High-current Electron Research Articles

The effect of low-energy high-current pulsed electron beam irradiation on the structure, phase composition and mechanical properties of Ni3Al and Ni3Al-TiC composites

Using scanning and transmission electron microscopy, X-ray diffraction, indentation and bending tests we studied the evolution of microstructure, phase composition and mechanical properties of TiC-free Ni3Al and Ni3Al-TiC composites (TiC content was 10 and 30 vol%) fabricated by self-propagating high-temperature synthesis (SHS) under pressure induced by low-energy high-current pulsed electron beam (LEHCEB) irradiation with the surface energy density of 8, 12 and 18 J/cm2. It was found that the irradiation results in the improvement of phase composition of the near-surface layer by way of the increase of yield of SHS reaction. LEHCEB irradiation enables formation of nanocomposite structure in the near-surface layer of Ni3Al-TiC composites with decreased grain size of Ni3Al matrix, refined TiC particles and increased volume fraction of TiC. This structure leads to the increase of microhardness but decrease of strength under bending. Two mechanisms of TiC particles refining are suggested. The effect of surface energy density on the manifestation degree of the found phenomena is discussed. The contribution of different hardening mechanisms to the overall hardening is considered.

Simulation of the prebreakdown processes in a cathode microprotrusion with the tip shape varying due to melting

A two-dimensional axisymmetric model of the prebreakdown processes that occur in a cathode microprotrusion exposed to an external dc electric field has been developed. The model assumes that the electrical breakdown of a vacuum gap occurs through the explosive emission mechanism. For the first time, the heating of a copper cathode microprotrusion has been simulated taking into account the variation in the shape of its tip after melting. The simulation was performed by solving numerically the Navier–Stokes equations for the melt, which was considered as a viscous incompressible fluid with a free surface immersed in an electric field strong enough for high-current electron emission from the surface to occur. It has been shown that the motion of the melt and the development of electrohydrodynamic instability on its surface result in the formation of a nanometer-sized conical protrusion on the microprotrusion tip. This significantly speeds up the heating of the microprotrusion by field emission current to the critical temperature.

Formation of Fe–Cr–Al–Zr Surface Alloy on a Zirconium Substrate Using a Low-Energy High-Current Electron Beam

Formation of Fe–Cr–Al–Zr Surface Alloy on a Zirconium Substrate Using a Low-Energy High-Current Electron Beam

Improved mechanical and tribological properties of TiAlN coatings by high current pulsed electron beam irradiation

High current pulsed electron beam (HCPEB) irradiation is an important surface engineering technique, which has been proved to be valid in modifying the surface microstructure and properties of various materials. In this work, HCPEB was employed to irradiate TiAlN coatings. The microstructure, mechanical and tribological properties of both original and irradiated TiAlN coatings were investigated. The results showed that the surface roughness of the TiAlN coatings first increased with 5 pulses of HCPEB irradiation, and then gradually declined with a further increase in pulse numbers. Compared with the original coating, the coating irradiated by 15 pulses demonstrated superior hardness (up to 33.4 GPa) and adhesion strength (112N), excellent wear resistance (wear rate of 3.3 × 10−6 mm3/Nm) and low friction coefficient (0.37). It is believed that the grain refinement, formation of the transition zone and adjustment of residual stresses after 15 pulses of HCPEB treatment are responsible for the improvement in both mechanical and tribological properties of the TiAlN coatings. These findings might suggest the potential applications of HCPEB irradiation for surface modification and hardness improvement of hard nitride coatings.

Ultrafast transformation of natural graphite into self-supporting graphene as superior anode materials for lithium-ion batteries

