Diagram showing geometry for CECE system relative to the vacuum vessel and equilibrium for a DIII-D plasma used in this experiment. The inset shows the relative locations of the CECE and BES sample volumes with respect to the vessel midplane at .
Plasma parameters for reference discharge 128913: (a) Injected neutral beam power and rotation (at ), (b) edge emission, (c) electron temperature at and ion temperature at , and (d) chord-averaged electron density. Dashed vertical lines indicate centers of time periods for CECE data analysis in Fig. 3. The time of interest for comparisons with BES and CECE data with GYRO is L-mode, .
Temperature fluctuation spectra normalized to the local temperature at four different times, (a) ramping L-mode, (b) flat , sawtooth-free L-mode, (c) ode, ELM-free, and (d) Ohmic. The measurements are made during shot 128915 at .
Plasma profiles of (a) density and (b) ion and electron temperature, measured with Thomson and CER averaged over in L-mode, shot 128913. One-sigma error bars are shown with green dashed lines. The second-harmonic ECE is far from being cut off by the right-hand wave (c). The plasma is optically thick across the measurement region (d).
Temperature and density fluctuations are similar in amplitude and spectrum. The spectra shown are measured at in shot 128915 averaged over .
The temperature fluctuation spectra normalized to the local temperature are shown at six radial locations. Different -axis scales are used. The spectrum is narrowest at largest radius and becomes broader at smaller radii. The fluctuation levels integrated between are shown. At , the fluctuation level is below the sensitivity limit, .
Profiles of normalized electron temperature and density fluctuations during the sawtooth-free L-mode, . Fluctuation levels increase with radius. The error bars plotted for the CECE measurements represent the sensitivity limit from the time average, . The error bars plotted for the BES measurements represent 15% uncertainties in the value from atomic physics corrections.
Growth rates (a) and real frequencies (b) of the most unstable linear mode from TGLF for shot 128913, at , 0.75, 0.85. The ITG is the dominant instability for low values of relevant to the CECE diagnostic: , .
Nonlinear GYRO results for the flux-tube centered at , with background shear included. Contours in the plane for (a) above the midplane and for (b) below the midplane are shown. The 50% power contours for the PSFs for the CECE (a) and BES (b) diagnostics are overlaid in white. The array of BES channels is also shown in (b).
Simulation results for the power spectra of electron temperature fluctuations in the laboratory frame at (a) and (b) are shown with the experimental results for comparison. The black dash-dotted curves indicate the spectra from the GYRO output before the synthetic diagnostic is applied. The red dashed curves are GYRO output with the synthetic diagnostic applied. The blue solid curves are the experimental spectra.
(a) The GYRO predicted phase between and are shown. (b) The heat flux driven by fluctuations in and , calculated from GYRO outputs at are shown as a function of . The term containing the temperature fluctuations drives 80% of the heat flux in contrast to the term containing density fluctuations that drives only 20% of the heat flux.
Article metrics loading...
Full text loading...