Scaling of Electron Thermal Conductivity during the Transition between Slab and Mixed Slab-Toroidal ETG Mode

Transition from the slab to the toroidal branch of the electron temperature gradient (ETG) mode has been successfully achieved in a basic experiment in Columbia Linear Machine CLM [1]. We found a modest increase in saturated ETG potential fluctuations $ (\sim 2 \times) $ and a substantial increase in the power density of individual mode peaks $( \sim 4-5 \times) $ with increased levels of curvature. We have obtained a set of experimental scalings for electron thermal conductivity $ \chi_{\bot e}$ as a function of the inverse radius of curvature $ R_c ^{-1} $ for different fluctuation levels of the initial slab ETG mode. We found that thermal conductivity for pure slab modes is larger than it is for mixed slab-toroidal ETG modes with the same level of mode fluctuation. This effective reduction in diffusive transport can be partly explained by the flute nature of the toroidal ETG mode.\\[4pt] [1] A. Balbaky, V. Sokolov and A.K. Sen, Phys.Plasmas 22.