DOI: 10.1073/pnas.1917905117
论文题名: Electron temperature of the solar wind
作者: Boldyrev S. ; Forest C. ; Egedal J.
刊名: Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
出版年: 2020
卷: 117, 期: 17 起始页码: 9232
结束页码: 9240
语种: 英语
英文关键词: Heliosphere
; Kinetic theory
; Magnetic field
; Plasma
; Solar wind
Scopus关键词: adiabaticity
; article
; electron
; energy transfer
; heat
; human tissue
; magnetic field
英文摘要: Solar wind provides an example of a weakly collisional plasma expanding from a thermal source in the presence of spatially diverging magnetic-field lines. Observations show that in the inner heliosphere, the electron temperature declines with the distance approximately as Te(r) ∼ r− 0 3 . . . r− 0 7, which is significantly slower than the adiabatic expansion law ∼r−4/3. Motivated by such observations, we propose a kinetic theory that addresses the nonadiabatic evolution of a nearly collisionless plasma expanding from a central thermal source. We concentrate on the dynamics of energetic electrons propagating along a radially diverging magnetic-flux tube. Due to conservation of their magnetic moments, the electrons form a beam collimated along the magnetic-field lines. Due to weak energy exchange with the background plasma, the beam population slowly loses its energy and heats the background plasma. We propose that no matter how weak the collisions are, at large enough distances from the source a universal regime of expansion is established where the electron temperature declines as Te(r) ∝ r− 2/5. This is close to the observed scaling of the electron temperature in the inner heliosphere. Our first-principle kinetic derivation may thus provide an explanation for the slower-than-adiabatic temperature decline in the solar wind. More broadly, it may be useful for describing magnetized collisionless winds from G-type stars. © 2020 National Academy of Sciences. All rights reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/163472
Appears in Collections: 气候变化与战略
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作者单位: Boldyrev, S., Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, United States, Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301, United States; Forest, C., Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, United States; Egedal, J., Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, United States
Recommended Citation:
Boldyrev S.,Forest C.,Egedal J.. Electron temperature of the solar wind[J]. Proceedings of the National Academy of Sciences of the United States of America,2020-01-01,117(17)