Numerical simulation of <inline-formula><tex-math id="Z-20231101091527">\begin{document}$\boldsymbol \alpha$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230700_Z-20231101091527.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230700_Z-20231101091527.png"/></alternatives></inline-formula> particle slowing-down process under CFETR scenario
Authors: Wu Xiang-Feng , Wang Feng , Lin Zhan-Hong , Chen Luo-Yu , Yu Zhao-Ke , Wu Kai-Bang , Wang Zheng-Xiong ,   Dalian University of Technology, Dalian 116024, China
Published: June 2023

The high-energy <i>α</i> particles produced by deuterium-tritium fusion are the primary heating source for maintaining high temperatures in future tokamak plasma. Effective confinement of <i>α</i> particles is crucial for sustaining steady-state burning plasma. The initial energy of <i>α</i> particles is <inline-formula><tex-math id="M1">\begin{document}$ 3.5 {\text{ MeV}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230700_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230700_M1.png"/></alternatives></inline-formula>. According to theoretical calculations, it takes approximately 1 second to slow down <i>α</i> particles through Coulomb collisions to an energy range similar to the energy range of the background plasma. In the slowing-down process, some <i>α</i> particles may be lost owing to various transport processes. One significant research problem is how to utilize <i>α</i> particles to effectively heat fuel ions so as to sustain fusion reactions in a reactor. Assuming local Coulomb collisions and neglecting orbital effects, a classical slowing-down distribution for <i>α</i> particles can be derived. However, considering the substantial drift orbit width of <i>α</i> particles and the importance of spatial transport, numerical calculations are required to obtain more accurate <i>α</i> particle distribution function. In this study, the particle tracer code (PTC) is used to numerically simulate the slowing-down process of <i>α</i> particles under different scenarios in the Chinese Fusion Engineering Test Reactor (CFETR). By combining particle orbit tracing method with Monte Carlo collision method, a more realistic <i>α</i> particle distribution function can be obtained and compared with the classical slowing-down distribution. The results show significant differences between this distribution function and the classical slowing-down distribution, particularly in the moderate energy range. Further analysis indicates that these disparities are primarily caused by the strong radial transport of <i>α</i> particles at these energy levels. The research findings hold profound implications for the precise evaluating of ability of <i>α</i> particles to heat the background plasma. Understanding and characterizing the behavior of <i>α</i> particles in the slowing-down process and their interaction with the plasma is critical for designing and optimizing future fusion reactors. By attaining a deeper comprehension of the spatial transport and distribution of <i>α</i> particles, it becomes possible to enhance the efficiency of fuel ion heating and sustain fusion reactions more effectively. This study establishes a foundation for subsequent investigations and evaluation of <i>α</i> particles as a highly efficient heating source for fusion plasmas.