Particle acceleration in astrophysical plasmas: geospace and beyond

269 Pages·2005·26.27 MB·English

by  Dennis Gallagher

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Geophysical Monograph 156
Particle Acceleration in Astrophysical
Plasmas: Geospace and Beyond
Dennis Gallagher
J. L. Horwitz
J. D. Perez
R. D. Preece
J. Quenby
Editors
American Geophysical Union
Washington, DC
Published under the aegis of the AGU Books Board
Jean-Louis Bougeret, Chair; Gray E. Bebout, Carl T. Friedrichs, James L. Horwitz, Lisa A. Levin, W.
Berry Lyons, Kenneth R. Minschwaner, Andy Nyblade, Darrell Strobel, and William R. Young,
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Library of Congress Cataloging-in-Publication Data
Particle acceleration in astrophysical plasmas : geospace and
beyond / Dennis Gallagher ... [et al.], editors.
p. cm. -- (Geophysical monograph, ISSN 0065-8448 ; 156)
Includes bibliographical references.
ISBN-13: 978-0-87590-421-4
ISBN-10: 0-87590-421-1
1. Particle acceleration. 2. Plasma astrophysics. 3. Space
plasmas. I. Gallagher, Dennis L. II. Series.
QB464.15.P369 2005
523.01'973«dc22 2005017995
ISBN-13: 978-087590-421-4
ISBN-10: 0-87590-421-1
ISSN 0065-8448
Copyright 2005 by the American Geophysical Union
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CONTENTS
Preface
D. L. Gallagher, J. L Horwitz, J. D. Perez, R. D. Preece, and J. J. Quenby vii
Introduction to Particle Acceleration in the Cosmos
D. L. Gallagher, J. L. Horwitz, J. D. Perez, and J. J. Quenby . . . 1
Shock Acceleration
Diffusive Shock Acceleration in Astrophysics
J. J. Quenby and A. Meli 9
On Bow Shock Source of Cusp Energetic Ions
Shen-Wu Chang and Karlheinz J. Trattner 21
Generation of Diamagnetic Cavities at the Bow Shock by Ion Kinetic Effects
Yu Lin 31
Diffusive Compression Acceleration
Joe Giacalone, Jack R. Jokipii, and Jozsef Kota 41
Particle Acceleration and Transport at CME-Driven Shocks: A Case Study
Gang Li, G. P. Zank, M. I. Desai, G M. Mason, and W.K.M. Rice 51
Cosmic Ray Acceleration at Relativistic Shock Waves With a "Realistic" Magnetic Field Structure
Jacek Niemiec and Michal Ostrowski 59
Kinetics of Particles in Relativistic Collisionless Shocks
Mikhail V. Medvedev, Luis O. Silva, Ricardo A. Fonseca, J. W. Tonge, and Warren B. Mori 65
Studies of Relativistic Shock Acceleration
A. Meli and J. J. Quenby 71
Energy Spectra of Energetic Ions Around Quasi-Parallel Shocks
T. Sugijama, M. Fujimoto, and H. Matsumoto 87
Particle Acceleration in Shell Supernova Remnants: Observational Evidence
Stephen P. Reynolds 97
Waves and Turbulence Acceleration
Overview: Particle Acceleration by Waves and Turbulence
Robert Y. Lysak 107
The Connection Between Parallel Electric Fields and Ion Acceleration in Astrophysical Plasmas
F.J. Lund 109
Simulation Study of Beam-Plasma Interaction and Associated Acceleration of Background Ions
X. Y. Wang and Y. Lin 117
CONTENTS
Particle Acceleration and Current Disruption From the Cross-Field Current Instability
Anthony T. Y. Lui 125
Magnetic Energy Storage and Stochastic Acceleration
The Role of Electron Acceleration in Quick Reconnection Triggering
Masaki Fujimoto and Iku Shinohara 139
The Hall Current System for Magnetic Reconnection in the Magnetotail
T. Nagai and M. Fujimoto 149
Plasma Acceleration due to Transition Region Reconnection
J. Buchner, B. Nikutowski, and A. Otto 161
RHESSI Observations of Particle Acceleration in Solar Flares
R. P. Lin 171
Magnetohydrodynamic Analysis of the January 20, 2001, CME-CME Interaction Effect
A. H. Wang, S. T. Wu, and N. Gopalswamy 185
The Quadrupole as a Source of Cusp Energetic Particles: I. General Considerations
Robert B. Sheldon, Theodore A. Fritz, and Jiasheng Chen 197
Adiabatic, Diffusive, and Double Layer Acceleration
Electron Phasespace Density Analysis Based on Test-Particle Simulations of Magnetospheric
Compression Events
Jennifer L. Cannon and Xinlin Li 205
Parameterization of Ring Current Adiabatic Energization
M. W. Liemohn and G. V. Khazanov 215
Interrelation Among Double Layers, Parallel Electric Fields, and Density Depletions
Nagendra Singh 231
Acceleration and Outflow of Matter From Celestial Objects
Rickard Lundin, Stanislav Barabash, and Anatol Guglielmi 249
