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Hood, Y. Voitenko, D. Van Eester, S. Poedts, R. Erdelyi, R. In addition to being instructive, it was fun. Thank you. My gratitude also goes to A. De Groof for her help in preparing this book and to P. It is a pleasure to thank Kluwer Academic Publishers for giving me the opportunity to publish my class notes in the Astrophysics and Space Science Library Series. I have benefitted from several good books on plasma physics, magnetohydrodynamics and solar physics.
Those that I like the best are listed at the end of the introductory chapter under references. These are, with one or two exceptions, the only references given in this book. The material covered in this book is at the basic elementary level and owned as it were by the community. It should be clear that nothing of the work described in this book is my own. The book is based on the work by the pioneering giants J. Maxwell, L. Boltzmann, I.
Langmuir, J. Larmor, H. The students who have taken this course over the years, probably do not realize it, but I have benefitted a lot from them. Their criticism and questions have helped me shaping the notes in their present form. The fact that several of these former students are pursuing scientific and academic careers in which mathematical modelling of plasmas and MHD still play a prominent role, is reassuring to me. It has not all been in vain. Most of the students who have taken the course, do not use its content in their daily professional life.
For them I dare hope that the course has contributed to their scientific training by learning them how mathematical modelling and physical intuition and interpretation can go hand in hand. The importance of mathematical modelling in this context must be stressed. Even when the mathematical description has been simplified by replacing a description using the Boltzmann equations for the distribution functions in phase space of the various species, with a description based on MHD, mathematical modelling is often essential. When solutions for simple situations are known, more and more effects may be added to make the model more realistic.
It is my hope that this book may help students at the K. Leuven and elsewhere to appreciate the intriguing and complicated behaviour of plasmas and to appreciate the power of mathematical modelling as a tool for exploring and understanding this complicated behaviour. The field of view of this instrument encompasses 32 diameters of the Sun. To put this in perspective, the diameter of this image is 45 million kilometers at the distance of the Sun, or half of the diameter of the orbit of Mercury.
During that time of the year, the Sun is located in the constellation Sagittarius. The center of the Milky Way is visible, as well as the dark interstellar dust rift, which stretches from the south to the north. Three prominent streamers can be seen two at the West and one at the East limb. It eventually plunged into the Sun. The kids really believe everything you tell them. Edna Crabapple. The Simpsons. This course is concerned with plasma physics with an emphasis on Magnetohydrodynam- ics. It is set in the framework of solar physics and astrophysics, but the focus is on basic concepts of plasma physics and on basic properties of plasmas.
An average student in physics or mathematics at the K. Leuven does not know very much about plasma physics. He is not particularly worried by this lack of scientific knowledge as he happens to live in a corner of the universe where matter is predominantly solid, liquid, or gaseous. The three states of matter which occur at the surface of the earth are however not typical of matter in the universe.
Most of the visible matter in the universe exists as plasma whereas lightning and the aurora are the only natural manifestations of the plasma state on earth. This Chapter is an exercise in public relations for plasma physics. Its aim is to show that plasmas are almost everywhere in the universe and to point out that they are extremely complicated physical systems fundamentally different from classic neutral gases, especially when there is a magnetic field present. The hope is that the reader is convinced that plasmas are exciting physical objects that are abundantly present in the universe and that he is prepared to make the effort to learn about the basic principles and properties of plasmas.
A plasma is essentially a gas consisting of neutral and charged particles, ions and electrons, rather than of neutral atoms and molecules only as illustrated on Fig.
Frontiers | Mixed Properties of MHD Waves in Non-uniform Plasmas | Astronomy and Space Sciences
It is important to be aware that a plasma cannot be treated simply as an ordinary gas which is electrically conducting. There is a fundamental difference between a neutral gas and a plasma that results from the different nature of the inter-particle forces. In a neutral gas the forces are very strong and short range, so that the dynamics of a neutral gas is dominated by two-body billiard-ball-like collisions. In a plasma the inter-particle forces be- tween charged particles are electromagnetic forces.
A charged particle interacts with the other charged particles through the Coulomb force. In addition a moving charged particle creates a magnetic field which produces a force on the other charged particles. The electromagnetic forces are comparatively weak and long-range. Due to the long range of the inter-particle forces each charged particle in a plasma interacts with a large number of other charged par- ticles resulting in collective plasma behaviour : hence the fact that plasma is referred to as the fourth state of matter.
