Maximum Electron Energy Research Articles

Novel approach to stochastic acceleration of electrons in colliding laser fields

The mechanism of stochastic electron acceleration in colliding laser waves is investigated by employing proper canonical variables and effective time, such that the new Hamiltonian becomes time independent when the perturbative laser wave is absent. The performed analytical analysis clearly reveals the physical picture of stochastic electron dynamics. It shows that when the amplitude of the perturbative laser field exceeds some critical value, stochastic electron acceleration occurs within some electron energy range. The conditions, at which the maximum electron energy gained under stochastic acceleration greatly exceeds the ponderomotive energy scaling based on the amplitude of the dominant laser, are derived.

Misjudging negative ions for electrons in intense laser plasma diagnostics

Intense laser produced plasmas are known to be novel compact sources of high energy electrons. Electrons deflected by magnetic fields and imaged on phosphorescent plates is a well used diagnostic for electron spectrum measurements. As only negatively charged particles are filtered by the magnetic field, it is a common practise to interpret the measured scintillation entirely as a signal due to the electrons. We show here that such an interpretation can be erroneous. Low energy H− ions arrive concurrently at the same position as high energy electrons and can lead to a wrong assessment of the maximum electron energy measured, which is often used in understanding the underlying physics. Conventional accelerator based experiments prove that the H− ions are indeed detected even when the image plate is covered with a metal foil.

On the maximum energy of protons in the hotspots of AGN jets

We study particle acceleration and magnetic field amplification in the termination shocks (hotspots) of radiogalaxy jets. The cut-off of the synchrotron spectrum in the hotspots of powerful radiogalaxies is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the jet termination shock is about 1 TeV for a canonical magnetic field of 100 μG. Based on theoretical considerations and observational data we show that the maximum energy of electrons cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonable large and most of the jet kinetic energy goes to non-thermal electrons. The maximum energy is ultimately determined by the ability to scatter particles back and forth the shock, and this limit applies to both electrons and protons. Therefore, the maximum energy of protons is also about 1 TeV when radiative cooling is not efficient. We show that non-resonant hybrid (Bell) instabilities generated by the streaming of cosmic rays can grow fast enough to amplify the jet magnetic field up to 100 μG and accelerate particles up to the maximum energies observed in the hotspots of radiogalaxies.

Experimental study of fast electron generation from intense laser irradiated mylar foil with thin metal coating on front or rear surfaces

We report angular and spectral distribution of fast electrons in the interaction of a high intensity laser pulse (30 fs, I∼1019 W/cm2) with uncoated transparent mylar foil (thickness: 8 μm). The effect of thin Al coating (50 nm) on either the front or rear surface of the mylar foil on fast electron generation was also investigated. An electron flux enhancement of ∼1.8× (from ∼45 pC to ∼80 pC) and an increase in the maximum electron energy from ∼ 400 keV to ∼ 800 keV were observed in the case of front coated foil compared to the uncoated one. In the case of rear coated foil, an enhancement of ∼1.4× in the electron flux with no change in maximum electron energy was observed compared to the uncoated foil. The observations are understood in terms of possible different preplasma conditions for various target configurations used, which is also supported by 1D hydrodynamic simulation carried out for the present experimental conditions. The observed enhancement in electron flux and temperature is also supported by 2D Particle in Cell (PIC) simulation.

Visualizing atomic sizes and molecular shapes with the classical turning surface of the Kohn–Sham potential

