Discharge In He Research Articles

Fourier Transform Infrared Emission Spectroscopy of theb1Π–a1Σ+System of BN

The emission spectrum of BN has been investigated in the 1800–9000 cm−1region using a Fourier transform spectrometer. BN was formed in a microwave discharge of He with a trace of BCl3and N2. The bands observed in the 3000–7800 cm−1interval have been assigned as theb1Π–a1Σ+transition, with the 0–0 band at 3513.99040(43) cm−1. This transition is analogous to theA1Πu–X1Σ+g(Phillips) system of the isoelectronic C2molecule. The rotational analysis of the 0–0, 1–1, 1–0, 2–1, 3–2, 2–0, 3–1, 4–2, and 4–1 bands has been obtained and the molecular constants for theb1Π anda1Σ+states have been determined. A local perturbation has been observed in thev= 1 vibrational level of theb1Π state nearJ= 18 caused by the interaction with thev= 3 vibrational level of thea1Σ+state. The principal equilibrium constants for thea1Σ+state are: ωe= 1705.4032(11) cm−1, ωexe= 10.55338(52) cm−1,Be= 1.683771(10), αe= 0.013857(16) cm−1, andre= 1.2745081(37) Å. Although theb1Π–a1Σ+transition has recently been seen in emission from boron nitride trapped in solid neon matrices [J. Chem. Phys.104,3143–3146 (1996)], our work represents the first observation of this transition of BN in the gas phase.

Investigation of Discharge Phenomena in a Cell of Color Plasma Display Panel I. One-Dimensional Model and Numerical Method

A numerical simulation method using a one-dimensional fluid model under the local field approximation is presented in order to understand pulsed-dc discharge in He–Xe gas mixture in a cell of a full-color plasma display panel. Spatiotemporal behaviors of the electric field and number densities of twelve independent particles, including electrons and four kinds of ions, were calculated self-consistently at a gas pressure of 200 Torr (27 kPa) and an electrode distance of 0.02 cm. The imprisonment of 147-nm-resonance radiation, the excitation source of phosphors, was also taken into account. Calculated results of the discharge current and voltage are consistent with those of experiment. The waveform of 147-nm-resonance radiation agreed well with experiment, although that of the discharge current showed some difference, probably due to the local field approximation.

Image process discharge classification under nonuniform fields in air and He at low pressure

This paper described the discharge classification under nonuniform electric field in air and He at low gas pressures for the application of HV technology to the power apparatus in space. In order to discuss quantitatively the change of the discharge, an image processing method was introduced. In the first place, four shape parameters were proposed to characterize the discharge pattern: the area S/sub H/, the flatness rate H/V, the location g of the center of luminosity of the luminous area, and the length L of the positive column. The analysis with the image processing for air revealed that S/sub H/, H/V and g continuously increased as the pressure decreased. Consequently, the discharge type in air was successfully classified into three regions with two boundary pressures 200 and 2000 Pa over the pressure range from 1.3/spl times/10/sup 4/ to 27 Pa. The discharge in He was also analyzed in the same way. Another parameter, the effective current density J/sub e/, was introduced, which was defined as a ratio of the discharge current to the luminous area viewed from the vertical direction. J/sub e/ proved to be independent of the discharge current I/sub d/, so that there is the possibility that J/sub e/, was suggested as a universal parameter to classify the discharge in a nonuniform electric field in vacuum. >

Characterization of a molecular beam containing metastable nitrogen and its use in scattering experiments with xenon

A thermal molecular beam containing metastable nitrogen, N2*, produced in a microwave discharge in He–N2 mixtures, is characterized by magnetic analysis and, after velocity selection, is used for scattering experiments with Xe. The magnetic analysis reveals that the excited N2 molecules are essentially in the A 3Σ+u metastable state but also evinces the presence of a small concentration of A′ 5Σ+g molecules, increasing with beam velocity. This allows us to estimate the mean collision free lifetime of the 5Σ+g metastable molecules by an experiment completely different from those usually performed to this purpose. Absolute total cross sections are measured both for the metastable and the ground state N2 by passing the molecular beam through a cooled scattering chamber containing Xe. From the analysis of the scattering data, the characterization of the intermolecular potential for both systems is obtained and from the potential parameters the average molecular polarizability of metastable N2 is obtained.

