Ionization coefficient

FIG. 25. Simulation results for quasi-Townsend discharges (a) ionization coefficients for SiHa, H2, and Ar (b) attachment coefficients for SiHa and CFa-... 

Unger, S. H. Cook, J. R. Hollenberg, J. S., Simple procedure for determining octanol-aqueous partition, distribution, and ionization coefficients by reverse-phase high-pressure liquid chromatography, J. Pharm. Sci. 67, 1364—1366 (1978). 

In order to achieve breakdown, electrons (either from the air or from the body) must be accelerated to a sufficient velocity to ionize the air and breed more electrons by any one of several processes. In an actual gas, however, some of the kinetic energy of the electrons is lost in collisions with air molecules without resulting in ionization. This combined effect has been expressed in terms of the Townsend ionization coefficient. As a body becomes smaller, its curvature increases and the electric field intensity drops off more rapidly with distance from the surface consequently, to accelerate electrons a given amount, the body surface field intensity must be higher than for a flat surface. Actually, because of increased attenuation resulting from the increased distance that an electron must travel through air to achieve a given acceleration, the required surface intensity must increase even faster. 

No attempts to calculate those limiting surface field intensities or gradients for small particles have been reported in the literature. However, point-to-plane corona has been studied in detail. Loeb (L8) has proposed a method for calculating positive corona threshold limits making use of established values of the Townsend first ionization coefficient. Loeb s threshold formula is... 

Unger, S.H., Cook, J.R., and Hollenberg, J.S. Simple procednre for determining octanol-aqneons partition, distribntion, and ionization coefficients by reversed-phase high pressnre liqnid chromatography, J. Pharm. Sci., 67(10) 1364-1366, 1978. Ungnade, H.E. and McBee, E.T. The chemistry of perchlorocyclopentadienes and cyclopentadienes, Chem. Rev., 58(2) 249-320, 1957. 

This equation describes the change of the density na as a result of ionization and recombination of bound pairs, the density of which is denoted by n(12). For this reason we call a the ionization coefficient, given by (na = nb = nc)... 

To describe the efficiency of ion formation, it is useful to define two parameters, the degree of ionization and the ionization coefficient. These are defined as follows ... 

J. Schwarz, P. Rambo, J. C. Diels, Measurements of multiphoton ionization coefficients with ultrashort ultraviolet pulses, Applied Physics B 72, 343-347 (2001)... 

Fig. 18.1. Series 4 concerns the ground and metastable populations of ions in a plasma and their preparation and calculation for dynamical plasma models. It operates with GCR recombination and ionization coefficients, associated power loss coefficients and metastable fractions. The scope of series 4 is quite large extending into short wavelength filters modifying observed radiative power, astrophysical contribution function generation and parametrization of ionization and recombination...

Ionization is treated analogously. It is described in terms of the ionization coefficient, / , which is the ratio of free electrons produced per vaporized atom. The number of free electrons per meter, q, is given by Refs. 29 and 30 ... 

From an analysis of 6000 meteors by radio echo techniques, Verniani concluded that the mean velocity was 34 km/s, and that their mean mass was 10" g. Verniani also found that the velocity distribution of the meteors shifted with meteor mass distribution. The physics of radar scatter from meteor trails extracts the ionization coefficient, Eq. (5), from the observed echo intensities and associated electron densities. More recent analysis of the ionization trails of meteors has indicated a slightly different expression than Eq. (6) for the ionization coefficient associated with faint, low velocity (< 35 km s ), radio meteors, namely (3 = 9.4 x 10" (u - 10) u , where v is in km s". The magnitude and velocity dependence of (3 remains a major puzzle. It must be noted that the calculations assume no chemical reactions in the trail this assumption is needed to make the calculations tractable and because many of the reaction cross sections are not known. Collision processes leading to ionization are discussed in Secs. 3.2.2 and 3.4. 

In Fig. 5, the relationship between the Townsend ionization coefficients (ion pair production) for air at atmospheric pressure at different temperatures and field strengths is given. 

Unger, S.H., J. Cook and J. Hollenberg, "Simple Procedure for Determining Octa-nol-Aqueous Partition, Distribution, and Ionization Coefficients by Reversed-Phase High-Pressure Liquid Chromatography, /. Pharm. Sci., 67, 1364-67 (1978). 

On the one hand, the cross sections that are derived from swarm data cannot be expected to possess the accuracy and detailed structure of good beam measurements or ab initio calculations, but, on the other hand, they naturally produce (if the procedure is carried out well) cross-section sets that accurately reproduce the macroscopic observables that are relevant to real plasmas. Such quantities are drift velocities or mobilities, which are directly connected with the power deposition in a discharge plasma, diffusion coefficients, and attachment and ionization coefficients, which are intimately related to the ionization balance of a plasma. These are the quantities that are used directly in most plasma models and that are measured in laboratory plasmas. 

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