Part VPLASMA PHYSICS1ContentsV PLASMA PHYSICS 119 The Particle Kinetics of Plasma 119.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119.2 Examples of Plasmas and their Density-Temperature Regimes . . . . . . . . 319.2.1 Ionization boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . 319.2.2 Degeneracy boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . 319.2.3 Relativistic boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . 519.2.4 Pair production boundary . . . . . . . . . . . . . . . . . . . . . . . . 519.2.5 Examples of natural and man-made plasmas . . . . . . . . . . . . . . 519.3 Collective Effects in Plasmas – Debye Shielding and Plasma Oscillations . . . 719.3.1 Debye Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719.3.2 Collective behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819.3.3 Plasma Oscillations and Plasma Frequency . . . . . . . . . . . . . . . 919.4 Coulomb Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019.4.1 Collision frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019.4.2 The Coulomb logarithm . . . . . . . . . . . . . . . . . . . . . . . . . 1219.4.3 Thermal Equilibration Times in a Plasma . . . . . . . . . . . . . . . 1219.4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1419.5 Transport Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1619.5.1 Anomalous Resistivity and Anomalous Equilibration . . . . . . . . . 1719.6 Magnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919.6.1 Cyclotron frequency and Larmor radius. . . . . . . . . . . . . . . . . 1919.6.2 Validity of the Fluid Approximation. . . . . . . . . . . . . . . . . . . 2 019.6.3 Conductivity Tensor . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 219.7 Adiabatic Invariants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2419.7.1 Homogeneous, time-independent magnetic field . . . . . . . . . . . . 2419.7.2 Homogeneous time-independent electric and magnetic fields . . . . . 2419.7.3 Inhomogeneous, time-independent magnetic field . . . . . . . . . . . . 2519.7.4 A slowly time varying magnetic field . . . . . . . . . . . . . . . . . . 282Chapter 19The Particle Kinetics of P lasmaVersion 0619.1.K.pdf, March 28, 2007.Please send comments, suggestions, and errata via email to [email protected] or on paperto Kip Thorne, 130-33 Caltech, Pasad ena CA 9112 5Box 19.1Reader’s Guide• This chapter relies significantly on portions of nonrelativistic kinetic theory as de-veloped in Chap. 2.• It also relies a bit but not greatly on portions of magnetohydrodynamics as devel-oped in Chap. 18.• The remaining chapters 20-22 o f Part V, Plasma Physics rely heavily on this chap-ter.19.1 Overvie wA plasma is a gas that is significantly ionized (through heating or photoionization) and thusis composed of electrons and ions, and that has a low enough density to behave classically,i.e. to obey Maxwell-Boltzmann statistics rather than Fermi-Dirac or Bose-Einstein. Plasmaphysics originated in the nineteenth century, in the study of gas discharges (Crookes 1879).However, it was soon realised that plasma is also the key to understanding the propagationof radio waves across the Atlantic (Heaviside 1902). The subject received a further boost inthe early 1950s, with the start of the cont rolled (and the uncontrolled) thermonuclear fusionprogram. The various confinement devices described in the preceding chapter are intendedto hold plasma at temperatures as high as ∼ 108K; the difficulty of this task has turnedout to be an issue of plasma physics as much as MHD. After fusion, the next new venue forplasma research wa s extraterrestrial. Although it was already understood that the Earth12was immersed in a tenuous outflow of ionized hydrogen known as the solar wind, the dawnof the space age in 1957 also initiated experiment al space plasma physics. More recently, theinterstellar and intergalactic media beyond the solar system as well as exotic astronomicalobjects like quasars and pulsars have allowed us to observe plasmas under quite extremeconditions, unreproducible in any laboratory experiment.The dynamical behavior of a plasma is more complex than the dynamics of the gases andfluids we have met so far. This dynamical complexity has two main origins:(i) The dominant form of int erparticle interaction in a plasma, Coulomb scattering, isso weak that the mean free paths of the electrons and ions are often larger than theplasma’s macroscopic length scales. This allows the particles’ momentum distribu-tion functions to deviate seriously from their equilibrium Maxwellian forms and, inparticular, to be highly anisotropic.(ii) The electromagnetic fields in a plasma are of long range. This allows charged particlesto couple to each other electromagnetically and act in concert as modes of excitation(plasma waves or plasmons) that behave like single dynamical entities. Much of plasmaphysics consists of the study of the properties and interactions of these modes.The dynamical behavior of a plasma depends markedly on frequency. At the lowest offrequencies the ions and electrons are locked together by electrostatic forces and behavelike an electrically conducting fluid; this is the regime of magnetohydrodynamics (MHD;Chap. 18). At somewhat higher frequencies the electrons and the ions can move relative toeach …
View Full Document
Unlocking...