A. S. Klimov

On the possibility of electron-beam processing of dielectrics using a forevacuum plasma electron source

An insulated target was irradiated by an electron beam generated by a forevacuum plasma electron source operating in the pressure range of 5–15 Pa. Measurements of the target potential showed that plasma formed in the region of electron beam transport ensured the almost complete neutralization of charge accumulated on the target. This effect results in the possibility of direct electron-beam processing of nonconducting materials, including the melting and welding of ceramics.

Electron beam treatment of non-conducting materials by a fore-pump-pressure plasma-cathode electron beam source

In the irradiation of an insulated target by an electron beam produced by a plasma-cathode electron beam source operating in the fore-vacuum pressure range (5‐15 Pa), the target potential is much lower than the electron beam energy, offering the possibility of direct electron treatment of insulating materials. It is found that in the electron beam irradiation of a non-conducting target in a moderately high pressure range, the electron charge on the target surface is neutralized mainly by ions from a volume discharge established between the negatively charged target surface and the grounded walls of the vacuum chamber. This allows the possibility of direct electron beam treatment (heating, melting, welding) of ceramics and other non-conducting and semiconductor materials.

Generating stationary electron beams by a forevacuum plasma source at pressures up to 100 Pa

It is shown that, as the gas pressure in a forevacuum plasma electron source increases, electric breakdown in the accelerating gap is caused by the reverse flow of ions from plasma that is generated by both the electron beam and high-voltage glow discharge (HGD). By modifying the electrode system geometry in the accelerating gap of the electron source, it is possible to provide for a two-to threefold decrease in the HGD current. This allows the upper pressure in the electron source to be increased up to about 100 Pa when air is used as the working gas and up to 160 Pa in the source filled with helium.

Expansion of the working range of forevacuum plasma electron sources toward higher pressures

It is shown that the pressure in forevacuum plasma electron sources is limited from above by a current component that arises in the accelerating gap from a high-voltage glow discharge and dominates in the electron beam. The working pressure range of such electron sources can be expanded toward higher pressures by limiting the current of the high-voltage glow discharge in the accelerating gap.

Electron beam focusing features in a plasma electron source under forevacuum pressures

Features of focusing electron beams generated by a forevacuum plasma source under pressures of 10–30 Pa are investigated and the principle possibility of obtaining submillimeter beams is demonstrated. A beam power density of 105 W/cm2 is reached at an electron beam diameter of 0.6 mm. The obtained beam parameters offer opportunities for precision electron beam processing of dielectric materials, including hightemperature alumina ceramics.

Specific features of the charge neutralization of silicon carbide in sintering by electron beam in the forevacuum range of pressures

It is shown that a noticeable role in the electron beam charge neutralization in the course of electron-beam sintering of compacted silicon carbide samples is played, as the sample temperature increases, by the electrical conductivity of a sample being sintered, as well as by thermionic emission from its surface. Experimental results obtained for compacted silicon carbide are used to determine its energy gap width and the electron work function.

Electron Beam Sintering of Zirconia Ceramics

The work demonstrated the sintering of zirconium dioxide ceramics by means of an electron beam produced by a plasma-cathode e-beam source operating at fore-vacuum pressure. The sintered ceramics consist of tetragonal-modified zirconium dioxide with grain size from 0.7 to 10 micrometers, depending on the sintering conditions. At constant sintering temperature, the density of the material and its grain size depend on the integrated energy injected into the sintered material by the electron beam.

Electron beam welding of ceramic to metal using fore-vacuum plasma electron source

The possibility of creating ceramic-metal joints by electron beam welding is considered. The welding of alumina ceramic to aluminum and titanium was performed in the fore-vacuum pressure range (5–20 Pa) using a plasma electron source. The structure and composition of the ceramic-metal transition layer are investigated. It is shown that the transition-layer thickness exceeds substantially the microroughness size of the initial ceramic, which confirms that intermixing of materials, i.e., welding, has occurred. The dependence of breaking strength of the obtained joints on the electron-beam power is measured. A sharp difference in the strength depending on the metal selection is found: the ceramic-aluminum weld strength is an order of magnitude higher than the strength of the ceramic-titanium system.

Parameters of the beam plasma formed by a forevacuum plasma source of a ribbon beam in zero-field transportation system

We have studied the generation of the beam plasma formed by a forevacuum plasma source of a ribbon electron beam in the conditions of its transportation without an accompanying magnetic field. The ignition conditions in the beam transportation region of the beam–plasma discharge producing a plasma formation of the plasma sheet type with a plasma concentration of ~1016 m–3 and an electron temperature of 1–2.5 eV have been determined. The attained values of parameters and the sizes of the plasma formation make it possible to use it in technologies of the surface modification of planar extended articles.

Plasma density distribution in a plasma source of a ribbon electron beam with an extended hollow cathode

The paper presents a study of the influence of the hollow cathode geometry in a plasma electron source on the plasma density distribution near the emission boundary and of the features of discharge ignition with an extended hollow cathode at forevacuum pressures. It is shown that the plasma density distribution is mostly influenced by the cathode cavity depth. Decreasing the cavity depth results in distribution maxima at the cavity edges. Decreasing the cavity width gives rise to a maximum in the middle of the cavity. The conditions that provide plasma inhomogeneity no more than 10 % lengthwise the cavity are determined.