Bipolar atmospheric-pressure corona discharge in a He/H2 mixture

Results are presented from a study of the characteristics of a steady-state plasma in a He/H₂ mixture at high pressures. The plasma is formed in the outer region of a multielectrode corona discharge. It is shown that molecules of helium hydride form in such a medium, and their decomposition is accompanied by continuum emission in the 350–650 nm region. The corona discharge is distributed over the length and can be used in systems for the transverse electric circulation of the working medium of atmospheric-pressure plasma radiation sources. The reference spectra of the plasma emission and the dependence of the relative intensity of the lines and the brightness of the bands of He ₂ ^* on the value of the discharge current, pressure, and composition of the working mixture are investigated. Zh. Tekh. Fiz. 69, 33–37 (July 1999)     

A broadband excimer source of visible radiation with barrier discharge pumping

We investigate the characteristics of a broadband cylindrical excimer source of visible radiation with a surface area of 230 cm² excited by a pulse-periodic barrier discharge based on multicomponent mixtures (mercury diiodide and dibromide with helium and admixtures of molecular nitrogen and xenon). The working mixture components were excited by a pulse-periodic (pulse repetition rate 500–5000 Hz, pulse duration ～150 ns) barrier discharge. We detected radiation from excimer HgI* and HgBr* molecules, the second positive system of molecular nitrogen, and mercury and xenon atoms. The amplitude, duration, and trailing edge of the radiation pulses in the HgI₂:HgBr₂:Xe:He and HgI₂: HgBr₂:N₂:He mixtures with admixtures of xenon and molecular nitrogen were found to change compared to the HgI₂:HgBr₂:He mixture. The optimal partial pressure of helium lies within the range 162–195 kPa. The most intense radiation from HgI* and HgBr* molecules (in a ratio of more than 3: 1) is observed in the HgI₂:HgBr₂: Xe:He mixture. The mean and pulse radiation powers are 45 W and 93 kW, respectively, at a pumping pulse repetition rate of 5000 Hz and an efficiency of 30%. We discuss the spectral and temporal characteristics of the radiation source and the dependence of the radiation intensity of excimer molecules of mercury monoiodide and monobromide on the partial pressures of xenon and nitrogen. We point out that the radiation source is of considerable interest for applications in biotechnology and medicine.     

Kr-KCl exciplex lamp

A new source of UV radiation (excilamp) based on Kr-KCl vapor-gas mixture excited by a longitudinal high-voltage pulsed-periodic discharge is created. The emission spectrum and time characteristic of the discharge radiation are studied. The B → X transition in the KrCl* excimer molecule (λ = 222 nm) is found to dominate in the radiation spectrum of the source. The dependence of the pulse output power of the lamp on various factors is investigated, and the mechanism of B state formation in the excimer molecule is discussed.     

DC corona ozone generation enhanced by TiO<Subscript>2</Subscript> photocatalyst

Non-thermal electrical discharges, such as corona discharge are apart of the source of ozone, charged, and excited species and acoustic noise also the source of electromagnetic radiation of different wavelengths. The important component of this radiation from the standpoint of photocatalyst activation is the ultraviolet radiation. We studied the role of UV radiation on corona discharge ozone production by placing the titanium dioxide photocatalyst into the discharge region. We used hollow needle to mesh DC corona discharge at atmospheric pressure with TiO₂ globules on the mesh. The discharge was enhanced by the flow of air through the needle. We found that for the needle biased negatively addition of TiO₂ photocatalyst on the mesh electrode drastically increases discharge ozone production as well as the ozone production yield. These quantities are also influenced by the mass of the used photocatalyst and its distribution in the discharge chamber.     

