Electron Beam Density Research Articles

Effect of the energy density of pulsed electron beam on the microstructure and properties of Mo-Zr surface alloys

Lasers and electron beams have been widely used to synthesize various surface alloys (SAs) but no data have been reported so far on the molybdenum-zirconium (Mo-Zr) ones. To partially fill this knowledge gap, Mo-Zr SAs were formed by processing molybdenum films on zirconium substrates with low-energy high-current electron beams (LEHCEBs). The effect of the energy density of LEHCEBs on the microstructure, phase composition, nanohardness and corrosion resistance of the Mo-Zr SAs were investigated. Basically, the Mo-Zr SAs consisted of a solid solution of Mo in the β-Zr phase, Mo2Zr second phase particles (SPPs) and a solid solution Zr in Mo. Increasing in the energy density decreased the concentration of the SPPs and enhanced the content of the β-Zr phase. Also, it affected the depth of the highest concentration of the SPPs. In the zones of the highest molybdenum contents, the nanohardness values reached 9.4–12.7 GPa, which was higher by 3.2–4.4 times than that of the zirconium substrates. In a 3.5 % NaCl solution at room temperature, the corrosion current densities and the corrosion potentials were greater than those of the zirconium substrates by six and almost two times, respectively.

Twisted terahertz excitation using pre-bunched relativistic electron beam in magnetic wiggler

This work presents a theoretical analysis of the generation of twisted terahertz (THz) radiation using laser-bunched relativistic electron beams in a magnetic wiggler. By employing a laser-bunched relativistic electron beam, which introduces a transverse modulation to the electron beam density, and a magnetic wiggler, which induces a transverse deflection to the electron trajectories, the generation of twisted THz radiation is achieved. The interaction between the modulated electron beam and the magnetic field leads to the emission of THz photons with a twisted phase structure. The findings of this study provide valuable insights into the generation and manipulation of twisted THz radiation contributing to the advancement of THz technology and its diverse applications.

Direct Imaging of Radiation-Sensitive Organic Polymer-Based Nanocrystals at Sub-Ångström Resolution.

Seeing the atomic configuration of single organic nanoparticles at a sub-Å spatial resolution by transmission electron microscopy has been so far prevented by the high sensitivity of soft matter to radiation damage. This difficulty is related to the need to irradiate the particle with a total dose of a few electrons/Å2, not compatible with the electron beam density necessary to search the low-contrast nanoparticle, to control its drift, finely adjust the electron-optical conditions and particle orientation, and finally acquire an effective atomic-resolution image. On the other hand, the capability to study individual pristine nanoparticles, such as proteins, active pharmaceutical ingredients, and polymers, with peculiar sensitivity to the variation in the local structure, defects, and strain, would provide advancements in many fields, including materials science, medicine, biology, and pharmacology. Here, we report the direct sub-ångström-resolution imaging at room temperature of pristine unstained crystalline polymer-based nanoparticles. This result is obtained by combining low-dose in-line electron holography and phase-contrast imaging on state-of-the-art equipment, providing an effective tool for the quantitative sub-ångström imaging of soft matter.

Analysis of the Mechanism of Microwave Radiation Generated by the Weak Interaction Between Relativistic Electron Beam and Plasma with a Transverse Magnetic Field

This article establishes a physical model of the interaction between a surface electron beam and the plasma with a transverse magnetic field. The dispersion relation of the beam-plasma interaction is derived by using the field matching method. The effects of magnetic field, electron beam electron density, and plasma density on the radiation frequency and z-direction wave vector are studied. The results indicate that the stronger the transverse magnetic field is, the higher is the cutoff frequency of plasma radiation. The higher the plasma density or electron beam electron density is, the higher are the corresponding radiation frequency and radiation wave number.

Control of the Electron Beam Density Distribution on the Collector in Sources with a Grid Plasma Cathode Based on a Low-Pressure Arc

Control of the Electron Beam Density Distribution on the Collector in Sources with a Grid Plasma Cathode Based on a Low-Pressure Arc

High Energy Density Welding of IN792 Ds Superalloy

Ni base superalloys are commonly employed in the industrial fields of aerospace, automotive and energy production due to their excellent mechanical properties and corrosion resistance at high temperature. Superficial defects and cracks may occur during both manufacturing process of components and their service life. High energy density welding techniques, electron beam (EBW) and laser beam (LBW) welding, can be used to create efficient repairs. Joints, obtained by EBW and LBW of IN792 directionally solidified (DS) superalloy, have been investigated to determine the presence of defects, and evaluate the mechanical properties related to specific microstructural features. The results showed that a pre-heating temperature (PHT) higher than 200 °C is always necessary to prevent the formation of hot cracks in the molten zone (MZ) and heat affected zone (HAZ). The process parameters have been optimized to get a good quality of the seams (lack of macro-defects, a good penetration depth and width). Some preliminary test of post-welding heat treatments (PWHTs) have been investigated to homogenize as far as possible the microstructure and the mechanical properties across the seams. The results obtained by the two techniques, EBW and LBW, have been compared and discussed.

Ion Acoustic Breathers in Electron-Beam Plasma

The nonlinear excitations of ion acoustic (IA) structures in an electron beam embedded plasma composed of Vasyliunas–Cairns (VC) distributed hot electrons has been studied. The nonlinear Schrödinger equation (NLSE) from the Kadomtsev–Petviashvili (KP) equation with suitable transformation has been derived from rational solutions of NLSE; breathers have been studied. It has been shown that the nonthermality and superthermality of the electrons, the electron beam density, and the beam velocity alter the characteristics of different kinds of breathers. This investigation may be important in interpreting the physics of nonlinear structures in the upper layer of magnetosphere.

Terahertz generation by a rotating relativistic electron beam in a magnetized plasma column

Terahertz (THz) field excitation by a rotating relativistic electron beam in a magnetized plasma column is described using numerical analysis and particle-in-cell simulation. A rotating electron beam propagating through a cylindrical plasma column excites plasma wakefields. The plasma wakefields couple with the electron beam to excite transverse currents at THz frequency. As a result, the energy of the wakefield directly converts into the form of electromagnetic radiation in the THz range. The magnetic field supports the transverse modes via electron cyclotron resonance. The strength of the THz field is enhanced due to scattering of the spiralling electron beam on the plasma density perturbation. The THz field amplitude is controllable by the electron beam velocity and beam density. On increasing the beam current, the THz field is enhanced significantly. The analytical results are compared with particle-in-cell simulations and are found to be in reasonable agreement.

The Research on the High-Current-Density Shielded Sheet Electron Beam Matching Focusing Magnetic Field

Increasing beam current density is a very effective approach to boost the output power in millimeter wave and terahertz vacuum devices. However, the current density of sheet electron beam (SEB) is severely limited, due to instabilities in the SEB transport, especially in the case of high current density. To overcome this limitation, a new approach for stably transporting a high-current-density SEB, named shielded SEB matching focusing magnetic field (shielded SEB-MFM), is presented in this article. This new focusing magnetic field consists of a small transverse magnetic field and a conventional shielded uniform magnetic field (shielded UM). Compared with the conventional shielded UM, about double the maximum beam current density can be transported by the shielded SEB-MFM, in the same strength as the magnetic field. In addition, an implementable scheme of an electron optical system based on the shielded SEB-MFM is designed and calculated to verify the feasibility of the shielded SEB-MFM. The results indicate that the SEB with a 636-A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> current density can be well focused by a 0.8-T shielded SEB-MFM in a 40-mm tunnel. To achieve the same expansion degree of thickness, the conventional shielded UM must be around 1.5 T.

Transmission grating couples and enhances the second harmonic of the electron beam to generate tunable high-power terahertz radiation.

Vacuum electronic devices utilizing free-electron-based mechanisms are a crucial class of terahertz radiation sources that operate by modulating electron beams. In this study, we introduce what we believe is a novel approach to enhance the second harmonic of electron beams and substantially increase the output power at higher frequencies. Our method employs a planar grating for fundamental modulation and a transmission grating operating in the backward region to augment the harmonic coupling. The outcome is a high power output of the second harmonic signal. Contrasting with traditional linear electron beam harmonic devices, the proposed structure can achieve an output power increase of an order of magnitude. We have investigated this configuration computationally within the G-band. Our findings indicate that an electron beam density of 50 A/cm2 at 31.5 kV can produce a 0.202 THz center frequency signal with an output power of 4.59 W. As the electron beam voltage is adjusted from 23 kV to 38.5 kV, the output signal frequency shifts from 0.195 THz to 0.205 THz, generating several watts of power output. The starting oscillation current density at the center frequency point is 28 A/cm2, which is significantly lower in the G-band compared to conventional electron devices. This reduced current density has substantial implications for the advancement of terahertz vacuum devices.

GW-Level Ku-Band Compact Coaxial TTO With Permanent Magnet Packaging Potential

When the O-type high-power microwave (HPM) sources are extended to the high band, the current density of the intense relativistic electron beam will increase, which requires a higher intensity of the guiding magnetic field. The coil of the excitation system will be bulkier, which is not conducive to the development of the device toward the direction of light and small. The transit time oscillator (TTO) has attracted much attention due to its ability to output GW-level HPMs in the small number of cavities. In order to replace solenoid with permanent magnet, the compact coaxial TTO with a low magnetic field is designed in this article. The coaxial structure reduces the need for magnetic field strength. In addition, the familiar reflector is removed and the axial size of the beam-wave interaction region is reduced, which not only reduces the risk of electron beam diffusion under low magnetic field, but helps to reduce the weight of permanent magnets in the future. In particle-in-cell (PIC) simulation, the proposed coaxial TTO can output more than HPMs of 1.0 GW under the magnetic field less than 0.4 T with the efficiency is over 30%. Therefore, it is feasible to use permanent magnet packaging for the device.

Theoretical Study on Weibel instability in the existence of large amplitude Langmuir wave inside a Plasma

This paper investigates how an electrostatic Langmuir wave having large amplitude affects the Weibel instability (WI) in the existence of ions and an electron beam. Two Langmuir side band waves are produced by coupling of EM perturbation to the Langmuir wave. The Langmuir wave (LW) increases the growth rate beyond its linear value. Here, we noticed that the growth rate Γ(sec−1) scales linearly with the electron beam velocity vbe and 1/2 power of the electron beam density nbe. As we increase the density of ions inside the plasma, the growth rate stabilizes. Additionally, we find that the growth rate is very sensitive to the plasma frequency of ions. Therefore, our work finds an application in space, galactic cosmic rays and supernovas. Also, our work covers a range of application from the development of fusion power to understand the various astrophysical phenomena.

Nonlinear ion acoustic wave structure in electron–ion plasma in presence of fully relativistic electron beam

Analytical description of large amplitude nonlinear ion acoustic (IA) waves in the presence of a cold relativistic electron beam is presented. The pseudopotential method is adopted to observe the effects of various parameters like beam density, ion temperature, etc. on the IA wave structures. Furthermore, the maximum amplitude of the IA wave is estimated, and its variation with fully relativistic electron beam parameters is investigated. The maximum allowed amplitude of the wave is found to decrease with the increase in the electron beam density as well as in the ion temperature. The Mach number has the effect to increase the maximum amplitude of the electric field.

Evidence of oblique electron acoustic solitary waves triggered by magnetic reconnection in Earth’s magnetosphere

Motivated by the recent Magnetospheric Multiscale (MMS) observations of oblique electron acoustic waves, we addressed the generation mechanism of the observed waves by utilizing the reductive perturbation technique. A nonlinear Zakharov-Kuznetsov (ZK) equation is derived for a collisionless, magnetised plasma composed of cool inertial background electrons, cool inertial electron beam, hot inertialess suprathermal electrons; represented by a κ-distribution, and stationary ions. Moreover, the instability growth rate is derived by using the small-k perturbation expansion method. Our findings revealed that the structure of the electrostatic wave profile is significantly influenced by the external magnetic field, the unperturbed hot, cool, and electron beam densities, the obliquity angle, and the rate of superthermality. Such parameters also have an effect on the instability growth rate. This study clarifies the characteristics of the oblique electron solitary waves that may be responsible for changing the electron and ion distribution functions, which alter the magnetic reconnection process. Moreover, the increase of the growth rate with the plasma parameters could be a source of anomalous resistivity that enhances the rate of magnetic reconnection.

A Raman quantum free-electron laser model

Operation of a Quantum Free Electron Laser (QFEL) could provide a compact and fully coherent source of X- and γ-rays. Imperative to experimental realization is allowing for decoherence effects of either spontaneous emission or space-charge to take place, having opposing constraints. Here, for the first time, we present a one-dimensional QFEL Wigner model that includes longitudinal space-charge effects by quantizing the periodic potential derived from the Fourier components of the longitudinal electron beam density. The model is used to investigate steady-state QFEL gain and momentum state dynamics for a variety of space-charge regimes. We find increased saturation lengths and lower saturation intensity as a result of attenuated transitions in the two-level quantum system. In addition, we characterize a space-charge regime where specific transitions outside the QFEL bandwidth are targeted, such that the conventional description breaks down. These findings serve as a consistent theoretical extension of existing QFEL models.

Effect of beam oscillation on microstructure, defect density, and resistivity of electron beam welded niobium

Effect of beam oscillation on microstructure, defect density, and resistivity of electron beam welded niobium

Research on the Induced Electrostatic Discharge of Solar Arrays under the Action of ESD EMP

In this paper, the electrostatic discharge of solar arrays in spacecraft energy systems is taken as the research object. The influence and internal mechanism of external electromagnetic radiation on electrostatic discharge is studied. Meanwhile, the charging and discharging test platform of spacecraft solar arrays under a strong field is first established. Then, the influence of irradiation field strength, electron beam energy and beam density on electrostatic discharge of solar arrays is analyzed and summarized. The results show that during the irradiation process of solar arrays using a high-energy electron beam under vacuum conditions, the higher the electron beam energy and the beam current density, the higher the discharge frequency of the solar array. When the intensity of the external electromagnetic radiation field increases, the discharge frequency also increases. Under the action of external radiation field with the same peak field strength, the larger the gap, the smaller the discharge frequency. With the increase in the field strength, the potential difference of each part of the solar array becomes smaller, and the peak of the discharge current decreases. The research results can provide technical reference for electrostatic protection of spacecraft solar arrays.

Characterization of Pseudospark Discharge-Based Multigap Plasma Cathode Electron Source for the Generation of Short Pulsed Energetic Electron Beam

Pseudospark (PS) discharge-based devices are known as excellent source for the generation of high current density and energetic self-focused electron beam in the hollow cathode (HC) phase. In this article, short pulsed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!\!\!&lt; 100$ </tex-math></inline-formula> ns) and high energetic (~20 keV) electron beam has been generated and propagated (up to ~60 mm) in the drift region without using any external guiding magnetic field from the four-gap configuration of PS discharge-based plasma cathode electron (PD-PCE) source. The particle-in-cell (PIC) simulation code OOPIC Pro has been employed, whose results have shown the strong dependence of beam propagation into the drift region on the penetration and distribution of potential lines. The combined experimental and simulation investigations have also been carried for the multigap (four-gap) with wide range of external storage capacitor (40 pF–18 nF) and operating voltages (5–35 kV). The circuit parameter controls the appearance of HC phase for the energetic (50%–70% applied voltage) electron beam and conductive phase for the high current (~10 A to ~0.5 kA) electron beam. The potential distribution has clearly indicated that the electron beam with higher applied voltages can propagate more focused in the drift region. The investigations have evidently shown the generation of low energy and high current to high energy and low current electron beams suitable to cover the potential applications in the field of extreme ultraviolet (EUV)/soft X-ray radiation generation, surface modification, and microwave-terahertz radiation generation.

Structure and properties of the CrMnFeCoNi high-entropy alloy irradiated with a pulsed electron beam

According to the technology of wire-arc additive manufacturing a nonequiatomic composition CoCrFeMnNi high-entropy alloy (HEA) was obtained. Deformation curves of samples in tension are plotted and analyzed after the HEA fabrication by the methods of wire-arc additive manufacturing (initial state) and after the electron-beam processing (EBP). The EBP results in a decrease in the HEA's strength and plastic properties. Along with a pit character of the fracture a presence of micropores and microlayerings are identified. A study of the HEA's fracture surface after the EBP except for regions with a ductile fracture mechanism revealed regions with a band (lamellar) structure. The area with a band structure increases with a growth in the beam electron density from 25% at 10 J/cm2 to 65% at 30 J/cm2. A diameter of separation pits in fracture bands varies in the limits (0.1–0.2) μm, which is considerably less than those of the remaining part of the HEA sample. An average size of crystallization cells formed in the EBP depends on the energy density of electron beam and increases from 310 nm at 15 J/cm2 to 800 nm at 30 J/cm2. A non-monotonous change in the scalar dislocation density, reaching a maximum value of ∼5.5 · 1010 cm-2 at a distance of 25 μm from the irradiation surface is revealed. It is suggested that defects being formed in surface layers in the EBP may be one of the reasons for decreasing the values of HEA strength and plasticity.

Fractography of fracture surface of CrMnFeCoNi high-entropy alloy after electron-beam processing

In the past decade the attention of scientists in the field of physical materials science is attracted to studying the high-entropy alloys. By the technology of wire-arc additive manufacturing (WAAM) a high-entropy alloy (HEA) of a nonequiatomic composition was obtained. Deformation curves obtained under uniaxial tension at a rate of 1.2 mm/min at room temperature using Instron 3369 unit were analyzed in two states: initial/after fabrication and after electron-beam treatment (EBT). EBT was conducted to detect its influence on structural-phase states and mechanical properties. The EBP leads to a decrease in strength and plastic properties of the HEA. By means of scanning electron microscope LEO EVO 50, analysis of structure of fracture surface and the near-surface zone was performed. Dependences of the ultimate strength and relative elongation to failure on EBT parameters were revealed, and it was shown that values of strength and plasticity decrease nonmonotonically with an increase in electron beam energy density in the range ES = 10 – 30 J/cm2 at constant values of duration, frequency, and number of pulses. Along with a pit character of the fracture a presence of micropores and microlayering was detected. Investigation of the HEA’s fracture surface after EBP except for areas with a ductile fracture mechanism revealed the regions with a band (lamellar) structure. At ES = 10 J/cm2, the area of such structure is 25 %; it increases nonmonotonically to 65 % at ES = 30 J/cm2. The diameter of pits of detachment in fracture bands varies in the limits of 0.1 – 0.2 μm, which is considerably less than that in the remainder of the HEA samples. After EBP the thickness of the molten layer varies in the limits of 0.8 – 5.0 μm and grows with an increase in the energy density of electron beam. EBT leads to generation of crystallization cells, the sizes of which change within the range 310 – 800 nm as ES increases from 15 to 30 J/cm2. It is suggested that the defects being formed in surface layers in ЕВР may be the reason for decreasing the HEA’s maximum values of strength and plasticity.