Features of edge magnetic turbulence in DIII-D expanded boundary divertor discharges

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Abstract
It is found that the magnetic fluctuation amplitudes abruptly decrease at L-H transitions and increase at H-ELM transitions (ELM is the edge localized mode). No other plasma parameter change precedes the magnetic signals, suggesting that the fluctuations are responsible for the increased edge transport in regimes with poor confinement. The fluctuation amplitude during L- and ELM-phases is largest at the points where the separatrix intersects the divertor plates. This is interpreted as evidence for the existence of line tied image currents in the scrape-off plasma.