Comparison of transient electron heat transport in LHD helical and JT-60U tokamak plasmas

Transient transport experiments are performed in plasmas with and without internal transport barriers (ITB) on LHD and JT-60U. The dependence of χ_e on the electron temperature, T_e, and on the electron temperature gradient, ∇T_e, is analysed with an empirical non-linear heat transport model. In plasmas without an ITB, two different types of non-linearity of the electron heat transport are observed from cold/heat pulse propagation: the χ_e depends on T_e and ∇T_e in JT-60U, while the ∇T_e dependence is weak in LHD. Inside the ITB region, there is none or weak ∇T _e dependence both in LHD and JT-60U. Growth of the cold pulse driven by the negative T_e dependence of χ_e is observed inside the ITB region (LHD) and near the boundary of the ITB region (JT-60U).