Rydberg States of CCl

The absorption spectrum of CCI has been observed on SUPERACO in Orsay (France) in a microwave discharge in He + CCl4 down to 1050 Å. The B2Σ+ state observed by Mélen et al. (J. Phys. B: Atom. Mol. Phys.16, 2523-2530 (1983)) has been confirmed. Nineteen states have been classified into five Rydberg series converging to 9.051 ± 0.002 eV.

Characterization of a helium discharge for hollow anode furnace atomization non-thermal excitation spectrometry

A discharge in He has been characterized for hollow anode furnace atomization non-thermal excitation spectrometry (HA-FANES). The small surface area of the cathode and high current densities make it possible to stabilize He discharges up to 1200 hPa using a d.c. power supply operating in the constant current mode. Current—voltage characteristics were determined for pressures up to 800 hPa. Characterization at higher pressures was not possible owing to limitations of the power supply. The release of thermionic electrons from the cathode surface at temperatures in excess of 1750 K caused a dramatic decrease in the discharge potential during the atomization cycle. Increased ohmic heating of the cathode with increased currents caused a time shift in the release of thermionic electrons. Excitation temperatures, obtained from Boltzmann plots of five He I lines, decreased slightly as a function of increasing pressure and increased as a function of increasing current. Dramatic decreases in the discharge potential were observed for high concentrations (250 mg ml–1) of NaCl. The potential decreases were too short-lived to permit the accurate measurement of excitation temperatures. Integrated analytical signals increased linearly with increasing pressure.

Electron temperature and plasma density of capacitive rf-discharges in noble gases

Electrical discharges in He, Ne, Ar, and Kr at medium pressure (density of neutral atoms from 1021 to 1023 m−3), sustained by an rf electric field of 27.12 MHz, are investigated. Electron temperature and plasma density were measured with a Langmuir probe at 8, 13, and 20 W total discharge power. The plasma density was found to increase with the input power, whereas the electron temperature depends only weakly on the input power.

Longitudinal diffusion of electrons in weakly ionized gas with Coulomb collisions

Equations describing the longitudinal electron diffusion in gases with Coulomb collisions in an electric field are derived. It is shown that the presence of electron-electron interactions leads to the renormalization of the longitudinal diffusion coefficient which is calculated in Ar, He, and N2. The numerical results are used in the investigation of the thermocurrent instability threshold in the glow discharge in He. The thermocurrent instability is retarded at high ionization levels.

Rotational Temperature of He2 in a DC Capillary Discharge

An experimental evaluation was made for the approximation which is used in the determination of rotational temperature from the analysis of electronic-rotational perturbation, and the approximation presented by Kovács was found to be adequate. The rotational temperature in the dc capillary discharge of He as derived by the present study was 500 ± 100 K.

Electron-energy distribution function measurements in capacitively coupled rf discharges

Measurements by Langmuir probes have been performed in a capacitively coupled, parallel- plate rf discharge of He and Ar with pressures ranging from 0.1 to 2 Torr and discharge power from 10 to 50 W at 27 MHz. The first part of this paper is devoted to a discussion of the preparation of the electrostatic probe technique, for which a rf discharge is well known to be a very hostile environment, and of its intrinsic limitations, in order to assess the reliability of the measurements. Results showing a marked non-Maxwellian character of the electron-energy distribution function are then presented and discussed in the light of the most recent theories about the sustainment of this kind of gas discharge.

Radial distributions of the charged particles in a He-Kr hollow cathode discharge

Radial distributions of He +, He + 2 and Kr + were measured in a hollow cathode discharge in He and in He-Kr mixtures using a mass spectrometer. The dimensions of the discharge were similar to those used in He-Kr + hollow cathode discharge lasers. From the ion densities the electron density was derived. Introducing krypton into the helium discharge results in decreasing both the densities of He + and He + 2 ions. During this process the radial distributions of the He +, H + 2 and electron density change from parabolic into saddle-like profiles. The changes of radial profiles of the charged particles in the He-Kr hollow cathode discharge may affect the lasing properties of the mixture.

Diode laser infrared spectra and potential energy curve for SH +

We have detected rovibrational transitions of the v = 2 ← 1, v = 3 ← 2, and v = 4 ← 3 hot bands of SH + in the 3Σ − electronic ground state. The signals were detected with velocity modulation in a high current discharge in He and H 2S. By combining the new results with earlier data on SH + we have obtained a set of molecular constants. From all available data on 32SH + and 32SD + we have derived a potential curve for the SH + molecular ion and obtained a value of 34 494(50) cm −1 for the dissociation energy D e.

