Heavy Ion Beam Study of Negative and Positive Potential Formation in Bumpy Torus Plasma

Abstract

Potential formation is studied in Nagoya Bumpy Torus (NBT-1M) by the use of a heavy ion beam probe. The concentric negative potential well and its positive rim are observed in the standard operation. The position of the rim moves with the second harmonic ECRH zone at the midplane of each mirror section. It is confirmed that the core electron heating is essential for the potential well formation. A stable positive potential is observed near T–M transition with a smooth change from the negative profile.