Plasma Cathode Electron Research Articles

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.

Investigation of Electron Beam Generation in Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the generation of electron beam in the pseudospark discharge-based plasma cathode electron (PD-PCE) source for a wide range of geometrical and operating parameters, such as cathode aperture, gas pressure, and seed electron energy, using 2-D kinetic plasma simulation code. It has been observed that the peak electron beam current’s time to appear at the anode surface decreases with an increase in the cathode aperture size, gas pressure, and injected seed electron energy. Investigation of the peak electron beam current and its time to appear at the anode is presented with reference to the variation of cathode aperture and gas pressure. It has been found that the generated electron beam current increases with increase in gas pressure while decreases with increase in the cathode aperture. The potential profile is also presented which is responsible for confinement of the plasma inside the hollow cathode (HC) cavity. The simulation has been performed for the required aperture size 2–10 mm, argon gas pressure 20–80 Pa, and seed electron energy 1–4 kV. The gas pressure, cathode aperture, and seed electron energy strongly influence the growth of plasma inside the HC cavity and also the generation of corresponding energetic electron beam. As a result, electron beams of different current amplitudes, sizes, and energies can be realized by proper control of the gas pressure, cathode aperture size, and seed electron energy of PD-PCE source for its use in extreme ultraviolet/X-ray and microwave applications.

2D imaging X-ray diagnostic for measuring the current density distribution in a wide-area electron beam produced in a multiaperture diode with plasma cathode

A simple and inexpensive X-ray diagnostic tool was designed for measuring the cross-sectional current density distribution in a low-relativistic pulsed electron beam produced in a source based on an arc-discharge plasma cathode and multiaperture diode-type electron optical system. The beam parameters were as follows: Uacc = 50–110 kV, Ibeam = 20–100 A, τbeam = 0.1–0.3 ms. The beam effective diameter was ca. 7 cm. Based on a pinhole camera, the diagnostic allows one to obtain a 2D profile of electron beam flux distribution on a flat metal target in a single shot. The linearity of the diagnostic system response to the electron flux density was established experimentally. Spatial resolution of the diagnostic was also estimated in special test experiments. The optimal choice of the main components of the diagnostic technique is discussed.

PIC Simulation to Analyze Peak Electron Current Generation in a Triggered Pseudospark Discharge-Based Plasma Cathode Electron Source

In this paper, an investigation has been carried out for the analysis of peak electron current at the anode surface in pseudospark discharge-based plasma cathode electron (PCE) source using 2-D kinetic plasma simulation code OOPIC-PRO. It has been observed that peak electron current is a function of hollow cathode (HC) dimension, gas pressure, and seed electron energy. The investigation has also been carried out for temporal evolution of the plasma formation inside the HC and electron-beam generation processes. Trends in size of the generated electron beams have been presented as a function of the potential distribution at the cathode aperture and applied gas pressure. As a result, on increasing gas pressure for the constant aperture size of HC, electron beam of higher current is generated while on other hand, by increasing cathode aperture for constant gas pressure, electron beam of lower current is achieved. The spatial characteristics of cathode fall region have also been presented for the different gas pressures and cathode aperture sizes. The simulation has been carried out for the variation of cathode apertures 1–10 mm as well as argon gas pressures 1–80 Pa. The gas pressure, cathode aperture and seed electron energy strongly influence the potential distribution in PCE source, and therefore, the peak electron currents as well as electron beams of different amplitudes and sizes can be realized.

Effect of the Enhanced Breakdown Strength in Plasma-Filled Optical System of Electron Beam Formation

The article presents recent results of the dramatically enhanced electric breakdown strength observed in the accelerating gap of a plasma-filled optical system for the formation and focusing of a wide-aperture pulsed electron beams with currents up to 80 A and energies up to 35 keV. This system is a plasma-optical diode type device in which the acceleration and formation of the electron beam occurs in the double layer between the emissive surface of the plasma cathode (electron emitter) stabilized by a fine mesh grid and the open surface of the anode plasma. The anode plasma is created by the toroidal plasma generator of original design based on the ion source with closed drift of electrons with an anode layer.

A tapered multi-gap multi-aperture pseudospark-sourced electron gun based X-band slow wave oscillator

The experimental study of a tapered, multi-gap, multi-aperture pseudospark-sourced electron gun based X-band plasma assisted slow wave oscillator is presented. The designed electron gun is based on the pseudospark discharge concept and has been used to generate a high current density and high energy electron beam simultaneously. The distribution of apertures has been arranged such that the field penetration potency inside the backspace of the hollow-cathode is different while passing through the tapered gap region. This leads to non-concurrent ignition of the discharge through all the channels which is, in general, quite challenging in the case of multi-aperture plasma cathode electron gun geometries. Multiple and successive hollow cathode phases are reported from this electron gun geometry, which have been confirmed using simulations. This geometry also has led to the achievement of ∼71% fill factor inside the slow wave oscillator for an electron beam of energy of 20 keV and a beam current density in the range of 115–190 A/cm2 at a working argon gas pressure of 18 Pa. The oscillator has generated broadband microwave output in the frequency range of 10–11.7 GHz with a peak power of ∼10 kW for ∼50 ns.

A long pulse width and high extraction rate arc plasma electron beam source

Based on the principle of vacuum arc discharge under magnetic field, a novel plasma cathode electron- beam source was designed. This device can be used to regulate electron-beam current so as to improve the extrication efficiency of electron beam through regulating the exciting current and thus controlling the density of the plasma electron beam source. Experiment results showed that the arc current change with the magnetic field, to be specific, the stronger the magnetic field was, the smaller the arc current will be, then the density of plasma that penetrated the anode hole to serve as electron beam will be higher. From this experiment, it can be seen that under the condition of 10−3 Pa air pressure, 100 V arc voltage, 30 A exciting current, we can obtain the electron beam of 40 ms pulse width, and 828 mA current in the extraction rate of 6.1%.

On the role of secondary electrons in beam plasma generation inside a dielectric flask by fore-vacuum plasma-cathode electron source

The paper presents the results of experimental research and numerical simulation, demonstrating a considerable influence of secondary electrons on parameters of the beam-produced plasma generated at a pressure range of 1–13 Pa by injection of a continuous (with current of tens mA) electron beam into a dielectric (quartz) flask. An electron beam was formed by a fore-vacuum plasma-cathode electron source based on a hollow cathode discharge. The secondary electrons were emitted as a result of high-energy (3–8 keV) electron beam bombardment mainly a bottom end of the flask. These electrons provide an additional contribution to the ionization of the gas and also affect on the longitudinal distribution of the plasma density along the flask.

Influence of gas pressure on electron beam emission current of pulsed cathodic-arc-based forevacuum plasma electron source

We describe our experimental investigation of the effect of background gas pressure on the emission parameters of a pulsed cathodic-arc-based forevacuum-pressure plasma-cathode electron source. We find that increased gas pressure over the range 4–16 Pa significantly reduces the beam current rise-time and significantly increases the emission current amplitude. For example, at a discharge current of 20 A, increasing the working gas pressure from 4 Pa to 16 Pa increases the emission current from 8 A to 18 A and shortens the beam rise-time from 50 μs to 20 μs. This influence of gas pressure on the electron beam parameters can be explained by the effect of arc discharge current switching from the anode to emission. In our case, the current switching effect is caused by increased working gas pressure. In the forevacuum pressure range, the increase of the electron emission current with the growth of gas pressure is due to a rise in the emission plasma potential which is caused by ion back-streaming from the plasma formed in the electron beam transport region. A model describing the influence of gas pressure on the electron emission from the plasma is presented.

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.

Analysis of Geometrical Design Parameters for High-Energy and High-Current-Density Pseudospark-Sourced Electron Beam Emission

Four different configurations of plasma cathode electron (PCE) guns have been designed and developed in which pseudospark discharge concept has been used. Experimental studies have been performed to identify the dependence of geometrical design parameters like shape of aperture, distribution of apertures, and the number of gaps between hollow cathode and anode on high-energy and high-current-density electron beam emissions. The beam current density has been increased around five times by changing the shape of aperture from circular to sheet keeping the aperture area and other geometrical parameters identical. The perveance of the electron beam has also been increased by increasing the number of apertures on hollow cathode and anode surface. The beam current density from single aperture to multiple apertures has increased from 225 to 900 A/cm2 with low beam energy for the multiple-aperture case. The multiple gaps between hollow cathode and anode increase the electron beam energy. The maximum beam energy is found to be 16–14.5 keV at an applied gap voltage of 16 kV from the developed multigap PCE gun, which is much higher than that from the single gap configuration.

Equipment and processes of vacuum electron-ion plasma surface engineering

The paper presents a COMPLEX laboratory setup for surface engineering, describes its components and principle of operation, and provides experimental data on its use for treatment of commercially pure VT1-0 titanium. The setup comprises gas and metal plasma generators based on a low-pressure arc discharge and a pulsed plasma-cathode electron source, allowing complex treatment of materials through nitriding in low-pressure arc plasma and subsequent TiN coating deposition in a single vacuum cycle. The experimental data demonstrate that such complex surface modification decreases the friction coefficient of VT1-0 titanium 1.3 times and increases its wear resistance more than 30 times.

Electron beam evaporation of boron at forevacuum pressures for plasma-assisted deposition of boron-containing coatings

We describe the use of a plasma-cathode electron source for electron beam evaporation of boron at forevacuum pressures (∼10 Pa) with subsequent deposition of boron-containing coatings on a titanium substrate. We analyze the process of electron beam heating and evaporation of boron, study the mass-to-charge composition of the gas and boron beam-produced plasma, apply such plasma for coating deposition, and investigate the elemental composition of the deposited film and its microhardness.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

The Use of an Electron Microchannel as a Self-Extracting and Focusing Plasma Cathode Electron Gun

A new and simple type of electron gun is presented. Unlike conventional electron guns, which require a heated filament or extractor, accelerator and focusing electrodes, this gun uses the collimated electron microchannels of an inertial electrostatic confinement (IEC) discharge to achieve the same outcome. A cylindrical cathode is placed coaxially within a cylindrical anode to create the discharge. Collimated beams of electrons and fast neutrals emerge along the axis of the cylindrical cathode. This geometry isolates one of the microchannels that emerge in a negatively biased IEC grid. The internal operating pressure range of the gun is 35-190 mTorr. A small aperture separates the gun from the main vacuum chamber in order to achieve a pressure differential. The chamber was operated at pressures of 4-12 mTorr. The measured current produced by the gun was 0.1-3 mA (0.2-14 mA corrected measurement) for discharge currents of 1-45 mA and discharge voltages of 0.5-12 kV. The collimated electron beam emerges from the aperture into the vacuum chamber. The performance of the gun is unaffected by the pressure differential between the vacuum chamber and the gun. This allows the aperture to be removed and the chamber pressure to be equal to the gun pressure if required.

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.

Pulsed Cathodic Arc for Forevacuum-Pressure Plasma-Cathode Electron Sources

We describe properties and parameters of a pulsed cathodic arc discharge, as applied in forevacuum-pressure plasma-cathode electron sources for the generation of broad electron beams. It is shown that during a single arc current pulse, the arc can operate in either of two modes, differing in their discharge operating voltage and plasma constitution. The radial plasma density distribution approximates a Gaussian. The effect of gas pressure on the plasma density is pronounced only at a considerable distance from the cathode.