Forevacuum-pressure Plasma-cathode Research Articles

Extending the Operating Pressure Range of a Forevacuum-Pressure Plasma-Cathode Ribbon Electron Beam Source

Extending the Operating Pressure Range of a Forevacuum-Pressure Plasma-Cathode Ribbon Electron Beam Source

SPECIFIC FEATURES OF THE CURRENT FLOW THROUGH AN ALUMINA-BASED METAL-CERAMIC COMPOSITE DURING ELECTRON BEAM IRRADIATION IN THE FOREVACUUM PRESSURE RANGE

We describe some specific features of the current passage through an Al<sub>2</sub>O<sub>3</sub>-Ti metal-ceramic composite sample during irradiation by a forevacuum-pressure plasma-cathode electron beam source. The composition ratio of the composite was 90% Al<sub>2</sub>O<sub>3</sub> and 10% Ti by weight. It is shown that during electron-beam irradiation, the magnitude and direction of the current through the sample depend on the temperature as well as on the sintering time at given temperature. The absolute value of the recorded current can reach 15 mA for an electron-beam current of 60 mA and electron energy of 10 keV. The dependence of the current is caused by redistribution of titanium over the depth of the sintered composite during heating, and provides a means for forming gradient metal-ceramic materials with variable content of components over the depth.

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.

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.

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> .

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.

Parameters and characteristics of a pulsed constricted arc discharge operating in a forevacuum-pressure plasma-cathode electron beam source

The parameters and characteristics of a pulsed constricted arc discharge operating in the forevacuum pressure plasma-cathode source of a large-radius (about 4 cm) low-energy (up to 10 keV) electron beam are presented. The constricted arc discharge is characterized by a rising current-voltage characteristic. Increase in gas pressure and the use of gas with greater ionization cross section lead to a decrease in arc voltage. We have determined the dependences of the maximum stable arc current on the operating conditions, and explored the emission properties of the plasma. Efficient electron emission from this plasma over the pressure range 5–21 Pa, and the influence of the beam generation processes on the constricted arc discharge have been demonstrated. A pulsed electron beam with current up to 20 A and energy up to 10 keV has been obtained using a forevacuum-pressure plasma-cathode electron source based on a constricted arc discharge.

Plasma formation near the beam collector of a forevacuum-pressure plasma-cathode electron beam source

It was shown that secondary electrons, emitted by the electron beam collector of a forevacuum-pressure plasma-cathode electron source, play an important role in beam plasma generation. Their yield is determined by the secondary electron emission properties of the collector, its negative potential, and the angle of incidence of the electron beam on the collector. Positioning the beam collector surface at an angle to the beam propagation direction results in spatial separation of the two plasma regions formed by the primary electron beam and by secondary electrons generated at the collector. This separation makes it possible to compare the parameters of both plasmas. It was found that the secondary plasma column is always directed perpendicular to the collector surface regardless of the primary beam angle of incidence. The secondary plasma is generated via gas ionization by secondary electrons accelerated by the collector potential. Under certain conditions (high values of secondary electron emission coefficient and collector potential), the contribution of secondary electrons to formation of the near-collector plasma can surpass the contribution from the primary electron beam itself.

Forevacuum plasma source of continuous electron beam

AbstractWe describe here the design, main parameters, and characteristics of a forevacuum-pressure plasma-cathode electron source based on a hollow-cathode discharge. The source generates a continuous focused electron beam with energy up to 30 keV and current up to 300 mA at a pressure of 10–50 Pa. The focused electron beam reaches a maximum power density of 106 W/cm2. The source utility has been demonstrated by its application for processing and cutting of ceramic.

Alumina coating deposition by electron-beam evaporation of ceramic using a forevacuum plasma-cathode electron source

We have explored the formation of alumina coatings by electron beam evaporation of bulk alumina ceramic using a forevacuum-pressure plasma-cathode electron beam source at a pressure of 60 mTorr of air. The alumina e-beam target material is evaporated at a rate up to 4.2 g/h, and the coating deposition rate is up to 18 μm/h. The evaporated ceramic is partially ionized by the energetic electron beam, and we have measured the plasma composition as a function of beam power. The deposited alumina coatings were characterized by scanning electron microscopy and energy-dispersive x-ray spectroscopy and found to be uniform and pore-free with a composition that is over 99% aluminum and oxygen, with less than 1% impurities including carbon, silicon and calcium.

Specifics of the focused electron beam transport in the forevacuum range of pressure

We have investigated electron beam transport at an elevated forevacuum pressure of tens of Pascals of helium. The continuous electron beam (6–14 keV, 300 mA) is generated by a forevacuum-pressure plasma-cathode electron source utilizing a hollow-cathode discharge. A beam-plasma discharge is generated in the beam transport zone, which is characterized by increased plasma density in the region of the most intense beam-plasma interaction. We find that the location and distribution of the beam-plasma discharge depend on the electron beam energy and current density. Under certain conditions, we observe that the beam plasma is stratified, with a periodic variation of plasma density and luminosity along the direction of electron beam propagation.

