Transition of Edge Particle Transport in CHS

A clear transition of edge particle transport was observed for the neutral beam heated plasmas in CHS. The heating power threshold for the transition is about 1 MW for a plasma with 2 × 10 19 m ‐3 average density. The Hα emission drops within 1 msec and the increase of the local edge density at the transition was confirmed by means of YAG Thomson scattering and beam emission spectroscopy. When the heating power is well above the threshold, the transport barrier is maintained for the full duration of NBI heating (100 msec). A clear back transition appears when the heating power is decreased during the discharge.