Pulsed Discharge In Helium Research Articles

Transverse magnetic field effects on the high-voltage pulsed discharge plasma in helium

This study investigates the effect of a transverse magnetic field on high-voltage pulsed discharge in helium at a pressure of 30 Torr. A simple two-dimensional fluid model that describes the high-voltage pulsed discharge in helium in a transverse weak magnetic field (B = 0.4 T) is presented, which uses an empirical relation to account for the magnetic field. The results of using the empirical relation for the effective field agree well with the experimental results. The dynamics of discharge development in the presence of the magnetic field is also investigated. The magnetic field does not significantly affect the gas-discharge development dynamics in helium at a pressure of 30 Torr.

Controlling the breakdown delay time in pulsed gas discharge

In experiment and 2D3V PIC MCC simulations, the breakdown development in a pulsed discharge in helium is studied for U = 3.2 kV and 10 kV and P = 100 Torr. The breakdown process is found to have a stochastic nature, and the electron avalanche develops in different experimental and simulation runs with time delays ranging from 0.3 to 8 μs. Nevertheless our experiments demonstrate that the breakdown delay time distribution can be controlled with a change of the pulse discharge frequency. The simulation results show that the breakdown process can be distinguished in three stages with (a) the ionization by seed electrons, (b) the ions drift to the cathode and (c) the enhanced ionization within the cathode sheath by the electrons emitted from the cathode. The effects of variation of seed electron concentrations, voltage rise times, voltage amplitudes and ion–electron emission coefficients on the breakdown development in the pulsed gas discharge are reported.

Townsend to glow discharge transition for a nanosecond pulse plasma in helium: space charge formation and resulting electric field dynamics

Stark polarization spectroscopy is used to investigate the temporal evolution of the electric field distribution in the cathode region of a nanosecond pulsed discharge in helium at 120 Torr. The measurements are performed on the He I transition at 492.19 nm, during the early stages of the discharge formation. The experimental results are compared with the predictions of a 1D fluid model. Time-resolved ICCD images show that the discharge develops as a diffuse, cathode-directed ionization wave with a Townsend-like feature before transitioning into a glow-like structure. Near anode instabilities characterized by filament formation were observed near the high voltage electrode. Within 30 ns, a reduction of the sheath thickness to about 250 μm is observed, coinciding with a gradual increase of the discharge current and proportional increase in electric field at the cathode. The cathode electric field corresponding to this sheath with a thickness of 250 μm is about 40 kV cm−1. A subsequent steep increase of the discharge current leads to a further reduction of the sheath width. The electric field evolution as obtained by the fluid model is in excellent agreement with the measurements and shows that an enhanced ionization near the cathode is causing the space charge formation responsible for the increase in electric field.

Fast Electron Generation in a Pulsed Discharge Plasma in Helium at a Pressure of 0.02–2.0 Torr

The results of experimental studies of the fast electron distribution function under the conditions of a nonequilibrium plasma of a pulsed discharge in helium are presented. It is established using various methods that a beam of fast electrons, the energy of which depends on the voltage applied to the discharge gap and gas pressure, is generated at a helium pressure of 0.02–2.0 Torr in the initial stage of the discharge, when the reduced electric field strength exceeds the critical value.

Generation of fast electrons in pulsed discharge plasma in helium

The results of experimental studies of the distribution function of fast electrons under conditions of non-equilibrium plasma of a pulsed discharge in helium are presented. It was established by various methods that at the initial stage of the discharge, when the reduced electric field exceeds the critical value, a beam of fast electrons is generated. The beam energy depends on the applied voltage to the discharge gap, and helium pressure.

Optical and Kinetic Characteristics of an Atmospheric Pressure Pulsed Discharge in Helium with Iron Vapor

The emission spectrum of a near-cathode plasma of a pulsed discharge in atmospheric pressure helium reveals spectral lines of electrode material. Numerical simulation of the kinetics by the Monte Carlo method shows that starting with a fraction of percent, the addition of iron atoms to helium strongly affect the ionization-drift characteristics of electrons in gas.

Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy

Single-photon multiple ionization processes of acetaldehyde (ethanal) have been experimentally investigated by utilizing a multi-particle coincidence technique based on the time-of-flight magnetic bottle principle, in combination with either a synchrotron radiation source or a pulsed helium discharge lamp. The processes investigated include double and triple ionization in the valence region as well as single and double Auger decay of core-ionized acetaldehyde. The latter are studied site-selectively for chemically different carbon core vacancies, scrutinizing early theoretical predictions specifically made for the case of acetaldehyde. Moreover, Auger processes in shake-up and core-valence ionized states are investigated. In the cases where the processes involve simultaneous emission of two electrons, the distributions of the energy sharing are presented, emphasizing either the knock-out or shake-off mechanism.

Line broadening in the neutral and ionized mercury spectra

The neutral, singly, doubly and triply ionized mercury (Hg I–IV, respectively) spectral line shapes and line center positions have been investigated in the laboratory helium plasma at electron densities ranging between 9.3×1022m−3 and 1.93×1023m−3 and electron temperatures around 19,500K, both interesting for astrophysics. The mercury (natural isotope composition) atoms were sputtered from the cylindrical amalgamated gold plates located in the homogenous part of the pulsed helium discharge operating at a pressure of 665Pa in a flowing regime. The mercury spectral line profiles were recorded using the McPherson model 209 spectrograph and the Andor ICCD camera as the detection system. This research presents Stark broadening parameters, the width (W) and the shift (d), of one Hg I, 19 Hg II, 6 Hg III and 4 Hg IV lines, not investigated so far. Our experimental W values were compared with the data calculated applying various approaches. The shape and intensity of astrophysically important 398.4nm Hg II spectral line was discussed taking into account the isotope shift, hyperfine structure and Penning effects. At the mentioned plasma parameters the Stark broadening is found to be a main line broadening mechanism of the lines (λ>200nm) in the Hg I–IV spectra.

Experimental Stark widths in the Pb IV and Pb V spectra

Context. The triply and fourthly ionized lead (Pb IV and Pb V, respectively) spectral line shapes have been investigated in the laboratory helium plasma at electron densities ranging between 5.1 × 1022 m-3 and 9.1 × 1022 m-3 and electron temperatures around 22 000 K (±9%), both interesting for astrophysics.Aims. The aim of this work is to present experimental Stark FWHM (full-width at half of the maximum line intensity, W ) for 34 spectral lines from Pb IV and 4 spectral lines from Pb V spectra emitted by the pulsed helium discharge, which is optically thin at the wavelengths of the investigated lines. The values presented in this paper are the first published experimental W data in the Pb IV and Pb V spectra.Methods. The lead atoms were sputtered from the cylindrical lead plates that are located in the homogenous part of the pulsed helium discharge at a pressure of 665 Pa in a flowing regime. The Pb IV and Pb V spectral line profiles were recorded using the McPherson model 209 spectrograph and the Andor ICCD camera as the detection system.Results. The Stark FWHM s of 34 Pb IV and 4 Pb V spectral lines were measured in the wavelength interval between 200 nm and 461 nm. Our experimental Pb IV W values are compared with the existing theoretical data. Twenty four Pb IV W values from the above mentioned set haven’t been calculated so far. The isotope shift, caused by the four natural Pb isotopes, and the hyperfine structure have no influence on the observed symmetry of the measured Pb IV and Pb V line shapes at our plasma parameters. Conclusions. At the mentioned plasma parameters we found a tolerable agreement (within the accuracy of the experiment and uncertainties of the theoretical approaches used) between the measured and calculated ten Pb IV W values. For the Pb V spectral lines no comparison is possible because as far as we are aware, no experimental and theoretical W data exist.

Periodic plasma structures in nanosecond discharge with a slit cathode

The spatial structure of optical emission from a transverse nanosecond pulsed electric discharge with a hollow (slit) cathode has been experimentally studied. A regular periodic plasma structure has been observed during nanosecond pulsed discharge in helium at medium pressures. Conditions of the plasma structure formation with respect to the discharge voltage and current are determined. It is shown that the observed plasma structure differs from the known types of striations.

