1629373397-425d4de58b7aea127ffc7c337418ea8d (Introduction to Plasma Physics and Controlled Fusion Francis F. Chen), страница 3

. . . . . . . . . . . . . . . . . . . .Equations of Nonlinear Plasma Physics . . . . . . . . . . . . . . . . . .8.8.1The Korteweg–de Vries Equation . . . . . . . . . . . . . . . .8.8.2The Nonlinear Schr€odinger Equation . . . . . . . . . . . . . .Reconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . .Turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Sheath Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2812822822842872872882912932952983013043073073123223243299Special Plasmas . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .9.1Non-Neutral Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.1.1Pure Electron Plasmas . . . . . . . . . . . . . . . . . . . . . . . . .9.1.2Experiments . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .9.2Solid, Ultra-Cold Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.3Pair-ion Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.4Dusty Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.4.1Dust Acoustic Waves . . . . . . . . . . . . . . . . . . .

. . . . . .9.4.2Dust Ion-acoustic Waves . . . . . . . . . . . . . . . . . . . . . . .9.5Helicon Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.6Plasmas in Space . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .9.7Atmospheric-Pressure Plasmas . . . . . . . . . . . . . . . . . . . . . . . . .9.7.1Dielectric Barrier Discharges . . . . . . . . . . . . . . . . . . . .9.7.2RF Pencil Discharges . . . . . . . . . . . . . . . . . . . . . . . . .33333333333433533733934234434634935035135210Plasma Applications . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.2 Fusion Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. .10.2.1 Magnetic Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.3 Plasma Accelerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.3.1 Free-Electron Lasers . . . . . . . . . . . . . . . . . . . . . . . . . .10.4 Inertial Fusion . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.4.1 Glass Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.4.2 KrF Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3553553563563863923933933998.48.58.68.78.88.98.108.11xiiContents10.510.6Semiconductor Etching . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .Spacecraft Propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10.6.1 General Principles . . . . . . . . . . . . . . . . . . . . . . . . . . .10.6.2 Types of Thrusters . . . . . . . . . . . . . . . . . . . . . . . . . . .Plasmas in Everyday Life .

. . . . . . . . . . . . . . . . . . . . . . . . . . .399405405407411Erratum to: Introduction to Plasma Physics and ControlledFusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E110.7Appendix A: Units, Constants and Formulas, Vector Relations . . . . .

. . 413Appendix B: Theory of Waves in a Cold Uniform Plasma . . . . . . . . . . . 417Appendix C: Sample Three-Hour Final Exam . . . . . . . . . . . . . . . . . . . . 423Appendix D: Answers to Some Problems . . . . . . . . . . . . . .

. . . . . . . . . . 429Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485The original version of this book was revised. An erratum to this book can be found at https://doi.org/10.1007/978-3-319-22309-4_11Chapter 1Introduction1.1Occurrence of Plasmas in NatureIt is now believed that the universe is made of 69 % dark energy, 27 % darkmatter, and 1 % normal matter. All that we can see in the sky is the part of normalmatter that is in the plasma state, emitting radiation. Plasma in physics, not to beconfused with blood plasma, is an “ionized” gas in which at least one of theelectrons in an atom has been stripped free, leaving a positively charged nucleus,called an ion.

Sometimes plasma is called the “fourth state of matter.” When asolid is heated, it becomes a liquid. Heating a liquid turns it into a gas. Uponfurther heating, the gas is ionized into a plasma. Since a plasma is made of ionsand electrons, which are charged, electric fields are rampant everywhere, andparticles “collide” not just when they bump into one another, but even at adistance where they can feel their electric fields.

Hydrodynamics, which describesthe flow of water through pipes, say, or the flow around boats in yacht races, or thebehavior of airplane wings, is already a complicated subject. Adding the electricfields of a plasma greatly expands the range of possible motions, especially in thepresence of magnetic fields.Plasma usually exists only in a vacuum.