A plasma is a macroscopically electrically neutral substance containing many interacting free electrons and ions which exhibit collective behaviour due to the long-range Coulomb forces. Figure 1. If your room where filled with plasma, however, the situation would be very different. The magnetic field exerts a force on the plasma Lorentz force which can be split into two parts. The first part is a magnetic pressure which acts, just like ordinary gas pressure, from regions of high to low pressure.
The second part is a magnetic tension force with the same effect as a tension in an elastic string. Since a magnetic field exerts a force on a plasma, it may store energy. Plasma motions that twist and shear magnetic field lines can inject energy in the magnetic field. Occasionally, the magnetic field may become unstable and the stored energy be released in a violent disruption.
It is largely stimu- lated by the importance of plasma physics for solar physics, space physics, astrophysics, and for the development of controlled thermonuclear fusion. The ranges of temperature and num- ber density of natural and man-made plasmas are huge as can be seen on Fig. The Sun and solar wind The Sun can be regarded as a source of radiated energy which appears to have been relatively constant for periods of millions of years and not to have changed a lot in the past 4.
The near constancy for the shorter times is easily understood once the origin of the radiated energy in nuclear reactions in the deep solar interior is appreciated. The Sun has such a large heat content that, if the central nuclear reactions were turned off, it would take yr before any knowledge of this reached the solar surface.
This view of the Sun with slowly varying properties has led to the study of spherically symmetric models of the Sun, which evolve slowly in time, and with corresponding models for the structure and evolution of all types of stars. The structure and the different layers of the Sun are illustrated on Fig. Superimposed on this very slowly varying Sun is an atmosphere of extreme complexity with rapid spatial and temporal variability which requires a totally different explanation.
Only since the s do we know that the solar atmosphere is controlled by the interactions of the magnetic field with the plasma. The old view of the solar atmosphere was a spheri- cally symmetric structure with a completely unimportant magnetic field, except in sunspots. Elsewhere the magnetic field was thought to be uniform. Observations from satellites e. Going up above the photosphere of the Sun these flux tubes spread out in the chromosphere and fill the whole space in the upper chromosphere and the corona with beautiful magnetic loop structures where the magnetic field is strong enough.
Elsewhere, the plasma stretches the magnetic field out into open structures leaving the Sun. Soft X- ray telescopes from space have revealed the corona in all its glory, emitting thermally at a few million K as can be seen on Fig. All the structure we see in the corona is caused by the magnetic field. If the Sun had no magnetic field, its atmosphere would be a rather dull object. The magnetic activity of the Sun is not constant but changes with a period of about 11yr, known as the solar cycle. This is most clearly seen in the total number of sunspots which varies from a maximum to a minimum and back to a maximum in 11yr as is shown on Fig.
The solar atmo- sphere has been identified as a gigantic plasma physics laboratory where the laws of modern plasma physics can be studied under conditions that cannot be realized on earth. The Sun emits a highly conducting tenuous plasma, called the solar wind, at very high speeds into the interplanetary space. It is not possible for a hot static corona to extend throughout interplanetary space.
It must expand and as a result the Sun loses mass. The solar wind is far from being spherically symmetric. The high speed solar wind originates from the open magnetic field structures in the solar corona. The earth resembles a small pebble in a stream of plasma flowing supersonically out from the Sun. The expansion of the solar wind, combined with the solar rotation, has two consequences.
First, the magnetic field, firmly rooted in the solar photosphere, is pulled outward since it is embedded in the radially outward-flowing plasma. Second, the magnetic field at larger distances is bent back azimuthally into a spiral as shown schematically on Fig. The solar wind does not flow steadily. Solar activity manifests itself through the sunspot cycle; it causes the plasma from a particular solar region to expand at a much greater speed setting up a shock that accelerates ions in situ to large energies.
The magnetosphere Plasma physics is also important closer at home. Although the main influence of the Sun on the Earth is through gravitation and electromagnetic radiation primarily in the optical part of the spectrum , the Sun also interacts with the Earth through its particle emission in the solar wind. The solar wind encloses the Earth and its local magnetic field in this magnetosphere as shown schematically on Fig.
The wind itself flows radially outward from the Sun. These interactions create the planetary magnetospheres whose sizes depend on the strength of the magnetic field and the plasma pressure within the magnetospheres. The magnetosphere of the Earth, or of any other planet, is that region surrounding the planet in which its magnetic field has a controlling influence on, or dominates, the motions of energetic charged particles such as electrons, protons, or other ions. In addition to changes induced by the rotation of the Sun, the energy transfer from the solar wind to the planetary magnetospheres varies with the solar magnetic cycle.
At times of strong solar magnetic activity, the intensity of the solar wind increases and its interaction with the magnetosphere causes magnetic storms and aurorae. During solar maximum in geomagnetic disturbances and auroral displays could be observed as far south as Florida. Strong solar magnetic activity can cause a compression of the magnetosphere at its day-side to about half its size and an expansion to about twice its size at the night side. These changes in the size of the magnetosphere have an effect on artificial satellites due to increased drag and direct exposure to energetic particles in the solar wind.
During the magnetic storms the magnetic field of the Earth is forced to change on a truly grand scale causing problems for geomagnetic navigation systems and disrupting radio communications. The disturbed magnetic fields can knock power plants out of service. So there is a practical interest in understanding the magnetosphere and its interaction with the solar wind.
This has led to international research programmes in space weather. In addition the magnetosphere like the solar atmosphere is a plasma physics laboratory where we can observe and study plasmas under unique conditions that we cannot realize on Earth. The Sun has its own magne- tosphere called the heliosphere; it is the region within the galactic medium where the solar plasma digs out, and fills a cavity.
A hot corona cannot be in static equilibrium with the interstellar medium and must expand. Once the solar wind is introduced there is a surface surrounding the Sun at which the pressure of the solar wind balances the pressure of the interstellar gas and there is a heliospheric boundary whose structure is basically similar to that of the magnetosphere. The global solar magnetic field organizes the heliosphere. The morphology of the heliosphere, its evolution over space and time, and the location of its boundaries are determined by the global solar magnetic field and by the properties of the local interstellar medium.
The position of the boundary is not known with great accuracy but is probably of order of AU. The heliosphere contains most of the solar system but not the most distant comets. Astrophysical plasmas Almost all astrophysical objects are in the plasma state. Here we list a few examples of magnetic astrophysical plasmas. Obvious examples of stellar magnetic plasmas are the solar type stars.
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The only unique property of the Sun is its proximity. The Sun is our nearest star. Apart from being the star that is by far the closest to the Earth, the Sun is an ordinary main sequence or dwarf star of spectral type G2. This means that we can expect that many other stars, whose gross properties mass, chemical composition, luminosity, effective temperature are similar to those of the Sun, also exhibit atmospheric activity superimposed on their average behaviour.
Because the Sun is so close to us, its activity is very apparent, but this would not be true even if the Sun were one of the other nearest stars to us. Because all other stars appear as point sources of radiation, it is impossible to observe their atmospheres with spatial resolution. Ultraviolet spectroscopic observations from IUE, X-ray observations from the Einstein Observatory, microwave detections from the VLA and new optical observations from the ground have shown that solar-like activity stellar spots, chromospheres, transition regions, coronae and stellar winds indeed occurs in a wide variety of stars.
If a solar-like star is defined as a star which has a turbulent magnetic field sufficiently strong to control the dynamics and energetics in its outer atmospheric regions, it then turns out that i dwarf stars of spectral type G-M and rapidly rotating subgiants and giants of spectral type F-K in spectroscopic binary systems are definitely solar-like, ii dwarf stars of spectral type A7-F7 are almost certainly solar-like, iii T Tauri stars and other pre-Main- Sequence stars are probably solar-like, iv slowly rotating single giants of spectral type F to early K are probably solar-like.
As a consequence plasma physics is important for astrophysics as a whole. The magnetic fields in the solar atmosphere are small scale magnetic fields concentrated in intense flux tubes and in sunspots in the photosphere. When averaged over the whole solar photosphere a small global field of a few Gauss is measured. The Ap stars are peculiar stars with enhanced lines of the Fe-peak elements and greatly enhanced lines of the rare earth elements compared with the spectra of normal stars. The line strength anomalies are caused by atmospheric abundance anomalies confined in a thin layer in the atmosphere.
The detected global magnetic fields vary in phase with the spectrum and light variations. The surface magnetic fields are predominantly dipolar, and their effective strengths range from a few hundred Gauss up to 34 kGauss.
