Fast Electron Beam Research Articles

Effect of temperature anisotropy formed by fast electron beams moving in the flare loop on its excited electron-cyclotron maser instability

Context. The electron-cyclotron maser instability (ECMI) is a significant coherent radio emission mechanism widely utilized in various astrophysical radio phenomena. It is well known that the velocity anisotropic distribution of energetic electrons, which leads to an inverted perpendicular population in the vertical direction with ∂fb/∂v⊥ > 0, can provide the free energy necessary for the ECMI. Aims. The initial velocity distribution of energetic electrons leaving the acceleration region is typically isotropic or beam-like. However, as these energetic electrons travel along the magnetic field as fast electron beams (FEBs) in magnetic plasma, various velocity anisotropic distributions can emerge. In this paper, we examine the impact of temperature anisotropy formed by beam electrons traveling along a flare loop on the ECMI. Methods. By neglecting the energy loss of energetic electrons as they traverse the corona and invoking the conservation of energy and magnetic moments, we established the relationship between momentum dispersion and the magnetic field. Utilizing the magnetic field model of the flare loop, we calculated the evolution of momentum dispersion and the growth rates of the ECMI as FEBs precipitate along the flare loop. Results. The results demonstrate that the temperature anisotropy arising as FEBs descend along the flare loop significantly impacts the ECMI. The maximum growth rates of the excited modes exhibit a gradual increase initially and then decline rapidly after reaching a critical height for β0 = 0.2c and 0.15c. The results also show that the growth rates of the O2 mode are one order of magnitude smaller than those of the O1 and X2 modes. This indicates that the harmonic radiation is X-mode polarized. Notably, the temperature anisotropy of FEBs as they precipitate along the flare loop with different magnetic field models or at different heights has similar effects on the ECMI.

Synthesis of Complex Oxide Ceramics in a Fast Electron Beam

Synthesis of Complex Oxide Ceramics in a Fast Electron Beam

The effect of a constant electric field in an undisturbed plasma on the stability of the electron beam–gas discharge collisional plasma system

This work is devoted to the study of a fast non-relativistic electron beam–gas discharge plasma system within the framework of the kinetic theory of stability. The influence of a constant electric field, collinear beam velocity, on the stability of the system in an undisturbed plasma is studied. It is shown that even a relatively small electric field, which does not significantly affect the energy of the electron beam, can lead to significant changes in the parameters of harmonic disturbances propagating in the electron beam–plasma system in the region of its instability. It was found that the reason for such changes is the drift of plasma electrons, which, as a consequence, leads to a change in the frequency of disturbances in the coordinate system associated with the plasma due to the Doppler effect. The results obtained are demonstrated by calculations based on the kinetic theory of perturbation parameters in a low-voltage beam discharge in rare gases, which is used in the development of plasma electronics devices. The effect of electron-atomic collisions on the stability of the electron beam–plasma system is investigated and compared with the results of other authors' works.

Modification of the Spectral Absorption Characteristics of ZnGeP2 in the THz and IR Wavelength Ranges Due to Diffusion Doping with Impurity Atoms of Mg, Se, Sn, and Pb

This study demonstrates that diffusion doping of ZGP single crystals with impurity atoms (Mg, Se, Sn, Pb) leads to a decrease in the specific conductivity of the samples. Consequently, this results in reduced absorption in the terahertz frequency range (150–1000 μm). It has been shown that doping ZGP samples with selenium (Se) and lead (Pb) atoms reduces absorption in the infrared region from 0.3–0.6 cm−1 to 0.06–0.09 cm−1. Doping with tin (Sn) leads to a decrease in absorption only in the wavelength region near 2.1 μm from 0.2 cm−1 to 0.05 cm−1. The proposed mechanism for the decrease in infrared absorption is a reduction in zinc vacancies due to doping with impurity atoms. This research lays the groundwork for a technology that produces ZGP crystals with minimal absorption within the 2–8 μm wavelength range, eliminating the need for fast electron beam irradiation technology. This advancement will facilitate the fabrication of ZGP crystals with arbitrary apertures.

