Abstract
A two-dimensional code based on the Wentzel–Kramers–Brillouin approximation is used to simulate the ability of reflectometry techniques to reproduce the average density profile in an ignition device to test engineering concept (ITER) size plasma with density turbulence. Analysis is mainly performed for frequency modulation [(FM) swept frequency] systems, with some comparison with the amplitude modulation techniques. The effects of turbulence with nonperpendicular reflection and plasma rotation are analyzed. Perturbation effects seem to appear for the FM technique, although the real impact for reflectometry in ITER will strongly depend on the parameters of turbulence and rotation. The influence of the turbulence level, fluctuation wavelengths, and antenna beam size on the density profile determination has been studied in a static plasma with perpendicular launching. The vector average of the reflected e field improves the resultant profiles in turbulent plasmas, while an inappropriate choice of the antenna beam size may cause additional errors. The code has also been used to simulate correlation measurements. The results show the correlation of the reflectometry signals for different turbulence parameters. Errors in the correlation length increase when two-dimensional effects become important, although the homodyne signal works better than the phase. Along with the use of these studies for turbulence analysis and code validation, the correlation measurements can be used as a robust method for the determination of the signal time delay and therefore of the density profile in highly turbulent plasmas with parasitic reflections.
Published Version
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