Helicon wave damping coefficient of Chinese fusion engineering testing reactor plasma

Abstract

The Chinese fusion engineering testing reactor (CFETR), complementing the ITER facility, is aimed at building up the science and technology base for the prototype of fusion power plant (PFPP). Based on the dispersion relation of fast wave, the analysis of the plasma dispersion function <inline-formula><tex-math id="M3">\begin{document}$ Z(\xi )$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20200222_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20200222_M3.png"/></alternatives></inline-formula> is performed and a numerical solution of <inline-formula><tex-math id="M4">\begin{document}$ Z(\xi )$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20200222_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20200222_M4.png"/></alternatives></inline-formula> is obtained. As the consequence, the dependence of helicon wave damping factor <i>G</i> on the plasma parameters and that on the wave properties are both achieved. The results show that an off-axis power deposition of the wave along the device radius can be achieved under the condition of plasma discharge on CFETR tokamak. Moreover, by calculating the ratio of the electron Alfven damping in the ion cyclotron range of frequencies to the electron Landau damping, we find that the electron Alfven damping is dominant at lower wave frequencies. With the wave frequency increasing, the electron Alfven damping remains unchanged while the Landau damping increases rapidly. With the discharge parameters of CTETR hybrid mode, the electron Landau damping proves to be dominant. Moreover, the off-axis power deposition and current drive profiles are produced. It is shown that the helicon wave damping factor increases with wave frequency increasing and it is closely related to the parallel refractive index of the injected wave spectrum, the plasma density, and plasma temperature. Significant off-axis power deposition and current drive are shown in CTETR hybrid mode operation, and the current drive efficiency reaches 50 kA/MW for helicon wave with a frequency of 800 MHz. Numerical simulation performed on the GENRAY/CQL3d shows a good consistence with the experimental results.