Hollow Cathode Discharge Research Articles

Numerical simulation of the cathode erosion by ion sputtering in hollow cathode arc discharges

Cathode erosion by ion sputtering is one of the primary erosion mechanisms in hollow cathode discharges. In this paper, the moving mesh approach coupling with a two-dimensional plasma fluid model was employed to simulate the cathode erosion process for 100 h in a hollow cathode arc discharge. In the numerical model, plasma transport, arc flow and heating, and cathode thermal balance were considered. In addition, the electron emission, ion bombardment, and surface radiation were taken into account on the cathode wall. The normal erosion depth on the cathode surface was defined to characterize the degree of cathode erosion. The results showed that the ion sputtering erosion was sensitive to the ion flux toward the cathode wall and the distribution of the plasma potential. The external magnetic field could mitigate the erosion process. The changes of erosion depth and position under different discharge currents, gas flow rates, and intensities of the applied magnetic field were also investigated in this paper.

Emission spectroscopic study of an analytical glow discharge with plane and hollow cathodes: Titanium and iron in argon discharge

An extensive analysis of Ti and Fe emission spectra from both plane and hollow cathode glow discharges in argon in Grimm-type geometry, measured by high resolution Fourier transform spectrometer has allowed a novel comparison of excitation mechanisms. Deviations from simple models of laboratory plasmas assuming local thermodynamic equilibrium are observed. Analyte ionization in both discharge modes is dominated by charge transfer (CT) between Ar+ ions and neutral analyte atoms, while this process is more pronounced in a plane cathode than hollow cathode discharge. Radiative decay of the CT-excited levels is found to cause overpopulation of long-lived ground term and metastable analyte ions, relative to the equilibrium number densities that would be expected from the Saha-Boltzmann distribution. This overpopulation is found to spread into high-energy levels of neutral atoms by collisional 3-body recombination with electrons. Lower atomic levels of the analytes are excited by collisions with electrons, the number density of which is not high enough to support conditions close to local thermodynamic equilibrium. The analysis of the spectra is based on experimental Boltzmann plots, transition rate diagrams and intensity ratios of emission lines measured in both discharge configurations. Uncertainty propagation in the data processing procedures is analyzed and described.

Synthesis and characterization of ZnO/ZnAl2O4/Zn2TiO4 composite films by Ar–O2 mixture hollow cathode glow discharge

In this study, ZnO/ZnAl 2 O 4 /Zn 2 TiO 4 composite nanostructured thin films are deposited assisted with hollow-cathode glow discharge (HCD). The films are deposited using various argon-oxygen gases mixture (0–50% O 2 ), and its effect on film quality, optical and electrical properties is examined. Remarkably, instead of metallic targets, ZnO, TiO 2, and Al 2 O 3 powders filled in hollow-cathode are used for deposition, and thus no specific metallic targets are required in this technique. The deposited films consist of hexagonal wurtzite ZnO structure, ZnAl 2 O 4, and Zn 2 TiO 4 phases, and the crystalline size of films increases for higher oxygen contents. The thickness of films reduced by increasing oxygen contents, and all deposited films exhibit transmittance higher than 82%. The carrier concentration and mobility increase, whereas resistivity decreases when a higher amount of oxygen is added. This study shows that HCD can effectively synthesize the composite film with good optical and electrical properties. Additionally, the film's properties and elemental composition can be tuned by changing the gas composition, and thus, no separate target metallic materials with the specific composition are required.

Comparison of high-resolution electric field measurements in a hollow cathode glow-discharge operated in hydrogen and deuterium

High-resolution measurements of the electric field strength in a hollow cathode discharge operated with deuterium gas are presented. The electric field strength is determined via Stark effect splitting of the 2S level of deuterium atoms using Doppler-free two-photon laser spectroscopy. The results are compared with equivalent measurements when the discharge was operated in hydrogen. The measured electric fields are analyzed using two classical models to obtain valuable parameters about the discharge dynamics, such as the energy of the ions and their mean free path in the cathode region. This information is compared with previous results for hydrogen and allows insight into the differences when gas discharges are operated with one of the isotopes.

A positively biased external anode for energy control of plasma ions: hollow cathode and magnetron sputtering discharge

The performance of a positively biased external ring anode in combination with a hollow cathode (HC) discharge or a magnetron sputtering (MS) discharge, both with a Ti cathode and with Ar as working gas, is investigated. Plasma and floating potential increase as function of anode voltage. Energy-resolved mass spectrometry reveals that the kinetic energy of argon and titanium ions is enhanced by a positive anode voltage allowing for an effective energy control of plasma ions.

