Properties Of Electron Beam Research Articles

Low-density plasmas generated by electron beams passing through silicon nitride window

In general, more attention is paid to how to improve the characteristic parameters of plasma in plasma applications. However, in some cases, it is necessary to produce plasma with low-electron density, such as in the laboratory simulation of ionospheric plasma in space science. In this study, a low-density plasma is generated by electron beams passing through a silicon nitride transmission window under low pressure condition. The transmission properties of electron beam passing through silicon nitride films are investigated by Monte Carlo simulation, and the plasma feature is studied by a planar Langmuir probe and a digital camera. It is found that the plasma exhibits a conical structure with its apex located at the transmission window. At a constant pressure, the cone angle of conical plasma decreases with the electron energy increasing. This is qualitatively consistent with the Monte Carlo simulation result. The frequency of electron-neutral collisions increases as the working pressure rising, which leads the plasma cone angle to increase. When the beam current is reduced from 10 μA to 0.5 μA at 40 keV, the electron density decreases, in a range between 10<sup>5</sup> and 10<sup>6</sup> cm<sup>–3</sup>, while the electron temperature does not change significantly but approaches 1 eV. It can be inferred that the electron density decreases with the distance <i>z</i> from the transmission window in the incident direction of the electron beam. A low-density plasma of less than 10<sup>5</sup> cm<sup>–3</sup> can be obtained further away from the transmission window.

Solar Electron Beam—Langmuir Wave Interactions and How They Modify Solar Electron Beam Spectra: Solar Orbiter Observations of a Match Made in the Heliosphere

Solar Orbiter's four in situ instruments have recorded numerous energetic electron events at heliocentric distances between 0.5 and 1 au. We analyze energetic electron fluxes, spectra, pitch-angle distributions, associated Langmuir waves, and type III solar radio bursts for three events to understand what causes modifications in the electron flux and identify the origin and characteristics of features observed in the electron spectrum. We investigate what electron beam properties and solar wind conditions are associated with Langmuir wave growth and spectral breaks in the electron peak flux as a function of energy. We observe velocity dispersion and quasilinear relaxation in the electron flux caused by the resonant wave–particle interactions in the deca-keV range, at the energies at which we observe breaks in the electron spectrum, cotemporal with the local generation of Langmuir waves. We show, via the evolution of the electron flux at the time of the event, that these interactions are responsible for the spectral signatures observed around 10 and 50 keV, confirming the results of simulations by Kontar and Reid. These signatures are independent of pitch-angle scattering. Our findings highlight the importance of using overlapping FOVs when working with data from different sensors. In this work, we exploit observations from all in situ instruments to address, for the first time, how the energetic electron flux is modified by the beam–plasma interactions and results in specific feature appearing in the local spectrum. Our results, corroborated with numerical simulations, can be extended to a wider range of heliocentric distances.

Microstructure characterization and mechanical properties of electron beam welded joints of WRe alloy and CoCrFeNi high entropy alloys

In this study, vacuum electron beam welding was performed on WRe/CoCrFeNi alloy, resulting in joint interfaces resembling brazing. The research primarily focused on microstructure, phase composition, grain orientation and texture, interface bonding characteristics, mechanical properties, and fracture mechanisms of the welded joints. The weld zone consisted of columnar, cellular, and equiaxed regions, influenced by solidification rate. Employing the PHACOMP method, it is predicted that the introduction of W element in the weld zone tends to precipitate the FCC phase into the μ-phase. Grain competition during weld growth led to differences in grain orientation. A strong cubic texture {001} <100> was observed in the weld, enhancing its ductility. The impact of Kirkendall voids and IMCs on the bonding at the WRe/WZ interface was discussed. Microhardness of the weld increased due to grain refinement and precipitation strengthening. The joint exhibited a tensile strength of 189 MPa and an elongation of 10 %, with a fracture mechanism characterized by interface brittle fracture and fusion zone ductile fracture. The interface fracture was attributed to Kirkendall voids, IMCs, and significant residual stresses induced by material CTE mismatch. Furthermore, deep dimples and slip bands on cleavage planes at the fracture surface bottom, along with low-angle grain boundaries promoting localized slip, indicated good plasticity in the fusion zone.

Prediction on X-ray output of free electron laser based on artificial neural networks

Knowledge of x-ray free electron lasers’ (XFELs) pulse characteristics delivered to a sample is crucial for ensuring high-quality x-rays for scientific experiments. XFELs’ self-amplified spontaneous emission process causes spatial and spectral variations in x-ray pulses entering a sample, which leads to measurement uncertainties for experiments relying on multiple XFEL pulses. Accurate in-situ measurements of x-ray wavefront and energy spectrum incident upon a sample poses challenges. Here we address this by developing a virtual diagnostics framework using an artificial neural network (ANN) to predict x-ray photon beam properties from electron beam properties. We recorded XFEL electron parameters while adjusting the accelerator’s configurations and measured the resulting x-ray wavefront and energy spectrum shot-to-shot. Training the ANN with this data enables effective prediction of single-shot or average x-ray beam output based on XFEL undulator and electron parameters. This demonstrates the potential of utilizing ANNs for virtual diagnostics linking XFEL electron and photon beam properties.

Microstructure evolution and mechanical properties of wire-fed electron beam directed energy deposition repaired GH4169 superalloy

In this paper, the microstructural evolution and failure behavior of GH4169 superalloy repaired using wire-fed electron beam directed energy deposition (EB-DED) are investigated in detail. Results show that in the deposited zone (DZ), the Laves phase is formed in the interdendritic zone, and the γ'' phase and γ′ phase precipitate around the Laves phase and are distributed gradiently along the building direction. In contrast, the substrate zone (SZ) is composed of fine equiaxed grains and uniform distributed γ'' and γ′ phases. Direct aging heat treatment cannot effectively dissolve the Laves phase, but can further precipitate the γ'' and γ′ phases, resulting in an increase in yield strength and ultimate tensile strength and a decrease in elongation. During the plastic deformation process, dislocation activity preferentially occurs in the γ matrix and forms accumulation at the Laves/γ interface, leading to the formation of cracks in the DZ, so that all tensile samples fail in the DZ. In addition, this study further elucidates the fracture mechanism of the Laves phase within grains and at grain boundaries.

Optical properties of electron beam evaporated Zn1−XTiXO thin films

Optical properties of electron beam evaporated Zn1−XTiXO thin films

An analytical model and experimental validation of annular heat source during scanning electron beam treatment

In this investigation, the maximum depth of penetration and power density coefficient are calculated by simulating the motion trajectories of electrons in surface layer of 5CrNiMo steel using Monte Carlo method, and the number of electrons is 500,000 in simulation. Then tomographic calculation is used to determine the distribution of power density coefficient on the section perpendicular to electron incidence direction, and a Gaussian columnar heat source model that matches the properties of electron beam is established. Finally, a mobile annular heat source model of scanning electron beam is then derived, combining it with the real operating mode. The temperature field during surface modification is simulated by using the mobile annular heat source model, and the simulation findings are compared to experimental data. The findings of Monte Carlo simulation demonstrate that the power density coefficient is Gaussian distributed on the section perpendicular to the depth of electron incidence and the peak power density at the center of each section changes with depth. The thickness and microstructure of re-melting layer predicted from the temperature field simulation is very close to the one from experimental findings. In our investigation, on top of deriving a model for the heat source of a single beam spot, we have also solved the problem of mathematical representation of the beam spot when it is doing high-speed rotational and linear composite motions. The aforementioned findings demonstrate that our study can provide methodological references for the construction of heat source models for different materials during electron beam treatment.

Microstructure and Mechanical Properties of Electron Beam Melted Nb–W and Nb–W–Zr Alloys

Microstructure and Mechanical Properties of Electron Beam Melted Nb–W and Nb–W–Zr Alloys

Influencing mechanisms of weld root tip on microstructure and mechanical properties of electron beam welded joints of titanium alloy thick plates

The welding of titanium alloy thick plates often formed a narrow weld seam in the weld root, named as ‘weld root tip’, because of insufficient fusion, which could reduce the joint properties. In this study, 30 mm-thick Ti-5Al-5Mo-5V-1Cr-1Fe alloy was butt welded via electron beam welding to reveal the influencing mechanisms of the weld root tip on joint microstructure and mechanical properties. The subparallel or parallel weld seam with the weld angles of 0°–3° between the centre line and edge of the fusion zone removed the weld root tip, achieving almost the same mechanical properties with those of the welding zone.

Target Design in SEM-Based Nano-CT and Its Influence on X-ray Imaging.

Nano-computed tomography (nano-CT) based on scanning electron microscopy (SEM) is utilized for multimodal material characterization in one instrument. Since SEM-based CT uses geometrical magnification, X-ray targets can be adapted without any further changes to the system. This allows for designing targets with varying geometry and chemical composition to influence the X-ray focal spot, intensity and energy distribution with the aim to enhance the image quality. In this paper, three different target geometries with a varying volume are presented: bulk, foil and needle target. Based on the analyzed electron beam properties and X-ray beam path, the influence of the different target designs on X-ray imaging is investigated. With the obtained information, three targets for different applications are recommended. A platinum (Pt) bulk target tilted by 25° as an optimal combination of high photon flux and spatial resolution is used for fast CT scans and the investigation of high-absorbing or large sample volumes. To image low-absorbing materials, e.g., polymers or organic materials, a target material with a characteristic line energy right above the detector energy threshold is recommended. In the case of the observed system, we used a 30° tilted chromium (Cr) target, leading to a higher image contrast. To reach a maximum spatial resolution of about 100 nm, we recommend a tungsten (W) needle target with a tip diameter of about 100 nm.

In Situ SEM Compression Study on Micro-mechanical Behavior of Electron Beam Melted Ti-6Al-4V Alloy

To investigate the mechanical properties of electron beam melted (EBM) Ti-6Al-4V alloy at the microscale, a series of in situ scanning electron microscope (SEM) compression experiments were performed in the current study. Firstly, a reconstruction of the original β phase of Ti-6Al-4V alloy was conducted using electron backscattering diffraction (EBSD) analysis. Micro-pillars were subsequently fabricated with a diameter of 2 μm within the same original β phase grain, and yield strength was measured using an in-situ mechanical compression device. The mechanical response of each micro-pillar was found to vary, and potential reasons for this phenomenon were discussed, including the impact of α-phase and β-dispersion on the material’s mechanical properties. Moreover, a clear size effect was observed when comparing the yield strength of the bulk material. Furthermore, the plastic deformation behavior of Ti-6Al-4V alloy was also investigated through compression tests on the micro-pillars.

Microstructure and mechanical properties of vacuum electron beam welded joints of Ti/Cu dissimilar metals

Sheets of TC4 titanium alloy and T2 pure copper were joined by vacuum electron beam welding with an offset on the copper side. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to study the microstructure of the welded joint, and the composition of the intermetallic compounds (IMCs) at the reaction layer was studied by energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM), followed by tensile testing to investigate the mechanical properties of the welded joints. The results show that electron beam welding can achieve an effective connection of Ti/Cu dissimilar metals. A multilayer structure composed of an IMCs layer, a final solidification zone, and a weld zone is formed at the Ti/Cu interface. The main composition of the IMCs layer is the faceted phase of TiCu and a small amount of the faceted phase of Ti2Cu, while the FS zone is composed of tiny equiaxed grains of copper. The tensile test results show that the ultimate tensile strength of the joints reaches 190 MPa, and the elongation rate reaches 4.27%. The joint presents brittle fracture characteristics with fracture occurring in the IMCs layer.

