Wakefield Excitation Research Articles

ELECTRON SOURCE BASED ON EMERGENCE OF SELF-INJECTED ELECTRON BUNCH AT PLASMA WAKEFIELD EXCITATION BY A TW LASER PULSE

Wakefield acceleration methods are known due to some their advantages. The main of them is the high accelerating gradient up to several teravolts per meter. In the paper another important advantage is concluded to the possibility of using a wakefield accelerator as a source of electrons by means of obtaining self-injected bunches and their acceleration. The result is the simulation of the process of plasma wakefield excitation by a laser pulse with an energy of tens of mJ and a power of 1…2 TW for obtaining the promising electron source. Homogeneous and Gaussian plasma profiles were investigated and compared to increase the energy of the self-injected bunches. The laser parameters were taken that corresponded to the parameters of the laser setup in the Institute of Plasma Electronics and New Methods of Acceleration of the National Scientific Center “Kharkiv Institute of Physics and Technology”. Based on the results of the simulation, the possibility of obtaining relativistic self-injected bunches that can be used for further laser acceleration experiments, including dielectric laser acceleration, was demonstrated.

Elevating electron energy gain and betatron x-ray emission in proton-driven wakefield acceleration

The long proton beams present at CERN have the potential to evolve into a train of microbunches through the self-modulation instability process. The resonant wakefield generated by a periodic train of proton microbunches can establish a high acceleration field within the plasma, facilitating electron acceleration. This paper investigates the impact of plasma density on resonant wakefield excitation, thus influencing the acceleration of a witness electron bunch and its corresponding betatron radiation within the wakefield. Various scenarios involving different plasma densities are explored through particle-in-cell simulations. The peak wakefield in each scenario is calculated by considering a long pre-modulated proton driver with a fixed peak current. Subsequently, the study delves into the witness beam acceleration in the peak wakefield and its radiation emission. Elevated plasma density increases both the number of microbunches and the accelerating gradient of each microbunch, consequently resulting in heightened resonant wakefield. Nevertheless, the scaling is disrupted by the saturation of the resonant wakefield due to the nonlinearities. The simulation results reveal that at high plasma densities, an intense and broadband radiation spectrum extending into the domain of the hard x-rays and gamma rays is generated. Furthermore, in such instances, the energy gain of the witness beam is significantly enhanced. The impact of wakefield on the witness energy gain and the corresponding radiation spectrum is clearly evident at elevated densities.

Terahertz field generation in a self-sustained magnetic laser-plasma channel

We theoretically investigate the terahertz field excitation from a laser-driven self-sustained magnetized plasma channel. The expulsion of plasma electrons by the laser ponderomotive force modifies the plasma density, which self-focuses the laser pulse. For the optimized laser parameters, the laser propagates without diverging in plasma and a plasma channel is created. The magnetic field applied along the laser propagation enhances the channel formation efficiency. We utilize this magnetic plasma channel to excite the transverse radiation field by the self-focused laser via wakefield excitation. The magnetic plasma channel maintains the laser intensity over a larger propagation distance, exciting wakefields efficiently. The second order perturbation technique is applied to calculate the wakefield components excited by the laser pulse in a self-sustained magnetic plasma channel. The density perturbation associated with the low-frequency ponderomotive force derives the transverse nonlinear current at terahertz frequency. Our results show that the magnetic field plasma channel can significantly enhance the terahertz conversion efficiency. The tunable terahertz radiation fields of 20 THz frequency with about 10 GV/m may be obtained using one Tesla magnetic field. The efficiency of the process may be optimized and controlled by the laser and plasma parameters. These high-field THz may be useful in various applications such as ultra-fast technology.

Plasmonic excitations in double-walled carbon nanotubes

The interactions of charged particles moving paraxially in multi-walled carbon nanotubes may excite electromagnetic modes. This wake effect has recently been proposed as a potential novel method of short-wavelength high-gradient particle acceleration and for obtaining brilliant radiation sources. In this work, the excitation of wakefields in double-walled carbon nanotubes is studied by means of the linearized hydrodynamic theory. General expressions have been derived for the excited longitudinal and transverse wakefields and related to the resonant wavenumbers which can be obtained from the dispersion relation. In the absence of friction, the stopping power of the wakefield driver, modelled here as a charged macroparticle, can be written solely as a function of these resonant wavenumbers. The dependencies of the wakefields on the radii of the double-walled carbon nanotubes and the driving velocity have been studied. Double-walled carbon nanotubes with inter-wall distances much smaller than the internal radius may be a potential option to obtain higher wakefields for particle acceleration compared to single-walled carbon nanotubes.