Synthesis of Aluminum Titanate Based Composite Ceramics Using High-Power Fast-Electron Beam

Synthesis of Aluminum Titanate Based Composite Ceramics Using High-Power Fast-Electron Beam

Synthesis of high-entropy ceramics (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 by electron beam heating

High-entropy ceramic materials are promising for creating functional ceramics for various purposes. The unique properties of such materials make it possible to create new thermal barrier coatings based on them. Reducing costs, time and simplifying the technology of synthesis of high-entropy ceramics is the subject of numerous studies. In this work, the synthesis of high-entropy ceramics (Y0,2Yb0,2Lu0,2Eu0,2Er0,2)3Al5O12 in a powerful beam of fast electrons was carried out for the first time. A powder mixture of initial oxides, placed in the volume of a massive copper cell, was exposed in air to a short-term exposure to a beam of powerful fast electrons with an energy of 2 MeV and a beam current of 12 mA. The speed of movement of the cuvette with the powder mixture under the beam was 1 cm/s. The total irradiation time was 10 s. During the irradiation process, at least 96 % of the mass of the powder mixture melted, resulting in the formation of highly porous ceramic formations in the form of droplets. X-ray phase analysis showed that the melt droplets are high-entropy ceramics (Y0,2Yb0,2Lu0,2Eu0,2Er0,2)3Al5O12. The powder product remaining in the cuvette and not participating in the formation of droplets contains phases of the original oxides and intermediate phases of synthesized high-entropy ceramics. Electron microscopy with EDS showed a uniform distribution of elements on the surface and in the volume of the formed ceramic droplets.

Electron cyclotron maser instability by evolving fast electron beams in the flare loops

The electron cyclotron maser instability (ECMI) stands as a pivotal coherent radio emission mechanism widely implicated in various astrophysical phenomena. In the context of solar activity, ECMI is primarily instigated by energetic electrons generated during solar eruptions, notably flares. These electrons, upon leaving the acceleration region, traverse the solar atmosphere, forming fast electron beams (FEBs) along magnetic field lines. It is widely accepted that as these FEBs interact with the ambient plasma and magnetic fields, they give rise to radio and hard X-ray emission. Throughout their journey in the plasma, FEBs undergo modifications in their energy spectrum and velocity spatial distribution due to diverse energy loss mechanisms and changes in ambient plasma parameters. In this study, we delve into the impact of the evolving energy spectrum and velocity anisotropic distribution of FEBs on ECMI during their propagation in flare loops. Our findings indicate that if we solely consider the progressively flattened lower energy cutoff behavior as FEBs descend along flare loops, the growth rates of ECMI decrease accordingly. However, when accounting for the evolution of ambient magnetic plasma parameters, the growth rates of ECMI increase as FEBs delve into denser atmosphere. This underscores the significant influence of the energy spectrum and velocity anisotropy distribution evolution of FEBs on ECMI. Our study sheds light on a more comprehensive understanding of the dynamic spectra of solar radio emissions.

Laser-driven pointed acceleration of electrons with preformed plasma lens

The simultaneous laser-driven acceleration and angular manipulation of the fast electron beam are experimentally demonstrated. The bunch of multi-MeV energy charged particles is generated during the propagation of the femtosecond laser pulse through the near-critical plasma slab accompanied by plasma channeling. Plasma is formed by the controlled breakdown of a thin-tape target by a powerful nanosecond prepulse. The electron beam pointing approach is based on the refraction of a laser pulse in the presence of a strong radial density gradient in the breakdown of the tape with a small displacement of the femtosecond laser beam relative to the breakdown symmetry axis. A shift of several micrometers makes it possible to achieve beam deflection by an angle up to 10° with acceptable beam charge and spectrum conservation. This opens up opportunities for applications for scanning objects with an electron beam and the multistage electron beam energy gain in consecutive laser accelerators without bulk magnetic optics for particles. Experimental findings are supported by numerical particle-in-cell calculations of laser-plasma acceleration and hydrodynamic simulations. Published by the American Physical Society 2024

Polarization properties of the decameter spikes

An analysis of the observational polarization properties of the decameter spikes is presented in the paper. It is shown that decameter spikes possess high degree of circular polarization with average value of about 60%. In the frames of “leading spot” theory we associated the spikes activity with a certain active region on the solar disk and determined the mode of the emission. Supposing plasma emission mechanism we link and determine coronal plasma and fast electron beam parameters.

