Edge Density Profiles of High Beta Plasma in CHS

The temporal behavior of electron density profiles of edge plasmas in the Compact Helical System (CHS) during high beta discharges was measured with a thermal neutral lithium beam probe. A large outward shift of the plasma edge boundary was observed with an increase in the beta value. The position of the plasma edge boundary measured experimentally was compared with that of the last closed flux surface (LCFS) calculated by the VMEC code, and qualitative agreement was found between experimental and theoretical results. The experiment on the dynamic poloidal field control during the discharge was also performed successfully to fix the position of the edge plasma boundary when the plasma beta was raised.