institute)

### Description

Reliable and robust resonant magnetic perturbation (RMP) on the edge-localized-mode (ELM) crash control is crucial for the success of ITER and beyond. In recent KSTAR experiments, a critical dependence of RMP-ELM coupling on the plasma shape was found to be as important as much as $\mathrm{q_{95}}$. In application of the low-n RMP fields, small variations in the lower triangularity by controlled $\mathrm{R_{X,lower}}$ (radial position of lower X-point) made significant changes on RMP coupling, suggesting a narrow window for the ELM-crash suppression. For the shape effects found in 2016, such $\mathrm{R_{X}}$ window for the RMP induced ELM-crash suppression was surprisingly narrow ($\mathrm{\delta_{lower}=0.74\pm0.04}$ and $\mathrm{R_{X,lower}=144\pm2cm}$), while the other shape parameters, such as $\mathrm{Z_{X}}$, seem to have weak effects. Also it was found that the same shape valid for the n=1 RMP was not effective for the n=2 RMP induced ELM-crash suppression. In 2017, further study revealed that such a strict condition of triangularity ($\mathrm{R_{X,lower}}$) can be relaxed by allowing for an additional small up-down asymmetry on the plasma shape. Applying this new optimized plasma shape led us to make substantial improvements on reliability and robustness of the RMP induced ELM-crash control. As a result, the n=1 RMP induced ELM-crash suppression were successfully demonstrated in a wide range of $\mathrm{q_{95}}$ even with a fixed RMP spectra, achieving a record-long sustainment of ELM suppression more than ~30 sec. Similarly, the n=2 RMP-induced ELM-crash suppression was achieved with the same shape (universality) at ITER-relevant low $\mathrm{q_{95}}$=3.3~3.5. Furthermore, we found a singular response to the shape change for the RMP-plasma coupling, with a support of ideal MHD modeling.
Country or International Organization Korea, Republic of EX/P7-15

### Primary author

Dr YoungMu Jeon (National Fusion Research Institute)

### Co-authors

Dr Gunyoung Park (National Fusion Research Institute) Prof. Hyeon K. Park (UNIST) Dr Hyunsun HAN (Nuclear Fusion Research Institute, Korea) Dr Jayhyun Kim (National Fusion Research Institute) Dr Jong-Kyu Park (Princeton Plasma Physics Laboratory) Dr Joon-Wook Ahn (Oak Ridge National Laboratory) Dr Kimin Kim (National Fusion Research Institute) Dr Si-Woo Yoon (National Fusion Research Institute) Dr Yeong-Kook Oh (National Fusion Research Institute) Prof. Yongkyoon In (Ulsan National Institute of Science and Technology)