Ion versus Electron Heating in Compressively Driven Astrophysical Gyrokinetic Turbulence
Ion versus Electron Heating in Compressively Driven Astrophysical Gyrokinetic Turbulence
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DOI：
10.1103/physrevx.10.041050
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发表时间：
2020-04
期刊：
影响因子：
--
通讯作者：
Y. Kawazura;A. Schekochihin;M. Barnes;J. TenBarge;Y. Tong;K. Klein;W. Dorland
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文献类型：
--
作者：
Y. Kawazura;A. Schekochihin;M. Barnes;J. TenBarge;Y. Tong;K. Klein;W. Dorland
The partition of irreversible heating between ions and electrons in compressively driven (but subsonic) collisionless turbulence is investigated by means of nonlinear gyrokinetic simulations. We derive a prescription for the ion-to-electron heating ratio $Q_{\text{i}}/Q_{\text{e}}$ as a function of the compressive-to-Alfvenic driving power ratio $P_{\text{compr}}/P_{\text{AW}}$, of the ratio of ion thermal pressure to magnetic pressure $\beta_{\text{i}}$, and of the ratio of ion-to-electron background temperatures $T_{\text{i}}/T_{\text{e}}$. It is shown that $Q_{\text{i}}/Q_{\text{e}}$ is an increasing function of $P_{\text{compr}}/P_{\text{AW}}$. When the compressive driving is sufficiently large, $Q_{\text{i}}/Q_{\text{e}}$ approaches $\simeq P_{\text{compr}}/P_{\text{AW}}$. This indicates that, in turbulence with large compressive fluctuations, the partition of heating is decided at the injection scales, rather than at kinetic scales. Analysis of phase-space spectra shows that the energy transfer from inertial-range compressive fluctuations to sub-Larmor-scale kinetic Alfven waves is absent for both low and high $\beta_{\text{i}}$, meaning that the compressive driving is directly connected to the ion entropy fluctuations, which are converted into ion thermal energy. This result suggests that preferential electron heating is a very special case requiring low $\beta_{\text{i}}$ and no, or weak, compressive driving. Our heating prescription has wide-ranging applications, including to the solar wind and to hot accretion disks such as M87 and Sgr A*.