The periodic variations in spectrum, light, and magnetic field are explained with the oblique rotator model as due to the rotation of the star with the period of the observed variations equal to the period of rotation. The oblique rotator model assumes that the magnetic field is frozen in the stellar atmosphere and has an axis which is inclined to the axis of rotation, which itself is inclined to the line of sight. Because of the rotation of the star the observer sees different aspects of the dipolar magnetic field and measures a variable effective magnetic field.
The spectrum and light variations are explained by assuming that the abundance anomalies are not uniform over the surface of the star.
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Hence the name magnetic Ap is too narrow but is still used for historical reasons. Far stronger global magnetic fields have been detected in white dwarfs and neutron stars. Very strong global magnetic fields are observed in neutron stars. Radio pulsars are a garden variety of neutron stars: hundreds have been detected since they were detected in They emit beams of radio waves which sweep through space as the stars rotate, like lighthouse beams, thus from afar pulsars seem to flicker or pulsate at their rotation period. Careful measurements have shown that pulsar periods increase over time, implying that the stars are gradually spinning down.
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This is attributed to their magnetic fields. The magnetic field is anchored to the neutron star surface, so as the star turns the field also must turn. This drives magnetic waves out, along with diffuse winds of charges particles which emit the radio beams from just above the magnetic poles , carrying off energy and causing the star to slowly spin down. The strongest magnetic fields ever detected occur in magnetars. The magnetic fields of magnetars are about Gauss.
To put these enormous magnetic field strengths in perspective, let us compare them with that of more familiar objects. White dwarfs and neutron stars require going beyond classic physics. The interaction of magnetic fields with plasmas play an important role in star formation. The magnetic fields provide a very efficient mechanism of support for self-gravitating molec- ular clouds where star formation is taking place.
They influence the conditions for collapse of a self gravitating cloud and help regulate star formation. Magnetic fields and plasma physics are also important for explaining the relatively slow rotation of non-degenerate stars. If dur- ing star formation angular momentum would be conserved on contraction, stars would be spinning much faster than they actually do. Without braking the Sun would not be a slow rotator with a period of 27 d but would rotate like mad with a rotational speed times faster than its actual speed. Magnetic braking combined with a magnetic wind plays a fundamental role here.
As a matter of fact all young Main sequence stars have undergone substantial braking during their formation, otherwise they would be spinning much faster than they actually do. Controlled thermonuclear fusion The Sun, like most stars, radiates an enormous amount of energy, because in its core the temperature and density are high enough to produce fusion of hydrogen into helium.
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Controlled nuclear fusion on earth would provide an almost unlimited and relatively clean means for energy production. The main obstacle in the way of harnessing this source of energy is the fact that the reactions will take place at a useful rate only if the temperature of the material is of the order of K. Material at this temperature is ionized. A way to confine and control this very hot plasma is by using magnetic fields in toroidal devices.
Early attempts to do this revealed that a magnetic plasma is a far more complicated system than had been anticipated. This has triggered off a programme of theoretical and experimental research into the properties of magnetic plasmas which still continues. That would be far too ambitious and actually a full course can be dedicated to each of these subjects.
However, before we can embark on a study of any of these subjects, we need to learn about the fundamental concepts of plasma physics and the basic properties of plasmas. Hence, the aim is to give a basic introduction to plasma physics with an emphasis on Magnetohydrodynamics MHD for short. Since this course is the first encounter with plasma physics for students at the K. Leuven, its level is elementary. Indeed, there are different options about what to teach in such an introduc- tory course.
A possible approach is to present a selection of plasma physics phenomena to convince the reader that plasma physics is indeed an important subject worthwhile pursuing and then to introduce the appropriate approximate plasma model to explain the phenomenon under discussion.
Even if the selection is narrowed down to e. Of course, time and space can be gained by presenting the plasma models with a minimal dis- cussion of their theoretical foundations. However, this obscures the overall logical structure of theoretical plasma physics. A plasma is a large N-body system of mobile charged particles and electromagnetic fields.
A complete simulation of such a macroscopic system by integration of the Lorentz force equations and the corresponding microscopic Maxwell equations is far beyond our reach, even with the most powerful computers. Even if we could solve the system exactly, we would have far more information than we would require.
For these reasons a number of plasma models have been developed. The models range from kinetic models which contain all the relevant physical phenomena, but are still largely unsolvable, to fluid models which selectively remove small-scale physics, but are more tractable and yield very useful large-scale solutions. Since it is impossible to cover all of the plasma models in a first course, I focus on Magnetohydrodynamics MHD for short.
MHD is a macroscopic, non-relativistic theory that is concerned with large-scale global and low-frequency slow phenomena in magnetic plasmas. This focus reflects a personal bias as I have been using MHD to a large extent, but not exclusively, as a mathematical model for carrying out my research on magnetic plasmas. However, I have convinced myself that there are indeed good reasons for starting with MHD. Firstly, MHD can be viewed as an extension of classic hydrodynamics. It can be expected that students in their third year are familiar with very basic results of classic fluids.
Hence, it makes sense to introduce to these students a plasma model that they can link to a classic fluid, on their first encounter with plasmas. Secondly, MHD gives an accurate description of many of the complicated interactions of magnetic fields with the plasmas of the Sun and stars and of fusion machines. Magnetohydrodynamics can be used to study the global equilibrium, stability, waves and heating of the basic magnetic structures in the solar atmosphere and of plasmas in thermonuclear magnetic fusion machines.
Thirdly, the model of ideal MHD has an attractive mathematical structure with well-defined conservation laws. MHD can be viewed as classical fluid dynamics with the additional complication that the fluid is electrically conducting. A possible way of introducing MHD is to write down the constitutive equations of classical fluid dynamics and to add the terms and equations due to the magnetic field.
This approach might be the best way to economically present the equations of MHD and it allows us to move on to various applications of MHD without much ado. However, this leaves the student without any idea how and where to place MHD in the wider context of plasma physics. I have opted to put an emphasis on fundamental concepts and first principles. The goal of this introductory course is to acquaint the student with basic properties of magnetic plasmas. Therefore, I shall begin from first principles with the fundamental microscopic equations and then systematically derive the equations of multi-fluid and single fluid MHD.
I start from the Boltzmann equation and derive the equations of MHD as moment equations of the Boltzmann equation. The student will not end up with the wrong impression that MHD covers all of plasma physics. Facts are of not much use, considered as facts. They bewilder by their number and apparent incoherency.
Let them be digested in theory, however, and brought into mutual harmony, and it is another matter. Theory is the essence of facts. Without theory scientific knowledge would only be worthy of the mad house. Electromagnetic theory O. I decided to set this course in the framework of solar and space plasma physics and as- trophysics. Again this decision reflects a personal bias as my research is in solar physics and plasma astrophysics.
Again, I am convinced that this is a good choice. Although solar physics is the framework in which I want to set my course, I have refrained myself from concentrating on a description of plasma physics phenomena in solar physics and astrophysics. The reader should by now understand that the emphasis of this course is on basic concepts of plasma physics and on basic properties of plas- mas.
Observational facts are essential in sciences. However, in order to fully appreciate the observations of the complicated behaviour of plasmas, the reader should have learned first the basic concepts. This course gives a well-structured presentation of basic concepts and fundamental prin- ciples of plasma physics and MHD and paves the way to a wide variety of subjects where plasma physics plays an important role. Of course, once we have a well-defined mathematical theory for describing a plasma system, we need to show its strength by applying it to specific situations.
Why would we bother with the effort of setting up a mathematical model, if it were not for explaining observations and experiments. The fact that the reader sees that MHD does work, is a strong motivation for going through its sometimes tedious derivations. The fifth Chapter is dedicated to MHD waves in uniform and unbounded plasmas. In the sixth and last Chapter we use hydrodynamics and MHD to study the solar wind.
It is the only Chapter that deals exclusively with solar physics. The amount of mathematics and physics required for this course is limited. A knowledge of vector calculus, real calculus and electromagnetic theory are the modest prerequisites from mathematics and physics. I like to think that both students in applied mathematics and physics benefit from a course where by starting from basic principles and by using realistic approximations a mathematical model is constructed for a complicated physical system as a magnetic plasma.
This mathematical model contains all the information of the system under study within the limitations of the approximations. It can be used to explain observed behaviour and to predict future behaviour of the system. Unfortunately, the mathematical model equations are often not co-operative and it often requires hard work to extract information from them. The mathematics involved in this course is most of the time rather elementary. I am not worried about this elementary level of mathematics and physics. This is an introductory course with the emphasis on basic concepts.
