Evolution of Filament Structures during Edge-Localized Modes in the MAST Tokamak

Abstract

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Convective transport by intermittent blob-filaments: Comparison of theory and experiment

“…Field-aligned holes left behind after filament ejection have also been reported in experiments. 306,307 The repulsive interaction of the current filaments with the holes left behind is consistent with the acceleration of ELMs into the SOL that has been observed in some experiments, 308 although other experiments have reported radial deceleration of ELMs. 258,273 Moreover, initial radial acceleration is also qualitatively consistent with explosive ballooning instability theory 309 such as seen in the initial phase of nonlinear ELM formation in simulations.…”

X-Point Effect on Plasma Blob Dynamics

“…However, experimental investigations close to X points are difficult, limiting the progress in the understanding of the X-point dynamics and simulationexperiment comparisons. In fusion plasmas, the diagnostic accessibility is challenged by the high power flux so that the generation and propagation of intermittent plasma blobs in the vicinity of an X point is largely unexplored [8][9][10].In this Letter, we present the first spatial and temporaldependent in situ measurements of turbulence-generated plasma blob dynamics around the X-point region. The blob motion towards the X point is tracked and analyzed, showing an acceleration in the initial phase that can be directly linked to the background radial flow and to the measured blob electric potential dipole.…”

“…The velocity v b can then be evaluated at each time step considering δn=n and B (hence, L ∥ ) the only position-dependent variables. We note that L ∥ is the most significant parameter in the spatial variation of the estimated speed, increasing in the range [7][8][9][10][11][12][13][14] m, while δn=n is almost constant for most of the trajectory. The coefficient C is determined by adjusting the plasma conductivity to make the analytically estimated speed coincide with the experimental value at τ ¼ −28 μs.…”

“…However, experimental investigations close to X points are difficult, limiting the progress in the understanding of the X-point dynamics and simulationexperiment comparisons. In fusion plasmas, the diagnostic accessibility is challenged by the high power flux so that the generation and propagation of intermittent plasma blobs in the vicinity of an X point is largely unexplored [8][9][10].…”

Enhanced Understanding of MHD Dynamics & ELM Control Physics via 2D/3D ECE Imaging in KSTAR

“…Edge-localized modes (ELMs) are constantly encountered in the high confinement mode (H-mode) of a tokamak plasma, where the edge pressure gradient is large over a short physical distance near the separatrix, and have been extensively studied in many tokamak devices [3][4][5][6][7][8][9][10] for the last three decades since their first observation in ASDEX [11]. The H-mode was adopted as a standard mode of operation in ITER, yet large ELMs can severely limit the life time of the divertor; thus, understanding and control of this instability became an essential research subject for all diverted tokamaks.…”