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Author(s):
S. -I. Itoh, K. Itoh and A. Fukuyama
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Title:
Modelling of ELMs and Dynamic Responses of the H-Mode
Date of publication:
Sep. 1992
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Key words:
IAEA, fusion energy conference, Wurzburg
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Abstract:
Based on the electric bifurcation model of the H-L transition, models of the Edge Localized Modes (ELHs) are developed and the dynamic responses of the H-mode are analyzed. The spatial-temporal evolution of the H-L transition is formulated in a form of the time-dependent Ginzburg-Landau equation which includes transport processes. The equation governs the development of the density and radial electric field. By solving this equation for the given boundary condition, we identify three classes of solutions which attribute to the H-state, L-state and ELMy-H state. The ELMy-H state is characterized by the self-generating oscillations under the condition of constant source. The parameter region of these states are identified. The radial extent of transport barrier during H- and ELMy-H states is characterized by the diffusion Prandtl number. Transient responses of the H-states to the external perturbations are also analyzed. Sudden change of the flux from the core causes transient ELMy oscillations. When the sinusoidal oscillations are imposed ( simulation of sawtoothing ), the ELMy oscillations with mode locking to the external oscillation frequency (or the sub-harmonics) appear. This suggests a possible scenario for the ELM control. We also develop the model for the Giant ELMs. Ballooning instability triggers the pulsive loss flux to the edge region. If its magnitude exceeds the threshold, the transport barrier is destroyed for a short period and the large solitary pulse in the outflux is generated.
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