Spectroscopic investigation of the cathode region of an independent glow discharge in He

Spectroscopic investigation of the cathode region of an independent glow discharge in He

Difference frequency laser spectroscopy of the ν3 fundamental band of NH+2

The ν3 band of NH+2 in the X̃ 3B1 ground electronic state was observed in direct absorption with a tunable difference frequency laser spectrometer in the 3 μ region, using velocity modulation detection. NH+2 and NH+3 ions were generated in an ac discharge of He and NH3, or of He, N2, and H2. Fifty-three rovibrational transitions were measured and fit to a triplet A-reduced Hamiltonian to determine rotational, centrifugal distortion, and spin–rotation constants. The band origin was found to be ν0=3359.932 cm−1, in excellent agreement with a recent calculation of Jensen, Bunker, and McLean. Indirect evidence from the spectrum suggested that NH+2 is quasilinear, but selection rules prevented a determination of the A rotational constant.

The use of the RG conditioning system to examine some recycling mechanisms occuring in an all-carbon surrounding

The plasma facing surfaces in TEXTOR consist of hydrogen (H/D)-rich carbon. The near surface H/D and oxygen concentrations at the start of a tokamak shot depend on the preceding tokamak or conditioning discharges and on the wall temperature. The subsurface layers — which are essentially free of oxygen after carbonization — collect significant amounts (5–10% per collected C atom) of oxygen during the tokamak discharges. This affects the plasma contamination. The amounts of 0 in the plasma and in the wall are similar during H, D and He shots. Short (e.g. 15 min long) RG discharges in He decrease the near surface 0 concentration and reduce the 0 radiation by a factor of ~ 4 in the following tokamak shots. Similarly, RG discharges in He and /or prolonged bake-out at 350–400 ° C reduce the subsurface concentration of H/D and affect its recycling in the next shots. The implications of these and related measurements concerning the recycling mechanisms of D and of O during tokamak operation are discussed. We conclude that, at low wall temperatures (≲ 200 dg C), the D and O inventories in the near surface layer are dominated by implantation and particle induced desorption events which occur during the discharge. At higher temperature (≳ 300 ° C), the thermal release of D 2, between discharges becomes more important. The near surface carbon layer is found to act as a buffer for oxygen of which the primary source is not on the plasma-facing surfaces but elsewhere in the vacuum vessel.

Optical diagnostic studies of trimethyl phosphine-containing radio-frequency discharges

We have investigated the decomposition of P(CH3)3 in 13-MHz, radio-frequency discharges in He and H2. Relative concentrations of atomic phosphorus were estimated actinometrically by measuring P emission intensities, relative to Ar, while quantitative, relative P2 number densities were measured by ArF excimer laser-induced fluorescence. A radiative lifetime of 10.5±1.0 ns was measured for the v′=11 level of the C1∑ u + state, resonantly excited by the 193 nm laser. Additions of P(CH3)3 to He discharges reduce the electron energy distribution as sensed by the quenching of optical emission from He and trace amounts of added Ar, and thereby causes the overall process P(CH3)3→P+3CH3 to occur with maximum efficiency at very low (∼0.5%) P(CH3)3 additions. H2 discharges are 10 times less efficient at producing P and P2, due to the lower electron energies, and possibly to hydrogenation reactions. P2 production in both He and H2 discharges increases linearly with pressure up to at least 10 torr. Under optimum conditions, plasma decomposition of P(CH3)3 (and by analogy PH3) promises to be an attractive source of phosphorus for growth of phosporus-containing thin films.

Investigations into the mechanisms of electrohydrodynamic spraying of liquids: I. Effect of electric field and the environment on pendant drops and factors affecting the formation of stable jets and atomization