Multiwave excimer lamps using XeF/XeCl/KrF/KrCl molecules

Results are presented of an investigation of the spectral and temporal characteristics of an electricdischarge excimer lamp emitting simultaneously on the 351 nm XeF, 308 nm XeCl, 249 nm KrF, and 222 nm KrCl transitions. The He/Kr/Xe/SF₆/HCl working mixtures were excited in a transverse discharge with ultraviolet spark preionization at a total pressure of 25–100 kPa. In order to obtain the same brightness the concentration ratio [Kr]/[Xe] for the excimer molecular transitions was 8/0.8 kPa, and that for the halogen-containing molecules was [SF₆]/[HCl][=[0.06–0.12]/[0.08–0.16] kPa. The duration of the radiation pulses for the excimer molecular transitions at atmospheric pressure was 100–200 ns and when the total mixture pressure was reduced to 250 kPa, this was doubled or trebled. The service life of the spontaneous radiation for B-X transitions in excimer molecules was 10⁵ pulses. Zh. Tekh. Fiz. 68, 64–67 (December 1998)     

Lichtemission gepulster Argon-Entladungen bei koaxialer Elektrodenanordnung

The spectrum of prompt and delayed light radiation was measured from a pulsed corona discharge in pure Argon. The prompt light consists of known Argon emission lines. The delayed radiation exhibits a band-like structure in the wavelength region between 300 and 400 nm and cannot be identified with known transitions in theA ^I orA ^II spectra. The decay time of this light is several orders of magnitude larger than that of the prompt component and is inversely proportional to the Argon pressure. Presumably Argon molecules in electronically excited states, which are mainly formed after the discharge, give rise to the delayed light and provide a mechanism to deexcite the metastable Argon atoms originating during the discharge.     

The characteristics of a negative corona discharge in He/Xe/SF6 mixture

The results of investigation of the electrical and optical characteristics of a negative corona discharge in the electrode system of the type needle-grid lit in a He/Xe/SF₆ mixture under the pressure of 100–300 kPa are presented in this paper. The given medium is working for a pulse-periodic excimer lamp on = 351 nm XeF(B–X). Distributed on the length of a lamp active media a bipolar corona discharge is intended for using in the electric circulation of the XeF-lamp working medium. It is shown that the given discharge is ignited steadily in the He/Xe/SF₆ mixture, containing 0, 5kPa SF₆ molecules and is characterised by a low power consumption; the current of the discharge is limited to the development of instability by increasing the voltage on the needles; in hot zones of corona discharge SF₆ molecules cause the effective population 6s of XeI state.     

Spectroscopic diagnostics of barrier-discharge plasma in mixtures of cadmium diiodide vapor with gases

The spectral characteristics of the emission of atmospheric-pressure gas-discharge plasma in mixtures of cadmium diiodide vapor with gases (Ne, Ar, Kr, Xe, and N₂) were investigated along with the time characteristics of the voltage and current. The gas-discharge plasma was produced and excited by a barrier discharge at a repetition rate of sine voltage pulses of up to 140 kHz. The discharge emission was analyzed in the spectral range 200–900 nm with a high resolution (0.05 nm). Radiation from exciplex CdI(B-X) molecules and excimer I₂* molecules was revealed, as well as the atomic lines of cadmium, iodine, and inert gases. In a mixture with xenon, radiation from exciplex molecules XeI(B-X, B-A) was also found. This radiation prevailed in the spectra at mixture temperatures up to 150°C. The further increase of the temperature leads to the prevalence of the CdI(B-X) radiation. It was found that the most intense CdI(B-X) radiation is observed in mixtures CdI₂/Xe(N₂)/Ne. Regularities in the spectral characteristics of the emission of the gas-discharge plasma are discussed.     

