Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 5
1
Overview
plas·ma: ′plaz-m (noun) [German, from late Latin, something molded, from Greek,
e
from plassein, to mold]: the most common form of visible matter in the cosmos,
consisting of electrically charged remnants of atoms in the form of electrons and
ions, moving independently of each other; as a result of their motion, these charged
particles generate electric and magnetic fields that, in turn, affect the plasma’s be-
havior.
DEFINITION OF THE FIELD
Plasmas seem simple enough. They’re a collection of free electrons and ions
governed largely by physical laws known to late 19th-century physicists. Yet the
sophisticated and often mysterious behavior of plasmas is anything but simple. This
is strikingly evident in, for instance, the dramatic images of solar flares—sudden
plasma eruptions from the surface of the Sun. Plasma is found almost everywhere
on Earth and in space; indeed only the invisible dark matter is more abundant.
The vast regions between galaxies in galaxy clusters are filled with hot magnetized
plasmas. Stars are dense plasmas heated by fusion reactions. Computer processors
are fabricated using cold chemically reacting plasmas. Powerful lasers make relativ-
istic plasmas in laboratories. And the enormously varied list goes on. None of these
plasmas are quiescent; they wriggle and shake with instabilities and turbulence, and
sometimes they erupt with spectacular force (Figure 1.1).
One of the great achievements of plasma science has been to show that the
bewildering variety and complexity of plasmas is understandable in terms of some
OCR for page 6
Plasma science
FIGURE 1.1 Exploding plasma on the Sun. X-ray image of one of the most dramatic of natural phe-
nomena, the solar flare, caused by the sudden destabilization of the magnetized plasma in the Sun’s
outer atmosphere (the corona). The eruption is lifting plasma above the Sun’s surface. The bright lines
are the illumination of some of the complicated magnetic field lines by plasma emission. Courtesy
of Transition Region and Coronal Explorer (TRACE), a mission of the Stanford-Lockheed Institute for
Space Research and part of the NASA Small Explorer program.
very elemental ideas that bind the field together (Figure 1.2). This is not to say that
all questions have been answered—they have not. Rather, it confirms that the sci-
ence is evolving rapidly and that there are fundamental principles that organize our
knowledge. Much of plasma science seeks to explain the plasma’s highly nonlinear
behavior and the order and chaos that result. Plasma science has, therefore, much
in common with many areas of modern complex system research, from climate
modeling to condensed matter studies. Indeed, plasma scientists have played a
pivotal role in the development of nonlinear dynamics and chaos theory, which
have a multitude of applications to complex systems.
Plasma science has made enormous advances in the last decade. Rapid progress
in our ability to predict plasma behavior has been fueled by new diagnostics that
OCR for page 7
overview
1010 100,000,000,000,000
Plasma
Accelerators
Black Hole
Accretion
Plasma
Relativistic
1,000,000,000
Temperature (eV)
Non-Relativistic
105 ITER
NIF
Magnetic
Inertial
Temperature (oK)
Fusion
Fusion
Magneto
-sphere
Ionized
Low Temperature White
Partially Plasmas 10,000
Dwarf
100 Ionized Stars
Ionosphere
ed d
lat
Neutral
rre elate
Dominated co r
Un Cor
al
Anti-matter
Qu sic
m
Plasmas
as
tu
an
Cl
Pure
0.1
Ion Plasmas
10–5
1 1010 1020 1030
Density (particles per cm3)
FIGURE 1.2 New regimes—new physics. Plasma science is expanding into new territory and discover-
ing new phenomena. Diagram shows some of the range of plasma phenomena. Regimes that are new
areas of study since 1990 are indicated in gray, including the future regimes of the National Ignition
fig 1-2
Facility (NIF) and the International Thermonuclear Experimental Reactor (ITER).
replacement
observe and measure an unprecedented level of detail and by computations that
10/30
resolve most of the essential physics. In many areas, from fusion plasma science to
the manufacture of computer chips, science-based predictive models are replacing
empirical rules. What is notable in the research examined for this report, further-
more, is that plasma science is moving beyond the understanding of complicated
but isolated phenomena and is entering an era in which plasma behavior will be
understood and described as a whole. Growth in fundamental understanding has
led to new applications and improved products such as the large-area plasma panel
televisions now found in many homes.
This report discusses the scientific highlights of the past decade and opportuni-
ties for further advances in the next decade. Detailed analyses are contained in five
chapters representing the subfields: low-temperature plasma science and engineer-
ing; high-energy-density (HED) plasma science; magnetic fusion plasma science;
space and astrophysical plasmas; and basic plasma science. Chapters 2 through 6,
the topical chapters, contain in their final sections the committee’s conclusion(s)
and recommendation(s) pertaining to the particular topic.
The remainder of this chapter, the Overview, summarizes key issues raised by
these analyses. The next section shows that plasma research is an essential part of
OCR for page 8
Plasma science
the nation’s science and technology enterprise and that its importance is growing.
Six scientific highlights of the past decade and the opportunities they create are
featured in the section after that. While these examples by no means constitute a
comprehensive survey, they give a flavor of the breadth and depth of the field. The
fourth section discusses the growth in predictive capability and the emergence of
new plasma regimes, two scientific themes that pervade recent advances. Further
progress on many applications is predicated on a better understanding of some key
plasma processes. These fundamental processes demonstrate the unity of the field
by cutting across the applications and the topical areas. They are addressed briefly
in the penultimate section, and they appear repeatedly in the topical chapters. The
last section of this chapter presents the principal conclusion and the principal
recommendation of the entire report.
IMPORTANCE OF PLASMA SCIENCE AND ENgINEERINg
The link between scientific development and increased prosperity, security, and
quality of life is well documented.1 Advances in plasma science have contributed
enormously to current technology and are critical to many future developments.
An effective national research enterprise must have breadth because scientific
discovery in any one area is often highly dependent on discovery in other areas.
Plasma science is an important part of the web of interdependent disciplines that
make up our essential core knowledge base. It contributes to at least four areas of
national interest:
• Economic security and prosperity. In the past decade, new plasma technolo-
gies have entered the home. Many families view entertainment on plasma
display televisions and illuminate their homes with plasma lighting. How-
ever, the enormous role plasma technologies play in manufacturing remains
largely hidden from view (Figure 1.3). Microelectronics devices would not
exist in their advanced state if not for the tiny features etched onto semicon-
ductor wafers by plasma tools. Surfaces of materials are hardened, textured,
or coated by plasma processes. The value of all this economic activity is
hard to estimate, but one small example is that displays and televisions
built by plasma tools and lit by special plasma (fluorescent) lights will be a
$200 billion market by 2010.2 The worldwide $250 billion semiconductor
1 See, for example, the National Academies report Rising Above the Gathering Storm: Energizing
and Employing America for a Brighter Economic Future, Washington, D.C.: The National Academies
Press, 2007.
2Alfonso Velosa III, research director for semiconductors, Gartner, Inc., “Semiconductor manu-
facturing: Booms, busts, and globalization,” presentation to the National Academy of Engineering,
September 2004.
OCR for page 9
overview
FIGURE 1.3 Plasmas in the kitchen. Plasmas and the technologies they enable are pervasive in
our everyday life. Each one of us touches or is touched by plasma-enabled technologies every day.
Products from microelectronics, large-area displays, lighting, packaging, and solar cells to jet engine
turbine blades and biocompatible human implants either directly use or are manufactured with, and
in many cases would not exist without, plasmas. The result is a better quality of life and economic
competitiveness. NOTE: CVD, chemical vapor deposition; HID, high-intensity discharge; LED, light-
emitting diode; LCD, liquid crystal display.
industry is built on plasma technology. In the absence of plasma technolo-
gies, the $2 trillion telecommunications industry would arguably not exist.
(See Chapter 2 for a more detailed discussion of this area of plasma science
and its many applications.)
• Energy and environmental security. Our prosperity and lifestyle rest on a
ready supply of moderately priced energy, but it is well known that fossil
fuel resources are limited and the environmental impact of their long-term
OCR for page 10
Plasma science
10
use is problematic. The search, therefore, for new and sustainable energy
sources and new technologies that can reduce energy consumption is, and
will remain, a high-priority research goal. Fusion energy has unparalleled
potential to meet the need. Deployment of fusion (the fusing of hydrogen
nuclei to make helium nuclei, a neutron, and energy) as an alternative
energy resource should remain a priority for the nation. The challenge of
fusion is that it requires plasmas with temperatures greater than those at
the center of the Sun. Plasma science has made great strides in controlling
and confining such plasmas (see Chapter 4 for a discussion of the science).
ITER, which exploits some of these achievements, aims to explore fusion
burning plasmas at the end of the next decade. This is a key and indeed
essential step on the path to fusion energy. Research in alternative paths
to fusion is also proceeding rapidly. In the meantime, plasma science has
contributed to near-term innovations in energy efficiency. For example,
the more than 1 billion light sources in operation in the United States use
22 percent of the nation’s electrical energy budget. Consumers are switching
to the more efficient plasma (fluorescent) lighting as innovations improve
the quality of the light and the life expectancy of the lamp. Plasmas also aid
the efficient combustion of fuels and the manufacture of materials for solar
cells, and they improve the efficiency of turbines and hydrogen production.
There is a small but growing use of plasmas to ensure a clean and healthy
environment. New applications exploit the ability of plasmas to break down
harmful chemicals and kill microbes to purify water and destroy pollutants.
(See Chapter 2 for a detailed discussion of the science.)
• National security. HED plasma science is central to Science-Based Stockpile
Stewardship (SBSS), the DOE program that ensures the safety and reliability
of the nation’s nuclear stockpile. The study of HED plasma physics has been
greatly enhanced by the remarkable progress in producing such plasmas
(and copious amounts of x rays) by passing large currents through arrays
of wires in Sandia National Laboratories’ Z machine. In the next decade,
the NIF (the world’s most powerful laser facility) at Lawrence Livermore
National Laboratory will create plasmas of unusually high energy densities
and seek to ignite pellets of fusion fuel. These facilities and experiments are
central to the stockpile stewardship program (see Chapter 3 for a discussion
of the science). It is perhaps less widely appreciated that plasma technology
is also critical to the manufacture of many conventional weapons systems.
For example, the turbine blades in the engines of high-performance fight-
ers are coated by a plasma deposition technique to substantially improve
their performance. Recently developed plasma-based systems for destroy-
ing chemical or biological hazards are answering homeland security needs.
OCR for page 11
overview 11
Atmospheric pressure plasma sources are being employed as “plasma hoses”
to decontaminate surfaces after a chemical spill or attack.
• Scientific discovery. Plasma science raises and answers scientific questions
that contribute to our general understanding of the world around us. Un-
raveling the complex and sometimes strange behavior of plasmas is in itself
an important scientific enterprise. The intellectual challenge of explaining
the intricacies of collective behavior continues to inspire serious scholar-
ship. Our current understanding is being stretched by, for example, the
properties of the curious forms of matter formed when plasmas become
correlated at extremely low temperatures (see Chapter 6 for a discussion).
Because most of the visible matter in the universe is plasma, many of the
great questions in astrophysics and space physics require a detailed un-
derstanding of plasmas. For example, while currents in the cosmic plasma
must create the magnetic fields that pervade much of the universe, it is not
known when these fields and currents first appeared in the universe or how
they were generated (see Box 1.1 and Chapter 5 for discussion).
The scientific challenges posed by these important goals are being addressed by
a large but diffuse U.S. community of plasma scientists and engineers.3 The plasma
research effort is global, however (see Box 1.2).
SELECTED HIgHLIgHTS OF PLASMA SCIENCE AND ENgINEERINg
The committee now describes six highlights of the scientific frontiers of plasma
research and development. This is neither an exhaustive survey nor a list of the
greatest discoveries—it is, rather, a sampling of exciting and important work. While
these examples demonstrate the enormous diversity in plasma research they also
illustrate the unity of the underlying science. Fundamental plasma processes are
the common threads that weave through all these applications.
3 In the United States, many plasma scientists participate in divisional meetings of the American
Physical Society (APS), the American Geophysical Union, the American Vacuum Society, and the
Institute for Electrical and Electronics Engineers. In 2006, the membership of the APS Division of
Plasma Physics numbered about 2,500; at about 5.5 percent of the entire membership, the Plasma
Physics Division is the fourth largest. Of course, there are at least as many plasma researchers who
are not members of the APS. For more information about the demographics of the plasma science
and engineering community, especially the fusion community, please see Fusion Energy Sciences
Advisory Committee, Fusion in the Era of Burning Plasma Studies: Workforce Planning for 2004-2014,
DOE/SC-0086, Washington, D.C.: U.S. Department of Energy, 2004; and E. Scime, K. Gentle, and A.
Hassam, A Report on the Age Distribution of Fusion Science Faculty and Fusion Science Ph.D. Produc-
tion in the United States, Washington, D.C.: University Fusion Associates, 2003.
OCR for page 12
Plasma science
12
BOX 1.1
Living and Working Inside a Plasma
In 2000, an important human milestone came to pass quietly: Our species became a permanent inhabitant
of space. Since then, the human presence in low Earth orbit has been continuous and uninterrupted on board the
International Space Station (ISS). Humans now inhabit Earth’s ionosphere, where the rain is meteor showers and the
wind is plasma, a place of awesome beauty and unforgiving hazards (Figure 1.1.1).
The plasma environment surrounding the ISS is itself a hazard since electrons from the plasma charge up the
structure. The pressurized modules of the ISS tend to act as large capacitors storing electrical energy hazardous to
space-walking astronauts. Electrical shocks and arcs caused by the charge buildup could puncture spacesuits or
damage critical instrumentation with catastrophic consequences. Recent measurements have also shown that the
charge buildup varies significantly from day to day as the spacecraft moves from equatorial to polar regions and
from daytime to nighttime.
The charge buildup is neutralized (and the astronauts protected) by devices called “plasma contactors,” which
serve the same function as grounding rods in well-designed homes on Earth. The ISS plasma contactors spray elec-
trons into the surrounding ionosphere by hollow cathode discharges fueled by xenon gas. The rate of electron spray
is sufficient to maintain the electrical ground of the station (its metal frame) at the same electrical potential as the
surrounding ionosphere.
Space plasma physics knowledge gained in the last few years through our continuous activities in space is
teaching us much about the environment in which our planet functions and the important plasma processes that
affect our life on the ground.
Biotechnology and Health Care
Dental patients might be surprised to know that their dentist is using a tiny
plasma to treat their teeth. Yet the use of plasmas in biological applications is
an emerging field that ranges from the surface treatment of human implants to
plasma-aided surgery. These applications exploit the fact that plasmas are uniquely
dry, hot, and cold, all at the same time. Plasma is dry in that the working medium
is a gas and not a liquid, so less material goes into and comes out of the process.
The hot electrons can drive high-temperature chemistry while the gas and surface
remain near room temperature.
• Biocompatibility of surgical implants. Plasma treatment is routinely used to
make surgical implants such as joints and stents biocompatible by either
OCR for page 13
Overview 13
FIGURE 1.1.1 Left: Committee member Frank-
lin Chang-Díaz conducting assembly tasks
outside the International Space Station (ISS) in
June 2002. Courtesy of NASA. Right: Aurora
australis photographed during a spacewalk
on mission STS 111 in June 2002. The ISS
routinely flies through the auroral plasma.
Courtesy of NASA.
depositing material or modifying the surface characteristics of the material
(Figure 1.4).
Sterilization. The goal fig plasma sterilization is to destroy undesirable
of 1.1.1 a, b
•
biological activity with absolute confidence. The current workhorse of
sterilization is the autoclave, in which medical instruments are exposed
to superheated steam for 15 minutes. Autoclaves can damage even metal
instruments and cannot be used on many thermosensitive materials. Fur-
ther, like any single treatment method, it is not universally effective and
in fact has been questioned for emerging threats like the prions associated
with Creutzfeldt-Jakob (mad cow) disease. Plasmas provide two agents
that destroy biological actvity: reactive neutral species and ultraviolet light.
Gaseous neutrals can diffuse into complex biological surfaces, whereas
OCR for page 14
Plasma science
14
BOX 1.2
Plasma Research Goes Global
The past decade has seen an acceleration of foreign research, investment, and discoveries in plasma
physics. Increasing foreign participation testifies to the compelling scientific opportunities.
The committee conducted a primitive exercise to crudely gauge the level of U.S. participation in the
global plasma science enterprise. The 200 most frequently cited papers over the past decade from each
of six major journals were reviewed and the proportion of foreign-based lead authors was tabulated. The
results were as follows: Nuclear Fusion, 68 percent foreign; Plasma Physics and Controlled Fusion, 78
percent foreign; Physics Review E (selecting the plasma-related articles by keyword), 75 percent foreign;
Physics of Plasmas, 39 percent foreign; Plasma Sources Science and Technology, 72 percent foreign;
Physical Review Letters (selecting the plasma-related articles by keyword), 54 percent foreign. Twenty
years ago, the U.S. share would have been much greater.
While these results could be taken to mean that U.S. activity in plasma research is decreasing, the
real cause is the large surge in research activities overseas. There are not fewer U.S. papers—there are
more and more foreign ones! Because it puts the smallest proportion of U.S. papers at 22 percent, this
exercise does after all support the notion that the United States has a globally significant community in
basic plasma science and HED physics.
ultraviolet photons can travel only along the line of sight—combined,
they could lead to efficient local sterilization techniques. Ongoing research
aims to improve the effectiveness of plasma sterilization while minimizing
instrument damage through careful selection of the working gas composi-
tion and plasma conditions.
• Plasma-aided surgery. While plasma sterilization is only beginning to be-
come a commercial process, surgery is already being performed with plasma
instruments. It is entirely routine to cut and cauterize tissue with plasma.
Emerging—and already in some use—are new plasma “knives” that gener-
ate nonequilibrium plasma “streamers” (like miniature lightning bolts) in
conducting liquids (saline). These streamers explosively evaporate water in
bubbles to cut soft tissue. Here is the convergence of almost all the themes
in low-temperature plasma science: selectivity to generate the desired spe-
cies; interaction with exceedingly complex surfaces; stochastic behavior and
multiphase media (bubbles in liquids); and the generation and stability
of high-density microplasmas. Most surgical procedures still aim to cut
and remove tissue, not modify it in a constructive way. However, there are
indications that more selective and constructive processes are possible. For
example, plasmas can change the metabolic behavior of cells and trigger
cell detachment.
The potential for plasmas in health care might best be viewed as an analog to
their use in semiconductor manufacturing. Four-bit microprocessors were manu-
OCR for page 15
overview 1
FIGURE 1.4 Plasmas and biology. Using low-temperature, reactive plasmas, the surface of polymers
may be functionalized and patterned to allow the cells to adhere. In this example, amine functional
groups were patterned on a polymer, resulting in a predetermined network of adhering cells. Courtesy
of INP Greifswald, Germany.
factured in liquid acid baths. Plasmas entered the scene and made possible 8- and
16-bit computers with megahertz clock speeds and kilobytes of memory. Today,
after two decades of research and development, desktop computers are 64-bit,
with gigahertz speeds and gigabyte memories, all enabled by plasmas. If this same
physical and chemical precision can be brought to plasmas in health care, will the
benefits be any less dramatic?
Accelerating Particles with Plasma Wake Fields
When an electron bunch moves at nearly the speed of light through a plasma,
the electrostatic repulsion of the bunch on the stationary plasma electrons pushes
them aside, punching a hole in the plasma electron density. The unbalanced posi-
tive charge in the hole attracts the plasma electrons back into the hole, setting up
OCR for page 27
overview 2
black holes as sources of radiation and outflows lies not in understanding the
physics of the black holes themselves (as predicted by general relativity) but rather
in understanding the physics of the accreting plasma that produces the observed
radiation. Further progress on understanding general relativistic plasma phys-
ics (i.e., plasma physics in curved space-time) is essential both for interpreting
observations of black holes in nature and for achieving the long-sought goal of
using such observations to test general relativity’s predictions for the strong grav-
ity around black holes. In general, inflowing plasma does not fall directly onto the
black hole but instead, because it has angular momentum, orbits the black hole.
The orbiting plasma forms a disc called an accretion disc, such as that shown in
the numerical simulation in Figure 1.13.
FIGURE 1.13 Left: Radio images of the galaxy M87 at different scales (1 kpc = 3,260 light-years) show, top left,
giant, bubblelike structures on the scale of the galaxy as a whole, where radio emission is powered by relativistic
outflows (“jets”) from the galaxy’s central black hole; top right, the jets coming from the core of the galaxy; and
bottom, an image of the region close to the central black hole, where the jet is formed. The small circle labeled
6RS shows six times the radius of the event horizon for the galaxy’s black hole (about 10 times the distance
from the Sun to Pluto). Courtesy of National Radio Astronomy Observatory (NRAO)/Associated Universities,
Inc. (AUI)/National Science Foundation (NSF); based on data from Junor, Biretta, and Livio, Nature 401: 6756.
fig 1.13 a, b
Right: The inner regions of an accretion disk around a black hole, as calculated in a general relativistic plasma
simulation. The black hole is at coordinates (0,0). The accretion disk rotates around the vertical direction (the
axis of the nearly empty funnel region). Its density distribution is shown in cross section, with red representing
the highest density and dark blue the lowest. Above the disk is a tenuous hot magnetized corona, and between
the corona and the funnel is a region with ejection of mildly relativistic plasma that may be related to the forma-
tion of the jets seen in the left panel. Image based on work that appeared in de Villiers et al. (2003), © American
Astronomical Society.
