Effect of electron emission on the charge and shielding of a dust grain in a plasma: A continuum theory

The continuum approximation is used to analyze the effect of electron emission from the surface of a spherical dust grain immersed in a plasma on the grain charge by assuming negligible ionization and recombination in the disturbed plasma region around the grain. A parameter is introduced that quantifies the emission intensity regardless of the emission mechanism (secondary, photoelectric, or thermionic emission). An analytical expression for the grain charge Z _d is derived, and a criterion for change in the charge sign is obtained. The case of thermionic emission is examined in some detail. It is shown that the long-distance asymptotic behavior of the grain potential follows the Coulomb law with a negative effective charge Z _eff, regardless of the sign of Z _d. Thus, the potential changes sign and has a minimum if Z _d > 0, which implies that attraction is possible between positively charged dust grains.     

Emission properties of an atmospheric-pressure helium plasma jet generated by a barrier discharge

The emission properties of an atmospheric-pressure helium plasma jet generated by a barrier discharge in a capillary blown with helium are studied. The spectral composition of the radiation of the studied plasma jet and the spatial-spectral distribution of its intensity are investigated in detail. It is shown that the emission spectrum of the generated plasma jet outside the capillary consists mainly of electronic-vibrational transitions of the first negative system of ionized nitrogen molecules N ₂ ⁺ (B ²Σ _u ⁺ → X ²Σ _g ⁺ ) and the second positive system of neutral nitrogen molecules N₂(C ³Π _u → B ³Π _g ).     

Infrared laser-emission study in a resonantly excited sodium vapor

We report on a study of time dependence of ir laser emission at 3.41 μm in a dense Na vapor that is resonantly excited to the 3² P levels by a flashlamp, pumped dye laser. Energy-pooling collisions (excitation transfer) between excited atoms create a large population inversion among the 5² S _1/2 and 4² P _3/2 states which is destroyed by electron collisions as a result of subsequent plasma formation. The ir laser emission may serve as a new diagnostic tool to follow the time evolution of such media.     

Optical emission spectroscopy investigation of sputtering discharge used for SiOxNy thin films deposition and correlation with the film composition

The r.f. discharge of sputtering silicon target using argon-oxygen-nitrogen plasma was investigated by optical emission spectroscopy. Electronic temperature (T_e) and emission line intensity were measured for different plasma parameters: pressure (from 0.3 to 0.7 Pa), power density (0.6-5.7 W cm⁻²) and gas composition. At high oxygen concentration in the plasma, both T_e and the target self-bias voltage (V_b) steeply decrease. Such behaviour traduces the target poisoning phenomenon. In order to control the deposition process, emission line intensity of different species present in the plasma were compared to the ArI (λ = 696.54 nm) line intensity and then correlated to the film composition analysed by Rutherford Backscattering Spectroscopy.     

Longitudinal rf discharge in Xe/Cl<Subscript>2</Subscript> mixtures

Results are presented from the studies of the electrical and emission characteristics of the low-temperature plasma of a longitudinal rf (f₀=1.76 MHz) discharge in Xe/Cl₂ mixtures at pressures of 100–800 Pa. The discharge was ignited in a cylindrical quartz tube with an inner diameter of 1.4 cm and interelectrode distance of 3.0 cm. The discharge emission within the spectral range of 190–670 nm is studied. The dynamics of the discharge current and discharge emission at different pressures and compositions of a Xe/Cl₂ mixture are investigated. It is shown that a discharge in a Xe/Cl₂ mixture acts as a wideband excimer-halogen lamp with a cylindrical output aperture emitting in the spectral range of 220–320 nm. The broad plasma emission spectrum is formed due to the overlap of the XeCl(D, B-X; B, C-A) bands that are broadened at low working-gas pressures. The composition of the working mixture is optimized to achieve the maximum power of the wideband UV plasma emission. Longitudinal rf discharges in low-pressure Xe/Cl₂ mixtures are of interest for developing small-size wideband (Δλ=220–450 nm) cylindrical-aperture lamps, whose efficiency can, on average, exceed the efficiency of conventional hydrogen lamps by more than one order of magnitude.     

