Multiscale Investigations of Drift-Wave Turbulence and Plasma Flows: Measurements and Total-Distribution-Function Gyrokinetic Simulations

Direct measurements of micro-, meso-, and macroscale transport phenomena in the FT-2 tokamak are shown to be quantitatively reproduced by global full $f$ nonlinear gyrokinetic simulation predictions. A detailed agreement with mean equilibrium $E\times B$ flows, oscillating fine-scale zonal flows, and turbulence spectra observed by a set of sophisticated microwave backscattering techniques as well as a good fit of the thermal diffusivity data are demonstrated. A clear influence of the impurity ions on the fluctuating radial electric field is observed.

Figure 1

The six top graphs: The experimental (shaded area) radial electron density ($N_e$), electron ($T_e$), and main ion ($T_i$) temperature profiles and the corresponding gradient scale lengths $L_s^{-1}=-\frac{d}{dr}\ln (s)$ compared to the Elmfire simulated flux surface averaged values at the startup (solid line) and at the end of the turbulent stage (dash-dotted line). The bottom two graphs: The radial flux surface and time averaged Elmfire predictions of the electron and main ion heat conductivity (${\chi }_{e/i}$) in the turbulence (solid line) and neoclassical (dash-dotted line) stage compared to ASTRA ion energy balance predictions.

Figure 2

DR spectra (solid line) compared to the corresponding synthetic Doppler spectra (dash-dotted line) from the Elmfire simulation including impurities at several radial positions.

Figure 3

(a) The poloidal velocity obtained from the ES (◊) and DR (□) measured frequency spectra and the synthetic DR spectra (o) compared to the $v_{E_r\times B}$ averaged over the DR domain. (b) The standard deviation of the simulated raw (solid line) and LP-filtered (dashed line) radial electric field fluctuations averaged over the ES domain compared to the ES measurements. (c) The dominant frequency of the ES (◊) and DR (□) measured radial electric field fluctuations compared to the Elmfire predictions with (o) and without (▵) impurities included. The analytical predictions for the geodesic acoustic frequency with (pink) and without (green) impurities are presented for the startup (solid line) and steady state (dashed line) profiles.

Figure 4

(a) The simulated raw (solid line) and low-pass-filtered (dashed line) radial electric field time trace averaged over the ES domain centered at $r=5.6\mathrm{cm}$ for the turbulent saturated stage. (b) The radial electric field measured by ES at $r=5.6\mathrm{cm}$ analyzed with FT (◊) and sliding FT (dash-dotted line).

Figure 5

The probability distribution function of the simulated LP-filtered (solid line) and sliding FT ES (dash-dotted line) measured radial electric field fluctuations at $r=5.6\mathrm{cm}$.