H-mode dithering phase studies on ST40

• DOI: 10.1098/rsta.2021.0225
• Publication Date: 2023-01-02T00:05:21Z
• Authors: Yasmin Andrew; James Bland; Peter Buxton; Alexei Dnestrovskij; Mikhail Gryaznevich; Eun-jin Kim; Michele Romanelli; Marco Sertoli; Paul Thomas; Jari Varje
• Keywords: Dither; Oscillation (cell signaling); Collisionality; Pedestal

The dithering H-mode phase, characterized by oscillations, is generally observed at input power values close to the L-H transition threshold and low plasma collisionalities (low electron density and/or high temperature). Measurements characterize phase are presented for aspect ratio, magnetic field tokamak, ST40. oscillation frequency between 400 800 Hz demonstrates an inverse relationship with core density. Dithering H-modes documented across a nonlinear, low-density operational space, signature low- high-density branches. minimum access measured core, line average of 4.7(±0.5) × 1019 m-3, predicted value 4.1(±0.4) m-3 from multi-machine studies. ASTRA calculated coupled ion species, transition, exhibit similar nonlinear dependence on This analysis points important contribution thermal channel transition. low-frequency D-alpha dithers appear be accompanied sudden bursts magnetohydrodynamic (MHD) activity. A simple model tested demonstrate possible scenario self-regulation among turbulence, zonal flows, pressure (density) gradient MHD activities. article part discussion meeting issue 'H-mode pedestal studies in fusion plasmas'.