Scrape-off Layer Plasma Flow in L- and H-Mode Plasmas on JT-60U

概要

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Significant progress has been made in understanding the scrape-off layer (SOL) mass transport along magnetic field lines — the SOL flow. Understanding the driving mechanisms of the SOL flow was summarized based on experiments in the JT-60U tokamak plasmas. Fast SOL flow with parallel Mach numbers of 0.2-1 was generated from the low magnetic field side (LFS) SOL to the high magnetic field side (HFS) divertor for the ion ∇B drift direction toward the divertor. The SOL flow pattern was formed mainly by the LFS enhanced in-out asymmetry in diffusion and by classical drifts in the torus. Detachment of the divertor plasma affected enhancement of the SOL flow at the HFS SOL. Dynamics of the SOL flow were measured during the transient event of edge localized modes (ELM), and the flow pattern of the plasma filaments was clarified at both SOLs. The radial movement of the ELM filaments at the LFS SOL was sometimes faster than the parallel convective transport to the divertor target, which caused the heat loading to the first wall. Filament structures with temporal peaks and flow velocities comparable to the ion sonic level were also determined in the HFS SOL, but they appeared only near the separatrix. The delay after start of the ELM was shorter than the parallel convection time from the LFS midplane, suggesting that part of the ELM filaments was ejected into the HFS SOL.