Confinement in electron cyclotron heating experiments on Doublet III

Electron Cyclotron Heating experiments have been performed on the Doublet III tokamak in the expanded boundary divertor configuration. Effective ECH heating is found even at densities twice the cutoff density, with no decrease in the global energy confinement time when the cutoff is exceeded. Analysis of the behavior of the sawteeth and of the soft x-ray emission indicates that for the overdense discharges the ECH heating is taking place near the plasma edge. A simplified transport analysis indicates that the electron thermal transport coefficient decreases a factor 2 when the heating is centrally localized. The transport analysis is confirmed by the behavior of the propagation of the heat pulse when ECH is initiated. The edge heating results in a large improvement in energy confinement over the inner two thirds of the plasma.