OCR for page 28
Plasma science
2
Unlike the planets orbiting the Sun, plasma is subject to frictional forces that
redistribute angular momentum and allow the plasma to flow inward. In the past
decade, it has been realized that magnetic fields in accretion disks are amplified
by a powerful instability known as the magnetorotational instability. Such mag-
netic fields provide the necessary viscous angular momentum transport in most
accretion disks and also help generate powerful outflows such as those seen in
Figure 1.13.
Much remains to be understood about plasma physics in the vicinity of black
holes. What determines the inflow rate of plasma in an accretion disc? How much
of the energy of the inflowing plasma is radiated away, ejected in outflows, or
swallowed by the black hole? How are jets launched, and why do only some black
holes, some of the time, have jets? In addition to progress on the theoretical front,
observations are rapidly improving and are providing information about the condi-
tions very close to the event horizon of black holes, by means of both direct images
of plasma near the event horizon (e.g., the picture of M87 in Figure 1.13) and the
indirect but powerful information about the velocity of the plasma provided by
spectral lines. Given the wealth of observational information and the diversity of
exciting and difficult problems, black hole plasma physics will remain a vibrant
research area in the coming decade.
KEY THEMES OF RECENT SCIENTIFIC ADvANCES
This section examines the overall trends in plasma research. Two themes frame
recent advances:
• Plasma science is developing a significant predictive capability.
• New plasma regimes have been found that expand the scope of plasma
research and applications.
Both themes are illustrated by the six examples of cutting-edge science in the pre-
ceding section. More complete descriptions of the scientific advances and questions
are contained in the ensuing topical chapters.
Prediction in Plasma Science
The recent growth of predictive capability in plasma science is perhaps the
greatest indicator of progress from fundamental understanding to useful science-
based models. It is due primarily to two factors: (1) advances in diagnostics that
can probe the internal dynamics of the plasma and yield much greater quantitative
understanding and (2) theoretical and computational advances that have led to
models that can accurately predict plasma behavior. Good examples are the pre-
OCR for page 29
overview 2
dictive modeling of turbulence in fusion plasmas, the modeling of reconnection
dynamics, and the modeling of industrial plasma processes. The cost of develop-
ment via an Edisonian approach, where multiple designs and prototypes are tried,
is prohibitive for many plasma science applications, notably but not exclusively
fusion. Predictive models provide a basis for steering investigation and ultimately
reduce development cost and time. Nonetheless, our understanding of many fun-
damental aspects of plasma behavior remains rudimentary, and further increases in
predictive capability require progress in understanding the basic plasma processes
outlined in the next section. That is, the next generation of improvements in pre-
dictive capabilities will probably be driven by theoretical insights.
New Plasma Regimes
New facilities and experimental techniques have revealed new plasma regimes.
The highly relativistic plasma physics in the beam plasma interaction at SLAC is
a good example (see the preceding section). The power of the SLAC beam has
opened up this regime to study. Another example is the very cold, highly correlated
plasmas being studied in basic experiments made possible by the development of
new techniques for cooling the plasma. Low-temperature microplasmas that blur
the distinction between the solid, liquid, and plasma states are being created to
explore novel plasma chemistry. In studying accretion discs, astrophysicists are
considering the behavior of plasmas in the curved space around black holes. These
new regimes are revealing unexpected new phenomena, challenging and extending
our understanding.
In the next decade, more new regimes are expected. For example, ITER will
begin studying magnetically confined plasmas heated by alpha particles produced
in fusion reactions—the burning plasma regime. The NIF will seek to produce a
fusion burn in a pellet compressed by lasers.
COMMON INTELLECTuAL THREADS OF PLASMA RESEARCH
Plasmas occur over a fantastic range of temperatures, densities, and magnetic
fields. However, there are a number of issues that are pervasive, and much of plasma
behavior can be characterized in terms of universal processes that are, at least
partially, independent of the particular context being considered. Some of these
processes have been well understood and the behavior can be predicted with near
certainty. The propagation of weak electromagnetic waves through plasmas, such
as radio waves through the ionosphere, is one example where predictive capability
has risen to a level of considerable certainty in the last decade.
However, six critical plasma processes are not well understood. They yield
some of the great questions of plasma science. Progress on any one of them would
OCR for page 30
Plasma science
0
advance many areas of plasma science simultaneously. Indeed they define the re-
search frontier.
• Explosive instability in plasmas. Some of the most striking events in plasmas
are the explosive instabilities that spontaneously rip apart plasmas. Such
instabilities give rise to a massive and often destructive release of energy
and accelerated particles. For example, disruptions in magnetically confined
fusion plasmas can deposit large fractions of the plasma energy (tens of
megajoules) on the solid walls of the experiment in less than a millisecond.
