Plasma-cathode Electron Source Research Articles

"Development and characterization of pseudospark discharge based plasma cathode electron (PD-PCE) source for high density and energetic e-beam generation for pulsed power applications"

"Development and characterization of pseudospark discharge based plasma cathode electron (PD-PCE) source for high density and energetic e-beam generation for pulsed power applications"

Electron-beam nitriding of carbon steel alloy in the forevacuum pressure range

We have explored the ion nitriding of AISI 5135 carbon steel alloy. Nitriding was performed in the plasma formed by an electron beam at the forevacuum pressure of 5 Pa. The beam was generated using a forevacuum-pressure plasma-cathode electron source. We report the results of SEM and X-ray diffraction pattern analysis of the surface of nitrided samples, as well as results of measured micro hardness, surface wear rate, coefficient of friction, roughness, and nitrogen penetration depth. We find that the sample temperature during nitriding affects the surface morphology and phase composition of surface layers. A threefold increase in surface micro hardness was achieved. The surface micro hardness increases with increasing nitriding duration. Samples nitrided at temperatures up to 500°С for a time of no less than 2 h show the greatest abrasive wear resistance. The nitrogen penetration depth is greater than 200 μm for all experimental conditions, with maximum of 450 μm.

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%.

Operation features of a forevacuum pulsed plasma-cathode broad-beam electron source with a double-mesh emission electrode

We report our experimental results on the operating features of a forevacuum-pressure pulsed broad-beam plasma-cathode electron source with a double-mesh emission electrode, which includes main and auxiliary meshes. In this source, the emission plasma is generated by a pulsed cathodic arc. It is shown that such an emission system provides an increase in the maximum operating pressure for pulse durations of up to several milliseconds. We find that at certain threshold pressure transient mode and quasi-stationary mode of electron beam generation appear. The transient mode observed at the beginning of the emission current pulse is characterized by a higher emission efficiency, which changes during the time. The time, after which the quasi-stationary mode occurs, depends on the gas pressure and the parameters of the auxiliary mesh.

The Effect of Temperature on Electron Beam Brazing of Titanium to Alumina Ceramic

The authors have investigated the effect of temperature on the composition and structure of the joint metal produced by electron beam brazing of titanium and alumina ceramic using a fore-vacuum-pressure, plasma-cathode electron source. We found that for brazing temperatures below the titanium polymorphic α-β transition temperature, conditions favorably affect the performance characteristics of the metal-ceramic joint produced. Based on these studies, a strong, tight metal-ceramic joint between titanium and alumina ceramic was obtained

Ionization mechanism of beam plasma generated by an electron beam in medium vacuum

We present the results of the measurements of the ionic composition of plasma generated by an accelerated electron beam at medium vacuum (fore-vacuum) pressures. Calculations of the contribution of plasma electrons and beam electrons to the mechanism of ionization are presented. Comparison of the calculated with the experimental data led us to the conclusion about the dominating contribution of beam electrons and to the ionization process. Keywords: beam plasma, fore-vacuum, electron beam, plasma-cathode electron source.

Contribution of thermal dissociation during steel nitriding in electron beam plasma

We report the results of measurements of mass-to-charge ion composition of the beam plasma generated by a forevacuum plasma-cathode electron source in a nitrogen atmosphere during electron beam interaction with the surface of a steel sample. It has been found that as the sample surface temperature increases from 540 ℃ to 930 ℃, the fraction of atomic nitrogen ions in the spectrum increases by 4-10%. This increase in atomic nitrogen occurs at the backdrop of decreasing number of molecular nitrogen monoxide ions and is associated with thermal dissociation of its molecules.

Hollow Cathode Glow Discharge Initiation in a Fore-Vacuum Plasma–Cathode Electron Source

In this article, we present the results of a study on the initiation of a hollow cathode discharge in the electrode system of a fore-vacuum plasma–cathode electron source. It is shown that the development of the hollow cathode effect is facilitated by the back-streaming ion flux of the high-voltage glow discharge (HGD) that arises in the accelerating gap of the electron source. The effect of the type of operating gas and the cathode hollow geometry on the value of the initiating accelerating voltage, which ensures the HGD back-streaming ion flux, have been studied. It is proposed to use an auxiliary pulsed surface flashover discharge to trigger the hollow cathode discharge. The two methods used jointly provide a stable discharge initiation in the entire operating pressure range of the source, including the ultimately low-pressure range where the operation of the hollow cathode discharge in its low-voltage form is still stable.

Electron-Beam Sintering of Al2O3-Cr-Based Composites Using a Forevacuum Electron Source

We describe our studies of the influence of Cr content in an Al2O3-Cr composite on its thermal and electrical conductivity properties during and after electron-beam sintering in the forevacuum range of pressure. Sintering was carried out using a plasma-cathode forevacuum-pressure electron source of an original design, capable of processing non-conducting materials directly. It is shown that the chromium content affects the efficiency of the beam power transfer to the irradiated composite. The efficiency decreases with increasing chromium content. Measurement of the composite’s coefficient of thermal conductivity, in the temperature range 50–400 °C, shows that it varies almost linearly from 25 W/(m∙K) to 68 W/(m∙K) as the Cr content in the composite increases from 25% to 75% wt. The electrical conductivity properties after sintering exhibit a non-linear behavior. The conduction activation energy Ea, measured via the dependence of the current through composites of different compositions, is slightly lower than the Al2O3 band-gap. The addition of metallic Cr results in a disproportionate decrease in Ea, almost by an order of magnitude, from 6.9 eV to 0.68 eV. By varying the chromium content, it is possible to form a material with thermal and electrical conductivities controllable over a wide range.

Operating regimes of a constricted arc discharge in a forevacuum-pressure, plasma-cathode electron source of pulsed large-radius electron beams

We have investigated the operating regimes of a pulsed constricted arc discharge in a forevacuum plasma-cathode electron source of large-radius electron beams. The configuration of the intermediate electrode (IE) with a constricting channel (CC) determines the maximum parameters (current and pulse duration) and operating regimes of the constricted arc. An IE with ceramic (aluminum nitride) CC and an IE with sectional tantalum CC, formed by several electrically insulated tantalum disks with co-axial holes, lead to an increase in the maximum parameters compared to an IE with metal CC. In particular, an IE with sectional tantalum CC provides the highest maximum parameters. The ceramic and sectional tantalum constricting channels also provide lower minimum pressure for which the constricted arc operates stably. When the pressure reaches a certain threshold value, which depends on arc current, a discharge system with IE with sectional tantalum CC provides stable operation for pulse duration up to 10 ms. An increase in pressure provides higher discharge current in the millisecond regime of the discharge operation. When the arc current reaches threshold values from 84 to 92 A (depending on gas pressure), a self-compressed (pinched) mode of operation of the constricted arc occurs. The pinched arc regime is characterized by the highest current and the longest pulse duration. The forevacuum electron source based on the constricted arc discharge with IE with sectional tantalum CC offers generation of low-energy (up to 8 keV) electron beam with current up to tens of amperes and pulse duration up to 10 ms.

Discharge in a long metal tube with an electron beam generated by a forevacuum plasma–cathode electron source

We describe our investigations of the current distribution in a non-self-sustained hollow-cathode glow discharge in a long metal tube. The discharge is initiated and sustained by injecting an electron beam generated by a forevacuum-pressure plasma–cathode electron source into the tube. It is shown that the distribution of discharge current along the inner sidewall over the tube length and, correspondingly, the distribution of plasma density along the tube depend primarily on tube geometry and electron beam current. The character of the discharge current distribution is determined by the ratio of contributions to ionization by beam electrons and by secondary electrons emitted from the tube bottom (if the lower end of the tube is closed) and from the tube sidewall. These processes may lead to a non-monotonic distribution of discharge current with a minimum in the middle. Increasing the discharge current levels out this minimum, improving the uniformity of the current distribution over the tube length.

Characterization of Pseudospark Discharge-Based Multigap Plasma Cathode Electron Source for the Generation of Short Pulsed Energetic Electron Beam

Pseudospark (PS) discharge-based devices are known as excellent source for the generation of high current density and energetic self-focused electron beam in the hollow cathode (HC) phase. In this article, short pulsed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!\!\!&lt; 100$ </tex-math></inline-formula> ns) and high energetic (~20 keV) electron beam has been generated and propagated (up to ~60 mm) in the drift region without using any external guiding magnetic field from the four-gap configuration of PS discharge-based plasma cathode electron (PD-PCE) source. The particle-in-cell (PIC) simulation code OOPIC Pro has been employed, whose results have shown the strong dependence of beam propagation into the drift region on the penetration and distribution of potential lines. The combined experimental and simulation investigations have also been carried for the multigap (four-gap) with wide range of external storage capacitor (40 pF–18 nF) and operating voltages (5–35 kV). The circuit parameter controls the appearance of HC phase for the energetic (50%–70% applied voltage) electron beam and conductive phase for the high current (~10 A to ~0.5 kA) electron beam. The potential distribution has clearly indicated that the electron beam with higher applied voltages can propagate more focused in the drift region. The investigations have evidently shown the generation of low energy and high current to high energy and low current electron beams suitable to cover the potential applications in the field of extreme ultraviolet (EUV)/soft X-ray radiation generation, surface modification, and microwave-terahertz radiation generation.

Characteristics of a Source for Oxide Coating Deposition by the Electron-Beam Evaporation of Dielectric Materials

We describe our investigations of a plasma-cathode electron source designed for the deposition of oxide coatings by the electron-beam evaporation of dielectric materials. Tests carried out using oxygen as the working gas showed that the source is operable without a change in parameters for at least ten hours of continuous operation. The current–voltage characteristics of the hollow-cathode plasma source in oxygen displayed a monotonically increasing character, and the voltage dependence of the discharge current was exponential. At the same time, for argon, nitrogen, and helium, the discharge voltage remained unchanged over a current ranging from 0.1 A to 1 A. A possible reason for these differences is the formation of oxides on the electrode surfaces for operation in the oxygen, impeding the discharge operation and requiring higher voltages for the same current as the other gases. The dependencies of the electron beam current on the accelerating voltage were monotonically increasing curves for all the gases except for helium, for which the beam current remained unchanged with increasing voltage over a range from two to ten kilovolts.

