Plasma Astrophysics

by Somov, Boris V.

• ISBN13: 9780387349480
• ISBN10: 0387349480
• Format: Hardcover
• Copyright: 2006-12-30
• Publisher: Springer Verlag

Summary

This well-illustrated monograph is devoted to classic fundamentals, current practice, and perspectives of modern plasma astrophysics. The first part of the book is unique in covering all the basic principles and practical tools required for understanding and work in plasma astrophysics. The second part represents the physics of magnetic reconnection and flares of electromagnetic origin in space plasmas in the solar system, single and double stars, relativistic objects, accretion disks, their coronae. The level of the book is designed mainly for professional researchers in astrophysics. The book will also be interesting and useful to graduate students in space sciences, geophysics, as well as to advanced students in applied physics and mathematics seeking a unified view of plasma physics and fluid mechanics.

Table of Contents

Introduction	1
1 Magnetic Reconnection	5
1.1 What is magnetic reconnection?	5
1.1.1 Neutral points of a magnetic field	5
1.1.2 Reconnection in vacuum	7
1.1.3 Reconnection in plasma	8
1.1.4 Three stages in the reconnection process	11
1.2 Acceleration in current layers, why and how?	13
1.2.1 The origin of particle acceleration	13
1.2.2 Acceleration in a neutral current layer	15
1.3 Practice: Exercises and Answers	19
2 Reconnection in a Strong Magnetic Field	21
2.1 Small perturbations near a neutral line	21
2.1.1 Historical comments	21
2.1.2 Reconnection in a strong magnetic field	22
2.1.3 A linearized problem in ideal MHD	26
2.1.4 Converging waves and the cumulative effect	28
2.2 Large perturbations near the neutral line	30
2.2.1 Magnetic field line deformations	31
2.2.2 Plasma density variations	34
2.3 Dynamic dissipation of magnetic field	34
2.3.1 Conditions of appearance	34
2.3.2 The physical meaning of dynamic dissipation	37
2.4 Nonstationary analytical models of RCL	38
2.4.1 Self-similar 2D MHD solutions	38
2.4.2 Magnetic collapse at the zeroth point	41
2.4.3 From collisional to collisionless reconnection	45
3 Evidence of econnection in Solar Flares	47
3.1 The role magnetic fields	47
3.1.1 Basic questions	47
3.1.2 Concept of magnetic reconnection	48
3.1.3 Some results of observations	50
3.2 Three-dimensional reconnection in flares	51
3.2.1 Topological model of an active region	51
3.2.2 Topological portrait of an active region	55
3.2.3 Features of the flare topological model	57
3.2.4 The S-like morphology and eruptive activity	60
3.3 A current layer as the source of energy	63
3.3.1 Pre-flare accumulation of energy	63
3.3.2 Flare energy release	64
3.3.3 The RCL as a part of an electric circuit	66
3.4 Reconnection in action	68
3.4.1 Solar flares of the Syrovatsky type	68
3.4.2 Sakao-type flares	69
3.4.3 New topological models	73
3.4.4 Reconnection between active regions	75
4 The Bastille Day 2000 Flare	77
4.1 Main observational properties	77
4.1.1 General characteristics of the flare	77
4.1.2 Overlay HXR images on magnetograms	79
4.1.3 Questions of interpretaion	82
4.1.4 Motion of the HXR kernels	83
4.1.5 Magnetic field evolution	84
4.1.6 The HXR kernels and field evolution	85
4.2 Simplified topological model	87
4.2.1 Photospheric field model. Topological portrait	87
4.2.2 Coronal field model. Separators	88
4.2.3 Chromospheric ribbons and kernels	89
4.2.4 Reconnected magnetic flux. Electric field	93
4.2.5 Discussion of topological model	96
5 Electric Currents Related to Reconnection	99
5.1 Magnetic reconnection in the corona	99
5.1.1 Plane reconnection model as a starting point	99
5.1.2 Three-component reconnection	105
5.2 Photospheric shear and corona]. reconnection	107
5.2.1 Accumulation of magnetic energy	107
5.2.2 Flare energy release and CMEs	109
5.2.3 Flare and HXR footpoints	110
5.3 Shear flows and photospheric reconnection	114
5.4 Motions of the HXR footpoints in flares	117
5.4.1 The footpoint motions in some flares	117
5.4.2 Statistics of the footpoint motions	118
5.4.3 The FP motions orthogonal to the SNL	119
5.4.4 The FP motions along the SNL	120
5.4.5 Discussion of statistical results	123
5.5 Open issues and some conclusions	125
6 Models of Reconnecting Current Layers	129
6.1 Magnetically neutral current layers	129
6.1.1 The simplest MHD model	129
6.1.2 The current layer by Syrovatskii	131
6.1.3 Simple scaling laws	134
6.2 Magnetically non-neutral RCL	136
6.2.1 Transversal magnetic fields	136
6.2.2 The longitudinal magnetic field	137
6.3 Basic physics of the SHTCL	139
6.3.1 A general formulation of the problem	139
6.3.2 Problem in the strong field approximation	141
6.3.3 Basic local parameters of the SHTCL	142
6.3.4 The general solution of the problem	143
6.3.5 Plasma turbulence inside the SHTCL	145
6.3.6 Formulae for the basic parameters of the SHTCL	146
6.4 Open issues of reconnection in flares	149
6.5 Practice: Exercises and Answers	151
7 Reconnection and Collapsing Traps in Solar Flares	153
7.1 SHTCL in solar flares	153
7.1.1 Why are flares so different but similar?	153
7.1.2 Super-hot plasma production	157
7.1.3 On the particle acceleration in a SHTCL	160
7.2 Coronal HXR sources in flares	160
7.2.1 General properties and observational problems	160
7.2.2 Upward motion of coronal HXR sources	162
7.2.3 Data on average upward velocity	163
7.3 The collapsing trap effect in solar flares	168
7.3.1 Fast electrons in coronal HXR sources	168
7.3.2 Fast plasma outflows and shocks	168
7.3.3 Particle acceleration in collapsing trap	171
7.3.4 The upward motion of coronal HXR sources	174
7.3.5 Trap without a shock wave	176
7.4 Acceleration mechanisms in traps	177
7.4.1 Fast and slow reconnection	177
7.4.2 The first-order Fermi-type acceleration	179
7.4.3 The betatron acceleration in a collapsing trap	180
7.4.4 The betatron acceleration in a shockless trap	183
7.5 Final remarks	184
7.6 Practice: Exercises and Answers	185
8 Solar-type Flares in Laboratory and Space	193
8.1 Solar flares in laboratory	193
8.1.1 Turbulent heating in toroidal devices	193
8.1.2 Current-driven turbulence in current layers	195
8.1.3 Parameters of a current layer with CDT	197
8.1.4 The SHTCL with anomalous heat conduction	198
8.2 Magnetospheric Physics Problems	200
8.2.1 Reconnection in the Earth Magnetosphere	200
8.2.2 MHD simulations of space weather	201
8.3 Flares in accretion disk coronae	202
8.3.1 Introductory comments	202
8.3.2 Models of the star magnetosphere	203
8.3.3 Power of energy release in the disk coronae	207
8.4 The giant flares	208
9 Particle Acceleration in Current Layers	211
9.1 Magnetically non-neutral RCLs	211
9.1.1 An introduction in the problem	211
9.1.2 Dimensionless parameters and equations	212
9.1.3 An iterative solution of the problem	214
9.1.4 The maximum energy of ail accelerated particle	217
9.1.5 The non-adiabatic thickness of current layer	218
9.2 Regular versus chaotic acceleration	219
9.2.1 Reasons for chaos	220
9.2.2 The stabilizing effect of the longitudinal field	222
9.2.3 Characteristic times of processes	223
9.2.4 Dynamics of accelerated electrons in solar flares	224
9.2.5 Particle simulations of collisionless reconnection	225
9.3 Ion acceleration in current layers	226
9.3.1 Ions are much heavier than electrons	226
9.3.2 Electrically non-neutral current layers	227
9.3.3 Maximum particle energy and acceleration rates	229
9.4 How are solar particles accelerated?	232
9.4.1 Place of acceleration	232
9.4.2 Time of acceleration	234
9.5 Cosmic ray problem	236
10 Structural Instability of Reconnecting Current Layers	237
10.1 Some properties of current layers	237
10.1.1 Current layer splitting	237
10.1.2 Evolutionarity of reconnecting current layers	239
10.1.3 Magnetic field near the current layer	240
10.1.4 Reconnecting current layer flows	241
10.1.5 Additional simplifying assumptions	242
10.2 Small perturbations outside the RCL	244
10.2.1 Basic assumptions	244
10.2.2 Propagation of perturbations normal to a RCL	244
