Motion Of Relativistic Electrons Research Articles

Relativistic electron motion in cylindrical waveguide with strong guiding magnetic field and high power microwave

In O-type high power microwave (HPM) devices, the annular relativistic electron beam is constrained by a strong guiding magnetic field and propagates through an interaction region to generate HPM. Some papers believe that the E × B drift of electrons may lead to beam breakup. This paper simplifies the interaction region with a smooth cylindrical waveguide to research the radial motion of electrons under conditions of strong guiding magnetic field and TM01 mode HPM. The single-particle trajectory shows that the radial electron motion presents the characteristic of radial guiding-center drift carrying cyclotron motion. The radial guiding-center drift is spatially periodic and is dominated by the polarization drift, not the E × B drift. Furthermore, the self fields of the beam space charge can provide a radial force which may pull electrons outward to some extent but will not affect the radial polarization drift. Despite the radial drift, the strong guiding magnetic field limits the drift amplitude to a small value and prevents beam breakup from happening due to this cause.

Two surface plasmon decay of plasma oscillations

The interaction of ultra-intense lasers with solid foils can be used to accelerate ions to high energies well exceeding 60 MeV [Gaillard et al., Phys. Plasmas 18, 056710 (2011)]. The non-linear relativistic motion of electrons in the intense laser radiation leads to their acceleration and later to the acceleration of ions. Ions can be accelerated from the front surface, the foil interior region, and the foil rear surface (target normal sheath acceleration (TNSA), most widely used), or the foil may be accelerated as a whole if sufficiently thin (radiation pressure acceleration). Here, we focus on the most widely used mechanism for laser ion-acceleration of TNSA. Starting from perfectly flat foils, we show by simulations how electron filamentation at or inside the solid leads to spatial modulations in the ions. The exact dynamics depend very sensitively on the chosen initial parameters which has a tremendous effect on electron dynamics. In the case of step-like density gradients, we find evidence that suggests a two-surface-plasmon decay of plasma oscillations triggering a Raileigh-Taylor-like instability.

Temporal resolution criterion for correctly simulating relativistic electron motion in a high-intensity laser field

Particle-in-cell codes are now standard tools for studying ultra-intense laser-plasma interactions. Motivated by direct laser acceleration of electrons in sub-critical plasmas, we examine temporal resolution requirements that must be satisfied to accurately calculate electron dynamics in strong laser fields. Using the motion of a single electron in a perfect plane electromagnetic wave as a test problem, we show surprising deterioration of the numerical accuracy with increasing wave amplitude a0 for a given time-step. We go on to show analytically that the time-step must be significantly less than λ/ca0 to achieve good accuracy. We thus propose adaptive electron sub-cycling as an efficient remedy.

Relativistic electron precipitation events driven by electromagnetic ion-cyclotron waves

We adopt a canonical approach to describe the stochastic motion of relativistic belt electrons and their scattering into the loss cone by nonlinear EMIC waves. The estimated rate of scattering is sufficient to account for the rate and intensity of bursty electron precipitation. This interaction is shown to result in particle scattering into the loss cone, forming ∼10 s microbursts of precipitating electrons. These dynamics can account for the statistical correlations between processes of energization, pitch angle scattering, and relativistic electron precipitation events, that are manifested on large temporal scales of the order of the diffusion time ∼tens of minutes.

Strophotron spontaneous emission in a Free-Electron Laser with transversally inhomogeneous magnetic field

A relativistic electron motion in a transversally inhomogeneous magnetic field of a wiggler is shown to consist of fast (undulator) and slow (strophotron) components. By separating fast and slow motions and by averaging equations of motion over fast undulator oscillations, we find spectral intensity of strophotron spontaneous emission in such a system. The strophotron intensity of spontaneous emission is shown to be well separated spectrally from the usual undulator parts.

Stability of hybrid modes of a single-component electron plasma containing an admixture of background gas ions

The spectrum of eigenmodes of a waveguide completely filled with a cold electron plasma containing a small admixture of ions produced due to electron-impact ionization of background gas atoms is calculated numerically. The calculations were performed within the entire range of allowable values of the radial electric and longitudinal magnetic fields for both magnetized and unmagnetized ions by using the earlier derived nonlocal dispersion relation [Plasma Phys. Rep. 36, 563 (2010)]. The spectrum consists of three families of electron modes with frequencies equal to the Doppler-shifted upper and lower hybrid frequencies and modified ion cyclotron (MIC) modes. When the Doppler shift caused by electron rotation in the crossed electric and magnetic fields compensates for the hybrid frequency, the electron modes become low-frequency modes and interact with the ion modes. For m = 1, only the lower hybrid modes can be low-frequency ones, whereas at m ≥ 2, both lower and upper hybrid modes can be low-frequency ones. The spectrum of modes having the azimuthal number m = 2 is thoroughly analyzed. It is shown that, in this case, the lower hybrid modes behave similar to the m = 1 modes. The dispersion curves of the upper hybrid modes intersect with all harmonics of the MIC frequency (positive, negative, and zero) and are unstable in the vicinities of the intersections. The maximum value of the instability growth rate is several times higher than the ion plasma frequency. The MIC modes are unstable within a wide range of the field strengths, and their growth rates are two orders of magnitude slower. Instabilities are caused by the relative motion of electrons and ions (the transverse current) and the anisotropy of the ion distribution function.

Stochastic electron motion driven by space plasma waves

Abstract. Stochastic motion of relativistic electrons under conditions of the nonlinear resonance interaction of particles with space plasma waves is studied. Particular attention is given to the problem of the stability and variability of the Earth's radiation belts. It is found that the interaction between whistler-mode waves and radiation-belt electrons is likely to involve the same mechanism that is responsible for the dynamical balance between the accelerating process and relativistic electron precipitation events. We have also considered the efficiency of the mechanism of stochastic surfing acceleration of cosmic electrons at the supernova remnant shock front, and the accelerating process driven by a Langmuir wave packet in producing cosmic ray electrons. The dynamics of cosmic electrons is formulated in terms of a dissipative map involving the effect of synchrotron emission. We present analytical and numerical methods for studying Hamiltonian chaos and dissipative strange attractors, and for determining the heating extent and energy spectra.

Nonlinear interaction of intense electromagnetic waves with a magnetoactive electron-positron-ion plasma

The nonlinear coupling between circularly polarized electromagnetic (CPEM) waves and acoustic-like waves in a magnetoactive electron-positron-ion (e-p-i) plasma is studied, taking into account the relativistic motion of electrons and positrons. The possibility of modulational instability and its growth rate as well as the envelope soliton formation and its characteristics in such plasmas are investigated. It is found that the growth rate of modulation instability increases in the case that ωc/ω<1 (ωc and ω are the electron gyrofrequency and the CPEM wave frequency, respectively) and decreases in the case that ωc/ω>1. It is also shown that in a magnetoactive e-p-i plasma, the width of bright soliton increases/decreases in case of (ωc/ω)<1/(ωc/ω)>1 by increasing the magnetic field strength.

ANALYSIS OF THE CYCLOTRON RADIATION FROM RELATIVISTIC ELECTRONS INTERACTING WITH A RADIO-FREQUENCY ELECTROMAGNETIC WAVE

The emission of electromagnetic radiation from charged particles spiraling around magnetic flelds is an important efiect in astrophysical and laboratory plasmas. In theoretical modeling, issues still not fully resolved are, among others, the inclusion of the recoil force on the relativistic electron motion and the detailed computation of the radiation power spectrum. In this paper, the cyclotron radiation emitted during the nonlinear interaction of relativistic electrons with a plane electromagnetic wave in a uniform magnetic fleld is examined, by analyzing the radiated power in both time and frequency domain. The dynamics of the instantaneous radiation and the emitted power spectrum from one particle, as well as from monoenergetic electron ensembles (towards a picture of the radiation properties independent of the initial conditions) is thoroughly studied. The analysis is performed for several values of the wave amplitude, focusing near the threshold for the onset of nonlinear chaos, in order to determine the alteration of the radiation in the transition from regular to chaotic motion.

Comparative study of relativistic electron motion stability in a Raman free-electron laser

In the Raman free-electron laser as a high-power radiation source with megawatt in millimeter and terahertz wave ranges, the stability of relativistic electron motion is of importance for the performance of the device. By making use of the reported MIT experimental data and Kolmogorov entropy, comparative study is carried out on the stability of the relativistic electron motion in a Raman free-electron laser with positive/reversed guide magnetic field. Results show that the wiggler adiabatic field has trivial influence on the stability of electron motion but substantially affects the electron motion itself in both positive and reversed guide magnetic field cases; the self-field of the electron beam deteriorates the motion stability in the case of a positive guide magnetic field, but favors the motion stability in the case of a reversed guide magnetic field.

A simplified approach to synchrotron radiation

Synchrotron radiation is examined in a simple and pedagogical way. The approach is that of Feynman and provides an intuitive, but rigorous graphical interpretation of the distinction between true and apparent relativistic electron motion. Feynman’s demonstration that the apparent motion in the field of a bending magnet follows a curtate cycloid is augmented by a novel derivation of the emission spectrum. A similar graphical analysis is applied to insertion device radiation, to highlight the distinction between a wiggler and an undulator.

The theory of spontaneous emission by electrons during their motion along the quantizing magnetic field of a star

The quantum motion of non-relativistic and relativistic electrons in the presence of constant magnetic fields at the surfaces of magnetic stars, magnetic white dwarfs, and pulsars is considered. The quantizing magnetic-field strengths for charged particles with specified energies are determined. The quantum motion of these particles in a plane perpendicular to the magnetic field is accompanied by spontaneous radiation due to electron transitions from higher to lower discrete energy levels, right down to the ground state. In the non-relativistic case, this emission is monochromatic. In the non-relativistic case, various frequencies are emitted, but lie within an order of magnitude of each other. The electron kinetic energy along the magnetic field varies from zero to a maximum value, due to the one-dimensional character of the motion along the field, between each pair of potential barriers corresponding to the discrete energy levels. The results may be relevant to describing gamma-ray flares of pulsars.

Optical Aharonov-Bohm effect on Wigner molecules in type-II semiconductor quantum dots

We theoretically examine the magnetoluminescence from a trion and a biexciton in a type-II semiconductor quantum dot, in which holes are confined inside the quantum dot and electrons are in a ring-shaped region surrounding the quantum dot. First, we show that two electrons in the trion and biexciton are strongly correlated to each other, forming a Wigner molecule: Since the relative motion of electrons is frozen, they behave as a composite particle whose mass and charge are twice those of a single electron. As a result, the energy of the trion and biexciton oscillates as a function of magnetic field with half the period of the single-electron Aharonov-Bohm oscillation. Next, we evaluate the photoluminescence. Both the peak position and peak height change discontinuously at the transition of the many-body ground state, implying a possible observation of the Wigner molecule by the optical experiment.

Magnetoluminescence from trion and biexciton in type-II quantum dot

We theoretically investigate optical Aharonov-Bohm (AB) effects on trion and biexciton in the type-II semiconductor quantum dots, in which holes are localized near the center of the dot, and electrons are confined in a ring structure formed around the dot. Many-particle states are calculated numerically by the exact diagonalization method. Two electrons in trion and biexciton are strongly correlated to each other, forming a Wigner molecule. Since the relative motion of electrons are frozen, the Wigner molecule behaves as a composite particle whose mass and charges are twice those of an electron. As a result, the period of AB oscillation for trion and biexciton becomes h/2e as a function of magnetic flux penetrating the ring. We find that the magnetoluminescence spectra from trion and biexciton change discontinuously as the magnetic flux increases by h/2e.PACS: 71.35.Ji, 73.21.-b, 73.21.La, 78.67.Hc

Antiparaxial expansions in the theory of bipolar beams

For the vicinities of arbitrary axially symmetric emitting surfaces, solutions to the beam equation are obtained in the case of counter motion of nonrelativistic nonmagnetized ions and relativistic electrons in an external magnetic field. The boundary value problem of determining the emission current in the ρ mode and the electric field on the cathode in the T mode or the problem of determining the shape of the plasma boundary in the r mode, which is related to the enhancement of the accuracy of trajectory analysis programs, is considered.

Relativistic birefringence induced by a high-intensity laser field in a plasma

Field-induced birefringence, also known as cross-polarization wave generation, has played an important role in ultrafast nonlinear optics. In this paper we analyze birefringence induced by relativistic collective motion of electrons driven by a high-intensity laser field. An analytical expression for the phase difference between the parallel and perpendicular polarizations of a weak probe pulse with respect to the polarization of a strong pump pulse as a function of intensity, density, and wavelengths is derived. It is shown that under typical experimental conditions of high-field physics, the effect is well above detection threshold. The analysis is compared with particle-in-cell simulations, and the agreement provides good support for the theory.

From exciton to photon condensation via polariton in electron-holephoton systems

We present a unified theoretical description of the quantum condensates in the electron-hole-photon (ehp) systems, which covers all condensates of exciton, polariton, and photon. To build such model, a phenomenological mean-field treatment for the exciton condensation is employed and extended to include the photon degree of freedom. We clarify changes from exciton/polariton condensations in the low-density limit to photon condensation in the high-density limit as a function of the detuning and the density. Clear change in the microscopic quantities are also found; the carrier distribution function shows broadening in the momentum space, and the minimal excitation energy for breaking an electron-hole (eh) pair increases even in the high density limit. Along this change, relative motion of electron and hole is confined within a tiny radius. In other words, the Wannier-type exciton-polariton picture is replaced by the Frenkel-type. This indicates that the smallest length scale of the system (corresponding to some ultraviolet cutoff) plays important roles due to the presence of coupling between carriers and coherent photons. These features show a remarkable contrast from the scenario of BEC-BCS crossover in the eh systems.

GENERATION OF ELECTRIC CURRENTS IN THE CHROMOSPHERE VIA NEUTRAL-ION DRAG

We consider the generation of electric currents in the solar chromosphere where the ionization level is typically low. We show that ambient electrons become magnetized even for weak magnetic fields (30 G); that is, their gyrofrequency becomes larger than the collision frequency while ion motions continue to be dominated by ion-neutral collisions. Under such conditions, ions are dragged by neutrals, and the magnetic field acts as if it is frozen-in to the dynamics of the neutral gas. However, magnetized electrons drift under the action of the electric and magnetic fields induced in the reference frame of ions moving with the neutral gas. We find that this relative motion of electrons and ions results in the generation of quite intense electric currents. The dissipation of these currents leads to resistive electron heating and efficient gas ionization. Ionization by electron-neutral impact does not alter the dynamics of the heavy particles; thus, the gas turbulent motions continue even when the plasma becomes fully ionized, and resistive dissipation continues to heat electrons and ions. This heating process is so efficient that it can result in typical temperature increases with altitude as large as 0.1-0.3 eV/km. We conclude that this process can play a major role in the heating of the chromosphere and corona

Laser–matter interaction at ultra-relativistic intensities

The chirped-pulse amplification technique has opened up a completely new scenario in laser–matter interaction. Radiation intensities in excess of 1018 W/cm2, leading to relativistic electron motion in the laser field, induce phenomena (sometimes very spectacular) concerning laser pulse propagation, particle acceleration and generation of energetic electromagnetic radiation. The suitable utilization of such phenomena allows for several applications, including the fast ignition of an inertially confined fusion target, the production of energetic particles (electrons, protons, ions and positrons), and X-gamma rays for medical diagnostics and therapy.

Modification of the theory of diffracted channeling radiation for axial electron and positron channeling

A new type of combinational channeling radiation induced by subbarrier (interband) transitions for the transverse motion of relativistic electrons (positrons) is studied. It is known as diffracted channeling radiation (DCR). The formula describing the DCR angular distribution in the case of axial channeling is obtained by taking into account the band structure of energy levels for the transverse motion of electrons (positrons). It is shown that, in the two-wave approximation of the wave function A(r) of virtual photons, the DCR matrix elements in the dipole approximation for axial and plane channeling coincide formally (with the dimension of the problem taken into account). However, the formulas for DCR angular distributions in the cases of axial and plane channeling differ considerably.