Electron beams traversing spherical nanoparticles: Analytic and numerical treatment

We present an analytic, Mie theory-based solution for the energy loss and the photon-emission probabilities in the interaction of spherical nanoparticles with electrons passing nearby and through them, in both cathodoluminescence and electron energy-loss spectroscopies. In particular, we focus on the case of penetrating electron trajectories, for which the complete fully electrodynamic and relativistic formalism has not been reported as yet. We exhibit the efficiency of this method in describing collective excitations in matter through calculations for a dispersive and lossy system, namely a sphere described by a Drude permittivity. Subsequently, we use the analytic solution to corroborate the implementation of electron-beam sources in a state-of-the-art numerical method for problems in electrodynamics, the discontinuous Galerkin time-domain (DGTD) method. We show that the two approaches produce spectra in good mutual agreement, and demonstrate the versatility of DGTD via simulations of spherical nanoparticles characterized by surface roughness. The possibility of simultaneously employing both kinds of calculations (analytic and numerical) facilitates a better understanding of the rich optical response of nanophotonic architectures excited by fast electron beams. Published by the American Physical Society 2024

Kinetic instability of whistlers in electron beam-plasma systems

The whistlers in space plasmas and in magnetic fusion experiments are destabilized by beams of fast electrons. While the linear regime of instability is analytically tractable, in most practical cases, the instability operates at the saturated level during the stages of observation and measurement. The saturated states, however, involve nonlinear whistlers, which remain best accessible for analysis by kinetic simulations. Results of electromagnetic Vlasov simulations are presented, analyzing an anisotropic electron beam driven whistler instability. The simulations cover the initially unstable regime followed by a saturated or marginally stable regime. Both regimes are separated by an intermediate nonlinear regime during which the electron distribution undergoes a kinetically self-consistent modification. A linearly obtained generalized marginal stability condition is applied to the stabilized state. The condition obtained in its dispersive version shows the β|| at threshold and, in turn, the residual anisotropy, to be a function of the whistler mode number k.

Collimated hot electron generation from sub-wavelength grating target irradiated by a femtosecond laser pulse of relativistic intensity

We investigate the production of hot electrons from the interaction of relativistically intense (I>1018 W/cm2) ultrashort (25 fs) laser pulses with sub-wavelength grating target. We measure the hot electron angular distribution and energy spectra for grating target and compare them with those from a planar mirror target. We observe that hot electrons are emitted in a collimated beam along the specular direction of the grating target. From the measurements, we see fast electron temperature and flux for grating are higher than those for mirror due to a stronger coupling with the laser. We performed numerical simulations, which are in good agreement with experimental results, and offer insights into the acceleration mechanism by resulting electric and magnetic fields. Such collimated fast electron beams have a wide range of applications in applied and fundamental science.

Observation of solar radio burst events from Mars orbit with the Shallow Radar instrument

Context. Multispacecraft and multiwavelength observations of solar eruptions, such as flares and coronal mass ejections, are essential to understanding the complex processes behind these events. The study of solar burst events in the radio frequency spectrum has relied almost exclusively on data from ground-based observations and a few dedicated heliophysics missions such as STEREO or Wind. Aims. By reanalysing existing data from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument, a Martian planetary radar sounder, we discovered the instrument was also capable of detecting solar radio bursts and that it was able to do so with unprecedented resolution for a space-based solar instrument. In this study, we aim to demonstrate the reliability and value of SHARAD as a new solar radio observatory. Methods. We characterised the sensitivity of the instrument to type III solar radio bursts through a statistical analysis of correlated observations using STEREO and Wind as references. Using 38 correlated detections, we established the conditions under which SHARAD can observe solar bursts in terms of acquisition geometry. As an example of scientific application, we also present the first analysis of type III characteristic times at high resolution beyond 1 AU. Results. A simple logistic model based purely on geometrical acquisition parameters can predict burst show versus no-show in SHARAD data with an accuracy of 79.2%, demonstrating the reliability of the instrument in detecting solar bursts and laying the foundation for using SHARAD as a solar radio observatory. The extremely high resolution of the instrument, both in temporal and frequency directions; its bandwidth; and its position in the Solar System enable SHARAD to make significant contributions to heliophysics. Notably, it could provide data on plasma processes on the site of the burst generation and along the propagation path of associated fast electron beams.

Probing optical anapoles with fast electron beams

Optical anapoles are intriguing charge-current distributions characterized by a strong suppression of electromagnetic radiation. They originate from the destructive interference of the radiation produced by electric and toroidal multipoles. Although anapoles in dielectric structures have been probed and mapped with a combination of near- and far-field optical techniques, their excitation using fast electron beams has not been explored so far. Here, we theoretically and experimentally analyze the excitation of optical anapoles in tungsten disulfide (WS2) nanodisks using Electron Energy Loss Spectroscopy (EELS) in Scanning Transmission Electron Microscopy (STEM). We observe prominent dips in the electron energy loss spectra and associate them with the excitation of optical anapoles and anapole-exciton hybrids. We are able to map the anapoles excited in the WS2 nanodisks with subnanometer resolution and find that their excitation can be controlled by placing the electron beam at different positions on the nanodisk. Considering current research on the anapole phenomenon, we envision EELS in STEM to become a useful tool for accessing optical anapoles appearing in a variety of dielectric nanoresonators.