10.2.3 The inclined propagation of perturbations	246
10.3 Perturbations inside the RCL	250
10.3.1 Linearized dissipative MHD equations	250
10.3.2 Boundary conditions	251
10.3.3 Dimensionless equations and small parameters	253
10.3.4 Solution of the linearized equations	255
10.4 Solution on the boundary of the RCL	258
10.5 The criterion of evolutionarity	260
10.5.1 One-dimensional boundary conditions	260
10.5.2 Solutions of the boundary equations	261
10.5.3 Evolutionarity and splitting of current layers	265
10.6 Practice: Exercises and Answers	266
11 Tearing Instability of Reconnecting Current Layers	269
11.1 The origin of the tearing instability	269
11.1.1 Two necessary conditions	269
11.1.2 Historical comments	270
11.2 The simplest problem and its solution	272
11.2.1 The model and equations for small disturbances	272
11.2.2 The external non-dissipative region	274
11.2.3 The internal dissipative region	276
11.2.4 Matching of the solutions and the dispersion relation	277
11.3 Physical interpretation of the instability	279
11.3.1 Acting forces of the tearing instability	279
11.3.2 Dispersion equation for tearing instability	281
11.4 The stabilizing effect of transversal field	282
11.5 Compressibility and a longitudinal field	285
11.5.1 Neutral current layers	285
11.5.2 Non-neutral current layers	287
11.6 The kinetic approach	288
11.6.1 The tearing instability of neutral layer	288
11.6.2 Stabilization by the transversal field	292
11.6.3 The tearing instability of the geomagnetic tail	293
12 Magnetic Reconnection and Turbulence	297
12.1 Reconnection and magnetic helicity	297
12.1.1 General properties of complex MHD systems	297
12.1.2 Two types of MHD turbulence	299
12.1.3 Helical scaling in MHD turbulence	301
12.1.4 Large-scale solar dynamo	302
12.2 Coronal heating and flares	304
12.2.1 Coronal heating in solar active regions	304
12.2.2 Helicity and reconnection in solar flares	305
12.3 Stochastic acceleration in solar flares	307
12.3.1 Stochastic acceleration of electrons	307
12.3.2 Acceleration of protons and heavy ions	309
12.3.3 Acceleration of 3He and 4He in solar flares	310
12.3.4 Electron-dominated solar flares	311
12.4 Mechanisms of coronal heating	313
12.4.1 Heating of the quiet solar corona	313
12.4.2 Coronal heating in active regions	315
12.5 Practice: Exercises and Answers	317
13 Reconnection in Weakly-Ionized Plasma	319
13.1 Early observations and classical models	319
13.2 Model of reconnecting current layer	321
13.2.1 Simplest balance equations	321
13.2.2 Solution of the balance equations	322
13.2.3 Characteristics of the reconnecting current layer	323
13.3 Reconnection in solar prominences	325
13.4 Element fractionation by reconnection	328
13.5 The photospheric dynamo	329
13.5.1 Current generation mechanisms	329
13.5.2 Physics of thin magnetic flux tubes	330
13.5.3 FIP fractionation theory	332
13.6 Practice: Exercises and Answers	334
14 Magnetic Reconnection of Electric Currents	339
14.1 Introductory comments	339
14.2 Flare energy storage and release	340
14.2.1 From early models to future investigations	340
14.2.2 Some alternative trends in the flare theory	344
14.2.3 Current layers at separatrices	345
14.3 Current layer formation mechanisms	346
14.3.1 Magnetic footpoints and their displacements	346
14.3.2 Classical 2D reconnection	348
14.3.3 Creation of current layers by shearing flows	350
14.3.4 Antisymmetrical shearing flows	352
14.3.5 The third class of displacements	354
14.4 The shear and reconnection of currents	355
14.4.1 Physical processes related to shear and reconnection	355
14.4.2 Topological interruption of electric currents	357
14.4.3 The inductive change of energy	357
14.5 Potential and non-potential fields	359
14.5.1 Properties of potential fields	359
14.5.2 Classification of non-potential fields	360
14.6 To the future observations by Solar-B	362
Epilogue	365
Appendix 1. Acronyms	367
Appendix 2. Notation	369
Appendix 3. Useful Formulae	371
Appendix 4. Constants	375
Bibliography	377
Index	407