Enhanced understanding of non-axisymmetric intrinsic and controlled field impacts in tokamaks

Journal Article · Thu Aug 24 00:00:00 EDT 2017 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aa791c· OSTI ID:1434245

In, Y. ^[1]; Park, J. -K. ^[2]; Jeon, Y. M. ^[1]; Kim, J. ^[1]; Park, G. Y. ^[1]; Ahn, J. -W. ^[3]; Loarte, A. ^[4]; Ko, W. H. ^[1]; Lee, H. H. ^[1]; Yoo, J. W. ^[1]; Juhn, J. W. ^[1]; Yoon, S. W. ^[1]; Park, H. ^[5]

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1. National Fusion Research Institute, Daejeon (Republic of Korea)
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. ITER Organization, St. Paul Lez Durance (France)
5. National Fusion Research Institute, Daejeon (Republic of Korea); Ulsan National Institute of Science and Technology, Ulsan (Republic of Korea)

Here, an extensive study of intrinsic and controlled non-axisymmetric field (δB) impacts in KSTAR has enhanced the understanding about non-axisymmetric field physics and its implications, in particular, on resonant magnetic perturbation (RMP) physics and power threshold (P _th) for L–H transition. The n=1 intrinsic non-axisymmetric field in KSTAR was measured to remain as low as δB/B ₀ ~ 4×10^–5 even at high-beta plasmas (β _N ~ 2), which corresponds to approximately 20% below the targeted ITER tolerance level. As for the RMP edge-localized-modes (ELM) control, robust n=1 RMP ELM-crash-suppression has been not only sustained for more than ~90 τ _E, but also confirmed to be compatible with rotating RMP. An optimal window of radial position of lower X-point (i.e. R _x = $$1.44\pm 0.02\,$$ m) proved to be quite critical to reach full n=1 RMP-driven ELM-crash-suppression, while a constraint of the safety factor could be relaxed (q ₉₅ = 5 $$\pm $$ 0.25). A more encouraging finding was that even when R _x cannot be positioned in the optimal window, another systematic scan in the vicinity of the previously optimal R _x allows for a new optimal window with relatively small variations of plasma parameters. Also, we have addressed the importance of optimal phasing (i.e. toroidal phase difference between adjacent rows) for n=1 RMP-driven ELM control, consistent with an ideal plasma response modeling which could predict phasing-dependent ELM suppression windows. In support of ITER RMP study, intentionally misaligned RMPs have been found to be quite effective during ELM-mitigation stage in lowering the peaks of divertor heat flux, as well as in broadening the 'wet' areas. Besides, a systematic survey of P _th dependence on non-axisymmetric field has revealed the potential limit of the merit of low intrinsic non-axisymmetry. Considering that the ITER RMP coils are composed of 3-rows, just like in KSTAR, further 3D physics study in KSTAR is expected to help us minimize the uncertainties of the ITER RMP coils, as well as establish an optimal 3D configuration for ITER and future reactors.

• Research Organization: Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Contributing Organization: 3D Physics Task Force in KSTAR
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1434245
• Journal Information: Nuclear Fusion, Vol. 57, Issue 11; ISSN 0029-5515
• Publisher: IOP Science
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
RMP
ELM control
power threshold
3D physics
ELM suppression
plasma response