The Kohn-Sham potential [Formula: see text] is the effective multiplicative operator in a noninteracting Schrödinger equation that reproduces the ground-state density of a real (interacting) system. The sizes and shapes of atoms, molecules, and solids can be defined in terms of Kohn-Sham potentials in a nonarbitrary way that accords with chemical intuition and can be implemented efficiently, permitting a natural pictorial representation for chemistry and condensed-matter physics. Let [Formula: see text] be the maximum occupied orbital energy of the noninteracting electrons. Then the equation [Formula: see text] defines the surface at which classical electrons with energy [Formula: see text] would be turned back and thus determines the surface of any electronic object. Atomic and ionic radii defined in this manner agree well with empirical estimates, show regular chemical trends, and allow one to identify the type of chemical bonding between two given atoms by comparing the actual internuclear distance to the sum of atomic radii. The molecular surfaces can be fused (for a covalent bond), seamed (ionic bond), necked (hydrogen bond), or divided (van der Waals bond). This contribution extends the pioneering work of Z.-Z. Yang et al. [Yang ZZ, Davidson ER (1997) Int J Quantum Chem 62:47-53; Zhao DX, et al. (2018) Mol Phys 116:969-977] by our consideration of the Kohn-Sham potential, protomolecules, doubly negative atomic ions, a bond-type parameter, seamed and necked molecular surfaces, and a more extensive table of atomic and ionic radii that are fully consistent with expected periodic trends.

Research of luminophores afterglow under influence of pulsed X-ray radiation of nanosecond duration

The work describes an investigation of afterglow of various luminophores under influence of pulsed X-ray radiation of nanosecond duration. As a source of radiation a pulsed X-ray “Yasen 01” apparatus is applied. Maximum impulse current of an X-ray tube is 300 A. Maximum electron energy is 120 keV. Half-height pulse duration of an X-ray burst is about 30 ns. A pulse repetition rate is up to 4 kHz. Two types of X-ray luminophores based on gadolinium oxysulfide Gd2O2S:Tb and cesium iodide CsI:Tl have been investigated. The novelty of the work is use of a fast-acting solid-state semiconductor photomultiplier. It allows recording changes of luminophores luminosity in the nanosecond time range. The photomultiplier is characterized by having two discreet outputs for measuring quickly and slowly time-changing light flows. Presence of two signal outputs allows recording changes of luminophores luminosity both during fast nanosecond excitation and during long-time afterglow. Obtained data about the nature of afterglow of investigated luminophores makes it possible to select the best one for use in conjunction with a pulsed X-ray apparatus with a high pulse repetition rate.

Impact of electron beam surface modification on deformation behavior and fracture properties of TiNi shape memory alloy

The study deals with the impact of the pulse number at low-energy High-Current Pulsed Electron Beam (HCPEB) treatment at constant energy density ES upon the deformation behavior of TiNi alloy, its inelastic properties and fracture pattern under quasistatic uniaxial tension. It is shown that inelastic properties of the TiNi alloy under study can be kept at the initial (constant) level whereas ductility and ultimate strength can be increased when the following parameters of low-energy high-current pulsed electron beam treatment are used: pulse duration τ = 2–2.5 μs, maximum electron energy 25 keV, energy density ES = 3.8 ± 0.7 J/cm2 as well as the pulsed irradiation mode and optimal number of irradiation HCPEB pulses (n) are taken. The HCPEB modification of the TiNi surface layer under uniaxial static tension results in the increase of martensite yield plateau length ΔεM, which is 15–30% larger than one in the unirradiated TiNi samples. The reasons of different impact of the HCPEB irradiation on strength and elastoplastic properties of TiNi alloy (with regard to the n) are discussed. The main reason for the strength properties decrease of the HCPEB-modified TiNi alloy at n = 15, 32 is attributed to the formation of a columnar structure in the matrix B2-phase with a particular crystalline lattice orientation (<110>B2) in the columnar B2 grains. Whereas after the HCPEB treatment at n = 5 these parameters are varied due to the change of the chemical composition, namely, the nickel depletion of the B2-phase in the surface layer. The mentioned variation of the chemical composition of the matrix B2-phase is responsible for the increase in the temperature of the martensite transformations. The latter results in a more complete realization of the mechanisms of inelastic strain accumulation induced by these transformations, as well as the accumulation of larger plastic strain in the ‘soft’ martensitic phase.

Cross-sectional analysis of the graded microstructure and residual stress distribution in a TiNi alloy treated with low energy high-current pulsed electron beam

A Ti-(55.08wt.%)Ni shape memory alloy (SMA) having a grain size of 30 μm, was subjected to low-energy high-current pulsed electron beam (HCPEB) irradiation with parameters: pulse duration τ = 2−2.5 μs, maximum electron energy 25 keV, energy density ES = 3.8 ± 0.7 J/cm2; beam diameter of ∼ 60 mm, number of pulses n = 32. Microstructure modifications, a value and distribution of residual stress induced by HCPEB treatment were investigated in detail. XRD and cross-sectional TEM/EDS/SAED analysis were used for microstructural characterization of the TiNi samples before and after HCPEB treatment. As a result, the HCPEB-modified TiNi surface layer consists of four successive sublayers differing in phase composition, type of texture and defect substructure. In total, the thickness of the HCPEB-modified TiNi surface layer is, at least, 10 μm. Based on the XRD and nanoindentation data, the dependences of residual stress values on the depth from the irradiated surface in the HCPEB-modified TiNi surface layer were estimated and plotted. The values and sings of the stress components in perpendicular (σI⊥) and parallel (σI||) directions to the TiNi sample surface were calculated: σI⊥ <0, σI||>0. The gradient of residual stress values is preserved in the HCPEB-modified TiNi surface layer: from ∼ 800 MPa (in absolute value) near the irradiation surface to ∼ 220 MPa at a depth of about ∼ 10 μm. The residual stress fields are localized in the near-surface layer I and sublayer III with different type of B2-structure. Their relaxation occurs in the sublayer II by means of the stress-induced В2 → R martensitic transformation.

Investigations of the physical nature of the emergence and spread of relativistic astrophysical jets

A series of experiments were carried out at the TSNIIMASH laser facility “Neodym” with a radiation power of 10 TW and an intensity of [Formula: see text]–[Formula: see text][Formula: see text]W/cm2 to simulate the formation and development of astrophysical relativistic jets. It was shown that proton beams are emitted symmetrically in the forward and backward directions to the normal of the target surface. The maximum energy of fast protons and electrons was 5 and 8[Formula: see text]MeV, respectively. At energies in the 0.8–1.7[Formula: see text]MeV range, the ring structures of proton beams are clearly distinguishable with an angular divergence in the range of 3–250. The numerical magnetohydrodynamic calculations have shown that such laboratory experiments can simulate the formation of astrophysical jets with an anomalously small divergence. Moreover, such a plasma stream can form a distinct circular structure. These structures also can be explained as Alfven vortex solitons formed under the conditions of a quasi-stationary superstrong ([Formula: see text]100 MG) magnetic field spontaneously generated in laser produced plasma. It is shown that this model can be used as a model of astrophysical relativistic jets.

GDR Isospin Splitting and Photoproton Reactions on Isotopes of Tin

Photonuclear reactions on a natural mixture of tin isotopes are studied by means of gamma activation. The experiment is performed using the bremsstrahlung γ-beam of an RTM55 racetrack microtron with a maximum electron energy of 55.6 MeV. The measured yields of photoproton and photoneutron reactions are compared to results from other experimental studies, and to calculations using the TALYS code and the combined model of photonucleon reactions (CMPR).

Evidence that particle acceleration in hotspots of FR II galaxies is not constrained by synchrotron cooling

We study the hotspots of powerful radiogalaxies, where electrons accelerated at the jet termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is ≲ TeV for a canonical magnetic field of ∼100 μG. We show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test this result by considering a sample of hotspots observed at radio, infrared and optical wavelengths.

On the Progress of Scanning Transmission Electron Microscopy (STEM) Imaging in a Scanning Electron Microscope.

Transmission electron microscopy (TEM) with low-energy electrons has been recognized as an important addition to the family of electron microscopies as it may avoid knock-on damage and increase the contrast of weakly scattering objects. Scanning electron microscopes (SEMs) are well suited for low-energy electron microscopy with maximum electron energies of 30 keV, but they are mainly used for topography imaging of bulk samples. Implementation of a scanning transmission electron microscopy (STEM) detector and a charge-coupled-device camera for the acquisition of on-axis transmission electron diffraction (TED) patterns, in combination with recent resolution improvements, make SEMs highly interesting for structure analysis of some electron-transparent specimens which are traditionally investigated by TEM. A new aspect is correlative SEM, STEM, and TED imaging from the same specimen region in a SEM which leads to a wealth of information. Simultaneous image acquisition gives information on surface topography, inner structure including crystal defects and qualitative material contrast. Lattice-fringe resolution is obtained in bright-field STEM imaging. The benefits of correlative SEM/STEM/TED imaging in a SEM are exemplified by structure analyses from representative sample classes such as nanoparticulates and bulk materials.