Drive Bunch Train for the Dielectric Trojan Horse Experiment at the Argonne Wakefield Accelerator

The recently demonstrated concept of the plasma photocathode, whereby a high-brightness bunch is initialized by laser ionization within a plasma wakefield acceleration bubble, is informally referred to as Trojan Horse wakefield acceleration. In a similar vein, the dielectric Trojan Horse concept incorporates a dielectric-lined waveguide to support a charged particle beam-driven accelerating mode and uses laser initiated ionization of neutral gas within the waveguide to generate a witness beam. One of the advantages of the dielectric Trojan Horse concept is the reduced requirements in terms of timing precision due to operation at a lower frequency. In this paper, we present experimental results on the generation and characterization of a four-bunch drive train for resonant excitation of wakefields in a cylindrical dielectric waveguide conducted at the Argonne Wakefield Accelerator facility. The results lay the foundation for the demonstration of a plasma photocathode scheme within a dielectric wakefield accelerating structure. Modifications to improve capture efficiency with improved beam transmission are suggested as well.

Nonlinear excitation of wakefields in quantum plasma channel

A detailed analytical study for wakefields excitation in a channel of quantum plasma is presented. The recently developed quantum hydrodynamic (QHD) model has been used to develop the interaction picture. Applying the perturbations in the laser fields orders, the magnetic and electric wakefields have been obtained for a Gaussian laser pulse. The electrons trapped by the wakefields are accelerated to extremely high energies. The quantum effects of Fermi statistical pressure and the quantum Bohm potential have been found to make significant changes in the nature of wakefields generated. The plasma channel helps in self-focusing and also contributes to acceleration. Both the longitudinal and transverse forces acting on the accelerating electron have been calculated.

Magnetic field effects in laser wakefield excitation: a study using Hermite–Gaussian laser pulses in homogeneous plasma

Magnetic field effects in laser wakefield excitation: a study using Hermite–Gaussian laser pulses in homogeneous plasma

Real-time visualization of the laser-plasma wakefield dynamics.

The exploration of new acceleration mechanisms for compactly delivering high-energy particle beams has gained great attention in recent years. One alternative that has attracted particular interest is the plasma-based wakefield accelerator, which is capable of sustaining accelerating fields that are more than three orders of magnitude larger than those of conventional radio-frequency accelerators. In this device, acceleration is generated by plasma waves that propagate at nearly light speed, driven by intense lasers or charged particle beams. Here, we report on the direct visualization of the entire plasma wake dynamics by probing it with a femtosecond relativistic electron bunch. This includes the excitation of the laser wakefield, the increase of its amplitude, the electron injection, and the transition to the beam-driven plasma wakefield. These experimental observations provide first-hand valuable insights into the complex physics of laser beam-plasma interaction and demonstrate a powerful tool that can largely advance the development of plasma accelerators for real-time operation.

Terahertz radiation generation from amplitude-modulated laser filament interaction with a magnetized plasma

The availability of high-power lasers open new frontiers of Terahertz (THz) optics. In this paper, we present a mechanism for the enhanced THz field generation from the laser wakefield excitation during the interaction of an amplitude-modulated laser filament with a magnetized plasma. The derivation of electric and magnetic wakefields in axially magnetized plasma is obtained using the perturbative approach. Amplitude-modulated laser filament generates a significantly stronger transverse current due to laser intensity redistribution by the amplitude modulation. The modulation index of the amplitude modulated laser pulse is used to control the transverse current at THz frequency. Fourfold enhancement takes place in THz field strength for higher values of the modulation index (0–0.4). Also, the conversion efficiency of this mechanism is estimated as [Formula: see text] that can be enhanced for higher modulation index. Scaling laws are provided for controlling and optimization of generated THz field. This work may be crucial in exploring THz optical phenomena such as THz field-induced Kerr effects and many other nonlinear effects.

