Tokamak elongation – how much is too much? Part 2. Numerical results

Journal Article · Fri Dec 11 00:00:00 EST 2015 · Journal of Plasma Physics

DOI:https://doi.org/10.1017/s0022377815001300· OSTI ID:1897627

Lee, J. P. ^[1]; Cerfon, A. ^[2]; Freidberg, J. P. ^[3]; Greenwald, M. ^[3]

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1. New York University (NYU), NY (United States); Massachusetts Institute of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
2. New York University (NYU), NY (United States)
3. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

We report the analytic theory presented in Paper I is converted into a form convenient for numerical analysis. A fast and accurate code has been written using this numerical formulation. The results are presented by first defining a reference set of physical parameters based on experimental data from high performance discharges. Scaling relations of maximum achievable elongation (κ_max) versus inverse aspect ratio (ε) are obtained numerically for various values of poloidal beta (β_p), wall radius (b/a) and feedback capability parameter (γ τ_w) in ranges near the reference values. It is also shown that each value of κ_max occurs at a corresponding value of optimized triangularity (δ), whose scaling is also determined as a function of ε. The results show that the theoretical predictions of κ_max are slightly higher than experimental observations for high performance discharges, as measured by high average pressure. The theoretical δ values are noticeably lower. We suggest that the explanation is associated with the observation that high performance involves not only n = 0 MHD stability, but also n ≥ 1 MHD modes described by β_N in the Troyon limit and transport as characterized by τ_E. Operation away from the n = 0 MHD optimum may still lead to higher performance if there are more than compensatory gains in β_N and τ_E. Unfortunately, while the empirical scaling of β_N and τ_E with the elongation (κ) has been determined, the dependence on δ has still not been quantified. This information is needed in order to perform more accurate overall optimizations in future experimental designs.

• Research Organization: New York Univ. (NYU), NY (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: FG02-86ER53223; SC0012398; FG02-91ER54109; FC02-99ER54512
• OSTI ID: 1897627
• Report Number(s): PSFC/JA-15-56; TRN: US2310816
• Journal Information: Journal of Plasma Physics, Vol. 81, Issue 6; ISSN 0022-3778
• Publisher: Cambridge University Press
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY