Summary of ion temperature gradient instability studies in the Columbia linear machine

Abstract

The toroidal ion temperature gradient (ITG) driven mode has been studied by starting with the slab mode and gradually turning on a mirror field in the Columbia Linear Machine (CLM). The magnetic curvature produces an extra drive for the mode and reduces its real frequency in the plasma frame, consistent with a new model of a hybrid ITG and trapped electron mode. Furthermore, the anomalous local ion thermal conductivity due to the slab mode has been measured to be 0.5 m2/sec, which is 3 orders of magnitude larger than the classical and 1 order of magnitude lower than the Bohm. Its scaling with the fluctuation amplitude, the linear growth rate and etai are all found to be linear. Lastly, flow shear is found to stabilize the ITG modes, but at levels nearly an order of magnitude larger than the theoretical predictions.