Xenon Discharge Research Articles

Electron extraction enhancement via the magnetic field in a miniature microwave discharge neutralizer

This study analyzes the dependence of electron extraction efficiency, which is defined as the ratio of the extracted electron current to the generated electron current, on the orifice shapes and magnetic fields of a miniature microwave discharge xenon neutralizer via three-dimensional particle-in-cell simulations with Monte Carlo collisions (PIC–MCCs). The PIC–MCC simulation results show that the orifice shapes do not significantly affect the discharge characteristics or the electron extraction efficiency. However, the efficiency achieves a 1.5-times higher value in a new magnetic field configuration, referred to as MF-2, where the magnetic field lines pass through nearly the entire area of the orifices. This improvement is attributed to the reduction in the electron backflow and the electron loss toward both the downstream inside surface and the outside wall of the discharge chamber. In addition, there are relatively small plasma fluctuations in the discharge chamber for MF-2 due to its low Bohm diffusion coefficient, where no rotating spokes, which are often seen in other E × B devices, are observed. As a result, the electron loss toward the downstream surface inside the discharge chamber is reduced, and this decrease in the electron loss also contributes to the increase in the extraction efficiency.

Характеристики излучения короткодуговых ксеноновых газоразрядных ламп высокого давления

The paper is devoted to the study of changes in characteristics of ultra-high pressure short-arc xenon lamps when a tungsten layer is sprayed onto the quartz shell, as a result of heating and local electrode erosion. The paper analyzes the mechanisms of phenomena occurring in the super-high pressure xenon discharge and the cathode spot, which affect the sputtering of the electrode material. The main negative effects of tungsten deposits appearing on the lamp shell inner surface are considered: a decrease in the optical transparency and mechanical strength of quartz glass, an increase of the bulb temperature, a change in spectral characteristics and spatial distribution of radiation of a gas-discharge lamp. The original method developed for studying the parameters of radiation of a gas-discharge lamp and based on the superposition of the optical axis of the photometer with the axis of the lamp passing through the cathode spot and the considered shell segment, transparent or sprayed, allowed us to compare radiation characteristics of the lamp without changing the plasma parameters. The thermodynamic analysis carried out within the research confirmed the absence of chemical interaction of tungsten layer with quartz glass. Spectral distribution of xenon discharge radiation in the visible and IR ranges is different for a transparent bulb and the bulb with a tungsten spot, which is due to the size of tungsten layer particles on the lamp bulb. A study of spatial distribution of radiation from a gas-discharge lamp showed a decrease in the intensity of radiation in a solid angle bounded by a tungsten spot. At the same time, in this region, there was observed an increase in the temperature of the quartz shell, leading to the appearance of a longitudinal gradient of the temperature field of the gas-discharge lamp.

Distinctions of the Design of UHP Xenon Lamps with Sapphire Envelope

This article describes the major development results of the first Russian sample of a UHP xenon discharge lamp with sapphire envelope. The article proposes a method of monitoring of thermal fields of semi-transparent materials and studies the thermal distribution of quartz and sapphire envelopes of UHP discharge lamps. Mechanical strength of sapphire tubes depending on the temperature is studied, the thickness of the discharge envelope wall is calculated, and distinctions of the design of a UHP xenon lamp with the sapphire envelope are considered.

Powerful source of VUV-UV radiation based on nanosecond volumetric discharge

The radiation of a volumetric gas discharge in xenon, excited by a compact high-current (5 kA) high-voltage (about 300 kV) sub-nanosecond generator, was investigated using a fast pin-diode. It was shown that the radiation lies mainly in the range of the vacuum ultraviolet with a wavelength of less than 200 nm, and the radiation intensity does not depend on the pressure of the working gas in the investigated range of 0.1–3.0 atm.

High-Brightness Bactericidal Light Source Based on Spark Discharges in Xenon

The radiative characteristics of high-current short-arc pulsed discharges in xenon are studied for working voltages from 0.5 to 2.0 kV, discharge energies from 0.25 to 8.0 J, xenon pressures of 4.0 and 6.5 atm, and interelectrode gaps of 4 and 6 mm. High radiative fluxes are obtained in the spectral range from 200–300 nm corresponding to bactericidal effects, so short-arc xenon lamps can be regarded as promising sources of UV radiation for application in bactericidal devices for various purposes.

