X mode Doppler Reflectometry k-spectral measurements in ASDEX Upgrade: experiments and simulations (Vol. 48, No. 4)

Doppler reflectometry is a microwave backscattering diagnostic for measuring flows and density fluctuation spectra in fusion plasmas. One longstanding problem is the discrepancy between the Doppler spectrum and the density fluctuation spectrum from turbulence simulations: The red "GENE" curve has its knee at a different wavenumber compared to the experimental Doppler measurements. The knee position is intrinsic to the turbulent drive mechanism and should be the same in both.

We coupled the sophisticated plasma turbulence code GENE to the fullwave code IPF-FD3D to model the scattering and the power response of the reflectometer in the presence of realistic turbulence. Dashed lines in the figure are the result of fullwave simulations. The blue curve (A=1) reproduces the knee position, but not the power law of the experiment. Reduction of the density fluctuation strength yields a better fit (A=0.5). The apparent shift of the knee is therefore a characteristic of the diagnostic.

This breakthrough reconciles turbulence simulations and experiment and shows that extra-ordinary mode scattering is taking place in the non-linear regime.

C. Lechte, G. D. Conway, T. Görler, C. Tröster-Schmid and the ASDEX Upgrade Team, X mode Doppler reflectometry k-spectral measurements in ASDEX Upgrade: experiments and simulations, Plasma Phys. Control. Fusion 59, 075006 (2017)
[Abstract]