Plasma Engineering. Applications from Aerospace to Bio and Nanotechnology

429 Pages·2013·17.72 MB·English

by  Michael Keidar and Isak Beilis (Auth.)

Plasma Engineering
Plasma Engineering
Applications from Aerospace to
Bio- and Nanotechnology
Michael Keidar and Isak I. Beilis
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Michael Keidar dedicates this book to his wife Victoria for her tremendous support
and sacrifice allowing him to focus on research over many years. He also dedi-
cates this book to the blessed memory of his mother, Dina. Isak I. Beilis would like
to thank his wife Galina for support. Special dedication of this book is to the
blessed memory of his parents and his brother.
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Preface
Plasma science and applications have been seeing great progress over the last few decades. This
progress is the consequence of development of modern plasma sources based on plasma generation
in electrical discharges in vacuum, in low- and high-pressure gases, RF-discharges, magnetrons,
etc. On the other hand, it is the result of novel plasma applications in plasma processing of materi-
als, in space propulsion and, especially, in plasma-based nano- and biomedical technology. An
important characteristic of the plasma research realm is the strong overlap between plasma science,
technology, and application. This interplay of the plasma science, technology, and application is
referred as the plasma engineering.
This book is an attempt to present aspects of plasma engineering by describing the physics of
plasmas,plasmagenerationindifferentconditions,andtechniqueofplasmaapplicationsfromauni-
fiedpointofview throughthetheoreticalandexperimentalprism.Thebookconsistsofsevenchap-
ters considering plasma fundamentals, plasma diagnostics and methodology of the plasma
engineeringandvariousplasmaapplications.Whiledescribingthestateoftheartofplasmaapplica-
tions, authors often included their own research results. The material in the book is self-contained
anditwasourintentiontomakethepresentationassimpleandeasilyunderstandableaspossible.
In the introductory part of the book (Chapter 1), basic plasma concepts and foundation of
plasma engineering are introduced. Fundamental plasma phenomena including the different types
of plasma particle collisions, waves, and instabilities are described. The boundary effects such as
plasma-wall transition, electron emission mechanisms, and ablation of the walls contacted with rel-
ativelyhotplasmasare detailed and explained.This is followed by the introduction ofvarious diag-
nostic tools used to characterize plasmas in engineering systems. Fundamental principles and
experimental methodology of plasma diagnostics are reviewed. The probe diagnostic description
includes the planar, spherical, and emissive probes as well as probes operating in a collision-
dominated plasma and in a magnetic field. Furthermore, electrostatic analyzer, interferometric tech-
nique, plasma spectroscopy, optical measurements, fast imaging, and others were explained giving
appreciation oftheir advantagesas well aslimitations.
Physics of different types of electrical discharges is considered. The description begins with the
classical Townsend mechanism of gas electrical breakdown and the Townsend discharge followed
by the streamer mechanism and glow discharges. The nature of gas breakdown according to
Paschen law is detailed. A broad range of high-current discharges including atmospheric and vac-
uum arcs are described taking into account recent developments. New results of simulation of very
complicated cathode phenomena inavacuum arc are presented.
Basic approaches and theoretical methodologies for plasma modeling and, in particular,
approachesthatarebased onnumericalsimulationsaredescribed. Theanalysis beginswithanalysis
of the behavior of a single particle in electric and magnetic fields. It is followed by the description
of two basic approaches. The first one is based on the fluid description of plasma solving numeri-
cally magnetohydrodynamic (MHD) equations. The second one is the kinetic model particle
techniques that take into account kinetic interactions among particles and electromagnetic fields.
This simulation is computationally extensive as it is able to resolve local parameters of the rarified
plasmas.
ix
x Preface
A significant part of this book is devoted to plasma engineering application in space propulsion.
Space propulsion is required for satellite motion in outer space. Plasma physics and engineering of
thrusters based mainly on the electromagnetic plasma acceleration are described. Hall thruster,
pulsed plasma thrusters, and microthruster are some examples of plasma thrusters considered. In
the case of a Hall thruster, the basic mechanisms of electron transport are considered. In the frame-
work of the pulsed plasma thruster, this book covers the ablation phenomena in the presence of
dense plasma.
The important part of the book covers the plasma effects in nanoscience and nanotechnology.
