Acceleration Of Bunches Research Articles

Electron bunch acceleration in the wake wave breaking regime

Results are presented from theoretical analysis and 2D PIC simulations of electron acceleration in a breaking wake plasma wave generated by a short intense laser pulse during its interaction with a finite-length underdense plasma layer. The high energy electron energy spectrum and transverse emittance are obtained. It is shown that, for laser pulse lengths above the plasma wake wavelength, the wakefield-accelerated electrons are further accelerated by the electromagnetic wave.

Wakefield acceleration of low energy electron bunches in the weakly nonlinear regime

We present a simple analytical model for the acceleration of low energy electron bunches in the wakefield created by a short laser pulse focused in a uniform plasma. Laser intensity is limited to I ∼ 10 18 W/cm 2 in order to avoid self-injection and strong nonlinear effects. In this weakly nonlinear regime, it is found that the quality of the accelerated electron bunch—in terms of bunch length and energy spread—depends crucially on the injection energy. Comparisons with numerical simulations show that most of the features of the acceleration process can be explained within the linear response framework, including both the reduction of energy spread and bunch length at low injection energies. The role of nonlinear effects is discussed.

Subfemtosecond, coherent, relativistic, and ballistic electron bunches generated at ω and 2ω in high intensity laser-matter interaction

Harmonics of the laser light have been observed from the rear side of solid targets irradiated by a laser beam at relativistic intensities. This emission evidences the acceleration of subfemtosecond electron bunches by the laser pulse in front of the target. These bunches emit coherent transition radiation (CTR) when passing through the back surface of the target. The spectral features of the signal recorded for targets of thicknesses up to several hundred microns are consistent with the electrons being accelerated by both the laser electric field—via vacuum heating and/or resonance absorption,—and the v×B component of the Lorentz force. The spatial study of the radiation shows that the relativistic electrons causing the CTR radiation are coherent and propagate ballistically through the target, originating from a source with a size of the order of the laser focal spot.

Laser Acceleration of Ion Bunches at the Front Surface of Overdense Plasmas

The acceleration of ions in the interaction of high intensity laser pulses with overdense plasmas is investigated with particle-in-cell simulations. For circular polarization of the laser pulses, high-density ion bunches moving into the plasma are generated at the laser-plasma interaction surface. A simple analytical model accounts for the numerical observations and provides scaling laws for the ion bunch energy and generation time as a function of pulse intensity and plasma density.

Electron bunch acceleration and trapping by ponderomotive force of an intense short-pulse laser

Electron ponderomotive acceleration in a vacuum by a short-pulsed laser of TEM (1, 0) + TEM (0, 1) mode is studied in this paper using a 3-dimensional (3D) particle simulation. It was found that the laser can trap electrons in transverse and accelerate them with the longitudinal ponderomotive force at the same time. Through this electron trapping and acceleration scheme of TEM (1, 0) + TEM (0, 1) mode laser, the electron bunch is confined well in transverse and compressed remarkably in longitudinal. Therefore, a high energy, high density, and low emittances electron bunch is generated. For example, the result shows that for a laser with intensity of a0 = eE0 /mωc = 10, the laser spot size of w0 = 15λ, and the laser pulse length of Lz = 10λ, the maximum energy gain reaches 301 MeV and the average energy 57.7 MeV. The electron bunch transverse radius is about 350λ and the longitudinal size about 20λ. The property of this accelerated bunch is improved compared with that generated by the laser of TEM (0, 0) mode.

Electron Bunch Acceleration by an Intense Laser Pulse with a Plasma Separator

We study an electron acceleration by using a focused TEM10 + TEM01 mode laser pulse with a plasma separator in vacuum. By using the TEM10 + TEM01 mode laser and the plasma separator, the electrons are accelerated strongly compared with that in the case of a TEM00 mode laser, and the divergence of the electron bunch accelerated is suppressed in the transverse direction by the transverse ponderomotive force of the laser. In both the TEM00 mode laser and the TEM10 + TEM01 mode laser, the electrons are decelerated by the laser at the deceleration phase of the laser pulse tail. In order to suppress the energy loss, we set an overdense plasma separator before the electrons are decelerated by the laser tail. Only the laser pulse is reflected by the plasma separator, and the high energy electrons pass through the plasma separator without the energy loss at the tail of laser pulse.

Compression and acceleration of dense electron bunches by ultraintense laser pulses with sharp rising edge

In this paper, the generation of a single ultrashort and coherent relativistic electron bunch (relativistic electron mirror) during interaction of an ultraintense femtosecond laser pulse having a sharp enough rising edge (nonadiabatic laser pulse) with a thin plasma layer is considered. It is shown that due to the action of the radiation reaction forces the Coulomb repulsion among the bunch electrons is partially compensated and the initial geometry of the bunch is supported in the acceleration process. Besides, the bunch can be compressed by many times in the longitudinal direction at the initial stage of interaction with the front of the nonadiabatic laser pulse. As a result, all of the bunch electrons can be synchronously accelerated to ultrarelativistic velocities during the first several half periods of the external electromagnetic field that can correspond to time intervals of hundreds of femtoseconds in the laboratory frame. The characteristics of the accelerated electron bunches for different laser-plasma parameters (shape of laser pulse, initial density of electrons in the target, and initial target thickness) are investigated. One possible application for relativistic electron mirrors is considered. It is shown that the reflection of a probe counter-propagating laser pulse from such a mirror can produce intense, ultrashort, and coherent hard x-ray pulse. The spectrum of the frequency up-shifted radiation is investigated.

