Electron Beam Characteristics Research Articles

Dosimetric Characteristics of a Real Time Shapeable Tungsten Containing Rubber with Electron Beams

This study investigated the dosimetric characteristics of electron beams shaped with a real-time shapeable tungsten-containing rubber (STR) collimator. Circular irradiation fields of 40 mm diameter were shaped using STR or low melting-point alloy (LMA) placed on the electron applicator. The STR heated with approximately 70-degree warm water was molded into the template bottom of the applicator. Percent depth doses (PDDs) and lateral dose profiles of 6 and 12 MeV electron beams were measured and compared between STR and LMA. For the PDDs, the depths of maximum dose (dmax), 90% dose (d90), and 80% dose (d80) were evaluated. For the lateral dose profiles, penumbra as the width of the off-axis distance from 80% to 20% doses and treatment diameter covering over 90% dose were evaluated at the surface, dmax, d90, and d80. The transmission of the STR was also investigated at thicknesses fit to electron applicator for 6 and 12 MeV electron beams. The STR was softened with 70-degree warm water. Therefore, it was easy to mold it and attach the applicator. The PDDs and penumbras at the surface, dmax, d90, and d80 for the STR were almost equal to those for the LMA with 6 and 12 MeV electron beams. The treatment diameters covering over 90% dose for the irradiation fields with 40 mm diameter at dmax (LMA vs. STR) were 20.9 vs. 21.1 mm and 19.2 vs. 18.4 mm for 6 and 12 MeV electron beams, respectively. The transmission of the STR was almost same as that of LMA. The dosimetric characteristics of the STR on the electron applicator were almost same as those of the LMA. The heated STR was shaped easily, flexibly, and immediately. The STR can be used as a substitute for LMA in electron radiotherapy.

Transient characteristics of electron beam induced current in dielectric and semiconductor sample

The electron beam induced current (EBIC) characteristics of dielectric/semiconductor thin films under the electron beam (e-beam) irradiation is the important means of implementing the electron microscopic detection. The transient EBIC characteristics of the SiO<sub>2</sub>/Si thin film irradiated by a high-energy e-beam are investigated by combining the numerical simulation and the experimental measurement. The scattering process of electrons is simulated by the Rutherford scattering model and the fast secondary electron model, and the charge transport, trapping and the recombination process are calculated by the current continuity equation and the Poisson equation. The transient charge distribution, EBIC and the transmission current are obtained, and influence of the beam current and the beam energy on them are analyzed. The results show that due to the electron scattering effect, the free electron density decreases gradually along the incident direction. The net charge density near the surface is positive and negative along the incident direction because of secondary electrons (SEs) emitted from the surface, and therefore the electric field intensity is positive near the surface and negative inside sample, which causes some electrons to be transported to the substrate and some SEs return to the surface. The negative charge density at the SiO<sub>2</sub>/Si interface is higher than that in the nearby region because some electrons are trapped by the interface trap. With the decrease of the net charge density with e-beam irradiation, the charging intensity decreases gradually. Meanwhile, electrons are gradually transported to the substrate, and consequently EBIC and the sample current increase and the electric field intensity decreases with e-beam irradiation. However, due to the weak charging intensity, the surface emission current and the transmission current remain almost invariant with e-beam irradiation. The EBIC, the transmission current and the surface emission current are approximately proportional to the beam current. For the SiO<sub>2</sub>/Si thin film in this work, the transmission current increases gradually to the beam current value with the increase of the beam energy, and the EBIC presents a maximum value at the beam energy of about 15 keV.

Coupling Effects in Multistage Laser Wake-field Acceleration of Electrons

Staging laser wake-field acceleration is considered to be a necessary technique for developing full-optical jitter-free high energy electron accelerators. Splitting of the acceleration length into several technical parts and with independent laser drivers allows not only the generation of stable, reproducible acceleration fields but also overcoming the dephasing length while maintaining an overall high acceleration gradient and a compact footprint. Temporal and spatial coupling of pre-accelerated electron bunches for their injection in the acceleration phase of a successive laser pulse wake field is the key part of the staging laser-driven acceleration. Here, characterization of the coupling is performed with a dense, stable, narrow energy band of <3% and energy-selectable electron beams with a charge of ~1.6 pC and energy of ~10 MeV generated from a laser plasma cathode. Cumulative focusing of electron bunches in a low-density preplasma, exhibiting the Budker–Bennett effect, is shown to result in the efficient injection of electrons, even with a long distance between the injector and the booster in the laser pulse wake. The measured characteristics of electron beams modified by the booster wake field agree well with those obtained by multidimensional particle-in-cell simulations.

Energy depth distribution of pulsed electron beam with wide electron kinetic energy spectrum for an aluminum target

Knowledges of pulsed electron beam characteristics is necessary for use it for scientific and practice applications. Current work analyses the pulsed electron beam extracted from the vacuum diode through a titanium foil (60 mkm) of the diode exit window. Electron beam energy depth distribution was measured for a target made of different number of aluminum foils. A pulsed electron beam with a wide range of kinetic energies was generated by the ASTRA-M accelerator (260 kV of accelerating voltage, up to 1 kA of beam current, 150 ns of beam pulse duration at FWHM). A calorimeter of total absorption and Faraday cup were used to measure beam characteristics. Calorimeter included two collectors: first one measures a beam energy after aluminum foils, and the second one measures a total beam energy. All measurements were performed at 10−5 Torr background pressure after the exit window foil. As a result, the electron kinetic energy spectrum of the beam out of diode has been reconstructed.

High power electron beam interaction with an aluminum target: Measurements and simulations

The study of the dynamic response of materials induced by electron beams requires precise knowledge of the beam when it interacts with the material. In this framework, the CESAR generator is used at CESTA. CESAR drives a field emission diode that delivers a single-shot intense electron pulse (≈1 MV, 300 kA, and 100 ns). The electron beam propagates into a gas-filled chamber where it is focused by a magnetic field onto an aluminum target. The analysis of the beam characteristics at the target position allows us to estimate the initial conditions required for precise hydrodynamic simulations. In this paper, we present the measurements of the electron beam characteristics. We paid particular attention to voltage, current, spatial homogeneity, dose rate, and incidence angles of electrons onto the target. Shocks induced in thin discs of aluminum are analyzed by using photon Doppler velocimetry, and the experimental data are compared with the predictions of simulations. Beam energy deposition is computed by using the 3D code Diane, and the hydrodynamic evolution of the target is performed with the code 2D/3D Hesione.

Dosimetric Characterization of a Novel Surface Collimator With Tungsten Functional Paper for Electron Therapy.

The aim of the study was to investigate the dosimetric characteristics of electron beams with a tungsten functional paper (TFP) surface collimator. The circular field of 6.0 cm diameter was created with the TFP collimator put on the phantom. Depth and lateral dose profiles for 4 and 6 MeV electron beams were obtained. The characteristics of lateral dose profile, treatment diameter as width over 90% of the dose, and penumbra as width of the off-axis positions from 80% to 20% dose levels were evaluated. Compared to the lead collimator, the TFP collimator generated higher surface doses, the treatment diameters were increased from 42.8 to 48.6 mm and from 40.0 to 41.4 mm, and the penumbras were reduced from 15.0 to 9.6 mm and from 16.4 to 13.0 mm for 4 and 6 MeV electron beams, respectively. The TFP surface collimator can provide an excellent dose distribution compared to the conventional lead collimator.

Applied calculations of accelerator characteristics for sterilization installation with local radiation shielding

The calculations of electron beam characteristics in the accelerator of sterilization installation with the local radiation shielding in relation to the use of a magnetron with a larger pulse power are made. It is shown that a simple method on the basis of “moving” of cathode- heating unit toward the anode plane of the injector may be used for increasing of current and power of accelerated beam.

A new cryo-EM system for single particle analysis

A new cryo-EM system has been investigated for single particle analysis of protein structures. The system provides parallel illumination of a highly-coherent 300 kV electron beam from a cold-field emission gun, and boosts image contrast with an in-column energy filter and a hole-free phase plate. It includes motorized cryo-sample loading and automated liquid-nitrogen filling for cooling multiple samples. In this study, we describe gun and electron beam characteristics, and demonstrate the suitability of this system for single particle reconstructions. The performance of the system is tested on two examples, a spherical virus and apoferritin. GUI programs have also been developed to control and monitor the system for correct illumination, imaging with less ellipticity and steady magnification, and timing of flashing and liquid-nitrogen filling. These programs are especially useful for efficient application of the system to single particle cryo-EM.