Friction and wear behavior of duplex-treated AISI 316L steels by rapid plasma nitriding and (CrWAlTiSi)N ceramic coating

Due to their high corrosion resistance, non-transformation, and non-magnetism, austenitic stainless steels can meet the service requirements. However, their low hardness and poor wear resistance impose serious drawbacks. A combination of plasma nitriding and coating as a surface treatment has been shown to improve the wear resistance without affecting the corrosion performance. In this work, the rapid plasma nitriding has been conducted on AISI 316L austenitic stainless steels using a hollow cathode discharge assisted plasma nitriding apparatus. The CrN/CrTiAlSiN/WCrTiAlN multilayers coating consisted of a CrN bottom-layer, a CrTiAlSiN interlayer, and a WCrTiAlN top-multilayer was successfully prepared using cathodic multi-arc evaporation. This ceramic coating was deposited on the surfaces of untreated and nitrided AISI 316L steels. Characterizations of the polished, rapid plasma-nitrided (RPN), only-coating, and duplex (RPN and Coating) samples were compared. Furthermore, the mechanical properties of the samples were evaluated by nano-indentation and Vickers micro-hardness tests. The dry sliding-wear characteristics were investigated by ball-on-disk wear tests against bearing steel counterparts. Tribology measurements revealed that an optimized multilayered coating followed by pre-nitriding results in excellent anti-friction and highly wear-resistant surfaces.

Diagnostic and modelling investigation on the ion acceleration and plasma throttling effects in a dual-emitter hollow cathode micro-thruster

Hollow cathode discharges are widely used as neutralizers for the electric propulsion systems and recently developed into micro-thrusters for the small satellites. In this work, a dual-emitter hollow cathode thruster is developed, which can be operated in two different modes—the neutralizer mode and the micro-thruster mode. For characterizing this kind of new device, the Langmuir probe, Faraday probe, and retarding potential analyzer are used to determine the electron temperature, electron density, ion flux, and ion energy distribution function. The operating parameters, including the thrust, and specific impulse, are also measured. A two-dimensional self-consistent extended fluid model is employed to calculate the spatial distribution of plasma parameters and the fluid field of electrons in the region around the emitters. By comparing the diagnostic and modelling results, it is found that the change in the electric field and ionization zone is the essential reason for the different performances of the device in the neutralizer and micro-thruster modes. Variation in the electric field leads to an ion acceleration effect in the micro-thruster mode; moving of the ionization zone raises the plasma pressure in the orifice region of the hollow cathode, and thus leads to enhanced plasma throttling and gas expanding effects. By analyzing the above mechanisms, the possible methods for improving this kind of hollow cathode micro-thruster are discussed.

Discovery of new even-parity fine structure levels of Pr I with angular momenta 1/2, 3/2, and 5/2

The spectrum of Praseodymium was investigated in the visible region from 4000 Å to 7500 Å based on previously recorded Fourier Transform spectra. Source of free Pr atoms was a hollow cathode discharge lamp. The investigation of spectral lines was performed using laser-induced fluorescence spectroscopy. A tunable single mode ring-dye laser, pumped by a frequency doubled Nd-YAG laser, was used as the light source to investigate selected lines. Hyperfine spectra of 129 lines were recorded and the magnetic dipole hyperfine structure constants of the involved energy levels were determined. This led to the discovery of up to now unknown levels. In this paper, 30 even parity levels, having J-values of 1/2, 3/2, and 5/2 are presented. The existence of all levels is confirmed by several laser excitations in the spectral range of our dye laser.

Influence of a longitudinal magnetic field on the parameters and characteristics of a forevacuum plasma electron source based on a hollow-cathode discharge

We report on the effect of a longitudinal magnetic field in the plasma emission system of a forevacuum-pressure, plasma-cathode electron beam source utilizing a hollow-cathode glow discharge, and on the electron emission properties of the magnetized plasma. We show that the degree and character of the magnetic field effect are in many ways determined by the geometry of the hollow cathode plasma source.

Synthesis of Al-Doped ZnO Films Assisted with Hollow-Cathode Glow Discharge and Their Characterization