Laser wake field acceleration with controlled self-injection by sharp density transition

Laser Wake Field Acceleration of relativistic electron bunches is a promising method to produce a large amount of energetic particles with table top equipment. One of the possible methods to inject particles in the appropriate acceleration phase of the wake behind the pulse takes advantage of the partial longitudinal breaking of the wake crests across a density downramp. In this paper results of 2.5D PIC simulations, showing the production of an electron bunch with reduced energy spread, are reported. Also, a possible method to produce the required plasma density transition by laser explosion of a suitable couple of thin foils is discussed.

Micro Electron Bunch Acceleration and Trapping by Intense Short Laser Pulse in Vacuum

We propose an electron bunch acceleration and trapping mechanism by an intense short laser pulse in vacuum. By using a short laser pulse obtained by the linear combination of a TEM10 mode and a TEM01 mode with the same amplitude and the relative phase shift of π/2, the electrons are accelerated in the longitudinal direction by a longitudinal ponderomotive force, and the electrons divergence in the transverse direction can be suppressed by a transverse ponderomotive force. In order to analyze the electron motion, the relativistic equation of motion including a relativistic radiation damping effect is solved. In our calculations, the electron is accelerated to 179 [MeV] with an acceleration gradient of 5.12 [GeV/m] at the laser intensity of 1.23×1018 [W/cm2]. The rms emittances of the electron bunch accelerated are (1.06, 1.21, 0.348) [mm mrad] in the x, y and z directions, and the spatial size of this electron bunch accelerated in the radial and longitudinal directions are 856 [μm] and 11.7 [μm], respectively.

Centrifugal acceleration of plasma in pulsar magnetosphere

We present a relativistic model for the centrifugal acceleration of plasma bunches and the coherent radio emission in pulsar magnetosphere. We find that rotation broadens the width of leading component compared to the width of trailing component. We explain this difference in the component widths using the nested cone emission geometry. We estimate the effect of pulsar spin on the Stokes parameters, and find that the inclination between the rotation and magnetic axes can introduce an asymmetry in the circular polarization of the conal components. We analyse the single pulse polarization data of PSR B032954 at 606 MHz, and find that in its conal components, one sense of circular polarization dominates in the leading component while the other sense dominates in the trailing component. Our simulation shows that changing the sign of the impact parameter changes the sense of circular polarization as well as the swing of polarization angle

Electron bunch acceleration and trapping by the ponderomotive force of an intense short-pulse laser

By utilizing a pulsed laser beam of TEM(1,0)+TEM(0,1) mode, it was found numerically for the first time that an electron bunch can be effectively trapped by the transverse ponderomotive force in the transverse direction and at the same time accelerated by the longitudinal ponderomotive force to about 378 MeV at the laser peak intensity of I∼5.48×1018 W/cm2. In addition, the electron bunch size is preferably small: at this laser intensity the electron bunch thickness is ∼10λ in the longitudinal direction and the bunch radius is about 625λ in the transverse direction.

Guided propagation of short intense laser pulses and electron acceleration

The dynamics of a guided laser pulse propagation and wakefield generation in plasma channels, ionizing gases and gas filled capillaries is investigated. The efficient generation of a regular wakefield over long distances suitable for laser wakefield accelerators is demonstrated. The different schemes of electron bunch injection and compression to provide monoenergetic electron acceleration to high energies are analysed. A possibility of effective multistage acceleration of short electron bunches with low emittance and energy spread is demonstrated. The analytical results are confirmed by the results of numerical modelling.

Acceleration of electron bunches by intense laser pulse in vacuum

This paper addresses the output characteristics of real electron bunches accelerated with ultra-intense laser pulse in vacuum by the capture & acceleration scenario (CAS) scheme (see, e.g., Phys. Rev. E66 (2002) 066501). Normally, the size of an electron bunch is much larger than that of a tightly focused and compressed laser pulse. We examine in detail the features of the intersection region, the distribution of electrons which can experience an intense laser field and be accelerated to high energy. Furthermore, the output properties of the accelerated CAS electrons, such as the energy spectra, the angular distributions, the energy–angle correlations, the acceleration gradient, the energy which can be reached with this scheme, the emittances of the outgoing electron bunches, and the dependence of the output properties on the incident electron beam qualities such as the emittance, focusing status, etc. were studied and explained. We found that with intense laser systems and electron beam technology currently available nowadays, the number of CAS electrons can reach 10 4–10 5, when the total number of incident electrons in the practical bunch reaches ∼10 8. These results demonstrate that CAS is promising to become a novel mechanism of vacuum laser accelerators.

