Density Collapse Events Observed in the Large Helical Device

A core density collapse (CDC) phenomenon is a rapid collapse events observed in super dense core (SDC) plasma with internal diffusion barrier (IDB) in the Large Helical Device (LHD). By CDC, the central beta is decreased by up to 50%. The collapse starts from the edge region of the plasma. CDCs appear with plasma parameters where the high-n ballooning modes are unstable at rho similar to 0.8. With less collisional conditions, m = 1 type oscillations are observed with similar beta profile. The origin of the m=1 oscillations is not clarified. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim