High-current Electron Beam Research Articles

Investigation of the parameters of a self-focused electron beam outputted behind the anode of a vacuum diode

The parameters of a high-current electron beam extracted from the self-focusing zone through a hole in the anode into a vacuum chamber are investigated. The beam parameters were determined from the measurement of the spatial distribution of destruction and glow arising in polymethyl methacrylate samples installed at different distances from the anode (electron beam autographs). The formation of two electron beams --- a self-focused with a high energy density, propagating along the axis of the cone facing the base to the anode with an apex angle of ~ 7o and a high-energy beam of low density, propagating in a hollow truncated cone and surrounding self-focused, was found. The oscillograms of the current and the energy of the electron beams were measured. Keywords: vacuum diode, electron beam, filamentation, self-focusing, polymethyl methacrylate, destruction, glow, high current pulsed electron beam

On the destruction of elastic polymer materials under the action of an electron beam

An explanation for a feature found in several experiments in the general picture of the destruction of non-brittle polymers under the influence of a shock wave initiated by a powerful electron beam is proposed. The distance of the cracking region from the surface of the material affected by the beam to a finite length in depth is associated with the three-dimensional nature of the propagation of elastic waves. The universality of the effect is demonstrated by the simplest isotropic model, which shows that large tensile stresses are effectively generated inside the target at its sufficiently large transverse and longitudinal size, even without taking into account nonlinear and shear processes. Keywords: high-current electron beams, shock waves, polymer materials, high pressures.

Influence of anode and cathode plasmas on the operation of an electronic diode with an explosive-emission cathode

The results of modeling and experimental investigation of the formation of anode and cathode plasmas in a vacuum diode with an explosive-emission cathode during the generation of a pulsed electron beam with a current density of 0.3-0.4 kA/cm2 and an accelerating voltage of 300-500 kV are presented. It is shown that the concentration of the anode plasma does not exceed 1010 cm-3 and it does not significantly contribute to the operation of the diode. However, the complete desorption of molecules from the working surface of the explosive-emission cathode and the high efficiency of shock ionization of atoms ensure the formation of a cathode gas plasma with a concentration of ~1016 cm-3. It is found that the charge of the explosive-emission plasma layer is significantly less than the charge of the electron beam and the main source of electrons is not an explosive-emission plasma, but a cathode gas plasma. In this case, the electron current is limited by the concentration of the cathode plasma. The use of a cathode with a developed surface (a cathode with a carbon fabric coating) allows increasing the total charge of the electron beam by more than 1.5 times without changing the cathode diameter and the anode-cathode gap. Keywords: high-current electron beam, explosive emission, plasma concentration, electronically stimulated desorption.

Short, High-Current Electron Beams and High-Power Microwave Pulses in the Forevacuum Pressure Range

Short, High-Current Electron Beams and High-Power Microwave Pulses in the Forevacuum Pressure Range

Current Characteristics of a High-Current Electron Gun with Multi-Gap Initiation of Explosive Emission by Dielectric Surface Flashover

Current characteristics of a plasma-filled, high-current electron gun at different accelerating voltages and densities of plasma preliminary filling the space between the cahode and collector have been investigated. Multi-gap initiation of explosive emission is performed with the use of parallel operated, resistively decoupled arc plasma sources which electrodes and tube ceramic isolators are built-in to the explosive-emission cathode. Experiments have demonstrated operability of high-current electron gun with a new cathode assembly at accelerating voltage up to 30 kV and its good emissivity (average in area current density) which was approximately 1.4-2.4times higher than an emissivity of traditional electron gun with plasma anode and multi-wire copper cathode. Keywords: high-current electron beams, explosive emission, cathode assembly, multi-gap initiation, dielectric surface flashover.

