The energy confinement response of DIII-D plasmas to resonant magnetic perturbations

Resonant magnetic perturbations (RMPs) are a leading method for edge localized modes (ELMs) Control in fusion plasmas. However they can also cause a rapid degradation in energy confinement. In this paper we show that the energy confinement in low collisionality (${\nu }_e^{\ast }$  <  0.3) DIII-D ITER similar shape (ISS) plasmas often recovers after several energy confinement times for RMP amplitudes up to the threshold for ELM suppression. Immediately following the application of the RMP, the plasma stored energy decreases in proportion to the decrease in the line-averaged density during density 'pump-out'. Later in the discharge confinement recovery is observed in the thermal ion channel and is correlated with the increase in the ion temperature at the top of the H-mode pedestal. A correlation between the inverse scale length of the ion temperature ($a/L_{Ti}$) and the $E\times B$ shearing rate at the top of the pedestal is seen during the confinement recovery phase. Transport analysis reveals that the confinement improvement in the ion channel results from the self-similarity in the ion temperature profiles in the plasma core combined with the observed increase in $a/L_{Ti}$ in the plasma edge following density pump-out. In contrast the electron temperature scale length ($a/L_{Te}$) remains essentially unchanged in response to the application of the RMP. At significantly higher RMP levels the edge $E\times B$ shearing rate and $a/L_{Ti}$ does not increase and the confinement does not recover following density pump-out. (paper)