Electron Acceleration Research Articles

Single-mode laser guiding in non-parabolic plasma channels for high-energy electron acceleration

Long-term preservation of the quality of meat and meat products is a complex task influenced by numerous factors, including physicochemical processes, microbial activity, and changes in sensory characteristics. In this regard, radiation processing is considered a promising method in the meat industry due to its ability to ensure microbiological safety. This study focuses on evaluating the effectiveness of using lowenergy electron irradiation.In the experimental part of the study, beef samples were irradiated using the ILU-10 accelerator, which emits nanosecond electron beams with energy less than 5 MeV. The beef samples were treated at doses of 3, 6, and 9 kGy. The results showed that a dose of 3 kGy led to a significant reduction in microbial contamination, particularly eliminating pathogenic microorganisms from the surface of the meat. The application of the optimal radiation dose prevented microbial growth throughout the storage period. Moreover, irradiation at a dose of 3 kGy did not significantly affect the integral quality indicators of the product. The findings confirm that radiation processing using an electron accelerator has the potential to extend the shelf life of food products. Thus, radiation treatment with an electron accelerator can be an effective tool for ensuring the safety of meat products and extending their shelf life.

Three-step Acceleration of the Radiation Belt Relativistic Electrons by Interplanetary Shocks

Modelling in recent decades suggests that electron acceleration in solar flares occurs on timescales of łeq1,s. Timeseries analyses of spatially integrated hard X-ray (HXR) emission from these electrons has shown similarly rapid variations. Further probing the acceleration process requires characterising the spatial and spectral evolution of the electrons with HXR imaging spectroscopy. However, this has not previously been available on such fast timescales. We provide the first HXR spectroscopic imaging of accelerated electrons in a solar flare on timescales of 1,s. We examined the evolution of non-thermal HXR source morphologies and their spatially averaged spectra in the solar flare SOL2024-05-20T05:14L171C109 (estimated-X16.5) with The non-thermal component of this flare was one of the most intense ever observed, and was the first solar HXR spectroscopic imager capable of 1,s (and sub-second) imaging. These observations are therefore the best so far for high-cadence non-thermal X-ray imaging spectroscopy. We observed physical changes in the non-thermal HXR source morphologies on timescales of 1,s, which is consistent with predictions for the acceleration process. The evolution of the the spatially averaged electron spectral index was slower, however. This may suggest a coherent driver between different acceleration events and/or pathways whose spectrum varies on timescales $>$1,s. Alternatively, it may be an illusion of the spatial averaging in the spectral analysis. Either way, these results show that sub-second electron acceleration in solar flares can be associated with morphological dynamics on similar timescales. This highlights the importance of high spatial resolution sub-second HXR imaging spectroscopy for elucidating this process.

Detecting coherent radio bursts from nearby M dwarfs provides opportunities for exploring their magnetic activity and interaction with orbiting exoplanets. However, it remains uncertain whether the emission is related to flare-like activity similar to the Sun or magnetospheric process akin to magnetized planets. Using observations (1.0 to 1.5 gigahertz) taken by the Five-hundred-meter Aperture Spherical radio Telescope, we found a type of millisecond-scale radio bursts with exceptionally high-frequency drift rates (~8 gigahertz per second) from an active M dwarf, AD Leo. The ultrafast drift rates point to a source region with a notably low magnetic scale height (<0.15 , as the stellar radius), a feature not expected in a commonly assumed dipole-like global field but highly possible in localized strong-field structures, i.e., starspots. Our findings suggest that a concentrated magnetic field above starspots could be responsible for some of the most intense radio bursts from M dwarfs, supporting a solar-like electron acceleration mechanism.

