Assessment of the Effect of Plasma Density Evolution of the T-15MD Tokamak on the Phase and Frequency Shift of the Signals of the Vertical Channel of the Microwave Interferometer

The article presents the results of estimating the parameters of the signals of the vertical channel of the microwave interferometer of the T-15MD tokamak with a probing wavelength of 0.9 mm. The estimation of parameters consisted of calculating the value of the phase shift due to the presence of plasma as well as estimating the frequency shift of the measuring intermediate frequency (IF) signal caused by the phase shift. These values determine the requirements for the measuring range, speed, and accuracy of the equipment for measuring the phase of the interferometer signals. The phase shift value is calculated for a range of average plasma densities from 1 × 10 19 to 1 × 10 20 particles/m 3 and is from 5 to 80 fringes of 2π for circular and elongated plasma-filament configurations, respectively. The frequency shift of the microwave interferometer IF signal is estimated by scaling the experimental data from the microwave interferometer of the T-10 tokamak. For the discharge with the maintenance of the set level of electron density through a feedback system on the working gas injection into the T-10 tokamak chamber, this value is 2 kHz, and in the discharge with a deuterium pellet injection, the IF shift reaches 20 kHz. In such discharges, the expected value of the frequency shift of the IF signal of the vertical channel of the microwave interferometer of T-15MD tokamak reaches 5 and 100 kHz, respectively, and the increase in plasma density caused by the pellet injection is scaled accordingly. Pellet injection into the T-15MD tokamak plasma using the injector from the T-10 tokamak is also simulated. In this case, the IF shift value reaches 10 kHz.