Graphite possesses remarkable potential as an anode material for lithium-ion batteries, thanks to its superb electrical conductivity and eco-friendliness. Nevertheless, challenging issues persist, such as its low maximum theoretical lithium storage capacity and constraints associated with the regular layered structure, which impede its practical application and advancement. In this regard, we proposed a novel approach to enhance the energy storage performance of lithium-ion batteries, involving the modification of natural graphite through irradiation with a high-current pulsed electron beam (HCPEB). Microscopic observations revealed that during the in-situ transformation of graphite particles into self-supporting graphene nanosheets, the high temperature generated by HCPEB irradiation led to the formation of structural defects, including Stone Wales and double vacancy defects. Consequently, the modified natural graphite electrode (particle size 12 μm) exhibited a reversible capacity of 420.4 mAh/g at 0.2C and maintained 94.5% of its reversible capacity after 500 cycles. In comparison to unmodified graphite (particle size 12 μm), the SEI film displayed enhanced stability, significantly improving cycling performance. These findings demonstrated that the defective graphene nanosheet structure enhances lithium storage activity sites, enlarges layer spacing, and enhances lithium storage performance. This study presents an efficient and environmentally friendly method for producing superior anode materials for lithium-ion batteries.

Nanobubbles and physical-mechanical properties of the Ti-Ni-Ta-Si-based metallic glass surface alloy fabricated on a TiNi SMA substrate by additive thin-film electron-beam method

An additive thin-film electron-beam method for the synthesis of micron-thick surface alloys is a promising method for modifying the surface layers of metallic materials. This method allows to functionalize the surface properties (corrosion resistance, radiopacity, biocompatibility), as well as to improve the physical-mechanical properties. The amorphous Ti-Ni-Ta-Si-based surface alloy (~1.6 μm thick) was synthesized by 10-fold alternation of operations of the deposition of an alloying film (Ti60Ta30Si10 (at. %), ~100 nm thick) and the liquid-phase mixing of the [film/substrate] system using a pulsed low-energy high-current electron beam. Spherical nanobubbles (diameter varies from ~2.5 up to ~50 nm) were observed within the surface alloy. The additional electron-beam treatments were used to reduce the concentration of the nanobubbles. The paper presents the results of the influence of the electron-beam treatments on the concentration and size of the nanobubbles, and their in-depth distribution. It was found that the single-step electron-beam treatment effectively reduced the concentration of the nanobubbles and affected on their size and distribution. The two-step electron-beam treatment almost restored the characteristics of the nanobubbles. The influence of the characteristics of the nanobubbles on the strength and elastic-plastic parameters of the amorphous Ti-Ni-Ta-Si-based surface alloy was revealed. The characteristics of the nanobubbles had a major effect on the elastic-plastic parameters of the surface alloy while the strength parameters remained practically the same. It was found that a purposeful change of the characteristics of the nanobubbles is an effective tool for controlling physical-mechanical properties of the amorphous Ti-Ni-Ta-Si-based surface alloy fabricated on a TiNi SMA substrate.

Beam current from downramp injection in electron-driven plasma wakefields

We study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser–wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimised by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density.

Fast spacecraft charging induced by a high-power electron beam emission and its mitigation through a plasma contactor

Active sounding experiments, including tracing magnetic field lines and magnetospheric sounding, may be accomplished in the GEO environment by the active emission of high-power electron beams. The continual emission of electron beam pulses during such experiments may result in the accumulation of positive charges on the spacecraft surface and a rise in the spacecraft potential, which might prohibit the normal emission of succeeding pulses. The plasma contactor has been shown to be a reliable method for neutralizing the spacecraft potential. But as the active charging effect brought on by the high-current electron beam manifests itself more quickly, it is still unknown whether the plasma contactor can reliably control the spacecraft potential in this circumstance. In this study, a two-dimensional PIC model is used to examine the active charging effect brought on by high-power electron beam emission. Findings indicate that the potential neutralization process may be affected by the ion sheath that forms close to the emitting surface of the plasma contactor, which cuts the electrical connection between the spacecraft and plasma in space. By evaluating the quantities and growth speeds of different particles during active charging, we discover that lowering the particle density or pre-emission time of the plasma contactor may bring the spacecraft potential to the equilibrium state. Additionally, the high-current electron beam raises the peak potential, making it more difficult to launch the electron beam properly before the spacecraft potential reaches equilibrium. In contrast, the high-energy electron beam is less susceptible to the active charging effect.

Effect of High-Current Pulsed Electron Beam Irradiation on the Microstructure and Mechanical Properties of Multilayered TiN/TiCN/Al2O3 Coatings

Effect of High-Current Pulsed Electron Beam Irradiation on the Microstructure and Mechanical Properties of Multilayered TiN/TiCN/Al2O3 Coatings

A magnetically insulated coaxial vacuum diode providing a reduced energy spread in the leading edge of a high-current electron beam

A magnetically insulated vacuum diode was modified to reduce the fraction of low-energy electrons in the leading edge of a high-current beam. The voltage pulse of duration ≈1 ns, rise time ≈250 ps, and amplitude ≈ –230 kV that arrives at the diode cathode from a transmission line is split in coupled coaxial lines (CLs) into two pulses with an amplitude ratio U2/U1 >1. The end of the common electrode of the CLs is close in profile to an equipotential surface and forms two gaps in the diode. In the first injection gap, at U0 < U1, explosive electron emission starts at the cathode. The pulse U1 arrives here with a delay at least equal to the duration of the leading edge, since there is a dielectric insert in the inner CL. The beam enters, through the window in the intermediate electrode, the acceleration gap, where the leading pulse U2, delivered from the outer CL, has already peaked. In the proposed device, unlike the one-gap prototype diode, electrons start from the cathode at a much smaller spread of the leading edge voltage. As a result, after acceleration of these electrons in the second gap, their energy spread relative to the maximum energy decreases multiply. This is confirmed by calculations and measurements of the beam current for a beam passed through aluminum filters.

THE SIMULATION OF EMERGENCY ACTION ON CONSTRUCTION MATERIALS BY HIGH CURRENT RELATIVISTIC ELECTRON BEAMS

Development of many innovative areas in energy, mechanical engineering, aircraft building and other industries is limited by the strength of materials under the action of temperature gradients. In this regard, the problem appears to find and justify technical means to model a complex of operating conditions. High-current relativistic electron beams reasonably belong to such instruments and means. As a result of their impact, pulsed electric and magnetic fields occur in the irradiated targets, temperature gradients are created, and shock waves are generated. The paper investigates the patterns of change in the internal structure of the blades of gas turbine engines and engineering materials, subjected to the action of an electron beam

Microstructural evolution of thermally grown oxide of an arc ion plated MCrAlX coatings after high-current pulsed electron beam treatment

An arc ion-plated NiCoCrAlYHfSi coating modified by a high-current pulsed electron beam (HCPEB) was examined in this study. The dynamic growth behavior and formation mechanisms of the thermally grown oxide (TGO) of the original and modified coatings were thoroughly compared by isothermal oxidation at 1050 °C. HCPEB irradiation led to the transformation of the rough original coating into a flat, smooth, and dense structure. Furthermore, Y-Al nanoparticles and high density of dislocations were also obtained in the modified layer. These modification characteristics can establish favorable conditions for the rapid accumulation and stable growth of the protective Al2O3 particles. With the extension of oxidation time, the CrO3 formed in the oxide film left many small pits after volatilization, but these pits were filled with Al2O3 particles. Compared with the oxide film of the original coating, the TGO of the modified coating is flat, continuous, and dense, and its growth rate is notably slower. Also, the growth of Ni, Cr, and Co rich oxides was expectantly restrained. Obviously, the HCEPB technique has the capacity to change the growth behavior of the TGO and significantly enhance the coating's resistance to high-temperature oxidation.

Direct density modulation of photo-assisted field emission from an RF cold cathode

This paper explores direct density modulation of high-current electron beam emission from an RF cold cathode using optical excitation. We theoretically study the photo-assisted field emission of periodically bunched electron beams of various pulse shapes under the combined excitation of an RF field and an optical field, using an exact quantum model. Both continuous-wave (CW) and pulsed optical fields are considered. The emission current pulse amplitude, pulse width, electron number density per pulse, as well as pulse shape and its harmonic contents are investigated in detail. For CW photon sources in the UV to NIR range (i.e., 200–1200 nm), increasing the optical intensity under an RF bias tends to change the current pulse from a Gaussian to sinusoidal-like shape, thus offering strong flexibility to control the frequency components in beam current emission. Pulsed photon sources combined with an RF field can produce sharp, high-current electron bunches with pulse duration comparable with or even less than that of the optical pulse. A contour map of the density modulation depth is constructed for different combinations of RF and laser fields. The results provide insight into unlocking new opportunities to achieve direct density modulation during electron current emission by optical means.

DIMUS: super-compact Dimuonium Spectroscopy collider at Fermilab

While dimuonium (μ + μ -) — the “smallest QED atom” — has not yet been observed, it is of utmost fundamental interest. By virtue of the larger mass, dimuonium has greater sensitivity to beyond the standard model (BSM) effects than its cousins positronium or muonium, both discovered long ago, while not suffering from large QCD uncertainties. Dimuonium atoms can be created in e + e - collisions with large longitudinal momentum, allowing them to decay a small distance away from the beam crossing point and avoid prompt backgrounds. We envision a unique cost-effective and fast-timeline opportunity for copious production of (μ + μ -) atoms at the production threshold via a modest modification of existing Fermilab Accelerator Science and Technology (FAST) facility to arrange collisions of 408 MeV electrons and positrons at a 75° angle. This compact 23 m circumference collider (DIMUS) will allow for precision tests of QED and open the door for searches for new physics coupled to the muon. The FAST facility is perfectly suited for DIMUS as there are existing SRF accelerators and infrastructure, capable of producing high energy, high current electron and positron beams, sufficient for O(1032)cm2 s-1 luminosity and ∼0.5 million dimuons per year. The expansion will require installation of a second SRF cryomodule, positron production and accumulation system, fast injection/extraction kickers and two small circumference intersecting rings. An approximately meter-sized detector with several layers of modern pixelated silicon detector and crystal-based electromagnetic calorimeters will ensure observation of the decays of dimuonium to electron-positron pairs in presence of the Bhabba scattering background. An expansion of the system to include solenoidal magnet outside of the calorimeter system, a layer of steel shielding behind the magnet, and a set of dedicated muon detectors would extend the physics program of DIMUS to include precision studies of rare processes with muons, pions, and η mesons produced in e + e - collisions.

Combined influence of airflows and a parallel magnetic field on the discharge characteristics of AC dielectric barrier discharge

The combined influence of airflows and a parallel magnetic field on an AC-driven dielectric barrier discharge plasma is experimentally investigated through image analyses, electrical measurements, and optical diagnoses. After applying a parallel magnetic field, more discharge filaments are generated during one discharge cycle. Besides, the electrical and optical diagnoses show that the magnetic field can increase the plasma parameters, such as the electron temperature and electron density. When airflows and a parallel magnetic field are applied in combination, the discharge uniformity presented in the long-exposure images is significantly enhanced by the airflows and slightly improved by the magnetic field. With increasing airflow velocity, the distribution of discharge filaments goes through four phases, namely, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution, among which the stripe-like distribution exhibits the highest discharge uniformity. High-speed video analyses reveal that the improved discharge uniformity can be attributed to the changed breakdown positions and the increased number of filaments. Although airflow can significantly improve the macroscopic uniformity of the discharge, it leads to a decrease in the maximum current pulse amplitude, electron temperature, electron density, and gas temperature. Applying a magnetic field in flowing air can not only improve the discharge uniformity but also ensure that the discharge has high maximum current pulse amplitude intensity, electron temperature, and electron density. Based on the analyses of the electron trajectory and the estimation of the force condition of the micro-discharge remnants, the modulated charged particles, reduced electric field, and pre-ionization degree are responsible for the changed discharge uniformity and plasma parameters in the parallel magnetic field and flowing air.

Preparation and surface alloying of Al@Dy and Al@Y core-shell particles by magnetron sputtering and pulsed electron beam treatment

The paper is devoted to preparation Al@Dy and Al@Y core-shell structures by magnetron sputtering of Dy and Y on an Al powder. A unique powder holder system is used to obtain continuous powder movement and conglomerates destruction during the treatment. It has been established that powder particles treated using the powder holder system have a uniform coating over the entire surface. The powder coating process regularities were studied depending on the deposition time and the powder charge weight. Simple evaluation criteria for powder coating system efficiency and deposited material content based on the deposition rate were proposed. The complex modification consists of the initial core-shell structure formation and subsequent pulsed low-energy high-current electron beam treatment in the surface layer melting mode was demonstrated. The main goal of the electron beam treatment is to provide better adhesion of the “shell” material to the “core” material. Such treatment led to the deposited shell element alloying into the depth of core particles. Moreover, such electron beam treatment led to the synthesis of intermetallic compounds. In further studies, the prepared structures will be used for the uniform distribution of Dy and Y over the frame elements of self-propagating high-temperature synthesized porous materials.

Increasing the Pulse Energy of a Radially Converging Low-Energy High-Current Electron Beam

Increasing the Pulse Energy of a Radially Converging Low-Energy High-Current Electron Beam

Hot corrosion behavior of NiCoCrAlY laser cladding coating on 17-4PH stainless steel before and after high-current pulsed electron beam irradiation

In this study, we employed high-current pulsed electron beam technology (HCPEB) to modify NiCoCrAlY coatings that were created via laser cladding on 17-4PH stainless steel. We compared and analyzed the hot corrosion behavior of the coatings before and after HCPEB irradiation using a molten salt of 75 wt. %Na2SO4 + 25 wt. %NaCl at 700 °C. We also elucidated the mechanism by which irradiation affects the hot corrosion performance of the coatings. Our findings demonstrate that the irradiated coating surface exhibited a dense remelting layer, which effectively prevented erosion by oxygen and molten salt, without any internal oxidation corrosion. Moreover, irradiation refined the grains on the coating surface and increased the diffusion rate of grain boundaries. Consequently, the irradiated coating formed laminated thermal growth oxides (TGO) during the hot corrosion process, with the interface between the TGO and the coating always covered by an Al2O3 layer. This TGO structure provided excellent protection, reduced the corrosion weight gain, and corrosion rate of the coating, and significantly improved the hot corrosion performance of the coating.

Impact of high-current pulsed electron beam modification on element diffusion and performance of Ti6Al4V/AISI 316 L stainless steel diffusion bonded joints

The diffusion bonding process between Ti6Al4V and 022Cr17NiMo2 stainless steel (AISI 316 L SS) was carried out under vacuum conditions, applying a 10 MPa load for 40 min within a temperature range of 800–900 °C. This study investigates the influence of high-current pulsed electron beam (HCPEB) modification on the microstructure at the interface and the shear strength of Ti6Al4V/AISI 316 L SS joints. After HCPEB pretreatment, a well-formed diffusion bond was achieved between Ti6Al4V and AISI 316 L SS at 900 °C. Through calculations, the diffusion coefficient and diffusion activation energy of Fe in the Ti6Al4V section were determined, which demonstrated that Fe exhibits higher diffusion rates in the HCPEB-modified joints. The modified joint, subjected to 900 °C, exhibited a maximum bond strength of 208 MPa, which is attributed to dispersion and solid solution strengthening. Consequently, the implementation of HCPEB modification proves effective in promoting element diffusion and enhancing the mechanical performance of the joints. The presence of abundant crystal defects, including vacancies, dislocations, and grain boundaries (GBs) generated by HCPEB, is believed to be responsible for the observed improvement in diffusion.

Effect of High Current Pulsed Electron Beam (HCPEB) on the Organization and Wear Resistance of CeO2-Modified Al-20SiC Composites.

This paper investigates the joint effect of high current pulsed electron beam (HCPEB) and denaturant CeO2 on improving the microstructure and properties of Al-20SiC composites prepared by powder metallurgy. Grazing Incidence X-ray Diffraction (GIXRD) results indicate the selective orientation of aluminum grains, with Al(111) crystal faces showing selective orientation after HCPEB treatment. Casting defects of powder metallurgy were eliminated by the addition of CeO2. Scanning electron microscopy (SEM) results reveal a more uniform distribution of hard points on the surface of HCPEB-treated Al-20SiC-0.3CeO2 composites. Microhardness and wear resistance of the Al-20SiC-0.3CeO2 composites were better than those of the Al matrix without CeO2 addition at the same number of pulses. Sliding friction tests indicate that the improvement of wear resistance is attributed to the uniform dispersion of hard points and the improvement of microstructure on the surface of the matrix after HCPEB irradiation. Overall, this study demonstrates the potential of HCPEB and CeO2 to enhance the performance of Al-20SiC composites.