Akihide Takeda

Comparison of electron diffusion coefficients defined in velocity and position spaces DV and DT in CF4

The transverse diffusion coefficient D T and the conventional expression D V for electrons in CF 4 are compared. The ratio of D V and D T reaches 6 at the maximum. The cause of such large differences between D V and D T are discussed from their definitions and also in relation to the cross sections of CF 4 . When inelastic collisions make the velocity distribution highly anisotropic, D V defined in velocity space is not appropriate to use in place of D T even as an approximate expression.

Spatially Resolved Electron Swarm Behavior in Steady State Townsend Condition

Spatially resolved electron transport properties in steady state (SST) under the uniform electric field are investigated. It is found that the balance of local energy gain and loss always holds by taking into account the divergence of the energy flow, that is, the energy conservation law and the continuity equation of the energy flow for an electron swarm are affirmed to hold with the numerical data. Further, the features of the electron flux and the energy flow, the effects of ionization, excitation and attachment on the formation of the energy distribution, the condition forming the equilibrium and non-equilibrium regions in conservative and non-conservative cases for the electron number due to ionization and attachment etc. are discussed in detail.

Analyses of Spatially Resolved Electron Energy Distribution and Transport Properties in Steady State in CF4.

Under homogeneous electrostatic field in gas between two plane electrodes, the electron energy distribution and transport properties near the electrodes are usually position dependent. Boltzmann equation analyses for such position dependent energy distribution and transport properties in steady state are very few due to its difficulty. In this paper, position dependent electron behaviors in CF 4 calculated using the Steady State Townsend flight time integral method (SST-FTI) for several boundary conditions are presented with the theory of the SST-FTI.

Mobility Analysis of Electrons in CF4 by FTI Method

Due to large cross sections for vibrational excitation which sharply rise in the bottom region of the Ramsauer minimum, electrons in CF 4 in low reduced electric fields E/N show particular transport properties. The transport property and velocity distribution of electrons in CF 4 are analysed using the FTI method of the authors over a wide range of E/N from 0.1 to 50 Td. The mobility, drift velocity and the negative differential conductivity are discussed with the flight behavior of electrons regarding the variation of elastic and inelastic collision frequencies with energy.

Transport Characteristics of Electron Swarm in Model Ramsauer Gases under Electric Field

Energy distribution and transport coefficients of an electron swarm in model Ramsauer gases under an electric field are calculated using a new procedure “Flight time integral” (FTI) method. Electron energy distributions and transport related quantities change remarkably depending on the shapes of the Ramsauer valley and of the excitation cross section, but the changes are well understood from the electron flight behaviour around the valley. Electron transport property mainly depends on the width of the Ramsauer valley but not on the depth. It is made apparent that the well known formulae for transport coefficients sometimes give erroneous values since these formulae are written by instantaneous probabilities for the transport.

Irreversible Relaxation of Velocity Distribution of Gas Particles through Collisions

The relaxation of the velocity distribution of gas particles proceeds only through collisions. The velocity dispersion probabilities through a collision draws the irreversible relaxation property clearly. The gas particles finally settle in the Maxwellian velocity distribution in which the energy exchange a collision is the maximum. The motive force to settle the gas particles in the Maxwellian velocity distribution is discussed with related problems.

Effect of anisotropic scattering on the electron transport properties in CF4 gas

The effects of anisotropy in scatterings in both elastic and inelastic collisions on the electron transport properties in CF 4 gas have been examined using the extended FTI (flight time integral) method over a wide E / N range from 0.1 to 50 Td. Here, E and N are the electric field and the gas density, respectively and 1 Td is 1×10 -17 Vcm 2 . In this analysis, the differential cross section q ( e , χ)= q 0 ( e )(1+ a cos χ), where χ is the scattering angle, is used. The effect of forward scattering with a positive value of “a” positively appears as the increase of drift velocity W particularly in the E / N range of highly anisotropic velocity distribution.

Effects of Model Anisotropies in Elastic and Inelastic Scatterings on the Electron Transport Properties in CF 4

In order to understand the effects of anisotropic scatterings on the electron transport properties, a trajectory analysis using extended FTI method has been performed in CF 4 . A model anisotropy in the form g (χ)=1+ a ·cos χ with adjustable parameter “ a ” is assumed in each of elastic and inelastic scatterings. A clear correspondence has been found between the fractional changes of transport properties due to anisotropies in elastic and inelastic scatterings and the anisotropy in the velocity distribution of electrons in flight.

Relaxation Properties of the Velocity Distribution of Gas Particles and the Variation of H Function.

Temporal relaxation properties of the velocity distribution of small amount gas A of mass m A injected into ambient gas B of mass m B in thermal equilibrium at temperature T B are investigated with...

Comparison of Procedures for Obtaining Electron Transport Properties by Traditional and Flight Time Integral Methods

Procedures for obtaining the transport properties of electrons in gas under a uniform electric field by traditional methods are compared with those by the flight time integral (FTI) method such that they conform to the two comment papers on the FTI method given by Kumar and Robson in 1995. The most important difference between traditional and FTI methods is that the starting rate distribution Ψ s ( v 0 ) is adopted in FTI as the principal unknown function instead of the velocity distribution in flight f ( c ), which has always been used in traditional theories. The use of Ψ s ( v 0 ) has advantages not only in the possibility of obtaining accurate transport coefficients but also in providing a deeper understanding of them based on the full flight data of electrons.