Introduction to Plasmas and Plasma Dynamics: With Reviews of Applications in Space Propulsion, Magnetic Fusion and Space Physics

350 Pages·2016·13.56 MB·English

by  York Th.M.

Introduction to
PLASMAS AND
PLASMA DYNAMICS
With Reviews of Applications in Space
Propulsion, Magnetic Fusion and Space Physics
THOMAS M. YORK
York Scientific Consultants
HAI-BIN TANG
Beijing University of Aeronautics and Astronautics
(BUAA), Beihang University
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PREFACE
The study of plasmasdionized gases which are generally electrically
neutraldemerged as an important topic because of the importance of the
subject in energy, communications, space exploration, and defense appli-
cations.Intenseinterestinthesubjectemergedfromastrophysics1andstudy
of thermonuclear processes2 in the 1950s. While the subject matter foun-
dation is inherently physical science, development and construction of
devices of a broad variety require interpretation to the engineering appli-
cations. This process was assisted in the 1950s with the publication of two
comprehensive volumes on Gas Discharge Physics.3
The material presented here has been organized and found useful in
instruction and research over a period of many years. One of the authors
(TMY)firstbegandealingwiththeuniqueaspectsofhightemperatureand
highenergygasesasaresultoftheworkonreentrytheoryandexperiments
withshocktunnelsinthe1960s.Thiswasnotanacademicendeavorperse,
but the study grew out of the need to build physical devices that had to
meetrealneeds.Followingperiodsofresearchweremotivatedbyproblems
of space propulsion, magnetic fusion, laser fusion, and space physics. The
second author (HBT) has been similarly motivated in the need to under-
standthephysicalinteractionsinrealdevices.Aswiththestudyofallfluids,
behaviors of plasmas are complex, and without simple observational
models,understandingcomeswiththecombinationofpreciseexperimental
evidence and appropriate theoretical and computational models. Experi-
ence has taught that the conception of principles and their application
in directed research efforts based on anecdotal results from either experi-
ment or theory have proven to be ineffective. Therefore, this material is
presentedinthecontextthatthereisaneedforaframeworkofknowledge
that can guide the student and researcher in the examination and explo-
ration of the intricate and exquisite behaviors that occur in gases which are
influenced by high temperatures and electric and magnetic fields.
1Alfven,H.,1950.CosmicalElectrodynamics.InternationalMonographsonPhysics.Clarendon,
Oxford.
2Proceedingsofthe2ndUnitedNationsConferenceonPeacefulUsesofAtomicEnergy,Geneva,
1958.
3Flugge,S.(Ed.),1956.HandbuchderPhysik,GasDischargesI:vol.21;andII,vol.22.Springer,
Berlin.
xi
xii Preface
It is clearly intended that this serves as introductory text for those
approachingthestudyofionizedgases.Itisnotintendedasatextinplasma
physicsorasareferenceforgasdischargeapplications;thereareanumberof
excellent works on those subjects, and they are given as references. It is
intended to provide an introduction based on physical concepts and
straightforward mathematical treatment so that the reader will gain a
comprehensive exposure to the basis, techniques, and problems encoun-
tered in plasma studies and applications. Physical understanding is para-
mount;theworkalwayspointstofurtherstudyandresearchonanysubject
ofinterest.Forthestudents,thereareanumberofnewareasofphysicsthat
need a basic foundation for the engineering applications. This work pre-
sumes an undergraduate degree involving fluid and thermal engineering or
in physics, and the text attempts to extend this into the introductory
domains of atomic physics, electricity and magnetism, and quantum
mechanics.Thisbackgroundisnecessaryinorderthattheultimateeffortof
applications of plasma principles does not remain in the framework of
simplesubstitutioninavailableequations.Thecoverageofkinetictheoryis
extendedinto regimesoftransfer andtransport ofinternal particle energies.
