Investigation of ETG mode-scale component of tokamak plasma turbulence by correlative enhanced scattering diagnostics

Abstract

Outline • Introduction. ETG mode, UHR back scattering, enhanced Doppler effect, correlative technique.• Measurements results.Two components of frequency and wave number spectra. • Modeling results.Reconstruction of turbulence wave number spectra and phase velocities.• Conclusions.

Spatial structure of the geodesic acoustic mode in the FT-2 tokamak by upper hybrid resonance Doppler backscattering

“…The UHR BS technique [7,8] utilizes X-mode microwave plasma probing out of the tokamak's equatorial plane from the high magnetic field side as shown in figure 1. The diagnostic is benefiting from the growth of electric field and wave numbers in the UHR resulting in enhanced scattering signal, sub-mm radial resolution and substantially increased Doppler frequency shift (f D ).…”

“…where A UHR (f 1 ), A UHR (f 2 ) and A UHR (f 1 ± f 2 ) are different harmonics of the complex Fourier spectrum of the UHR BS signal (one of two sine-cosine homodyne detected signals), which are proportional to density fluctuations at the same frequency [7,8], f D (f 2 ) and f D (f 1 ± f 2 ) are harmonics of the Doppler frequency shift signal spectrum extracted from the UHR BS signal using procedures described above. The level of b 2 will exceed the noise level if the phase of the turbulence spectral components (associated with the UHR BS signal) are coupled with the phase of the Doppler frequency shift f D under the conditions of three-wave interaction.…”

“…As it is clearly seen in figure 9(a-c) the level of frequency ranges: f 1/2 < 700 kHz and f 1/2 > 2 MHz, demonstrating the strong nonlinear threewave interaction between small-scale turbulence and GAM. In the low-frequency domain (f 1/2 < 700 kHz ) where the turbulence amplitude is high and radial wave number is relatively small [7,8] one can expect generation of GAMs by the Reynolds stress via the three-wave coupling. On contrary, at high frequency of turbulent fluctuations (f 1/2 > 2 MHz ) and radial wave number their amplitude is small [7,8] and Reynolds stress should be negligible.…”

Analogous Saturation Mechanisms of the Ion and Electron Temperature Gradient Drift Wave Turbulence

“…Extensive theoretical and simulation work clearly establish both ion and electron dynamic behaviors, both linear and nonlinear [4][5][6][7][8][9][10][11][12].In contrast, experimental validation of theories of electron transport is lacking. The number of experiments about identifications of ETG mode and consequent electron transport is very limited [13][14][15][16] due to certain diagnostic problems with the high frequency and short wavelengths of electron turbulence.…”

Measurements of Electron Thermal Transport due to Electron Temperature Gradient Modes in a Basic Experiment

“…The number of experiments with identifications of ETG mode and consequent electron transport is very limited [12][13][14] due to certain diagnostic problems with the high frequency and short wavelengths of electron turbulence. Although the electron scale fluctuations were identified in a tokamak experiment [14], the ETG characterization was not complete and its role in the electron transport was not directly verified.…”