Transparent conductive oxides, such as aluminum-doped zinc oxide (AZO), are of substantial importance for use in a broad range of applications because of their excellent optical and electrical properties. AZO film can be deposited by using several conventional techniques, although they suffer from limitations such as long deposition time, high cost, and the requirement for complex deposition equipment. Here, we used hollow-cathode glow discharge, which produces a high-density plasma and achieves high deposition efficiency. Remarkably, instead of metallic target materials, we used Al2O3 and ZnO powders filled in the hollow cathode as a target, thus avoiding the need for specifically designed targets in this technique. The films were deposited using mixtures of argon and oxygen at various ratios (0% to 50% oxygen), to improve the film characteristics. The films deposited under all conditions exhibited hexagonal wurtzite ZnO structure, while the grain size increased with increasing oxygen content. The film was thick and porous when using low oxygen content, but became thin and dense with increasing oxygen content. The optical transmittance was found to be strongly dependent on the processing gases used, with the highest transmittance of 84% being attained when using 25% oxygen gas. The bandgap of the films lay between 3.27 eV and 3.33 eV. The highest carrier concentration and mobility were attained when using 25% oxygen, and the Hall resistivity decreased with increasing oxygen content. Besides the excellent transmittance and electrical properties of the deposited films, it is expected that the results of this study will be useful for solar cells and optoelectronic applications due to the relatively low cost of this technique and the lack of specific target requirements.

Discharge Systems and Plasma-Assisted Electron Emission in Forevacuum Pressure Range

The paper presents a review of the current status of research into processes in hollow-cathode and arc discharges that provide the electron emission from forevacuum plasma sources. The paper studies the general operation of such electron-emitting sources, discharge initiation, achievement of the required parameters of the emitting plasma, and the efficiency improvement of the electron extraction. The goals and objectives of further research are suggested herein.

Plasma Maintenance Mechanisms in Large-Volume Hollow Anode

The paper presents research into the low-pressure hollow-cathode and hollow-anode glow discharge. The data are obtained for the plasma potential, concentration and electron temperature in the hollow anode. The proposed model explains the plasma maintenance mechanisms in the hollow anode. The basic idea of the model is that the plasma inside the hollow anode is a potential electron trap. The discharge current is transported to the anode by not only electrons, but also ions. The plasma parameters in the hollow anode are estimated in this paper. It is shown that the theoretical calculations are in good agreement with the experimental data.

Generation of Plasma with Increased Ionization Degree in a Pulsed High-Current Low-Pressure Hollow Cathode Discharge

The paper presents the results of research of the processes of generation of pulsed beam-plasma formations in a high-current non-self-sustained glow discharge with a hollow cathode at low (0.025–0.25 Pa) pressures. In the hollow cathode volume of 0.34 m3, the glow discharge pulsed currents up to 800 A were obtained at injected electron currents up to 150 A, discharge burning voltages up to 400 V, and a pulse duration of 1 ms. The plasma with a density of about 1012 cm-3 was formed with ionization degree up to 16%. It has been shown that the electron free path length λC between the Coulomb interactions in the pressure range 0.025–0.05 Pa is by a factor of about 3.5 less than the electron free path length λe when interacting with neutrals at high (10–15%) degree of plasma ionization. The measured saturation electron current density on the single electric probe was 3.7 (0.025 Pa), 5 (0.05 Pa), and 6.7 A/cm2 (0.25 Pa). Relatively homogeneous beam-plasma formations generated in the glow discharge are promising for the formation of intensive pulsed electron beams of large cross section.

Diagnostics and comparative analyzes of plasma parameters in micro hollow cathode discharges with an open and covered external surface of cathode in helium using an additional electrode

In this work, diagnostics and comparative analysis of microhollow cathode discharges with an open and covered external surface of the cathode in helium at atmospheric pressure were carried out. It is shown that by covering the external surface of the cathode, it is possible to achieve the effect when the current–voltage characteristics of the discharge grows in a wider range of discharge currents. Obviously, in this case, the negative glow (NG) plasma of the hollow cathode occupies a significant part of the discharge cell, as evidenced by the measurements carried out with the additional electrode. The electron temperature values determined from the I–U characteristic of the additional electrode are 0.3–0.4 eV for a microhollow cathode discharge with a covered external surface, which indicates that the plasma of such discharge is similar to NG plasma of glow discharge. The fast parts of the second derivatives of the I–U characteristic of the additional measuring electrode demonstrate the detection of the spectra of fast electrons produced as a result of Penning ionization reactions. Moreover, by covering the external surface of the cathode, conditions are created under which the entire discharge volume is occupied by a NG plasma, which makes it possible to achieve a better resolution for recording the spectra of fast electrons.

