Distribution Of Electron Beam Research Articles

Reduction of the Downward Energy Flux of Nonthermal Electrons in the Solar Flare Corona due to Cospatial Return-current Losses

High-energy electrons carry much of a solar flare’s energy. Therefore, understanding changes in electron beam distributions during their propagation is crucial. A key focus of this paper is how the cospatial return current reduces the energy flux carried by these accelerated electrons. We systematically compute this reduction for various beam and plasma parameters relevant to solar flares. Our 1D model accounts for collisions between beam and plasma electrons, return-current electric-field deceleration, thermalization in a warm target approximation, and runaway electron contributions. The results focus on the classical (Spitzer) regime, offering a valuable benchmark for energy flux reduction and its extent. Return-current losses are only negligible for the lowest nonthermal fluxes. We calculate the conditions for return-current losses to become significant and estimate the extent of the modification to the beam’s energy flux density. We also calculate two additional conditions that occur for higher injected fluxes: (1) where runaway electrons become significant, and (2) where current-driven instabilities might become significant, requiring a model that self-consistently accounts for them. Condition 2 is relaxed and the energy flux losses are reduced in the presence of runaway electrons. All results are dependent on beam and cospatial plasma parameters. We also examine the importance of the reflection of beam electrons by the return-current electric field. We show that the interpretation of a number of flares needs to be reviewed to account for the effects of return currents.

Wave Optical Modeling of the SEM Column From Source to Specimen.

Probe formation in scanning electron microscope (SEM) is often reduced to objective lens action modeling based on a point-spread function or Fourier transforms. In this study, we present the first complete wave optical modeling of the whole SEM column based on plane-by-plane propagation of the electron beam wavefunction without simplifying the optical system. We identify the challenges in plane-by-plane beam propagation and show how sampling limitations produce aliased results. Through a careful selection and combination of propagators, we have developed a general wave optical propagation method that is able to overcome the aliasing problem to achieve the appropriate probe widths. Using a two-step propagator, we show that it is possible to model the electron beam distribution throughout the column from the virtual source plane to the specimen plane. We also show that our results from the wave optical simulations are consistent with the geometrical theory of probe formation. Finally, as a direct application of this method, we demonstrated that the combined effect of aberrations in the condenser lens and the probe forming objective lens cannot be accurately represented using only the objective lens. Designing beam shaping experiments and studying the effect of partial coherence can be some novel applications.

Impact of Scattering Foil Composition on Electron Energy Distribution in a Clinical Linear Accelerator Modified for FLASH Radiotherapy: A Monte Carlo Study.

This study investigates how scattering foil materials and sampling holder placement affect electron energy distribution in electron beams from a modified medical linear accelerator for FLASH radiotherapy. We analyze electron energy spectra at various positions-ionization chamber, mirror, and jaw-to evaluate the impact of Cu, Pb-Cu, Pb, and Ta foils. Our findings show that close proximity to the source intensifies the dependence of electron energy distribution on foil material, enabling precise beam control through material selection. Monte Carlo simulations are effective for designing foils to achieve desired energy distributions. Moving the sampling holder farther from the source reduces foil material influence, promoting more uniform energy spreads, particularly in the 0.5-10 MeV range for 12 MeV electron beams. These insights emphasize the critical role of tailored material selection and sampling holder positioning in optimizing electron energy distribution and fluence intensity for FLASH radiotherapy research, benefiting both experimental design and clinical applications.

Effects of External Magnetic Field on Focusing and Energy Distribution of Primary Electrons in an Ion Source

The effect of the applied voltage and magnetic field on the defining slot in focusing and energy distribution of the primary filament electron beam was studied theoretically. In this work, SIMION 8.1 software was used to determine the best operational conditions for focusing and the distribution of the electron beam in the ion source system. Furthermore, the Larmor radius on the slot was calculated in two dimensions for different values of magnetic flux density. The results showed that the values of flux density and slot voltage play an effective role in improving the dimensions of beam spot andenergy distribution in the source. The dimensions of beam spot were reduced by about 71% at voltage value of slot 75 volt and flux density 780 G. In addition; the kinetic energy distribution for electrons were computed at different magnetic flux and obtaining a homogeneous beam energy. The results of this research support the calculations of plasma source designers.

