Table Of ContentAtmosphere, Earth, Ocean & Space
De-Jin Wu
Ling Chen
Kinetic Alfvén Waves
in Laboratory, Space,
and Astrophysical
Plasmas
Atmosphere, Earth, Ocean & Space
Editor-in-Chief
Wing-Huen Ip, National Central University, Institute of Astronomy,
Jhongli District, Taoyuan City, China
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Masataka Ando, Nagoya University, Nagoya, Japan
Chen-Tung Arthur Chen, Department of Oceanography, National Sun Yat-Sen
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Kaichang Di, Institute of Remote Sensing and Digital Earth, Chinese Academy
of Sciences, Beijing, China
Jianping Gan, Hong Kong University of Science and Technology, Hong Kong,
China
Philip L.-F. Liu, Department of Civil and Environmental Engineering,
National University of Singapore, Singapore
Ching-Hua Lo, Geology, National Taiwan University, Taipei, China
James A. Slavin, Department of Atmospheric, Oceanic and Space Sciences,
University of Michigan–Ann Arbor, USA
Keke Zhang, University of Exeter, UK
R. D. Deshpande, Geosciences Division, Physical Research Laboratory,
Gujarat, India
A. J. Timothy Jull, Geosciences and Physics, University of Arizona AMS
Laboratory, Tucson, AZ, USA
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De-Jin Wu Ling Chen
(cid:129)
é
Kinetic Alfv n Waves
in Laboratory, Space,
and Astrophysical Plasmas
123
De-JinWu LingChen
ChineseAcademy of Sciences ChineseAcademy of Sciences
PurpleMountain Observatory PurpleMountain Observatory
Nanjing, Jiangsu,China Nanjing, Jiangsu,China
ISSN 2524-440X ISSN 2524-4418 (electronic)
Atmosphere, Earth, Ocean & Space
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Foreword
Kinetic Alfvén waves (KAWs) are small-scale dispersive Alfvén waves and can
effectively exchange energy and momentum with plasma particles through the
wave-particleinteraction.Therefore,KAWscanplayanimportantroleintheheating
of high-temperature plasmas, the acceleration of high-energy particles, and the
anomalous transport of plasma particles, which occur commonly and frequently in
various plasma environments from laboratory to space and astrophysics. In partic-
ular,alargeamountofinvestigationsbasedoninsitumeasurementsbysatellitesin
spaceplasmashasrevealedthatkinetic-scalefluctuationsinthesolarwindaswellas
in the magnetosphere can be identified well as the KAW-associated turbulence.
BycombiningtheVoyager1in-situmeasurements(Lee&Lee,NatureAstronomy,
3, 154, 2019) with the earlier ground remote observations (Armstrong et al.,
Astrophys. J., 443, 209, 1995), the interstellar turbulence spectrum is found to
extend from 50 m ((cid:1) the Debye length) to 1018 m ((cid:1)30 pc), over 16 orders of
magnitude. The turbulence spectrum consists of a Kolmogorov inertial range
(106–1018m)andakineticrange(50–106m).ThisimpliesthattheKAWturbulence
can ubiquitously exist in various cosmic plasma environments, just like the AW
turbulence.
The monograph Kinetic Alfvén Waves in Laboratory, Space, and Astrophysical
Plasmas by Drs. De-Jin Wu and Ling Chen presents a comprehensive description
oftheapplicationsofKAWsinspaceandastrophysicalplasmas.Afterintroducing
and summarizing the main physical properties of KAWs and their experimental
demonstrations in Chaps. 1 and 2, they focus on the applications of KAWs to the
crucial processes in the solar-terrestrial coupling system, including the auroral
electron acceleration in the magnetosphere-ionosphere coupling (Chap. 3), the
anomalous particle transport occurring at the magnetopause in the solar
wind-magnetosphere interaction (Chap. 4), the turbulent cascading process of the
large-scale AW turbulence towards the small-scale KAW turbulence in the solar
wind turbulence (Chap. 5), and the solar corona and solar wind heating (Chap. 6).
