Experimental studies on E/spl times/B drift rotational transform and confinement in the bumpy torus NBT-1M

Experimental studies on E/spl times/B drift rotational transform for toroidal plasma confinement were carried out using a bumpy torus NBT-1M. An inward radial electric field was observed, which induced E/spl times/B poloidal precession and formed closed drift surfaces in a conventional ECH configuration. However, the confinement was degraded by the plasma convective loss due to the asymmetric potential profile and core electrostatic fluctuations. By the use of a combination of two frequencies for ECH (18 GHz and 8.5 GHz), we could reduce both the potential asymmetry and the fluctuation. In this operation, the plasma confinement by E/spl times/B drift rotational transform was demonstrated more clearly than that in the conventional single frequency operation.<
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