Electricity and magnetism coverage emphasizes not only Maxwell’s
equations, but the application and effects of those equations to physical
experiments and devices that utilize plasmas. The equations of fluid
mechanicsareextendedtoincludeelectromagneticenergyandmomentum
components,butaseriousattemptismadetodevelopunderstandingofthe
complex fluid mechanical behaviors that result when interactions include
plasma physics and transport processes. This complex behavior is made
more intractable by the occurrence of both collisional and collisionless
behavior in plasma devices. The authors believe that sound preparation for
workwithplasmasinvolvesdetailedconsiderationofspecificplasmadevices
and phenomena. The applications and examples are taken from plasma
accelerators/thrusters, compression/heating devices including magnetic
fusion, and space physics descriptions of magnetospheres/ionospheres. The
solution of numerous problems in the future involving energy, electronics,
communications, and transportation fields will involve understanding
plasmasandplasmadynamics.Wehopethisworkwillassistthosewhowill
face these challenges.
ACKNOWLEDGMENTS
A work of this type and extent has drawn its integrity from a number of
contributorsinanumberofways.Forbothauthors,eachofusowesadebt
to some exceptional teachers who opened our vision to understanding
thoughts, concepts, and goals that became a driving force. We have gained
immeasurably from coinvestigators on research projects, colleagues in
research laboratories and in universities. We have gained insights from the
unique relationships with our students in the process of defining and
executing their research accomplishments. These individuals are too
numerous to name and recognize here.
For the first author (TMY), it is appropriate to recognize the con-
tribution of his academic affiliation with Professor Bob Jahn at Princeton
University;intheformativeperiodofhisPhDwork,hewasencouragedto
pursue a broader academic inquiry into the scientific foundations of his
research activity.
Forthesecondauthor(HBT),itisrealpleasuretoacknowledgetheidea
and understanding of plasma and plasma propulsion from Professor Yu Liu
at Beihang University who not only gave encouragement but also shared
his keen insight into the best way to present difficult concepts at the
beginning of the author’s research.
Inthepreparationofthespecificdocument,theauthorsareappreciative
of the help at BUAA of Dr. Chaojin Qin, who transformed written text
equationsintoprecisedocumentform.Anextensivecontributionwasmade
by Mengdi Kong (MS candidate), who prepared numerous drawings and
confirmedthedetailsofthemathematicaldevelopmentsthatare presented.
Finally,inaworkofthisextent,thereaderwillfindtheinevitableerror;
for this the authors assume complete responsibility.
xiii
CHAPTER 1
The Plasma Medium
and Plasma Devices
INTRODUCTION
The world in which we function is consistent with our physical charac-
teristics defined by mass, volume, and energy. Our natural environment is
benignda gaseous atmosphere of nitrogen and oxygen at pressures of
105N/m2,temperaturesof0–40(cid:1)C,andparticledensitiesof1025m(cid:3)3.We
are continuously receiving radiant energy from the Sun at a rate of about
300W/m2, in a 24-h cyclical pattern due to the Earth’s rotation, which is
modifiedbytheannualcycleoftheEarth’sorbitalmotionaroundtheSun.
In the course of history, we have observed in our local environment
exceptional natural displays of energy that demonstrate the existence of
forces and energies well beyond our control. The Sun itself is clearly of a
very high temperature and is capable of transient, powerful eruptions.
Storms in the atmosphere display enormous wind power; electrical light-
ningstrikesgeneratingshockwavesandcreatinglocaltemperaturesthatcan
ignite combustion. Polar latitudes evidence dynamic geophysical scale
displaysoflightthatinspireaweandrequireunderstanding.Allthesenatural
eventsdemonstrateandtestifytothehigh-energyexcitationofourgaseous
atmosphere in response to geophysical electric and magnetic field-based
mechanisms. In fact, in the total physical world, with the exception of
thenear-Earth environment,themediumweexistiniscomposedof high-
energy particles with electric charges, and they are in incessant motion,
sometimes directed and sometimes random. In short, the physical universe
is largely composed of plasma.
This work is an introduction to the properties and behavior of that
electrically active medium and of some of the devices that have been
developed to utilize the characteristics of energy and force transfer with
the plasma. Plasma is a medium that includes species of charged particles,
and plasma dynamics is the description and analysis of force generation and
energy transfer with that medium. The important characteristic of gaseous
plasmas is their physical makeup, which allows reaction to electric and
IntroductiontoPlasmasandPlasmaDynamics ©2015ThomasM.York.
