Plasma-cathode Electron Beam Source Research Articles

SPECIFIC FEATURES OF THE CURRENT FLOW THROUGH AN ALUMINA-BASED METAL-CERAMIC COMPOSITE DURING ELECTRON BEAM IRRADIATION IN THE FOREVACUUM PRESSURE RANGE

We describe some specific features of the current passage through an Al<sub>2</sub>O<sub>3</sub>-Ti metal-ceramic composite sample during irradiation by a forevacuum-pressure plasma-cathode electron beam source. The composition ratio of the composite was 90% Al<sub>2</sub>O<sub>3</sub> and 10% Ti by weight. It is shown that during electron-beam irradiation, the magnitude and direction of the current through the sample depend on the temperature as well as on the sintering time at given temperature. The absolute value of the recorded current can reach 15 mA for an electron-beam current of 60 mA and electron energy of 10 keV. The dependence of the current is caused by redistribution of titanium over the depth of the sintered composite during heating, and provides a means for forming gradient metal-ceramic materials with variable content of components over the depth.

ELECTRON-BEAM SINTERING OF ZIRCONIUM DIOXIDE/TITANIUM CERAMICS FOR MICROELECTRONICS PRODUCTS

Zirconium dioxide (ZrO<sub>2</sub>) has excellent physical, chemical, and mechanical properties. These properties make it an excellent material for composite ceramics. High values of dielectric permittivity, mechanical resistance, and high radiation resistance allow it to be used to protect integrated circuits (ICs) from external influences. In this study, we fabricated ZrO<sub>2</sub>/titanium (Ti) ceramic composites by employing electron-beam sintering and a forevacuum-pressure plasma-cathode electron-beam source. We used a scanning electron microscopy method to study the properties of the ceramics after sintering. The results obtained showed that with an increase in the sintering temperature up to 1700°C, the Ti content in the near-surface layer of the composite decreased to almost 0. The depth of the region with low metal component content also increased with an increase in the sintering temperature and reached 2 mm in 3-mm-thick samples. This method can be used in the production of composite materials used in IC packaging.

Influence of a longitudinal magnetic field on the parameters and characteristics of a forevacuum plasma electron source based on a hollow-cathode discharge

We report on the effect of a longitudinal magnetic field in the plasma emission system of a forevacuum-pressure, plasma-cathode electron beam source utilizing a hollow-cathode glow discharge, and on the electron emission properties of the magnetized plasma. We show that the degree and character of the magnetic field effect are in many ways determined by the geometry of the hollow cathode plasma source.

Parameters and characteristics of a pulsed constricted arc discharge operating in a forevacuum-pressure plasma-cathode electron beam source

The parameters and characteristics of a pulsed constricted arc discharge operating in the forevacuum pressure plasma-cathode source of a large-radius (about 4 cm) low-energy (up to 10 keV) electron beam are presented. The constricted arc discharge is characterized by a rising current-voltage characteristic. Increase in gas pressure and the use of gas with greater ionization cross section lead to a decrease in arc voltage. We have determined the dependences of the maximum stable arc current on the operating conditions, and explored the emission properties of the plasma. Efficient electron emission from this plasma over the pressure range 5–21 Pa, and the influence of the beam generation processes on the constricted arc discharge have been demonstrated. A pulsed electron beam with current up to 20 A and energy up to 10 keV has been obtained using a forevacuum-pressure plasma-cathode electron source based on a constricted arc discharge.

Plasma formation near the beam collector of a forevacuum-pressure plasma-cathode electron beam source

It was shown that secondary electrons, emitted by the electron beam collector of a forevacuum-pressure plasma-cathode electron source, play an important role in beam plasma generation. Their yield is determined by the secondary electron emission properties of the collector, its negative potential, and the angle of incidence of the electron beam on the collector. Positioning the beam collector surface at an angle to the beam propagation direction results in spatial separation of the two plasma regions formed by the primary electron beam and by secondary electrons generated at the collector. This separation makes it possible to compare the parameters of both plasmas. It was found that the secondary plasma column is always directed perpendicular to the collector surface regardless of the primary beam angle of incidence. The secondary plasma is generated via gas ionization by secondary electrons accelerated by the collector potential. Under certain conditions (high values of secondary electron emission coefficient and collector potential), the contribution of secondary electrons to formation of the near-collector plasma can surpass the contribution from the primary electron beam itself.

Broad-beam plasma-cathode electron beam source based on a cathodic arc for beam generation over a wide pulse-width range.

We describe the design, parameters, and characteristics of a modified wide-aperture, plasma-cathode electron beam source operating in the pressure range of 3 Pa-30 Pa and generating large-radius, low-energy (up to 10 keV) electron beams with a pulse width varying from 0.05 ms to 20 ms and a beam current up to several tens of amperes. A pulsed cathodic arc is used to generate the emission plasma, and a DC accelerating voltage is used to form the electron beam. Modernization of the design and optimization of the operating conditions of the electron source have provided a multiple increase in the pulse duration of the electron beam current and the corresponding increase in the beam energy per pulse, as compared to previously developed pulsed forevacuum electron sources.

Plasma electron source for generating a ribbon beam in the forevacuum pressure range.

We describe a plasma-cathode electron beam source based on a hollow cathode glow discharge and operating in the forevacuum pressure range that produces a steady-state ribbon beam. The electron beam is generated in the pressure range of 10-30 Pa. A multi-aperture electron extraction and beam formation system is used to provide beam stability and enhanced uniformity of beam current density, allowing the use of this kind of device for beam-plasma surface modification over relatively large areas.

Forevacuum-pressure plasma-cathode high-power continuous electron beam source.

We describe a plasma-cathode electron beam source based on a hollow-cathode discharge that is capable of generating a 9 kW dc electron beam at an accelerating voltage of 20 kV, with helium as a working gas at a pressure of 30 Pa. A test run of ∼50 operational hours did not indicate any significant degradation of the electron source extraction system or other structural components, and we estimate the operational lifetime of the source at about 100-120 h.

Generation of focused high-current electron beam with millisecond pulse duration by a forevacuum plasma-cathode electron source based on cathodic arc

We describe our work on the generation of low-energy (up to 10 keV) pulsed high-current electron beams with pulse duration up to 7 ms, compressed (focused) by a magnetic field in the forevacuum pressure range (3–30 Pa). We show that the focusing system, consisting of two coaxially arranged coils, provides effective compression of the beam. In the forevacuum pressure range, the gas pressure and type of gas affect the focusing of the beam at fixed emission current, accelerating voltage and magnetic field. Increased pressure leads first to increased beam current density, but beyond a certain optimal value further pressure increase leads to a decrease in the current density of the electron beam. The use of gas with greater ionization cross-section results in stronger compression of the beam at lower gas pressure, but also leads to decreased maximal operating gas pressure of the plasma-cathode electron beam source. Variation of magnetic fields provides control of the beam current density and the position of the beam crossover (focus). A low-energy electron beam with current density up to 15 A·cm−2 and pulse duration up to 7 ms is obtained in the forevacuum pressure range. The use of the focused beam for evaporation of high-temperature ceramics is demonstrated.

Alumina coating deposition by electron-beam evaporation of ceramic using a forevacuum plasma-cathode electron source

We have explored the formation of alumina coatings by electron beam evaporation of bulk alumina ceramic using a forevacuum-pressure plasma-cathode electron beam source at a pressure of 60 mTorr of air. The alumina e-beam target material is evaporated at a rate up to 4.2 g/h, and the coating deposition rate is up to 18 μm/h. The evaporated ceramic is partially ionized by the energetic electron beam, and we have measured the plasma composition as a function of beam power. The deposited alumina coatings were characterized by scanning electron microscopy and energy-dispersive x-ray spectroscopy and found to be uniform and pore-free with a composition that is over 99% aluminum and oxygen, with less than 1% impurities including carbon, silicon and calcium.

Effect of collector potential on the beam-plasma formed by a forevacuum-pressure plasma-cathode electron beam source

We consider the beam-plasma formed by an energetic electron beam at fore-vacuum pressure, when the beam is terminated by an electron collector plate. We show that in the pressure range of 1–10 Pa, the dependence of beam-plasma density n on the electron beam collector potential φ has a maximum. The maximum plasma density nm at the optimum collector potential can be much greater than the plasma density when the collector is at ground or at floating potential. The nonmonotonic dependence n(φ) is found to be caused by the contribution of secondary electrons from the collector to plasma generation.

