Abstract
Guided by predictions from nonlinear gyrokinetic simulations, two new turbulence diagnostics were designed and installed at ASDEX Upgrade (AUG) to probe the fundamentals of ion-scale turbulent electron heat transport. The first, a 30-channel correlation ECE (CECE) radiometer (105-128 GHz, 2nd harmonic X-mode), introduces a novel channel comb arrangement. This allows measurements of high radial resolution profiles (0:5 < r/a < 0:8) of low-k (k⍬⍴s < 0:3) temperature fluctuation amplitudes, frequency spectra and radial correlation length profiles in unprecedented detail. The second diagnostic is formed by the addition of two W-band and one V-band X-mode reflectometers on the same line of sight as the CECE to enable measurements of the phase angle between turbulent density and temperature fluctuations. Historically, the radial alignment between reflectometer and radiometer has been a challenge due to the requirement that alignment is achieved within a radial correlation length (< 5 10 mm). This challenge is significantly alleviated by using the CECE channel comb arrangement and the maximal coherence between reflectometer and radiometer can be unambiguously captured. Measurements of these quantities have been made in an AUG L-mode plasma, at the same radial location and have provided simultaneous quantitative constraints on realistic gyrokinetic simulations [Physics of Plasmas 25, 055903 (2018)] using the gyrokinetic code GENE. Here we present diagnostic detail for this study.
Highlights
Understanding the turbulent driven heat flux in a tokamak remains one of the key goals of fusion research
In order to study in detail the turbulence giving rise to electron heat transport, the ASDEX Upgrade (AUG) correlation ECE (CECE) diagnostic was significantly upgraded, introducing a channel comb arrangement
The AUG CECE channel comb provides the first measurements of high radial resolution profiles of Lr(Te⊥) using the CECE channel comb, showing the proportionality of Lr(Te⊥) to the ion sound gyroradius, ρs
Summary
Understanding the turbulent driven heat flux in a tokamak remains one of the key goals of fusion research. In order to study in detail the turbulence giving rise to electron heat transport, the ASDEX Upgrade (AUG) correlation ECE (CECE) diagnostic was significantly upgraded, introducing a channel comb arrangement. This new diagnostic measures high radial resolution fluctuation amplitude, δTe⊥/Te profiles. The phase angle between temperature and density fluctuations αnT has been measured in the core plasma by the combination of a reflectometer and radiometer [5, 6] We follow this approach here, combining two W-band (75-110 GHz) and one V band (50-75 GHz) X-mode reflectometers along the same line of sight as the AUG CECE. It is found that both electron and ion heat flux can be matched, along with αnT and Lr(Te⊥), δTe⊥/Te is higher in the simulations than measured
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