Observation of Self-Generated Flows in Tokamak Plasmas with Lower-Hybrid-Driven Current

Abstract

In Alcator C-Mod discharges lower hybrid waves have been shown to induce a countercurrent change in toroidal rotation of up to 60 km/s in the central region of the plasma (r/a~<0.4). This modification of the toroidal rotation profile develops on a time scale comparable to the current redistribution time (~100 ms) but longer than the energy and momentum confinement times (~20 ms). A comparison of the co- and countercurrent injected waves indicates that current drive (as opposed to heating) is responsible for the rotation profile modifications. Furthermore, the changes in central rotation velocity induced by lower hybrid current drive (LHCD) are well correlated with changes in normalized internal inductance. The application of LHCD has been shown to generate sheared rotation profiles and a negative increment in the radial electric field profile consistent with a fast electron pinch.