Nanoscience and Nanotechnology study nanoscopic objects used across many scientific fields, such
as chemistry, biology, physics, materials science, and engineering. Application of low-temperature
plasmas in nanoscience and nanotechnology is a relatively new and quickly emerging area at the
frontier of plasma physics, gas discharge, nanoscience, and bioengineering. The description
involves recent original experimental and theoretical results in the field of plasma-based techniques
of nanomaterial synthesis. Particular emphasis is given on the carbon-based nanoparticle synthesis
such as single-walled carbon nanotubes and graphene which are fundamental building blocks.
A magnetically based novel approaches to control length and electric properties of nanoparticles in
plasma-based synthesisare described.
Plasma medicine is an emerging field combining plasma physics and engineering, medicine,
and bioengineering to use plasmas for therapeutic applications. This field is emerging due to
advance in the cold atmospheric plasma (CAP) technology. The latest original results on CAP
applications in medicine are presented in the last part of the book. Physics of cold plasmas and
diagnostics employed such as fast imaging, microwave scattering, and so on are covered. The
effects associated with CAP interaction with cells such as cell migration, apoptosis, and integrins
activation are explained. The therapeutic potential of CAP with a focus on selective tumor cell
eradication capabilitiesand signaling pathway deregulationis shown.
We should note that the aforementioned topics cover an extensive research field and we cer-
tainly understand that the present book does not exhaustively answer all questions. While we tried
to address plasma engineering issues in both width and depth, we could not avoid just “scratching
the surface” by considering some aspects. However, we hope that the wide range of research areas
described will be very useful for understanding the physics and the plasma engineering applications
and ultimatelywill stimulate future research.
This book can be used as a text for courses on Plasma Engineering or Plasma Physics in
Departments of Aerospace Engineering, Electrical Engineering, and Physics. It can also be useful
asa reference for early career researchersand practicing engineers.
The authors would like to acknowledge colleagues and friends, their encouragement, fruitful
discussions,and support.
Firstly, we would like to thank our colleagues Raymond Boxman and Samuel Goldsmith with
whom the original models of the plasma jet expansion in vacuum arc were developed. We are par-
ticularly thankful to Ian Brown who guided one of us (MK) during his tenure as a postdoctoral sci-
entist at Berkeley and with whom we collaborated on some important aspects of multiple-charged
ion transport. We thank Andre Anders with whom we worked on problems related to plasma trans-
port in curved magnetic field and ion implantation. Very special thanks goes to Iain Boyd with
whom we worked for a number of years and who introduced one of us (MK) to the world of parti-
cle simulation of rarefied gases and plasmas. Results of our collaborative work served as the
Preface xi
foundation of a significant part of Chapter 5 dealing with modeling of plasma propulsion devices.
The work on Hall thruster modeling and simulation would not be possible without the experimental
insight and experience of Yevgeny Raitses with whom we have long-term collaboration of various
aspects of plasma propulsion physics and most recently plasma-based nanotechnology. Our long-
term collaboration with Nathaniel Fisch produced many important results used in this book. One of
us (MK) would like to thank Michael Schulman with whom we collaborated on fundamental
aspects of high-current vacuum arc interrupters. Michael Schulman, Paul Slade, and Eric Taylor
contributed greatly in developing models of the high-current vacuum arcs and the interruption pro-
cess. The work on carbon arcs for synthesis of carbon nanotubes performed with Anthony Waas
triggered our consequent work on the plasma-based nanotechnology. We are particularly very
thankfultoIgor Levchenko andKostya (Ken) Ostrikov with whom wehave long-termresearchcol-
laboration on various topics related to plasma nanoscience and nanotechnology. Our joint work
with Mary Ann Stepp on cold plasma(cid:1)controlled cell migration planted seeds for development of
the cold plasma application inmedicine. Most recent work on cold plasma cancer therapy would be
impossible without contributions from Barry Trink, Anthony Sandler, Jonathan Sherman, Alan Siu,
and Jerome Canady. We are very grateful to Mikhail Shneider who contributed a lot to understand-
ing on the cold plasma physics. Our great appreciation and thanks to our colleague Alexey
Shashurin for his contribution to a number of original works described in this book. We are also
grateful to our coauthors (in alphabetic order) Robert Aharonov, Erik Antonsen, Rodney Burton,
Jean Luc Cambier, Yongjun Choi, Uros Cvelbar, Jeffrey Fagan, Alec Gallimore, Brian Gilchrist,
Rafael Guerrero-Preston, Terese Hawley, Michael Kong, Mahadevan Krishnan, Richard Miles,
Othon Monteiro, Anthony Murphy, Leonid Pekker, Frederick Phelan, Claude Phipps, Jochen
Schein, Vladimir Sotnikov, Gregory Spanjers, and John Yim who made very significant contribu-
tions to the original publications used in this book. We are particularly grateful to our former and
current graduate students Andrew Porwitzky, Minkwan Kim, Madhu Kundrapu, Jarrod
Fenstermacher, Therese Suaris, Lubos Brieda, Jian Li, Taisen Zhuang, and Olga Volotskova who
contributed tosomeoriginal workused inthe book.