Planar dose calculation of electron therapy

Purpose. The aim of this study is to determine the planar dose distribution of irregularly-shaped electron beams at their maximum dose depth (z max) using the modied lateral build-up ratio (LBR) and curve-fitting methods. Methods. Circular and irregular cutouts were created using Cerrobend alloy for a 14 × 14 cm2 applicator. Percentage depth dose (PDD) at the standard source-surface-distance (SSD = 100 cm) and point dose at different SSD were measured for each cutout. Orthogonal profiles of the cutouts were measured at z max. Data were collected for 6, 9, 12, and 15 MeV electron beam energies on a VERSA HDTM LINAC using the IBA Blue Phantom2 3D water phantom system. The planar dose distributions of the cutouts were also measured at z max in solid water using EDR2 films. Results. The measured PDD curves were normalized to a normalization depth (d 0) of 1 mm. The lateral-buildup-ratio (LBR), lateral spread parameter (σ R (z)), and effective SSD (SSD eff ) for each cutout were calculated using the PDD of the open applicator as the reference field. The modified LBR method was then employed to calculate the planar dose distribution of the irregular cutouts within the field at least 5 mm from the edge. A simple curve-fitting model was developed based on the profile shapes of the circular cutouts around the field edge. This model was used to calculate the planar dose distribution of the irregular cutouts in the region from 3 mm outside to 5 mm inside the field edge. Finally, the calculated planar dose distribution was compared with the film measurement. Conclusions. The planar dose distribution of electron therapy for irregular cutouts at z max was calculated using the improved LBR method and a simple curve-fitting model. The calculated profiles were within 3% of the measured values. The gamma passing rate with a 3%/3 mm and 10% dose threshold was more than 96%.

Simplification of selective imaging of dislocation loops: diffraction-selected on-zone STEM

ABSTRACT Contrary to the conventional belief that, in transmission electron microscopy (TEM), selective and sharp imaging of dislocation loops can be realized only by accurate tilting of a specimen from the condition that the symmetrical axis of incident electron beam distribution is parallel to a zone axis of the TEM specimen (on-zone condition), we demonstrate that selective dark-field (DF) imaging of dislocation loops at on-zone condition is possible with a scanning TEM (STEM) mode that uses an objective lens aperture to select a diffraction disk of interest. Diffraction-selected on-zone STEM (DsoZ-STEM) has been applied to selective DF imaging of dislocation loops with a short axis length of <2 nm in a single-crystal aluminum irradiated by argon ions and an electron beam at room temperature. It was found that a Kikuchi line enhances the contrast among the dislocation loops and the matrix of DsoZ-STEM images. DsoZ-STEM obeyed g·b invisibility criterion and showed good agreement with a typical visibility change of a dislocation line and a loop in conventional DF images with a specific pair of ± g. In addition, dislocation loops always showed much higher brightness in the inner side compared to the outer side in DsoZ-STEM images, simplifying the distinction of dislocation loops with apparently the same long-axis direction but different b. Thus, DsoZ-STEM can simplify the selective DF imaging for the determination of the number and the character of dislocation loops.

Investigation of the possibility of shaping an electron dose field of a clinical accelerator with 3D printed polymer products

The improvement of existing dose delivery techniques is a constant goal in cancer radiation therapy, since it increases the treatment efficiency. For example, the use of so-called boluses and compensators offers ways to correct for surface irregularities or tissue inhomogeneities in some irradiated areas. While compensators are usually inserted along the radiation beam at a certain distance from the patient, boluses are located directly on the surface of the patient's body and follow its contours. Depending on their thickness and shape, these beam modifiers enable a shift of the depth of the dose maximum and control the depth-dose distribution. However, an accurate production of beam modifiers often requires complex procedures, thus limiting their use in the clinic. This study suggests the fused filament fabrication technique to produce polymer-based beam modifiers for shaping the dose of clinical electron beams. The feasibility of this approach was studied through a series of experiments and simulations using the Monte Carlo method. The results show that therapeutic electron beams with energies of 6–12 MeV can be effectively modified using such polymer samples. The numerical model can also be used to evaluate the dose distribution of electron beams shaped by plastic absorbers prior to production, thereby making it possible to select the compensator geometry for specific purposes.