Otherwise, air will cool the plasma sothat the ions and electrons will recombine into normal neutral atoms. In thelaboratory, we need to pump the air out of a vacuum chamber. In the vacuum ofspace, however, much of the gas is in the plasma state, and we can see it. Stellarinteriors and atmospheres, gaseous nebulas, and entire galaxies can be seen becausethey are in the plasma state. On earth, however, our atmosphere limits our experience with plasmas to a few examples: the flash of a lightning bolt, the soft glow ofthe Aurora Borealis, the light of a fluorescent tube, or the pixels of a plasma TV.

Welive in a small part of the universe where plasmas do not occur naturally; otherwise,we would not be alive.© Springer International Publishing Switzerland 2016F.F. Chen, Introduction to Plasma Physics and Controlled Fusion,DOI 10.1007/978-3-319-22309-4_1121 IntroductionThe reason for this can be seen from the Saha equation, which tells us the amountof ionization to be expected in a gas in thermal equilibrium:niT 3=2 Ui =KTe 2:4 1021ninnð1:1ÞHere ni and nn are, respectively, the density (number per m3) of ionized atoms andof neutral atoms, T is the gas temperature in K, K is Boltzmann’s constant, and Uiis the ionization energy of the gas—that is, the number of joules required to removethe outermost electron from an atom. (The mks or International System of units willbe used in this book.) For ordinary air at room temperature, we may takenn 3 1025 m3 (see Problem 1.1), T 300 K, and Ui ¼ 14.5 eV (for nitrogen),where 1 eV ¼ 1.6 1019 J.

The fractional ionization ni/(nn + ni) ni/nn predictedby Eq. (1.1) is ridiculously low:ni 10122nnAs the temperature is raised, the degree of ionization remains low until Ui is only afew times KT. Then ni/nn rises abruptly, and the gas is in a plasma state. Furtherincrease in temperature makes nn less than ni, and the plasma eventually becomes fullyionized.

This is the reason plasmas exist in astronomical bodies with temperatures ofmillions of degrees, but not on the earth. Life could not easily coexist with a plasma—at least, plasma of the type we are talking about. The natural occurrence of plasmas athigh temperatures is the reason for the designation “the fourth state of matter.”Although we do not intend to emphasize the Saha equation, we should point outits physical meaning. Atoms in a gas have a spread of thermal energies, and an atomis ionized when, by chance, it suffers a collision of high enough energy to knock outan electron. In a cold gas, such energetic collisions occur infrequently, since an atommust be accelerated to much higher than the average energy by a series of “favorable” collisions.

The exponential factor in Eq. (1.1) expresses the fact that thenumber of fast atoms falls exponentially with Ui /KT. Once an atom is ionized, itremains charged until it meets an electron; it then very likely recombines with theelectron to become neutral again. The recombination rate clearly depends on thedensity of electrons, which we can take as equal to ni. The equilibrium ion fraction,therefore, should decrease with ni; and this is the reason for the factor ni1 on theright-hand side of Eq. (1.1).

The plasma in the interstellar medium owes its existenceto the low value of ni (about 1 per cm3), and hence the low recombination rate.1.2Definition of PlasmaAny ionized gas cannot be called a plasma, of course; there is always some smalldegree of ionization in any gas. A useful definition is as follows:A plasma is a quasineutral gas of charged and neutral particles which exhibitscollective behavior.1.2 Definition of Plasma3Fig.

1.1 Illustrating the long range of electrostatic forces in a plasmaWe must now define “quasineutral” and “collective behavior.” The meaning ofquasineutrality will be made clear in Sect. 1.4. What is meant by “collectivebehavior” is as follows.Consider the forces acting on a molecule of, say, ordinary air. Since the moleculeis neutral, there is no net electromagnetic force on it, and the force of gravity isnegligible. The molecule moves undisturbed until it makes a collision with anothermolecule, and these collisions control the particle’s motion. A macroscopic forceapplied to a neutral gas, such as from a loudspeaker generating sound waves, istransmitted to the individual atoms by collisions.