Spectral characteristics of a barrier discharge in cadmium dihalide vapor-inert gas mixtures

Spectral characteristics of a barrier-discharge plasma produced in atmospheric-pressure mixtures of cadmium diiodide and cadmium dibromide vapors with neon, krypton, and xenon at a repetition rate of sine voltage pulses up to 130 kHz are studied. The emission from the discharge is studied within the spectral range 200–900 nm with a resolution of 0.05 nm. Emission of exciplex molecules CdI(B → X) and CdBr(C, B → X), and cadmium and inert gas atoms is revealed, as well as emission of exciplex molecules XeI(B → X, A) and XeBr(B → X, A) in xenon-containing mixtures. The emission of xenon halides prevails in the spectra at a mixture temperature up to 200°C. With a further temperature increase, the emission of cadmium halides becomes dominating. It is ascertained that the most intense emissions of CdI(B → X) and CdI₂/CdBr₂/Xe/Kr and CdBr(B → X) molecules are observed, respectively, in CdI₂/CdBr₂/Xe/Kr and CdI₂/CdBr₂/Xe mixtures. The cadmium dihalide-inert gas mixtures are of interest for the use as a radiating gas in a multiwavelength and broadband excilamp emitting in the UV and visible spectral ranges.     

Plasmaresonanzemission und Plasmaresonanzabsorption an dünnen Kaliumschichten

Optical transmission and emission spectra in the region of the plasma frequencyω _p were measured on thin potassium films evaporated on sapphire substrates of various temperatures. For the foils condensed at a temperatures of the substrateT _a T _a >?165 °C transmission spectra were observed which transmission minima are displaced to frequencies less thanω _p . Plasma resonance emission was observed from these foils. Comparison with calculated emission spectra gives an approximate agreement.     

Emission characteristics of a high-power glow discharge plasma in a mixture of inert gases with bromine and iodine vapor

The results of an investigation of the UV radiation from the plasma of a dc glow discharge in mixtures of inert gases with bromine and iodine molecules are presented. The current-voltage and spectral characteristics of a longitudinal glow discharge with a power of 10–250 W are studied. The power and the efficiency of the total UV radiation of the plasma, as well as the power of radiation at the spectral line of the iodine atom at 206.2 nm, are optimized as functions of the power deposited into the plasma and the composition of the gas mixture. In active media based on Kr-Br₂ mixtures, the molecular emission of the plasma was represented by bands at 207 (KrBr(B-X)) and 289 nm (Br ₂ ^* ), while, in He-Xe-I₂ mixtures, it was represented by bands at 253 (XeI(B-X)) and 342 nm (I₂).     

Investigation of the plasma of a 308-nm XeCl excimer light emitter based on an inert-gas-CCl4 mixture

Results are presented from optical measurements of the plasma of a transverse volume discharge in He(Ar)/Xe/CCl₄(HCl) mixtures (at pressures of P=10–100 kPa) that are used in excimer lamps emitting the XeCl 308-nm band. Emission spectra in different stages of the formation and degradation of the active medium, as well as temporal and resource characteristics of the emitter, are studied. The main products of decomposition of CCl₄ molecules that are detected by the plasma emission are C* atoms and C ₂ ^* and CN* radicals. The operating resource of the XeCl emitter is found to be (3–5)×10⁴ pulses and depends strongly on the pressure and composition of the active medium. The duration of the emission pulse at a wavelength of λ=308 nm is 200–300 ns.     

Spectroscopic diagnostics of a laser erosion plasma formed from CuSbS<Subscript>2</Subscript> polycrystals

The spectra and dynamics of emission from regions of a laser plasma torch located at different distances from a polycrystalline CuSbS₂ target irradiated by a neodymium laser (W=(3–5)×10⁸ W/cm², ?=20 ns, f=12 Hz, 73x03BB;=1.06μm) were investigated. The emission data were used to estimate the average temperature (≤0.82 eV) and the electron density ((1.82?1.92)×10¹⁶ cm^?3) in the laser torch and the recombination times of ions (t _r(S²⁺)=15 ns, t _r(Cu⁺)=65?85 ns), as well as to analyze the efficiency of filling of excited atomic levels. A model describing the target destruction and the evolution of the processes accompanying spread of the laser plasma is proposed.     