Studies of Exotic Acceleration Processes and Fundamental Physics
Exotic Acceleration Processes and Fundamental Physics
Giovanni Amelino-Camelia 265
Improving Limits on Planck-Scale Lorentz Symmetry Test Theories
Giovanni Amelino-Camelia 269
Spectral Evolution of Two High-Energy Gamma-Ray Bursts
Yuki Kaneko, Robert D. Preece, Maria Magdalena Gonzalez, Brenda L. Dingus, and
Michael S. Briggs 275
PREFACE
Space is dominated by plasma and a myriad of physical ena fundamental to the exploration of the universe. Whether
processes through which it has been evolving for billions working the details of how cold 0.1 eV ions and electrons in
of years. In our effort to understand what the universe has the Earth's ionosphere escape outward and possibly become
been and what it will become, we turn to the nature of accelerated more than 10,000 times to later rain down to
matter, space, and the various interactions that change this form the auroras or how Exa-eV (1018 eV) particles can be
environment. Our contact with the remote regions of the created in cosmic events deep in space, the same basic
universe is dominated by the photons and high-energy parti­ physical processes that exchange energy between particles
cles produced there long ago, with light often the result of and electric and magnetic fields must be considered. Al­
physical processes that involve particles accelerated to high though we believe we have gained at least a partial under­
energy. Developing our knowledge of particle acceleration standing of a number of these processes, we cannot say
across all spatial scales and energies is one of the keys to the same for many other processes, which remain largely
understanding the evolving universe. It is also the subject unknown and untested.
of this book. Researchers from the three fields of study mentioned
Our ability to advance knowledge about the universe above have made this book possible. Some participated di­
springs from what we gain by experiments in Earth-based rectly in the founding workshop for the monograph, ' 'Astro-
plasma laboratories and our attempt to apply that knowledge physical Particle Acceleration in Geospace and Beyond"
in space near Earth and in the solar system where available (the fall 2002 Huntsville Workshop in Chattanooga, Tennes­
to direct measurement. A key feature is the experimental see) by testing the idea that we could work together toward
ability to test theoretical knowledge of astrophysical plasma a common goal. Many of their names and affiliations can
at least partially through in situ measurement. We must be found on the papers that follow. Many others contributed
know not only what can happen if we manufacture a specific through their thoughtful evaluation of the papers in this
set of circumstances in the laboratory but also which of book. The workshop participants, contributing authors, and
these circumstances occur naturally in space and the role reviewers have made immensely valuable contributions to
they play in evolving plasma systems. this book and to the proposition that we should be involved in
We hope that the current monograph—which draws from carrying hard-won knowledge about the evolution of plasma
research in magnetospheric physics, solar physics, and astro­ systems across all the spatial scales and energies that make
physics—will guide the reader in considering the full signifi­ up our universe.
cance of what we have learned, and continue to learn, in D. L. Gallagher
the laboratory, in Earth's magnetosphere, in the solar wind, J. L. Horwitz
at the Sun, and beyond in the astrophysical plasma. Linking J. D. Perez
the physical processes in all these places is the fundamental R. D. Preece
nature of matter and energy and their evolving properties. J. J. Quenby
The acceleration of particles is one of the unifying phenom­ Editors
Particle Acceleration in Astrophysical Plasmas
Geophysical Monograph Series 156
Copyright 2005 by the American Geophysical Union
10.1029/156GM01
vii
Introduction to Particle Acceleration in the Cosmos
D. L. Gallagher,1 J. L. Horwitz,2 J. D. Perez,3 and J. J. Quenby4
Accelerated charged particles have been used on Earth since 1930 to explore the
very essence of matter, for industrial applications, and for medical treatments.
Throughout the universe, nature employs a dizzying array of acceleration processes
to produce particles that span 20 orders of magnitude in energy range, while
shaping our cosmic environment. Here, we introduce and review the basic physical
processes causing particle acceleration in astrophysical plasmas, from geospace
to the outer reaches of the cosmos. These processes are chiefly divided into four
categories: adiabatic and other forms of nonstochastic acceleration, magnetic
energy storage and stochastic acceleration, shock acceleration, and plasma wave
and turbulent acceleration. The purpose of this introduction is to set the stage and
context for the individual papers included in this monograph.
1. INTRODUCTION theoretical studies. Early experiments in the development
of atomic theory led Rutherford to first speculate on the
Particle acceleration is ubiquitous in space. Energy gains value of laboratory acceleration devices as tools for probing
of even less than 1 eV can cause atmospheric outflow from matter [Rutherford, 1919, 1928]. R. Wideroe proposed the
planetary ionospheres illuminated by stellar light. Indica­ first accelerator design in 1928, soon followed by D. H.
tions of extremely high-energy (~1020 eV) cosmic rays chal­ Sloan and E. O. Lawrence in 1931 [Persico et ai, 1968];
lenge our basic understanding of matter and space. Across all the first operating model was constructed at Cambridge Uni­
energies, accelerated particles carry energy and information versity by John Cockroft and E. T. S. Walton [Gamov, 1961].
concerning the physical processes that produce these acceler­ The promise of new insight into the fundamental structure
ations. Accelerated particles are therefore diagnostic of the of matter fueled the rapid development of more and more
flow of mass and energy as stellar, planetary, and galactic energetic particle accelerators, which continues today. To­
systems evolve. Our understanding of the behavior of these ward the end of the 19th century, electromagnetic diagnostics
systems is dependent on our understanding of the processes of accelerated particles began to be appreciated. In 1895,
that accelerate particles and our resulting ability to interpret Wilhelm Konrad Roentgen noticed the production of electro­
those processes through remote measurement. magnetic radiation by bombarding a target with electrons
Much of what we know about acceleration processes has [Gamov, 1961]. This radiation later became known as
been derived from laboratory experiments and associated Bremsstrahlung radiation. Although anticipated for many
years [Lienard, 1898], the first experimental evidence of
synchrotron radiation from accelerated electrons was ob­
tained with a 70 MeV accelerator assembled by Robert Lang-
1 Space Science Branch, Marshall Space Flight Center, National Aeronautics
and Space Administration, Huntsville, Alabama. muir and Herbert Pollock in 1948 [Pollock, 1982]. The leap
department of Physics, University of Texas in Arlington, Arlington, Texas. into space and astrophysics came with the first cosmic radia­
3Department of Physics, Auburn University, Auburn, Alabama.
tion measurements by Hess in 1912 in a balloonborne experi­
4Astrophysics Group, Blackett Laboratory, Imperial College of Science,
Technology and Medicine, London, United Kingdom. ment [Sekido and Elliot, 1985] and with the launch of the
space program on the LUNIK 1 and 2 [Gringzuz et ai, 1960]
and Explorer 1 and 3 [Van Allen, 1959] satellites [see account
in Lemaire and Gringauz, 1998].
Particle Acceleration in Astrophysical Plasmas
Geophysical Monograph Series 156 The study of acceleration processes and accelerated parti­
Copyright 2005 by the American Geophysical Union cles is intended to help us understand the operating and
10.1029/156GM02 evolutionary processes taking place in the cosmos. The study
1
2 INTRODUCTION TO PARTICLE ACCELERATION IN THE COSMOS
of these processes in regions of space accessible to us enables process is thought to be at least partially operative in the
a highly detailed diagnostic of the physical properties of formation of the ring current from inward injections or mo­
space plasma undergoing change, which in turn leads to tions of the inner plasma sheet of the magnetosphere. In
much enhanced constraints on the physical descriptions of this volume, Liemohn and Khazanov determine, through
those processes we develop. The attributes of accelerated simulations of a magnetospheric storm, that a good parame­
particles and the circumstances of their existence directly ter for determining the net adiabatic energy gain is the instan­
reflect the basic physics of the cosmos and must be consistent taneous value of the product of the maximum westward
with any theory we may develop to explain the nature of the electric field at the outer boundary with the nightside plasma
universe. Therefore each measurement reflects an attempt to sheet density.
temper or strengthen our collective understanding of the For particles mirroring along a magnetic field line, the
cosmos. integral of the parallel velocity between mirror points gives
The study of acceleration processes within accessible re­ the second invariant [e.g., Chen, 1984, p. 46]. When such
gions such as the solar system, particularly geospace, offers mirroring particles are transported onto shorter field lines,
the opportunity to understand at least some processes for their parallel energies increase. This process may be impor­
acceleration of charged particles in detail and to subject tant for energizing cosmic ray particles mirroring between
concepts to some level of rigorous experimental testing. approaching magnetic clouds, and for increasing parallel
Astrophysical observations, on the other hand, offer indica­ energies of particles convected Earthward from distended
tions of particle acceleration levels and types that appear field lines in the deep magnetotail toward more dipolar-
quantitatively different from those in the solar system in shaped field lines., The acceleration that Sheldon et al.
terms of parameter regimes. We can thus learn from the full suggest occurs in the magnetospheric cusp [this volume]
range of apparent particle acceleration mechanisms associ­ is partially related to Fermi acceleration in magnetic
ated with regions extending from geospace to the furthest geometries.
reaches of the universe. The purpose of this monograph A third invariant [e.g., Chen, 1984, p. 49] is the total
is to bring together observations and theories on particle magnetic flux encompassed by a complete drift path of a
acceleration for regions throughout the cosmos to help foster charged particle, e.g., an energetic particle gradient drifting
greater understanding from multiple perspectives. around the Earth, if changes in external agents do not occur
Particles are accelerated through a wide range of physical more rapidly than the full periods for such drifts. Gannon
processes. Here we discuss these processes in the following and Li [this volume], considering test-particle simulations of
four sections, organized by physical mechanism. Our objec­ magnetospheric compression events, argue that the radiation
tive is to provide an overall perspective on particle accelera­ belt particles involved tend to conserve their third adiabatic
tion physics and the dynamic processes occurring in space invariants.
where acceleration takes place. Another form of smooth, nonstochastic particle accelera­
tion is "centrifugal" acceleration [Cladis, 1986; Horwitz et
2. ADIABATIC AND OTHER FORMS OF ai, 1994] in which convection of magnetic field lines with
NONSTOCHASTIC ACCELERATION changing directions "whips" the particles outward along
the lines. This energization may be relevant to acceleration
One general category for acceleration of charged particles of outflows from planetary ionospheres (and perhaps other
in geospace and beyond could be those types of particle objects) to substorm-associated dipolarization events in the
acceleration that are relatively smooth. Acceleration by magnetosphere of the Earth [e.g., Liu et al, 1994], and
quasi-DC electric fields parallel to the magnetic field can perhaps elsewhere, and to large, rapidly rotating planetary
be of this type. Such acceleration is believed to occur under magnetospheres such as that of Jupiter. A characteristic of
some circumstances in auroras. Another type of acceleration this type of acceleration is that the velocity gains tend to be
that may often be relatively smooth occurs when adiabatic constant for different ion species, so that ions with different
invariants are conserved during motion in nonuniform mag­ masses receive different energy boosts.
netic fields. For example, if charged particles in the middle Another nonstochastic parallel electric field acceleration
terrestrial magnetosphere are moved Earthward toward re­ of ionospheric plasma transport may result from the effects
gions of higher magnetic fields by convection electric fields, of photoelectrons. In this phenomenon, to limit the net cur­
they may conserve their first adiabatic invariants [e.g., Chen, rent and maintain quasi-neutrality in ionospheric polar wind
1984, p. 44], the ratio of their energies perpendicular to the plasma transport in the presence of upward-moving photo-
magnetic field to the strength of the magnetic field, thereby electrons, an upward electric field develops to suppress the
increasing their perpendicular energies in this process. This upward photoelectron flow; consequently, ionospheric ions
GALLAGHER ET AL. 3
are accelerated upward. Su et al. [1998] used a combination Magnetic reconnection involves a breakdown of the ideal
fluid-kinetic steady-state treatment to indicate that the pho- magnetohydrodynamic frozen-field approximation in which
toelectron-produced electric potential should concentrate charged particles that are connected by a magnetic field line
into a thin double layer 2-4 R in altitude, with drops of at one instant of time must remain connected by a field line
E
10s of volts to accelerate polar ions to energies of a few for all time. This process, which is mathematically singular
10s of electron volts. Lundin and Bar abash [this volume] and usually highly nonlinear, induces electric fields parallel
discuss aspects of acceleration and outflow from celestial to the magnetic field and thus accelerates the plasma parti­
objects. Though these authors do not specifically mention cles. For a review of early work on the theory of and evidence
centrifugal and photoelectron-driven acceleration processes, for magnetic reconnection, see Hones [1984]. For a descrip­
both are examples of nonstochastic acceleration that could tion of the mathematical theory for the structure of magnetic
be important in acceleration and outflow from planetary reconnection layers, see Lin and Lee [1993].
