Suppression of Sawtooth Oscillations by Lower-Hybrid Current Drive in the ASDEX Tokamak

The sawtooth oscillations in tokamak discharges with Ohmic and neutral-beam heating could be suppressed when a large part of the plasma current was driven by lower hybrid waves ($\frac{{I}_{\mathrm{HF}}}{{I}_{p}}\ensuremath{\approx}0.5$). The stabilization is due to a flattening of the current profile $j(r)$ and an increase of $q(0)$ above 1. Higher central electron temperatures are obtained with neutral-beam heating if the sawteeth are stabilized. The increase in total energy content in this case was 30% higher than in the presence of sawteeth.