Energy exchange and entropy balance in ITG and TEM turbulence*

In magnetically confined plasmas, turbulence induces energy exchange between electrons and ions as well as particle and heat fluxes [1]. In a study focusing on ITG turbulence, in which ions drive the instability [2], it is found that turbulent energy exchange transfers energy from ions to electrons regardless of whether the ions or electrons are hotter, which is significantly different from the equipartition due to Coulomb collisions. In addition, it is conjectured that energy is generally transferred by turbulence from a particle species with larger entropy production due to particle and heat transport driven by the instability to other species.

In this study, we extend the previous work [2] and investigate the energy exchange due to TEM turbulence and mixed ITG-TEM turbulence. As expected by the above-mentioned conjecture based on the entropy balance, we find that TEM turbulence transfers energy from electrons to ions, which occurs in the opposite direction of the energy exchange to that of ITG turbulence. Furthermore, it is clarified that the magnitude of the energy exchange is proportional to the difference between the entropy productions due to electron and ion transport fluxes. We also investigate the predictability of turbulent energy exchange in ITG-TEM turbulence by the quasilinear model.

[1]H. Sugama et al., Phys. Plasmas 3, 2379(1996).

[2]T. Kato et al., Phys. Plasmas 31, 062510(2024).