Power Density Distributions in Electron Beams

Measuring and controlling the power density distribution of electron beams used for welding is critical for producing repeatable welds and for transferring welding parameters between different machines. On any given machine, the power density distribution is controlled by defocusing the beam relative to its sharpest focused condition. However, measuring the power density distribution can be difficult due to the intense nature of welding beams and is further complicated by imperfect electron optics that can distort the beam, making it difficult to quantify. The enhanced modified Faraday cup (EMFC) diagnostic method was used here for beam analysis that utilizes computed tomography to reconstruct the beam’s power density distribution. These results were compared to the International Standards Organization (ISO) method for characterizing laser beams using a second-moment D4σ calculation. For ideal Gaussian-shaped beams, both methods would give the same result. However, for imperfect beams, the calculated D4σ diameter was shown to be about 25% larger relative to the FWe2 diameter measured by the EMFC due to the heavier weighting of data in the tails of the beam by D4σ. Although both methods produce repeatable welds, it is important to understand the differences in the reported beam diameters, divergence angles, and beam parameter products when transferring parameters between machines.

Suprathermal Electron Transport and Electron Beam Formation in the Solar Corona

Electron beams that are commonly observed in the corona were discovered to be associated with solar flares. These “coronal” electron beams are found ≥300 Mm above the acceleration region and have velocities ranging from 0.1c up to 0.6c. However, the mechanism for producing these beams remains unclear. In this paper, we use kinetic transport theory to investigate how isotropic suprathermal energetic electrons escaping from the acceleration region of flares are transported upwardly along the magnetic field lines of flares to develop coronal electron beams. We find that magnetic focusing can suppress the diffusion of Coulomb collisions and background turbulence and sharply collimate the suprathermal electron distribution into beams with the observed velocity within the observed distance. A higher bulk velocity is produced if energetic electrons have harder energy spectra or travel along a more rapidly expanding coronal magnetic field. By modeling the observed velocity and location distributions of coronal electron beams, we predict that the temperature of acceleration regions ranges from 5 × 106 to 2 × 107 K. Our model also indicates that the acceleration region may have a boundary where the temperature abruptly decreases so that the electron beam velocity can become more than triple (even up to 10 times) the background thermal velocity and produce the coronal type III radio bursts.

Quantum description of free electron laser radiation and nonlinear amplitude equations

A relativistic quantum mechanical model to describe the quantum free electron laser dynamics has been developed. Neglecting the spin of electrons in the impacting beam, this model is based on the Klein–Gordon equation coupled to the Poisson equation for the space-charge potential and the wave equation for the transverse components of the radiation field. Furthermore, a system of coupled nonlinear envelope equations for the slowly varying amplitudes of the electron beam distribution and the radiation field has been derived. The fundamental system of basic equations has been cast into a suitable hydrodynamic formulation. In the framework of the hydrodynamic representation, a new dispersion relation has been derived and analyzed in both the quantum and the quasi-classical regimes, where the space-charge oscillations of the electron beam are taken into account.

Dependence of Induced Biological Damage on the Energy Distribution and Intensity of Clinical Intra-Operative Radiotherapy Electron Beams.

The survival fraction of epithelial HaCaT cells was analysed to assess the biological damage caused by intraoperative radiotherapy electron beams with varying energy spectra and intensities. These conditions were achieved by irradiating the cells at different depths in water using nominal 6 MeV electron beams while consistently delivering a dose of 5 Gy to the cell layer. Furthermore, a Monte Carlo simulation of the entire irradiation procedure was performed to evaluate the molecular damage in terms of molecular dissociations induced by the radiation. A significant agreement was found between the molecular damage predicted by the simulation and the damage derived from the analysis of the survival fraction. In both cases, a linear relationship was evident, indicating a clear tendency for increased damage as the averaged incident electron energy and intensity decreased for a constant absorbed dose, lowering the dose rate. This trend suggests that the radiation may have a more pronounced impact on surrounding healthy tissues than initially anticipated. However, it is crucial to conduct additional experiments with different target geometries to confirm this tendency and quantify the extent of this effect.

