Lecture 3. INTRODUCTION TO PLASMA PHYSICS Lecture № 2. Basic concepts of chemical kinetics The subject of chemical kinetics. The rate of chemical reactions. The law of mass action. The rate constant of chemical reaction. Arennius equation. The internal energy of the molecule.

The object of plasma chemistry is a low-temperature plasma in molecular gases. Plasma chemistry studies the kinetics and mechanism of chemical reactions and physical-chemical processes in low-temperature plasmas. Chemistry Chemical kinetics Plasma-chemistry Physics Plasma Physics

Plasma is an ionized gas When a gas is heated enough that the atoms collide with each other and knock their electrons off in the process, a plasma is formed: the so-called ‘fourth state of matter’ Irving Langmuir, the Nobel laureate who pioneered the scientific study of ionized gases, gave this new state of matter the name ‘plasma’.

In any gas at non-zero absolute temperature some atoms are ionized, i In any gas at non-zero absolute temperature some atoms are ionized, i.e., along and neutral there are some charged particles - electrons and ions. However, a significant influence on the properties of the gas charged particles is made only at concentrations at which they create a space charge restricting their movement. Typical vertical distribution of electron density in the ionosphere for daytime and nighttime

Понятие плазмы. Plasma in Space In the plasma state is the vast majority of visible matter in the universe - stars, stellar atmospheres, galactic nebulae and the interstellar medium.

What is plasma? Plasma = quasi-neutral gas of charged particles gas crystal liquid gas plasma Thermonuclear 1 eV 10 eV 10 keV melting evaporation ionization Phase transition energy

Plasma types by electron density and temperature

Plasma = quasi-neutral gas of charged particles Coulomb interaction * Collective effects (cooperative particle motion) The difference between the properties of plasma and neutral gases is determined by two factors: First, the interaction between plasma particles are characterized by Coulomb forces of attraction and repulsion, which decreases with the distance much more slowly than the force of interaction of neutral particles.

The potential distribution around a charged particle in vacuum (1) and plasma (3).

Particles trajectories gas plasma

The difference between the properties of plasma and neutral gases is determined by two factors: Second, the electric and magnetic fields have a very strong effect on the plasma (while they are very weak in the neutral gas), giving a rise of the space charge in plasma.

The potential of a particle in plasma The potential distribution around a charged particle in vacuum (1) and plasma (3).

Classification of plasma 1 cm3 = 2.7 ∙ 1019 molecules

Classical plasma : Классическая и вырожденная плазма. The classical and degenerate plasmas Density: Temperature: T – plasma temperature in energy units m – electron mass p - electron momentum Classical plasma : "Quantum" scale- de Broglie wavelength "Plasma" scale- distance between the particles

Classical plasma : "Quantum" scale- de Broglie wavelength "Plasma" scale- distance between the particles Classical plasma :

Классическая и вырожденная плазма. Classical plasma a particle can be considered as a point charge Degenerate plasma There are quantum-mechanical effects AT the average electron energy of 1 eV the de Broglie wavelength scale is 10-8 cm (1Ǻ), i.e. an order of an atom dimensions. At plasma concentrations below 1019 cm-3 the distance between particles d ~ 3 ∙ 10-6 cm and a lot more than the de Broglie wavelength. 1 cm3 = 2.7 ∙ 1019 molecules Therefore the plasma obeys the Maxwell-Boltzmann statistics

Ideal and nonideal plasma Идеальная и неидеальная плазма. Ideal and nonideal plasma Ideal Nonideal plasma. Plasma electrons is Fermi-gas Fermi energy

The condition of ideality of the plasma can be expressed as the number of particles in a volume with a diameter equal to the Debye radius ND. This number must be much greater than 1. An amount equal to 1/ND, is taken a plasma coupling parameter.

Е=0 Debye shielding Plasma is quasi-neutral We will consider the classical ideal plasma Debye shielding Plasma is quasi-neutral How long the plasma is quasineutral? Е=0

Е When does a plasma remain its quasi-neutrality? ? l Debye length(radius) Е

The electrons flying out of the plasma violate its quasi-neutrality on a length of order of the Debye shielding rD and enhance the potential of plasma (ni, and ne -, the density of ions and electrons, respectively).

Debye length is the spatial scale at which the charge separation occur Plasma oscillation Debye length is the spatial scale   at which the charge separation occur Time scale: x Forth Е

Any charge separation in the plasma leads to the fluctuations in charge density. On average, over many periods of oscillation plasma behaves as a quasi-neutral. Lets consider the electrons motion after the neutrality is destroyed. In the region of an electron layer the electron experiences a force of attraction to ions, which is equal to It describes harmonic oscillations with a frequency

Fluctuations in the space charge the neutrality is violeted were first discovered by Langmuir. They are called plasma, or Langmuir oscillations. Frequency ωp is called a plasma frequency ωp =5.6·104·(ne)0.5, Hz at ne in cm-3

2. Low-temperature plasma Т < 10 000 К 3. Ideal plasma Weakly ionized plasma α < 0.01 2. Low-temperature plasma Т < 10 000 К 3. Ideal plasma Coulomb interaction of particles Kinetic energy of particles Classical plasma A particle can be considered as a point charge For weakly ionized plasma the electron mean free path when they interact with the plasma ions is greater than the mean free path for interaction with neutral particles, α <0.01. It is such a plasma which is used in most plasma-devices.

The ionization equilibrium constant Let ionization occurs by electron impact, and recombination though triple collisions. From the law of mass action it follows that the ionization rate is proportional to the concentration of neutral atoms and free electrons vi = k1·na·ne. Recombination rate vr = k2·ni·n2e, where nа, ni, ne— concentration of atoms, ions and electrons, respectively. The coefficients k1 and k2 (rate constants) are the functions of temperature, but do not depend on concentration. In the steady state rate of the forward and reverse processes must be equal, k1·na·ne = k2·ni·n2e, From which K is called the equilibrium constant

Степень ионизации. Формула Саха Thus, the general form of the condition of equilibrium ionization is A special case of this dependence for an ideal plasma is the Saha equation.

Степень ионизации. Формула Саха

Recommended textbooks: Introduction to Plasma Physics: R.J. Goldston, and P.H. Rutherford (The University of Texas at Austin) Lectures on Plasma Physics: Professor of physics Richard Fitzpatrick (Cambridge University Press, Cambridge UK, 1994).