Observation of a new pedestal stability regime in MAST Upgrade H-mode plasmas

K. Imada, T.H. Osborne, S. Saarelma, J.G. Clark, A. Kirk, M. Knolker, R. Scannell, P.B. Snyder, C. Vincent, H.R. Wilson2024年8月Nuclear FusionIF 3 出版社

The first pedestal stability and structure analysis on the new MAST Upgrade (MAST-U) spherical tokamak H-mode plasmas is presented. Our results indicate that MAST-U pedestals are close to the low toroidal mode number (n) peeling branch of the peeling-ballooning instability, in contrast with MAST H-mode pedestals which were deeply in the high-n ballooning branch. This offers the possibility of reaching the ELM-free quiescent H-mode (Burrell et al 2005 Plasma Phys. Control. Fusion47 B37–B52) or high-performance super H-mode (Snyder et al 2015 Nucl. Fusion55 083026; Snyder et al 2019 Nucl. Fusion59 086017) regimes. In addition, the coupling between the peeling and ballooning branches is weak in MAST-U, suggesting that a path to very high pedestal pressure gradient at high density may exist with sufficient heating power. A possible explanation for the differences between MAST and MAST-U pedestal stability is given in terms of plasma shaping parameters, in particular squareness and elongation, as well as the pedestal top temperature and collisionality.

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ENThis paper should be read by fusion researchers interested in understanding the pedestal stability and structure in spherical tokamaks, as well as those working on developing high-performance H-mode regimes.#PedestalStability #SphericalTokamak #H-modeRegimes #PeelingBallooning

This paper presents the first analysis of pedestal stability and structure in the new MAST Upgrade spherical tokamak. The results show that MAST-U pedestals are close to the low toroidal mode number peeling instability, unlike the MAST pedestals which were in the high-mode ballooning regime. This offers the possibility of reaching the ELM-free quiescent H-mode or high-performance super H-mode regimes. The weak coupling between peeling and ballooning branches suggests a path to very high pedestal pressure gradient at high density.

この論文では、新しい MAST Upgrade 球状トカマクの H 型プラズマの台座安定性と構造について分析しています。結果は、MAST-U の台座が低トロイダルモード数の剥離分岐に近いことを示しており、ELM フリーの静穏 H 型モードや高性能の超 H 型モードの可能性を示唆しています。また、剥離と気球の分岐のカップリングが弱いため、十分な加熱パワーがあれば非常に高い台座圧力勾配に到達できる可能性があります。