Non-uniformity effects of the edge radial electric field, E r, on edge transport barrier (ETB) formation have been identified with high-spatiotemporal resolution spectroscopic measurement. We identified the decisive importance of E r-curvature (i.e. 2nd derivative of E r) on ETB formation corresponding to a local peak value in the pedestal region of the normalized ion temperature gradient,LTi-1 ≡ - Ti/Ti. On the other hand, the E r-shear (i.e. 1st derivative of E r) was discovered to promote the expansion of pedestal width, compensating an unfavorable effect of the E r-curvature having its sign dependence on the transport reduction/enhancement - predicted by a theoretical model as LTi-1∞(E'r E'r- ErE''r)0.5. A significant reduction of the inferred ion thermal transport coefficient in the pedestal region, Xiped. , due to the non-uniformity effects of E r was also confirmed quantitatively in the H-mode plasma at the initial ELM-free phase. When the inhomogeneity of radial electric field became strong enough, the inferred Xiped. value was close to its neoclassical one at the later ELM-free H-phase until 1st type-I ELM onset. Nevertheless, we observed the further reduction of electron density fluctuations (in the range up to 300 kHz) and D δsignals in association with the increment of electric field inhomogeneity. These suggest that the electron turbulent transport is suppressed further.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics