Electron Energy Gain Research Articles

Electron Injection for Direct Acceleration by A Gaussian Laser Field Under the Influence of Azimuth Magnetic Field

Electron injection for direct acceleration by a circularly polarized Gaussian laser field under the influence of azimuth magnetic field is studied. The electron energy gain, \(\gamma\) versus electron's injection angle \(\delta\) at different values laser intensity parameters and laser spot size shows the energy enhancement on increasing the parameters. For a small change in angle of injection then there appears a significant change in electron energy gain also for the variation of energy gain and magnetic field energy gain increases when value of \(\delta\) $ is 8.5, 8.0, 13.5 and 13, respectively. It is observed that \(\delta\) should be small and optimized for appropriate momentum to maximize the electron energy gain due to a relativistic longitudinal momentum and the variation of the scattering angle of the electron \(\theta\) with respect to electron's injection angle \(\delta\) in the presence of magnetic field shows a relatively lower scattering is observed with optimized values of injection angle in the presence of magnetic field.

INCREASE OF EFFICIENCY OF ACCELERATION OF THE TEST ELECTRON BUNCH BY SEQUENCE OF ELECTRON BUNCHES IN THE RECTANGULAR DIELECTRIC RESONATOR AT PLASMA FILLING

A result of numerical simulation of acceleration of the test electron bunch following a sequence of relativistic electron bunches in the rectangular dielectric resonator when filling the drift channel with plasma of different density is provided. We have found out that at change of plasma density the linear growth of energy gain of test bunch electrons is observed. It is connected with structure ordering of longitudinal accelerating electric field in the resonator and also with increase in its amplitude. It is due to that at periodic injection of drive bunches on resonator axis the areas with the increased plasma electrons density are formed.

X-ray laser wakefield acceleration in a nanotube

Plasma-based accelerator technology enables compact particle accelerators. In Laser Wakefield Acceleration, with an ultrafast high-intensity optical laser driver, energy gain of electrons is greater if the electron density is reduced. This is because the energy gain of electrons is proportional to the ratio of laser’s critical density to electron density. However, an alternative path for higher energy electrons is increasing the critical density via going to shorter wavelengths. With the advent of Thin Film Compression, we now see a path to a single cycle coherent X-ray beam. Using this X-ray pulse allows us to increase the plasma density to solid density nanotube (carbon or porous alumina) regime and still be under-dense for a Laser Wakefield Acceleration technique. We will discuss some implications of this below.

Energy Conversion and Dissipation at Dipolarization Fronts: A Statistical Overview

AbstractDipolarization fronts (DFs) are important for energy conversion, particle acceleration, and flux transport in the magnetotail. The partition of energy conversion between ions and electrons and the energy dissipation at DFs are not well understood. In this paper, we present a statistical study of energy conversion and dissipation of 122 DFs observed by Magnetospheric Multiscale mission in the magnetotail. Statistically, electromagnetic energy transfers to plasma at DF. The released energy is mainly transferred to ions rather than electrons. On average, ions gain energy across the whole DF, while electrons gain energy at the leading part but lose energy at the trailing part of DFs. Joule dissipation J · (E+ve × B) can be either positive or negative at DFs, and its average value is very small. The kinetic energy dissipation parameter Pi − D does not exhibit clear signatures at the DFs; hence, it is not suitable for quantifying the energy dissipation at DF.

Electron–Ion Recombination Effect on Electron Acceleration by an Intense Laser Pulse

Electron–ion recombination effect on electron acceleration by a high-intensity laser pulse propagating through a tunnel ionizing gas is investigated in order to observe the actual electron energy gain during acceleration. An intense short-pulse laser with a Gaussian radial profile propagates through a vacuum followed by gas. The point at which the peak of the pulse interacts with the electron is the initial point of the gas region. Tunnel ionization causes defocusing of the laser pulse due to high-density plasma formation on the propagation axis. The electron experiences an additional acceleration during the trailing part of the pulse and, thus, gains net energy. In the presence of electron–ion recombination, the laser pulse focuses more, and hence, the net energy gain is affected significantly for specific parameters region. A model that self-consistently evolves the laser electron acceleration as it ionizes a neutral gas is presented. The model incorporates the electron–ion recombination effects for multiple ionization stage and for tempospatial variations in the neutral gas density appropriate for studying gas-jet system. The electron energy gain during acceleration is calculated in He gas, where the conditions are appropriate for recombination. It is found that for a given laser intensity, there is always an optimal spot size and focal position with respect to the gas jet, which minimizes the refraction and maximizes the acceleration length for higher energy gain of the electrons. The inclusion of electron–ion recombination is more realistic if the pulse duration is longer in a laser–gas-jet experiment.

Phase-resolved profiles of electron energy deposition in inductively coupled radio-frequency plasmas driven under confronting divergent magnetic fields

Electron motion in a cylindrical chamber under RF electric field and confronting divergent magnetic fields was simulated to evaluate the phase-resolved profiles of power deposition to electrons in a low-pressure inductively coupled magnetized plasma. There were three primary regions where the power deposition was high; a region near the RF antenna, a region near the sidewall, and a region of the partial resonance. The phase-resolved profiles of the electron energy gain G(t) and azimuthal electron velocity vθ(t) were obtained in every section defined in the chamber, and were fitted by functions with sinusoidal terms. The characteristics of G(t) and vθ(t), e.g. their asymmetry and directionality, particular to the position were discussed by comparisons between different regions with the fitting parameters and their factors, such as the amplitude of electric field, that of the azimuthal velocity, the power factor, and the phase differences from the RF electric field.

The Effect of Oxygen and Argon Gas Flow Rate on OH Radical Production and Dye Decolorization by Pulsed Discharge in Spray Droplet Reactor

Nonequilibrium plasma is an effective and one of versatile advanced oxidation process due to the formation of reactive species such as hydroxyl radicals, oxygen atom, and hydroperoxyl radicals. In pulsed discharge, free electrons gain energy from an imposed electric field and lose this energy through collisions with neutral gas/liquid molecules. The transfer of energy to the molecules leads to the formation of a variety of new species including atoms, free radicals, and ions. These products are all active chemically, and in our case, we measure the amount of hydroxyl radicals generated in the reactor and also the amount of escaped ozone generated in the reactor and decolorized indigo reagent in a graduated cylinder (GC). In this paper, we used oxygen and argon gases in various flow rate and mixed ratios to feed a gaseous phase in a water spraying droplet reactor. The experimental results indicated that the oxygen and O2/Ar mixture flow rates in spraying reactor have an effect on both hydroxyl radical generation and decolorization of indigo reagent solution. Argon gas discharge has less effect on hydroxyl radical production compared to the oxygen gas discharge with the same flow rates and no effect on the decolorization of indigo reagent solution in GC. We obtained remarkable results on both hydroxyl radical generation rate and decolorization efficiency of indigo reagent solution when we discharged with the mixture of O2/Ar “especially when the ratio has more oxygen than argon gas.” Hence, the presence of oxygen in the water spray plasma discharge is very important as it influence the generation of reactive species such as O atoms and ozone in the gas and liquid phase, which can react directly with organic contaminants and also contribute to more production of hydroxyl radicals in the aqueous phase.

Observation of Plasmon Energy Gain for Emitted Secondary Electron in Vacuo

Plasmon gain by core-level electrons or elastic electrons observed in past studies seems to be of no practical value in material characterization, mainly because of their ultralow signal intensities. Nevertheless, in the emission spectra of Au samples, we have observed plasmon gain in secondary electrons. The electrons gain energy from surface plasmons after escaping from the surface and thereby only carry surface-plasmon information in the vacuum above the surface. Because the intensity of the emitted SEs is strong, rivaling that of core-level or elastic electrons, the observed phenomenon has in practice the potential to image directly in space the surface plasmon near but exterior to the metal surface.

Electron Energy Gain in laser ion channel affected by the space-charge potential and helical wiggler and external uniform magnetic fields

Electron Energy Gain in laser ion channel affected by the space-charge potential and helical wiggler and external uniform magnetic fields

About Azimuthal Acceleration of the Electrons by Azimuthal Surface Waves in a Dielectric-Lined Circular Waveguide With Two Thin Annular Rotating Electron Beams

Considering two annular rotating electron beams in a dielectric-lined waveguide, the frequency spectrum of the azimuthal waves and their field profile distribution are investigated. The charged particle acceleration due to the tangential component of the electric field is simulated. The simulation is carried out for important factors, such as the electron energy gain (acceleration gradient) and the deflection angle in two different vacuum regions (the core and clad of the dielectric waveguide). The graphs of the mentioned parameters versus the traveled distance by the electron are presented, and they are compared with each other. It is found that in some cases, the tangential acceleration of the charged particle in the clad of the cylindrical waveguide can be more effective.

Direct laser acceleration of electrons in the plasma bubble by tightly focused laser pulses

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the course of the resonant acceleration of relativistic electrons by a tightly confined laser beam. It is shown that this laser field component always counteracts the transverse one and effectively decreases the final energy gain of electrons via the direct laser acceleration (DLA) mechanism. This effect is demonstrated by carrying out particle-in-cell simulations of the DLA of the electrons injected into the accelerating phase of the plasma wake. It is shown that the electron energy gain from the wakefield is substantially compensated by the quasiresonant energy loss to the longitudinal laser field component. The analytically obtained scalings and estimates are in good agreement with the results of the numerical simulations.

High‐Resolution Measurements of the Cross‐Shock Potential, Ion Reflection, and Electron Heating at an Interplanetary Shock by MMS

AbstractThe Magnetospheric Multiscale (MMS) spacecraft obtained unprecedented high‐time resolution multipoint particle and field measurements of an interplanetary shock event on 8 January 2018. The spacecraft encountered the supercritical forward shock of a forward/reverse shock pair in the pristine solar wind upstream of the bow shock near the subsolar point as they neared apogee at ~25 RE. The high‐time resolution measurements from the four spacecraft, separated by only ~20 km, allowed direct measurement of particle distributions revealing evidence of electron heating and near specularly reflected ions. The cross‐shock potential is calculated directly from 3‐D electric field measurements. This is the first reported direct high temporal resolution (<1 s) observation at an interplanetary shock of near specularly reflected ions. Calculation of the cross‐shock potential yields a potential jump significant enough to reflect at least some of the protons from the incident solar wind beam. The cross‐shock potential calculated here is consistent with previous estimations based on particle measurements and numerical/analytical simulations. The ambipolar contribution to the cross‐shock potential calculated from the four‐spacecraft divergence of the electron pressure tensor is somewhat higher than that inferred form the Liouville‐mapped electron energy gain across the shock. Furthermore, the high‐time‐resolution 3‐D electric field measurements reported here reveal small‐scale nonlinear structures embedded in the shock layer that contribute to the nonmonotonic shock transition.

On the role of the pre-ionization mechanism in the optical breakdown of molecular oxygen induced by CO2 laser: Numerical investigation

A numerical study is presented to investigate the threshold intensity dependence on the gas pressure in the breakdown of molecular oxygen induced by CO2 laser radiation with a wavelength of 10.591 μm and a pulse FWHM of 64 ns [Camacho et al., J. Phys. D: Appl. Phys. 41, 105201 (2008)]. This experiment allowed for a new method of providing an adequate density of the seed electrons required to ignite the breakdown mechanism. The investigations are based on a modification of a previously developed model [Gamal and Omar, Radiat. Phys. Chem. 62(5), 361–370 (2001)], which solves a differential equation and designates the time evolution of the electron energy distribution numerically and a set of rate equations that describe the change of the excited state population. The model considered inverse bremsstrahlung absorption as the main electron energy gain process leading to oxygen breakdown. As an interesting finding, in comparing the calculated and measured thresholds as a function of gas pressure, computations could precisely reveal the densities of the created seed electrons at each value of the tested pressures. The unsystematic variation of these densities with the gas pressure clarified the origin of the slight oscillations observed in the measured thresholds. Analyzing the electron energy distribution function and its parameters in three gas pressure regions could determine the correlation between the gas pressure and the electron gain and loss processes responsible for oxygen breakdown. This analysis explained the violation from the simple p−1 law observed experimentally in the relation between threshold intensity and gas pressure.

High-efficiency transverse-field acceleration by a laser with a spatially variant state of polarization

Strict single-body dynamics theory and numerical experiments on particle acceleration by a laser with a class of spatially variant state of polarization are presented. Because such a class of spatially variant state of polarization also corresponds to a spatially variant, over wavelength-level space scale intensity profile, it can cause the electronic response to the driving field to be dependent on its initial transverse position. A suitable value of the initial transverse position can correspond to a suitable phase delay between the electronic transverse oscillating velocity υ and the driving electric field E, which leads to −e∫0tE·υdt′>0, and hence implies an aperiodic time growth rate of the electronic kinetic energy. Under the same value of laser power, the electronic energy gain can be several orders of magnitude higher than that in the case of a spatially homogeneous state of polarization. This suggests that choosing a suitable state of polarization is an efficient way of achieving a compact high-efficiency accelerator.

Variation in the nature of the neutral-ionic transition in DMTTF−QCl4 under pressure probed by NQR and NMR

We have investigated the microscopic charge/lattice/spin states in the neutral-ionic transition material $\mathrm{DMTTF}\ensuremath{-}{\mathrm{QCl}}_{4}$ under pressure by $^{35}\mathrm{Cl}\ensuremath{-}\mathrm{NQR}$ and $^{1}\mathrm{H}\ensuremath{-}\mathrm{NMR}$ measurements to reveal the mechanism of the phase transition and the nature of the pressure-temperature phase diagram. At ambient pressure, the $^{35}\mathrm{Cl}\ensuremath{-}\mathrm{NQR}$ frequency indicates low ionicity and shows neither discontinuous jump nor precursory decrease around the transition, suggesting that the spin degrees of freedom are not involved in a dimerization transition. These experimental features are consistent with the theoretically proposed picture that the electronic energy gain is acquired by modulations in transfer integrals (so-called Peierls mechanism) with the lattice dimerization. As pressure is applied, the ionicity is increased and the system is driven into an ionic state with the degree of charge transfer exceeding 0.5 above $\ensuremath{\sim}9\phantom{\rule{0.28em}{0ex}}\mathrm{kbar}$ at room temperature, where the $^{1}\mathrm{H}\ensuremath{-}\mathrm{NMR}$ captures paramagnetic spin fluctuations indicative of the emergence of a nondimeric ionic phase. Furthermore, $^{35}\mathrm{Cl}\ensuremath{-}\mathrm{NQR}$ and x-ray-diffraction measurements found a distinct antiferroelectric state at high pressures above 11 kbar. Based on these results, we propose a pressure-temperature phase diagram.

Nonlinear effect of microwave longitudinal ponderomotive force on the dynamics and energy of an externally injected electron in an inhomogeneous plasma-filled circular and elliptical cylinder waveguides

ABSTRACT Dynamics and energy of an externally injected single electron in inhomogeneous plasma-filled circular and elliptical cylinder waveguides in the electromagnetic fields of wave mode, particularly paying attention to the effect of the longitudinal ponderomotive force is studied. It is shown that by considering this effect in the background plasma the electron energy gain during its movement in the waveguide is changed. Here it is considered two cases for two different background electron densities in the absence of the microwave field including the constant density and linear density profile. We employe the fourth-order Runge–Kutta method for simulating the injected electron momentum and energy equations and the nonlinear wave equation obtained from Maxwell's equations for the mode in the considered configurations. Effect of the longitudinal ponderomotive force acting on the plasma electrons in the balance with the pressure gradient force on the kinetic and total energy of the externally injected electron during its motion in the waveguide is graphically presented.

Electron acceleration by Bessel–Gaussian laser pulse in a plasma in the presence of an external magnetic field

The wakefield acceleration of electron by Bessel–Gaussian laser pulse in a homogeneous plasma in the presence of an external magnetic field is investigated and compared with results of electron acceleration by Gaussian pulse. For this purpose, the analytical expressions for the longitudinal wakefield behind the pulse and electron energy-gain are obtained and discussed for these types of pulses by making the pulse duration the same as the electron plasma period. The results show that the wakefields excited by laser pulses are strongly dependent on the plasma electron density, pulse intensity, pulse frequency and pulse length. Moreover, the results of the present analysis indicate that the wakefield and the electron energy-gain get enhanced for the larger external magnetic field, but with increasing laser intensity, the external magnetic field is unaffected on the electron acceleration. Using typical parameters and comparing the results obtained for two different laser pulses, the Bessel–Gaussian pulse is found to be significant as in this case the wakefield amplitude and electron energy-gain can be received up to 250 GV/m and 150 MeV, respectively when I=3×1022Wm2, Bo=40T and no=7.5×1024m−3.

Stimulated electron energy loss and gain in an electron microscope without a pulsed electron gun

We report on a novel way of performing stimulated electron energy-loss and energy-gain spectroscopy (sEELS/sEEGS) experiments that does not require a pulsed gun. In this scheme, a regular scanning transmission electron microscope (STEM) equipped with a conventional continuous electron gun is fitted with a modified EELS detector and a light injector in the object chamber. The modification of the EELS detector allows one to expose the EELS camera during tunable time intervals that can be synchronized with nanosecond laser pulses hitting the sample, therefore allowing us to collect only those electrons that have interacted with the sample under light irradiation. Using ∼ 5 ns laser pulses of ∼ 2 eV photon energy on various plasmonic silver samples, we obtain evidence of sEELS/sEEGS through the emergence of up to two loss and gain peaks in the spectra at ± 2 and ± 4 eV. Because this approach does not involve any modification of the gun, our method retains the original performances of the microscope in terms of energy resolution and spectral imaging with and without light injection. Compared to pulsed-gun techniques, our method is mainly limited to a perturbative regime (typically no more that one gain event per incident electron), which allows us to observe resonant effects, in particular when the plasmon energy of a silver nanostructure matches the laser photon energy. In this situation, EELS and EEGS signals are enhanced in proportion to n+1 and n, respectively, where n is the average plasmon population due to the external illumination. The n term is associated with stimulated loss and gain processes, and the term of 1 corresponds to conventional (spontaneous) loss. The EELS part of the spectrum is therefore an incoherent superposition of spontaneous and stimulated EEL events. This is confirmed by a proper quantum-mechanical description of the electron/light/plasmon system incorporating light–plasmon and plasmon–electron interactions, as well as inelastic plasmon decay.

Electron acceleration by a radially polarized laser pulse in the presence of an intense pulsed magnetic field

An external pulsed magnetic field is applied to accelerate the electron by a radially polarized laser pulse in vacuum. The unique fields of radially polarized laser beams are utilized which leads to an improvement in trapping and acceleration of electrons so that an electron can be accelerated to a very high energy level. Moreover, a pulsed magnetic field is applied that further enhances the electron acceleration. The enhancement in electron energy is due to fact that the radial field vanishes on the axis and only the longitudinal field survives, which accelerates the electron axially. As time increases, the magnetic field plays a crucial role due to the resonance between the electrons and the electric field of the laser pulse at an optimum value. The combined role of radial polarization and a pulsed magnetic field can enhance the electron energy gain significantly.

Effects of magnetic wiggler field and chirped laser pulse on the wakefield amplitude and electron energy gain in a wiggler-assisted laser wakefield accelerator

Wakefield generation and GeV electron acceleration in a plasma medium by an ultra-short and intense chirped laser pulse in the presence of a magnetic wiggler field are presented. To increase the wakefield amplitude and to maximize the acceleration gradient, we employ a helical magnetostatic wiggler. An analytical theory of wakefield generation and electron energy gain has been presented which includes the effects of the wiggler field. It was found that the wakefield spectrum and electron energy gain in the wiggler-assisted wakefield accelerator can be increased significantly compared to the non-wiggler situation ones. Numerical simulations reveal that for moderate wiggler magnetic field strengths, wakefield amplitude and electron energy gain have significant peaks in bubble-like structures. Besides, when the wiggler wavelength is clearly larger than the plasma wavelength, the wakefield amplitude and electron energy gain significantly enhance. In addition, it was found that the electron bunches can be enhanced by increasing the wiggler field strength or wiggler wavelength. The effect of the laser chirp parameter on wakefield and electron energy gain have also been investigated. It was concluded that in a wiggler-assisted laser wakefield accelerator, the electron energy and wakefield evolution can be tuned by the wiggler field strength, wiggler wavelength, and laser chirp parameter. This concept opens a path toward new generation of plasma accelerators based on wiggler structures.