However, the authors do not stop at these well-known phenomena and proceed
furtheracrosstheextrasolarastrophysicalplasmas.InChap.7,theydiscussfurther
v
vi Foreword
possibleapplicationsofKAWstoextrasolarastrophysicalplasmas,inparticular,to
theheatingofcosmichotgases suchasstellarandaccretion-disk coronae,galactic
hot halos, and intracluster hot medium, as well as to the reacceleration of
high-energy electrons and the collimation of radio jets in extragalactic extended
radio sources.
KAWs and their applications are without doubt an increasingly interesting
subject. The physics of KAWs can sensitively depend on the local plasma
parameters.Thisindicatesthattheymayplayverydifferentrolesinvariouscosmic
environments. This important and interesting characteristic of KAWs also is fully
displayedinthismonograph,whichcollectsanumberofKAW-relatedapplications
scatteredinvariousjournalsandproceedings,butnotalwayseasilyaccessible.Ina
word, this is a particularly useful monograph for graduate students and young
scientistsjoiningthefieldsofplasmaphysics,spacephysics,andastrophysics.The
materials collected in this monograph also are interesting for the most advanced
researchers working actively in these fields.
October 2019 Prof. Lou-Chuang Lee
Institute of Earth Sciences
Academia Sinica, Taipei, Taiwan
Preface
Alfvén waves (AWs) are low-frequency and long-wavelength electromagnetic
fluctuations in conducting fluids and ubiquitous in various space and astrophysical
magnetic plasma environments. The most important property of AWs is that they
can efficiently transport energy and momentum between distant plasma regions
connected to each other by steady magnetic fields because the group velocity of
AWs propagates exactly along the steady magnetic fields, independent of the ori-
entation of the wave front. Therefore, AW can play an important role in the elec-
trodynamical coupling of active and passive magnetic plasmas and has been a
subjectofintensestudysinceitwasfoundbyHannesAlfvénin1942.Inparticular,
itisthediscoveryofAWsthatledtoawholenewfieldofmagnetohydrodynamics
(MHD), which combines electromagnetic theory and fluid dynamics and creates
fruitful applications in different parts of plasma physics.
Kinetic Alfvén waves (KAWs) are dispersive AWs with a short wavelength
comparable to the kinetic scales of plasma particles, such as the ion (or
ion-acoustic) gyroradius or the electron inertial length. Although KAWs retain
some basic properties of MHD AWs, such as the quasi-parallel propagation of the
wavegroupvelocity,theyhavealotofthenovelimportantcharacteristicstheMHD
AWs do not possess. These new characteristics can be attributed to the so-called
kinetic effects of plasma particles due to the wave scale matching with that of the
particle motion. This implies that KAWs may exchange effectively energy and
momentum with plasma particles and can be responsible for the acceleration or
heatingofplasmaparticles,whichareverycommonoccurrencefromlaboratoryto
spaceandastrophysicalplasmas.SincethepioneerworkofChenandHasegawain
the early 1970s, KAWs have been attracting a lot of attention of researchers from
different fields of laboratory, space, and astrophysical plasmas. In particular,
observational identifications of KAWs in space plasmas and experimental mea-
surementsofKAWsinlaboratoryplasmasinthe1990sresultedinthereevaluation
of the importance of KAWs in the dynamics of various magnetic plasmas and
remotivatedtheinterestofKAWstudies.Since2000s,thestudyofKAWsisfurther
extendedandgeneralizedtosolarphysicsandotherastrophysics,inparticular,one
vii
viii Preface
finds that KAWs can play important roles in the dynamics of solar wind AW
turbulence as well as in the inhomogeneous heating of the solar atmosphere.
Why are KAWs an important and interesting subject? First, the most important
reason is that their characteristic scales are comparable to the kinetic scales of
plasma particles. These scales are that between macroscopic phenomena and
microscopic processesof plasmas, andhence are themost typical scalesof plasma
collective phenomena and fine structures, which are the most distinctive feature of
plasma physics. It is in these scales that plasma waves and particles can most
effectively exchange theirenergy and momentum,ori.e., theplasma wave-particle
interaction can occur most efficiently. This makes KAWs capable of playing an
important role in both the particle energization and fine structure phenomena of
magnetic plasmas, which can be observed universally in space and solar plasmas.
