TY - JOUR
T1 - Ion versus Electron Heating in Compressively Driven Astrophysical Gyrokinetic Turbulence
AU - Kawazura, Y.
AU - Schekochihin, A. A.
AU - Barnes, M.
AU - Tenbarge, J. M.
AU - Tong, Y.
AU - Klein, K. G.
AU - Dorland, W.
N1 - Funding Information:
Y. K., M. A. B., and A. A. S. are grateful to S. Balbus and F. Parra for very fruitful discussions. Y. K. thanks G. Howes for providing the numerical code for the recursive expansion method . Y. K., A. A. S., and M. A. B. are supported by the STFC Grant No. ST/N000919/1. Y. K. is supported by JSPS KAKENHI Grants No. JP19K23451 and No. JP20K14509. A. A. S. and M. A. B. are supported in part by the UK EPSRC Grant No. EP/R034737/1. J. M. T. is supported by NSF SHINE Grant No. AGS-1622306. K. G. K. is supported by NASA Grant No. 80NSSC20K0521. J. M. T., K. G. K., and Y. T. acknowledge the 2014 ISSI meeting that originally motivated the development of compressive driving code. Numerical computations reported here are carried out on the EUROfusion HPC (Marconi-Fusion) under project MULTEI, on ARCHER through the Plasma HEC Consortium EPSRC Grant No. EP/L000237/1 under Projects No. e281–gs2, on Cray XC50 at Center for Computational Astrophysics in National Astronomical Observatory of Japan, and on the University of Oxford’s ARC facility.
Publisher Copyright:
© 2020 authors. Published by the American Physical Society.
PY - 2020/12/11
Y1 - 2020/12/11
N2 - The partition of irreversible heating between ions and electrons in compressively driven (but subsonic) collisionless turbulence is investigated by means of nonlinear hybrid gyrokinetic simulations. We derive a prescription for the ion-To-electron heating ratio Qi/Qe as a function of the compressive-To-Alfvénic driving power ratio Pcompr/PAW, of the ratio of ion thermal pressure to magnetic pressure βi, and of the ratio of ion-To-electron background temperatures Ti/Te. It is shown that Qi/Qe is an increasing function of Pcompr/PAW. When the compressive driving is sufficiently large, Qi/Qe approaches ≃Pcompr/PAW. 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 Alfvén waves is absent for both low and high βi, 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 βi 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∗.
AB - The partition of irreversible heating between ions and electrons in compressively driven (but subsonic) collisionless turbulence is investigated by means of nonlinear hybrid gyrokinetic simulations. We derive a prescription for the ion-To-electron heating ratio Qi/Qe as a function of the compressive-To-Alfvénic driving power ratio Pcompr/PAW, of the ratio of ion thermal pressure to magnetic pressure βi, and of the ratio of ion-To-electron background temperatures Ti/Te. It is shown that Qi/Qe is an increasing function of Pcompr/PAW. When the compressive driving is sufficiently large, Qi/Qe approaches ≃Pcompr/PAW. 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 Alfvén waves is absent for both low and high βi, 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 βi 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∗.
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U2 - 10.1103/PhysRevX.10.041050
DO - 10.1103/PhysRevX.10.041050
M3 - Article
AN - SCOPUS:85097574541
VL - 10
JO - Physical Review X
JF - Physical Review X
SN - 2160-3308
IS - 4
M1 - 041050
ER -