Intermittent Magnetic Fluctuations Associated with High-Temperature Bubbles in an ECR Plasma

Abstract

Magnetic probe measurement has been performed in a cylindrical electron cyclotron resonance plasma in which localized high temperature electron region, i.e. high-temperature bubble, has been generated intermittently. It is found that the high-temperature bubble is accompanied by a pulsed magnetic fluctuation perpendicular to the external magnetic field. Polarities of the magnetic fluctuation suggest that it should be induced by a transient upstream electric current. This hypothesis has been validated by a simultaneous increase of electron flux in the downstream direction. No enhancement of electron flux in the upstream direction has been observed even under the existence of the bubbles. The result suggests that the electron velocity distribution function in the bubble should be an asymmetric one, which gives rise to an effective upstream electric current.