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1、Space plasma physics Basic plasma properties and equations Space plasmas, examples and phenomenology Single particle motion and trapped particles Collisions and transport phenomena Elements of kinetic theory Fluid equations and magnetohydrodynamics Magnetohydrodynamic waves Space plasma physics Boun
2、daries, shocks and discontinuities Plasma waves in the fluid picture I Plasma waves in the fluid picture II Fundamentals of wave kinetic theory Concepts of plasma micro- and macroinstability Kinetic plasma microinstabilities Wave-particle interactions Basic plasma properties and equations Definition
3、 of a plasma Space plasmas - phenomenology Parameters Currents and charge densities Composition and ionization Maxwells equations and forces Induction equation Definition of a plasma A plasma is a mixed gas or fluid of neutral and charged particles. Partially or fully ionized space plasmas have usua
4、lly the same total number of positive (ions) and negative (electrons) charges and therefore behave quasineutral. Space plasma particles are mostly free in the sense that their kinetic exceeds their potential energy, i.e. they are normally hot, T 1000 K. Space plasmas have typically vast dimensions,
5、such that the free paths of thermal particles are larger than the typical spatial scales they are collisionless. Different types plasmas Plasmas differ by their chemical composition and the ionization degree of the ions or molecules (from different sources). Plasmas are mostly magnetized (internal a
6、nd external magnetic fields). Solar interior and atmosphere Solar corona and wind (heliosphere) Planetary magnetospheres (plasma from solar wind) Planetary ionospheres (plasma from atmosphere) Coma and tail of a comet Dusty plasmas in planetary rings Schematic topography of solar-terrestrial environ
7、ment solar wind - magnetosphere - iononosphere Different plasma states Plasmas differ by the charge, ej, mass, mj, temperature, Tj, density, nj, bulk speed Uj and thermal speed, Vj=(kBTj/mj)1/2 of the particles (of species j) by which they are composed. Long-range (shielded) Coulomb potential Collec
8、tive behaviour of particles Self-consistent electromagnetic fields Energy-dependent (often weak) collisions Reaction kinetics (ionization, recombination) Variable sources (pick-up) Debye shielding The mobility of free electrons leads to shielding of point charges (dressed particles) and their Coulom
9、b potential. The exponential function cuts off the electrostatic potential at distances larger than Debye length, D, which for ne = ni and Te = Ti is: The plasma is quasineutral on large scales, L D, otherwise the shielding is ineffective, and one has microscopically a simple ionized gas. The plasma
10、 parameter (number of particles in the Debye sphere) must obey, = ne D3 1, for collective behaviour to prevail. Ranges of electron density and temperature for geophysical plasmas Some plasmas, like the Suns chromosphere or Earths ionosphere are not fully ionized. Collisions between neutrals and char
11、ged particles couple the particles together, with a typical collision time, n, say. Behaviour of a gas or fluid as a plasma requires that: pen 1 Specific plasma parameters Coulomb force - space charge oscillations Lorentz force - gyration about magnetic field Any perturbation of quasineutrality will
12、 lead to electric fields accelerating the light and mobile electrons, thus resulting in fast collective motions - plasma oscillations around the inert and massive ions at the plasma frequency: The Lorentz force acts perpendicularly to the magnetic field and bends the particle motion, thus leading to
13、 circulation (electrons in clockwise, and ions in anti- clockwise sense) about the field - gyromotion at the gyro- or cyclotron frequency: Theoretical descriptions of a plasma Plasma dynamics is governed by the interaction of the charged particles with the self-generated (by their motions through th
14、eir charge and current densities) electromagnetic fields. These internal fields feed back onto the particles and make plasma physics difficult. Single particle motion (under external fields) Magnetohydrodynamics (single fluid and Maxwells equations) Multi-fluid approach (each species as a separate f
15、luid) Kinetic theory (Vlasov-Boltzmann description in terms of particle velocity distribution functions and field spectra) Electromagnetic field (Maxwells) equations The motion of charged particles in space in strongly influenced by the self-generated electromagnetic fields, which evolve according t
16、o Amperes and Faradays (induction) laws: where 0 and 0 are the vacuum dielectric constant and free-space magnetic permeability, respectively. The charge density is and the current density j. The electric field obeys Gauss law and the magnetic field is always free of divergence, i.e. we have: Electromagnetic forces
