scholarly journals Drift Velocity and DT/m Ratio for Electrons in a 0.5% Hydrogen?Xenon Mixture at 295 K

1994 ◽  
Vol 47 (3) ◽  
pp. 253 ◽  
Author(s):  
MT Elford ◽  
S Sasaki ◽  
KF Ness
Keyword(s):  
Cross Section ◽  
Drift Velocity ◽  
Diffusion Chamber ◽  
Number Density ◽  
Velocity Measurements ◽  
Transverse Diffusion ◽  
Xenon Mixture ◽  
Time Of Flight Method ◽  
Momentum Transfer Cross Section ◽  
Electron Transport Coefficient

The momentum transfer cross section for electrons in xenon, am, has been studied using electron transport coefficient measurements for a dilute hydrogen-xenon mixture (0�47% H2- 99 �53% Xe). Drift velocity measurements were made using the Bradbury-Nielsen time-of-flight method at E/N values from 0 �12 to 2�50 Td, pressures from 10�3 to 94�0 kPa and a temperature of 295 K (E is the electric field strength and N the gas number density; 1 Td == 10-17 Vcm2). The ratio DT/f.t (where DT is the transverse diffusion coefficient and {� the electron mobility) was measured using a Townsend-Huxley diffusion chamber at E/N values from 0�035 to 1� 70 Td, pressures from 13�4 to 40�3 kPa, and a temperature of 294 K. Three recently published Urn values for xenon have been tested and shown to be incompatible with both the present drift velocity and DT / f.t measurements.

scholarly journals Drift Velocity, Longitudinal and Transverse Diffusion in Hydrocarbons derived from Distributions of Single Electrons

1992 ◽  
Vol 45 (3) ◽  
pp. 351 ◽  
Author(s):  
Bernhard Schmidt ◽  
Michael Roncossek
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Drift Velocity ◽  
Simultaneous Measurement ◽  
Diffusion Coefficients ◽  
Number Density ◽  
Transverse Diffusion ◽  
Single Electrons ◽  
Time Of Flight Method

A time of flight method is described which allows the simultaneous measurement of drift velocity w and the ratios of the longitudinal and transverse diffusion coefficients to mobility (DL/JL, DT/JL) of electrons in gases. The accuracy achieved in this omnipurpose experiment is comparable with that of specialised techniques and is estimated to be �1 % for w and �5% for the D / JL measurements .. Results for methane, ethane, ethene, propane, propene and cyclopropane for values of E/N (the electric field strength divided by the number density) ranging from 0�02 to 15 Td are presented and discussed (1 Td = 10-21 Vm2 ).

scholarly journals Momentum Transfer Cross Section for Electrons in Mercury Vapour Derived from Drift Velocity Measurements in Mercury Vapour?Gas Mixtures

1991 ◽  
Vol 44 (6) ◽  
pp. 647 ◽  
Author(s):  
JP England ◽  
MT Elford
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Personal Communication ◽  
Mercury Vapour ◽  
Semi Empirical ◽  
Time Of Flight Method ◽  
Momentum Transfer Cross Section ◽  
Good Agreement

The Bradbury-Nielsen time-of-flight method has been used to measure electron drift velocities at 573 K in pure mercury vapour, a mixture of 46�80% helium-53� 20% mercury vapour and a mixture of 9�37% nitrogen-90� 63% mercury vapour. The E/N and pressure ranges used were O� 2 to 1� 5 Td and 5�4 to 15�2 kPa for pure mercury vapour, 0 �08 to 3�0 Td and 5 �40 to 26�88kPa for the mixture containing helium and 0�06 to 5�0Td and 3�33 to 16�67kPa for the mixture containing nitrogen. It is shown that the use of mixtures significantly reduces the dependence of the measured drift velocity on the pressure, due to the effect of mercury dimers, from that measured in pure mercury vapour. An iterative procedure to derive the momentum transfer cross section for electrons in mercury vapour over the range 0�04 to 4 eV with an uncertainty between �5 and 10% is described. It is concluded that previously published momentum transfer cross sections for mercury vapour derived from drift velocity data are significantly in error, due to diffusion effects and the procedure used to correct for the influence of dimers. The present cross section is in good agreement with the semi-empirical calculations of Walker (personal communication).

The Drift Velocity of Electrons in Water Vapour at Low Values of E/N

1990 ◽  
Vol 43 (6) ◽  
pp. 755 ◽  
Keyword(s):  
Momentum Transfer ◽  
Water Vapour ◽  
Cross Section ◽  
Drift Velocity ◽  
Velocity Measurements ◽  
Low Energies ◽  
Momentum Transfer Cross Section

The drift velocity of electrons in water vapour at 294 K has been measured over the E/N range 1�4 to 40 Td with an error estimated to be 35 Td. The present data show that J.lN decreases monotonically with decreasing E/N at low E/N values as observed by Wilson et al. (1975) and does not become independent of E/N as indicated by Lowke and Rees (1963). The present values, although lower than those of Lowke and Rees, lie within the combined error limits, except for values below 2 Td. The present data suggest that the momentum transfer cross section at low energies is approximately 10% larger than that obtained by Pack et al. (1962) from their drift velocity measurements.

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 Drift Velocity of Electrons in Oxygen at 293 K

1973 ◽  
Vol 26 (6) ◽  
pp. 771 ◽  
Author(s):  
RW Crompton ◽  
MT Elford
Keyword(s):  
Drift Velocity ◽  
Drift Tube ◽  
Time Of Flight ◽  
Velocity Measurements ◽  
Time Of Flight Method ◽  
Good Agreement

The drift velocity of electrons in oxygen at 293 K has been measured over the range 0.8 ≤ E/N ≤ 12 Td by the Bradbury–Nielsen time-of-flight method. The factors governing the range over which measurements can be made are discussed and it is shown that long drift tubes should be used for drift velocity measurements in oxygen at low values of E/N. A 50 cm drift tube is described. The error in the present results is estimated to be less than 1 % for 1.8 E/N E/N > 6 Td and at 1.5 Td, 5 % at 1 Td, and 10 % at 0.8 Td. The present data are in good agreement with those of Fleming et al. (1972) and Nelson and Davis (1972) over the E/N range where the sets of data overlap.

scholarly journals Momentum Transfer Cross Section for Electrons in Krypton Derived from Measurements of the Drift Velocity in H2?Kr Mixtures

1988 ◽  
Vol 41 (5) ◽  
pp. 701 ◽  
Author(s):  
JP England ◽  
MT Elford
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Personal Communication ◽  
Electron Drift ◽  
Velocity Data ◽  
The Cross ◽  
Momentum Transfer Cross Section ◽  
Made In

Measurements of electron drift velocities have been made in 0�4673% and 1�686% hydrogenkrypton mixtures at 293 K and values of E/ N from 0�08 to 2�5 Td with an estimated uncertainty of <�0�7%. The data have been used in conjunction with the H2 cross sections of England et aL (1988) to derive the momentum transfer cross section for krypton over the energy range 0�05 to 6�0 eV. The drift velocity data have also been used to test the Kr momentum transfer cross sections of Koizumi et aL (1986) and Hunter (personal communication 1988). The cross section of Koizumi et aL is clearly incompatible with the present measurements while the cross section of Hunter has been used to predict these measurements to within 1% to 3%.

scholarly journals The Drift Velocity of Electrons in Mercury Vapour at 573 K

1980 ◽  
Vol 33 (2) ◽  
pp. 239
Author(s):  
MT Elford
Keyword(s):  
Density Dependence ◽  
Drift Velocity ◽  
Time Of Flight ◽  
Mercury Vapour ◽  
Number Density ◽  
Sources Of Error ◽  
Time Of Flight Method

The drift velocity of electrons in mercury vapour at 573 K has been measured using the Bradbury-Nielsen time-of-flight method at vapour number densities ranging from 3�40x 1017 to 1�83x1018 cm-3 and at E/Nvalues from 0�1 to 3�0 Td. The measured drift velocities increase linearly with mercury vapour number density, the magnitude of the dependence being a function of E/ N. This number density dependence has been attributed to the presence of mercury dimers and the drift velocity corresponding to dimer-free mercury vapour has been obtained by extrapolation. Sources-of error are examined and the present results are compared with those of previous workers.

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'.

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