Effect of collector potential on the beam-plasma formed by a forevacuum-pressure plasma-cathode electron beam source

We consider the beam-plasma formed by an energetic electron beam at fore-vacuum pressure, when the beam is terminated by an electron collector plate. We show that in the pressure range of 1–10 Pa, the dependence of beam-plasma density n on the electron beam collector potential φ has a maximum. The maximum plasma density nm at the optimum collector potential can be much greater than the plasma density when the collector is at ground or at floating potential. The nonmonotonic dependence n(φ) is found to be caused by the contribution of secondary electrons from the collector to plasma generation.

Stability of electron beam generation by forevacuum-pressure plasma-cathode electron beam source based on a cathodic arc

We describe our experimental research on the stable generation of large-radius pulsed high-current electron beams using a forevacuum-pressure plasma-cathode electron beam source with cathodic arc plasma generation. We find that increased gas pressure and the use of gas with a higher ionization cross-section considerably decrease the stable emission current due to loss of electric strength of the acceleration gap (breakdown). Increased pulse duration results in a decrease in the emission current, but the influence of the gas species and its pressure remains for all pulse durations. There is an extremum in the dependence of emission current on the acceleration gap length and the optimum gap length depends on the gas pressure and the kind of gas. The experiment results can be explained by the effect of back-streaming ion flow, which charges dielectric inclusions on the emission electrode (anode grid) and thereby amplifies the electric field.

Generation of high-power-density electron beams by a forevacuum-pressure plasma-cathode electron source

We report on our work directed towards increasing the power density of the focused electron beam produced by a forevacuum-pressure plasma-cathode electron beam source at a pressure of 10–30 Pa. We have optimized the geometry of the plasma discharge system, emission channel and acceleration gap, and simultaneously increased the beam acceleration voltage. The beam power density achieved was 106 W cm−2, an order of magnitude greater than that typical of forevacuum plasma electron sources, and is quite sufficient to allow the use of these beams for the treatment of high-temperature bulk dielectrics.

Influence of gas pressure on electron beam emission current of pulsed cathodic-arc-based forevacuum plasma electron source

We describe our experimental investigation of the effect of background gas pressure on the emission parameters of a pulsed cathodic-arc-based forevacuum-pressure plasma-cathode electron source. We find that increased gas pressure over the range 4–16 Pa significantly reduces the beam current rise-time and significantly increases the emission current amplitude. For example, at a discharge current of 20 A, increasing the working gas pressure from 4 Pa to 16 Pa increases the emission current from 8 A to 18 A and shortens the beam rise-time from 50 μs to 20 μs. This influence of gas pressure on the electron beam parameters can be explained by the effect of arc discharge current switching from the anode to emission. In our case, the current switching effect is caused by increased working gas pressure. In the forevacuum pressure range, the increase of the electron emission current with the growth of gas pressure is due to a rise in the emission plasma potential which is caused by ion back-streaming from the plasma formed in the electron beam transport region. A model describing the influence of gas pressure on the electron emission from the plasma is presented.

Millisecond Pulsed Arc Discharge in a Forevacuum-Pressure Plasma-Cathode Electron Source

We have explored the parametric behavior of a quasi-continuous (1.8 ms) vacuum arc discharge operating as plasma source of a forevacuum-pressure plasma-cathode electron beam source. The current-voltage characteristic of the arc is presented and we show that the discharge becomes unstable at a current below 5–6 A (for our copper cathode). The operating discharge voltage increases weakly with increasing arc current over the pressure range 3–15 Pa. At a pressure greater than 15 Pa the arc shows two possible modes, differing in discharge voltage, as observed earlier for submillisecond arcs. The ratio between the currents to the hollow and plane anode sections are measured to study the arc modes. It is shown that discharge current and pressure affect that ratio. The influence of the arc modes on the electron emission in the forevacuum pressure range is discussed.

Sintering of oxide and carbide ceramics by electron beam at forevacuum pressure

Novel approaches for electron beam sintering of zirconia and silicon carbide ceramics have been investigated: application of forevacuum pressure plasma-cathode to compensate the charge induced by the electron beam on the green compact surface, and previous dry powder compaction under powerful ultrasound assistance. Dense YSZ ceramics with submicron and micron grains have been consolidated by electron beam sintering after powder compaction using ultrasound.

Generation of uniform electron beam plasma in a dielectric flask at fore-vacuum pressures

We describe a system for the generation of spatially uniform and homogeneous dense plasma in a dielectric flask using a forevacuum-pressure plasma-cathode electron beam source. At optimum beam energy and gas pressure, the non-uniformity in plasma density distribution along the length of the flask is less than 10%, and the plasma density and electron temperature in the flask are greater than for the plasma produced in the vacuum chamber with no flask. The measured parameters of the beam plasma in the flask are compared to the predictions of a model based on balance equations.

Pulsed Cathodic Arc for Forevacuum-Pressure Plasma-Cathode Electron Sources

We describe properties and parameters of a pulsed cathodic arc discharge, as applied in forevacuum-pressure plasma-cathode electron sources for the generation of broad electron beams. It is shown that during a single arc current pulse, the arc can operate in either of two modes, differing in their discharge operating voltage and plasma constitution. The radial plasma density distribution approximates a Gaussian. The effect of gas pressure on the plasma density is pronounced only at a considerable distance from the cathode.