ionospheres and other cosmic objects. In this volume, Fujimoto and Shinohara describe a rapid,
Many papers in auroral physics investigations have treated spontaneous triggering mechanism for magnetic reconnec­
the parallel electric potential distribution as approximately tion in an ion-scale current sheet. Nagai and Fujimoto pre­
stationary for electron acceleration, driven variously by im­ sent direct evidence of the Hall current system that plays
posed field-aligned electric currents, imposed large-scale such a vital role for reconnection in the Earth's magnetotail.
drops in potential, or differential anisotropy in hot plasma A.-H. Wang et al. report the results of numerical simulations
distributions [e.g., Knight, 1973; Evans, 191 A; Block, 1978; of the interaction of two coronal mass ejections and the
Ergun etal, 2002]. Singh [this volume] presents simulations associated reconnection.
of electric double layers driven by imposed voltage drops Acceleration from reconnection sites is the result of elec­
and currents. Such electric double layers can be important tric fields parallel to the local magnetic field. Likewise,
in quasi-smooth versions of the observed parallel accelera­ diffusive acceleration at shocks, referred to as first-order
tion of electrons [e.g., Burch et al., 1976] and ions [e.g., Fermi acceleration and discussed elsewhere in this volume,
Steinbach-Nielsen et al, 1984] in the auroral regions. occurs when the electric field generated by the changing
Downward versions of such parallel electric fields can magnetic field is parallel to the magnetic field. In contrast,
also play an indirect role in energizing ions in the auroral stochastic acceleration results from randomly oriented elec­
regions through the so-called pressure-cooker effect [e.g., tric fields associated with magnetohydrodynamic waves or
Gorney et al., 1985; Wu et al., 2002], in which downward turbulence. This mechanism has been used to address the
electric fields trap in or slow the transit of ions through origin and transport of solar energetic particles and interstel­
regions of transverse wave heating, thereby increasing the lar pickup ions [Committee on Solar and Space Physics,
wave-driven heating itself. In this case, the main energization 2004].
agent (the transverse ion heating) is stochastic in nature, but In this volume, Sheldon et al. propose stochastic accelera­
the important contributing factor of the downward electric tion in a magnetic quadrupole trap in the Earth's cusp as
field may comparatively smooth. Lund [this volume] consid­ the source of the observed cusp energetic particles. They
ers a version of this process through test-particle simulations suggest that this mechanism may be important elsewhere,
and also suggests that similar processes may be operative in e.g., magnetic cusp geometries in the heliosphere and the
the solar corona and perhaps in other astrophysical processes. galaxy. Also, R. P. Lin [this volume] presents exciting new
data from the NASA Reuven Ramaty High Energy Solar
3. MAGNETIC ENERGY STORAGE AND Spectroscopic Imager (RHESSI) small explorer spacecraft
STOCHASTIC ACCELERATION launched 5 February 2002. The capability of using the data
from RHESSI along with detailed quantitative analysis to
A fundamental process in plasmas is energy storage in probe the particle acceleration mechanism(s) in flares and
magnetic fields and its subsequent conversion to kinetic related phenomena was foreshadowed in Lin et al. [2002].
energy of particles. The idea that what we now call magnetic
reconnection plays a key role in this process was first ad­ 4. SHOCK ACCELERATION
vanced by Giovanelli [1947] to explain particle acceleration
in solar flares. Hoyle [1941] and Dungey [1961] applied the Another important category of cosmic particle accelera­
idea to the Earth's magnetosphere. Priest and Forbes [2000] tion is energization by shock structures that may occur in
have reviewed magnetic connection phenomena from labora­ the Earth's bow shock, within the solar wind as driven by
tory machines, the Earth's magnetosphere, and the Sun's coronal mass ejections, solar flares, supernovae remnants
atmosphere to flare stars and astrophysical accretion disks. (SNR), jets of Active Galactic Nuclei (AGN), relativistic