Membrane potential manipulation with visible flash lamp illumination of targeted microbeads

The electrical membrane potential (Vm) is a key dynamical variable of excitable membranes. Despite the tremendous success of optogenetic methods to modulate Vm with light, there are some shortcomings, such as the need of genetic manipulation and limited time resolution. Direct optical stimulation of gold nanoparticles targeted to cells is an attractive alternative because the absorbed energy heats the membrane and, thus, generates capacitive current sufficient to trigger action potentials [1, Carvalho-de-Souza et al., 2015]. However, focused laser light is required and precise location and binding of the nanoparticles cannot be assessed with a conventional microscope. We therefore examined a complementary method to manipulate Vm in a spatio-temporal fashion by non-focused visible flashlight stimulation (Xenon discharge lamp, 385-485 nm, ∼500 μs) of superparamagnetic microbeads. Flashlight stimulation of single beads targeted to cells resulted in transient inward currents under whole-cell patch-clamp control. The waveform of the current reflected the first time derivative of the local temperature induced by the absorbed light and subsequent heat dissipation. The maximal peak current as well as the temperature excursion scaled with the proximity to the plasma membrane. Transient illumination of light-absorbing beads, targeted to specific cellular sites via protein-protein interaction or direct micromanipulation, may provide means of rapid and spatially confined heating and electrical cell stimulation.

Investigation of Short-Arc High-Pressure Xenon Discharge: Effect of Electrode Material Evaporation on Discharge Properties and Pulse Operation

This paper presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources.

An overview of discharge plasma modeling for Hall effect thrusters

The current status and challenges of the discharge plasma modeling capabilities in Hall effect thrusters (HETs) are reviewed. Partially magnetized plasmas in HETs present unique physics in that collisions with neutral atoms (a feature of low-temperature plasmas) and instabilities and oscillations (a feature of high-temperature plasmas) coexist. A discharge plasma model is constructed by choosing the numerical methods, e.g. fluid or kinetic, for individual plasma constituents, including neutral atoms, ions, and electrons. The governing equations, boundary conditions, and collision models of a xenon discharge plasma in HETs are discussed. Various models are used to illustrate device-scale phenomena, including the breathing mode and azimuthally rotating spokes, as well as small-scale physics, such as the electron cyclotron drift instability and current-carrying instability that may occur in a hollow cathode plume.

Моделирование плазмы короткодугового ксенонового разряда сверхвысокого давления

AbstractWe have studied a high- (ultrahigh-) pressure short-arc discharge in xenon with thoriated tungsten cathodes. A system of equations formulated based on earlier experimental data indicating possible emission of cathode material (thorium) into the discharge gap has made it possible to determine the electric field strength, plasma temperature, and concentration of thorium atoms as well as thorium and xenon ions in the plasma. The problem has been solved for a model discharge between planar electrodes. The results indicate the key role of thorium atoms in the cathode region. Thorium atoms determine the ionization balance and other electrokinetic properties of plasma. Emission of thorium atoms reduces the plasma temperature at the cathode, which turns out to be noticeably lower than the plasma temperature near the anode; this is a new result that agrees with experimental data. Other electrokinetic characteristics of the plasma (in particular, charged particle concentration and electric field strength) are also in good agreement with the experiment.

Controllable synthesis of ultra-long YCexOy:Eu3+ nanowire arrays and fluorescence activation of Ce3+

Ultra-long YCexOy:Eu3+ nanowire arrays(NWAs) have been synthesized in anodic aluminum oxide (AAO) templates by chemical co-deposition at negative pressure suction, which are amorphous, and possess precise dimension and homogeneous morphologies. The SEM, TEM, XRD and EDS were employed to investigate the morphology, structure and elemental composition of YCexOy:Eu3+ NWAs. The fluorescence properties of the YCexOy:Eu3+ NWAs were measured by fluorescence spectrometer (PerkinElmer LS-55) using Xenon discharge lamp as the excitation light source. There are two emission peaks at 615 nm and 702 nm with excitation wavelength of 394 nm, which corresponds to the 5D0-2F2 and 5D0-7F4 energy level transition of Eu3+, respectively. The fluorescence intensity of YCexOy:Eu3+ NWAs is related to the doping concentration of Eu3+ ion, which reaches a maximum with doping concentration of Eu3+ at 8%, and remarkably decreases at higher concentrations. Ce3+ ion dominates the fluorescence activation in YCexOy:Eu3+ NWAs.

Green photoluminescence and photoconductivity from screen-printed Mg doped ZnO films

Dominant green emission, more than five times stronger than the accompanying UV emission, is obtained from screen printed ZnO films with 15 at%Mg doping, although no such emission was present in the starting oxide powders. Photoexcitation was done by 325 nm radiation obtained from xenon discharge lamp. Photoresponse to 365 nm illumination is studied and photosensitivity gets enhanced by nearly three times by doping. All the films; undoped and doped; are polycrystalline with hexagonal wurtzite structure and predominant orientation along (101) plane. Crystallite size lies between 60 and 146 nm. Absorption peak shifts from 379 to 371 nm with successive increase in doping indicating an increase in band gap of the film. Surface structure consists of microclusters of dodecahedron-type and nearly spherical grains reducing in size with doping. EDX confirms the presence of Zn, O and Mg.