Determination of temperature in a plasma jet emanating from a plasma torch with sectioned inter-electrode insert from the molecular emission spectrum of nitrogen

Results of application of a method for measuring the distribution of temperature in a nitrogen plasma jet emanating from a dc plasma torch with sectioned inter-electrode insert from the relative intensities of the molecular emission bands of nitrogen in the N₂ ⁺(B²Σ_u ⁺ − X²Σ_g ⁺) first negative and N₂(C³Π_u ⁺ − B³Π_g ⁺) second positive systems are reported. The emission spectra were registered using a small-size spectrometer with medium-range spectral resolution enabling a contour analysis of ro-vibrational bands in molecular emission spectra. The obtained distribution of temperature was compared with the distribution that was determined from the emission lines due to copper atoms and with the mean-mass plasma temperature of the air plasma jet.     

Compositional analysis of ferroelectric films coated with carbon layer using laser-induced plasmas spectroscopy

An experimental investigation of the effect of different thickness of carbon layer coated on ferroelectric films on the atomic emission intensity using laser-induced plasmas spectroscopy technique with charge-coupled device (CCD) experimental system has been conducted. The experimental results show that the intensity of the spectra emitted with the carbon layer thickness of 15 μm is much higher than that of pure ferroelectric films. By using this best experimental condition, the atomic concentration ratios of ferroelectric films are evaluated by rationing the integrated intensities of selected spectral emission lines of the plasma produced from the films. And the experimental results show that N_La/N_Co and N_Sr/N_Co atomic concentration ratios are almost in agreement with the corresponding values obtained by traditional compositional analysis techniques of inductively coupled plasma (ICP).     

Droplet spot as a new object in physics of vacuum discharge

It is established experimentally that the burning of a low-current (several and tens of amperes) pulsed (microseconds) vacuum discharge is accompanied by the formation of plasma microbunches around some of the droplets leaving the cathode spot. The parameters of these bunches (electron concentration n _e～10²⁶ m^?3 and equilibrium temperature T _e～1 eV) are close to the parameters of cathode-spot plasma. The data obtained suggest that the initial temperature of droplets and the thermionic emission from them play a key role in the formation of such plasma microbunches. By analogy with the well-known cathode and anode spots in vacuum discharges, these droplet plasma formations are classified as “droplet spots.” This work reports the first results on studying the formation dynamics and the characteristics of the droplet spots. It is noted that the concept of droplet spots will require a certain refinement of the plasma formation mechanism in vacuum discharges.     

Power determination and hydrino product characterization of ultra-low field ignition of hydrated silver shots

Hydrated silver shots comprising a source of H and HOH catalyst were ignited by passing a low voltage, high current through the shot to produce explosive plasma that emitted brilliant light predominantly in the short-wavelength 10 to 300 nm region. Based on Stark broadening, the initially optically thick essentially 100% ionized plasma expanded at sound speed or greater and thinned to emit EUV and UV light. The peak power of 20 MW was measured using absolute spectroscopy over the 22.8–647 nm region wherein the optical emission energy was 250 times the applied energy. Synchronized high-speed video and spectroscopic recording of the plasma emission and the measurement of the applied ignition power over time showed that plasma persisted even after the ignition power decayed to zero. Continuous megawatt-level power was recorded on a hydrino reactor wherein continuous brilliant plasma was maintained by HOH and H produced from water-entrained injected molten silver matrix. The molten fuel produced the same EUV spectrum as the shots, but converted to 5700 K blackbody radiation of about 1 m² surface area with a positive feedback cycle of silver vaporization and absorption of the hydrino reaction emission with the plasma becoming increasingly optically thick. The calorimetrically measured power of a typical 80 mg, 10 microliter shot ignition released by the nascent HOH catalyzed transition of H to hydrino state H₂ (1/4) was 400,000 W. Based on the shockwave propagation velocity and the corresponding pressure, the high-current ignition of water in a silver matrix was measured to produce a shock wave that was equivalent to about 10 times more moles of gunpowder. The catalysis reaction product H₂(1/4) was identified by Raman spectroscopy, photoluminescence emission spectroscopy, X-ray photoelectron spectroscopy, and MAS ¹H NMR.     

Luminescence from the laser transition 5d[3/2]1-6p[3/2]1 of atomic xenon upon excitation of He-Ar-Xe mixture by a pulsed electron beam of short duration

The spontaneous emission yield from the 5d[3/2]₁ → 6p[3/2]₁ transition in atomic xenon with a wavelength of 2.03 μm upon excitation of a He-Ar-Xe medium by an electron beam of short duration (～3 ns) was measured as a function of time for a wide range of partial composition of the gas mixture. The obtained data are analyzed. The experimental data agree with the calculated total lifetime of the level 5d[3/2]₁ of XeI in He-Ar-Xe mixtures with different partial composition. It is shown that the lifetime of this level determined by quenching induced by heavy particles is not established immediately following beam injection, but rather with a certain time delay determined by recombination processes in plasma.     