Solar flares convert magnetic energy equivalent to billions of nuclear weap-
ons to plasma energy in 10 to 1,000 seconds. It is not understood when and
how plasmas explode.
• Multiphase plasma dynamics. Multiphase plasmas—plasmas that are in-
teracting with nonplasmas (such as neutral gas, solid surfaces, particulates,
and liquids)—are widespread. For example, low-temperature multiphase
plasmas are used to perform tasks such as emitting light of a particular
color, destroying a pollutant or sterilizing a surface. A host of basic ques-
tions about these plasmas have at best been only partially answered.
• Particle acceleration and energetic particles in plasmas. In supernova shocks,
laser–plasma interactions, the wakes of particle beams, solar flares, and
many other phenomena, we observe the acceleration of some plasma par-
ticles to very high energies. Particles may be accelerated by surfing on waves
in the plasma or by being randomly scattered by moving plasma irregulari-
ties. It is still not clear how nature accelerates particles so effectively or what
can be learned from this behavior in the laboratory.
• Turbulence and transport in plasmas. Magnetic fusion plasmas, accretion
discs around black holes, Earth’s magnetosphere, laser-heated plasmas, and
many industrial plasmas are permeated with turbulence that transports
heat, particles, and momentum. The effects of this turbulence often domi-
nate these plasmas, yet many aspects are not understood. For example, can
we reduce and control turbulence?
• Magnetic self-organization in plasmas. In many natural and laboratory
plasmas, the magnetic field and the plasma organize themselves into a
structured state. For example, although it is not known how, the Sun’s
turbulent plasma produces an ordered magnetic field that cycles with an al-
most constant 22-year period. Laboratory plasmas often seek out preferred
configurations called relaxed states. Magnetic reconnection is almost always
a key part of the relaxation processes that lead to self-organization.
• Correlations in plasmas. In cool, dense plasmas, the electrostatic forces
between the ions and electrons begin to dominate the motion of the par-
ticles. This induces ordering and structure into the particle positions. The
OCR for page 31
overview 1
behavior of such plasmas in stars, HED systems, laboratory experiments,
and industry is of great current interest. Unraveling the properties of highly
correlated plasmas is an ongoing challenge.
It is notable that each of these six processes plays a role in four or more of the
(five) topical areas treated in Chapters 2-6. A variety of approaches are needed to
advance our knowledge of these processes. Some phenomena must be studied at
a large scale and therefore can only be addressed in the context of (well-funded)
applications or space/astrophysics research. Other phenomena can be best under-
stood through a series of small-scale laboratory experiments whose objectives are
to peel back the layers of complexity. Clearly, progress on understanding these six
fundamental processes will benefit a broad range of applications. Such advances
in understanding will lead (via modeling and simulation) to improvements in
predictive capability.
THE REPORT’S PRINCIPAL CONCLuSION AND
PRINCIPAL RECOMMENDATION
Plasma science is on the cusp of a new era. It is poised to make significant
breakthroughs in the next decade that will transform the field. For example, the
international magnetic fusion experiment—ITER—is expected to confine burn-
ing plasma for the first time, a critical step on the road to commercial fusion. The
NIF plans to ignite capsules of fusion fuel with the goal of acquiring the knowl-
edge necessary for maintaining the safety, security, and reliability of the nuclear
stockpile. Low-temperature plasma applications are ushering in new products and
techniques that will change everyday lives. And plasma scientists are being called
upon to help crack the mysteries of exotic plasmas in the cosmos. This dynamic
future will be exciting and challenging for the field. It will demand a well-organized
national plasma science enterprise.
Principal Conclusion: The expanding scope of plasma research is creating
an abundance of new scientific opportunities and challenges. These oppor-
tunities promise to further expand the role of plasma science in enhancing
economic security and prosperity, energy and environmental security, na-
tional security, and scientific knowledge.
Plasma science has a coherent intellectual framework unified by physical pro-
cesses that are common to many subfields. Therefore, and as this report shows,
plasma science is much more than a basket of applications. The committee believes
that it is important to nurture fundamental knowledge of plasma science across
all of its subfields to advance the science and to create opportunities for a broader
range of science-based applications. These advances and opportunities are, in
OCR for page 32
Plasma science
2
turn, central to the achievement of national priority goals such as fusion energy,
economic competitiveness, and stockpile stewardship.
The vitality of plasma science in the last decade testifies to the success of
some of the individual federally supported plasma science programs. However, the
emergence of new research directions necessitates a concomitant evolution in the
structure and portfolio of programs at the federal agencies that support plasma
science. The committee has identified four significant research challenges that the
federal plasma science portfolio as currently organized is not equipped to exploit
optimally:
• Fundamental low-temperature plasma science. The many emerging appli-
cations of low-temperature plasma science are challenging and even out-
stripping fundamental understanding. A basic research program in low-
temperature plasma science that links the applications and advances the
science is needed. Such a government-sponsored program of long-range
research would capitalize on the considerable benefits to economic com-
petitiveness offered by key breakthroughs in low-temperature plasma sci-
ence and engineering. No such program or federal steward for the science
exists at present. The detailed scientific case for this program is presented
in Chapter 2.
