1. The control of exfoliated dust sizes to less than ~1mm is indispensable for steady state discharge operation
Fig.3: Traces of exfoliation of carbon-rich mixed material layers were found at the source of the dust emission in the closed divertor region.
Fig.1: Recent long pulse plasma discharges in LHD have been terminated with abrupt increase of carbon ion emission.
Fig.2: A sequential image of a long pulse plasma discharge in LHD taken with a fast framing camera just before the end of the discharge. It have been terminated with release of a large amount of dusts from a closed divertor region.
Fig.4: A dust transport simulation in a three dimensional geometry proves that large sized dusts (>1mm) can penetrate into the main plasma confinement region through the peripheral plasma.