Energy and Emission Characteristics of a Short-Arc Xenon Flash Lamp Under "Saturated" Optical Brightness Conditions

We present the results of a study of the electrical, energy, and spectral brightness characteristics of an experimental three-electrode high-pressure xenon flash lamp under conditions ensuring close to maximum possible spectral brightness for the xenon emission. We show that under saturated optical brightness conditions (brightness temperature in the visible region of the spectrum ~30,000 K), emission of a pulsed discharge in xenon is quite different from the emission from an ideal blackbody: the maximum brightness temperatures are 24,000 K in the short-wavelength UV region and 19,000 K in the near IR range. The relative fraction of UV radiation in the emission spectrum of the lamp is >50%, which lets us consider such lamps as promising broadband sources of radiation with high spectral brightness for many important practical applications.

Ultraviolet Radiation of Repetitively Pulsed High-pressure Discharges in Xenon

Pulsed quartz-jacketed high-pressure xenon lamps, operating in the periodic pulse repetition modes, despite the appearing UV radiation sources of other types, remain a critical component of the processing equipment used in photochemistry, photo-medicine, nanoelectronics, biology, etc. Their main advantages, namely high power and radiation energy are slightly devalued by a relatively low efficiency of the shortwave radiation. Available literature data concerning the influence of various factors on the energy level of short-wave radiation in xenon need to be systematised and generalised because they have been obtained under conditions of uncontrolled quartz-jacketed transmission. The transmission of quartz can degrade after a while and, in addition, undergo great changes during the pulse. Besides, as a rule, in the literature, there is no detailed description of a complete kit of experimental setting. As a result, to analyse the factors affecting the efficiency of studying in the UV range is difficult, and there arises a relevant problem to optimise this type of discharge parameters to increase the efficiency in the range of 220-400 nm. A mathematical model of the radiation source, realistically describing the processes in the xenon plasma and in the stabilising envelope, can be a reliable ground for such a study. The paper shows an impact of the discharge channel diameter and length, the filling pressure of xenon, the pulse duration, the parameters of discharge circuit, and the current of pilot arc on the radiation yield. Based on the simulation-found relationship of internal plasma parameters (temperature distributions, fields of particle concentration and radiation, dynamics of electrical resistance of discharge channel, and plasma emission spectra) with radiation characteristics of discharge, are determined conditions to ensure the greatest radiation yield in the UV region. The experimental data prove the computational results. A material obtained gives practice-critical guidelines for development and correct selection of the short-wave radiation source.

Reservoir Hollow Cathode for Electric Space Propulsion

We report on a mechanically robust reservoir-type hollow cathode suitable for use in electric space propulsion for long duration space flights. It represents the first instance in which the reservoir technology has been successfully adapted to the hollow geometry used in ion engines and Hall thrusters. A novel construction technology was employed that uses flexible elements to reduce stress concentrations in the reservoir wall due to transient thermal effects. The new design was subjected to 12 000 thermal cycles without degradation in performance. Seventeen new cathodes were constructed and tested in both vacuum and xenon discharge modes. Four cathodes were vacuum and xenon discharge pulse tested for periods up to 10 000 h, with no degradation in performance. One cathode was tested in DC discharge mode for 1000 h at Colorado State University with no change in performance. Life test details will be presented. Both discharge and vacuum emission performance on the new cathodes were measured and compared with their impregnated cathode counterparts. A variety of compositions, both in the matrix and emissive material, were studied in the reservoir geometry. These provide the basis for a more exhaustive study of specific formulations in future work. In particular, cathodes with mixed metal matrices, consisting of tungsten–iridium and tungsten–osmium were tested and compared with pure tungsten. They were tested in both vacuum and discharge modes and provided superior performance over tungsten matrices. A tungsten–osmium matrix achieved a discharge current of 50 A at a temperature 100 °C lower than cathodes with tungsten matrices.

Observation of Shell Structure, Electronic Screening, and Energetic Limiting in Sparks.

We study the formation of micron-sized spark discharges in high-pressure xenon on the nanosecond time scale. The spark's energy per length is measured through the expansion dynamics of the generated shock wave, and is observed to scale linearly with the spark radius. At the same time, the surface temperature of the spark channel remains constant. Together, these observations allow us to conclude that the spark channel, up to 40 μm in overall radius, is actually an energetically hollow shell about 20 μm thick. Further, the energy per nucleus in the shell is about 15eV, independent of size and density. To reconcile these findings with the opacity to visible light, we appeal to collective screening processes that dramatically lower the effective ionization potential, allowing a much higher electron density than is otherwise expected. Thus, nanosecond measurements of sparks provide access to the thermodynamics and kinetics of strongly correlated plasmas.