On the operating conditions of the electrical blowing module for a periodic-pulse laser based on fluorine atoms and molecules

The results of an investigation of the ignition conditions and characteristics of a multiple-electrode corona discharge, intended to be used in the module which performs electrical blowing of the working media of high pressure lasers operating on fluorine atoms and molecules, in a tip-grid system are reported. The electrical and optical characteristics of corona discharges of positive and negative polarity, which were distributed along the length of a transverse discharge of lasers operating on the transitions F(3s-3p) and F₂(D′-A′), were studied. The characteristics of corona discharges were studied in a mixture He/F₂ at atmospheric pressures. Zh. Tekh. Fiz. 68, 84–87 (September 1998)     

Emission characteristics of plasma of a transverse volume discharge in mixtures of helium, argon, and krypton with sulfur hexafluoride

The emission characteristics of the plasma of repetitively pulsed spontaneous UV-VUV radiation sources on the basis of ArF* (193 nm) and KrF* (249 nm) molecules, and the products of decomposition of sulfur hexafluoride molecules pumped by a transverse volume discharge in a mixture of inert gases with sulfur hexafluoride molecules have been investigated. The discharge emission spectra in the range of 190–780 nm at the low-current and high-current stages of the transverse discharge, the time characteristics of the voltage across the electrodes, the pump current, and the emission of excimer molecules and the products of decomposition of sulfur hexafluoride have been studied. It is shown that, in the gas-static operation mode of the radiator at the number of discharge pulses smaller than 10³, the 193-nm ArF* and 249-nm KrF* bands are main in the emission spectrum. Upon further operation of the radiator, a spectral continuum is formed on the basis of sulfur molecular bands in the range 260–550 nm.     

Temporal characteristics of emission of working mixtures of a HgBr/HgCl excimer lamp

Results of a study of temporal characteristics of the emission of gas-discharge plasma of atmospheric pressure in multicomponent mixtures (mercury dibromide and dichloride with helium and additions of molecular nitrogen and xenon) of working media of HgBr/HgCl excimer lamps are presented. Gas-discharge plasma was produced and components of the working mixture were excited by high-frequency barrier and surface discharges occurring simultaneously. The repetition rate of the pumping pulse and its duration are 1000 Hz and ～100 ns, respectively. It is found that the amplitude and the length of emission pulses and their trailing edge are modified in HgBr₂: HgCl₂: Xe: He and HgBr₂: HgCl₂: N₂: He mixtures when xenon and molecular nitrogen are added, as compared to a HgBr₂: HgCl₂: He mixture. Regularities observed in temporal characteristics of gas-discharge plasma emission are discussed.     

Ultraviolet radiation sources on (H2O,D2O) water vapor

Emission characteristics of ultraviolet (UV) radiation from water vapor (H₂O, D₂O, and a mixture of H₂O and D₂O vapors) excited by pulse-periodic discharges with open electrodes, as well as electrodes outside the discharge tube (capacitive discharge), are presented. Radiation is studied in a spectral range of 175–350 nm. The emission characteristics of a UV radiation source based on vapors of ordinary and “heavy” water, as well as the results of optimization of brightness of radiation bands from the OH and OD radicals as functions of pressure and the composition of the He-H₂O and He-D₂O mixtures, are reported.     

Multi-wavelength excimer ultraviolet sources from a mixture of krypton and iodine in a dielectric barrier discharge

New ultraviolet (UV) sources (excimer lamps) have been demonstrated using mixtures of krypton and iodine in a high-pressure dielectric barrier discharge to provide intense multi-wavelength radiation at λ=183 nm (atomic iodine line, ⁴ P _5/2?² P _3/2), 191 nm (KrI^*, B _1/2?X _1/2), 206 nm (atomic iodine line, ² P _3/2?² P _1/2), and 342 nm (I^* ₂, D _1/2?X _1/2). The characteristics of the optical emission spectra of the atomic species and the excited dimers (excimers) formed for different total gas pressures and in the presence of a buffer gas have been investigated. The highest intensity, at 183 nm, is obtained at pressures up to 1 bar while the overall emission spectra can be controlled by adjusting the total pressure. The results show that these strong multi-wavelength lamps offer an interesting alternative to conventional UV sources. Received: 1 March 2000 / Revised version: 5 April 2000 / Published online: 30 June 2000     

Optical characteristics of a transverse volume discharge in a helium-hydrogen chloride mixture

