Hollow Cathode Glow Discharge Plasma Research Articles

Forevacuum plasma-cathode electron source for generation of a ribbon beam over a wide pressure range.

We describe the results of our investigations of the generation of a ribbon electron beam (10 × 220mm2) by a two-stage discharge system based on a hollow-cathode glow discharge plasma. The source design enables operation in the pressure range 2 × 10-2 to 10Pa. At a beam accelerating voltage of 8kV, the beam current is 450 mA at a pressure of 2 × 10-2Pa and 150 mA at a pressure of 10Pa. To achieve a uniform current density distribution of the beam over its cross-sectional area, a special design of emission electrode was employed. This enabled us to reduce non-uniformities of the beam current density distribution to a level of 10%.

Influence of Electron Injection on the Characteristics of a Hollow Cathode Glow Discharge

The article presents the results of experimental studies of a glow discharge with a hollow cathode in helium and argon gases using an auxiliary discharge as an electron emitter. The authors proposed to make the electrode common for both discharges in the form of a cylindrical metal mesh. The advantage of this design is explained as follows. The connection between the discharges is carried out through holes in the grid with a geometric transparency of 0.2, which makes it possible not only to smoothly control the glow discharge current, but also to enhance the discharge current. Plasma is known to be one of the most efficient electron emitters; however, its use as a cathode in devices with a glow discharge at low gas pressures is complicated by the fact that a grid with small holes is required to separate the electron flow from the plasma, and it is impractical to use such a system in view of low mechanical strength of the grid Since the hollow cathode works effectively at low gas pressures, the release of an electron flux from the plasma of some auxiliary discharge is possible with much larger holes in the grid separating the plasma and the hollow cathode cavity. In this case, the grid can be made such that it can withstand sufficiently high thermal loads and can operate in typical discharge modes with a hollow cathode. The injection of electrons into the cathode cavity of the glow discharge changes the radial distribution of the glow intensity, the width of the cathode dark space, and other parameters of the plasma in the cathode cavity. The influence of electrons penetrating from the auxiliary discharge into the cathode cavity of the main discharge becomes significant when the current of these electrons is comparable to or exceeds the current of electrons leaving the grid cathode surface as a result of γ-processes. In parallel with the measurement of the optical and electrical characteristics of the hollow cathode glow discharge plasma, measurements of the electron concentration were carried out by the microwave sounding method. The entire current of the auxiliary discharge penetrates into the cavity of the main discharge; however, after acceleration in the cathode dark space, the electrons penetrating from the auxiliary discharge ionize gas atoms and noticeably increase the current of the main discharge. Additional ions formed due to the ionization of the gas by the injected electrons knock out new electrons from the cathode surface, which makes it possible to increase the discharge current.

Formation of an oxide layer on a biomaterial Co-Cr-Mo alloy by using a hollow-cathode glow discharge plasma with argon-oxygen and neon-oxygen mixed gases

A plasma treatment was investigated as a way to form an oxide layer on a biomaterial Co-Cr-Mo alloy (CCM alloy); the method uses a hollow-cathode-type glow discharge as the atomization/reaction source, and it is under in situ monitoring of the emission signal from the plasma. This study focused on how the plasma condition could be optimized to form a stable passivation layer on the CCM alloy based on the spectrometric information. For this purpose, a hollow-cathode-type glow discharge source was employed to form an oxide layer with a pure chromium target to be sputtered in argon-oxygen and neon-oxygen mixed gas plasmas. The thickness of the layer gradually became elevated with increasing oxygen gas partial pressure, and the layer grew more rapidly when neon mixed gas was used in place of argon. A notable feature of this method is that a surface layer of Cr2O3 can be produced with a thickness of up to several hundred nanometers after a treatment time of only a few minutes, which could occur when neon mixed gas plasma was operated under the optimized discharge condition.

Influence of the hole diameter in the perforated electrode on the parameters of electron beam generated by a forevacuum plasma electron source

We present experimental results on geometry optimization of the emission electrode in a plasma cathode electron source operating in the forevacuum range of pressure. For the 2-mm thick emission electrode, we have determined an optimal diameter of the emission aperture that provides the most efficient electron extraction from a hollow cathode glow discharge plasma in helium. At the working pressure of helium in the vacuum chamber 30 Pa, the beam power during emission from a single aperture can vary from 2 to 6 kW, while the beam diameter does not exceed 0.5 mm.

Effect of the Geometric of (Al) Hollow Cathode on Paschen Curves in Nitrogen

In this paper, an experimental study of DC hollow cathode glow discharge plasma at different nitrogen pressures ranged from (0.065 to 0.75Torr) has been proposed. Investigated was carried out under the influence of the hollow cathode geometry such as diameter and depth of hollow cathode on the breakdown voltage of the nitrogen gas, the discharge system consists of two electrodes, the cathode forms various geometrical shapes and anode as a disc- shaped with diameter (8.8cm). The electrodes are enclosed in a large cylindrical glass chamber of pyrex filled with nitrogen gas. Three important physical parameters affecting the condition of the discharge are the gas pressure, constant inter-electrode distance and the cathode geometry. We used the hollow cathode with geometric shapes such as Cylindrical, conical, oppressive and variable dimensions. The cylindrical and conical shapes have inner diameters (3 & 6) cm and repressive shapes have inner diameter (1 & 2) cm. The breakdown voltage Vb is shown to depend on the product (p.d), for lower values of pressure, p or gap, d. This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the distance between electrodes and the cathode geometry. The minimum value of breakdown voltage increases with increases gap d or increase the diameter of the hollow cathode with the length of the cavity is fixed.

