Dynamics Of Relativistic Electron Beam Research Articles

Carrier-envelope phase controlled dynamics of relativistic electron beams in a laser-wakefield accelerator

In laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma in order to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use near-single cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarisation direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultra-short electron bunches are periodically injected off-axis by the transversally oscillating bubble associated with the slipping carrier-envelope phase.

Model analysis of relativistic electron beam dynamics in a rarefied plasma

A mathematical model for describing the nonlinear dynamics of a relativistic electron beam in a rarefied plasma is discussed. The model can be applied for the analysis of the behavior of an electron beam in accelerators, as well as in electromagnetic radiation generators based on relativistic electron beams. The equation for the beam envelope and the results of its numerical solution are presented and shortly discussed.

Beam-plasma instability in charged plasma in the absence of ions

We report on the possibility of the beam-plasma instability development in the system with electron beam interacting with the single-component hot electron plasma without ions. As considered system, we analyse the interaction of the low-current relativistic electron beam (REB) with squeezed state in the high-current REB formed in the relativistic magnetically insulated two-section vircator drift space. The numerical analysis is provided by means of 3D electromagnetic simulation in CST Particle Studio. We have conducted an extensive study of characteristic regimes of REB dynamics determined by the beam-plasma instability development in the absence of ions. As a result, the dependencies of instability increment and wavelength on the REB current value have been obtained. The considered process brings the new mechanism of controlled microwave amplification and generation to the device with a virtual cathode. This mechanism is similar to the action of the beam-plasma amplifiers and oscillators.

The development and interaction of instabilities in intense relativistic electron beams

We report on the physical mechanisms of development, coexistence and interaction of Pierce-Bursian and diocotron instabilities in the non-neutral relativistic electron beam (REB) in the classic vircator. The analytical and numerical analysis is provided by means of 3D electromagnetic simulation. We conducted an extensive study of characteristic regimes of REB dynamics determined by the instabilities development. As a result, a regime map has been obtained. It demonstrates sequential switching of the REB dynamics from the regime with N=1 to the regime with N = 7 electron bunches in the azimuth direction with the beam current growth for the different external magnetic fields. The numerical analysis of bunch equilibrium states has identified the physical causes responsible for the REB regime switchings.

Phase-space moment-equation model of highly relativistic electron-beams in plasma-wakefield accelerators

We formulate a new procedure for modelling the transverse dynamics of relativistic electron beams with significant energy spread when injected into plasma-based accelerators operated in the blow-out regime. Quantities of physical interest, such as the emittance, are furnished directly from solution of phase space moment equations formed from the relativistic Vlasov equation. The moment equations are closed by an Ansatz, and solved analytically for prescribed wakefields. The accuracy of the analytic formulas is established by benchmarking against the results of a semi-analytic/numerical procedure which is described within the scope of this work, and results from a simulation with the 3D quasi-static PIC code HiPACE.

Effect of self-magnetic fields on the nonlinear dynamics of relativistic electron beam with virtual cathode

The report is devoted to the results of the numerical study of the virtual cathode (VC) formation conditions in the relativistic electron beam (REB) under the influence of the self-magnetic and external axial magnetic fields. The azimuthal instability of the relativistic electron beam leading to the formation of the vortex electron structure in the system was found out. This instability is determined by the influence of the self-magnetic fields of the relativistic electron beam, and it leads to the decrease of the critical value of the electron beam current (current when the non-stationary virtual cathode is formed in the drift space). The typical dependencies of the critical current on the external uniform magnetic field value were discovered. The effect of the beam thickness on the virtual cathode formation conditions was also analyzed.

Simulating the emission of electromagnetic waves in the terahertz range by relativistic electron beams

Aims. We investigate the dynamics of relativistic electron beams propagating along a uniform magnetic field and the emission process of electromagnetic waves within the terahertz range from the solar photosphere. Our aim is to understand a new solar burst component emitting only in the terahertz range during the solar flare observed by Kaufmann et al. (2004). Methods. We used a 2D3V fully relativistic electromagnetic particle-in-cell (PIC) simulation. Results. We did three different kinds of simulations. The first simulation confirmed that the growth rate of relativistic electron beam instability agrees well with the theoretical estimation. From the second simulation of the electron beam with finite width, we found that the beams are confined along the magnetic field and the electromagnetic waves are generated forward of the electron beams. Some fraction of the electrons are accelerated more than the initial beam velocity. From the third simulation where the electron beams propagate into the high density region, we found that strong electromagnetic waves are generated backward to the electron beams. We also found that the higher frequency emission like 405 GHz, which originate in the strong magnetic field region, becomes stronger than the 212 GHz emission, as shown in the observation by Kaufmann et al. (2004). These simulation results could be applied to the electromagnetic wave emission from the solar photosphere during the solar flares.