Emission spectra of working mixtures of a HgBr/HgCl excimer lamp

A study of emission spectra of a gas-discharge plasma produced in a HgBr/HgCl excimer lamp, which is filled with multicomponent working mixtures at atmospheric pressure (HgBr₂ and HgCl₂ with additions of molecular nitrogen and xenon), are reported. A gas-discharge plasma was produced by high-frequency (pulses ～100 ns long with a repetition rate of up to 2000 Hz) barrier and surface discharges, which took place simultaneously. Emission of HgBr* and HgCl* excimer molecules, the second positive system of molecular oxygen, and helium and xenon lines in the UV, visible, and IR spectral regions was observed. The strongest emission of HgBr* and HgCl* molecules (the emission intensities were in the ratio 10:1) was observed in the HgBr₂: HgCl₂: N₂: He mixture. Regularities in spectral and integrated characteristics of gas-discharge plasma emission are discussed.     

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.     

Effect of the electromagnetic field of an eruptive prominence on coronal and chromospheric plasmas (CME and Hα emission formation)

The frozen- in chromospheric and coronal plasma motions during an eruption of a filament with a magnetic field configuration described by the inverse polarity model are considered. At the initial stage of the filament motion the magnetic field compresses the chromospheric gas within two strips located symmetrically about the inversion line. The compression is accompanied by plasma heating and emission enhancement in the lineH _α. The distance between the strips increases with filament altitude above the photosphere. This mechanism is sufficient to describe the dynamics ofH _α emission kernels in two- ribbon flares. In the corona region in which the magnetic pressure of the filament field is greater than the gas pressure, plasma rarefaction and cavity formation occur. Near the boundary β=1the plasma is decelerated and its density increases, which corresponds to the formation of an outer shell of the CME.     

Refined interpretation of broadband radiation from a gas-discharge plasma of a krypton-xenon mixture

The earlier interpretation of the broadband continuum observed in the VUV emission spectra of a gas-discharge plasma in a Kr + Xe mixture is refined. On the assumption that this continuum is caused by the bound-free transitions v,0⁺(³ P ₁) → ε, 0⁺(¹ S ₀) in KrXe* and Xe₂ molecules, the distribution of the population over the vibrational levels v of the states 0⁺(³ P ₁) of both molecules is obtained and the vibrational temperature for different methods of excitation of the spectrum is determined. Internuclear potentials 0⁺(³ P ₁) and 0⁺(¹ S ₀) available from the literature are used. To improve the agreement between the calculated and experimental spectra, it is proposed to modify the positive branch of the potential curve 0⁺(¹ S ₀) of the KrXe* molecule.     

Initiation of ecton processes by interaction of a plasma with a microprotrusion on a metal surface

Evolution of rapid (～10 ns) Ohmic overheating of a microprotrusion on a surface in contact with a plasma by emission current is studied taking into account the energy carried by plasma ions and electrons, as well as Ohmic heating, emissive source of energy release (Nottingham effect), and heat removal due to heat conduction. Plasma parameters were considered in the range of n = 10¹⁴?10²⁰ cm^?3 and T _e = 0.1 eV?10 keV. The threshold value of energy transferred to the surface from the plasma is found to be 200 MW/cm²; above this value, heating becomes explosive (namely, an increase in the temperature growth rate (δ² T/δt ² > 0) and in passing current (δJ/δt > 0) is observed in the final stage at T ～ 10⁴ K and j ～ 10⁸ A/cm²). In spite of the fact that Ohmic heating does not play any significant role for plasmas with a density lower than 10 18 cm^?3 because the current is limited by the space charge of electrons, rapid overheating of top of microprotrusion is observed much sooner (over a time period of ～1 ns) when the threshold is exceeded. In this case, intense ionization of vapor of the wall material leads to an increase in the plasma density at the surface, and the heating becomes of the Ohmic explosion type. Such conditions for the formation of a micr?xplosion on the surface and of an ecton accompanying it can be created during the interaction of a plasma with the cathode, anode, or an insulated wall and may lead to the formation of cathode and anode spots, as well as unipolar arcs.