The effect of an applied electric field on pendant and flowing drops (through a capillary) was studied by observing the droplet profile as a function of applied voltage. With pendant drops of hexadecane, application of the electric field caused a reduction in the apparent surface tension, γ app. In surrounding gases such as N 2, CO 2, and Ar, droplet profiles similar to those in air were observed. While gases such as He and Ne have low breakdown potentials, no change in droplet profile upon application of an electric field was detectable. The glow discharge in He was investigated for oil (insulator), water, glycerol, and a brass tip, for both positive and negative potentials. Conducting liquids such as water and glycerol permitted discharge to take place from the surface of the droplet, whereas insulating oils forced the discharge to occur at the metal tip, where the drop is attached. With flowing drops, the liquid conductivity was a major factor in the electrostatic disruption of the liquid surface. With insulating liquids such as paraffinic oil, no disruption occurred due to the lack of sufficient free ions in the bulk liquid. With conducting liquids such as water, very unstable streams were produced. Stable jets having a conical base were only produced with semiconducting liquids (nonpolar liquids with dissolved ionic materials). The cone angle at the base of the jet increased, whereas its length decreased with an increase in applied voltage. At higher voltages, secondary jets were produced from the primary one, whose number increased with an increase in the applied field. The effect of liquid conductivity, applied voltage, flow rate, and capillary diameter on the stability of jets was investigated by measuring the critical voltage, φ c, at which transition from the pulsating mode to the stable jet mode occurred. By measuring the current carried by the jet, the charge-to-mass ratio could also be calculated. Some measurements of droplet size distribution were made using a practical sprayer and a particle measuring system for measuring droplet diameters in flight. These measurements were made as a function of applied voltage, conductivity, and flow rate. The results obtained clearly demonstrate the importance of applied voltage, liquid conductivity and flow rate in the formation of stable jets and the subsequent process of electrohydrodynamic atomization. At a given voltage and flow rate an optimum conductivity range is necessary for producing the most stable jet, the narrowest size distribution, and the smallest droplet size. This could be accounted for in terms of the electric forces acting on the liquid, which are related to the relaxation time of the liquid. The influence of flow rate on the production of stable jets and the subsequent atomization could also be understood in terms of the inertial and electrostatic forces which act in the same direction. At a given conductivity and voltage, stability is enhanced by increasing the flow rate, but at the expense of producing larger droplets.

High resolution optogalvanic spectroscopy of He 3 1,3D–2 3P transitions

He 3 1,3D–2 3P lines have been investigated by optogalvanic spectroscopy in the hollow cathode discharge of He to reveal the presence of the 3 1D2–2 3P2 component which is predicted at 0.0764 cm−1 above the 3 1D2–2 3P1 line appearing at 17 018.137±0.004 cm−1. The assignment of the latter has also been experimentally established by the present study through the use of optogalvanic double resonance methods. The spin-orbit interaction of the 3 1D2 level with the 3 3D2 level is responsible for the appearance of the 3 1D2–2 3P2 line. The relaxation processes among the 3 1D, 3 3D, and 2 3P levels have also been briefly discussed on the basis of the observations of mysterious dips on the double resonance signals and of a broad background signal on Doppler-free intermodulation spectrum.

Spectroscopic study of the afterglow excited by intense electrical discharges in high-pressure helium hydrogen mixtures

In this work, we report the study of afterglow plasmas with initial electron density over 1015 cm−3 excited by repetitive 3 kA, 7 ns duration discharges in He–H2 mixtures with helium pressure in the range 310–760 Torr and partial pressure of hydrogen from 20 to 400 mTorr. The afterglow radiation was emitted in He2 transitions as well as in atomic hydrogen spectral lines, with Lα being particularly intense. The ground state H concentration was estimated from the profile of the self-absorbed Lα line, indicating that dissociation of hydrogen occurs mainly in the afterglow by electron–ion recombination. He (2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were analyzed in terms of rate coefficients for various quenching processes. Among these, the Penning reaction with atomic hydrogen was found to be important.

Formation of MoSi2 by pulsed electron beam irradiation onto a vapor deposited molybdenum/silicon structure

A molybdenum disilicide layer was formed by pulsed electron beam irradiation onto a vapor deposited Mo film on a Si substrate. The electron beam with a duration of almost 1 μs was generated by glow discharge of He at a pressure of 1×10−5 Torr in a vacuum chamber equipped with a capacitor of 1 μF that was charged at 7 kV. The total energy stored in the capacitor was 25 J and the irradiated area was almost 1 in. in diameter. The qualitative and structural characterizations were performed by Auger electron spectroscopy (AES), transmission electron diffraction (TED), and transmission electron microscopy (TEM). A depth profile by AES showed that a uniform MoSi2 layer was formed toward the Mo surface from the Mo/Si interface and that C and O contaminants were swept away from the silicide. The hexagonal MoSi2 phase was uniquely identified in the irradiated layer and the TEM micrographs showed uniform polycrystalline grains of a size of 800 Å.