On the line intensity ratios of prominent Si II, Si III, and Si IV multiplets

Line intensities of singly, doubly and triply ionized silicon (Si II, Si III, and Si IV, respectively) belonging to the prominent higher multiplets, are of interest in laboratory and astrophysical plasma diagnostics. We measured these line intensities in the emission spectra of pulsed helium discharge. The Si II line intensity ratios in the 3 s3 p 22 D–3 s 24 p 2 P o , 3 s 23 d 2 D–3 s 24 f 2 F o , and 3 s 24 p 2 P o –3 s 24 d 2 D transitions, the Si III line intensity ratios in the 3 s3 d 3 D–3 s4 p 3 P o , 3 s4 p 3 P o –3 s4 d 3 D, 3 s4 p 3 P o –3 s5 s 3 S, 3 s4 s 3 S–3 s4 p 3 P o , and 3 s4 f 3 F o –3 s5 g 3 G transitions, and the Si IV line intensity ratios in the 4 p 2 P o –4 d 2 D and 4 p 2 P o –5 s 2 S transitions were obtained in a helium plasma at an electron temperature of about 17,000 ± 2000 K. Line shapes were recorded using a spectrograph and an ICCD camera as a highly-sensitive detection system. The silicon atoms were evaporated from a Pyrex discharge tube designed for the purpose. They represent impurities in the optically thin helium plasma at the silicon ionic wavelengths investigated. The line intensity ratios obtained were compared with those available in the literature, and with values calculated on the basis of available transition probabilities. The experimental data corresponded well with line intensity ratios calculated using the transition probabilities obtained from a Multi Configuration Hartree–Fock approximation for Si III and Si IV spectra. We recommend corrections of some Si II transition probabilities.

Line broadening in the Si I, Si II, Si III, and Si IV spectra in the helium plasma

Context. The neutral and ionized silicon spectral line shapes have been investigated in the laboratory helium plasma at electron densities ranging between $3.7\times 10^{22}$ m -3 and $1.1\times 10^{23}$ m -3 and electron temperatures between 12 500 K and 19 000 K, both interesting for astrophysics. Aims. The aim of this work is to present experimental Stark FWHM (full-width at half of the maximum line intensity, W ) for number of spectral lines from neutral (Si I), singly (Si II), doubly (Si III), and triply (Si IV) ionized silicon spectra emitted by the pulsed helium discharge, which is optically thin at the wavelengths of the investigated ionic silicon lines. A specific method for estimating self-absorbtion is presented in detail. For investigated Si I spectral lines, applying the proposed method, an optical depth of less than 0.38 is found. Appropriate corrections of the Si I Stark widths were made. The Stark widths of different ionic species, presented in this paper, are measured for the first time in the essentially same laboratory plasma. Methods. The silicon atoms were evaporated from the walls of the specially designed pyrex discharge tube in the pulsed helium discharge at a pressure of 665 Pa in a flowing regime. The Si I, Si II, Si III, and Si IV spectral line profiles were recorded using the McPherson model 209 spectrograph and the Andor ICCD camera as the detection system. Results. The Stark FWHM s of 13 Si I, 15 Si II, 28 Si III, and 9 Si IV spectral lines were measured in the wavelength interval between 206 nm and 640 nm. Five Si I, four Si II, eleven Si III, and one Si IV W values from the above set not had measured or calculated. Our W values are compared with the existing theoretical and experimental data. Conclusions. At the mentioned plasma parameters tolerable agreement was found (within the accuracy of the experiment and uncertainties of the theoretical approaches used) between measured and calculated Stark FWHM values. We recommend the Stark FWHM s of the intense 254.182 nm, 308.624 nm, and 309.342 nm Si III, and 314.956 nm and also 316.571 nm Si IV lines for the plasma diagnostic purposes.

Measured Cd III Stark widths

The Stark FWHM (Full-Width at Half of the Maximal line intensity, W) have been measured for 16 doubly ionized cadmium (Cd III) spectral lines in a pulsed helium discharge in the wavelength interval between 200 nm and 304 nm. The helium discharge was created in the linear low pressure pulsed arc operated at 19 000 K electron temperature and 5.0 × 10 22 m − 3 electron density. The cadmium atoms were sputtered from the cadmium (99.9% purity) cylindrical plates located in the linear part of the discharge tube. The high density of the Cd III ions is boosted by cascade ionization processes via the well populated Cd II energy levels due to the Penning and charge exchange effects. The shapes of the Cd III lines are recorded using a spectrograph (McPherson model 209, 1.33 m focal-length with 2400 grooves/mm holographic grating) and intensified CCD camera (Andor DH740-18F-03) as a high-sensitive detection system. The Stark parameters introduced in this Letter are the first published experimental Cd III Stark widths.