On the influence of the initial pitch angle distribution on relativistic electron beam dynamics

Simulations of the evolution of a relativistic electron beam injected into the Earth's magnetosphere are examined. It is found that the lifetime of beam particles strongly depends on the initial pitch angle distribution and that lifetimes similar to those found for the radiation belts are obtained for nearly equatorially mirroring injections. It is concluded that the results of our previous study on beam propagation [Khazanov et al, 1999], which only considered upper ionospheric injections, are consistent with other relativistic electron studies and should be regarded as an examination of the loss cone edge population, whether naturally occurring or artificially injected into near‐Earth space.

Self-consistent analysis of 3D undulator radiation and relativistic electron beam dynamics using Lienard-Wiechert fields

Abstract Lienard-Wiechert (LW) fields, which are exact solutions of the wave equation for a point charge in free space, and the Lorentz force equations are employed to formulate a self-consistent treatment of electron beam dynamics and radiation field evolution in magnetic undulators. In a relativistic electron beam the internal forces leading to the interaction of the electrons with each other can be computed by means of retarded LW fields. The resulting electron motion enables us to obtain three dimensional undulator radiation by summing up the field contribution of each electron in the beam. The approach used is particularly well suited to the investigation of self amplified spontaneous emission (SASE) without introducing a seed wave at start-up. In this paper, we present studies of non-periodic multi-bucket electron phase dynamics as well as temporal and angular characteristics of the electromagnetic fields radiated by a relativistic short filamentary electron beam interacting with a circularly polarized magnetic undulator.

Computer simulation of virtual cathode oscillations

The dynamics of relativistic electron beam and the oscillations of the virtual cathode in the vircator (virtual cathode oscillator) have been investigated by electrostatic particle-in-cell computer simulations. A specially developed PIC (particle-in-cell) computer code is employed in this study. In the diode region, cathode to anode, the solid electron beam is modeled by one-dimensional sheets for simplicity. In the drift tube region the potential at the center line is obtained by solving the Poisson’s equation analytically in the radial direction and via PIC simulation in the axial direction. The electron beam in the drift tube region is modeled as a solid and uniform beam of constant radius equal to the cathode radius. The simulation results show that the potential minimum in the drift tube region oscillates at broad-band frequencies. The injected electron beam in the diode region is found to be modulated by the bunched reflex electrons. The oscillation frequency of the potential minimum in the drift tube region is found to have strong dependence on the transit time of the electrons between the real cathode and the virtual cathode, and it scales inversely proportional to the cathode to anode distance. The effect of applied voltage, injected current, cathode-to-anode distance, and beam radius on the oscillation frequency has also been studied. The results are compared with predictions of theoretical and empirical formulas. The potential minimum is found to oscillate at a single constant frequency when the reflected electrons are not allowed to enter the diode region.

Effect of self fields on the dynamics of relativistic electron beams in a cusp magnetic field

Experimental measurements using a long pulse relativistic electron beam of about 800 ns duration and peak energy of about 200 keV were used. Numerical calculations, for the determination of the trajectories of the beam electrons, were also carried out using a model for the self-fields based on measurements. The beam diamagnetic field, radial loss at the cusp etc. were calculated and compared with the experimental results. Axial beam diamagnetism was observed in the precusp region. The external cusp field was seen to be drastically modified by the self fields. The peak radial loss of beam electrons in the cusp region was seen to occur along the shifted cusp plane. Total radial loss in the cusp region was seen to depart from the single particle value for self fields comparable to the external field. The postcusp beam diamagnetism was also seen to be enhanced over the value estimated from the single particle description in the range of beam self fields comparable to and larger than the external field.

Thermal sensitive paper as a diagnostic for intense relativistic electron beam dynamics

Thermal sensitive paper has been used as a diagnostic for an intense relativistic electron beam propagating in a rippled magnetic field. The E(r)xB(z) rotation of the beam has been measured from the exposed pattern on the thermal paper and used to calculate the electrostatic field of the beam E(r), and the corresponding values of electron density and beam current. Exposed strips of thermal paper show longitudinal modulation of the radial electron velocity with a period corresponding to that of a rippled magnetic field; modulation of the radial electron velocity at the cyclotron frequency has also been observed.

Calculation of the Pinch Dynamics in Relativistic Electron Beam Diodes

The pinch dynamics of relativistic electron beams in large aspect ratio diodes are calculated numerically, including both ion and electron currents. The effect of the ions on the pinch phenomenon is demonstrated. The roles of the time scales for ion emission and flow are discussed. Fair agreement with experiment is obtained.