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 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.