Hiroaki Tagashira

The development of electron avalanches in argon at high E/N values. II. Boltzmann equation analysis

For pt.I see ibid., vol.10, no.7, p.1035 (1977). The electron swarm parameters for the steady-state Townsend, pulsed Townsend and time-of-flight experiments are calculated using a Boltzmann equation for argon at E/N values from 85 to 566 Td, when electron impact ionization is appreciable. The results suggest that the value of an electron swarm parameter depends on the type of the experiments involved, because of the presence of the ionization, in agreement with the Monte Carlo simulation work in the previous paper. The drift velocities and diffusion coefficients when ionization is present, are discussed.

Boltzmann equation analysis of the electron swarm development in SF6

The electron swarm development in SF6 gas is studied for E/p20 values from 15 approximately 200 V cm-1 Torr-1 (E/N=45.6-607 Td) by a Boltzmann equation method in which the effect of ionisation and electron attachment is considered properly. The momentum transfer, vibration, ionisation and attachment cross-sections are taken from experiments, but the electronic excitation cross-section is determined by fitting the calculated ionisation and attachment coefficients to previous measurements. The calculation is performed for the steady-state Townsend, pulsed Townsend and time-of-flight experiments. The results show that the deduced electron drift velocities and diffusion coefficients agree reasonably well with experiment and the value of a swarm parameter should depend on the type of experiment not only at high E/p20 values, at which ionisation is appreciable, but also at low E/p20 values, at which electron attachment is appreciable. The electron energy distribution, which is found to have depressions at low E/p20 values, the electron mean energy and the excitation coefficients are also calculated and discussed.

The development of electron avalanches in argon at high E/N values. I. Monte Carlo simulation

The behaviour of electron avalanches in argon when appreciable electron impact ionization occurs, is studied by a Monte Carlo simulation. The values of electron swarm parameters are obtained for steady-state Townsend, pulsed Townsend and time-of-flight experiments, by applying sampling techniques appropriate to the respective experiments. The results suggest that the value of an electron swarm parameter, such as the ionization frequency or the electron drift velocity, depends on the type of experiments for which there is appreciable electron impact ionization. The properties of electron avalanches in an electron energy non-equilibrium region, for example the variation of the electron energy distribution with distance from the cathode, and the effect of anisotropic scattering of electrons on the swarm parameters very close to the anode, are also studied.

Effects of additives on prebreakdown phenomena in n-hexane

Prebreakdown phenomena in n-hexane are observed in detail for positive and negative polarities by using simultaneously a high speed schlieren technique and an LED current measuring system, when an impulse voltage (1.1/225 /spl mu/s) is applied to a point-to-plane electrode gap. Furthermore, the effects of several additives on the streamer propagation are investigated. Especially the effects of electron-trapping additives on negative streamer propagation and of low ionization potential additives on the positive streamer propagation, are examined, as is a correlation between the shape and the propagation velocity of the streamers. >

Boltzmann equation analysis of the electron swarm development in nitrogen

The electron swarm development in nitrogen is studied for E/N values from 56.6 to 1131 Td by a Boltzmann equation method in which the effect of ionisation is considered properly. Alteration of the electron collision cross-sections from the literature is limited to a minimum, although minor amendments are found necessary for the ionisation coefficient to agree well with previous measurements. The cross-sections for vibrational excitation are considered separately for its quantum number v=1-10. The electron swarm parameters are calculated for the time-of-flight, pulsed Townsend and steady-state Townsend experiments. The results show that the deduced electron drift velocity, diffusion coefficient and mean energy are generally in good agreement with previous experimental and theoretical values.

The drift velocity and longitudinal diffusion coefficient of electrons in nitrogen and carbon dioxide from 20 to 1000 Td

The distribution of arrival time spectra (ATS) of electrons in nitrogen and carbon dioxide has been measured over the range of E/N from 20 to 1000 Td (1 ) at room temperature by a double-shutter drift tube. The drift velocity of electrons in and was evaluated from these distributions by the ATS method. Moreover, the ratio of the longitudinal diffusion coefficient to the electron mobility was measured. The values of and in and were in good agreement with experimental and theoretical values obtained by previous investigators except for a few of the earlier studies.

