scholarly journals Computer Simulation of an Electron Swarm at low E/p in Helium

1974 ◽  
Vol 27 (1) ◽  
pp. 59 ◽  
Author(s):  
AI McIntosh
Keyword(s):  
Computer Simulation ◽  
Diffusion Coefficient ◽  
Cross Section ◽  
Electron Energy Distribution Function ◽  
Recent Theory ◽  
Electron Drift ◽  
Longitudinal Diffusion ◽  
Transverse Diffusion ◽  
And Diffusion ◽  
Momentum Transfer Cross Section

A computer simulated electron swarm at E/P293 = 1�0 V cm -1 tore 1 in a model gas has been used to examine the validity of a recent theory of electron drift and diffusion. The computed results are in agreement with well-established theories for the electron energy distribution function, drift velocity and transverse diffusion coefficient, and confirm that, for a constant momentum transfer cross section, the longitudinal diffusion coefficient is approximately half the transverse coefficient. However, significant differences have been found between the computed swarm and the predictions of the theory of Huxley (1972). In particular, over the time scale considered, the electron swarm is not symmetric about its centroid but is spatially anisotropic in such a way that it could appropriately be described as 'pear shaped'.

scholarly journals Drift Velocity and Longitudinal Diffusion Coefficient of Electrons in CO2?Ar Mixtures and Electron Collision Cross Sections for CO2 Molecules

1995 ◽  
Vol 48 (3) ◽  
pp. 357 ◽  
Author(s):  
Y Nakamura
Keyword(s):  
Diffusion Coefficient ◽  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Vibrational Excitation ◽  
Electron Collision ◽  
Longitudinal Diffusion ◽  
Excitation Cross Sections ◽  
Momentum Transfer Cross Section

The drift velocity and longitudinal diffusion coefficient of electrons in 0�2503% and 1� 97% C02-Ar mixtures were measured for 0�03 ~ E/N ~ 20 Td. The measured electron swarm parameters in the mixtures were used to derive a set of consistent vibrational excitation cross sections for the C02 molecule. Analysis of electron swarms in pure C02 using the present vibrational excitation cross sections was also carried out in order to determine a new momentum transfer cross section for the C02 molecule.

scholarly journals The Ratio DL/ for Electrons in Helium at 293 K

1974 ◽  
Vol 27 (2) ◽  
pp. 235 ◽  
Author(s):  
MT Elford
Keyword(s):  
Diffusion Coefficient ◽  
Momentum Transfer ◽  
Cross Section ◽  
Electron Mobility ◽  
Absolute Error ◽  
Longitudinal Diffusion ◽  
Experimental Errors ◽  
The Common ◽  
The Absolute ◽  
Momentum Transfer Cross Section

The Bradbury–Nielsen method has been used to measure the ratio of the longitudinal diffusion coefficient DL to the electron mobility μ in helium at 293 K over the E/N range 0024–0.607 Td. The absolute error is estimated to be less than � 3 %. The present results agree with those of Wagner et al. (1967), to within the combined experimental errors over the common range of E/N values, and are also compatible with the values predicted by Lowke and Parker (1969) from calculations based on the momentum transfer cross section of Crompton et al. (1967).

scholarly journals Monte Carlo Simulation of an Electron Swarm in an Argon-like Gas

1987 ◽  
Vol 40 (1) ◽  
pp. 61 ◽  
Author(s):  
Katsuhisa Koura
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Diffusion Coefficient ◽  
Cross Section ◽  
Drift Velocity ◽  
Atomic Mass ◽  
Deep Minimum ◽  
Longitudinal Diffusion ◽  
Transverse Diffusion

A Monte Carlo simulation (MCS) of an electron swarm in an argon-like gas (of atomic mass a.m.u.), with Golden's cross section with a very deep minimum, is presented in order to examine the breakdown of the validity of the conventional two-term expression for the transverse diffusion coefficient Dr indicated by Milloy and Watts. It is found that the MCS value of Dr approaches the two-term value much slower than other swarm parameters such as the drift velocity Wand the longitudinal diffusion coefficient ~. The discrepancy between the MCS and two-term values of Dr revealed by Milloy and Watts is attributable to the evaluation of Dr at the long transient (correlation) stage in the MCS. It is concluded that the two-term expressions for Dr and ~ (and other swarm parameters) are sufficiently accurate even for Golden's cross section with a very deep minimum.

scholarly journals The Cross Section for the J = 0 → 2 Rotational Excitation of Hydrogen by Slow Electrons