Stability of electron beam generation by forevacuum-pressure plasma-cathode electron beam source based on a cathodic arc

We describe our experimental research on the stable generation of large-radius pulsed high-current electron beams using a forevacuum-pressure plasma-cathode electron beam source with cathodic arc plasma generation. We find that increased gas pressure and the use of gas with a higher ionization cross-section considerably decrease the stable emission current due to loss of electric strength of the acceleration gap (breakdown). Increased pulse duration results in a decrease in the emission current, but the influence of the gas species and its pressure remains for all pulse durations. There is an extremum in the dependence of emission current on the acceleration gap length and the optimum gap length depends on the gas pressure and the kind of gas. The experiment results can be explained by the effect of back-streaming ion flow, which charges dielectric inclusions on the emission electrode (anode grid) and thereby amplifies the electric field.

Generation of high-power-density electron beams by a forevacuum-pressure plasma-cathode electron source

We report on our work directed towards increasing the power density of the focused electron beam produced by a forevacuum-pressure plasma-cathode electron beam source at a pressure of 10–30 Pa. We have optimized the geometry of the plasma discharge system, emission channel and acceleration gap, and simultaneously increased the beam acceleration voltage. The beam power density achieved was 106 W cm−2, an order of magnitude greater than that typical of forevacuum plasma electron sources, and is quite sufficient to allow the use of these beams for the treatment of high-temperature bulk dielectrics.

Millisecond Pulsed Arc Discharge in a Forevacuum-Pressure Plasma-Cathode Electron Source

We have explored the parametric behavior of a quasi-continuous (1.8 ms) vacuum arc discharge operating as plasma source of a forevacuum-pressure plasma-cathode electron beam source. The current-voltage characteristic of the arc is presented and we show that the discharge becomes unstable at a current below 5–6 A (for our copper cathode). The operating discharge voltage increases weakly with increasing arc current over the pressure range 3–15 Pa. At a pressure greater than 15 Pa the arc shows two possible modes, differing in discharge voltage, as observed earlier for submillisecond arcs. The ratio between the currents to the hollow and plane anode sections are measured to study the arc modes. It is shown that discharge current and pressure affect that ratio. The influence of the arc modes on the electron emission in the forevacuum pressure range is discussed.

Ceramic coating deposition by electron beam evaporation

We describe a new method for the deposition of protective ceramic-based coatings. The novelty of the method lies in the unique interaction of the electron beam with a dielectric target, in which ions in the beam-produced plasma neutralize the target surface charge build-up. This effect is brought about by the use of our novel forevacuum-pressure, plasma-cathode electron beam source, which can produce energetic, focused electron beams, with associated beam-produced plasmas, in the previously inaccessible pressure range of 1–100Pa. The work described here demonstrates the evaporation of aluminum oxide ceramic by electron beam bombardment and the subsequent deposition of an alumina coating. A significant increase in the microhardness of the ceramic-coated Ti substrate and a uniform depth-distribution of the elemental composition has been determined. The approach described here opens up new opportunities for the deposition of coatings in various fields of industry.

Generation of uniform electron beam plasma in a dielectric flask at fore-vacuum pressures

We describe a system for the generation of spatially uniform and homogeneous dense plasma in a dielectric flask using a forevacuum-pressure plasma-cathode electron beam source. At optimum beam energy and gas pressure, the non-uniformity in plasma density distribution along the length of the flask is less than 10%, and the plasma density and electron temperature in the flask are greater than for the plasma produced in the vacuum chamber with no flask. The measured parameters of the beam plasma in the flask are compared to the predictions of a model based on balance equations.

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.

Physics and technique of plasma electron sources

Reviews the properties of electron emission from a gas discharge plasma. Interest in electron emission from plasma is due to the possibility of creating reliable and effective sources of high-current electron beams. The constricted arc discharge, vacuum arc and superdense glow discharge in crossed E*H fields are used for the creation of the plasma emission surface. Grid stabilization of the plasma emission surface is used to stabilize the plasma parameters. Electron current switching is used to increase plasma cathode efficiency. The plasma cathode emission current is controlled by variation of the plasma concentration, the emission electrode potential and the crossed magnetic field. The plasma cathode electron beam source, with 200 keV energy and microsecond pulse duration, provides electron beams with a cross section up to 104 cm2, beam current from 10 to 1000 A and current density up to 1 A cm-2. The annular electron beam source provides an electron beam with 10 cm diameter, 1 mm width, 15 mu s pulse, 600 A current and current density of 75 A cm-2.