Study for the microwave interferometer for high densities plasmas on COMPASS-U tokamak

The present COMPASS tokamak at the Institute of Plasma Physics in Prague is equipped with the 2-mm interferometer, which gives a possibility to measure line-average electron densities up to 1.2 x 10(20) m(-3). A high magnetic field tokamak COMPASS-U will be designed and built to replace COMPASS. Higher line-average plasma densities in COMPASS-U of about 5 x 10(20) m(-3) will require a new design of the interferometer. This will provide measurements in a wide density range and will allow using a real-time gas puff density feedback. A solution based on the solid-state technology is proposed. The system will use two microwave transceivers with close sub-millimeter wavelengths and will fulfill the principle of the unambiguous measurement. An assessment of signal corrections corresponding to non-linearity effects caused by plasma refractive index is performed. The ray-tracing FIESTA-8 code was used to model the propagation of the probing waves through COMPASS-U plasmas.