N. N. Koval

Generation and propagation of high-current low-energy electron beams

High-current electron beams with a current density of up to 100 A/cm 2 generated by a plasma-cathode gas-filled diode at low accelerating voltages are studied. Two types of gas discharges are used to produce plasma in the cathode. With glow and arc discharges, beam currents of up to 150 A and 400 A, respectively, have been obtained at an accelerating voltage of 16 kV and at a pressure of 1–3·10 −2 Pa in the acceleration gap. The ions resulting from ionization of gas molecules by electrons of the beam neutralize the beam charge. The charge-neutralized electron beam almost without losses is transported over a distance of 30 cm in a drift channel which is in the axial magnetic field induced by Helmholtz coils. The results of calculations for the motion of electrons of the charge-neutralized beam with and without axial external field are presented and compared with those of experiments.

Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: structure and osteoblast-like MG63 cells in vitro study

Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to −50 and −100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates.

Properties and structural state of the surface layer in a zirconium alloy modified by a pulsed electron beam and saturated by hydrogen

A pulsed action of an electron beam on a Zr-1% Nb zirconium alloy is studied. Alloy samples are irradiated by three 50-μs pulses at an energy density of 15–25 J/cm2, a power of (3–6) × 104 W/cm2, a current density of 10–50 A/cm2, and an electron energy of 18 keV. This method of processing is found to modify the surface layer of the alloy without changing the structure-phase state of its volume. This surface modification increases the hydrogen saturation resistance of the alloy.

Self-sustained low pressure glow discharge with a hollow cathode at currents of tens of amperes

Self-sustained glow discharge with a hollow cathode was studied at high discharge currents (up to 30 A). Using a grid analyzer placed on the side flange of the hollow cathode, the ion and electron currents flowing in the cathode sheath were measured. At a discharge current of 30 A, pressure of 0.2–2 Pa, and plasma density of 1011 cm−3, the coefficient of secondary ion-electron emission λ calculated from the experimental data is found to be 0.1–0.15. The dependences of the plasma parameters on the area of the small anode placed inside the larger hollow cathode are determined.

Hollow-Cathode Low-Pressure Arc Discharges and Their Application in Plasma Generators and Charged-Particle Sources

This paper presents the results of a study of hollow-cathode arc discharges which generate gas-discharge plasmas of densities 1010–1012 cm–3 in large volumes (∼1 m3) at low pressures (10–2–1 Pa) and at discharge currents of up to 200 A. Consideration is given to the design and peculiarities of hot-cathode and cold-cathode discharge systems. The parameters of plasma generators and charged-particle sources where use is made of arc discharges are cited and the problems of the most efficient application of such systems in technological processes of solid surface modification are discussed.

Surface modification of steels by complex diffusion saturation in low pressure arc discharge

A technique for surface hardening of type 4140 structural steel is proposed. The technique is based on the use of low pressure arc discharges. The complex treatment in one vacuum cycle involves a sequence of operations: ion cleaning of the surface and heating the sample, diffusion surface alloying with aluminum and nitriding. The sample temperature is not over 620 °C at all stages of the process. The structure, phase and element constitution, and microhardness of the surface layer have been investigated. It has been established that the significant increase in microhardness from 2.5 in the original state to 13 GPa in the modified layer after complex diffusion saturation in an arc discharge is due to the formation of iron nitride containing dispersed particles of aluminum nitride.

Adhesion properties of a silicon-containing calcium phosphate coating deposited by RF magnetron sputtering on a heated substrate

Silicon-containing hydroxyapatite coatings 400–700 nm in thickness are prepared by means of radio-frequency (RF) magnetron sputtering on a heated (to 200°C) titanium substrate chemically etched and treated with a pulsed electron beam. The morphology and phase composition of the coating are studied. The morphology and roughness of the composite “calcium-phosphate coating-titanium substrate” differ depending on the treatment procedure of the substrate before deposition. The scratch test method is used to assess the adhesion strength of the coatings formed at different values of bias potential applied to the substrate. It is observed that the adhesion strength of the coating changes with decreasing crystallite size.

Enhanced emission during submillisecond low-energy electron beam generation in a diode with grid-stabilized plasma cathode and open anode plasma boundary

We have experimentally studied the phenomenon of emission enhancement in a gas-filled diode with grid-stabilized plasma cathode and open (mobile) anode plasma boundary at an accelerating voltage of up to 20 kV. As the working gas pressure is increased to p ≥ 10−2 Pa and the longitudinal magnetic field is increased to Bz ≥ 20 mT, the current in the accelerating gap exhibits significant growth, sometimes by a factor of two or more. Experimental data show that the most probable mechanism responsible for this effect is ion-induced secondary electron emission from the emitting electrode surface bombarded by ions from plasma generated by the electron beam in the drift space. These ions are accelerated in the space charge layer between the emitting electrode surface and the mobile boundary of the beam-generated (anode) plasma.

Nanosecond high current and high repetition rate electron source

A broad electron beam source with a plasma hollow cathode has been developed which is intended for the production of nanosecond electron beams with a high repetition rate. The source lifetime is over 10/sup 9/ shots. To reduce the operating pressure and shorten the time required for the formation of plasma in the cathode cavity, an auxiliary triggering glow discharge with a hollow cathode is used. With an accelerating voltage of 40 keV, a pulse repetition rate of 50-1000 Hz, and a pulse duration of 100 ns, an electron beam of current up to 200 A and risetime 25 ns has been produced.

Surface Modification of TiC–NiCrAl Hard Alloy by Pulsed Electron Beam

The mechanisms by which nanostructural states are realized in e-beam-irradiated TiC-NiCrAl cermet depending on the irradiation mode have been revealed. Mechanical testing and tribotesting have yielded criteria for a substantial (a factor of 1.5-3) increase in performance characteristics of the cermet alloy (micro- and nanohardness, cutting resistance, coefficient of friction, and bending resistance).