Generation of meter-scale hydrogen plasmas and efficient, pump-depletion-limited wakefield excitation using 10 GeV electron bunches

High repetition rates and efficient energy transfer to the accelerating beam are important for a future linear collider based on the beam-driven plasma wakefield acceleration scheme (PWFA-LC). This paper reports the first results from the Plasma Wakefield Acceleration Collaboration (E300) that are beginning to address both of these issues using the recently commissioned FACET-II facility at SLAC national accelerator laboratory. We have generated meter-scale hydrogen plasmas using time-structured 10 GeV electron bunches from FACET-II, which hold the promise of dramatically increasing the repetition rate of PWFA by rapidly replenishing the gas between each shot compared to the hitherto used lithium plasmas that operate at 1–10 Hz. Furthermore, we have excited wakes in such plasmas that are suitable for high gradient particle acceleration with high drive-bunch to wake energy transfer efficiency- a first step in achieving a high overall energy transfer efficiency. We have done this by using time-structured electron drive bunches that typically have one or more ultra-high current ( > 30 kA) femtosecond spike(s) superimposed on a longer (∼0.4 ps) lower current ( < 10 kA) bunch structure. The first spike effectively field-ionizes the gas and produces a meter-scale (30–160 cm) plasma, whereas the subsequent beam charge creates a wake. The length and amplitude of the wake depends on the longitudinal current profile of the bunch and plasma density. We find that the onset of pump depletion, when some of the drive beam electrons are nearly fully depleted of their energy, occurs for hydrogen pressure ⩾ 1.5 Torr. We also show that some electrons in the rear of the bunch can gain several GeV energies from the wake. These results are reproduced by particle-in-cell simulations using the QPAD code. At a pressure of ∼2 Torr, simulation results and experimental data show that the beam transfers about 60% of its energy to the wake.

Hydrodynamic Model for Particle Beam-Driven Wakefield in Carbon Nanotubes

The charged particles moving through a carbon nanotube (CNT) may be used to excite electromagnetic modes in the electron gas produced in the cylindrical graphene shell that makes up a nanotube wall. This effect has recently been proposed as a potential novel method of short-wavelength-high-gradient particle acceleration. In this contribution, the existing theory based on a linearized hydrodynamic model for a localized point-charge propagating in a single wall nanotube (SWNT) is reviewed. In this model, the electron gas is treated as a plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the gas. The governing set of differential equations is formed by the continuity and momentum equations for the involved species. These equations are then coupled by Maxwell’s equations. The differential equation system is solved applying a modified Fourier-Bessel transform. An analysis has been realized to determine the plasma modes able to excite a longitudinal electrical wakefield component in the SWNT to accelerate test charges. Numerical results are obtained showing the influence of the damping factor, the velocity of the driver, the nanotube radius, and the particle position on the excited wakefields. A discussion is presented on the suitability and possible limitations of using this method for modelling CNT-based particle acceleration.

Effect of wiggler magnetic field on wakefield excitation and electron energy gain in laser wakefield acceleration

Abstract Laser wakefield acceleration is a frequently utilised research methodology for enhancing the energy levels of lighter charged particles, specifically electrons, to relativistic magnitudes. In this investigation, we utilised a linear polarised Gaussian-like laser pulse that propagated along the z-axis through cold collisionless underdense plasma in weakly nonlinear regime. An external planer magnetic wiggler field is applied along the y-axis. The influence of various critical parameters, such as amplitude and propagation constant of wiggler magnetic field, amplitude of laser electric field and laser pulse length on the wakefield and electron energy gain has been studied. A wiggler-assisted laser wakefield accelerator, the electron energy and wakefield evolution can be tuned by the wiggler magnetic field strength. The numerical findings demonstrate that by varying the strength of wiggler magnetic field and laser electric field, the amplitude of the wakefield is affected significantly. Furthermore, the equality of the order of pulse length and plasma wavelength is essential to obtain energy efficient acceleration mechanism. By employing specific parameters, a maximum energy increase of 2.26 GeV is achieved. This research will aid in the development of an energy-efficient electron acceleration technology by choosing suitable laser and plasma parameters.

EXCITATION OF WAKE SURFACE PLASMON-PHONON OSCILLATIONS BY A RELATIVISTIC ELECTRON BUNCH IN A POLAR SEMICONDUCTOR WAVEGUIDE

The process of surface wakefields excitation by the relativistic electron bunch in a polar semiconductor waveguide with a vacuum channel for electron bunch propagation is studied. The spectra and spatio-temporal structure of the excited surface wakefield in such system are investigated. It is shown that the excited full surface wakefield in the terahertz and infrared frequency ranges consists of the fields of LF and HF hybrid plasmon-phonon oscillations. The amplitudes of them are determined.