Influence of electron beam generation on the parameters and emission characteristics of a constricted arc discharge in a pulsed forevacuum plasma-cathode electron source

We have explored the influence of accelerating voltage, gas pressure, and accelerating gap length on the discharge parameters and emission characteristics of the plasma of a constricted arc discharge which forms the emission plasma in a forevacuum-pressure, plasma-cathode, broad-beam electron source. We find that the back-streaming ion flux from beam plasma, formed by electron beam in the accelerating gap and beam propagation region, leads to increase in the maximum current and pulse duration of the constricted arc. The rise-time of the emission current pulse (and electron beam current pulse) depends not only on the formation of the emission plasma but also on changes in arc current flow conditions in the constricting channel, which occur during the pulse duration due to the back-streaming ion flux. There is a significant influence of accelerating gap length on the emission characteristics. Varying the accelerating gap length provides control of the delay time and rise time of the emission current pulse (e-beam current pulse), as well as the electron emission efficiency.

Electron Beam Sintering of Composite Al2O3-ZrO2 Ceramics in the Forevacuum Pressure Range

We describe our investigations of electron beam sintering of multilayer ZrO2-Al2O3 composite ceramics in the forevacuum pressure range (~30 Pa). To generate the electron beam, a plasma-cathode electron source operating in the forevacuum pressure range was used; this kind of source provides the capability of direct processing of non-conducting materials. We studied the effect of electron beam sintering on the temperature drop with sample depth for different layer thicknesses and determined the optimal layer thickness to ensure minimal temperature drop. We show that in order to minimize the temperature difference and improve the sintering, it is necessary to take into account the thermophysical parameters of the sintered materials. Forming a layered structure taking into account the coefficient of thermal conductivity of the layer materials allows a reduction in the temperature gradient by 150 °C for samples of 3 mm thickness.

Electron Beam Propagation in a Metal Tube at 1–10-Pa Pressures

Some features of electron-beam propagation through a narrow metal tube at a gas pressure of 1–10 Pa have been investigated. A forevacuum-pressure, plasma-cathode electron source was used to generate the electron beam. The results obtained are described and compared with the case of electron-beam propagation in free space. A comparison shows that the tube makes it difficult for the beam to pass. Calculations based on the Rutherford scattering and Monte Carlo method show satisfactory agreement with experimental results.

Features of the Formation of a Focused Electron Beam by a Forevacuum-Pressure Plasma-Cathode Source With Single Emission Channel

We have explored the formation processes of a focused electron beam generated by a forevacuum plasma-cathode electron source with a single emission channel in the higher-pressure range (5–10 Pa). Appropriate design of the beam formation system geometry together with decrease in working gas pressure and increase in beam accelerating voltage leads to a decrease in the convergence angle of the electron beam. The convergence angle decreases with decreasing diameter of the emission channel aperture and of the extractor, as well as with increasing accelerating gap length. In this case, the dependence of the beam cross-sectional diameter at crossover (focus) on the beam accelerating field has a non-monotonic form. With optimized discharge gap geometry, the minimum convergence angle of the electron beam was 0.1° and its brightness <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{6}$ </tex-math></inline-formula> A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{m}^{-2} \cdot $ </tex-math></inline-formula> sr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> .

Electron beam synthesis of silicon-carbon coatings in the forevacuum pressure range

We describe our investigations of the synthesis of silicon-carbon coatings obtained by electron-beam evaporation of silicon carbide at forevacuum background gas pressure. The electron beam was generated by a forevacuum-pressure, plasma-cathode electron source operating at a gas pressure of 5–10 Pa. The effect of electron beam parameters on the morphology and tribology of the deposited coatings was explored, and the results are described here.

Suppression of instabilities in the transport of a high-power electron beam in the forevacuum pressure range using low-energy thermionic electrons

We report the results of our study on the effect of injection of low-energy thermionic electrons on the suppression of instabilities of the beam-plasma discharge (BPD) type in a beam plasma during the transport of a powerful continuous electron beam generated by a plasma–cathode electron source in the forevacuum range of pressure. As result of thermionic electron injection, the plasma electron temperature decreased to 0.3 eV and the plasma density decreased by an order of magnitude to 1015 m−3. The minimal thermoelectron current required for suppressing the BPD increases with increasing emission current and decreases with increase of the beam accelerating voltage.

Processing of polyethylene in the beam-plasma generated by a ribbon electron beam at forevacuum pressure range

We present research results of the surface modification of polyethylene film by plasma produced by the ribbon electron beam formed by a forevacuum-pressure plasma-cathode electron source. The electron beam was of energy 3 keV and current 150 mA. The gaseous environment was argon at a pressure of 10 Pa. The argon plasma so formed in the electron beam vicinity and at the location of the polyethylene samples was of density about 3 x 1015 m−3. Both direct plasma bombardment, and also energetic ion bombardment with ions accelerated to the sample from the e-beam produced plasma, were investigated. We show that this plasma or ion treatment imparts improved hydrophilic properties to the film and decreased light transmittance in the ultraviolet region.