Patterns of inhibition of the culture of Salmonella

Studies on the inhibition effectiveness of the initial degree of inoculation of the Salmonella microorganism were carried out. In this paper, the irradiation efficiency of model systems with electron beams with beam energy of 6.5 and 10 MeV was studied. The investigations were carried out at UELV-10-10-C-70 accelerator at Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences (IPCE RAS) with an average beam power of 6.5 MeV and at radiation-technological center with an electron accelerator UELR-10-10-40 at A.I. Burnazyan Federal Medical Biophysical Centre of Federal Medical Biological Agency with an average electron energy of 10 MeV. The conducted researches on studying and revealing the dependence of inhibition of pathogenic microflora, irradiation with different intensity, on the structure (density) of the studied samples, which model liquid and solid nutrient media. The study used a strain Salmonella enterica subsp. Enterica serovar Typhimurium. The results of the effective inhibition of the initial degree of contamination for the two plants were obtained. Studies have shown that the effectiveness of inhibition of Salmonella culture can vary depending on the characteristics of electron beams. For example, when samples were irradiated with electrons with energy of 6.5 and 10 MeV at doses from 3 to 7 kGy, various results of the inhibition effectiveness of Salmonella culture on media with different work were obtained. When processing samples with studied strains of cultures in the dose range from 4 to 5 kGy, there is an increase in the growth of microorganisms for all processing conditions. In the remaining studied ranges their inhibition are observed. It is important to take into account not only the effectiveness of the oppression of microflora on specific products, but also the efficiency of the installation for a specific sample.

Influence of weld parameters on weld regimes and vaporization rate in electron beam welding of Ti6Al4V alloy

Electron beam welding (EBW) is the most preferable and efficient joining technique to weld titanium alloys, since it provides a vacuum atmosphere and eliminates the use of shielding gas during the welding process. The present work is focused on understanding the electron beam weld parameters which controls the weld limits, microstructural and mechanical properties and vaporization rate of metal elements in the Ti6Al4V alloy. The influence of power density on characteristics of electron beam welded Ti6Al4V alloy at constant linear energy conditions is examined. The welding experiments were performed to evaluate the weld geometry, weld regimes, microstructural properties and microhardness characteristics using fundamental parameters such as power density and interaction energy per unit volume (IE). Moreover, the vaporization heat transfer model of the EBW process is developed by employing Fourier’s law of heat conduction to estimate the vaporization rate of Ti6Al4V alloying elements. The rate of vaporization of major alloying elements of Ti6Al4V is analysed with respect to power density. Based upon the results obtained, it is witnessed that the weld bead geometry, weld limits and grain size are controlled by power density for constant linear energy conditions. Also, the solidified microstructure in the weld zone at different power density significantly effects the final strength of the weld joint. The conduction and keyhole weld limits are identified for power density values below 0.31 W cm−2 and above 2.12 W cm−2, respectively. The transition mode welding in the Ti6Al4V alloy is identified by a nominal increase in aspect ratio for a wide range of power density and IE values. The results also established that the size of β grain in the fusion zone reduces with increase in power density at constant linear energy condition. Also, the average α1 martensitic grain size in the weld zone is determined to be higher in keyhole welds (128 µm) relative to conduction welds (48 µm) on account of higher solidification rate. In effect, the solidified martensitic phases influence the microhardness distribution proportionately across the weld sample of Ti6Al4V alloy. Vaporization of metal elements of the Ti6Al4V alloy is induced in few milliseconds and evaporation rate of ‘Al’ element is least followed by ‘Ti’ and ‘V’ elements. It is also observed that by reducing the power density from 2.54 to 2.12 W cm−2, keyhole mode welding can be acquired and vaporization rate of ‘Al’ is reduced by 20.5%.

