Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
The highly localized ECRH in the current ramp-up phase has produced high electron temperature plasma (15 keV) in the on-axis heating experiments on FTU. Off-axis ECRH has been used to study the electron energy transport in the ramp-up scenario, characterized by a variety of current density radial profiles j(r), due to the details the plasma startup, gas feed and impurity content. Previous analysis have already shown that the electron temperature radial profile T_e(r) is consistent with standard diffusive transport models in the region where j(r) is flat or hollow. The focus has now shifted to the experiments with very peaked profiles j(r) and early onset of sawtooth activity in the pre-ECRH phase. Off-axis heating of these discharges results in peaked T_e(r) inside the deposition layer due to a decrease of the electron thermal diffusivity in the plasma core, as shown by the local energy balance. This experiment can be interpreted as the result of a modification of the electron thermal transport that depends on the proximity to a "critical" temperature gradient, as shown by other recent ECRH experiments both on ASDEX-Upgrade and FTU tokamaks.