G.E. Ozur

Use of low-energy, high-current electron beams for surface treatment of materials

Abstract This article describes the characteristics of original sources of low-energy (10–45 keV), high-current (up to 50 kA) electron beams of microsecond duration, designed for the surface thermal treatment of materials. Under the action of this type of beam, graded structures are formed which may impart improved physicochemicai properties and strength to the surface layers. This permits the use of these beams for improving the strength and electrochemical properties of pieces and tools, and for increasing the electric strength of vacuum insulation. Some technological operations, such as the deposition and removal of coatings and surface alloying, can be realized in the intense evaporation mode.

A РИТМ-СП facility for the surface alloying

A combined РИТМ-СП facility intended for forming thin alloy layers on the sample surface during the single vacuum cycle (in situ) is described. The facility consists of a low-energy (10–30 keV) high-current (up to 25 kA) pulsed (2–4 μs) electron beam source and a magnetron sputtering device mounted together with the electron gun of the source on the common vacuum working chamber. The chamber is equipped with the manipulator intended to move the working table with samples without vacuum failures. The facility contains a computer-aided system for controlling the pumping, filling of the chamber with the working gas, power supply units, synchronization of pulse processes during the generation of the electron beam, deposition of films, displacements of the sample, etc. To illustrate the operation of the facility, results of experiments on surface alloying for the Ni-Cu system are given.

A mechanism of microcrater formation in metallic material irradiated by a low-energy high-current electron beam

Experiments with stainless steel (304L grade) samples exposed to microsecond pulses of high-current low-energy (10–30 keV) electron beam have been performed to determine dependences of the morphology, average diameter, and density of irradiation-induced microcraters on the beam energy density. A mechanism is proposed, according to which the crater formation is caused by radial spreading of the melt from the site of localization of a MnS inclusion under the action of the surface tension gradient caused by overheating of the inclusion. Estimations of the dimensions of microcraters are in satisfactory agreement with experimental data.

On the Current of the Low-Energy High-Current Electron Beam Formed in a Plasma-Filled Diode

The reasons for the limitation of the current of a high-current electron beam formed in a plasma-filled diode have been investigated. It has been revealed that the beam current is largely limited, on the one hand, by the transmission capacity of the double layer between the cathode and anode plasmas and, on the other hand, by the rate of charge neutralization of the beam in the drift channel. Experiments and estimates have shown that, even with these limitations, the beam current can be considerably greater than the critical currents for the buildup of aperiodic instabilities which result in the formation of a virtual cathode.

Field Enhancement and Ion-Flow Focusing at the Multiemitter Cathode of a High-Current Plasma-Filled Diode

In this paper, the evolution of a nonsteady ion sheath in a plasma-filled diode with cylindrical protrusions present on the cathode has been investigated by numerical methods. The values of bursts of electric field strength (E C) and ion current density (J C) at the cathode surface that accompany the formation of the ion sheath have been predicted. It has been shown that the bursts of E C and J C at protrusion tips are greater in amplitude than those at the plane part of the cathode. Approximation formulas have been derived for the plane part of the cathode (or for a protrusion-free plane cathode) which allow one to predict the amplitudes of E C and J C bursts as functions of voltage-rise rate, peak voltage, ion mass and charge, and plasma-electron density and temperature. It has been shown that the considerably increased J C at protrusion tips is due to the ion-flow focusing related to the fact that the plasma boundary around a protrusion is curved during a short time interval at the stage of growth of the ion sheath. The calculation results correlate with the measured delay times to the initiation of explosive electron emission at the multiwire cathode of a plasma-filled diode.

Application of the pulsed electron-beam treatment of electrode surfaces for increasing the electric strength of vacuum gaps

A method for preliminary treatment of electrodes with a low-energy, high-current electron beam of microsecond duration is proposed. This method, combined with subsequent conditioning of the vacuum gap by pulsed discharges, makes it possible to achieve high values of the breakdown electric field. Projected uses of the method for increasing the electric strength of high-power electrodynamic systems are described.

Development of compact high-voltage electronic vacuum devices

The issues of improvement of hold-off capability and reliability of high-voltage vacuum tubes, for example, X-ray tubes were studied. Two methods are suggested for improvement of the tubes operation. The first method is based on deposition of special coatings on the inner surface of tube isolator in the regions where electric field strength is high. These coatings have bulk electric conductivity higher than for isolator material but their surface conductivity is almost equal. The second method is based on pulsed surface melting of the tube electrodes with non-relativistic, high-current electron beam. Pulsed surface melting drastically reduces parasitic field emission, which results in the decrease of the charge density both in the bulk and surface of isolator providing high hold-off voltages through the tube. The tests of 160-kV and 250-kV X-ray tubes made utilizing the new above mentioned technologies have shown that parasitic currents do not exceed 1 μA and conditioning time decreases from 5 hours to 15 minutes. The new technology also allows to reduce dimensions of the tube.

A High-Current Electron Gun Integrated with a Magnetron Sputtering System

The description and the main performance specifications are presented for a device in which a high-current electron gun and a magnetron sputtering system are integrated in a common casing. This device is efficient for surface alloying on metallic materials. It is shown that the magnetic system of the magnetron does not degrade the characteristics of an electron beam that is formed in the gun and passed through a hole in the magnetron sputtering system.

Surface structure and physicomechanical properties of NiTi exposed to electron beam and ion-plasma treatment

The paper presents research data on the physicomechanical surface properties of NiTi alloy after microsecond low-energy high-current electron beam treatment and subsequent magnetron TiTa coating deposition. Nanoindentation shows that after electron beam treatment, the material at a depth of 2 µm, these properties correspond to their initial values. After subsequent deposition of a TiTa coating 1 µm thick, the material reveals changes in its bulk physicomechanical properties. The dependences of Hµ, δH, and η on the indentation depth h feature three quasilinear portions with constant slopes of Hµ, δH, and η which correlate with the multilayer structure formed in the material during electron beam treatment and coating deposition.