• Discovery-driven, HED plasma science. Fueled by large new facilities and
breakthroughs in technologies that have enabled access to previously un-
explored regimes, our understanding of the science of HED plasmas has
grown rapidly.6 Mission-driven HED plasma science (such as the advanced
accelerator program in the DOE Office of High-Energy Physics or the Iner-
tial Confinement Program in the National Nuclear Security Administration
[NNSA]) is thriving. New regimes revealing new processes and challenging
our fundamental understanding of plasmas will be discovered in the next
decade at the new HED facilities (such as NIF and upgrades elsewhere). It
is very likely that some of the science that will emerge in these new regimes
and new processes cannot be adequately explored by the current suite of
facilities given the specificity of their purposes. By extension, discovery-
driven research in HED plasmas cannot grow inside the facilities’ parent
programs that are dedicated to specific missions. However, there is no other
home for this research in the present federal portfolio.
6 Thisscience is discussed in Chapter 3 in the NRC report Frontiers of High Energy Density Physics:
The X-Games of Contemporary Science, Washington, D.C.: The National Academies Press, 2003; and
Frontiers in High Energy Density Physics, July 2004, prepared by the National Task Force on High En-
ergy Density Physics for the Office of Science and Technology Policy’s (OSTP’s) interagency working
group on the physics of the universe.
OCR for page 33
overview
• Intermediate-scale plasma science. Some of the most profound questions in
plasma science are ripe for exploitation right now and are best addressed
at the intermediate scale. These questions can only be studied in facilities
that are intended for groups larger than single-investigator groups. They
do not, however, require the very large national and international ex-
perimental facilities on the scale of NIF and ITER. For example, magnetic
reconnection research would be advanced significantly by an experiment
at an intermediate scale, where the collisionless physics is dominant. Such
intermediate-scale facilities might be sited within national laboratories or
at universities. The current mandates of the mission-driven programs of
the NNSA and OFES do not provide for the development of intermediate-
scale facilities that pursue discovery-driven research directions in plasma
science that are not clearly applicable to their missions. The discoveries that
intermediate-scale facilities would foster are unlikely to happen within the
current paradigm of federal support for plasma science.
• Crosscutting research. Federal stewardship of plasma research is disaggre-
gated and dispersed across four main agencies—the Department of Energy,
the National Science Foundation, the Department of Defense, and the
National Aeronautics and Space Administration—and within those, across
many offices (e.g., magnetic fusion is primarily supported through DOE’s
Office of Science, and inertial confinement fusion is primarily supported
through DOE’s NNSA). This dispersion hinders progress in many areas
of plasma science because it does not allow for an intellectual juxtaposi-
tion of disparate elements that will force dialogue on common issues and
questions. There are significant opportunities at the interfaces between the
subfields, but the current federal structure fails to exploit them.
Notwithstanding the success of individual federal plasma science programs, the
lack of coherence across the federal government ignores the unity of the science
and is an obstacle to overcoming many research challenges, to realizing scientific
opportunities, and to exploiting promising applications. The committee observes
that the stewardship of plasma science as a discipline will likely expedite the appli-
cations of plasma science. The need for stewardship was identified in many reports
over two decades.7 The evolution of the field has only exacerbated the stewardship
problem and has driven this committee to conclude that a new, integrated way of
managing the federal support for the science is necessary.
7 SeeNRC, Plasma and Fluids, Washington, D.C.: National Academy Press, 1986; NRC, Plasma Sci-
ence: From Fundamental Research to Technological Applications, Washington, D.C.: National Academy
Press, 1995; and NRC, An Assessment of the Department of Energy’s Office of Fusion Energy Sciences
Program, Washington, D.C.: National Academy Press, 2001.
OCR for page 34
Plasma science
4
The committee considered a wide range of options to provide stewardship
without disrupting the vigor and energy of the ongoing plasma research. Recogniz-
ing the potentially far-reaching consequences of any recommendation to integrate
research programs in plasma science, the committee considered four options in
great detail:
Option 1: Continue the current structure of federal plasma science programs
•
unchanged. It is apparent that many plasma science programs were very
successful in the past and some continue to be successful. Certainly, the
pace of discovery would remain high in many areas if the system remains
unchanged. However, the status quo option does not position the nation to
exploit the emerging new directions in plasma science and their potential
applications. Even now, the committee judges, the structure is impeding
broad progress in plasma science.
Option 2: Form a plasma science interagency coordinating organization. In-
•
teragency working groups have facilitated crosscutting science and technol-
ogy initiatives such as nanotechnology and information technology. With
some of the fundamental questions in plasma science being investigated by
as many as three agencies (and several offices within those agencies) it is
clear that a coordinated effort that is supported at the highest levels within
the government would be beneficial. However, while such an approach
might stimulate some crosscutting research, it would not, in itself, create
research initiatives in fundamental low-temperature plasma science and
discovery-driven, HED plasma science. An interagency task force cannot
facilitate the development of intermediate-scale facilities for the emerging
science if those facilities are all within one large agency. Furthermore, an
interagency advisory panel cannot directly provide stewardship nor can it
provide advice on coordination if the roles and responsibilities of the par-
ticipating agencies are too diffuse. Arguably, the future of plasma science
requires more than a coordinating effort.
Option 3: Create an office for all of plasma science, pulling together programs
•
from DOE, NSF, NASA, DOD, and other government agencies. Such an
office would centrally manage all plasma science and engineering in the
federal portfolio. It would naturally emphasize the unity of plasma science
and the commonality of the physical processes. Certain efficiencies would
be realized through common administration and management. However,
this move would uproot many successful activities, separating flourishing
programs from their applications and isolating others from their related
areas of science. It might create more problems than it would solve.
