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Journal Articles

Cross-scale interactions between turbulence driven by electron and ion temperature gradients via sub-ion-scale structures

Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Ishizawa, Akihiro*; Nunami, Masanori*

Nuclear Fusion, 57(6), p.066036_1 - 066036_10, 2017/05

 Times Cited Count:7 Percentile:51.38(Physics, Fluids & Plasmas)

Multi-scale plasma turbulence including electron and ion temperature gradient (ETG/ITG) modes has been investigated by means of electromagnetic gyrokinetic simulations. Triad transfer analyses on nonlinear mode coupling reveal cross-scale interactions between electron and ion scales. One of the interactions is suppression of electron-scale turbulence by ion- scale turbulence, where ITG-driven short-wavelength eddies act like shear flows and suppress ETG turbulence. Another cross-scale interaction is enhancement of ion-scale turbulence in the presence of electron-scale turbulence. This is caused via short-wavelength zonal flows, which are created by the response of passing kinetic electrons in ITG turbulence, suppress ITG turbulence by their shearing, and are damped by ETG turbulence. In both cases, sub-ion-scale structures between electron and ion scales play important roles in the cross-scale interactions.

Journal Articles

Cross-scale interactions between electron and ion scale turbulence in a tokamak plasma

Maeyama, Shinya*; Idomura, Yasuhiro; Watanabe, Tomohiko*; Nakata, Motoki*; Yagi, Masatoshi; Miyato, Naoaki; Ishizawa, Akihiro*; Nunami, Masanori*

Physical Review Letters, 114(25), p.255002_1 - 255002_5, 2015/06

 Times Cited Count:68 Percentile:95.12(Physics, Multidisciplinary)

Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and $$beta$$ value are realized for the first time, where the $$beta$$ value is given by the ratio of plasma pressure to magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real- mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. When the ion-scale modes are stabilized by finite-$$beta$$ effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport.

Oral presentation

Three wave coupling in gyrokinetic multi-scale interaction

Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Ishizawa, Akihiro*; Nunami, Masanori*

no journal, , 

In order to analyze multi-scale interactions in fine scale gyrokinetic simulations covering both ion and electron scales, we develop a fluid moment based analysis method for three wave coupling. In analyzing three wave coupling of gyrokinetic equations, one needs to keep interactions of five dimensional (5D) distribution functions. However, it is prohibitive to store such massive data. In this talk, we propose an approximate analysis method based on 3D fluid moments, which are reduced by integrating 5D distribution functions over velocity space, and discuss its accuracy. By applying this method, we found a new damping mechanism of ion scale zonal flows due to electron scale turbulence.

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