Description
The electron-temperature-gradient (ETG) turbulence in tokamaks is investigated by nonlinear gyrokinetic global code NLT [1] with adiabatic ions. In the linear simulation, global properties of ETG mode, including real frequency, growth rate and detailed two-dimensional (2D) mode structure, are obtained under Cyclone base parameters. A clear scaling relationship between the radial envelope width and the device size is revealed, demonstrating that the envelope of the ETG mode resides at a meso-scale, i.e., $\Delta r_{\rm{env}}=\sqrt{a\rho_e}$, with $\Delta r_{\rm{env}}$ the radial envelope width, $a$ the minor radius and $\rho_e$ the electron Larmor radius, which is consistent with the conclusions of GT3D simulations [2]. The linear results are compared with the 2D global eigenvalue solver [3], which is based on the two-order ballooning mode transformation; the comparison shows good consistency. In the nonlinear simulation, the relaxation evolution of ETG turbulence is investigated. The electron thermal transport level of ETG turbulence is in good agreement with the mixing-length estimate using linear growth rate and radial envelope width, suggesting that the radial streamer structure [4] is closely related to ETG turbulent transport. Furthermore, the relationship between the electron thermal transport level and the temperature gradient is investigated, and the critical temperature gradient is obtained.
References
[1] L. Ye, Y. Xu, X. Xiao, Z. Dai, and S. Wang, Journal of Computational Physics 316, 180–192 (2016).
[2] Y. Idomura, S. Tokuda, and Y. Kishimoto, Nucl. Fusion 45(12), 1571–1581 (2005).
[3] Y. Qiu, J. Wang, and S. Wang, Phys. Plasma 31(3), 032107 (2024).
[4] W. Dorland, F. Jenko, M. Kotschenreuther, and B.N. Rogers, Phys. Rev. Lett. 85(26), 5579–5582 (2000).