In the last Chapter the mathematical model is applied to the solar wind. Here the mathematics is a little bit more advanced as we are required to solve non-linear ordinary differential equations. The theoretical analysis remains pretty straightforward, but the actual computation of the solutions turns out to be a tough problem of numerical mathematics. The exercises take a special place in this course. A first class of exercises invites the reader to fill in gaps in the often long derivation of equations.
In the Belgian educational system students do have to take exams. References What one man can invent another can discover. Sherlock Holmes, The Adventure of the Dancing Men Sir Arthur Conan Doyle The reader is advised to consult the following good textbooks in order to get some perception of what the present course has tried to teach him of the vast field of plasma physics and MHD.
Baumjohann and R. Goldston and P. Hazeltime and F. Polovin and V. Carovillano and J. Forbes, D. Reidel Publishing Company, Kibble and F. KB very helpful. Chapter 2 Basic plasma properties Like all other arts, the Science of Deduction and Analysis is one which can only be acquired by long and patient study, nor is life long enough to allow any mortal to attain the highest possible perfection in it.
Before turning to those moral and mental aspects of the matter which presents the greatest difficulties, let the enquirer begin by mastering more elementary problems. Sherlock Holmes, A study in Scarlet Sir Arthur Conan Doyle A plasma is an ionized gas that is in a state of electrical quasi-neutrality, the behaviour of which is governed by collective effects due to the long range electromagnetic interaction between the charged particles. In this Chapter we shall study the two basic characteristics that are used in the definition of a plasma : quasi-neutrality and collective behaviour.
We shall determine basic consequences arising from the long-range Coulomb interactions and we shall point out the necessity of taking into account the collective behaviour of many charged particles brought about by the long-range interactions. Plasma oscillations and Debye screening are typical examples of this collective behaviour; the plasma thus strongly exhibits a medium-like behaviour. We identify major plasma parameters that characterize the high- frequency behaviour associated with the dynamics of the electrons and the low-frequency behaviour associated with the dynamics of the ions.
Each charged particle creates its own microscopic electric and magnetic fields and reacts to the microscopic fields of all other particles. The actual electric and magnetic fields are the sum of all the microscopic contributions of the particles. These fields have an extremely complicated spatial structure and vary on different time scales. Solving the classic electromagnetic many-body problem for a plasma is a hopeless and hardly interesting task. It is hardly interesting because it would give us far more information than required. We are not interested in knowing the position and velocity of each individual particle at any given time.
Hence we replace the real plasma consisting of discrete particles with a smeared-out density distribution function in phase space.
This might be expected to be reasonable if each particle feels the effect of many other particles simultaneously and not just that of a few of its nearest neighbours. This is what happens when there are many particles in the Debye sphere, which we shall discuss in Sections 2. In analogy with the configuration space defined by the position coordinates x, y, z, it is convenient to consider the phase space defined by the six coordinates x, y, z, wx , wy , wz.
This is a finite element volume, sufficiently large to contain a large number of particles, yet sufficiently small in comparison with the characteristic lengths associated with the spatial variation of physical quantities as, for example, density and temperature. Also in an element of volume with very large velocity coordinates wx , wy , wz , the number of representative points has to be relatively small, since in any macroscopic system, there can only be relatively few particles with very large velocities.
The types of particles that occur in a plasmas are electrons, ions and also neutrals when the plasma is only partially ionized. When this is the case it is said to be nonuniform. When it is independent of position, the distribution function is uniform. The description of different plasmas requires the use of uniform and nonuniform, isotropic and anisotropic, time independent and time dependent distribution functions. Macroscopic quantities The distribution functions contain all the information on the system under study.
This temperature is the kinetic temperature, a quantity which we can formally calculate for any type of distribution function. Therefore it is not necessarily a true temperature in the thermodynamic sense, which can only be calculated for plasmas in or close to thermal equilibrium. This kinetic temperature is rather a measure for the spread of the particle distribution in velocity space. Moreover, because each particle species may have its own distribution function, the kinetic temperatures of the plasma components may differ from each other.
In addition, in an anisotropic plasma the temperatures parallel and perpendicular to the magnetic field are in general different, because the particle distributions have different dependencies in the parallel and perpendicular directions. When this equipartition is absent, it makes sense to define thermal velocities and temperatures in more than one direction.
