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-k_r ( 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-k_r 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 k_r, , and are radial wavenumber, poloidal wavenumber, perpendicular wavenumber and ion gyroradius at electron temperature, respectively. Both high-k_r/ turbulence power and energy confinement time are found to be temporally correlated to line-averaged electron density n_e in the plasma current flat-top phase (I_p  =  0.4 MA): when the n_e shows continuous increase/decrease, the high-k_r/ turbulence power increases/decreases correspondingly and the shows corresponding decrease/increase; the stable n_e is related to stable both and high-k_r/ turbulence power. Statistical results of high-k_r/ turbulence power versus further imply that high-k_r/ turbulence shows a strong correlation with plasma energy confinement degradation in high line-averaged n_e condition, but high-k_r and high- turbulence have relatively weak and no dependence on the transition between linear range in low-n_e condition and energy confinement degradation in the high-n_e condition, respectively. Moreover, profiles of electron temperature T_e and n_e 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 n_e. [ABSTRACT FROM AUTHOR]