Corrosion Behavior of W-Mo Co-Penetrated Layer Produced by Glow Discharge Plasma Technique in Acid Solution

Abstract To improve the corrosion resistance of Ti6Al4V alloys in acid solution, a W-Mo co-penetrated top layer was prepared by hollow-cathode glow discharge plasma technique below the β phase transition point. The surface morphology, chemical composition and crystal structure of the coatings were determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray power diffraction (XRD), respectively. Results indicate that a dense co-penetrated layer is produced with maximum thickness of approximately 23 μm. The layer is composed of AlMoTi2 and TixW1-x phases. The static corrosion test is conducted in acid (H2SO4 and HCl, separately) at room temperature (RT) by the electrochemical workstation. The results show that the W-Mo co-penetrated layer could achieve relatively stable corrosion potential in reducing acid and the Icorr of co-penetrated layers occupy merely 1/10 and 1/6 of that of Ti6Al4V substrates. In addition, there is barely any corroded product and crack on the corroded surface of co-penetrated layers, indicating no corroded shedding phenomenon occurs. So the corrosion resistance are obviously improved in the premise of keeping the basic properties of the substrate.

Emission Spectrometric Evaluation of a Hollow-Cathode Glow Discharge Plasma with Helium–Oxygen Mixed Gas for Surface Modification of Co–Cr–Mo Alloy

This paper represents emission spectrometric analysis of a hollow-cathode glow discharge plasma with helium–oxygen mixed gas for surface treatment of a cobalt-based alloy, together with surface analysis of the resulting oxide layer. A Co–28Cr–6Mo alloy was employed as a specimen. The objective of this work is to obtain plasma information for the operating conditions to be optimized for producing a stoichiometric oxide layer on the alloy surface. Helium atomic lines, atomic and ionic lines of oxygen atom, and band heads of oxygen molecule ion were observed in the emission spectra. These intensities drastically changed depending on a mixing ratio of helium–oxygen mixed gas; particularly, the emission intensity of the molecular bands was largely enhanced in the mixed gas plasma compared to the pure oxygen plasma. This band spectrum is assigned to an electronic transition from the 4 Σ g to 4 Π u states of oxygen molecule ion, whose excitation energies are 18–19 eV from the ground state of oxygen molecule. It is thus suggested that a Penning-type ionization process with metastables of helium atom (1s2s 1 S 0, 20.6 eV and 3 S 1, 19.8 eV) is an excitation mechanism how the number density of the corresponding excited state can be elevated in the helium–oxygen mixed gas plasma. This effect, which more populated the excited oxygen species in the plasma, also exerted influence on the resultant oxide layer, such as the chemical composition and the layer thickness. Surface analysis by X-ray photoelectron spectroscopy indicated that an oxide layer consisting of iron and chromium oxides was formed by this plasma treatment, and that chromium atom was enriched in it. The thickness of the oxide layer varied with a mixing ratio of the plasma gas.

Compression of pulsed electron beams for material tests

In order to strengthen the surface of machine parts and investigate behavior of their materials exposed to highly dense energy fluxes an electron gun has been developed, which produces the pulsed beams of electrons with the energy up to 300 keV and the current up to 250 A at the pulse width of 100–200 µs. Electrons are extracted into the accelerating gap from the hollow cathode glow discharge plasma through a flat or a spherical grid. The flat grid produces 16-cm-diameter beams with the density of transported per one pulse energy not exceeding 15 J·cm −2 , which is not enough even for the surface hardening. The spherical grid enables compression of the beams and regulation of the energy density from 15 J·cm −2 up to 15 kJ·cm −2 , thus allowing hardening, pulsed melting of the machine part surface with the further high-speed recrystallization as well as an explosive ablation of the surface layer.

Equipment for deposition of thin metallic films bombarded by fast argon atoms

Deposition of thin metallic films on dielectric substrates using a source of metal atom flow combined with a flow fast argon atoms has been investigated and the investigation results are presented. The fast atoms are produced due to charge-exchange collisions in a vacuum chamber of argon ions, which are accelerated by potential difference between the hollow-cathode glow-discharge plasma and an emissive grid and enter the chamber through the grid. The metal atoms produced due to ion sputtering of a metallic foil placed on the inner surface of the hollow cathode enter the chamber through the same grid. Substrate pretreatment and pulse-periodic bombardment of the growing film by ∼1-keV argon atoms both ensure adhesion of copper to glass up to 2 × 107 Pa. The use of a hollow substrate holder, whose inner surface is also covered with the same foil, makes it possible to exclude losses of the depositing metal and allows recommendation of the equipment for beam-assisted deposition of precious metal films.

