Axial and radial potential structure and current flow in GAMMA 10

Tandem mirror experiments have proved generation of a plug potential and strong suppression of end loss ions has been realized. A substantial improvement of plasma confinement by potential is obtained in the GAMMA 10 tandem mirror. This paper presents experimental observations about potential formation in GAMMA 10. The plug ECRH of fundamental resonance at the plug region plays a largest role in the potential formation. On application of the plug ECRH, the axial and radial potential structures show significant changes. Since plugging reshapes the density distribution of the ions near the plug region, potential generation is a dynamic process. In addition, an intense axial flow of warm electrons driven by the plug ECRH is a key factor of the potential distribution. The potential difference between the plug and the barrier mid plane increases with the temperature of the warm electrons, while the barrier depth scales with the bulk electron temperature. The warm electron flow also connects the plug potential to the potential in the end region. (author)