Last but not least, we owe very special gratitude to our families for their support and
encouragement.
MichaelKeidar,
Washington DC
Isak I.Beilis
Tel Aviv, Israel
November 2012
CHAPTER
1
Plasma Concepts
1.1 Introduction
When aneutralgas isionized,itbehaves asaconductivemedia. Ionizationprocess isthephenome-
non associated with striping electrons from the atoms thus creating the pair of negatively and posi-
tively charged particles. Electrical properties of such ionized gas depend on the charged particle
density. One of the most important distinctions between the ionized gas and the neutral media is
that Coulomb interaction between charged particles determines the dynamic of the gas. Ionized gas
is able to conduct the current. This property is of particular interest in the presence of the magnetic
field when the interaction of the current and magnetic field leads to electromagnetic body force
thus altering its flow dynamics. There are weakly ionized gases and strongly ionized gases. Weekly
ionized gas is characterized by a relatively small fraction of charged particles and its behavior can
be largely described by neutral gas laws while one needs to invoke electrodynamics to describe
appropriately the strongly ionized media. We shall call a physical state of an ionized gas in which
the densities of positively and negatively charged particles are approximately equal as a quasi-
neutrality state. Plasma is defined as anionized gas, which satisfies the quasi-neutrality condition.
Development of the plasma physics was always associated with particular applications. Starting
from lighting sources, current interrupters, thermonuclear fusion, and plasma accelerators, nowa-
days plasma applications range from plasma processing, space propulsion, nanotechnology, and
plasma medicine.
Prominent physicists contributed to developing the field of the plasma physics and engineering.
Irving Langmuir (1881(cid:1)1957) initiated an active study of the plasma as a new direction of science.
The term “plasma” was introduced in 1928 in his article describing the positive column of low-
pressure gas discharge. While Langmuir introduced the term plasma, the matter in the plasma state
was known to human since much early times. Lighting, northern light, solar wind, and Earth iono-
sphere are some examples of plasmas. Irving Langmuir received the Nobel Prize in Chemistry,
1932. Mott-Smith indicated in his letter [1] that Langmuir takes the term by analogy between “the
blood plasma carries around red and white corpuscles and germs” and the multicomponent ionized
gas. The great success in developing the foundation of the plasma science was achieved by
Langmuir due to effective collaboration with his famous coworkers Compton, Tonks, Mott-Smith,
Jones, Child, and Taylor.
Hannes Alfven (1908(cid:1)1995) is widely known, as a father of the plasma magnetohydrodynam-
ics. He developed theories regarding the nature of the galactic magnetic field and space plasmas.
Prof. Alfven received a Nobel Prize in Physics in 1970 for “fundamental work and discoveries in
magnetohydrodynamics.”
PlasmaEngineering. 1
©2013ElsevierInc.Allrightsreserved.
2 CHAPTER 1 Plasma Concepts
Plasma physics, as it is known today, was developed over last 50 years and encompasses many
areas ranging from the high-temperature plasmas of thermonuclear fusion to the low-temperature
plasma in material processing. The plasma fundamentals and configurations for thermonuclear
fusion applications were formulated and developed by Igor Tamm, Andrei Sakharov, Lev
Artzimovich, Marshall Rosenbluth, Lyman Spitzer, andmany others. Science ofthe interstellar ion-
ized medium and astrophysical plasmas was by Yakov Zeldovich and Vitaly Ginsburg. Gas dis-
charge plasma physics was introduced by A. von Engel, M. Steenbeck, and then developed by
Loeb, Townsend,Thomson, Kaptzov,Granovsky,and Raizer.