1969 ◽  
Vol 22 (6) ◽  
pp. 715 ◽  
Author(s):  
RW Crompton ◽  
DK Gibson ◽  
AI McIntosh
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Vibrational Excitation ◽  
The Cross ◽  
Excitation Processes ◽  
Slow Electrons ◽  
And Diffusion ◽  
Momentum Transfer Cross Section ◽  
Section Analysis

The results of electron drift and diffusion measurements in parahydrogen have been analysed to determine the cross sections for momentum transfer and for rotational and vibrational excitation. The limited number of possible excitation processes in parahydrogen and the wide separation of the thresholds for these processes make it possible to determine uniquely the J = 0 → 2 rotational cross section from threshold to 0.3 eV. In addition, the momentum transfer cross section has been determined for energies less than 2 eV and it is shown that, near threshold, a vibrational cross section compatible with the data must lie within relatively narrow limits. The problems of uniqueness and accuracy inherent in the swarm method of cross section analysis are discussed. The present results are compared with other recent theoretical and experimental determinations; the agreement with the most recent calculations of Henry and Lane is excellent.

scholarly journals Electron Drift And Diffusion In Deuterium At 293°K

1966 ◽  
Vol 19 (6) ◽  
pp. 805 ◽  
Keyword(s):  
Diffusion Coefficient ◽  
Drift Velocity ◽  
Electron Drift ◽  
And Diffusion

The drift velocity and the ratio of diffusion coefficient to mobility have been measured for electrons in deuterium at 293�K over the ranges 0�006 � E/p � 5�0 and 0�006 � E/p � 2�0 respectively. The results are compared with those of other workers.

Ambipolar Drift, Deformation, and Diffusion of a Plasma in a Magnetic Field

1973 ◽  
Vol 51 (5) ◽  
pp. 564-573 ◽  
Author(s):  
Richard L. Monroe
Keyword(s):  
Magnetic Field ◽  
Diffusion Coefficient ◽  
Effective Magnetic Field ◽  
Theoretical Problem ◽  
Direction Parallel ◽  
Transverse Diffusion ◽  
Weakly Ionized ◽  
Plasma Diffusion ◽  
Ambipolar Drift ◽  
And Diffusion

The theoretical problem of a weakly ionized, constant temperature, three particle plasma in an externally generated magnetic field is reformulated by transforming the set of 14 macroscopic plasma equations (continuity and momentum equations for ions and electrons plus Maxwell's equations) in 14 unknowns (ion and electron number densities and velocities plus the effective electric and magnetic fields) into an equivalent set of 4 integral equations in 4 unknowns. In the course of this transformation, it is shown that the plasma behavior can be interpreted in terms of three ambipolar processes : drift, deformation, and diffusion. Plasma diffusion is characterized by two diffusion coefficients : the usual Schottky formula applying in the direction parallel to the effective magnetic field and a new expression for the ambipolar transverse diffusion coefficient applying in directions perpendicular to the effective magnetic field. The new ambipolar coefficient differs markedly from the familiar ambipolar coefficient associated with the names of Bickerton, Lehnert, Holway, Allis, and Buchsbaum; and, in general, it gives values for the transverse diffusion coefficient which are two orders of magnitude larger than those given by the latter. It is concluded that ambipolar diffusion can produce a transverse diffusion coefficient large enough to account for the diffusion rates measured by Bohm, Burhop, Massey, and Williams in argon arc discharges.

Unipolar Flow of Charge Carriers in a Dense Gas with and without Consideration of Diffusion

1970 ◽  
Vol 25 (10) ◽  
pp. 1447-1452
Author(s):  
W. Dällenbach
Keyword(s):  
Diffusion Coefficient ◽  
Electric Field ◽  
Cross Section ◽  
Current Density ◽  
Charge Carriers ◽  
Einstein Relation ◽  
Dense Gas ◽  
Modified Equations ◽  
Basic Equations ◽  
And Diffusion

Abstract The basic equations for the unipolar, stationary, one-dimensional flow of charge carriers in a dense gas, characterized by mobility and diffusion coefficient, can be integrated numerically. The discharge gap generally has a finite length; as far as in the end cross-section either density of particles and intensity of electric field tend towards infinity, or the density of particles becomes zero. Which of these two cases occurs depends on the current density of the discharge and on the intensity of the electric field in the initial cross-section. The notions mobility and diffusion coefficient will lose their applicability close to a pole like singularity as well as in a "dilution to zero", so that from a certain cross-section onwards the continuation of discharge is determined by modified equations.It is shown that in case the diffusion component of the current density is neglected, the integrals of the basic equations change fundamentally. Neglecting the diffusion is inadmissible. This is finally a consequence of the relationship between mobility and diffusion coefficient, as expressed by the Einstein-relation.

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