Wakefield Excitation Research Articles

Resonance excitation of nonlinear wake field by non-uniform train of laser pulses

Wake field excitation by a train of the laser pulses is an attractive branch of the laser wake field acceleration (LWFA). In this paper, we first discuss analytical formalism for constructing uniform and non-uniform train of laser pulses from a chirped laser pulse in the Michelson interferometer. Afterward, special criteria for resonance generation of wake field with the laser multi-pulses (MP-LWFA) are discussed numerically. We show that in the nonlinear regime of the laser wake field, a non-uniform train of laser pulse can be attractive in maintaining the resonance condition. For large laser amplitudes, 3 < a 0 < 10 (a 0 = eE/mcω), the optimized non-uniform train of laser pulses shows >30% increase in the acceleration gradient compared to the uniform train of laser pulses.

All-metal wakefield accelerator: Two-dimensional periodic surface lattices for charged particle acceleration

Interest in ``all-metal'' surface periodic structures to control charged particle beam dynamics and properties, and to generate coherent radiation in the THz frequency range has recently risen exponentially. While such structures have the benefits of metal, they are capable of providing similar properties to a dispersive dielectric. All-metal structures allow good temperature and space charge management. Transportation of high energy charge particle beams in the vicinity of the structure without risking material degradation makes them very attractive for particle acceleration and terahertz radiation generation applications. Here, the results of theoretical studies (via numerical modeling) of the electron beam dynamics and wakefield excitation and evolution along the cylindrical two-dimensional periodic surface structure will be presented, and the properties of the wakefields generated will be discussed. The wakefield acceleration of the witness bunch in the potential reaching $1\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ will be demonstrated. The challenges will be identified and discussed, and the concept of the cascade accelerator based on such all-metal wakefield accelerator (AMWA) structures will be presented.

EXCITATION OF WAKE FIELDS BY A RELATIVISTIC ELECTRON BUNCH IN A POLAR SEMICONDUCTOR WAVEGUIDE

The process of wake fields excitation by a relativistic electron bunch in polar semiconductors is studied. Cylindrical semiconductor waveguide, in which relativistic electron bunch moves along axis, is considered. It is shown that the excited wake field in the terahertz and infrared frequency ranges consists of the field of longitudinal HF and LF hybrid plasmon-phonon oscillations and the field of the HF and LF transverse polaritons, which are a set of eigen electromagnetic waves of the polar semiconductor waveguide. The spatio-temporal structure of the total excited wake field is obtained, the intensity of the excited wake waves is determined.

Excitation and enhancement of wakefield by beating of two laser beams in a preformed plasma channel: An analytical study

We investigate analytically the nonlinear interaction of two beating laser beams with plasma by considering electron density inhomogeneity in the axial and radial directions. We apply the fluid model coupled with Maxwell equations to obtain a nonlinear equation for studying the plasma wave. We solve this nonlinear equation using the hypergeometric and Airy functions and present the damping and outgoing wave solutions. Our results show that the longitudinal and transverse wakefields generated in the preformed density-ramped plasma channel are much stronger than the inhomogeneous plasma with density-ramped profile.

Kinetic theory of longitudinal stability analysis of a non-laminar electron beam in self-consistent plasma wake field excitation

We carry out a stability analysis of a relativistic nonlaminar electron beam which is experiencing the self-consistent plasma wake field excitation. This is done in overdense regime (i.e. plasma density much greater than beam density) in a cold plasma. We adopt the self-consistent kinetic model for the plasma wake field excitation, that is based on the pair of Vlasov-Poisson-type equations. The latter governs the phase-space spatiotemporal evolution of the beam and its linearized form leads to a Landau-type approach to the beam stability analysis. Thereby, the analysis, performed for the case of a Gaussian electron beam distribution, shows the existence of the unstable modes for both cold and warm beams, respectively.

To study the effect of laser frequency-chirp on trapped electrons in laser wakefield acceleration

The wakefield excitation and electron acceleration is investigated in the presence of laser pulse with and without frequency-chirp in an under-dense plasma via particle in cell simulation. For this purpose, first 1D model of laser wakefield acceleration is revisited. The analytical expressions for the longitudinal wake-potential and wakefield generated behind the laser pulse are obtained. The results show that the wake-fields excited by laser pulses are strongly dependent on the chirp parameter. These results could be very useful as a starting point for optimization studies for a real LWFA experiment.

Theory of wakefields excited by an off-axis drive bunch in a plasma–dielectric waveguide

A linear theory of wakefield excitation by a drive electron bunch in a plasma–dielectric accelerating structure has been constructed for the case of off-axis bunch injection. The structure under investigation is a round dielectric-loaded metal waveguide with a channel for charged particles, filled with homogeneous cold plasma. The developed theory was used to investigate the spatial distribution of the bunch-excited transverse wakefield components, which act on the drive electron bunch. The numerical simulations using the particle-in-cell method have confirmed the predictions of the linear theory in terms of transverse drive bunch dynamics. The numerical analysis has shown stable drive bunch transport through the plasma–dielectric accelerating structure compared with the corresponding dielectric-loaded structure.

