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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]

Electron-scale turbulence (for ) was measured during the L–H transition in the National Spherical Torus Experiment (NSTX) (Ono et al 2000 Nucl. Fusion40 557) using a coherent microwave scattering system. The measurements were carried out at a radial region adjacent to the edge transport barrier (ETB) (at smaller radius than ETB). The observed L–H transition occurred during current flattop, which facilitated the measurement of electron-scale turbulence. The measured electron-scale turbulence is observed to be quasi-stationary before the L–H transition, and an intermittent phase for electron-scale turbulence is observed after the start of the L–H transition with a gradual decrease in overall turbulence density fluctuation spectral power with intermittent large relative variations (on  ∼0.5–1 ms time scale) in the total spectral power. A turbulence-quiescent phase is observed following the intermittent phase, and a significant reduction in the electron-scale turbulence spectral power is only observed at lower wavenumbers, namely –10, which is also seen in different operational NSTX scenarios due to different stabilization mechanisms. A recovery phase is seen after the quiescent phase, where the electron-scale density fluctuation power starts to gradually increase. Simultaneous ion-scale turbulence measurements at larger radius than the electron-scale turbulence measurement location show similar temporal behavior in ion-scale turbulence as in the measured electron-scale turbulence. These observations demonstrate that the suppression of turbulence during the L–H transition is not just limited to the ETB region. None of the measured electron-scale turbulence and ion-scale turbulence from edge into core is found to be obviously leading in the response to the L–H transition, and the overall turbulence suppression after the start of the L–H transition at different radii seems to start at the same time and is a gradual process happening on a tens-of-ms time scale. The trend of decrease in electron-scale turbulence during the L–H transition is found to be consistent with a decrease in the maximum electron-temperature-gradient linear growth rate from linear gyrokinetic stability analysis. However, the observed intermittency in electron-scale turbulence during the intermittent phase cannot be explained by the linear analysis. [ABSTRACT FROM AUTHOR]