REGULARIZATION OF WAKEFIELD IN A WEAKLY NONLINEAR REGIME

In blowout regime of wakefield excitation, strong chaotization of wake occurs. However, for electron-positron colliders and X-ray microscopes, a weakly nonlinear regime is proposed with the formation of a regular short chain of bubbles. To increase the efficiency of the wakefield accelerator, it is necessary that not separate bunches participate. In this paper in 2D plane geometry, the dependence of the number of formed bubbles and their regularization on the degree of wake non-linearity and parameters: driver current, ion mobility, transverse plasma size and profile is studied. We will show that in a weakly nonlinear regime the regular chain of bubbles becomes longer.

Excitation of wakefields in carbon nanotubes: a hydrodynamic model approach

The interactions of charged particles with carbon nanotubes (CNTs) may excite electromagnetic modes in the electron gas produced in the cylindrical graphene shell constituting the nanotube wall. This wake effect has recently been proposed as a potential novel method of short-wavelength high-gradient particle acceleration. In this work, the excitation of these wakefields is studied by means of the linearized hydrodynamic model. In this model, the electronic excitations on the nanotube surface are described treating the electron gas as a 2D plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the gas. General expressions are derived for the excited longitudinal and transverse wakefields. Numerical results are obtained for a charged particle moving within a CNT, paraxially to its axis, showing how the wakefield is affected by parameters such as the particle velocity and its radial position, the nanotube radius, and a friction factor, which can be used as a phenomenological parameter to describe effects from the ionic lattice. Assuming a particle driver propagating on axis at a given velocity, optimal parameters were obtained to maximize the longitudinal wakefield amplitude.

Effect of Frequency Chirp and Pulse Length on Laser Wakefield Excitation in Under-Dense Plasma

Effect of Frequency Chirp and Pulse Length on Laser Wakefield Excitation in Under-Dense Plasma

ELABORATION OF THE PLASMA-DIELECTRIC WAKEFIELD ACCELERATOR WITH A PROFILED SEQUENCE OF DRIVER ELECTRON BUNCHES

A theoretical and experimental study of wakefield excitation by a profiled sequence of relativistic electron bunches in the plasma-dielectric structure, the parameters of which provide the conditions for the excitation of a small decelerating field for all driver bunches with simultaneous growth with the number of bunches of the accelerating total wakefield was carried out. Theoretically, the transformation ratio was found for the parameters of the experiment as the ratio of the total wakefield of the sequence to the field that decelerates driver bunches. In the performed experiments, the total wakefield was measured by the microwave probe. The magnitude of the decelerating field is determined by the shift of the maximum of the spectrum measured by the magnetic analyzer before and after wakefield excitation in the structure. The obtained transformation ratio increases with the number of bunches in the sequence and significantly exceeds this one for a nonprofiled sequence.

SCHEMES FOR ACCELERATION A PART OF ELECTRONS OF DRIVE ELECTRON BUNCHES IN THE DIELECTRIC WAKEFIELD STRUCTURE

The paper presents several schemes for obtaining the main (witness) bunches from a long sequence of electron bunches, as well as from a part of a single electron bunch in the dielectric wakefield structure. The selected part of the electron bunches passes into the accelerating phase of the wake field due to the difference in the geometric path length between the separated electrons and the excited wakefield.

Excitation of the Laser wakefield by asymmetric chirped laser pulse in under dense plasma

Excitation of the Laser wakefield by asymmetric chirped laser pulse in under dense plasma

Numerical study of electron acceleration driven by two-color laser pulses

The use of two-color relativistic femtosecond laser pulses for large-amplitude wakefield excitation and electron acceleration to relativistic energies in very short distances is a promising candidate that has recently been investigated experimentally and numerically by using the particle-in-cell method. Here, we have numerically studied the evolution of a large-amplitude wakefield excited by two-color relativistic femtosecond laser pulses in an underdense plasma. Moreover, the effects of some physical parameters such as two-color pulse polarization and time delay on the wakefield, and the electron acceleration are investigated. The results show that the wakefield amplitude and the energy of the accelerated electrons can be controlled by these parameters. We compare some results with those obtained by applying single-color pulses with similar energy. According to the comparison results, by applying two-color laser pulses, a stronger wakefield and higher electron energies can be obtained. We also show that our results are in good agreement with the experimental data obtained earlier.