Pulsed Electron Beam Research Articles

A Highly Versatile X-ray and Electron Beam Diamond Dosimeter for Radiation Therapy and Protection.

Radiotherapy is now recognized as a pillar in the fight against cancer. Two different types are currently used in clinical practice: (1) external beam radiotherapy, using high-energy X-rays or electron beams, both in the MeV-range, and (2) intraoperative radiotherapy, using low-energy X-rays (up to 50 keV) and MeV-range electron beams. Versatile detectors able to measure the radiation dose independently from the radiation nature and energy are therefore extremely appealing to medical physicists. In this work, a dosimeter based on a high-quality single-crystal synthetic diamond sample was designed, fabricated and characterized under low-energy X-rays, as well as under high-energy pulsed X-rays and electron beams, demonstrating excellent linearity with radiation dose and dose-rate. Detector sensitivity was measured to be 0.299 ± 0.002 µC/Gy under 6 MeV X-ray photons, and 0.298 ± 0.004 µC/Gy under 6 MeV electrons, highlighting that the response of the diamond dosimeter is independent of the radiation nature. Moreover, in the case of low-energy X-rays, an extremely low limit of detection (23 nGy/s) was evaluated, pointing out the suitability of the device to radiation protection dosimetry.

The structure of the contact zone of the surfacing-substrate subjected to electron-beam processing

Using scanning and transmission electron microscopy, the analysis of the structure, phase and elemental composition of the contact zone of the system coating (high-entropy FeCrCoNiMn alloy)-substrate (5083 alloy) after electron-beam processing was performed. The formation of a multiphase, multielement submicro- and nanocrystalline structure has been established. The structure of high-speed cellular crystallization in the contact layers adjacent to the coating and substrate is revealed, and the formation of lamellar crystals in the central region of the contact zone is also found. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.

Структура зоны контакта наплавка-подложка, подвергнутой электронно-пучковой обработке

Using scanning and transmission electron microscopy, the analysis of the structure, phase and elemental composition of the contact zone of the system coating (high-entropy FeCrCoNiMn alloy)-substrate (5083 alloy) after electron-beam processing was performed. The formation of a multiphase, multielement submicro- and nanocrystalline structure has been established. The structure of high-speed cellular crystallization in the contact layers adjacent to the coating and substrate is revealed, and the formation of lamellar crystals in the central region of the contact zone is also found. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.

Поверхностный Ti-Ni-Ta-сплав, синтезированный на TiNi-подложке электронно-пучковым способом: структура и физико-механические свойства

The structure and physical-mechanical properties of Ti-Ni-Ta-based surface alloy synthesized on the NiTi-substrate through additive thin-film electron-beam method have been studied. The synthesis of the surface alloy was carried out by 30-fold alternation of operations of deposition of a dopant film (Ti60Ta40 (at.%), ~50 nm thick) and liquid-phase mixing of the film/substrate using a pulsed low-energy high-current electron beam. It was found that Ti-Ni-Ta-based surface alloy, whose thickness is ~1.8 μm, has an amorphous structure. It has been established that the surface alloy has ~2 and ~1.5 times higher values of microhardness HOP and elastic modulus EOP compared to the initial NiTi-substrate, but parameter of plasticity δh and shape recovery ratio η close to the substrate. It is shown that the nature of the change in physical-mechanical properties in Ti-Ni-Ta-based surface alloy and the transition zone depends on the number and thickness of the sublayers, as well as on the structural states of the phases in the sublayers. The evaluation of the mechanical compatibility of the surface alloy with the NiTi-substrate is given.

Влияние материала мишени и размеров облучаемого объема на эффективность синтеза озона в плазме, создаваемой импульсным пучком электронов в воздухе

The effect of the target material and the size of the irradiated volume on the efficiency of ozone synthesis in air under the action of a pulsed electron beam is investigated. Graphite and lead targets were used. The highest concentration of ozone was observed in a chamber without a target, and the highest specific ozone yield without consideration of electron reflection (230 g(kWh)–1) was observed in a chamber with a lead target at a minimum air gap (3 cm). The results are explained by the processes of multiple reflection of electrons from elements with a high atomic number at small air gaps compared to the size of the target.

