Electron Temperature Gradient Turbulence: Validation in the Columbia Linear Machine Experiments

The electron temperature gradient (ETG) mode, which is a dominant mechanism for turbulent electron thermal transport in plasmas, is produced and verified by a recent experiment conducted in the Columbia linear machine[1]. They report modes at $\sim 0.3 - 0.5 \;\rm MHz$, with azimuthal wave numbers $m\sim 14-16$ and parallel wave number $k_\parallel \sim 0.003\; \rm cm^{-1}$. We study these results using a gyro-fluid simulation code DTRANS and a gyro-kinetic simulation code GTC[2]. The results show that in the linear phase, the dispersion relation is consistent with kinetic theory for a slab ETG model and the radial structure of the fluctuation agrees with the experiment. We also investigate the saturation of ETG mode using the ${\bf E}\times {\bf B}$ turbulent mixing and coupling to low frequency modes. It turns out that low frequency drift-ion acoustic waves as in [1] interact with high frequency ETG modes to extract energy and saturate the ETG fluctuations. \\[4pt] [1] X. Wei, V. Sokolov, and A. K. Sen, Physics of Plasmas 17, 042108(2010). \\[0pt] [2] I. Holod, W. L. Zhang, Y. Xiao, and Z. Lin, Physics of Plasmas 16, 122307(2009).