Forevacuum Pressure Range Research Articles

Short High-Current Electron Beams and High-Powermicrowave Pulses in the Forevacuum Pressure Range

Short High-Current Electron Beams and High-Powermicrowave Pulses in the Forevacuum Pressure Range

Pressureless electron beam sintering of Al2O3–Ti composite in the forevacuum pressure range

The results of our investigations of pressureless electron beam sintering of Al2O3/Ti composite in the fore-vacuum range of pressure are described. A novel kind of electron source for irradiation the surface of a compacted composite with a focused electron beam at a pressure of 30 Pa was used. The effect of different electron-beam irradiation regimes and compact size on the sintered material hardness, density and porosity is described. The measured and calculated temperature variation across the sample thickness are discussed. It is shown that after the electron-beam sintering there are formed in the bulk of the sample three regions with different porosity and hardness. The microhardness in the middle of the sample reached 29 GPa. These regions are formed due to the low thermal conductivity of the alumina ceramic component of the composite. The sintering regimes that produce samples with low porosity are determined.

Generation of beam plasma near a dielectric target irradiated by a pulsed large-radius electron beam in the forevacuum pressure range

We have investigated generation of beam plasma near a dielectric (ceramic) target irradiated by a pulsed large-radius electron beam in the forevacuum pressure range 3–15 Pa. The electron beam was accelerated with voltage up to 8 kV. Under a certain threshold accelerating voltage increase in the plasma density was observed near the dielectric target as compared with beam plasma density without the target. A decrease in gas pressure leads to smaller value of this threshold voltage. The observed dependencies are apparently caused by two factors: secondary electrons being emitted from the ceramic target and charging of surface of the ceramic target by the e-beam. The secondary electrons, emitted from the ceramic target, provide “additional” ionization of the gas. The charge on the dielectric target surface creates a field that accelerates the slow secondary electrons, which provides an increase in plasma density near the ceramic target. The negative charge on the target slows down the beam electrons, and thus increases total ionization cross section of gas by electron impact. The value of negative charge on the dielectric surface increases with decreasing gas pressure.

Measurement of mass-to-charge beam plasma ion composition during electron beam evaporation of refractory materials in the forevacuum pressure range

We describe here the design of the modernized ion-optical system (IOS) of the standard residual gas analyzer (RGA). IOS electrodes are made of stainless steel. The electrodes are powered outside the vacuum chamber. Reducing the diameter of the entrance aperture to 0.6 mm made it possible to expand the measurement range. These design features of this system makes it possible to measure the mass-to-charge composition of beam plasma ions generated by electron beam evaporation of ceramics and refractory metals in the forevacuum pressure range under a prolonged exposure to high temperature. We present the results of the measured plasma composition during evaporation of aluminum oxide and zirconium ceramics, as well as of titanium.

Influence of the composition of Al2O3-ZrO2 ceramics on the distribution of thermal fields during its electron beam sintering

The article presents the results of sintering a composite graded ceramic based on Al2O3 / ZrO2 using a focused electron beam. To prevent surface charging, sintering was carried out in the forevacuum pressure range. It was demonstrated that under electron beam exposure, the surface temperature reaches 1600 degrees within 20 minutes. The distribution of elements over the depth of sintered specimens is presented. The dependence of the temperature difference over the sample as a function of the number of layers in the sample is shown. The value of the temperature drop along the depth of the sintered sample is calculated and recommendations are given for reducing the temperature drop.

Electron-beam modification of nitrile butadiene rubber in the fore-vacuum pressure range

We have studied the modification of nitrile butadiene rubber surface properties by pulsed and by continuous electron beams generated in inert (argon, helium) and in chemically active (oxygen, nitrogen, air) gas atmosphere in the fore-vacuum range of pressure (∼10 Pa). Relative measurements of the wear rate, friction coefficient, and contact (wetting) angle of the sample surfaces before and after beam treatment have been made. We have found that the electron-beam treatment of nitrile butadiene rubber does not result in any significant thermal damage to its surface, and that dependencies of the coefficient of friction and the wear rate on the surface treatment duration have a non-monotonic character. For optimal electron beam treatment conditions, the friction coefficient decreases by a factor of about two.

Effects of gas pressure and bias potential on electron beam nitriding of titanium

We have studied the effects of gas pressure and bias potential on ion-plasma nitriding of titanium in an electron beam-produced plasma generated in the forevacuum pressure range. We present the results of scanning electron microscopy, x-ray analysis, and tribological studies of the modified layers of nitrided samples. The results of measurements are given, and the correlation between parameters (ion mass-to-charge composition, plasma density, electron temperature) of the beam-plasma and of the nitrided surface is found. Increased working gas pressure leads to an increase in the fraction of atomic nitrogen ions in the plasma, which results in increased surface layer hardness, depth of penetration of nitrogen atoms into the sample, and wear resistance. Higher absolute values of sample bias potential contribute to increased plasma density near the sample surface and a corresponding increase of hardness and wear resistance of the sample.

Ion Composition of the Beam Plasma Generated by Electron-Beam Evaporation of Metals and Ceramic in the Forevacuum Range of Pressure

We present the results of measurements of the ion composition of the plasma generated by an accelerated electron beam in the forevacuum pressure range. It has been found that the main contribution to ionization processes comes from beam electrons. It has been shown that, during the electron-beam evaporation of metal or ceramic targets, the number of ions evaporated from the materials in the beam plasma significantly exceeds the number of ions produced from the residual atmosphere and admitted gases. Together, electron beams and beam-produced plasma can catalyze the processes of coatings deposition or modification of the surface layer of the samples.