Abstract Improving the efficiency of electron acceleration in a vacuum presents a significant challenge in sophisticated laser-driven acceleration methodologies. This research examines the combined effects of Hermite-Sinh-Gaussian (HShG) laser beams (laser electric field amplitude, Hermite polynomial mode index, Decentered parameter of Sinh function) and magnetic wigglers (wiggler magnetic field amplitude, wiggler field propagation constant) on electron dynamics to facilitate high-energy acceleration. The distinct intensity and phase distribution of HShG beams alter the trajectory of electrons, facilitating effective energy transfer. The periodic magnetic field of the wiggler enhances resonance conditions, thereby sustaining prolonged interactions between electrons and the laser field. The numerical analysis indicates that the integration of these two mechanisms markedly enhances the relativistic factor (γ) of electrons, resulting in greater energy gains. The findings demonstrate that customized laser beam configurations and external magnetic fields can enhance laser-driven acceleration in vacuum, presenting a viable strategy for future compact accelerators. This study offers insights into optimizing acceleration efficiency for high-energy physics applications, free-electron lasers, and advanced radiation sources.

Abstract We study electron energization in turbulence-generated current sheets in the shock transition region by means of fully kinetic collisionless plasma simulations and theory. Using parameters in the Earth’s bow shock, we perform a two-dimensional particle-in-cell simulation of a quasi-parallel shock. In shock turbulence, many current sheets are produced, including those exhibiting magnetic reconnection and those that are not reconnecting. The electron temperature is enhanced in nonreconnecting current sheets as well as in reconnecting current sheets and magnetic islands. Performing electron trajectory tracing analysis, we find that energetic electrons are produced in nonreconnecting thinning current sheets. The motional electric field during the thinning process of a current sheet energizes both magnetized and unmagnetized electrons. We analytically show that the energization rate for unmagnetized electrons is slightly less than that of adiabatic energization for magnetized electrons, but unmagnetized electrons can be effectively trapped in magnetic field structures formed in thinning current sheets and continue to be energized. These nonreconnecting current sheets produce energetic electrons whose energies are comparable to the energetic electrons produced in magnetic islands, and they can reach the injection energy for diffusive shock acceleration, which is an acceleration mechanism for producing cosmic rays. The number of electrons that are energized in nonreconnecting current sheets is about a quarter of that in reconnection regions. The energization mechanism can be applicable to various space and astrophysical environments, including planetary bow shocks and supernova remnant shocks.

Low-energy electrons, with their large scattering cross sections and exceptional sensitivity to electric fields, have attracted considerable attention for probing ultrafast surface structural and electronic dynamics, particularly through techniques such as low-energy electron diffraction and imaging. However, the significant dispersion of low-energy electron pulses during transport poses a critical challenge to achieving high temporal resolution in time-resolved experiments. In this Letter, we present an at-the-source compression method for low-energy electron pulses using terahertz surface waves on a micrometer-sized tip cathode. Simultaneous electron acceleration and compression have been achieved directly at the emitter surface within a few tens of micrometers. A low-energy (1.5keV) electron beam with near femtocoulomb charge is temporally compressed by a factor of 3.5, producing 74-femtosecond (FWHM) electron bunches. The quality of the compressed electron bunches is validated through high-quality diffraction patterns of few-layer graphene and projection imaging of a copper mesh. Furthermore, the compressed electrons are applied to investigate the transient electric field propagation generated by photoexcited charged particles on metal surfaces, demonstrating the enhanced temporal resolution. This advancement presents the most compact solution for an electron gun that integrates electron generation, acceleration, and compression into a unified system, paving the way for investigating surface dynamics and complex material phenomena with unprecedented precision.

Solar flares accelerate electrons, creating non-thermal energy distributions. However, the acceleration sites and dominant acceleration mechanisms remain largely unknown. We study the characteristics of electron acceleration and subsequent non-thermal energy distribution in a 2D coronal plasmoid-mediated reconnecting current sheet. We used test particles and the guiding centre approximation to transport electrons in a static coronal 2D fan-spine topology magnetohydrodynamic (MHD) snapshot. The snapshot was from a Bifrost simulation that featured plasmoid-mediated reconnection at a current sheet. To sample initial particle conditions that lead to non-thermal energies, we used importance sampling. In this way, the characteristics of the non-thermal electrons were statistically representative of the MHD plasma. The energy distribution of the electrons forms a non-thermal power law that varies with our tolerance of the guiding centre approximation's validity, from no obvious power law to a power law with an exponent of -4 (the power law also depends on the statistical weighing of the electrons). The non-thermal electrons gain energy through a gradual betatron acceleration close to magnetic null points associated with plasmoids. In this static, asymmetric, coronal, 2D fan-spine topology MHD configuration, non-thermal electron acceleration occurs only in the vicinity of null points associated with magnetic gradients and electric fields induced by plasmoid formation and ejection. However, the guiding centre approximation alone is not sufficient to properly estimate the shape of the non-thermal power law since, according to our results, electron acceleration is correlated with the adiabaticity of the particles' motion. The results also show that the particle power law formation is biased by the test particle sampling procedure.