Particle Beams in the Vicinity of Magnetic Separatrix According to Near‐Lunar ARTEMIS Observations

AbstractWe study characteristics of ion and electron beams observed during 101 crossings of the near‐separatrix region by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in the magnetotail. We found that accelerated ion beams are observed under any level of geomagnetic activity. A duration of earthward moving ion beams is statistically longer (≤ 10 min) than a duration of tailward ion beams (≤ 4 min), which can be due to the transient character of ion acceleration in the vicinity of the near‐Earth neutral line (NENL). Energetic characteristics of earthward and tailward ion beams are similar indicating similar acceleration conditions at ion kinetic scales at both sides of an X line independently of its location. Conversely, electron velocity distributions observed near magnetic separatrix earthward of the distant neutral line (DNL) differ from those observed tailward of the NENL. Earthward of the DNL a scattered and thermalized electron population without energetic field‐aligned beams is observed near the separatrix. On the contrary, tailward of the NENL field‐aligned electron beams accelerated to a few kiloelectron volts are detected. These observations show that near DNL the electron scattering and thermalization dominate over the direct acceleration, whereas stronger electric fields in the NENL produce substantial population of field‐aligned kiloelectron volt electrons.

Parametric X-ray radiation in the Smith-Purcell geometry for non-destructive beam diagnostics

We investigate parametric X-ray radiation (PXR) under condition of the extremely asymmetric diffraction, when the ultra-relativistic electron bunch is moving in vacuum parallel to the crystal-vacuum interface, close to the crystal surface. This type of geometry coincides with the well known mechanism of generation of radiation, when the self-field of the particle beam interacts with the reflecting metal grating, namely the Smith-Purcell effect. We demonstrate that in this geometry the main contribution is given via a tail region of the beam distribution, which penetrates the crystal and X-rays are radiated along the normal to the crystal surface. We determine the electron beam characteristics, when this phenomenon can be observed. It is essential that in this geometry the majority of electrons does not undergo multiple scattering and consequently the characteristics of the particle beam are not changed, thus allowing the usage of the emitted X-rays for the purpose of non-destructive beam diagnostics, which can complement the traditional knife-edge method.

A comparative study on laser beam and electron beam welding of 5A06 aluminum alloy

With the increasing of laser power and energy density, laser welding has the potential to replace electron beam welding for aluminum alloy in many conditions. This paper present an comparison investigation between laser beam welding and electron beam welding for 5A06 aluminum alloy. The characteristics of laser beam and electron beam welded joints are compared, including the micro-structure, mechanical property, area of melting zone and depth-to-width ratio. Moreover, the component distribution in different zones of the welded joints is analyzed. It is found that the micro-structure and mechanical property of electron beam welded joint is better than that of laser beam welded joint.

Investigation of Bunch Compressor and Compressed Electron Beam Characteristics by Coherent Transition Radiation

A magnetic chicane bunch compressor for a new compact accelerator-based terahertz (THz) radiation source at the Institute of Advanced Energy, Kyoto University, was completely installed in March 2016. The chicane is employed to compress an electron bunch with an energy of 4.6 MeV generated by a 1.6-cell photocathode radio frequency (RF)-gun. The compressed bunch is injected into a short planar undulator for THz generation by coherent undulator radiation (CUR). The characteristics of the bunch compressor and the compressed bunch were investigated by observing the coherent transition radiation (CTR). The CTR spectra, which were analyzed by using a Michelson interferometer, and the compressed bunch length were also estimated. The results were that the chicane could compress the electron bunch at a laser injection phase less than 45 degrees, and the maximum CTR intensity was observed at a laser injection phase around 24 degrees. The optimum value of the first momentum compaction factor was around −45 mm, which provided an estimated rms bunch length less than 1 ps.