Simulation on hollow cathode discharge in oxygen

本文利用流体模型对气压为266Pa的氧气环境下空心阴极放电的放电特性及不同粒子的生成损耗机制进行了模拟研究.模型中包含11种粒子和48个反应.在该模拟条件下，周围阴极所对应的负辉区产生重叠，表明放电中存在较强的空心阴极效应.计算得到了不同带电粒子与活性粒子的密度分布.带电粒子密度主要位于放电单元中心区域，电子和负氧离子O-是放电体系中主要的负电荷，其密度峰值分别达到5.0×1011 cm-3和1.5×1011 cm-3；O+ 2是放电体系中主要的正电荷，其密度峰值为6.5×1011 cm-3.放电体系中同时存在丰富的活性氧粒子，并且其密度要远高于带电粒子密度值，按其密度高低依次为基态氧原子O、单重激发态氧分子O2(a1Δg)、激发态氧原子O(1D)和臭氧分子O3.论文进而对电子、O-和O+ 2的生成和损耗的反应动力学过程进行了深入分析，同时给出了不同活性氧粒子的生成损耗路径概要图.结果表明各粒子之间存在一个复杂的相互耦合的过程，每一个反应在生成某种粒子的同时也在消耗相应的其他粒子，最终各种粒子密度达到一个动态平衡.

On the Time Resolved Optogalvanic Spectroscopy of Neon in a Hollow Cathode Discharge

On the Time Resolved Optogalvanic Spectroscopy of Neon in a Hollow Cathode Discharge

Mechanical and Wear Properties of 42CrMo Steel by Plasma Nitriding assisted Hollow Cathode Ion Source

Plasma nitriding is a plasma-activated thermochemical method widely used to increase the fatigue strength, hardness and wear resistance of low-alloy steels. In this work, a new structure consisting of a hollow cathode metal plate can produce a hollow cathode discharge and heat the workpiece by radiation. This principle is used to perform hollow cathode source plasma nitriding (HCSPN). Herein, 42CrMo steels were treated by conventional plasma nitriding (CPN) and HCSPN treatments. The 42CrMo steels were nitrided at 525 °C for 6 h in NH3 atmosphere. The mechanical and dry wear properties were measured by nano-indentation, Vickers micro-indentation and ball-on-disk tribometer, respectively. The H3/E⁎2 ratio was 0.0274 GPa (H=11.51 GPa and E⁎=235.84 GPa) for the CPN sample and 0.0276 GPa (H=10.87 GPa and E⁎=215.54 GPa) for the HCSPN sample. Compared with the untreated 42CrMn steel, all the nitrided samples possess increased fracture toughness. Because the workpiece was not used as a discharge cathode, this HCSPN treatment overcame the disadvantages of the conventional CPN treatment. Additionally, results showed that the surface of the HCSPN sample was smoother than that of the CPN sample, and its tribological performance was better.

The Spectrum and Term Analysis of Singly Ionized Manganese

Abstract An extensive analysis of the Mn spectrum was carried out using high-resolution Fourier transform (FT) and grating spectroscopy of Mn–Ne and Mn–Ar hollow cathode discharge sources, over the range 82–5500 nm (1820–121,728 cm−1). Spectral wavelengths for a total of 6019 Mn ii lines have been measured, of which 1345 are obtained through FT spectroscopy. These wavelengths are given to at least an order of magnitude lower uncertainty than previous measurements. These lines were used to identify 6256 Mn ii transitions and improve the values of 505 previously published energy levels with typical uncertainties of a few thousandths of a cm−1, representing an order-of-magnitude reduction in uncertainty. We have verified and improved an additional 57 Mn ii energy levels, previously established through observation of stellar spectra alone, using our FT spectra. In addition, 52 new energy level values have been established. The number of classified lines reported is approximately 50% more than previously published. The new accurate data for 614 energy levels and 6019 lines will allow a more reliable analysis of Mn ii spectral lines in astrophysical spectra.

Surface ionization of metastable calcium atoms

We report on an experimental study of surface ionization of metastable calcium atoms on a hot polycrystalline tungsten surface in vacuum. We implemented a hollow-cathode discharge to excite a fraction of calcium atoms in an atomic beam to metastable states and collected the resulting calcium ions. We observed that metastable calcium atoms are ionized with a significantly greater efficiency than ground-state atoms, and the results suggest that virtually every metastable atom impacting the hot surface is ionized. These results demonstrate the potential of metastable atom surface ionization as a means of enriching calcium isotopes for applications in medicine, metrology, and fundamental science.

Распределение тока по поверхности полого катода для тлеющего разряда низкого давления

The results of investigation of low-pressure glow discharge with the hollow cathode for the conditions when the cathode cavity depth is comparable with cavity diameter are presented. Data on current distribution over the hollow-cathode surface using sectioned electrodes are obtained and the length of the cathode sheath is measured. It is shown that for the regime of suppressed glow discharge the main fraction of the total discharge current closes to the nearest to the anode cathode section. For the regime of ordinary glow discharge, when the cavity depth is equal to cavity diameter, discharge current over the cathode surface is distributed uniformly. The estimations of the discharge parameters and the values of the cathode sheath using the model of hollow-cathode discharge sustainment were done. Model agrees well with the experimental data.