Positron driven high-field terahertz waves via dielectric wakefield interaction

Advanced acceleration methods based on wakefields generated by high energy electron bunches passing through dielectric-based structures have demonstrated $>$GV/m fields, paving the first steps on a path to applications such as future compact linear colliders. For a collider scenario, it is desirable that, in contrast to plasmas, wakefields in dielectrics do not behave differently for positron and electron bunches. In this Letter, we present measurements of large amplitude fields excited by positron bunches with collider-relevant parameters (energy 20 GeV, and $0.7 \times 10^{10}$ particles per bunch) in a 0.4 THz, cylindrically symmetric dielectric structure. Interferometric measurements of emitted coherent Cerenkov radiation permit spectral characterization of the positron-generated wakefields, which are compared to those excited by electron bunches. Statistical equivalence tests are incorporated to show the charge-sign invariance of the induced wakefield spectra. Transverse effects on positron beams resulting from off-axis excitation are examined and found to be consistent with the known linear response of the DWA system. The results are supported by numerical simulations and demonstrate high-gradient wakefield excitation in dielectrics for positron beams.

Experimental investigation of supertransmission for an intrinsic localized mode in a cyclic nonlinear transmission line.

In this experimental study of the nonlinear loss mechanism between traveling localized excitation and the underlying extended normal mode spectrum for a 1D lattice, three types of cyclic, electric, nonlinear transmission lines (NLTLs) are used. They are nonlinear capacitive, inductive, and capacitive+inductive NLTLs. To maintain a robust, steady-state traveling intrinsic localized mode (ILM), a traveling wave driver is used. The ILM loses energy because of a resonance between it and the extended NLTL modes. A wake field excitation is detected directly from ILM velocity experiments by the decrease in ILM speed and by the observation of the wake. Its properties are quantified via a two-dimensional Fourier map in the frequency-wavenumber domain, determined from the measured spatial-time voltage pattern. Simulations support and extend these experimental findings. We find for the capacitive+inductive NLTL configuration, when the two nonlinear terms are theoretically balanced, the wake excitation is calculated to become very small, giving rise to supertransmission over an extended driving frequency range.

ACCELERATING OF THE ELECTRONS OF ELECTRON BUNCHES IN A WAVEGUIDE LOADED DIELECTRIC STRUCTURE

The paper presents some results of experimental studies of the excitation of wake fields and the acceleration of electrons in waveguide-dielectric structures (DS) upon injection of a sequence of electron bunches into them. Exper-iments have shown an increase in the amplitude of the wake wave and the acceleration of a small fraction of elec-trons when the wavelength of the excited field is equal to the doubled bunch length. A simple physical model of the observed phenomenon is given. Also, the paper proposes a method for accelerating a part of each electron bunch in the steady-state mode of the resonator dielectric structure. Some of the electrons are “cut out” by the collimator and enter the accelerating phase of the previously excited wake wave. The wave is displaced due to the difference in the distances traveled by the wave and the accelerated part of the electrons.

Electron transport in a nanowire irradiated by an intense laser pulse

Electron transport in a nanowire exhibits a distinct behavior following the irradiation of intense laser pulse. Using particle-in-cell simulation, we observe a large-amplitude particle-driven wakefield excitation followed by electron acceleration in the solid density. Besides, we observed the quiver of the electrons across the nanowire under the action of the surrounding laser electric field facilitating deeper wakefield propagation in the nanowire with $2.5\ifmmode\times\else\texttimes\fi{}$ energy gain over a flat target. These results open insights into the laser-energy coupling with nanostructure targets and radiation sources, and motivate the wakefield acceleration in solid density plasma.

Experimental demonstration of two-color x-ray free-electron-laser pulses via wakefield excitation

Several beam manipulation methods have been studied and experimentally demonstrated to generate x-ray multipulses in free-electron-laser (FEL) facilities, advancing the fields of material science, molecular physics, and photochemistry by enabling x-ray pump/x-ray probe experiments. We have demonstrated a novel method to generate hard x-ray multipulses using a hybrid compression scheme. Compared to other methods, this approach minimizes the time jitter among the FEL subpulses, produces large power FEL subpulses, is suitable for high repetition rate machines, since it does not imply the generation of losses, and it works at short and hard x-ray FEL wavelengths as well. All of these aspects make this approach attractive for the novel FEL facilities aiming to explore the hard x-ray region and to work at high repetition rate.

WAKEFIELD EXCITATION BY A RAMPED ELECTRON BUNCH TRAIN IN A PLASMA-DIELECTRIC WAVEGUIDE

A linear theory of wakefield excitation by a ramped electron bunch train in a cylindrical plasma-dielectric waveguide is presented. It is shown that during an excitation process the drive bunches are in the focusing field due to the radial electric field excitation of the plasma wave. The possibility of both obtaining a high transformer ratio and focusing the drive and witness bunches is demonstrated.