Longitudinal stacking of ion beams with pulsed electron beam cooling

Longitudinal ion beam stacking with the combination of barrier rf system and beam cooling has been demonstrated in several experiments. Based on the bunching effect found in the pulsed electron beam cooling experiment at HIRFL-CSRm, we propose a new beam stacking scheme using only pulsed electron beam, in which the barrier voltage and cooling effect can be realized simultaneously. In this paper, we introduce this longitudinal stacking scheme along with the theory of beam dynamics and present a simple analytical model. The simulation demonstrates that this approach could be a useful beam stacking technique without the need for barrier bucket hardware. Moreover, the optimization and limitation of this stacking scheme are discussed, and the effect of the electron beam distribution on the barrier voltage is studied. We expect this stacking method can be applied to accumulate RIBs in low and medium energy storage rings for high-precision experiments, such as the SRing of the HIAF project.

High‐Efficiency E‐Beam Pumped Deep‐Ultraviolet Surface Emitter Based on AlGaN Ultra‐Thin Staggered Quantum Wells

AbstractA 2‐inch wafer‐scale electron‐beam (e‐beam) pumped deep‐ultraviolet surface emitter (DUVSE) with high efficiency and high output power at an emission wavelength of 248 nm is reported. This DUVSE benefits from ultra‐thin staggered AlN/AlGaN/GaN multiple quantum wells (MQWs), which compromise the electron–hole overlap and carrier confinement and thus significantly improve the emission efficiency. The wall‐plug‐efficiency (WPE) is increased by six times to 5.25% in comparison to that of conventional DUV light‐emitting devices (LEDs) based on AlGaN MQWs. This WPE is achieved under an anode voltage and current of 8 kV and 1 mA, where the output power is 420 mW. This output power can be further enhanced to 702 mW by increasing the anode current to 3 mA. The enhanced WPE and uniform electron beam distribution lighten the avenue to achieve a wafer‐scale high power dense DUV light source, which is a challenge for conventional DUV‐LEDs, in particular with an emission wavelength of less than 250 nm.

Movie-mode visualization of terahertz fields inside subwavelength metallic structures using ultrashort relativistic electrons

Strong terahertz (THz) fields enhanced by subwavelength structures have great potential in manipulating the 6D phase space distribution of free electrons. Accurate measurement of the spatiotemporal distribution of the THz field inside the subwavelength structure is essential for understanding the physics behind such THz manipulation. Here, we demonstrate a method to directly probe the enhanced THz field inside subwavelength metallic structures in movie mode with ultrashort relativistic electrons. Information about the enhanced THz field is encoded into the deflected electron beam distribution at various time delays. Using rectangular slits as representative examples, we show that the spatiotemporal distribution of the THz field can be accurately retrieved. Furthermore, the measurement of the beam deflection demonstrates that the field can be enhanced by a factor of 20 in a rectangular slit by synthesis of a pulse train. We anticipate that this noninvasive way of probing electromagnetic fields with ultrashort electrons can find wide applications in many areas of research.

Bunch shaping in electron linear accelerators

Modern electron linear accelerators are often designed to produce smooth bunch distributions characterized by their macroscopic ensemble-average moments. However, an increasing number of accelerator applications call for finer control over the beam distribution, e.g., by requiring specific shapes for its projection along one coordinate. Ultimately, the control of the beam distribution at the single-particle level could enable new opportunities in accelerator science. This review discusses the recent progress toward controlling electron beam distributions on the "mesoscopic" scale with an emphasis on shaping the beam or introducing complex correlations required for some applications. This review emphasizes experimental and theoretical developments of electron-bunch shaping methods based on bounded external electromagnetic fields or via interactions with the self-generated velocity and radiation fields.

Kinetic theory of longitudinal stability analysis of a non-laminar electron beam in self-consistent plasma wake field excitation

We carry out a stability analysis of a relativistic nonlaminar electron beam which is experiencing the self-consistent plasma wake field excitation. This is done in overdense regime (i.e. plasma density much greater than beam density) in a cold plasma. We adopt the self-consistent kinetic model for the plasma wake field excitation, that is based on the pair of Vlasov-Poisson-type equations. The latter governs the phase-space spatiotemporal evolution of the beam and its linearized form leads to a Landau-type approach to the beam stability analysis. Thereby, the analysis, performed for the case of a Gaussian electron beam distribution, shows the existence of the unstable modes for both cold and warm beams, respectively.

Theoretical studies of low and high frequency electrostatic solitary waves in the magnetopause associated with asymmetric magnetic reconnection

In a comprehensive analysis of Cluster data, Graham et al. (2015) have reported the existence of slow and fast electrostatic solitary waves (ESWs) associated with asymmetric magnetic reconnection arising from the merger of the magnetic fields, and mixing, of the hot tenuous magnetospheric plasma and the cooler dense magnetosheath plasma. Their analysis also reveals the presence of four electron species, two background Maxwellian distributions and a pair of counter-streaming electron beams. Using the measured plasma parameters and a plasma model consistent with the observations, together with an ion component for charge neutrality, we use fluid dynamic theory in an attempt to identify the plasma modes associated with the ESWs, as well as the polarity and admissible range in speed of the fast and slow structures. It can be inferred from the data sets in Figure 4 in Graham et al. (2015) obtained during the crossing of the Cluster satellites C3 and C4 of the separatrix near the ion diffusion region that the distributions of the two counterstreaming electron beams vary from having identical characteristics to showing small differences over the period during which the ESWs were observed. Accordingly, we align the theoretical parameters in our study with Cluster observations by considering the effect of identical and non-identical counterstreaming electron beam distributions on the existence of ESWs.

Characteristics of Dose Distributions of Electron Beams Used in the Radiation Processing of Food Products

Characteristics of Dose Distributions of Electron Beams Used in the Radiation Processing of Food Products

Microdosimetry-based relative biological effectiveness calculations for radiotherapeutic electron beams: a FLUKA-based study.

Based on FLUKA, the present study is aimed at calculating the microdosimetric distributions of electron beams (6, 12 and 18MeV) for radiotherapy as a function of depth in water at a site-size of 1μm using a tissue-equivalent proportional counter (TEPC). Using the calculated microdosimetric distributions, the depth-specific relative biological effectiveness (RBE) of electron beams used in radiotherapy is calculated based on the theory of dual radiation action (TDRA) and the microdosimetric kinetic model (MKM). The TDRA-based calculation shows the variation of RBE of an electron beamwith the absorbed dose and depth in water. In this study, we compared the RBE values calculated based on the TDRA and MKM. The FLUKA-based microdosimetric distributions in water obtained using the pre-calculated electron fluence spectra resulted in an improvement in the computational efficiency by a factor of 110 when compared with a full simulation. Depending on the beam energy and depth of water, RBETDRA was in the range 0.67-0.78. RBEMKM at 10% survival of HSG tumor cells was 0.84, which was nearly independent of the depth and beam energy.

DISTRIBUTION OF THE BEAM DENSITY AT THE TARGET OF SUBCRITICAL FACILITY “NEUTRON SOURCE”

NSC KIPT subcritical facility “Neutron Source” uses rectangular tungsten or uranium target of 6464 mm top cross-section. To generate maximum neutron flux, prevent overheating of the target and reduce thermal stress during the facility power operation one should provide uniform electron beam distribution at the target top surface. During the facility design three different possibilities of electron beam density redistribution above the target surface were considered. These were the fast beam scanning with two dimensional scanning magnets; the method of uniform beam distribution formation with linear focusing elements (dipole and quadrupole magnets) and nonlinear focusing elements (octupole magnets), when final required rectangular beam shape with homogeneous beam density is formed at target; and combined method, when one forms the small rectangular beam with homogeneous beam density distribution and scan it over the target surface with scanning magnets. In the paper the all three methods are considered and discussed taking into account the layout of the transportation channel of NSC KIPT subcritical facility “Neutron Source”. For the first stage of the facility start-up and pilot operation the fast scanning method was chosen, realised and tested. The results of the beam distribution measurements over the surface of the target during the facility adjustment and start up are presented.