Electronic and optical properties of graphene-like InAs: An ab initio study

The present work initially investigates structural, optical, and electronic properties of graphene-like InAs by using the full potential linear augmented plane wave method in the framework of density functional theory and is then compared with the bulk Indium Arsenide in the wurtzite phase. The lattice parameters are optimized with GGA-PBE and LDA approximations for both 2D- and 3D-InAs. In order to study the electronic properties of graphene-like InAs and bulk InAs in the wurtzite phase, the band gap is calculated by GGA-PBG and GGA-EV approximations. Moreover, optical parameters of graphene-like InAs and bulk InAs such as the real and imaginary parts of dielectric function, electron energy loss function, refractivity, extinction and absorption coefficients, and optical conductivity are investigated. Plasmonic frequencies of 2D- and 3D-InAs are also calculated by using maximum electron energy loss function and the roots of the real part of the dielectric function.

X-Ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A

Abstract We present new evidence that the bright nonthermal X-ray emission features in the interior of the Cassiopeia A supernova remnant are caused by inward-moving shocks, based on Chandra and NuSTAR observations. Several bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000–2014. These inward-moving shock locations are nearly coincident with hard X-ray (15–40 keV) hot spots seen by NuSTAR. From proper-motion measurements, the transverse velocities were estimated to be in the range of ∼2100–3800 km s−1 for a distance of 3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of ∼5100–8700 km s−1, which is slightly higher than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent with an amplified magnetic field of B ∼ 0.5–1 mG. The high speed and low photon cut-off energy of the inward-moving shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k 0 = D 0/D 0,Bohm ∼ 3–8) for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is estimated to be ∼8–11 TeV, which is smaller than the values of ∼15–34 TeV that were inferred for the forward shock. Cassiopeia A is dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead that the inward-moving shocks are a consequence of the forward shock encountering a density jump of ≳5–8 in the surrounding material.

Electron transport with re-acceleration and radiation in the jets of X-ray binaries

This paper studies acceleration processes of background thermal electrons in X-ray binary jets via turbulent stochastic interactions and shock collisions. By considering turbulent magnetized jets mixed with fluctuation magnetic fields and ordered, large-scale one, and numerically solving the transport equation along the jet axis, we explore the influence of such as magnetic turbulence, electron injections, location of an acceleration region, and various cooling rates on acceleration efficiency. The results show that (1) the existence of the dominant turbulent magnetic fields in the jets is necessary to accelerate background thermal electrons to relativistic energies. (2) Acceleration rates of electrons depend on magnetohydrodynamic turbulence types, from which the turbulence type with a hard slope can accelerate electrons more effectively. (3) An effective acceleration region should be located at the distance $>10^3R_{\rm g}$ away from the central black hole ($R_{\rm g}$ being a gravitational radius). As a result of acceleration rates competing with various cooling rates, background thermal electrons obtain not only an increase in their energies but also their spectra are broadened beyond the given initial distribution to form a thermal-like distribution. (4) The acceleration mechanisms explored in this work can reasonably provide the electron maximum energy required for interpreting high-energy $\gamma$-ray observations from microquasars, but it needs to adopt some extreme parameters in order to predict a possible very high-energy $\gamma$-ray signal.

A high-current subnanosecond electron accelerator with a gas-filled former

A subnanosecond electron accelerator prototype based on the ARSA small-size accelerator with a gas-filled former (nitrogen ~4 MPa) has been developed and studied. The operation principle of the former involves charging of a short storage line and its discharge to a stepped line with an accelerating tube that generates electrons. The recorded electron-beam current pulse length was t0.5 = 0.3 ns, the current amplitude was at least 1.5 kA, and the maximum electron energy was ~850 keV.