Measurement of the effective ionisation coefficient and the static breakdown voltage in SF6 and nitrogen mixtures

The effective ionisation coefficient alpha /p20 is measured for E/p20 from 70 to 160 V cm-1 Torr-1, and the static breakdown voltage Vs between parallel plates for p20d from 8 to 130 Torr cm, for SF6 and nitrogen mixtures. It is found that the alpha /p20 of the mixtures may be approximated by a linear function of the partial pressure of SF6 at fixed E/p20 and that Paschens law holds for the p20d may be estimated with good accuracy from the Vs of the respective pure gases using an experimental formula of Takuma et al. (1972) which has been used for much larger p20d.

Optical emission diagnostics of H2+CH4 50‐Hz–13.56‐MHz plasmas for chemical vapor deposition

The emission spectra of H2+CH4 plasmas excited at 50 Hz–13.56 MHz were measured. The emission intensity ratios of Hα/H*2 (3Σg →3Σu) from H2+CH4 plasma at 50 Hz and 13.56 MHz were about 0.7 and 0.05, respectively. The electron temperature was obtained from the two‐line radiance ratio method using the Balmer lines (Hα and Hβ), and rapidly decreased with an increase above 200 kHz. The electron temperature for H2+CH4 plasma is 16 000 K at 1 kHz and 8200 K at 13.56 MHz. The plasma‐maintaining voltages for H2 and H2+CH4 mixtures were also measured. The maintaining voltages were constant below 200 kHz, and rapidly decreased between 200 kHz and 13.56 MHz. The position dependence of emission intensity was also measured for Hα, Hβ, and H*2 at 50 Hz and 13.56 MHz. The results are interpreted in terms of the electron distribution in the plasma.

Boltzmann equation analysis of the electron swarm development in SF6 and nitrogen mixtures

The ionisation alpha and electron attachment eta coefficients and other electron swarm parameters are calculated for SF6 and nitrogen gas mixtures for E/p0=75-200 V cm-1 Torr-1 by a Boltzmann equation method, in which the effect of generation and loss of free electrons due to ionisation and attachment are fully considered, for the steady-state Townsend (SST) experiment. The results show that the deduced values of the effective ionisation coefficient alpha (= alpha - eta ) are in good to fair agreement with those measured by Itoh et al. (1979) by a SST method, but agreement is less satisfactory with the experimental values of Aschwanden (1979) by a pulse method. The limiting E/p0 value, at which alpha = eta , is also calculated to give slightly higher values than previous experiments. The variation of the electron energy distribution, electron drift velocity, diffusion coefficient and mean energy, and the excitation frequency to C3 Pi u of nitrogen, as a function of the partial SF6 pressure, are calculated and discussed.

Boltzmann equation analyses of electron swarm parameters in Ar/Ne, Kr/Ne, Xe/Ne, Hg/Ar and Hg/Kr mixtures and derived effective excitation cross sections for metastable states of rare atoms

The steady-state electron swarm parameters in a series of Penning gases, Ar/Ne, Kr/Ne, Xe/Ne, Hg/Ar and Hg/Kr mixtures, were analysed using a Boltzmann equation in which generation of secondary electrons through Penning ionization and ionization collision between two metastable Hg atoms, as well as electron-impact ionization, are property considered. The ratios of the Townsend first ionization coefficient to the field strength, alpha /E, calculated using the present equation in Ne gas with admixtures of Ar, Kr and Xe, were strongly influenced by Penning electrons. On the other hand, in Ar and Kr gases with Hg vapour, the ionization between two metastable Hg atoms was found to be the dominant ionization process at low E/N. The present alpha /E in every gas agrees well with experimental values over a wide range of alpha /E. The effective cross section of excitation for the metastable states of the rare atoms was derived by comparing the present alpha /E with the experimental values.