Experimental study of high-k turbulence during an energy confinement degradation phase in EAST ohmic plasmas.

In this paper, we present experimental studies of both high-kr ( cm−1, and , respectively; ) and high- ( cm−1, and , respectively; ) turbulence behavior during an ohmic energy confinement degradation phase in experimental advanced superconducting tokamak (EAST). High-kr turbulence from density fluctuation at and high- turbulence from density fluctuation at –0.97 were measured by tangential and poloidal CO2 laser collective scattering diagnostics, respectively. Note that kr, , and are radial wavenumber, poloidal wavenumber, perpendicular wavenumber and ion gyroradius at electron temperature, respectively. Both high-kr/ turbulence power and energy confinement time are found to be temporally correlated to line-averaged electron density ne in the plasma current flat-top phase (Ip  =  0.4 MA): when the ne shows continuous increase/decrease, the high-kr/ turbulence power increases/decreases correspondingly and the shows corresponding decrease/increase; the stable ne is related to stable both and high-kr/ turbulence power. Statistical results of high-kr/ turbulence power versus further imply that high-kr/ turbulence shows a strong correlation with plasma energy confinement degradation in high line-averaged ne condition, but high-kr and high- turbulence have relatively weak and no dependence on the transition between linear range in low-ne condition and energy confinement degradation in the high-ne condition, respectively. Moreover, profiles of electron temperature Te and ne as well as their normalized gradients in a part of high- density fluctuation measurement region also have been given to qualitatively explain the enhancement of turbulence power with the increase of line-averaged ne. [ABSTRACT FROM AUTHOR]