A jump in temperature gradient induced by the transition from density-gradient to temperature-gradient driven mode in L-mode edge

Motivated by a recent work [J. Y. Kim et al., Phys. Plasmas 24, 042503 (2017)], a more detailed study is presented on the transition process from the density gradient to temperature gradient driven one in L-mode edge-like plasmas. Based on an approximate estimate of the turbulent heat flux using the simple mixing length formula, with an assumed form of density profile evolution, it is shown that a jump in the temperature gradient can occur during the transition to meet the power balance. The possible connection of this mechanism to the confinement improvement in temperature, observed in the low to improved mode (L-I) transition, is discussed.