Ion-temperature-gradient modes in stellarator geometry

The ion-temperature-gradient (ITG)-driven drift mode. is studied in three d imensional stellarator geometry using a two-fluid reactive model in the ele ctrostatic limit. The model includes first-order FLR effect in the presence of parallel ion dynamics and using the Boltzmann distribution for the elec trons. The resulting eigenvalue is solved numerically using the ballooning mode theory. The results are contrasted with the corresponding tokamak resu lts with positive shear. In stellarators, the level of the maximum growth r ate of the ITG mode is found to be smaller and the threshold (eta (i) simil ar or equal to 2.2) is somewhat higher. The effects of small and large temp erature ratios and density gradients are found to be stabilizing on electro static ITG modes in stellarators.