Simulations of Reflectometer Response to ITER Plasma Perturbations Caused by Alfvén Modes

Abstract

The KINX and VENUS codes were used for simulation of the baseline inductive and steady-state scenarios of the ITER tokamak operation. The perturbations of plasma electron density and magnetic field caused by the Alfvén modes were calculated in the flux coordinates for these scenarios. The perturbation fields obtained were converted into the engineering coordinates in order to calculate the propagation of probe electromagnetic radiation of the reflectometer using the two-dimensional full-wave TAMIC RτX code in the expected geometry of the experiment. The calculations performed show that for the baseline inductive scenario, in the case of reflection of the extraordinary wave at the lower cutoff frequency from the high magnetic field side, the electric field relative perturbations of the reflected reflectometer signal correspond to the margin of linear range of the diagnostics operation or even go out of this range. It was found that in a number of scenarios, not only the electron density perturbations, but also the magnetic field perturbations significantly contribute to the total signal perturbations that makes even more difficult the further data interpretation. Another possible problem is the narrow frequency range of probing frequencies where the Alfvén mode can be observed. In addition to simulating the reflection of electromagnetic waves from plasma, it was analyzed also the possibility of measuring the Alfvén modes parameters when the extraordinary wave pass through the plasma in the transparency window between the upper and lower cutoff frequencies of the extraordinary wave (refractometry). It is shown that at the fundamental frequency, the phase perturbations range from 3 to 60 degrees, which makes it impossible to use the amplitude-modulated refractometer for analyzing signals. The “synthetic diagnostics” approach was used, which showed itself well for simulating the operation of reflectometers at plasma facilities.