Simulation of electron postacceleration in a two-stage laser wakefield accelerator

Electron bunches produced in self-modulated laser wakefield experiments usually have a broad energy distribution, with most electrons at low energy (1--3 MeV) and only a small fraction at high energy. We propose and investigate further acceleration of such bunches in a channel-guided resonant laser wakefield accelerator. Two-dimensional simulations with and without the effects of self-consistent beam loading are performed and compared. These results indicate that it is possible to trap about $40%$ of the injected bunch charge and accelerate this fraction to an average energy of about 50 MeV in a plasma channel of a few mm.

Acceleration of dense electron bunches at the front of a high-power electromagnetic wave

The acceleration of dense electron bunches (e.g., those produced by the ionization of thin films) at the front of a high-power electromagnetic wave in vacuum is considered. It is shown that the reaction force of the intrinsic radiation of a bunch can play a significant role in the acceleration process because it gives rise to an additional accelerating force acting on the bunch and to forces that compress the bunch in the longitudinal direction. As a result, all of the bunch electrons can be synchronously accelerated during the first several half-periods of the external electromagnetic field.

The use of a variety of synchrotron techniques in the study of cementitious materials

The electron synchrotron ’revolution’ is barely twenty years old yet its impact on materials science is immeasurable. Fig.1 captures the essence of synchrotron radiation with the dipole magnet, which is associated with a highly collimated fan of radiation due to the centripetal acceleration of electron bunches responding to the inwardly acting Lorentz force; however dipole magnets often play a secondary role in current “third generation” synchrotrons which also utilize more advanced magnet configurations (wigglers and undulators) that are capable of producing even more brilliant sources of X-radiation. The five main attributes of synchrotron X-ray beams are:• The X-ray beam is intense, such that up to 1012 photons per second might be incident on a sample, thus enabling measurements with excellent counting statistics and/or short collection times.• The radiation is horizontally polarized in the plane of the electron orbit.• The X-ray beam is highly collimated, with a typical working divergence of ∼mrads, such that there is less wastage during its passage through the optical components and a superior angular resolution in the eventual measurement.• The radiation has a smooth continuous 'white' spectrum extending into the hard (penetrating) X-ray region, thus offering the choice of conducting experiments with white radiation or alternatively enabling a free choice of wavelength by use of a monochromator.• Since the electrons move in bunches the synchrotron X-ray source is actually pulsed, at a frequencies in the region of 3×108 s−1.

Acceleration and compression of charged particle bunches using counterpropagating laser beams

The nonlinear interaction between counterpropagating laser beams in a plasma results in the generation of large (enhanced) plasma wakes. The two beams need to be slightly detuned in frequency, and one of them has to be ultrashort (shorter than a plasma period). Thus produced wakes have a phase velocity close to the speed of light and can be used for acceleration and compression of charged bunches, The physical mechanism responsible for the enhanced wake generation is qualitatively described and compared with the conventional laser wakefield mechanism. We also demonstrate that depending on the sign of the frequency difference between the lasers, the enhanced wake can be used as a "snow-plow" to accelerate and compress either positively or negatively charged bunches. This ability can be used in an electron-positron injector.

Laser wakefield acceleration of short electron bunches

The theory of electron acceleration in a plasma wake wave is developed, and the dependence of the main characteristics of accelerated electron bunches on the wakefield parameters is investigated, It is shown that using a prebunching stage, under proper conditions, the final electron density of a compressed and accelerated bunch can exceed the initial electron beam density by orders of magnitude and that longitudinal bunch compression provides quasi-monoenergetic acceleration to high energies, It is demonstrated that, for an initial electron beam radius smaller than the optimal one for efficient beam trapping, the energy spread of the compressed and accelerated electron bunch and its length can be evaluated by using the simple analytical predictions of a one-dimensional (1-D) theory. The obtained analytical results are confirmed by three-dimensional (3-D) numerical modeling.

A longitudinal bunch rotation and acceleration scheme for a short bunch and high energy spread muon beam

A neutrino factory for ν μ would require a high-power proton beam bombarding a target to produce pions that decay to muons which can be accelerated. Such a proton driver could be realized with a high-power linac, which could produce short bunches in the interaction point. If the bunch structure could be maintained to the input of a linear accelerator, the re-bunching of muons would be avoided. A preliminary design of the longitidinal beam dynamics for the acceleration of short muon bunches with a large-energy spread will be presented. Muons bunches are assumed at the linac input to consist of a phase space occupying a region from 200–400 MeV with a bunch length of 24 ps. They are captured and accelerated to 1 GeV with a resulting bunch length of 100 ps. Seventy five percent of the muons are transported within these limits.

Generation and acceleration of high-charge short-electron bunches

We report experimental results on the high peak current electron beam generated at the Argonne Wakefield Accelerator facility for wakefield applications. The facility produces bunch charges in the range 15--100 nC by using a photocathode based RF electron gun. The energy of the beam is 14 MeV. Our measurements show that for bunches of 100 nC, the pulse length can be as short as 30 ps. A detailed systematic study of pulse length versus charge is reported, as well as comparisons with numerical simulations. Dark current beam loading in the high field RF gun is also discussed.