In the following as a way of introduction to plasma physics, we will discuss some basic plasma
properties.Itcanbeindicativeofwhatkindofplasmaisconsideredbyanalyzingtwomaincharacter-
istics of plasma behavior in time and space-plasma, i.e. plasma oscillation and Debye length. These
twoparametersquantitativelydescribetheplasmaanddependonplasmadensityandtemperature.
Let us first focus on understanding of the plasma quasi-neutrality phenomena and its impor-
tance.Anyperturbationinplasmasuchasshiftofelectronswithrespecttoionsleadstochargesep-
aration. The charge separation produces the electric field that works to restore the unperturbed
plasma. Let us consider the quasi-neutrality phenomena in the plasma of the high-current vacuum
interrupter. As an example, fully ionized plasma is formed with the electron density of about
1022m23 and in the volume with radius of about 1mm. If plasma quasi-neutrality is violated due
tochargeseparationatthecharacteristicdistanceofabout1mm,theelectricfieldofabout1011V/m
will appear. This means that the voltage drop of about 108V will be set at the distance of about
1mm. It is clear that such large electricfield willworktorestore the charge neutrality. However,if
relatively small plasma volume is considered, such electric field and potential drop might not be
strong enough to affect the particle motion and restore the quasi-neutrality. Thus, quasi-neutrality
condition can be violated at the small scale. The characteristics scale where charge separation can
existiscalledtheDebyelength.
1.1.1 Debye length
The electrical neutrality or quasi-neutrality is preserved over some characteristic length scale. Let
us determinethis length scale.
The characteristic length can be obtained from the following argument. The potential energy
of the charged particle in the case of full charge separation by distance of about L is of the order
D
of the particle thermal energy kT . Maximum possible potential energy due to full separation of
e
charges can beestimatedin the planar capacitor case asðe2L2N2=ε Þ: Thusone can obtain that
D 0 0
e2L2N2
eϕB D 0BkT
ε e
0
where N is the charge particle density. Frpomffiffiffiffiffitffihffiffiiffiffisffiffiffiffieffiffiqffiffiuffiffiaffiffiffilffiiffiffity, one can obtain that the characteristic
0
distance of the charge separation is L 5 ðε kT =e2N Þ: This distance we shall call the Debye
D 0 e 0
length.
The same expression for the Debye length can be obtained by considering potential shielding in
plasmas. We shall examine initially electrically neutral plasma with density N . To this end it can
0
be supposed that an electric field disturbs the plasma equilibrium state by, for example, immersing
the transparent sheet having the negative potential Φ with respect to the plasma as shown in
0
1.1 Introduction 3
Potential
φ
0
0
FIGURE1.1
Debyelengthdefinitionfromtheelectricfieldshieldingargument.
Figure 1.1. We will consider one-dimensional plane geometry. As response to the charge perturba-
tion ion and electron distribution will be rearranged to a new state that will correspond to the dis-
turbed electric field. Since ions are heavy particle, their response time is much larger than that of
electrons. By taking this into account, we can assume that ions will not be moving on the timescale
of interest. This allows us to assume that ion density N in the entire plasma region will remain the
i
sameas before, i.e., equal N .
0
On the other hand, electrons with temperature T will respond to the repelling electric field and
e
their density will decrease. Electron density can be calculatedfrom the Boltzmann relation as
N 5N expðeϕ=kT Þ (1.1)
e 0 e
here ϕ is the potential. The potential ϕ distribution in the perturbed region can be calculated using
the Poisson equation:
d2ϕ e
5 ðN 2NÞ (1.2)
dx2 ε e i
0
Substituting Eq. (1.1) into Eq. (1.2) will lead tothe following:
d2ϕ e
5 N ðexpðeϕ=kT Þ21Þ (1.3)
dx2 ε 0 e
0
Assuming that the disturbed energy is small in comparison with the temperature yielding expan-
sion in the Taylor series:
eϕ
expðeϕ=kT Þ(cid:3)11 1? (1.4)
e kT
e
Taking into account only first-order terms in the Taylor series (Eq. (1.4)), the Poisson equation
will have the followingform:
d2ϕ e2ϕ
5 N (1.5)
dx2 ε kT 0
0 e