The emission characteristics of a transverse volume discharge in a He: HCl = 10: 1 mixture at a total pressure of 1–8 kPa were investigated. The plasma volume was 18 × 2.2 × 1 cm³, the interelectrode distance was d=2.2 cm, and the charging voltage of the main storage capacitor was 5–10 kV. The emission characteristics of the discharge were studied in the spectral range of 500–1000 nm. This type of discharge can be used in pulsed dry-etching plasmochemical reactors. The density of atomic chlorine radicals in the plasma was optimized in terms of the pressure of the initial working He-HCl mixture by measuring the relative radiation intensity of the Cl 837(5)-nm spectral line. The density of molecular radicals can be monitored indirectly by recording radiation from the excited chlorine-free decomposition products of HCl molecules (the H_α 656-nm line).     

Excitation of iron atoms in a plasma of excimer emitters under transverse-discharge pumping

The optical characteristics of a transverse-discharge plasma initiated in He/Xe(Kr)/HCl(CF₂Cl₂) mixtures were studied. The mixtures contained a small amount of iron vapor due to metal cathode erosion. The iron atoms were shown to be excited by the spontaneous emission of KrCl (λ=22 nm) and XeCl (λ=308 nm) molecules in a nanosecond transverse discharge.     

Intensity enhancement of the C5+ Balmer radiation excited by capillary discharge pumping

The intensity of the 18.2 nm Balmer α-transition in C⁵⁺ excited in a capillary discharge using alumina and polyacetal tubes was studied. For discharge currents of up to 80 kA in tubes filled with C₂H₂, intense radiation from the excitation of C⁵⁺ ions and from the recombination of C⁶⁺ ions was observed. With increasing length of the discharge, the intensity in the falling edge of the recombination pulse rises faster than proportional. In contrast to previous investigations, gain by stimulated emission is excluded. The enhancement is ascribed to an optical guiding of the XUV radiation in the dense plasma created by ablation from the tube walls. Received: 1 April 1999 / Revised version: 22 July 1999 / Published online: 30 November 1999     

A multiwavelength low-pressure radiation source based on argon and xenon chlorides

The characteristics of an excimer radiation source pumped by a subnormal dc glow discharge in an Ar/Xe/Cl₂ mixture with the source operating in a spectral range of 160–310 nm were studied. The emission intensities of the 175, 236, 258, and 308 nm bands due to the transitions ArCl (B-X), XeCl (D-X), Cl₂ (D′-A′), and XeCl (B-X), respectively, were optimized in relation to the pressure, composition, and discharge current of the mixture.     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

Narrowband emission of argon dimers in a dc discharge with supersonic expansion

Narrowband emission of Ar₂ ^* at 126 nm was observed in a dc discharge with supersonic expansion and cooling of Ar gas through a metallic nozzle. The bandwidth of the excimer emission was 5.7 nm, which was lower than the values reported in the literature. The short bandwidth was attributed to the increased contribution of the singlet excimer state to the emission that could lead to a partial amplification of the radiation. PACS 33.20.Ni; 42.55.Lt; 52.80.Yr     

Spectroscopic diagnostics of barrier discharge plasmas in mixtures of zinc diiodide with inert gases

The spectral characteristics of the emission of gas discharge atmospheric pressure plasmas in mixtures of zinc diiodide vapor with inert gases (He, Ne, Ar, Kr, and Xe) are investigated. The formation of a gas discharge plasma and the excitation of the components of a working mixture were performed in a high-frequency (with a repetition frequency of sinusoidal voltage pulses of 100 kHz) barrier discharge. The gas discharge emission was analyzed in the spectral range 200–900 nm with a resolution of 0.05 nm. Emission bands of ZnI(B-X) exciplex molecules and I₂* excimer molecules, lines of inert gases, and emission bands of XeI* exciplex molecules (in Xe-containing mixtures) were revealed. It is ascertained that the strongest emission of ZnI* molecules is observed in ZnI₂/He(Ne) mixtures. The regularities in the spectral characteristics of the gas discharge plasma emission are considered.