Mitigation and control of the particle pinch in the Electric Tokamak

Abstract

The Electric Tokamak [R. J. Taylor, T. A. Carter, J.-L. Gauvreau et al., Nucl. Fusion 45, 1634 (2005)] operates at high plasma density (one and a half times the Greenwald limit) due to a strong particle pinch. However, particle accumulation causes several problems. The operation of the machine can suffer several violent disruptions that hinder the study of many plasma phenomena. Plasma motion and large density swings are undesirable because they alter continuous processes, leaving only transient regimes to study. Particle source and local temperature control can defeat the fundamental mechanisms of this ‘‘electric’’ pinch. If edge fueling feedback is not sufficient to induce quiescent behavior, the fast ion loss caused by second harmonic ion-cyclotron rf injection functions as a particle sink deep within the outer plasma cross section. By linking these strong effects to the fueling feedback, stable medium density (2×1018particles∕m3) plasmas can be sustained for several seconds. This new regime yields surprisingly long and calm discharges.