(a) Time-averaged velocity field superimposed on time-averaged GPI intensity contours (gray contours). The separatrix is indicated by the dot-dashed line, and the cropped field of view is indicated by the dashed box. The maximum time-averaged velocity magnitude for the cropped region is 1.5 km/s, while the maximum instantaneous velocity magnitude is 7.4 km/s. The direction is radially outward. (b) Radial profiles of time-averaged poloidal flow for time periods preceding the L-H transition. Root-mean-square values of the fluctuating velocity are shown for shot 135042.
Normalized GPI intensity (top), poloidal velocity (middle), and radial velocity (bottom) inside the separatrix. All traces represent poloidally averaged quantities from shot 135042.
(a) Traces from shot 135042 of filtered, and (b) poloidally averaged poloidal velocity inside, at (c), and (d) outside the separatrix. filtered has had the low frequency components above zero frequency and below 1 kHz removed. Gray bars indicate time periods where filtered is below 0.16.
Spectrogram of for the L-mode portion of shot 135042 plotted with a linear color scale.
Map of phase differences of fluctuations for: (a) GPI signal with reference GPI signal, (b) with reference , and (c) GPI signal with . Reference signals are at , . Plots (a) and (c) have had the phase discontinuity remapped so that the contour plots appear smooth. Plots cover the time range of shot 135042. The dashed-line indicates the separatrix.
Phase of mode plotted vs spatial coordinates for GPI signal and poloidal velocity for periods of shots 135042–135045 with “rotating mode” visible in bandpass filtered. Time periods are 512 frames (1.8 ms) and begin at: 135042 , 135043 , 135044 , and 135045 .
Coherence and phase plots vs frequency for poloidal velocity signals separated by poloidally at inside the separatrix.
Plot shows coherence of poloidal velocity vs separation for 2.8 kHz mode (◇) and background turbulence between 20 and 30 kHz (△) for poloidal velocity of shot 135042. Velocities are measured at inside the separatrix. Solid lines are fits to exponential decays with correlation lengths of 56 cm for the 2.8 kHz mode and 4 cm for the background turbulence.
Autopower spectra of poloidal velocity at three radial positions for of shot 135042. The feature at 2.5 kHz does not appear to shift in frequency.
Traces from shot 135042 of , poloidal velocity (km/s), shearing rate (MHz), and the Reynolds stress . Poloidal velocity and Reynolds stress are taken at inside the separatrix, and the shearing rate is taken at the separatrix. Traces have been smoothed with a three point boxcar average.
Poloidal velocity profiles for of shot 135042 are plotted in (a). The averages are over times where is greater than its mean value (dashed—bursty) and less than its mean value (solid—quiet). Error bars indicate (standard deviation) about the average value for the low case, and indicate the level of fluctuation. Standard deviations are shown in (b), and skewness is shown in (c).
Traces of , poloidal velocity (km/s), shearing rate , and the Reynolds shear stress. Traces are from a SOLT simulation illustrating the bursty regime. The frequency of bursts is 3.6 kHz.
Radial profiles of the Reynolds shear stress averaged over the poloidal direction and 10 ms directly preceding the L-H transition for four shots. Error bars indicate estimated level of uncertainty assuming uncertainties in the velocity measurements of 0.5 km/s.
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