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 ($\frac{I_{\mathrm{HF}}}{I_p}\approx 0.5$). The stabilization is due to a flattening of the current profile $j\left(r\right)\mathrm{}$ and an increase of $q\left(0\right)\mathrm{}$ 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.