A new slow transition process for energy transport in magnetically confined plasmas is reported. The slow transition is characterized by the change between two metastable transport conditions characterized by a weak and a strong electron temperature ($T_e$) dependence of normalized heat flux. These two branches are found to merge at the critical $T_e$ gradient. In metastable transport, the derivative of normalized heat flux to the $T_e$ gradient, $\partial (Q_e/n_e)/\partial (-\nabla T_e)$, is positive, while it becomes negative during the transition phase. The time for the transition increases as the normalized $T_e$ gradient is increased and exceeds the transport time scale characterized by the global energy confinement time.

• Received 3 October 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.125006