Very-high-energy electron (VHEE) beams, ranging from 50 to 300 or 400 MeV, are the subject of intense research investigation, with considerable interest concerning applications in radiation therapy due to their accurate energy deposition into large and deep-seated tissues, sharp beam edges, high sparing properties, and minimal radiation effects on normal tissues. The very-high-energy electron beam, which ranges from 50 to 400 MeV, and Ultra-High-Energy Electron beams up to 1–2 GeV, are considered extremely effective for human tumor therapy while avoiding the spatial requirements and cost of proton and heavy ion facilities. Many research laboratories have developed advanced testing infrastructures with VHEE beams in Europe, the USA, Japan, and other countries. These facilities aim to accelerate the transition to clinical application, following extensive simulations for beam transport that support preclinical trials and imminent clinical deployment. However, the clinical implementation of VHEE for FLASH radiation therapy requires advances in several areas, including the development of compact, stable, and efficient accelerators; the definition of sophisticated treatment plans; and the establishment of clinically validated protocols. In addition, the perspective of VHEE for accessing ultra-high dose rate (UHDR) dosimetry presents a promising procedure for the practical integration of FLASH radiotherapy for deep tumors, enhancing normal tissue sparing while maintaining the inherent dosimetry advantages. However, it has been proven that a strong effort is necessary to improve the main operational accelerator conditions, ensuring a stable beam over time and across space, as well as compact infrastructure to support the clinical implementation of VHEE for FLASH cancer treatment. VHEE-accessing ultra-high dose rate (UHDR) perspective dosimetry is integrated with FLASH radiotherapy and well-prepared cancer treatment tools that provide an advantage in modern oncology regimes. This study explores technological progress and the evolution of electron accelerator beam energy technology, as simulated by the ASTRA code, for developing VHEE and UHEE beams aimed at medical applications. FLUKA code simulations of electron beam provide dose distribution plots and the range for various energies inside the phantom of PMMA.

Abstract We present an analysis of a GOES C1-class flare from 2022 September 6, which was jointly observed as occulted by Nuclear Spectroscopic Telescope ARray (NuSTAR) and on-disk by Spectrometer/Telescope for Imaging X-rays (STIX). NuSTAR observed faint coronal nonthermal emission as well as plasma heating &gt;10 MK, starting 7 minutes prior to the flare. This onset emission implies that during this time, there is a continuous electron acceleration in the corona, which could also be responsible for the observed heating. The nonthermal model parameters remained consistent throughout the entire onset, indicating that the electron acceleration process persisted during this time. Furthermore, the onset coincided with a series of type III radio bursts observed by Long Wavelength Array-1, further supporting the presence of electron acceleration before the flare began. We also performed spectral analysis of the impulsive flare emission with STIX (thermal and footpoint emission). STIX footpoints and the onset coronal source were found to have similar electron distribution power-law indices, but with increased low-energy cut-off during the flare time. This could suggest that the nonthermal onset is an early signature of the acceleration mechanism that occurs during the main phase of the flare.