Формирование плазмы в атмосфере азота импульсным электронным пучком вблизи диэлектрической мишени при форвакуумных давлениях

Features of the processes of beam plasma formation near a dielectric (aluminum oxide ceramic) target being irradiated by an intense pulsed electron beam in the forevacuum pressure range (4–15 Pa) have been investigated. It has been established that the density of the beam plasma near the irradiated dielectric target is higher than in the case of "free" propagation of the electron beam. The observed increase in plasma density depends on the emission current (electron beam current), gas pressure, and accelerating voltage. The influence of the dielectric target on the beam plasma density is due to emission of electrons from the target surface and the uncompensated negative potential on the target surface, which determines the energy of emitted electrons. An increase in gas pressure leads to a smaller increase in the beam plasma density due to a decrease in the absolute value of the negative potential. Varying the electron beam current and accelerating voltage provide to control the beam plasma density.

From transparent to black amorphous zinc oxide thin films through oxygen deficiency control

Despite the fact that zinc oxide is a well-known transparent oxide, several recent studies on “black” ZnO have renewed its potential for photocatalytic applications. We report on the control of oxygen deficiency in ZnO thin films grown at 300 °C on c-cut sapphire single-crystal substrates by pulsed electron beam deposition (PED) through a slight variation of argon pressure in PED. At a pressure of 2 × 10−2 mbar transparent, stoichiometric (ZnO) and crystalline films are obtained, while at 9 × 10−3 mbar black, oxygen-deficient (ZnO0.85) and amorphous films result. Stoichiometry, structural, and optoelectronic properties of transparent and black ZnO thin films were comparatively analyzed as a function of oxygen deficiency. Black ZnO thin films exhibit enhanced absorption in the visible and near-infrared due to oxygen deficiency, thus extending the range of applications of zinc oxide thin films from transparent electronics to solar absorbers and photocatalysis.

Temporal resolution in transmission electron microscopy using a photoemission electron source.

Temporal resolution in transmission electron microscopy (TEM) has progressed to the sub-picosecond level with the stroboscopic method using a photoemission mechanism with an ultrafast laser for the electron gun. Time-resolved TEM in conjunction with a photocathode (PC)-type electron source pumped by a pulsed laser has been actively developed to exceed sub-nanosecond time resolution. Here, we provide an overview of the trends in this field and discuss the measurement targets that can be obtained by time-resolved measurements. Furthermore, we consider the types and characteristics of PC materials and their related physical quantities for evaluation of electron beam properties. Experimental results obtained by time-resolved TEM using a semiconductor PC that has a surface with a negative electron affinity are presented, and application results based on quantum mechanics are given. We also describe new techniques for improving the time resolution and new applications of pulsed electron beams in electron microscopy and discuss the measurement targets that are expected for time-resolved electron microscopy.

Electron-ion-plasma boriding of a multilayer nanostructural high-entropy alloy

The structure and properties of a high-entropy alloy (HEA) subjected to saturation with boron atoms by a combined electron-ion-plasma method are characterized. On a HEA film of 5 μm thickness deposited on AISI 304 steel, a film (boron + chromium) with a thickness of 1 μm was deposited and then the system “(Cr + B) film / (HEA film deposited on AISI 304 steel) substrate” was irradiated with a pulsed electron beam. It is shown that the wear resistance of the resulting alloy is more than 30 times higher than that of the original HEA film. The microhardness of the alloy is 10.5 % higher than that of HEA in the initial state. It has been revealed that irradiation of the system with a pulsed electron beam leads to the formation of a multi-element surface alloy of composition (at.%) 5.8Al-11.6Ti-12.9Cr-13.0Fe-2.4Ni-13.1Cu-10.4Zr-8.8Nb, the rest (22 at.%) is oxygen and boron. Thus, seven-element HEA of non-stoichiometric composition, the concentration of metal elements of which varies within (5.8 –13.0) at.%, and additionally containing atoms of nickel, oxygen and boron was formed. It has been established that the high tribological and strength properties of the surface alloy are due to the formation of a multiphase submicron-nanocrystalline structure of high-speed cellular crystallization in the modified layer 6 µm thick. High-speed crystallization is accompanied by alloy delamination with the formation of extended interlayers enriched with copper atoms located along the boundaries of crystallization cells.

Strengthening Analysis of Ni-Sn Alloy Layer by Double Alloying Method Combined with First-Principles Calculation.

Surface modification improves the performance of materials in practical applications. In this paper, mechanical alloying pretreatment is adopted. Advanced non-equilibrium processing of a high-current pulse electron beam is then used to obtain an Sn-rich Ni-Sn alloy layer, characterized by a higher surface hardness than the initial pure nickel layer. In addition, the atomic structure of the Sn-doped nickel substrate in the alloy layer is simulated, and the improvement of the alloy layer is analyzed based on the first principle. Mechanical alloying and electron beam irradiation form fine and even nanocrystals on the surface of the nickel. Sn doping is also important for enlarging the lattice and increasing the stress.