ISBN978-0-12-801661-9 PublishedbyElsevierInc.
http://dx.doi.org/10.1016/B978-0-12-801661-9.00001-5 Allrightsreserved. 1
2 IntroductiontoPlasmasandPlasmaDynamics
magneticfields,particularlyandincludingtheconductionofcurrent.There
is a conceptual similarity of plasmas with solid electrical conductors
whereby flowing electrons and electromagnetic waves move through static
ions in response to electric and magnetic fields. The charged plasma par-
ticles develop organized (collective) behavior due to interaction with large
numbers of nearby charged particles. Due to the energy equilibrium but
mass differences of plasma component species, there is the occurrence of
localelectricfieldgeneration,whichisthebeginningofacomplexinterplay
ofparticle motion andelectric andmagneticfields. Thesebehaviorsare the
ingredients that allow unique device performance using plasmas.
With our relatively recent discovery (and still developing knowledge) of
atomic structure,electricalchargesand currents,electricand magneticfields,
and electromagnetic radiation, we have begun the process of defining and
controlling particle behavior to develop new devices to serve our needs.
Particularlyinthelast50years,wehaveseentheapplicationofsuchknowl-
edgetocreatedeviceswithenhancedcapabilityinlightandpowergeneration,
communications,scientificdiagnosticsinthephysicalandbiologicalsciences,
and space exploration (National Research Council, 1995). This work in-
troducesthestudentandresearchertothebasicmechanicsoftheparticlein-
teractions inherent in devices that utilize charged particles and presents the
frameworkforunderstandingtheirfurtherapplicationinnewdevices.
PLASMAS IN NATURE
General Description
A generalrepresentation ofplasmas thatare observedinnatureis presented
in Figure 1.1.
The plasma regions are identified by their properties of particle density
and particle temperature.
The Solar Plasma
It can be identified that gases in the solar system occur over the range of
1033p/m3and107Kinthesolarcoreto109p/m3and105KintheEarth’s
aurora (Kivelson and Russell, 1993). Both these extremes in properties
represent plasmas that have important physical characteristics and if pro-
duced in the laboratory can be utilized in practical devices. It can be seen
that lightning, which occurs at atmospheric pressure conditions, is typified
by temperatures of 10,000K or more.
ThePlasmaMediumandPlasmaDevices 3
NEBULA
SOLAR CORE
K)106 SOLAR
e ( CORONA LIGHTNING
ur
at SOLAR WIND
er
p
m INTERSTELL AR SPACE GASES,
Te 104 LIQUIDS
AURORA FLAMES & SOLIDS
DENSE & COOL
SO NO CLASSICAL
PLASMA BEHAVIOR
102
103 109 1015 1021 1027 1033
Number Density (Charged Particles / m3)
Figure 1.1 Property domains of plasmas occurring in space and natural
environment. Adapted from web site: http://www.cpepphysics.org/fusion_chart_view.
html,Contemporary PhysicsEduc.Project (2010),withpermission.
As the solar plasma and its energies are so significant in our envi-
ronment,itis usefulto identifyasareferencetheordersofmagnitudeofa
set of specific properties and parameters relative to the Earth. The plasma
in the interplanetary system originates from the Sun. The Sun has a mass
of 2(cid:4)1030kg, diameter of 1.4(cid:4)106km, and a composition of 75%
hydrogen and 25% helium. The thermonuclear fusion of hydrogen to
helium produces a core temperature of 1.6(cid:4)107K and a corona tem-
peratureof5(cid:4)106K.Thisplasma oftheSunescapesinall directionsand
expands into all regions of the solar system. At the Earth radius from the
Sun the particle proton and electron densities are about 10 cm(cid:3)3, with
proton temperature of 4(cid:4)104K and electron temperature of
1.5(cid:4)105K, and most importantly a solar wind flow speed of about
400m/s.TheinteractionofthisflowingplasmawiththeEarth’smagnetic
fieldproducesthehypersonicflowfieldoftheasymmetricmagnetosphere
(Bothmer, 1999), as shown in Figure 1.2.
PLASMAS IN LABORATORY/DEVICE APPLICATIONS
General Description
Because of the potential for application in new revolutionary devices that
canextendourcapabilitiesinanumberoftechnologies(Charles,2009),the
behavior of ionized gas plasmas has been explored over a broad range of
densities and temperatures, steady state and transient conditions, small and