Xenon Z-Pinch Discharge Plasma EUV Source Driven by Ultrashort Current Pulse

The extreme ultraviolet (EUV) spectrum has significant interest both for basic science and for industrial applications, especially lithography-related studies. Discharge-produced plasma (DPP) EUV source efficiently generates EUV radiation. Current pulse parameter is the most important and sensitive factor in DPP EUV source, which is determined by the discharge loop inductance. This paper reports on shortening the current pulsewidth by reducing discharge loop inductance on a xenon gas Z-pinch DPP EUV source. The inherent inductance of the discharge loop was reduced to about 17 nH from the previous 34 nH, and the short-circuit current pulsewidth was shortened to 85 ns. Pulsewidth of discharge plasma current was only about 110 ns. DPP EUV source was characterized in terms of EUV signals (7–16 nm) and images. The experimental results show that a shorter current pulse produces sharper EUV signals. Ultrashort current pulse discharge radiated a sharp EUV signal with a narrow pulsewidth [full-width at half-maximum (FWHM)] of only 10 ns. Axial and radial sizes (FWHM) of EUV-emitting plasma were 2 mm and $400~\mu \text{m}$ , respectively. EUV source resembles an ellipse differing from the jet shape driven by longer current pulses. Thus, a DPP EUV source driven by an ultrashort current pulse may suit high temporal and spatial resolutions required for EUV application. Corresponding plasma dynamics are observed and discussed. A comparison of time-resolved visible and EUV light images indicates that EUV emission radiates from two adjacent stagnated hot plasma columns and localizes along the central axis. This also differs from longer current driven plasma dynamics, in which EUV emission radiates from the neck part between two separate cooler plasma zones and moves with the current flow. This implies that ultrashort current pulse may inhibit axial development of EUV-emitting plasma, thus improving EUV source spatial stability and reducing EUV radiation size.

Eksperimentalna preverjanja in numerične toplotne simulacije avtomobilskih žarometov

Over the last decade lamps became a design feature of a car body and to preserve their primary purpose they are much more complex than in the past. Today’s car lamps contain powerful light sources, which utilize new technologies such as dot-concentrated light (LED chips or xenon discharge tubes). One of the unfavourable properties of these products is a high amount of thermal energy produced in a small area, causing a high thermal stress on the components. For this reason, it is important to know the temperature in critical locations to avoid damaging the lamp body or causing a defect in the light source itself. This paper presents the results of a numerical simulation of the working conditions of a lamp, the measurement inside the environmental-simulation chamber with a real lamp, providing the same conditions and the verification of the simulation results with the measurement, which confirmed the precision of the numerical simulation. The verification procedure was developed at the Heat Transfer and Fluid Flow Laboratory of the BUT in partnership with [koda Auto a.s.

Experimental and Theoretical Characterization of Dielectric Barrier Discharge in Mercury Diiodide Vapor, Xenon and Helium Gaseous Mixture

The results of studies of dielectric-barrier discharge (DBD) plasma optical characteristics in mixtures of mercury diiodide vapor, xenon and helium are presented. Regularities in spectral, temporal and energy characteristics of plasma, depending on the partial pressures of the mixture components are established. An average and pulsed radiation power of 0.8 Watts and 293 Watts is reached respectively from the emission volume 111ˑ10^-6 m³ in violet-blue spectral range.

Interaction of near-IR laser radiation with plasma of a continuous optical discharge

The interaction of 1.07-μm laser radiation with plasma of a continuous optical discharge (COD) in xenon and argon at a pressure of p = 3–25 bar and temperature of T = 15 kK has been studied. The threshold power required to sustain COD is found to decrease with increasing gas pressure to P t 20 bar and to P t 15 bar. This effect is explained by an increase in the coefficient of laser radiation absorption to 20−25 cm–1 in Xe and 1−2 cm–1 in Ar due to electronic transitions between the broadened excited atomic levels. The COD characteristics also depend on the laser beam refraction in plasma. This effect can be partially compensated by a tighter focusing of the laser beam. COD is applied as a broadband light source with a high spectral brightness.

Xenon plasma sustained by pulse-periodic laser radiation

The possibility of sustaining a quasi-stationary pulse-periodic optical discharge (POD) in xenon at a pressure of p = 10–20 bar in a focused 1.07-μm Yb3+ laser beam with a pulse repetition rate of frep ⩾ 2 kHz, pulse duration of τ ⩾ 200 μs, and power of P = 200–300 W has been demonstrated. In the plasma development phase, the POD pulse brightness is generally several times higher than the stationary brightness of a continuous optical discharge at the same laser power, which indicates a higher plasma temperature in the POD regime. Upon termination of the laser pulse, plasma recombines and is then reinitiated in the next pulse. The initial absorption of laser radiation in successive POD pulses is provided by 5p56s excited states of xenon atoms. This kind of discharge can be applied in plasma-based high-brightness broadband light sources.