Structure and Properties of Al-Co-Cr-Fe-Ni High-Entropy Alloy Subjected to Electron–Ion Plasma Treatment

High-entropy alloys (HEAs) are a new class of materials consisting of at least five elements in equiatomic or near-equiatomic ratio. HEAs are subjected to various types of surface treatment to improve their properties. One of the most promising methods of surface hardening is electron beam processing. This study aims to examine the structure, elemental, and phase composition of the AlCrFeCoNi HEA surface layer after the deposition of a (B + Cr) film and irradiation with a pulsed electron beam. HEA samples of non-equiatomic composition (33.4 Al; 8.3 Cr; 17.1 Fe; 5.4 Co; 35.7 Ni, at. %), fabricated by wire-arc additive manufacturing (WAAM), were used as study objects. Modification of the HEA surface layer was carried out by a complex method combining deposition of (B + Cr) film samples on the surface and irradiation with a pulsed electron beam in an argon medium. The mode of modification was identified. It makes it possible to increase microhardness (almost two times) and wear resistance (more than five times), reduce the friction coefficient of the HEA surface layer by 1.3 times due to the decrease in the average grain size, formation of particles of borides and oxyborides of complex elemental composition, the introduction of boron atoms into the crystal lattice of HEA.

Time response measurement of pulsed electron beam from InGaN photocathode

The photocurrent from a semiconductor photocathode with a negative-electron affinity surface can be arbitrarily controlled by the excitation laser power. Applying this characteristic to a scanning electron microscope allows the probe current to be arbitrarily controlled at any location on the sample. A photocathode with a fast time response is required to control the probe current at high speed. This study used an InGaN photocathode for pulsed electron beam generation and investigated its time response. A pulsed electron beam with 3.8 ns pulse width and 8.1 × 103 A cm−2 current density was observed, and the rise and fall times of the photocurrent were found to be 1.7 and 2.0 ns, respectively. The results show that despite the bottleneck of the time response of the laser power, the InGaN photocathode generates an electron beam that can control the probe current on a pixel-by-pixel for a 270 MHz scan speed.

Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

Effect of High-Current Pulsed Electron Beam on Properties of Graphene-Modified Aluminum Titanium Carbide Composites.

High-current pulse electron beam (HCPEB) is an advanced surface modification technology developed in recent decades. This paper focuses on the effect of 0.3 wt.% graphene on the electrical conductivity and microhardness of HCPEB-treated Al-20TiC composites. The SEM results show that the titanium carbide was uniformly distributed in the aluminum matrix of the initial sample. Conversely, the graphene showed a small aggregation, and there were holes and cracks on the top surface of the sample. After HCPEB modification, the agglomeration of graphene gradually improved, and the number of surface pores reduced. The X-ray diffraction results show that after HCPEB treatment, the aluminum diffraction peak widened and shifted to a higher angle and the grain was significantly refined. Compared with the initial Al-20TiC composite samples, the conductivity of graphene-modified HCPEB-treated sample increased by 94.3%. The microhardness test results show that the microhardness of the graphene-modified HCPEB-treated sample increased by 18.4%, compared with the initial Al-20TiC composite samples. This enhancement of microhardness is attributed to the joint effects of fine grain strengthening, dispersion strengthening of the second phase, solution strengthening and dislocation strengthening. In brief, HCPEB has good application prospects for powder metallurgy in future.

Experimental study on plasma channel formation with spark discharges in high current pulsed electron beam source

The formation of plasma channel with the use of eight spark discharge sources was experimentally investigated in a high current pulsed electron beam (HCPEB) equipment. A triple Langmuir probe system was developed to diagnose the real-time plasma parameters. The spark discharges were initiated by using a high-voltage pulse of −7.0 kV and decoupling resistors of 40 Ω. Displacing the measurement positions, the plasma density distributions in a column of diameter 60 mm and length 175 mm were obtained. The duration of spark discharge is 11.0 μs and the maximum discharge current of 1.4 kA appears at 4.3 μs. Initially, the plasma concentrates in the peripheral region. With the accumulation in radial direction, the plasma density in the central region increases. After 6.6 μs, the maximum plasma density of 8.4 × 1018 m−3 appears at the center of the plane where the spark sources located. Thereafter, the plasma dissipation plays a dominant role. The plasma maintains about 20 μs. Depending on the formation features of plasma channel, the selection of timing control available was illustrated, while the transportation of HCPEB can be realized effectively within a limited distance, i.e. less than 60 mm beyond the source outlet in this case.

A new compact linear beam-plasma discharge simulator BPD-PSI

A new BPD-PSI line-type plasma simulator is introduced.The device features two vacuum units: a target unit and an electron gun unit, connected to each other by a water-cooled electron beam transport channel.The Pierce-type electron gun is used to generate stationary or pulsed electron beam, utilized for beam-plasma discharge generation. The plasma electron density can be varied in the range of n e = 1 × 1016 - 1 × 1018 m-3 with electron temperature in the range of T e = 1-20 eV. The ion flux of 1 × 1021 m-2 s-1 and heat fluxes up to 5 MW m-2 are obtained. A set of utilized plasma and plasma-surface interaction diagnostics are described. Five demonstration experiments are presented: 1) high vs low power beam-plasma operation, 2) beam-plasma discharge with/without presence of an external magnetic field, 3) incident ion flux composition analysis, 4) incident ion energy distribution function measurement, 5) in-situ target surface temperature control and in-vacuo thermal desorption spectroscopy measurement.All of the technical features of the setup described in this paper make it a new tool for studying plasma-surface interactions.

On radiation dynamics in plasma relativistic microwave amplifier at the edge of electron beam pulse

We consider dynamics of radiation of a plasma microwave amplifier on a surface wave at the leading edge of the relativistic electron beam pulse. It has been shown that depending on the electron density of the plasma, different modes of operation of the amplifier are possible. At low plasma density, there is an early activation of the amplifier with large gain at the leading edge of the electron beam pulse and a significant decrease in the amplification of the signal when the electron energy reaches a plateau. With a higher plasma density, a later activation takes place with an almost constant output amplitude. The effect of ponderomotive force on plasmas was discussed.

Optimizing a superconducting radio-frequency gun using deep reinforcement learning

Superconducting photoelectron injectors are a promising technique for generating high brilliant pulsed electron beams with high repetition rates and low emittances. Experiments such as ultra-fast electron diffraction, experiments at the Terahertz scale, and energy recovery linac applications require such properties. However, optimization of the beam properties is challenging due to the high amount of possible machine parameter combinations. In this article, we show the successful automated optimization of beam properties utilizing an already existing simulation model. To reduce the amount of required computation time, we replace the costly simulation by a faster approximation with a neural network. For optimization, we propose a reinforcement learning approach leveraging the simple computation of the derivative of the approximation. We prove that our approach outperforms common optimization methods for the required function evaluations given a defined minimum accuracy.

Point scintillator dosimetry in ultra-high dose rate electron “FLASH” radiation therapy: A first characterization

FLASH radiation therapy is a novel technique combining ultra-high dose rates (UHDR) with very short treatment times to strongly decrease normal tissue toxicity while preserving the anti-tumoral effect. However, the radiobiological mechanisms and exact conditions for obtaining the FLASH-effect are still under investigation. There are strong indications that parameters defining the beam structure, such as dose per pulse, instantaneous dose rate and pulse repetition frequency (PRF) are of importance. UHDR irradiations therefore come with dosimetric challenges, including both dose assessment and temporal ones. In this work, a first characterization of 6 real-time point scintillating dosimeters with 5 phosphors (Al2O3:C,Mg; Y2O3:Eu; Al2O3:C; (C38H34P2)MnBr4 and (C38H34P2)MnCl4, was performed in an UHDR pulsed electron beam. The dose rate independence of the calibration was tested by calibrating the detector at conventional and UHDR. Dose rate dependence was observed, however, further investigation, including intermediate dose rates, is needed. Linearity of the response with dose was tested by varying the number of pulses and a linearity with R2> 0.9989 was observed up to at least 200 Gy. Dose per pulse linearity was investigated by variation of the pulse length and SSD. All point scintillators showed saturation effects up to some extent and the instantaneous dose rate dependence was confirmed. A PRF dependence was observed for the Al2O3:C,Mg and Al2O3:C- based point scintillators. This was expected as the luminescence decay time of these materials exceeds the inter-pulse time.

Attosecond electron-beam technology: a review of recent progress.

Electron microscopy and diffraction with ultrashort pulsed electron beams are capable of imaging transient phenomena with the combined ultrafast temporal and atomic-scale spatial resolutions. The emerging field of optical electron beam control allowed the manipulation of relativistic and sub-relativistic electron beams at the level of optical cycles. Specifically, it enabled the generation of electron beams in the form of attosecond pulse trains and individual attosecond pulses. In this review, we describe the basics of the attosecond electron beam control and overview the recent experimental progress. High-energy electron pulses of attosecond sub-optical cycle duration open up novel opportunities for space-time-resolved imaging of ultrafast chemical and physical processes, coherent photon generation, free electron quantum optics, electron-atom scattering with shaped wave packets and laser-driven particle acceleration. Graphical Abstract.