Secondly, one of the important reasons is their ubiquitous existence in various
plasma environments. It is well-known that AWs are low-frequency electromag-
neticfluctuationsobservedmostcommonlyinextensiveplasmaenvironments,such
as in the magnetosphere, solar wind and solar atmosphere, and interstellar and
intergalacticmedia.ThestandardGoldreich-Sridhartheoryofinterstellarturbulence
implies that KAWs are natural and inevitable results of AWs cascading toward
smaller scales. Recent observation studies indeed show that KAWs exist ubiqui-
tously in space and solar plasmas and play important roles in the auroral electron
acceleration, magnetospheric particle transport, solar wind turbulent cascade, and
solar atmospheric heating.
The third reason for KAWs to be important and interesting is the richness and
diversity of their wave-particle interaction. In space, solar, and other astrophysical
plasma environments, existing plasmas almost all are complex plasmas, which
consist of electrons and multiple ion species, including electrons, protons, alpha
particles, other heavy ions, and sometimes even charged dust particles. In general,
differentspeciesofparticleswithdifferentchargesandmasseshavedifferentkinetic
scalesandthewave-particleinteractionofKAWssensitivelydependsonthekinetic
scales of the species. In consequence, a significant difference can appear among
different species components in plasmas, which often presents in observations of
space and solar plasmas.
Finally, the sensitive dependence of the KAW physics on local plasma param-
eters also is an important reason for KAWs to be an important and interesting
subject.ThephysicsofKAWs,especiallytheirelectromagneticpolarizationsenses,
sensitively depends on the plasma kinetic scales and hence on the local plasma
parameters, such as the static magnetic field, the unperturbed plasma density and
temperatures, the plasma kinetic to magnetic pressure ratio b, and so on. These
plasma parameters can vary remarkably in the order of magnitude in the magne-
tosphere, the solar wind, the solar atmosphere, and other astrophysical plasma
environments. This results in the distinctness of the wave-particle interaction of
KAWs in various environments as shown in observations.
Sevenyearsago,IwroteamonographonKAWs,KineticAlfvénWave:Theory,
Experiment, and Application (2012, Science Press, Beijing), which is the first
monographfocusingonKAWsandprovidesasystematicandbroadintroductionto
Preface ix
the KAW physics with the emphasis on the basic theories of KAWs. KAWs have
been an actively and increasingly interesting subject. In these years, a lot of
observations and applications of KAWs from laboratory and space plasmas have
greatly enriched and advanced our understanding of KAWs. Without a doubt, the
solar-terrestrial coupling system provides us a unique natural laboratory for the
comprehensive and thorough study of KAWs. The present book is a companion
volume of the monograph above and is finished cooperatively by me with my
colleague Dr. Ling Chen. In this companion, we will show you an interesting
journey of KAWs from laboratory plasmas to space and astrophysical plasmas,
especiallyinthesolar-terrestrialcouplingsystem.Youcanfindthedifferentphysics
propertiesofKAWsinvariousplasmaenvironmentsandtheirdiverserolesplayed
inthesedifferentenvironmentsduetothesensitivelyparametricdependenceofthe
physics properties of KAWs on local plasma parameters.
This companion volume focuses on the applications of KAWs in space and
astrophysicalplasmas,especiallyonsomecrucialphenomenainthesolar-terrestrial
couplingsystem,includingthemagnetosphere-ionospherecouplingandtheauroral
electron acceleration (Chap. 3), the solar wind-magnetosphere interaction and the
anomalous transport of particles at the magnetopause (Chap. 4), the solar wind
turbulence (Chap. 5), and the solar corona and solar wind heating (Chap. 6). In
addition, for the sake of consistency, this volume also covers a concise review
of the main physics properties of KAWs (Chap. 1) and the experimental demon-
strations of these properties in laboratory plasmas (Chap. 2). Finally, in closing,
some possible applications of KAWs to extrasolar astrophysical plasmas are dis-
cussed in Chap. 7.
It is a very difficult, arduous, and never ending task to make the text error-free
although we have made all efforts. We would always appreciate deeply it if the
readersofthisbookwillkindlyinformusaboutanyerrorsandmisprintstheyfind,
preferentially by e-mail to [email protected].
Nanjing, China De-Jin Wu
October 2019
