Description
Micro-tearing mode (MTM), which is an electromagnetic turbulence for driving anomalous transport, have been observed in the pedestal [1]. Using DIII-D experimental parameters of the strong-gradient pedestal region where MTM is dominate [2], we first derive the dispersion relation of MTM instability including impurity effects via the semi-collisional theory [3, 4]. The dispersion equation is obtained through asymptotic matching between electron and ion regions, where eigen-equations are reduced to a Bessel equation and a hypergeometric equation, respectively. Then, we further calculate the electron particle and heat transport fluxes driven by MTM instability based on the quasi-linear theory. The analytical results show that the impurity dilution effect modifies the linear characteristics of MTM by increasing collisional terms (first destabilize then stabilize MTM) and decreasing diamagnetic terms (destabilize MTM); additionally, the increase of beta can stabilize the MTM instability. The corresponding transport coefficients reveal that the effective electron diffusivity D_e^eff is much smaller than the effective electron heat conductivity χ_e^eff, as D_e^eff/χ_e^eff~0.1, which is consistent with Ref. [1]. Moreover, the electron transport flux driven by the magnetic flutter effect is strongly non-ambipolar, exceeding the ion and impurity fluxes. Parametric dependencies are also analyzed. For example, the presence of impurity can stabilize the MTM instability and decrease the real frequency as compared to the case without impurity. And the increase of the impurity charge number Z can also decrease both real frequency and the growth rate of MTM instability. Detailed results about other parametric dependence are still under analyzing.
Key words: impurity transport, electromagnetic turbulence, MTM, pedestal
References
[1] M. Kotschenreuther, X. Liu, D. R. Hatch, et al. Nuclear Fusion, 2019, 59:096001
[2] M. T. Curie, D.R. Hatch, M. Halfmoon, et al. Nuclear Fusion, 2022, 62:126061
[3] A. Zocco, N. F. Loureiro, D. Dickinson, et al. Plasma Physics and Controlled Fusion, 2015, 57:065008
[4] J. W. Connor, R. J. Hastie, A. Zocco. Plasma Physics and Controlled Fusion, 2012, 54:035003