A combination of recently installed state-of-the-art imaging and profile diagnostics, together with established plasma simulation codes, are providing for the first time on Mega Ampère Spherical Tokamak (MAST) the tools required for studying confinement and transport, from the core through to the plasma edge and scrape-off-layer (SOL). The H-mode edge transport barrier is now routinely turned on and off using a combination of poloidally localized fuelling and fine balancing of the X-points. Theory, supported by experiment, indicates that the edge radial electric field and toroidal flow velocity (thought to play an important role in H-mode access) are largest if gas fuelling is concentrated at the inboard side. H-mode plasmas show predominantly type III ELM characteristics, with confinement HH factor (w.r.t. scaling law IPB98[y, 2]) around ∼1.0. Combining MAST H-mode data with the International Tokamak Physics Activities (ITPA) analyses, results in an L–H power threshold scaling proportional to plasma surface area (rather than PLH ∼ R2). In addition, MAST favours an inverse aspect ratio scaling PLH ∼ ε0.5. Similarly, the introduction of type III ELMing H-mode data to the pedestal energy regression analysis introduces a scaling Wped ∼ ε−2.13 and modifies the exponents on R, BT and κ. Preliminary TRANSP simulations indicate that ion and electron thermal diffusivities in ELMing H-mode approach the ion-neoclassical level in the half-radius region of the plasma with momentum diffusivity a few times lower. Linear flux-tube ITG and ETG microstability calculations using GS2 offer explanations for the near-neoclassical ion diffusivity and significantly anomalous electron diffusivity seen on MAST. To complement the baseline quasi-steady-state H-mode, newly developed advanced regimes are being explored. In particular, 'broad' internal transport barriers (ITBs) have been formed using techniques developed at conventional aspect ratio. Electron and ion energy diffusivities are reduced towards the ion-neoclassical level in the ITB region of both co- and counter-injection NBI heated plasmas, with momentum diffusivity up to 10 times lower. Moving out to the edge and SOL, OSM2/EIRENE modelling is being used to extract edge perpendicular particle and heat diffusivities, results being consistent with the ballooning nature of power-flow seen in L-mode and reduction in outboard turbulence seen in ELM-free and inter-ELM H-mode. Modelling of parallel SOL transport requires the inclusion of the mirror force (∼10 times higher in MAST than at the conventional aspect ratio) and B2SOLPS5.0 simulations show the edge electric field to be well modelled by neoclassical theory. Transient edge transport phenomena are being studied in detail using a variety of techniques (e.g. probability density function (PDF) and power spectrum analysis, differencing and rescaling methods). Intermittent transport is associated with a radial efflux at up to a tenth of the sound speed and up to 30 cm from the separatrix. Arguably, the most dramatic edge events seen in the plasma periphery are the ELMs. Recent results using fast, high-resolution visible imaging confirm the hypothesis that ELMs have both poloidal and toroidal structures (n ∼ 10 at q = 4), consistent with recent theories of the non-linear evolution of ballooning modes.
メガアンペア球状トカマク（MAST）において、最近設置された先進的な診断装置と確立された加熱システムを組み合わせることで、閉じ込め、輸送、安定性、および周辺部物理に関する前例のない知見が得られている。Hモード閉じ込めは、MASTの高ベータ球状トカマク（ST）形状において、低アスペクト比で観測される強い径電場せん断と関連する特性を示す。閉じ込めスケーリング則は、標準的なトカマク形状からの外挿と概ね一致するが、密度およびベータ依存性には差異が認められる。ELM（周辺局在モード）は自然に発生し、タイプI ELMは標準的なトカマクで観測されるものと同様の特性を示すが、MASTの低トロイダル磁場ではELM誘起粒子流束が相対的に大きくなる。ELMの空間構造は、MASTの高ベータ・低アスペクト比条件において、標準トカマクとは異なる特性を示す。MASTにおけるELM緩和の研究は、ELM制御戦略の開発に重要な示唆を与えている。LモードからHモードへの遷移は、標準トカマクと比較して低いパワー閾値で発生し、その閾値はプラズマ密度および磁場に依存する。Hモード遷移は、周辺部での径電場せん断の増大と関連しており、これは主にイオン圧力勾配によるものと考えられる。MASTにおけるHモードプラズマの閉じ込め特性は、標準トカマクの経験則と比較して、閉じ込め改善度が高いことを示している。これは、球状トカマク形状におけるExBフローせん断の強化に起因すると考えられる。MASTのHモードプラズマでは、密度および温度分布が標準トカマクと異なる形状を示し、これは輸送機構の違いを反映している。周辺部輸送障壁（ETB）の特性は、MASTの低アスペクト比条件において、標準トカマクとは異なるスケーリングを示す。ELMと周辺部乱流の相互作用は、MASTの高ベータ条件において重要な研究対象となっている。MASTにおけるELM研究は、ELM緩和の物理機構の理解と、将来の核融合装置におけるELM制御戦略の開発に貢献している。