Electron-beam heating of ceramics to moderate temperature at fore-vacuum pressure

We have studied the electron-beam heating of ceramic targets (AlN, ZrO2, and Al2O3) in the fore-vacuum pressure range (2–5 Pa) to temperatures below their phase transformation temperatures (melting, evaporation; < 1700 0C). It is shown that in this temperature range, conductive heat transfer through the lower face plays a dominant role in the thermal balance of the ceramic target; heat transfer by thermal conduction through the gas, and by thermal radiation play no significant role in heat removal from the target. Mass-to-charge analysis of the ion composition of the beam plasma, generated by the electron beam itself, shows that even at these moderate temperatures, intense sublimation of low melting point volatile components of the ceramic target occurs. Depositing on the substrate surface, these components may negatively affect the coating parameters and properties. Our investigations indicate the necessity of taking special measures to minimize the effect of ceramic target volatile components prior to their intense evaporation during the deposition of protective and functional coatings.

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 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.

Dielectric Coating Deposition Regimes during Electron-Beam Evaporation of Ceramics in the Fore-Vacuum Pressure Range

We present experimental results on the deposition of dielectric coatings on metal surfaces by electron-beam evaporation of alumina ceramics in nitrogen and oxygen gas medium at the pressures of 5–30 Pa. The feasibility of implementing this approach is associated with the use of unique fore-vacuum plasma electron sources. The effect of electron beam power on the rates of ceramic target evaporation and, consequently, on the coating deposition rate is investigated. The structure, electrical-insulating and mechanical (wear resistance, adhesion) properties of the deposited coatings is investigated. We also show the possibility of using coatings for electrical insulating of wires and monolithic integrated circuits.

Short, High-Current Electron Beams and High-Power Microwave Pulses in the Forevacuum Pressure Range

Short, High-Current Electron Beams and High-Power Microwave Pulses in the Forevacuum Pressure Range

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.

Features of glow discharge ignition through a small hole in the hollow cathode of a large volume

The influence of the size of a cathode gap on the initiation of the effect of a hollow cathode in a glow discharge system with an extended hollow cathode in the forevacuum pressure range is shown. It was found that the threshold current for the transition of the discharge to the burning mode with a hollow cathode is determined by the ratio of the longitudinal and transverse dimensions of the cathode slit. With a decrease in the width of the slot, the threshold current increases disproportionately; at the same time, with an increase in the length of the slot, this current sharply decreases.

Effect of extinction beam-plasma discharge while the injection thermoelectrons during transportation of the electron beam in the forevacuum pressure range

The article presents the results of experiments aimed at studying the effect of low-energy thermoelectrons on the parameters of the beam plasma and plasma of the beam-plasma discharge generated during the transportation of a powerful electron beam in the pressure range of the medium vacuum. It is shown that the injection of a sufficiently small current of low-energy thermoelectrons is capable of violating the conditions for the combustion of the beam-plasma discharge and reducing the power loss of the electron beam for SPR generation. In this case, the plasma concentration decreases by almost an order of magnitude (to 1015 m–3) and the temperature of plasma electrons decreases by almost three (to 0.3 eV).

Influence of electron emission on operation of a constricted arc discharge in a pulsed forevacuum plasma-cathode electron source

The research of influence of electron emission and processes associated with the formation of a pulsed large-radius electron beam on operation of a constricted arc discharge, which forms emission plasma in a forevacuum plasma-cathode electron source, is presented. Processes, occurring in case of generation of the electron beam at forevacuum pressure range 3–20 Pa, provide lower operating voltage of the constricted arc discharge. The constricted arc voltage decreases with increasing pressure and increasing accelerating voltage. However, at pressure more than 15 Pa, the arc voltage decreases until a certain minimum value is reached, and then arc voltage is almost independent on pressure and accelerating voltage. This minimum value of the constricted arc voltage is on average 1.5–2 times higher as compared with voltage of the cathodic arc at the same discharge current. The observed decrease of operating voltage of the constricted arc is most likely caused by accelerated back-streaming ions, which move toward the emission electrode from beam-produced plasma. These accelerated ions partially penetrate into the hollow anode of discharge system through the mesh emission electrode and facilitate formation of the arc plasma, and thus provides lower voltage of the constricted arc.

Generation of a Pulsed Electron Beam by a Forevacuum Plasma-Cathode Source Based on a Constricted Arc Discharge

We describe the features of electron emission from the plasma formed by a constricted arc discharge, and the generation of a pulsed (100–150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> ) low-energy (up to 10 keV) electron beam by a plasma-cathode electron source based on this type of arc in the forevacuum pressure range (5–20 Pa). The electron beam current pulse is delayed relative to the arc discharge current pulse. Limitation of the discharge current to the cylindrical part of the anode, increasing the gas pressure, and increasing the beam accelerating voltage all serve to reduce this delay time and provide a sharper rise time of the electron beam current pulse. The emission of electrons from the plasma formed by the constricted arc discharge is accompanied by a decrease in arc voltage and a corresponding increase in arc current. These characteristics are due to the specifics of operating the constricted arc discharge in the forevacuum pressure range and also the influence of backstreaming ions penetrating into the discharge system from the downstream electron beam region.

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.