The study about the relationship between plasma current in open magnetic field and the formation of closed flux surface in CPD

We investigate the physics of the formation of closed flux surfaces under the condition that a radio frequency (RF) wave is injected into the Compact Plasma Wall Interaction Experimental Device (CPD). From the orbits of the energetic electrons calculated for the open magnetic flux configuration, we estimate the plasma current Ies due to energetic electrons. We find that Ies increases with decreasing poloidal magnetic field, and observe the formation of closed flux surfaces in the experiments under the condition of low poloidal magnetic field (i.e., high Ies condition). This result suggests that the condition of high Ies is suitable for forming closed flux surfaces and that Ies can be used as an indicator to optimize the operational magnetic field condition for forming closed flux surfaces. (author)