Application of a conceptual electron temperature fluctuation diagnostic based on soft X-ray imaging to simulations of tokamak turbulence

The measurements of temperature fluctuations is important for understanding transport that determines the fusion gain of tokamaks. A new electron temperature fluctuation diagnostic based on soft X-ray imaging has been proposed and has been proven feasible on a simplified model with artificial fluctuations in a circular poloidal cross section[1] and on a more realistic model using fluctuations generated from gyrokinetic simulations in a real D-shape poloidal cross section in NSTX-U. However, the fidelity of the reconstruction of the latter model is lower compared to the former toy model. The applicability of the diagnostic can be sensitive to a number of factors such as the nature of the fluctuations(ITG, ETG...), the configuration of the tokamak, and the plasma conditions in equilibrium(electron density/temperature profile etc.). In this work, we run gyrokinetic simulations for several cases to obtain fluctuation data and then feed it into the diagnostic model to assess the quality of fluctuation reconstructions. The final goal of this work is to fully understand what conditions are favored by the diagnostic, and possibly for those unfavorable conditions, what measures can be taken to improve the quality of reconstructions.

[1]X. Chen et al, Rev. Sci. Instrum., 92:053537, 2021.