Commissioning the First Mobile Dedicated Accelerator for Intraoperative Electron Radiotherapy in Iran

Introduction: Intraoperative radiotherapy is a radiotherapy technique in which a high single fraction of radiation dose is delivered to the patient after surgery and Concurrent with anesthesia time. The most frequent method for IORT implementation is Intraoperative electron radiotherapy (IOERT), in which, some dedicated and high dose per pulse electron accelerators are employed for radiotherapy. Recently, Iran is also equipped to these dedicated machines for IOERT. Commissioning procedure of this dedicated IOERT machine and dosimetric characteristics of intraoperative electron beam have been evaluated in current study. Materials and Methods: LIAC accelerator, a mobile dedicated IOERT machine with the maximum energy of 12 MeV, was commissioned in this study. Commissioning procedure was performed inside a MP3-XS automatic water phantom which is introduced for small field dosimetry. 10 cm diameter reference applicator was considered and applicator edge was in contact to the phantom surface. All of measurements including percentage depth dose (PDD) along clinical axis, transverse dose profiles (TDP) at the depth of maximum dose and output factors (OF) were performed using ionometric dosimetry. During the measurements, Advanced Markus and Semiflex ion chambers were employed as field and reference detector, respectively. All of the obtained data were processed and analyzed using Mephysto Navigator software. Results: Measured PDDs showed that the intraoperative electron beam has a steep dose fall-off gradient which increases with decrement of electron energy. This fact can effectively spare the underlying healthy tissues. The symmetry and flatness of obtained TDPs at all studied energies were less than 2% which can improve the dose uniformity inside the tumor bed. As expected, the OFs were increased with increment of electron energy, but In contrast to the conventional accelerator, OF values reduce at greater radiation field sizes. Conclusion: According to the obtained results, it can be concluded that dosimetric characteristics of intraoperative electron beam are quite favorable regarding to the mandatory issues which should be satisfied in intraoperative radiotherapy.

Physical characteristics of electron beam from conventional and beam shaper IOERT applicator: A comparison study

Introduction: Intraoperative electron radiation therapy (IOERT) is one of the cancer treatment techniques that delivers high doses to tumor bed during surgery. IOERT can be performed by either conventional LINACs or dedicated IORT accelerators such as LIAC (Light Intraoperative Accelerator). Two types of applicators can be used with LIAC dedicated accelerator including conventional applicator and beam shaper one. Standard applicators are cylindrical ones which can produce circular fields. On the other hand, beam shaper applicator is able to produce various square and rectangular fields through dedicated shielding blades located at the distal end of applicator. The aim of this study is to compare the dosimetric parameters and physical characteristic of electron beam produced by these two different types of IOERT applicators through Monte Carlo simulation. Materials and Methods: The LIAC head in conjunction with conventional cylindrical and beam shaper applicator were simulated by MCNPX Monte Carlo code. The validity of simulated models was evaluated through comparing the Monte Carlo Based data (including PDDs and TDPs) and ionometric measured ones for both conventional and beam shaper applicator at different energies. Then, the energy and angular distribution of electron beam at the distal end of mentioned applicators were calculated for different combinations of energy/field sizes and obtained physical characteristics were quantitatively compared. Results: For both types of studied applicators, the mean electron energy increases with increment of electron field size at the same energy. For conventional cylindrical applicators, the variations of mean electron energy with increasing field sizes ranges from 4.48 to 4.57, 5.63 to 6.13, 6.61 to 7.44 and 7.25 to 8.35 at 6, 8 10 and 12 MeV, respectively. Also, with increasing the field size for beam shaper applicator, the mean electron energy varies from 4.47 to 4.86, 5.76 to 6.65, 6.67 to 8.10 and 7.27 to 9.06 at 6, 8 10 and 12 MeV, respectively. Increasing the electron energy at the same field size causes the increment of mean scattering angle of electron beam at the distal end of both applicators understudy. With increasing field size for conventional applicators, the mean scattering angle of electron beam varies from 5.98 to 7.24, 5.62 to 6.68, 5.75 to 6.43 and 5.98 to 6.29 at 6, 8 10 and 12s MeV, respectively. Variations of mean scattering angle with increasing field sizes for beam shaper applicator also ranges from 6.89 to 7.19, 6.23 to 6.39, 5.93 to 5.95 and 5.50 to 5.69 for 6, 8 10 and 12 MeV, respectively. Conclusion: Based on the obtained results, it can be concluded that the physical characteristics of produced electrons by shaper applicator are different from those of conventional applicator. This fact can be mainly attributed to the presence of shielding blades in design of beam shaper applicator.

Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 718

Effects of build layout and orientation consisting of (a) height from the build plate (Z-axis), (b) distance between samples, and (c) location in the build plate (X-Y plane) on porosity, NbC fraction, and hardness in electron beam melted (EBM) Alloy 718 were studied. The as-built samples predominantly showed columnar structure with strong ˂001˃ crystallographic orientation parallel to the build direction, as well as NbC and δ-phase in inter-dendrites and grain boundaries. These microstructural characteristics were correlated with the thermal history, specifically cooling rate, resulted from the build layout and orientation parameters. The hardness and NbC fraction of the samples increased around 6% and 116%, respectively, as the height increased from 2 to 45 mm. Moreover, by increasing the height, formation of δ-phase was also enhanced associated with lower cooling rate in the samples built with a greater distance from the build plate. However, the porosity fraction was unaffected. Increasing the sample gap from 2 to 10 mm did not change the NbC fraction and hardness; however, the porosity fraction increased by 94%. The sample location in the build chamber influenced the porosity fraction, particularly in interior and exterior areas of the build plate. The hardness and NbC fraction were not dependent on the sample location in the build chamber.

Controlling the transverse dimensions of the electron beam in the solenoidal field of a magnetron gun

The results of the study on the formation of transverse dimensions of an electron beam by a magnetron gun with a secondary emission cathode in the voltage range of 25..90 kV are presented. Investigations of the formation of electron beams in electron sources with cold metal cathodes operating in the secondary emission regime are carried out. The electron source is a magnetron gun. The principle of operation of such gun s is based on the reverse bombardment of the cathode by electrons returned by the magnetic field, the formation of an electron cloud near the cathode a nd the formation of a beam in crossed electric and magnetic fields. Their main difference from thermionic guns is the large current density from a unit of the cathode’s cross-sectional area ~ 50 A/cm² and a long service life. Therefore, the search and investigation of electron sources with a long service life is an urgent task. On the basis of a magnetron gun with a secondary-emission cathode, an electron accelerator is created in which an axial electron beam is used to irradiate metal targets and the inner cylindrical surface with a radial electron beam. The article presents the experimental data and the results of modeling calculations on the formation and control of the electron beam distribution by a magnetron gun with a secondary-emission cathode in motion in a solenoidal magnetic field. The dependence of the formation of the radial dimensions of the electron beam on the amplitude and gradient of the solenoidal magnetic field in the gun, which grows or falls in the channel of the beam transport, is studied. The results of numerical simulation of the motion of a tubular electron beam in a magnetic field of a solenoid are presented. Based on the motion model of the electron beam, the characteristics of the resultant electron beam are considered. It is shown that the diameter of the beam can be adjusted by varying the control magnetic field. The results of numerical modeling on the motion of a tubular electron flux in a magnetic field of a solenoid are given. The possibility of controlling the transverse dimensions of the beam is studied.

The structure and phase condition's evolution in the silicon carbide ceramics surface layer under the electron-beam treatment

The elemental constituents, phase composition and substructural evolution were investigated in the article in the silicon carbide ceramics surface layer which was subjected to the intense pulsed electron beam the density of the electron beam being varied. It was shown that the ceramic layer surface's structure and phase conditions were controlled by the electron beam characteristics. The SiC-ceramics surface layer nanostructuring was detected and the electron beam treatment conditions which lead to this effect were defined.

Correlation between macroscopic plasma dynamics and electron beam parameters in a laser-plasma accelerator

Ultrafast laser-based shadowgraphic-interferometric imaging of a high-density plasma generated by intense laser-matter interactions is a key diagnostic technique providing information on the evolution and ultrafast dynamics of such a plasma state. However, shadowgraphic techniques have received modest attention in diagnosing low-density gaseous plasmas similar to those used in laser-plasma wakefield accelerators. Here, by using an ultrafast 30 fs probe laser beam, we derived a correlation between the plasma dynamics and electron beam characteristics in a laser-plasma acceleration experiencing ionization injection in the plasma of a He-N2 gas mixture. The ultrafast transverse expansion dynamics of the laser-plasma channel front tends to be faster at higher nitrogen concentrations, which leads to an increase in the divergence angle and yield (charge) of the 100−200 MeV electron beams generated in the current experiment. Computer simulation shows a distinct difference between the dynamics of the self-injection and that of the ionization-injection processes and supports the experimental observations.