Numerical simulation of super-short pulsed discharge in helium with particle-in-cell Monte Carlo collisions technique

This paper reports that a simulation of glow discharge in pure helium gas at the pressure of 1.333 × 103 Pa under a high-voltage nanosecond pulse is performed by using a one-dimensional particle-in-cell Monte Carlo collisions (PIC-MCC) model. Numerical modelling results show that the cathode sheath is much thicker than that of anode during the pulse discharge, and that there exists the phenomenon of field reversal at relative high pressures near the end of the pulse, which results from the cumulative positive charges due to their finite mobility during the cathode sheath expansion. Moreover, electron energy distribution function (EEDF) and ion energy distribution function (IEDF) have been also observed. In the early stage of the pulse, a large amount of electrons can be accelerated above the ionization threshold energy. However, in the second half of the pulse, as the field in bulk plasma decreases and thereafter the reverse field forms due to the excessive charges in cathode sheath, although the plasma density grows, the high energy part of EEDF decreases. It concludes that the large volume non-equilibrium plasmas can be obtained with high-voltage nanosecond pulse discharges.

Kinetics of the active medium of a He—Sr+ recombination laser: 1. Spatiotemporal characteristics

A self-consistent mathematical model of a He—Sr+ recombination laser is developed and used to study the establishment of a repetitively pulsed regime in the active medium. The spatiotemporal characteristics are analysed in the stationary regime under different excitation conditions, the contraction of a repetitively pulsed discharge in helium is investigated and the discharge decontraction upon addition of strontium vapour, which is fundamentally important for metal vapour lasers is studied. Numerical simulations are shown to be a convenient tool for investigating the kinetics of the active medium of a He—Sr+ laser, which enables predicting the optimal excitation conditions and calculating the limiting lasing characteristics.

Recombination population of excited states of the hydrogen atom in an He-H2 plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H2] ≈ 1012 cm−3) has been studied spectroscopically. The contribution from electron-ion recombination Γ 3 rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ 3 rec (T e ∼ T e −(0.9–1.0) has been obtained in the region kT e = 0.026–0.064 eV.

Light, Plasma, and Microscopic Processes

Glow discharges with different gases in the Large Helical Device (LHD at the National Institute for Fusion Science (NIFS show different visual colors of the plasma and these colors are ascribed to different spectra in the UV and visible wavelength range. From the wavelengths of the observed emission lines these gases are identified as neon helium and hydrogen. The emission line intensity is given by the upper level popula‑ tion density of the corresponding transition via the spontaneous transition probability or Einstein's A coeffi‑ cient. On the assumption of corona equilibrium relative emission line intensities of neutral helium are esti‑ mated for thetotransitions. The results are in gross disagreement with the glow discharge spec‑ trum. For a single pulsed helium discharge in a Pyrex tube line emissions are intense during the beginning of the pulse and after the pulse [A. Hirabayashi et al., Phys. Rev. A 37 77 (1988]. The population distribution over the levels is determined for these two emission peaks and neither of the results agrees with the expectationsfromcoronaequilibrium.Itisalsofoundthatthecoloroftheplasmaobservedforamaindischarge withhelium inLHDisdrasticallydifferent dependingontheplasmaconditionandnevershowsasimilarcolor tothatintheglowdischarge.Alltheseresultsindicatebreakdownofcoronaequilibriumanddemandusdeeper considerations.

Measurement o Rate Coefficients or Atom-Atom Collisions in a Pulsed Helium Discharge by Laser-induced Fluorescence

We present experimentally obtained rate coefficients for atom-atom collisions for Δn = 0 transitions of neutral helium. Results for the transitions 3 3 S - 3 3 P, 3 3 S - 3 3 D and 3 3 P - 3 3 D were acquired with the help of a laser perturbation method in a pulsed helium discharge. The filling pressure was in the range of 400 to 1100 Pa. The obtained data are compared with experimental data from the literature.

Optical characteristics of a plasma of a pulsed discharge in helium at atmospheric pressure

Optical characteristics of a plasma of a pulsed discharge in helium at atmospheric pressure

Relationship between ionization processes and the geometric parameters of a pulsed discharge in helium

The relationship between ionization processes and the geometric parameters of a pulsed discharge in helium is analyzed. The conditions are determined for obtaining a homogeneous volume discharge in helium without preionization of the gas discharge gap. Good agreement is obtained between the calculated and experimental data for different pulsed discharge conditions.