Effects of the energetic particles on the anomalous transport driven by the ion temperature gradient instability

Abstract

When the charge exchange time (τcx) is sufficiently shorter than the slowing-down time (τsl), the distribution of energetic particles (EPs) is bump-on-tail. In this work, the effects of EPs on the anomalous transport driven by the ion temperature gradient (ITG) instability are investigated. The dispersion relation is theoretically derived and numerically solved to analyze the effects of EPs on the linear frequency of ITG instability. Two kinds of bump-on-tail distribution, denoted by τ=13τsl/τcx=1.133 and 6.8, and the slowing-down distribution, denoted by τ = 0, are considered. Based on the linear results, the quasilinear particle and energy fluxes of bulk ions are analyzed. It is found that effects of the EPs on the ITG linear frequency and quasilinear transport are obvious in the regions with the EPs initial energy E0/Te<60 and the EPs charge concentration Zhεh>0.01, where Te is the electron temperature, Zh and εh are the charge number and fraction of EPs, respectively. Existence of the EPs is beneficial for the stabilization of ITG instability. Moreover, the ITG instability can be better stabilized with the bump-on-tail distribution of energetic deuterium (D) and the slowing-down distribution of energetic helium (He). However, in the cases with the slowing-down distribution of D and the bump-on-tail distribution of He, the particle fluxes of bulk ions are inwardly largest and the energy fluxes of bulk ions are outwardly smallest, which indicate that the better particle and energy confinement appear with the slowing-down distribution of D and the bump-on-tail distribution of He.