Excitation of high cyclotron harmonics in a high-current relativistic gyrotron in the frequency multiplication regime

Using the averaged equations supplemented with 3D particle-in-cells simulation methods, we have studied the frequency multiplication regime in a high-current relativistic gyrotron. The paper shows that the ratio between the output power of the higher (fifth or sixth) harmonics and that of the fundamental cyclotron resonance may be of about 0.1-0.3%. Accordingly, the nonlinear transformation coefficient is several orders of magnitude higher than the values achievable in gyrotrons with weakly-relativistic electron beams. Keywords: gyrotron, harmonic excitation, high-current relativistic electron beams.

Luminescent studies of bisphenol A solutions under the action of the electron beam

The results of measuring the luminescence of ambient air and solutions of an organic compound during their irradiation with a high-current pulsed electron beam with an average energy of Ee=170 keV and a duration of 2 ns, generated by the RADAN-303 accelerator, are presented. It is shown that, under such exposure, the transformation of dissolved bisphenol A occurs, which is accompanied by an increase in the absorption coefficient of the solution in the wavelength range of more than 300 nm and, as a consequence, a decrease in the intensity of air luminescence bands with an increase in the number of irradiation pulses. The results showed the degradation of the BPA solution to complete decomposition under the action of an electron beam treatment. Keywords: electron beam, air, solutions of organic compounds, luminescence, absorption, decomposition.

Люминесценцентные исследования растворов бисфенола A под действием электронного пучка

The results of measuring the luminescence of ambient air and solutions of an organic compound during their irradiation with a high-current pulsed electron beam with an average energy of Ee=170 keV and a duration of 2 ns, generated by the RADAN-303 accelerator, are presented. It is shown that, under such exposure, the transformation of dissolved bisphenol A occurs, which is accompanied by an increase in the absorption coefficient of the solution in the wavelength range of more than 300 nm and, as a consequence, a decrease in the intensity of air luminescence bands with an increase in the number of irradiation pulses. The results showed the degradation of the BPA solution to complete decomposition under the action of an electron beam treatment.

Люминесцентный контроль светодиодных гетероструктур, выращенных методом металлоорганической газофазной эпитаксии на сапфире

The paper presents the results of spectral and cardinal characteristics of AlGaN/GaN and InGaN/GaN LED heterostructure pulsed cathodes and photoluminescence grown on sapphire by metal organic vapor phase epitaxy are introduced. The effects of high current electron beam energy density on the luminescence spectra and amplitude characteristics of heterostructures are studied. The spatial distribution of fluorescence characteristics on the wafer surface was studied. It is found that in InGaN/GaN heterostructures, the maxim shifts of stimulated cathodoluminescence spectra measured at different points of the sample. This result is due to the changes in the composition and thickness of the quantum dimensional active region, and this change is not due to the ideality of the plate growth process.

О порогах плавления системы «пленка - подложка» при облучении низкоэнергетическим сильноточным электронным пучком

The effect of film material thermal conductivity on the melting threshold of the film-substrate system depending on the film thickness during a low-energy high-current electron beam (LEHCEB) irradiation was analyzed based on the numerical solution of the one-dimensional unsteady heat equation with a volumetric thermal source. Experimentally obtained oscillograms of the beam current at the collector and the accelerating voltage were used to simulate the heating source. Numerical variations of the film thermal conductivity were carried out within a wide range, overlapping the entire range for real materials. The dependence of the melting threshold of a homogeneous material on thermal conductivity was determined. The general regularities of the behavior of film and substrate melting thresholds depending on the film thickness were also established.

Энергия в импульсе нерелятивистского сильноточного электронного пучка

Energetic characteristics of a high-current electron gun with a cathode assembly based on multi-gap initiation of explosive emission by dielectric surface flashover in the mode of vacuum and gas-filled diode were investigated. It has been shown that it is better to measure high-current electron beam pulse energy using a calorimetric (thermal imaging) method than to calculate it from the waveforms of accelerating voltage and beam current onto collector (target) since the beam current values may be essentially overstated because of decay current of a dense plasma emergent under the bombardment of a collector by the beam electrons. The best efficiency of the energy transfer from the capacitive storage of the high-voltage pulsed generator supplying an electron gun was observed in the case of gas-filled diode at a moderate pressure of the working gas (argon, 0.093 Pa).

Исследование параметров самосфокусированного электронного пучка, выведенного за анод вакуумного диода

The parameters of a high-current electron beam extracted from the self-focusing zone through a hole in the anode into a vacuum chamber are investigated. The beam parameters were determined from the measurement of the spatial distribution of destruction and glow arising in polymethyl methacrylate samples installed at different distances from the anode (electron beam autographs). The formation of two electron beams - a self-focused with a high energy density, propagating along the axis of the cone facing the base to the anode with an apex angle of ~ 7º and a high-energy beam of low density, propagating in a hollow truncated cone and surrounding self-focused, was found. The oscillograms of the current and the energy of the electron beams were measured.

Оптическое и электронно-пучковое инициирование пленок пористого кремния с различным содержанием окислителя и графена

Laser and electron-beam initiation of the combustion process of energy-saturated composite films were studied. Composites were produced from porous silicon, a fluorine-containing polymer, and graphene. It is shown that the impact of a high-current electron beam of nanosecond duration does not lead to the excitation of the combustion process. Moreover, the process of film combustion during laser initiation is accompanied in some cases by the appearance of a zone of secondary flame and white smoke.

Technical Note: Effect of High-Current Pulsed Electron Beam Processing of Zr-1%Nb Alloy on Its Oxidation Kinetics at 1,200°C in Air and Steam

The paper reports the effect of high-current pulsed electron beam (HCPEB) processing of the Zr-1%Nb alloy as one of the most widely used in water-cooled nuclear reactors, based on the kinetics of its oxidation at 1,200°C in air and steam (these conditions are typical for potential loss-of-coolant accidents). It was shown that HCPEB processing caused a change in the surface morphology of the samples. In particular, craters with diameters of about 100 μm were found on the modified surfaces. They had initiated at an energy density of 5 J/cm2 and were characterized by relevant reliefs with microcracks. After HCPEB processing at 10 J/cm2, the craters were deeper with fractured surface layers. In addition, a pronounced surface relief corresponding to quenched martensitic microstructures was observed on the modified sample surfaces that had formed due to high heating and cooling rates. Due to sufficient degradation of the sample surfaces after HCPEB processing at 10 J/cm2, the kinetics of high-temperature oxidation was estimated only for the as-received samples and ones treated at 5 J/cm2. It was found that the as-received samples showed slightly greater weight gain levels in both air and steam environments, which fully correlated with the thickness ratio of the oxide, α-Zr(O), and prior-β layers. These phenomena and further research directions were discussed.

The properties of AISI 316L steel after surface treatment with Ti surface alloy and a-C:H:SiOx coating

The paper presents the research results of corrosion and mechanical properties of the AISI 316L stainless steel after the surface treatment. This treatment includes the formation of the titanium-based surface alloy provided by the low-energy high-current electron beam. The obtained surface alloy used as an underlayer, is then coated with the a-C:H:SiOx film using the PACVD method. It is shown that such a combined treatment of the steel surface improves its corrosion resistance, i. e., reduces the current density from 110-7 to 910-10 A/cm2 and corrosion rate from 1.110-3 to 9.310-6 mm/year. The resulted modified steel surface possesses high mechanical and tribological properties

Performance of bialkali photocathode in DC-SRF photoinjector

To obtain a low emittance, high current electron beam, a bialkali photocathode (K-Cs-Sb) was adopted in an upgraded DC-SRF photoinjector at Peking University. Based on the design and manufacture of the preparation and transport systems, a study of the K-Cs-Sb photocathode deposition and an electron beam performance test was carried out. The main improvement in the recipe is to reduce the cesiation process from ∼50 min to ∼6 min, and the lifetime of K-Cs-Sb photocathode can be increased, obviously, while the QE remains the same. During a performance test with a beam, a degradation in QE was found at 36 K, which is the lowest temperature for the operation of K-Cs-Sb photocathode in gun to date. However, the QE of K-Cs-Sb photocathode still exceeds 0.3% and can deliver an electron beam with a bunch charge of ∼150 pC and a repetition rate of 1 MHz. This QE is higher than reported at cryogenic temperature for SRF electron guns.

Nanoscale Electrostatic Modulation of Mega-Ampere Electron Current in Solid-Density Plasmas.

Transport of high-current relativistic electron beams in dense plasmas is of interest in many areas of research. However, so far the mechanism of such beam-plasma interaction is still not well understood due to the appearance of small time- and space-scale effects. Here we identify a new regime of electron beam transport in solid-density plasma, where kinetic effects that develop on small time and space scales play a dominant role. Our three-dimensional particle-in-cell simulations show that in this regime the electron beam can evolve into layered short microelectron bunches when collisions are relatively weak. The phenomenon is attributed to a secondary instability, on the space- and timescales of the electron skin depth (tens of nanometers) and few femtoseconds of strong electrostatic modulation of the microelectron current filaments formed by Weibel-like instability of the original electron beam. Analytical analysis on the amplitude, scale length, and excitation condition of the self-generated electrostatic fields is clearly validated by the simulations.

Pseudospark-Driven High-Current Miniaturized Voltage-Tunable Sheet-Electron-Beam Source

For high-power and compact sub-terahertz (THz) sources, a high-current electron beam is a crucial component. In this article, a miniaturized sheet-electron-beam source has been developed for generation of the high-current-density electron beam. It consists of a hollow cathode with a 3-mm diameter circular aperture, an anode with a 1.25 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.25$ </tex-math></inline-formula> mm rectangular aperture, and an interelectrode three-gap region with optimized dimension. The developed electron beam source has been operated in self-breakdown conditions for applied gap voltage ranging between 10 and 30 kV. The sheet electron beam has been successfully propagated for nearly 45 mm inside the drift space without the assistance of an external magnetic field due to the space charge neutralization effect. It has demonstrated good transmission characteristics with more than 50-A beam current and beam current loss of around 25%.

Spheroidization Behavior of Nano-Primary Silicon Induced by Neodymium under High-Current Pulsed Electron Beam Irradiation

The spheroidization behavior of the nano-primary silicon phase induced by Nd under high-current pulsed electron beam (HCPEB) irradiation was investigated in this study. The study results revealed that, compared to the Al–17.5Si alloy, spheroidized nano-primary silicon phase emerged in the alloy’s HCPEB-irradiated surface layer due to the presence of Nd. Because Nd was abundantly enriched on the fast-growing silicon crystal plane, its surface tension was reduced under the extreme undercooling caused by HCPEB irradiation, causing the growth velocity of each crystal plane to be the same and spherical nanometers of silicon to appear. The spheroidization of nano-primary silicon phases occurred in the remelted layer. The microhardness test revealed that Nd could depress the microhardness of the Al matrix at the same number of pulses, but conversely increase the microhardness of the primary silicon phase, compared to the Al–17.5Si alloy. The tribological test showed that the presence of spherical nano-primary silicon could significantly improve the alloy’s tribological property.

Modification of stainless steel based on synergistic of low-energy high-intensity ion implantation and high-current electron beam impact on the surface layer

The results of experiments on low-energy implantation of AISI 321 stainless steel by nitrogen ions are presented. The treatment was carried out by a pulsed beam of nitrogen ions obtained using a ballistic ion focusing system. The surface modification occurs with the formation of a two-layer structure, which is typical for ion-plasma nitriding processes of stainless steels. The thickness of the modified layer can reach 27 μm after 1 hour of ion-plasma treatment. The influence of subsequent modification of the ion-doped layer by the action on the surface of the pulsed high-current electron beam of microsecond duration is studied. The work presents the results of the studying the regularities of changes in the depth distribution of dopants, microstructure and phase composition of the modified and matrix layers by optical metallography, diffraction analysis and transmission electron microscopy.