Abstract We investigate the acceleration and transport of electrons in the highly fine-structured current sheet that develops during magnetic flux rope (MFR) eruptions. Our work combines ultraresolved magnetohydrodynamic (MHD) simulations of MFR eruption, with test-particle studies performed using the guiding center approximation. Our grid-adaptive, fully 3D, high-resolution MHD simulations model MFR eruptions that form complex current-sheet topologies, serving as background electromagnetic fields for particle acceleration. Within the current sheet, tearing-mode instabilities give rise to mini flux ropes. Electrons become temporarily trapped within these elongated structures, undergoing acceleration and transport processes that significantly differ from those observed in 2D or 2.5D simulations. Our findings reveal that these fine-scale structures act as efficient particle accelerators, surpassing the acceleration efficiency of single X-line reconnection events, and are capable of energizing electrons to energies exceeding 100 keV. High-energy electrons accelerated in different mini flux ropes follow distinct trajectories, due to spatially varying magnetic field connectivity, ultimately precipitating onto opposite sides of flare ribbons. Remarkably, double electron sources at the flare ribbons originate from different small-flux-rope acceleration regions, rather than from the same reconnecting field line, as previously suggested. Distinct small flux ropes possess opposite magnetic helicity, to accelerate electrons to source regions with different magnetic polarities, establishing a novel conjugate double-source configuration. Furthermore, electrons escaping from the lower regions exhibit a broken-power-law energy spectrum. This spectral break arises from electrons accelerated in disparate mini flux ropes, each exhibiting magnetic reconnection rates and acceleration efficiencies, which reflect the varying local reconnection conditions.

Epithermal neutron resonance spectroscopy is a key nondestructive approach for discerning material properties. However, the existing spallation and accelerator-based photonuclear neutron sources employed in this spectroscopy are huge and immobile, restricting their application in specialized scenarios. Here, we demonstrate a compact short-pulsed photonuclear neutron source driven by a terawatt femtosecond laser-based electron accelerator. After moderation, this neutron source maintains an outstanding time-resolution of 0.8 [Formula: see text]s at 5 eV, and its energy resolution can be less than 3% at a flight distance 1.72 m. When this compact neutron resonance spectroscopy facility is utilized to examine silver (Ag) and indium (In) metal sheets with a high signal-to-noise ratio, it distinctly reveals the shape of resonance absorption peaks for 115In at 1.46 eV and 109Ag at 5.19 eV. This laser-driven electron accelerator offers a solution, overcoming traditional source drawbacks and holding great potential for on-site nuclear material analysis and high-precision nuclear data acquisition.

The acceleration of electrons by surface plasma waves (SPWs) generated during the interaction of ultrashort, linearly polarized, and contrast-enhanced laser pulses at a peak intensity of ∼6×10^{20} W cm^{-2} with flat, noncorrugated foils at parallel incidence (with respect to the target surface) is investigated. We experimentally demonstrate the generation of a collimated electron beam (<0.6 mrad) with a non-Maxwellian spectrum, characterized by peaks at superponderomotive energies (30-36MeV) and total charge ∼120 pC. Through particle-in-cell (PIC) simulations, we identify the J×B force at the front edge as the primary mechanism for injecting electrons into the SPW, where they are further accelerated. Furthermore, our simulation findings reveal that lateral surface contaminants influence SPW dynamics and give rise to a long-ranging plasmonic mode.

Design of high-energy X-ray conversion target based on linear electron accelerator.

Abstract Anti‐dipolarization front (ADF), characterized by the sharp increase of the southward magnetic field (BZ,GSM &lt; 0), is a magnetic structure with reconnected magnetic field enhancement in the magnetotail reconnection. It is considered to be an important region for energy conversion in the tailward reconnection jet. In this paper, we report an ADF event within the magnetotail reconnection diffusion region, which may comprise two ADFs and exhibit a significant enhancement of energetic electron flux. We analyze the corresponding electron acceleration mechanisms and find that the Fermi acceleration dominates the local electron energy gain, contributing to the production of energetic electrons. The magnetic mirror effect and large‐scale parallel electric potential may effectively trap the energetic electrons and facilitate Fermi acceleration. Our study provides important information for further understanding the mechanisms of energetic electron generation in space plasma.

Abstract Precise experimental control and characterization of electron wave packet dynamics driven by external optical fields remain a fundamental challenge, particularly at ultrafast temporal and sub-microscopic spatial scales. To overcome these challenges, we introduce a photon-based simulation platform employing a traveling-wave electro-optic phase-modulated waveguide. In our setup, the incident electromagnetic pulse serves as an analog to the electron wave packet, while the traveling-wave modulation simulates the external optical driving field. Our experimental study systematically explores pulse evolution under three distinct regimes defined by the relation between the pulse duration (Δt) and the modulation period (T). When the pulse duration is significantly shorter than the modulation period, we observe a uniform spectral shift analogous to electron acceleration in dielectric laser accelerators, where spectral phase gradients represent electron momentum accumulation. Conversely, when the pulse duration greatly exceeds the modulation period, discrete diffraction patterns emerge, closely resembling the discrete sideband features of electron–photon coupling observed in photon-induced near-field electron microscopy. Notably, in the intermediate regime (T/4 &lt; Δt &lt; T/2), the pulse spectrum exhibits Airy-function-type characteristics with self-healing effects. These experimental results provide critical insights into electron-wave interactions under external optical fields and establish a robust, programmable framework for further investigation.

