Core electron temperature profile flattening is observed in a large helical device [A. Iiyoshi Nucl. Fusion 39, 1245 (1999)] inward shifted plasma with counter-neutral beam injection. To study this phenomenon, heat pulse experiments are performed by on-axis electron cyclotron heating power modulation. A unique feature of heat pulse propagation is observed near the mn=21 rational surface (m, n are the poloidal and toroidal mode numbers, respectively). A simultaneous response of the temperature perturbation on radially separated flux surfaces is shown. The change in the magnetic field topology due to the presence of a magnetic island structure can explain this nonmonotonic heat pulse propagation. The estimated O-point position of the island is located near the mn=21 rational surface.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics