Pulsed Electron Beam Research Articles

Photocatalytic activity of ZnO-Zn nanoparticles after nanosilver covering and annealing

The research evaluated the photocatalytic activity (PCA) of zinc oxide nanoparticles (NPs) produced by pulsed electron beam evaporation (PEBE). The ability of NPs to accelerate the photodegradation of methyl violet dye under UV exposure was considered. The paper presents an analysis of changes in catalytic activity after annealing and coating with nanosilver of the studied samples. It has been shown that as the annealing temperature increases, the PCA increases, especially for doped particles. The highest catalytic ability was shown by doped NPs ZnO-Zn+Ag annealed at a temperature of 400 °C. This sample allowed to increase the photodegradation of the organic dye by more than 6.5 times compared to the control.

Effect of high current pulsed electron beam on surface microstructure and properties of cold-rolled austenitic stainless steel

High current pulsed electron beam (HCPEB) was used to modify the surface microstructure and performance of AISI 304 stainless steel with different cold-rolling deformation. The phase, microstructure, microhardness, and corrosion performance were characterized and analyzed after cold-rolling and HCPEB treatment. The results show that after cold-rolling, deformation-induced martensites (DMs) are generated in the deformation twin lamellae or at the intersections of multiple twin lamellae, resulting in a grid-like morphology, smaller size, and a certain orientation relationship with the parent austenite. The content of DMs increases with increasing cold-rolling deformation. After HCPEB treatment, many craters with different sizes and similar densities are produced on the sample surface, and the DMs are transformed into austenite again in the surface layer. The difference is that the grain size of the regenerated austenite after HCPEB is much smaller than that of the initial austenite (before cold-rolling). Such high-density equiaxed ultrafine grains (UFGs) of austenite formed after HCPEB present a twin feature, which is the inheritance of the orientation relationship between DMs and austenite formed during rolling. HCPEB treatment can effectively reshape the phase and microstructure of the surface layer of the cold-rolled deformed austenitic steel but reduce the surface hardness and increase pitting corrosion tendency.

Study of nanosecond pulsed hollow-cathode electron beam generation and transportation based on PIC-MCC simulation

This work employs the PIC-MCC (Particle-in-Cell Monte-Carlo collisions) method to study the nanosecond pulsed electron beam time-varied beam current profiles through the hollow-cathode discharge plasma evolution and electron beam transportation process. The electron beam’s energy and current distribution characteristics at the anode hole are investigated, and the simulation’s grid and step sizes are set as 0.04 µm and 5×10-13s, respectively. Experimental parameters are used in the simulation, and experimental results are also used to verify the simulation accuracy. The simulations investigate the transportation characteristics of the electron beam under different conditions and obtain the effects of voltage, current, and ion density on the distribution characteristics of the electron beam. The electron beam current generated by the hollow-cathode discharge is gradually transformed from a random distribution in the central region to a Gaussian distribution. Due to the ion-forced channel formed by the runaway electron pre-ionization, the high-energy electron beam achieves focused transport over a certain distance, and the high-energy electron beam has a smaller Gaussian radius than the source input. Besides, the ion-focusing channel formed by the high-energy electron transportation process can realize the transportation of the high-current electron beam in the conduction stage.

STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices.

Practical techniques to identify heat routes at the nanoscale are required for the thermal control of microelectronic, thermoelectric, and photonic devices. Nanoscale thermometry using various approaches has been extensively investigated, yet a reliable method has not been finalized. We developed an original technique using thermal waves induced by a pulsed convergent electron beam in a scanning transmission electron microscopy (STEM) mode at room temperature. By quantifying the relative phase delay at each irradiated position, we demonstrate the heat transport within various samples with a spatial resolution of ~10 nm and a temperature resolution of 0.01 K. Phonon-surface scatterings were quantitatively confirmed due to the suppression of thermal diffusivity. The phonon-grain boundary scatterings and ballistic phonon transport near the pulsed convergent electron beam were also visualized.

Technical note: A small animal irradiation platform for investigating the dependence of the FLASH effect on electron beam parameters.

The recent rediscovery of the FLASH effect, a normal tissue sparing phenomenon observed in ultra-high dose rate (UHDR) irradiations, has instigated a surge of research endeavors aiming to close the gap between experimental observation and clinical treatment. However, the dependences of the FLASH effect and its underpinning mechanisms on beam parameters are not well known, and large-scale in vivo studies using murine models of human cancer are needed for these investigations. To commission a high-throughput, variable dose rate platform providing uniform electron fields(≥15cm diameter) at conventional (CONV) and UHDRs for in vivo investigations of the FLASH effect and its dependences on pulsed electron beam parameters. A murine whole-thoracic lung irradiation (WTLI) platform was constructed using a 1.3cm thick Cerrobend collimator forming a 15 × 1.6 cm2 slit. Control of dose and dose rate were realized by adjusting the number of monitor units and couch vertical position, respectively. Achievable doses and dose rates were investigated using Gafchromic EBT-XD film at 1cm depth in solid water and lung-density phantoms. Percent depth dose (PDD) and dose profiles at CONV and various UHDRs were also measured at depths from 0 to 2cm. A radiation survey was performed to assess radioactivation of the Cerrobend collimator by the UHDR electron beam in comparison to a precision-machined copper alternative. This platform allows for the simultaneous thoracic irradiation of at least three mice. A linear relationship between dose and number of monitor units at a given UHDR was established to guide the selection of dose, and an inverse-square relationship between dose rate and source distance was established to guide the selection of dose rate between 20 and 120Gy·s-1 . At depths of 0.5 to 1.5cm, the depth range relevant to murine lung irradiation, measured PDDs varied within±1.5%. Similar lateral dose profiles were observed at CONV and UHDRs with the dose penumbrae widening from 0.3mm at 0cm depth to 5.1mm at 2.0cm. The presence of lung-density plastic slabs had minimal effect on dose distributions as compared to measurements made with only solid water slabs. Instantaneous dose rate measurements of the activated copper collimator were up to two orders of magnitude higher than that of the Cerrobend collimator. A high-throughput, variable dose rate platform has been developed and commissioned for murine WTLI electron FLASH radiotherapy. The wide field of our UHDR-enabled linac allows for the simultaneous WTLI of at least three mice, and for the average dose rate to be modified by changing the source distance, without affecting dose distribution. The platform exhibits uniform, and comparable dose distributions at CONV and UHDRs up to 120Gy·s-1 , owing to matched and flattened 16 MeV CONV and UHDR electron beams. Considering radioactivation and exposure to staff, Cerrobend collimators are recommended above copper alternatives for electron FLASH research. This platform enables high-throughput animal irradiation, which is preferred for experiments using a large number of animals, which are required to effectively determine UHDR treatment efficacies.

Induced ageing of ZnS:Ag microparticles exposed to 13 keV electron beam

Phosphorescent microparticles made of ZnS:Ag were exposed to pulsed electron beams with an energy of 13 keV for periods of time between 30 min and 240 min. An XRD analysis showed no modification of crystalline structure. The average cristalites of ZnS:Ag was 62 nm deduced from SEM imaging. The luminescence spectra showed a decreasing activity with 40% after 30 min of irradiation at a fluence of 5.79 ×1016 electrons/cm2. The broad peak between 445 nm to 480 nm centered aroud 460 nm with a FWHM almost constant aroud 80 nm show no shifting. After a long exposure (over 240 min) and a fluence of 4.60 ×1017 electrons/cm2, the powder suffered a blackening effect attributed to formation of dead layers under electronic excitation combined with increasing of Sulphur vacancies, quantitatively confirmed by EDS analysis, where the proportion of S in ZnS:Ag decreases from 31.42% to 13.75%. Also, the luminescence at this moment dropped to almost 90% under the electron beam effect. The thermal effect could not be correlated with luminescence quenching, which was attributed to the increase in the number of impurities.

A Tutorial on the One-Dimensional Theory of Electron-Beam Space-Charge Effect and Steady-State Virtual Cathode

The space-charge effects of pulsed high-current electron beams are very important to high-power particle beam accelerators and high-power microwave devices. The related physical phenomena have been studied for decades, and a large number of informative publications can be found in numerous scientific journals over many years. This review article is aimed at systematically summarizing most of the previous findings in a logical manner. Using a normalized one-dimensional mathematical model, analytical solutions have been obtained for the space-charge-limited current of both planar diode and drifting space. In addition, in the case of a beam current higher than the space-charge-limited current, the virtual cathode behavior and beam current reflection are quantitively studied. Furthermore, the criteria of steady-state virtual cathode formation are investigated, which leads to the physical understanding of the unstable nature of the virtual cathode. This review article is expected to serve as an integrated source of related information for young researchers and students working on high-power microwaves and pulsed particle beams.

Microstructure and physico-mechanical properties of steel, processed by a pulsed electron beam

Microstructure and physico-mechanical properties of steel, processed by a pulsed electron beam

CSR-induced Projected Emittance Growth Study For The Beam Switchyard At The European XFEL

Minimizing projected emittance of high brightness electron beam is important for efficient overlap between electron beam and radiation pulse in an FEL facility. Coherent synchrotron radiation (CSR) emission in a single bending section in the beam transport system usually introduces different slice energy modulation hence different slice transverse kicks in the designed dispersion-free lattice, causing projected emittance growth. Here we present theoretical and simulation study of CSR effect on the projected emittance growth in the beam switchyard arc before SASE2 undulator beamline at the European XFEL. We analyze arc optics impact on CSR effect and discuss possible schemes for emittance degradation compensation.