Abstract The magnetopause boundary layer often exhibits flux enhancements in keV electrons. Intriguingly, these enhancements frequently occur in the afternoon sector, which is typically magnetopause‐shadowed. They are usually attributed to local production by dayside reconnection, wave‐particle interactions, or radial diffusion by ultra‐low frequency waves. However, under standard magnetospheric conditions, these mechanisms fail to explain the rapid appearance of the electron fluxes and acceleration from magnetosheath energies (tens of eV) to tens of keV. Using data from the THEMIS mission, we report an energetic electron enhancement forming on hour timescales. A test‐particle simulation shows it can result from rapid, non‐diffusive radial transport driven by asymmetric drift‐orbit bifurcation. While this does not exclude alternative interpretations involving radial diffusion, the finding underscores the role of drift‐orbit bifurcation in controlling energetic electron dynamics near the magnetopause, which should be considered alongside conventional mechanisms.

Abstract Recent observations and simulations indicate that solar flares undergo extremely complex 3D evolution, making 3D particle transport models essential for understanding electron acceleration and interpreting flare emissions. In this study, we investigate this problem by solving Parker’s transport equation with 3D MHD simulations of solar flares. By examining energy conversion in the 3D system, we evaluate the roles of different acceleration mechanisms, including reconnection current sheet (CS), termination shock (TS), and supra-arcade downflows (SADs). We find that large-amplitude turbulent fluctuations are generated and sustained in the 3D system. The model results demonstrate that a significant number of electrons are accelerated to hundreds of keV and even a few MeV, forming power-law energy spectra. These energetic particles are widely distributed, with concentrations at the TS and in the flare looptop region, consistent with results derived from recent hard X-ray (HXR) and microwave (MW) observations. By selectively turning particle acceleration on or off in specific regions, we find that the CS and SADs effectively accelerate electrons to several hundred keV, while the TS enables further acceleration to MeV. However, no single mechanism can independently account for the significant number of energetic electrons observed. Instead, the mechanisms work synergistically to produce a large population of accelerated electrons. Our model provides spatially and temporally resolved electron distributions in the whole flare region and at the flare footpoints, enabling synthetic HXR and MW emission modeling for comparison with observations. These results offer important insights into electron acceleration and transport in 3D solar flare regions.

In recent decades, the accumulation of nitrates and nitrites in vegetables and root crops has become a pressing issue due to the increasing use of mineral fertilizers and the growing demand on the agro-industrial sector. Excessive levels of these compounds pose risks to human health, reducing the nutritional value of products and contributing to the formation of carcinogenic compounds. The aim of this study was to investigate the effect of braking (X-ray) radiation on the reduction of nitrates in root crops and tuberous agricultural products, as well as to determine optimal treatment doses for practical use in the food industry. The scientific significance of the work lies in identifying an effective radiation treatment method that ensures product safety and prolongs storage life. The methodology included irradiation of potato, carrot, and beet samples using the ILU-10 industrial electron accelerator at doses of 0.1–0.5 kGy, followed by nitrate determination using the potentiometric method. Results demonstrated that nitrate content in potatoes and beets significantly decreased at doses above 0.2 kGy, whereas carrots exhibited an opposite trend with increased accumulation. This indicates crop-specific sensitivity to radiation exposure related to physiological and varietal characteristics. The contribution of this research is the clarification of nitrate metabolism alterations under ionizing radiation and the development of approaches for applying braking radiation as a method for nitrate reduction. The practical significance lies in the potential application of radiation treatment in the agro-food sector of Kazakhstan and beyond to enhance food safety and extend shelf life.