They satisfy the global macroscopic Maxwell equations. It is left as an exercise to the reader to determine the elements of the matrix M. Recall that in the Boltzmann descrip- tion there are two types of forces that act on the particles. Second there are the collisions which are related to short-range forces on the length scale of the Debye sphere. For plasmas of astrophysical and fusion interest, the dominant collisions are elastic Coulomb collisions. The Boltzmann equation 2. Examples of distribution functions Let us now look at the equilibrium state of a system of particles that is free from external forces.
In the equilibrium state the particle interactions do not cause any change in the distribution function with time and there are no spatial variations in the particle number density.
The equilibrium distribution function is given by the Maxwell-Boltzmann distribution function:! The Maxwell-Boltzman distribu- tion function is time independent, uniform and isotropic. Whatever the velocity distribution of a system of particles initially not in equilibrium may be, it tends to the Maxwell-Boltzmann distribution 2.
The distribution function g wx andR also the Maxwell-Boltzmann R function 2. The Maxwell-Boltzmann function 2. The thermal velocity can be used to rewrite the Maxwell-Boltzmann function 2. The classic Maxwell-Boltzmann distribution 2. The Maxwell-Boltzmann distribution function 2. This is in sharp contrast with the ubiquitous presence of spatial and temporal variations in density, pressure and tempera- ture in nature. The assumption of full thermodynamic equilibrium has to be relaxed. Often we are dealing with a system of particles that, although not in equilibrium, is not very far from it.
It is then a good approximation to assume that, in the neighbourhood element of volume of any point in the system, there is an equilibrium situation described by a local Maxwell-Boltzmann distribution function. For larger spatial scales gradients of T may exist, but these scales are so large that, locally, the equilibrium is not perturbed. In addition, time variations of T may exist, but on such a slow time scale that instantaneous equilibrium is a very good approximation. The assumption of full thermodynamic equilibrium is replaced with local thermodynamic equilibrium LTE.
In a plasma we have at least two types of particles, electrons and ions. This means that under equilibrium conditions with no external forces present, in a volume sufficiently large to contain a large number of particles and yet sufficiently small compared with the characteristic lengths for variation of macroscopic quantities such as density and temperature, the net resulting electric charge is zero.
In the interior of the plasma the microscopic space charge fields cancel each other and no net space charge exist over a macroscopic region. Let us now see what electrical quasi-neutrality means by looking at what happens when there are deviations from charge neutrality in the plasma. The electrons and the ions are treated as interpenetrating fluids. We take the economic principle of minimal effort for maximal result as guideline and we use a very simple mathematical model for describing the plasma.
We hope that the relevant physics is contained in this mathematical model and that the physics that we leave out is unimportant. We assume that there are not any random thermal motions. This idealized system is referred to as a cold plasma. Here I am going to commit a major pedagogical crime. I am going to use the two-fluid equations for a plasma consisting of an electron and ion fluid although I shall derive these equations in the following Chapter. I know this is bad behaviour, but the other option is to start from the equation of motion for a single electron and to use intuitive geometric arguments.
Goossens, Marcel. Astrophysics and space science library v. A Look Inside Reviews. Being a well-written text on plasma physics with a strong bias towards astrophysics, it is highly recommended. This is a book produced specifically for university students, but which has relevance to a much wider potential readership. Dave Fearn "The book gives a general introduction to plasma astrophysics and magnetohydrodynamics, and discusses phenomena important for magnetic confinements of the plasma.
The main parts of the book include recapitulations and problems. This book may be useful to advanced graduate students and scientists who are working in other fields of physics. To find out how to look for other reviews, please see our guides to finding book reviews in the Sciences or Social Sciences and Humanities.
Main Description. Introductions of new species appear to be increasing and threaten native species and communities. The complexity of marine ecosystems challenges easy solutions to prevention, management, and control of introduced species. This book highlights issues of timely importance in marine bioinvasion science. Selected topics examine the potential evolutionary consequences of introduced organisms; examine the feasibility of biological control, and patterns of introductions. These papers were presented at the Second International Conference on Marine Bioinvasions that features new research and understanding of ecosystems and the impacts of invasions in the short- and long-term.
These papers should be of interest to scientists, students and managers with an interest in marine bioinvasions and the application of knowledge to management concerns. Most of the visible matter in the universe exists in the plasma state. Plasmas are of major importance for space physics, solar physics, and astrophysics. On Earth they are essential for magnetic controlled thermonuclear fusion. This textbook collects lecture notes from a one-semester course taught at the K. Leuven to advanced undergraduate students in applied mathematics and physics.