Option 4: Expand the stewardship of plasma science at DOE’s Office of
•
Science. Since the heart of the science at stake resides within DOE, this op-
OCR for page 35
overview
tion would address directly the four problems identified by the committee.
As the home of many large plasma science applications (fusion, stockpile
stewardship, and so on), DOE has abundant interest in the effective devel-
opment of the science. It has also successfully nurtured basic plasma science
through the NSF-DOE partnership. Furthermore, DOE has experience (and
success) in operating large and intermediate-scale science facilities as part
of broader research programs. An expanded stewardship of plasma science
in the Office of Science would not, however, exploit all the connections that
the science presents. Nonetheless, by linking together a large part of the core
science, the Office of Science could coordinate effectively with other offices
and agencies on common scientific issues. Thus a stewardship focused in
the Office of Science would be at the heart of a balanced strategy that would
bring coherence without sacrificing connections to applications and the
broader science community.
The scientific advantages of the fourth option are compelling to the committee.
After careful assessment, this is the route the committee recommends. Assessing
the bureaucratic and managerial issues involved in effective pursuit of this option,
however, is beyond this committee’s charge.
Principal Recommendation: To fully realize the opportunities in plasma
research, a unified approach is required. Therefore, the Department of En-
ergy’s Office of Science should reorient its research programs to incorporate
magnetic and inertial fusion energy sciences; basic plasma science; non-
mission-driven, high-energy-density plasma science; and low-temperature
plasma science and engineering.
The new stewardship role for the Office of Science would extend well beyond
the present mission and purview of the OFES. It would include a broader portfo-
lio of plasma science as well as the research OFES presently supports. Two of the
thrusts would be new: (1) a non-mission-driven, HED plasma science program and
(2) a low-temperature plasma science and engineering program. These changes
would be more evolutionary than revolutionary, starting modestly and growing
with the expanding science opportunities. The committee recognizes that these
new programs would require new resources and perhaps a new organizational
structure for the Office of Science. However, the scale and extent should evolve
naturally from community proposals and initiatives through a strategic planning
process such as outlined below and the usual budget and operation planning within
the government.
The committee’s intention is not to replace or duplicate the plasma science
programs in other agencies. Rather, it would create a science-based focal point for
federal efforts in plasma-based research. Space and astrophysical plasma research
OCR for page 36
Plasma science
would remain within the space and astrophysical research programs in NASA and
NSF. The NSF-DOE partnership in basic plasma science would continue. HED
programs in plasma accelerators would remain in the DOE Office of High Energy
Physics. Inertial confinement fusion research enabling the stockpile stewardship
mission of DOE’s NNSA would remain there. With a renewed and expanded re-
search focus, the Office of Science would also be naturally positioned to accept a
lead scientific role in interagency efforts to exploit HED physics.8 Finally, current
programs at NIST and NSF wrestling with the engineering applications of low-
temperature plasma science would continue. In fact, they would be substantially
enhanced by the inception of the new DOE plasma science programs that could
provide directed scientific inquiry on key issues as well as coordination and com-
munication of the most compelling breakthroughs in the basic research.
The committee is aware that there are substantial challenges and risks associ-
ated with its chief recommendation. A comprehensive strategy will be needed in
order to ensure a successful outcome. The planning should do the following:
• Develop a structure that integrates the scientific elements,
• Initiate a strategic planning process that not only spans the field but also
provides guidance to each of the subfields, and
• Identify the major risks and develop strategies to avoid them.
The committee recognizes that there is no optimal strategy without risk. In-
deed, the status quo is not without considerable risk. Some things could be done,
however, to mitigate the most obvious risks:
• Strong leadership to achieve these ambitious goals and inspire the elements
of the program to rise above their particular interests.
• Careful consultation among the communities, their sponsors, and constitu-
encies to build trust and a strong consensus.
• An advisory structure that reflects the breadth and unity of the science.
• Scientific and programmatic connections to related disciplines in the
broader physical sciences and engineering.
DOE’s magnetic fusion and inertial fusion programs are currently focused
on large developing facilities (ITER, NIF, and Z). The next decade will see these
facilities mature into vibrant and exciting scientific programs. Looking beyond that
8 Under the direction of the National Science and Technology Council’s interagency working group
on the physics of the universe, an ad hoc National High Energy Density Physics Task Force has been
formed to coordinate federal activities in HED physics. A report from this group was expected by
mid-2007.
OCR for page 37
overview
phase, however, the committee has two observations. First, NNSA’s support for
HED science will become uncertain when NIF and Z complete their stockpile stew-
ardship missions. Yet, by that time, HED science will have flowered and expanded in
many directions. Second, if ITER is successful and 15 years from now the nation is
actively pursuing the development of fusion energy, DOE’s fusion science program
is likely to have changed dramatically. The fusion energy effort may move outside
the Office of Science. Which entity will then become the de facto steward of plasma
science? The committee concludes that the Office of Science would naturally fill
this role. A broad-based plasma science program within the Office of Science would
explicitly include (among other research programs) the science of magnetic fusion
and the science of inertial fusion. Indeed, the Office of Science will steward plasma
science long after the current large facilities have come and gone.
There is a spectacular future awaiting the United States in plasma science and
engineering. But the national framework for plasma science must grow and adapt
to new opportunities. Only then will the tremendous potential be realized.