DEPENDENCE OF WAKEFIELD EXCITATION IN PLASMA BY NON-RESONANT SEQUENCE OF ELECTRON BUNCHES ON THEIR LENGTHS

The present paper describes the results of numerical simulation (using 2d3v code LCODE) of the regime, when the wakefield is excited at maximum growth rate in the plasma by a nonresonant sequence of relativistic electron bunches. As a result, the wakefield increases approximately in steps. The paper gives the parameters, at which this regime is achieved. It is shown that for smaller bunch radii, the amplitude of the excited wakefield is larger. At long lengths of the bunches, the amplitude of the wakefield is larger, in contrast to the excitation by the resonant sequence of bunches.

Wakefield Excitation by a Sequence of Laser Pulses in Plasma

Wakefield Excitation by a Sequence of Laser Pulses in Plasma

Wakefield Excitation in Plasma of Metallic Density by a Laser Pulse

Wakefield Excitation in Plasma of Metallic Density by a Laser Pulse

Numerical research on mechanism of the effect of propeller shaft brackets on wake field and propulsion performance

Ship drag and self-propulsion simulations of a twin-screw high-speed displacement vessel were performed using the unsteady Reynolds-averaged Navier–Stokes (RANS) method. The sliding mesh and overset mesh methods were applied concurrently to simulate the coupling of the propeller rotation and the ship motion. The effects of the propeller shaft brackets on the drag, propulsion performance, wake field, and propeller excitation force were studied. The influence of the shaft brackets on the wake field was visualized. The high numerical accuracy of the proposed simulation method was proven through verification and validation analyses. The low-speed zones of nominal wake within the propeller disc were mainly caused by vortex shedding from the vicinity of the shaft brackets and the speed reduction of the frictional wake resulting from the velocity stagnation in front of the rudder. The tangential wake velocity, which was affected by the twist angle and vortex shedding, had a considerable effect on the propulsion performance. The wake non-uniformity coefficient was highly correlated with the vortex shedding. The spatial structure of the shaft bracket and the inward curved streamline around the stern aggravated the non-uniformity further, but the shaft bracket had a limited impact on the unsteady propeller bearing force in the absence of cavitation.

Excitation of plasma wakefields by intense ultra‐relativistic proton beam

AbstractWe report here an exact analytical travelling wave solution for a non‐linear electron plasma wave excited by an intense ultra‐relativistic proton beam. It demonstrates the underlying physics of longitudinal electric field characteristics of the excited wake wave formed behind the drive beam. The results are further supplemented by a fully relativistic particle‐in‐cell code OSIRIS in two‐dimensional geometry. The investigation is further extended by providing an analytical description of the wake wave excited by an equi‐spaced train of small proton bunches with the inclusion of the non‐relativistic plasma ion dynamics. Our results show that the amplitude of the wake field does not grow indefinitely with the increase in the number of proton bunches. On the contrary, it saturates to a definitive limit.

Theoretical and numerical studies of the phase velocity of wakefields in plasma driven by self-modulated proton beams with electron beam seeding

Significant progress has been made in the studies of wakefield excitation in plasma by a self-modulated high energy proton beam in the past decade. The electron beams accelerated up to 2 GeV by using such a wakefield were demonstrated in the AWAKE experiment at CERN in 2018. Aiming at the application of high energy particle accelerators, new ideas have been investigated in recent years, such as seeding the proton beam self-modulation with an electron beam in order to enhance the strength and stability of the wakefield or adding a density transition in the plasma distribution to enhance the phase velocity and the strength of the wakefield. Here in this work, we investigate the effects of electron beam seeding on the phase velocity of the wakefield generated by the modulated proton beam in plasma. The physical mechanisms responsible for the phase velocity change and the roles played by the electron beam seeding are discussed. The theoretical analysis and two-dimensional particle-in-cell simulations show that both the growth rate and the phase velocity of the wakefield generated by the modulated proton beam can be enhanced by the electron beam seeding. The higher the charge density of the electron beam, the more significant the enhancement effects. The effects of electron beam energy and proton beam longitudinal profiles on the increase of phase velocity are also studied. It is shown that the evolution of the electron beam distribution has a significant effect on the seeding self-modulation process, and thus affecting the phase velocity. A self-focusing electron seeding beam can increase the phase velocity of the wakefield even to superluminal while an expanding seeding beam can reduce the phase velocity and destroy the stability of the whole process. This work may benefit the proton beam seeding self-modulation acceleration and its applications.

Longitudinal current profile reconstruction from a wakefield response in plasmas and structures

Present-day and next-generation accelerators, particularly for applications in driving wakefield-based schemes, require longitudinal beam shaping and attendant longitudinal characterization for experimental optimization. Here we present a diagnostic method which reconstructs the longitudinal beam profile at the location of a wakefield-generating source. The methods presented derive the longitudinal profile of a charged particle beam solely from measurement of the time-resolved centroid energy change due to wakefield effects. The reconstruction technique is based on a deconvolution algorithm that is fully generalizable to any analytically or numerically calculable Green's function for the wakefield excitation mechanism. This method is shown to yield precise features in the longitudinal current distribution reconstruction. We demonstrate the accuracy and efficacy of this technique using simulations and experimental examples, in both plasmas and dielectric structures, and compare to the experimentally measured longitudinal beam parameters as available. The limits of resolution and applicability to relevant scenarios are also examined.