Study of nonlinear oscillations in a glow discharge plasma using empirical mode decomposition and Hilbert Huang transform

Hilbert Huang transform (HHT) based time series analysis was carried out on nonlinear floating potential fluctuations obtained from hollow cathode glow discharge plasma in the presence of anode glow. HHT was used to obtain contour plots and the presence of nonlinearity was studied. Frequency shift with time, which is a typical nonlinear behaviour, was detected from the contour plots. Various plasma parameters were measured and the concepts of correlation coefficients and the physical contribution of each intrinsic mode function have been discussed. Physically important quantities such as instantaneous energy and their uses in studying physical phenomena such as intermittency and non-stationary data have also been discussed.

Effect of Nitrogen Gas Pressure and Hollow Cathode Geometry on the Luminous Intensity Emitted from Glow Discharge Plasma

The paper investigates the luminous intensity emitted from dc hollow cathode glow discharge plasma (HCGD) .The experiments were conducted at different nitrogen gas pressures ranged from (0.015 to 0.75Torr) and constant discharge current (Id=1.88 mA).The influence of both pressure and hollow cathode geometry such as diameter and depth of hollow cathode have been studied .The results show that the Photo-Luminous Efficiency emitted from the hollow cathode glow discharge decrease nearly exponentially with the increasing gas pressure. This is due to the characteristics of hollow cathode at the low pressures to produce more energetic excitation. On the other hand, the luminous efficiency increase linearly with the increasing inter-cathode distance of hollow, this is because increasing the inter - cathode distance of hollow cathode is equivalent to the decreasing of gas pressure. However the luminous intensity increase linearly with the depth of hollow cathode ranged from (1up to2.5) cm and then decrease. This behavior of the intensity with both the gas pressure and hollow cathode geometry is satisfactory agreement with previous works.

Continuous wavelet transform based time-scale and multifractal analysis of the nonlinear oscillations in a hollow cathode glow discharge plasma

Continuous wavelet transform (CWT) based time-scale and multifractal analyses have been carried out on the anode glow related nonlinear floating potential fluctuations in a hollow cathode glow discharge plasma. CWT has been used to obtain the contour and ridge plots. Scale shift (or inversely frequency shift), which is a typical nonlinear behavior, has been detected from the undulating contours. From the ridge plots, we have identified the presence of nonlinearity and degree of chaoticity. Using the wavelet transform modulus maxima technique we have obtained the multifractal spectrum for the fluctuations at different discharge voltages and the spectrum was observed to become a monofractal for periodic signals. These multifractal spectra were also used to estimate different quantities such as the correlation and fractal dimension, degree of multifractality, and complexity parameters. These estimations have been found to be consistent with the nonlinear time series analysis.

Nitriding of Technical-Purity Titanium in Hollow-Cathode Glow Discharge

The process of nitriding at low pressures and temperatures (≤550°C) in hollow-cathode glow discharge plasma was studied for technical-purity titanium of the VT1-0 commercial grade. The diffusion saturation of titanium with nitrogen in plasma with a concentration of n = 1010–1011 cm−3 takes place at an ion current density on the cathode within 1.6–4.0 mA/cm2. It is established that a key role in the process of metal saturation is played by atomic nitrogen. The experiments revealed the formation of a layer of gradient structure with a high microhardness (∼14 GPa) on the surface of nitrided titanium.

Laser absorption spectroscopy with a blue diode laser in an aluminum hollow cathode discharge

A GaN-based blue diode laser is employed for laser absorption spectroscopy in an aluminum hollow cathode glow discharge plasma. A Littrow grating stabilized external resonator is used for tuning the wavelength of laser emission. Scanning the wavelength of the laser probes the absorption profile of aluminum transitions yielding ground state aluminum densities. Hyperfine structure has to be taken into account in order to obtain correct temperatures. The diode laser is used to investigate both the temperature and the density of aluminum atoms sputtered from a cathode surface by ion bombardment from the cathode fall region. The blue diode laser allows quick and easy access to aluminum ground state atoms at low costs.

Low-pressure hollow-cathode glow discharge plasma for broad beam gaseous ion source

We have developed a hollow-cathode glow discharge plasma for a dc broad beam ion source. For a broad beam ion source, it is hard to obtain adequate pressure drop between the discharge space and the extraction region. The high-current low-voltage mode of discharge is limited to a pressure about 10−3 Torr, but for stable extraction of ions without breakdown the pressure needs to be at least one order of magnitude lower. To decrease the limited operation pressure for the high-current mode of the hollow-cathode glow, an external electron beam was used. These electrons were generated in a “keep-alive” discharge and are accelerated in the cathode layer of the primary discharge. In this way we successfully decreased the operation pressure to 10−4–3×10−5 Torr, as well as reaching a value of the discharge voltage as low as 80 V. The characteristics of this discharge system are presented, and the influence of external electrons on the discharge parameters is discussed.