On the maximum energy of non-thermal particles in the primary hotspot of Cygnus A

We study particle acceleration and magnetic field amplification in the primary hotspot in the northwest jet of radiogalaxy Cygnus A. By using the observed flux density at 43 GHz in a well resolved region of this hotspot, we determine the minimum value of the jet density and constrain the magnitude of the magnetic field. We find that a jet with density greater than $5\times 10^{-5}$ cm$^{-3}$ and hotspot magnetic field in the range 50-400 $\mu$G are required to explain the synchrotron emission at 43 GHz. The upper-energy cut-off in the hotspot synchrotron spectrum is at a frequency < $5\times 10^{14}$ Hz, indicating that the maximum energy of non-thermal electrons accelerated at the jet reverse shock is $E_{e, \rm max} \sim 0.8$ TeV in a magnetic field of 100 $\mu$G. Based on the condition that the magnetic-turbulence scale length has to be larger than the plasma skin depth, and that the energy density in non-thermal particles cannot violate the limit imposed by the jet kinetic luminosity, we show that $E_{e,\rm max}$ cannot be constrained by synchrotron losses as traditionally assumed. In addition to that, and assuming that the shock is quasi-perpendicular, we show that non-resonant hybrid instabilities generated by the streaming of cosmic rays with energy $E_{e, \rm max}$ can grow fast enough to amplify the jet magnetic field up to 50-400 $\mu$G and accelerate particles up to the maximum energy $E_{e, \rm max}$ observed in the Cygnus A primary hotspot.

Erratum: Reconnection and particle acceleration in interacting flux ropes – II. 3D effects on test particles in magnetically dominated plasmas

We analyze particle acceleration in explosive reconnection events in magnetically dominated proton-electron plasmas. Reconnection is driven by large-scale magnetic stresses in interacting current-carrying flux tubes. Our model relies on development of current-driven instabilities on macroscopic scales. These tilt-kink instabilities develop in an initially force-free equilibrium of repelling current channels. Using MHD methods we study a 3D model of repelling and interacting flux tubes in which we simultaneously evolve test particles, guided by electromagnetic fields obtained from MHD. We identify two stages of particle acceleration; Initially particles accelerate in the current channels, after which the flux ropes start tilting and kinking and particles accelerate due to reconnection processes in the plasma. The explosive stage of reconnection produces non-thermal energy distributions with slopes that depend on plasma resistivity and the initial particle velocity. We also discuss the influence of the length of the flux ropes on particle acceleration and energy distributions. This study extends previous 2.5D results to 3D setups, providing all ingredients needed to model realistic scenarios like solar flares, black hole flares and particle acceleration in pulsar wind nebulae: formation of strong resistive electric fields, explosive reconnection and non-thermal particle distributions. By assuming initial energy equipartition between electrons and protons, applying low resistivity in accordance with solar corona conditions and limiting the flux rope length to a fraction of a solar radius we obtain realistic energy distributions for solar flares with non-thermal power law tails and maximum electron energies up to 11 MeV and maximum proton energies up to 1 GeV.

Explaining a few discoveries

Explaining a few discoveries

Influence of an external axial magnetic field on betatron radiation from the interaction of a circularly polarized laser with plasma

In this paper, theoretical analyses and numerical calculations are carried out to investigate the influence of an externally applied axial constant magnetic field on electrons' betatron radiation when an ultra-short, circularly polarized laser pulse of a peak intensity I0 = 5 × 1019 W/cm2 propagates in plasma of an electron density n0 = 1020/cm3. Ring-like x-ray radiation is emitted from the electrons' betatron oscillations. The applied magnetic field can modulate the resonance process between an electron's betatron oscillation and the laser electric field, and the electron energy gain from the direct laser acceleration is thus changed. When a magnetic field of strength B0=3 × 103 T is applied, which is in anti-parallel to the self-generated axial magnetic field, both the trapping efficiency of electrons by the wakefield and the maximum accelerated energy are increased. The maximum electron energy, the peak of angular radiation, and the total radiation energy are increased by 11.0%, 45.6%, and 41.1%, respectively, and the radiation spectra are blue-shifted significantly.