Internally generated currents in a small-aspect-ratio tokamak geometry

Abstract

Pressure driven currents are observed in an electron cyclotron resonance (ECR) heated, small-aspect-ratio toroidal plasma in the CDX-U device. A toroidal current of 1.05 kA was generated with \ensuremath{\sim}8 kW of ECR power. At this current level, the poloidal field created by these currents is significantly larger than the vacuum field and produces closed flux surfaces in a small-aspect-ratio tokamak geometry. After flux surface formation we hypothesize that bootstrap currents are driven to maintain the discharge. This internally driven current may offer an attractive method to start up and maintain the tokamak discharge.