D.I. Proskurovsky

Pulsed electron-beam technology for surface modification of metallic materials

This article concerns the foundations of a new technology for surface modification of metallic materials based on the use of original sources of low-energy, high-current electron beams. The sources contain an electron gun with an explosive-emission cathode and a plasma anode, placed in a guide magnetic field. The acceleration gap and the transportation channel are prefilled with plasma with the use of spark plasma sources or a low-pressure reflected discharge. The electron-beam sources produce electron beams with the parameters as follows: electron energy 10–40 keV; pulse duration 0.5–5 μs; energy density 0.5–40 J/cm2, and beam cross-section area 10–50 cm2. They are simple and reliable in operation. Investigations performed with a variety of constructional and tool materials (steels, aluminum and titanium alloys, hard alloys) have shown that the most pronounced changes of the structure-phase state occur in the near-surface layers quenched from the liquid state, where the crystallization front velocity rea...

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.

The effect of pulsed electron-beam treatment of electrodes on vacuum breakdown

A method for preliminary treatment of electrodes by a microsecond low-energy intense electron beam is proposed. It has been demonstrated that such a beam melts off the electrode surface and cleans the surface layers from impurities and dissolved gases. In combination with subsequent conditioning of the vacuum gap with low-current pulsed discharges, high breakdown electric fields can be attained. >

Electrohydrodynamic phenomena on the explosive-emission liquid-metal cathode

The paper describes the results of a direct experimental observation of the development of an electrohydrodynamic instability at an explosive-emission liquid-metal cathode along with a theoretical analysis of the growth and destruction of the protrusion formed on the cathode surface. >

Plasma parameters of an arc cathode spot at the low-current vacuum discharge

This paper is devoted to the results of an experimental study of plasma parameters of cathode spot burning on a liquid-metal cathode in vacuum at a low-current (less than 200 A) vacuum arc discharge. Picosecond laser interferometry and absorption shadow imaging were used in a single experiment. Plasma fragments as dense as 10/sup 26/ m/sup -3/ were observed at discharge currents less than 50 A. Such fragments were never observed in arc discharges with currents higher than 100 A or in the breakdown stage of the discharge.

Pulsed HV vacuum breakdown of polished, powder coated, and e-beam treated large area stainless steel electrodes with 0.5 to 7 mm gaps

An investigation of the HV vacuum breakdown between polished, powder coated, and e-beam treated 304L and 316L stainless steel electrodes is described. Tests were performed with 160 ns, 1-cos(/spl omega/t), and 260 ns flat-top voltage pulses of up to 500 kV. The high voltage hold-off for the 160 ns pulse was /spl sim/130 kV/mm for 2 mm gaps for 80-mm diameter polished stainless steel electrodes, and 15% lower for 120-mm polished and e-beam treated electrodes. The longer 260 ns pulse gave 15% lower hold-off for 80-mm electrodes. These electrodes showed voltage hold-off that scaled as the square root of the gap between 0.5 and 7 mm. This total voltage effect has been interpreted in the past as due to accelerated particles. We analyze our data in terms of this mechanism and show that only nanoparticles of molecular size could be responsible. We also discuss how ions or background gas could affect the breakdown thresholds but existing models do not predict square root dependence. We test how extremely fine powers affect hold-off and show that contaminated surfaces have relatively constant reduced breakdown E-fields that intersect the clean-electrode voltage-dependent breakdown at critical gaps defined by the type and quantity of contamination. The hold-off was /spl sim/55 and 65 kV/mm with copper powder on the cathode and anode for 2 to 6.5 mm gaps, respectively, and /spl sim/95 and 75 kV/mm for talc powder on the cathode and anode for gaps <3.5 and 6.5 mm. Optical diagnostics show no difference in the light emission from clean and contaminated electrode breakdown arcs.

Resonant atomic interfero- and shadowgraphy of vacuum arc with gallium cathode

The mechanism of the emission of neutral atoms of the cathode material into the discharge gap of a microsecond low-current vacuum arc with a liquid Ga cathode has been investigated by the method of subnanosecond resonance laser interfero- and shadowgraphy. It has been shown that the cathode material vaporization has a pronounced nonstationary character and occurs both isotropically and in the form of constricted weakly ionized jets with the atom concentration in a jet over 10/sup 17/cm/sup -3/.

On priorities of cathode and anode contaminations in triggering the short-pulsed voltage breakdown in vacuum

Modern theoretical notations on electrical breakdown in vacuum consider cathode triggering mechanisms to be most responsible on short-pulsed (<1 /spl mu/s) breakdowns while anode mechanisms to be responsible in a part on DC and long-pulsed breakdowns. Following those notations, we tried to reveal conditions at which either mechanism steps aside to another one. The study involved several experimental techniques including the anode-probe surface scanning, pulsed electron-beam surface melting in vacuum for surface cleaning, and intentional dust particle contamination of electrode surfaces. Breakdown tests were performed using a pulser capable of producing 220 kV quasi-square pulses that were adjustable to /spl sim/30 to 80 ns pulse length. Our experiments showed that cathode emission sites are responsible for breakdowns at relatively low hold-off fields. At higher electric fields of up to 1 MV/cm, the anode share in the mechanism of triggering breakdown becomes probably more significant than the cathode mechanism.

Explosive Electron Emission From Liquid-Metal Cathodes

Since the discovery of explosive electron emission 40 years ago, the overwhelming majority of investigations of this phenomenon have been performed with solid-state metal cathodes. At the same time, liquid-metal pool point cathodes, by virtue of some favorable properties, allow one to perform more reliable physical experiments. The peculiarities of liquid-metal cathodes are related to the features of the formation of an emitting protrusion under the action of a strong electric field. The high stability of this process in space and in time for a cathode repetitively operating under the conditions of pure high vacuum and moderate voltages (10-30 kV) ensures highly reliable experimental data. Liquid-metal cathodes may be of great practical importance. This paper is a review of the studies of the explosive electron emission from liquid-metal point cathodes.

Increasing the electric strength of vacuum insulation by irradiating the electrodes with a low-energy high-current electron beam

The paper describes how irradiation of the electrode surface with a LEHCEB (low-energy high-current electron beam) affects the prebreakdown current and the electric strength of vacuum insulation. This study is an extension of a study described earlier. Experiments have been performed for 0.1 mm vacuum gaps formed by refractory metal electrodes and for millimeter vacuum gaps with a pulsed voltage of amplitude 250 kV and duration 30 to 100 ns, both in a high oil-free vacuum and in technical-grade oil vacuum. Based on the results obtained, it is stated that the LEHCEB irradiation of electrode surfaces is a promising technique for increasing the electric strength of vacuum insulation over a wide range of voltages and under varied vacuum conditions.