Characterization of a LaB6 tip as a thermionically enhanced photoemitter

There is a widespread interest in time-resolved electron spectroscopies such as ultrafast electron diffraction, ultrafast electron microscopy, and ultrafast electron energy loss spectroscopy. These techniques require pulsed electron beams with both high current and brightness. LaB6 is commonly used as a thermionic emitter because of its low work function and high electron yield. However, its use as a pulsed photocathode has not been widely explored. Here, we present measurements of the electron yield from a LaB6 filament exposed to 392 nm UV ultrafast laser pulses under a wide range of filament temperatures. We find that sample heating strongly enhances photoelectron yield, an effect known as thermionically enhanced photoemission. However, it also creates potentially undesirable, continuous thermionic background. We conclude that the ideal optimal operating conditions strongly depend on the type of measurement and require defining and quantifying an appropriate figure of merit.

Demin K.A. Role of pulsed electron beam treatment in forming of operational properties of working surfaces of biomedical titanium alloy products

The article presents the study of the effect of pulsed electron beam treatment on the surface roughness of samples made of titanium alloy VT-6, obtained by two methods: mechanical processing and additive manufacturing. It has been established that electron beam treatment allows reducing the roughness of titanium alloys in both cases, which can be extremely important for polishing small-sized products, particularly those with low mechanical strength or unique microrelief surface.

Analysis of contact zone of coating-substrate system exposed to irradiation with a pulse electron beam

Using the wire-arc additive manufacturing method (WAAM) on a 5083 aluminum alloy substrate, a non-equiatomic Mn – Cr – Fe – Co – Ni high-entropy alloy (HEA) coating was formed. By scanning and transmission electron diffraction microscopy we analyzed the structure, phase and elemental composition of the contact zone after irradiation with high-current low-energy electron beams with the following parameters: accelerated electron energy 18 keV, electron beam energy density 30 J/cm2, electron beam pulse duration 200 µs, number of pulses 3, pulse repetition rate 0.3 s–1. Multiphase multielement submicro- and nanocrystalline structures are formed predominantly in the substrate, which has a lower melting temperature compared to HEAs. Mutual doping of the coating – substrate system occurs in the contact layer, which has sinuous boundaries. The contact layers adjacent to the substrate and coating have the structure of high-speed cellular crystallization. In the layer adjacent to the substrate, the cells are formed by a solid solution of magnesium in aluminum. Interlayers of the second phase, enriched in atoms of the coating and substrate, are revealed along the cell boundaries. In the layer adjacent to the coating, the cells are formed by an alloy of composition 0.17Mg – 20.3Al – 4.3Cr – 16.7Fe – 9.3Co – 49.2Ni corresponding to the coating. Interlayers of the second phase, enriched mainly in magnesium and, to a lesser extent, in atoms of the HEA coating, are located along the cell boundaries. Central region of the contact zone with a thickness of ~1700 μm is formed by lamellar crystallites, which indicates the eutectic nature of its formation. Its main element is aluminum (≈77 at. %).

THERMOLUMINESCENT AND DOSIMETRIC PROPERTIES OF ZIRCONIUM DIOXIDE CERAMICS IRRADIATED WITH HIGH DOSES OF PULSE ELECTRON BEAM

The paper presents the results of a study of thermoluminescent (TL) and dosimetric properties of monoclinic zirconium dioxide ceramics of two types: synthesized by sintering in an electric furnace at T = 700–1700 °C and in a flow of high-energy electrons (1.4 MeV) with a high power density. It has been established that annealing of ceramics of the first type at T>1000 °C leads to a significant increase in the crystallite size, which correlates with a significant increase in the intensity of the TL peak at 390 K after irradiation of the samples with high doses (on the order of kGy) of a pulsed electron beam (130 keV). Type 2 ceramics synthesized by the electron beam method have the maximum TL response. The work also discusses the patterns of influence of synthesis conditions on the kinetic parameters of TL and the nonlinearity coefficients of dose dependencies. The presence of an intense isolated TL peak, the sublinear nature of most dose dependencies, and negligible fading indicate the promise of the ceramics synthesized in this work for measuring high doses (several to tens of kGy).

Investigation of the influence of pulse parameters on the resulting weld seam quality in pulsed electron beam welding of AW 6061

Utilizing pulsed lasers in favor of a continuous wave in laser beam welding is a well-established method to achieve higher process efficiency and reduce heat input into the workpiece, which is especially useful for thin-walled workpieces (Steen, 2005). In addition, pulsed processes have shown to lead to smaller grain sizes due to higher cooling rates, which can lead to a reduction in hot cracks in some aluminum alloys (Beiranvand et al., 2019). Since an electron beam can also be pulsed, a technique industrially utilized in electron beam drilling, the same principles apply (Schultz, 2000). However, pulsed electron beam welding is rarely used in industrial welding applications due to the risk of pores, spiking and sputtering resulting from the pulsed process dynamic, especially in the deep welding regime (Kautz, 1991). This study aims to develop a pulsed electron beam welding process for AW 6061 sheet metal, which is susceptible to hot cracking. The influence of the welding and pulse parameters, as well as the combination of a pulsed beam with high frequency beam oscillation is discussed. Furthermore, suitable welding parameters for pulsed electron beam welding of AW 6061 are developed, and the increased efficiency of pulsed welding is shown by comparison to continuous welds.

Hot corrosion behavior of NiCoCrAlYSi laser cladding coating modified using high-current pulsed electron beam in different corrosive salt environments

The investigation focused on microstructural changes and hot corrosion behavior in various salt environments (Na2SO4 + 25 wt% K2SO4 and Na2SO4 + 25 wt% NaCl) at 900 °C of NiCoCrAlYSi laser cladding coatings before and after high-current pulsed electron beam (HCPEB) irradiation. HCPEB treatment effectively eliminated imperfections like micropores and segregation of the components, creating a remelted layer with high-density dislocations and nanostructure. The irradiated impacts including polishing, purification, composition homogenization, and grain refinement facilitated the development and self-repair of a compact and tenacious oxide scale. This enhanced oxide layer effectively mitigates extensive corrosive media erosion. The utilization of HCPEB treatment has shown significant potential in enhancing the hot corrosion resistance of NiCoCrAlYSi laser claddings.

Investigation on the properties of anodic oxides grown on aluminium-silicon alloys irradiated by pulsed electron beam

Al-Si alloys are among the most common aluminium based materials for cast products due to theirhigh strength-to-weight ratio, excellent processability and relatively low cost. The presence of Si inthe molten Al phase improves the castability and decreases the solidification shrinkage. Hard anodicoxidation is largely employed to improve their surface mechanical properties and corrosion resistance.However, the presence of high Si contents (> 3%) and the size of Si particles in the alloy makethe process challenging or even not possible. The surface pretreatment of Al-Si alloys with intensepulsed electron beams (EB) can effectively overcome the aforementioned limitations. Electron beamsources can be employed to reduce Si content and to refine and disperse Si particles, and effectivelycreate an Al substrate that is more prone to oxidization. In the present work, two electron beamunits were used, RITM-SP and SOLO, to modify the surface properties of hypoeutectic, eutectic andhypereutectic Al-Si alloys, by investigating the effect of energy density and number of pulses. Theelectron beam treated substrates were hard anodized and characterized in term of microstructure,elemental distribution, corrosion resistance and surface mechanical properties.

Effect of Irradiation with a Pulsed Electron Beam on the Defect Structure Formation and the Properties of the Surface Layer of Zr–Nb–H System Alloys

Effect of Irradiation with a Pulsed Electron Beam on the Defect Structure Formation and the Properties of the Surface Layer of Zr–Nb–H System Alloys

The Positron Spectroscopy of the Zr–1Nb Alloy after Modification by High-Current Pulsed Electron Beam

The Positron Spectroscopy of the Zr–1Nb Alloy after Modification by High-Current Pulsed Electron Beam

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.

Thermoluminescent and Dosimetric Properties of Zirconium Dioxide Ceramics Irradiated with High Doses of Pulsed Electron Beam

Thermoluminescent (TL) properties of monoclinic zirconium dioxide ceramics were studied in order to assess the possibility of their use for measuring high doses (on the order of kGy) of pulsed electron beams (130 keV). Two types of samples were used: those synthesized by sintering in an electric furnace at T = 700–1700 °C and those synthesized in a flow of high-energy electrons (1.4 MeV) with a high power density. Analysis of the X-ray diffraction patterns using the Scherrer method revealed that annealing of ceramics of the first type at T > 1000 °C leads to a significant increase in the size of crystallites, which correlates with a significant increase in the intensity of the TL peak at 390 K. Type 2 ceramics synthesized by the electron beam method have the maximum TL response. Using the peak shape analysis method, the kinetic parameters of TL (activation energy, frequency factor, and kinetic order) were calculated. This study marks the first instance of establishing the patterns of influence of synthesis conditions and crystallite size on their values. The presence of an intense isolated TL peak, the sublinear nature of most dose dependencies, and negligible fading indicate the promise of the ceramics synthesized in this work for measuring high doses (several to tens of kGy).