The Dynamics of Core and Outer Micro-turbulence During the L–I–H Confinement Transition on the EAST Superconducting Tokamak

Abstract

The dynamics of the core and outer micro-turbulence during the low–intermediate–high (L–I–H) confinement transition have been investigated simultaneously by a tangential CO2 laser collective scattering system on EAST. It is found that, the intensity of micro-turbulence decreases most strongly near the outer region of the plasma, with less dramatic reduction deeper into the plasma. During the transition, the cross-coherence between broadband turbulence at neighboring wave-numbers in the same region of the plasma increase from less than 0.3 to greater than 0.8 just after the I–H transition. Besides, the magnetic fluctuations in the LCO frequency range reaches a maximum just before the final transition to H-mode, indicating the plausible underlying role of the perturbation of the pressure gradient in the triggering of the transition dynamics. These results would help to achieve a more comprehensive understanding of the L–H transition mechanism.