Weakly ionized plasma electrons

A major point of importance is that the electron energy balance, and therefore the average electron energy, in weakly ionized plasmas is independent of electron density. As a consequence, the energy balance can be treated on a per electron basis. From equation (15) the total power density can be established by multiplying by the product of electron and neutral densities. 

The problems involved in modelling weakly ionized plasmas in molecular gases, operated at pressures below about 100 mbar and with average electron energies in the range 0.5—3 eV, are typically those of non-equilibrium systems. 

One notices that 1) all processes start from the ground vibro-electronic state of H2. 2) rotational excitation and thermalization effects of electron- electron interactions have not been included. In fact rotational excitation is important at values of the reduced field E/N lower than those considered in the calculations and electron-electron interactions can be neglected in weakly ionized plasmas (ionization degree Zi 10 5). 

THE BOLTZMANN EQUATION AND TRANSPORT COEFFICIENTS OF ELECTRONS IN WEAKLY IONIZED PLASMAS... 

Weakly ionized plasmas are complex systems involving several interacting particle components. In the simplest case, they consist largely of unexcited atoms, i.e., neutral gas particles, and to a lesser extent of electrons and positive ions. 

The electrons in weakly ionized plasmas generally undergo two basic impacts, namely, the action of an electric (and possibly of an additional magnetic) field and the interaction with heavy particles in binary elastic and inelastic collisions (Desloge, 1966 Shkarofsky et al., 1966 Golant et al, 1980). 

The different microphysical processes—the field action and the various binary collision processes—in which the electrons are involved in a weakly ionized plasma lead to a complex redistribution of the electrons in their phase space, i.e., their combined coordinate and velocity space. 

To illustrate the behavior of electron kinetic quantities in steady-state conditions, weakly ionized plasmas in neon and molecular nitrogen are considered as typical representatives of atomic and molecular gas plasmas. 

By the preceding representations, an attempt has been made to give, on the basis of the electron Boltzmann equation, an introduction to the kinetic treatment of the electron component in steady-state, time-dependent, and space-dependent plasmas and to illustrate by selected examples the large variety of electron kinetics in anisothermal weakly ionized plasmas. 

The Boltzmann Equation and Transport Coefficients of Electrons in Weakly Ionized Plasmas, R. Winkler... 

The temperatiue difference between electrons and heavy neutral particles due to Joule heating in the collisional weakly ionized plasma is conventionally proportional to the sqirare of the ratio of the electric field ( ) to the pressure p). Only in the case of small values of E/p do the temperatiues of electrons and heavy particles approach each other. Thus, this is a basic requirement for local thermodynamic equilibrium (LTE) in plasma. Additionally, LTE conditions require chemical equilibrium as well as restrictions on the gradients. The LTE plasma follows the maj or laws of equilibrium thermodynamics and canbe characterized by a single temperature at each point of space. Ionization and chemical processes in such plasmas are determined by temperature (and only indirectly by the electric fields through Joule heating). The quasi-equilibrium plasma of this kind is usually called thermal plasma. Thermal plasmas in nature canbe represented by solar plasma (Fig. 1-4). 

Although the relationship between different plasma temperatures in non-thermal plasmas canbe quite sophisticated, it canbe conventionally presented in the collisional weakly ionized plasmas as > E > E Ti Tq. Electron temperature (Te) is the highest in the system, followed by the temperature of vibrational excitation of molecules (TV). The lowest temperature is usually shared in plasma by heavy neutrals (To, temperature of translational... 

Second, in the collision term only electron-neutral collisions are considered, because RF plasmas are weakly ionized. The inelastic collisions considered are ionization, dissociation, excitation, and attachment (see also Table II). The crude... 

Investigations on the doubly excited states of two electron systems under weakly coupled plasma have been performed by several authors. Such states usually occur as resonance states in electron atom collisions and are usually autoionizing [225]. Many of these states appear in solar flare and corona [226,227] and contribute significantly to the excitation cross-sections required to determine the rate coefficients for transitions between ionic states in a high temperature plasma. These are particularly important for dielectronic recombination processes which occur in low density high temperature plasma, occurring e.g. in solar corona. Coronal equilibrium is usually guided by the balance between the rates of different ionization and... 

Typical low-temperature plasmas are usually only weakly ionized and quasineutral but are thermally in a non-equilibrium state, i.e. the different plasma species (molecules, atoms, ions and electrons) possess different kinetic energy distributions. Because of their small mass electrons acquire much more kinetic energy than atomic or molecular species and thus show an energy distribution which corresponds to a much higher temperature than in the case of much heavier particles. The stability of ionic liquids towards reduction by these hot electrons... 

Thus, we examine a single spherical grain of a radius a imbedded in a weakly ionized high pressure gas. In this case, it is natural to use the drift-diffusion (DD) approach, because collisions of plasma particles with neutrals play here a dominant role. Assuming two types of plasma particles (ions and electrons) only, we write the general time-dependent equations for the unknown ion/electron densities ri-Le and self-consistent potential < > in the form,... 

In a weakly ionized low-temperature plasma, various molecular species are abundantly generated either directly or indirectly as a consequence of electron collisions with molecules, and many of the molecular species readily react with other species. For this reason, one sometimes calls such a plasma chemically reactive. Applications of chemically reactive plasmas are widespread over organic and inorganic materials, in part because of the relatively low cost of generating of such plasmas. The large variety of chemically active species generated in a plasma is sometimes a disadvantage because they may initiate many reaction pathways, which may be difficult to analyze and to control. 

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