Synthesis of Technical Ceramics in a Beam of Fast Electrons

Synthesis of Technical Ceramics in a Beam of Fast Electrons

One-dimensional longitudinal space charge calculation based on integrated green function approach

For fast longitudinal electron beam dynamics study or optimization in an x-ray free electron laser (FEL) linear accelerator, the one-dimensional longitudinal space charge (1D LSC) impedance, assuming a round cylinder beam with uniform transverse distribution is extensively used in both analytical analysis and numerical simulation. In this paper, instead of employing the impedance model in the frequency domain, we directly calculate the longitudinal electric field by convolving the longitudinal beam density with the slice green function, i.e., the longitudinal electric field generated by a slice beam. For high-energy electron beam, the slice green function rapidly diminishes to zero within a distance significantly smaller than the bunch length. In order to resolve the sharp variation, we report on a fast and high-precision method by applying the integrated green function (IGF) approach to compute the 1D LSC field numerically with few grid points, therefore, providing us with an alternative approach to the impedance model.

Iron Corrosion in the Radiative Plasma of Moist Air

The rate of iron corrosion in a low-temperature plasma of moist air formed under the action of a fast electron beam, depending on the relative air humidity, was measured. It is shown that a beam of fast electrons (radioactive β-radiation) significantly intensifies the corrosion of iron in a plasma-forming gas medium in which oxygen and water vapour are simultaneously present. It has been established that the rate of corrosion under conditions of radioactive irradiation increases sharply when the relative air humidity exceeds 10%. Numerical simulation of the ionic composition of the plasma is carried out taking into account 12 types of positive and 12 types of negative hydrated ions at different intensities of the external ionization source and at different values of relative humidity from 10–6 to 100%. A hypothesis has been put forward about the determining role of cluster hydrated ions, which are formed in the plasma of moist air at atmospheric pressure, in heterogeneous processes of iron oxidation.

Influence of irradiation with fast electron beam on energy transport in praseodymium-ion doped phosphates

This paper reports the spectroscopic properties of praseodymium-doped phosphates, KLuP2O7, Sr9Sc(PO4)7, K3Lu(PO4)2 doped with Pr3+ ions. Spectra of photoluminescence (PL) upon selective UV photon excitation, PL excitation spectra as well as luminescence spectra and decay kinetics upon pulse synchrotron X-ray excitation were studied. Recordings of luminescence spectra were done with pure samples and after irradiating with fast electrons (E = 10 MeV) using linear electron accelerator. The absorbed dose varied in the range of 150–300 kGy. Pure samples demonstrated three typical channels of emission: interconfigurational d – f transitions, intraconfigurational f – f transitions and defect-related luminescence. After irradiating, two scenarios of changing optical properties were investigated: increasing of defect-related luminescence impact in total light output and “suppressing” of defect-located energy emission.

Hybrid PIC–fluid simulations for fast electron transport in a silicon target

Ultra-intense laser-driven fast electron beam propagation in a silicon target is studied by three-dimensional hybrid particle-in-cell–fluid simulations. It is found that the transverse spatial profile of the fast electron beam has a significant influence on the propagation of the fast electrons. In the case of a steep spatial profile (e.g., a super-Gaussian profile), a tight fast electron beam is produced, and this excites more intense resistive magnetic fields, which pinch the electron beam strongly, leading to strong filamentation of the beam. By contrast, as the gradient of the spatial profile becomes more gentle (e.g., in the case of a Lorentzian profile), the resistive magnetic field and filamentation become weaker. This indicates that fast electron propagation in a solid target can be controlled by modulating the spatial gradient of the laser pulse edge.

Optical Radiation during Sputtering of Lithium into a Noble Gas Using a Nanosecond Electron Beam

The optical radiation in a gaseous medium upon the irradiation of a lithium layer with a fast electron beam of a 5 ns duration has been studied. The irradiation chamber was filled with argon, krypton, or xenon at a pressure of 10 kPa up to 60 kPa. The lines of lithium atoms appear in the emission spectrum at a lithium layer temperature of 650–680 K, and the intensity of these lines sharply increases with the increasing temperature of the lithium layer. The optical radiation arises from both the transitions of noble gas atoms and the transition of the lithium atom in a time of about 20–30 ns. The duration of the radiation pulses at half maximum at temperatures above 800 K was 60–100 ns at a wavelength of 610.4 nm and 140–220 ns at 670.8 nm in krypton and argon. The various mechanisms for the population of lithium levels during the radiation pulse are discussed.