The influence of electron beam welding technology on mechanical properties of GH4169 welded joints

Super-alloy GH4169 and related welded structures were widely used in the aero-engine industry region. Vacuum electron beam welding is one of the most advanced welding technologies, and the influence of the mechanical property caused by the welding technology still needs further research. Firstly, the hardness, microstructure, and tensile properties of the GH4169 electron beam welded joint were tested. After electron beam welding and two-stage aging treatment, the weld zone was strengthened and its hardness is higher than that of the base metal zone. The microstructure characterization results showed that the grain size of the weld and heat-affected zone was larger than that of the base metal. The tensile results show that the static properties of the welded joint are similar to that of the base metal, and the residual height has no obvious effect on the static strength of the welded joint. The high-temperature creep properties of GH4169 electron beam welded joints with residual height were tested. The results show that residual height will lead to a transient fracture of welded joints under relatively safe service conditions. The fatigue performance of GH4169 welded joints with and without residual height was tested respectively. The results show that the fatigue life of the welded joints without residual height was about 10 times longer than that of the welded joints with residual height under the same stress level, and for the welded joint with residual height, the residual height position will become the main fatigue crack source.

Laser-driven muon production for material inspection and imaging

We numerically show that laser-wakefield accelerated electron beams obtained using a PetaWatt-scale laser system can produce high-flux sources of relativistic muons that are suitable for radiographic applications. Scalings of muon energy and flux with the properties of the wakefield electron beams are presented. Applying these results to the expected performance of the 10-PW class laser at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) demonstrates that ultra-high power laser facilities currently in the commissioning phase can generate ultra-relativistic muon beams with more than 104 muons per shot reaching the detector plane. Simple magnetic beamlines are shown to be effective in separating the muons from noise, allowing for their detection using, for example, silicon-based detectors. It is shown that a laser facility like the one at ELI-NP can produce high-fidelity and spatially resolved muon radiographs of enclosed strategically sensitive materials in a matter of minutes.

The Effect of the Heat Treatment Condition of the Base Material on the Microstructure and Mechanical Properties of 17-4PH Stainless Steel Electron Beam Welded Joints

The Effect of the Heat Treatment Condition of the Base Material on the Microstructure and Mechanical Properties of 17-4PH Stainless Steel Electron Beam Welded Joints

Slipping instability of an inhomogeneous relativistic electron beam

The charged particle beams, such as electrons, ions, and plasma compression flow, have received considerable attention due to their applications in science and technology; therefore, studying the stability of these beams is of particular importance. Here, we examine theoretically the stability properties of a cold relativistic electron beam with a transverse velocity shear and non-uniform density profile. We consider a plane-parallel beam propagating along an external magnetic field and evaluate its macroscopic equilibrium state. We derive the dispersion relation of the slipping instability based on the linear electrodynamics of an inhomogeneous plasma and kinetic theory. In this model, the oscillation spectrum and the growth rate are derived by using the eikonal equation and the quasi-classical quantization rule. A linear velocity shear and a non-linear density gradient are assumed. Furthermore, we analyze numerically the dispersion relation of the slipping instability. The impacts of the inhomogeneity parameter and the relativistic factor on the properties of the slipping instability are discussed.

Grating Optimization for Smith–Purcell Radiation: Direct Correlation Between Spatial Growth Rate and Starting Current

Smith–Purcell radiation (SPR) is generated when electrons travel close to a metallic periodic grating. It was found that the starting current of SPR varies by orders of magnitude by simply varying the grating parameters (groove’s heights and widths) while keeping the grating period and the electron beam properties fixed. In this article, we demonstrate that this strong dependence of starting current on the grating parameters is directly related to the spatial growth rate of the SPR. Using the hot-tube dispersion relation, we optimize the grating parameters to minimize the starting current to excite coherent SPR.

Propagation and focusing dependency of a laser beam with its aberration distribution: understanding of the halo induced disturbance

In various applications, it is necessary to understand laser field dynamics during its propagation, especially at the focal position including the dispersed energy surrounding the main pulse, called the halo effect. For instance, the properties of electron beams produced by laser wakefield acceleration (LWFA) strongly depend on the laser energy distribution and its halo in the vicinity of the focus. Indeed, under certain conditions, this halo, or even its internal structures, can propagate and be self-focused independently of the main pulse in the plasma. This paper aims to provide sufficient tools to properly describe the behavior of a focused laser beam, including the halo. Subsequently, an optical description regarding the source of this halo is provided. A more accurate estimation of the input laser beam that should be used in simulations of high-power laser applications may now be obtained. Finally, one may also find ways to positively manipulate the laser beam. Using Fresnel diffraction theory, the propagation and focusing of an experimental high-power (sub-petawatt) aberrated beam is numerically calculated. The shape of the focused beam pattern within a few Rayleigh lengths is analysed as a function of main aberrations (up to the 14 th term of Zernike polynomials). Furthermore, at the focus position, the spreading of the energy is compared to both the case of a perfect diffraction-limited Gaussian and a super-Gaussian beam.

Effect of Hf addition on the microstructure and mechanical properties of electron beam welded Mo-La2O3 alloy

Electron beam welding of La2O3 dispersion strengthened molybdenum alloy is conducted in this research. Hf interlayers with different thicknesses are introduced to joining Mo alloy via in-situ alloying to avoid grain boundary oxidation and improve the mechanical properties of joints. The porosity ratio within the weld reduces from 7.53% (without Hf interlayer) to 1% ∼ 2% (with Hf interlayers of 0.1 mm–0.35 mm). The microstructure of the weld is mainly composed of Mo base solid solution for the joints with a Hf interlayer of 0.05 mm. As the thickness of the Hf interlayers increases from 0.1 mm to 0.35 mm, HfMo2 is generated within the weld and the content of HfMo2 phase increases significantly. The introduction of Hf promotes the grain refinement of the weld owing to the generation of HfO2 precipitates, which provide more heterogeneous nucleation sites for the liquid metal to nucleate. In addition, the formation of HfO2 consumes the O elements in the weld and prevents the generation of MoO2 along grain boundaries, which is beneficial for the improvement of the mechanical properties of the joints. The results show that the introduction of Hf significantly improves the strength of the joint. The ultimate strength of the joint with a Hf interlayer of 0.1 mm especially for the joint with a Hf interlayer of 0.1 mm reaches 333 MPa, which is 6 times more than that of the joint without a Hf interlayer of 54 MPa.

Microstructure and mechanical properties of electron beam welded TC4 titanium alloy structure with backing plate

This study investigates the microstructure characterization and residual stress differences of a welded TC4 titanium alloy structure to determine the optimum electron beam welding parameters. A finite element model is constructed on the basis of the actual weld morphology under different welding parameters, and the Mises stress of the titanium alloy electron beam joint is compared. The residual stress distribution in the shell structure with a backing plate under superimposed working stress conditions is analyzed. Results show that the change of microstructure and mechanical properties of each area do not show remarkable changes with variations in welding speed. However, the macroscopic morphology varies greatly, and the microhardness and maximum shear strength distribution appears as follows: the weld metal > heat affected zone > base metal. The finite element simulation reveals that the peak residual stress of WM along the longitudinal and transverse directions is 782 MPa and 583 MPa respectively, which is consistent with the distribution of the measured results. The finite element calculation results of the shell structure under internal pressure show that the Mises stress of the WM appears the smallest value when the welding speed reaches 8 mm/s, and its value is 650.59 MPa. Therefore, a smaller the welding speed (from 14 mm/s to 8 mm/s) of the shell structure has a positive effect on service behavior.