Plasma 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.

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.

Self consistent hydrodynamic description of the plasma wake field excitation induced by a relativistic charged-particle beam in an unmagnetized plasma

A self-consistent nonlinear hydrodynamic theory is presented of the propagation of a long and thin relativistic electron beam, for a typical plasma wake field acceleration configuration in an unmagnetized and overdense plasma. The random component of the trajectories of the beam particles as well as of their velocity spread is modelled by an anisotropic temperature, allowing the beam dynamics to be approximated as a 3D adiabatic expansion/compression. It is shown that even in the absence of the nonlinear plasma wake force, the localisation of the beam in the transverse direction can be achieved owing to the nonlinearity associated with the adiabatic compression/rarefaction and a coherent stationary state is constructed. Numerical calculations reveal the possibility of the beam focussing and defocussing, but the lifetime of the beam can be significantly extended by the appropriate adjustments, so that transverse oscillations are observed, similar to those predicted within the thermal wave and Vlasov kinetic models.

Plasma wakefield excitation in a cold magnetized plasma for particle acceleration

A numerical study has been done to find a travelling wave solution for a highly relativistic electron beam driven cold magnetized plasma. The presence of magnetic field has an effect to reduce the transformer ratio (the ratio of energy gain to the drive beam energy) from its unmagnetized value. The effects of the beam shape on the nonlinear structures of different dynamical variables are also discussed. The results owe its significance in the laboratory context of particle acceleration or in the study of generation of ultrahigh accelerating charged particles by strong plasma waves in astrophysical situations.

Self-modulated dynamics of a relativistic charged particle beam in plasma wake field excitation

The self-modulated dynamics of a relativistic charged particle beam is provided within the context of the theory of plasma wake field excitation. The self-consistent description of the beam dynamics is provided by coupling the Vlasov equation with a Poisson-type equation relating the plasma wake potential to the beam density. An analysis of the beam envelope self-modulation is then carried out and the criteria for the occurrence of the instability are discussed thereby.

The concept of coupling impedance in the self-consistent plasma wake field excitation

Within the framework of the Vlasov–Maxwell system of equations, we describe the self-consistent interaction of a relativistic charged-particle beam with the surroundings while propagating through a plasma-based acceleration device. This is done in terms of the concept of coupling (longitudinal) impedance in full analogy with the conventional accelerators. It is shown that also here the coupling impedance is a very useful tool for the Nyquist-type stability analysis. Examples of specific physical situations are finally illustrated.

Vlasov’s kinetic theory of the collective charged particle beam transport through a magnetized plasma in the strongly nonlocal regime

Within the Vlasov’s kinetic theory, describing the plasma wake field interaction, the collective transport of a warm nonlaminar relativistic charged particle beam is analyzed in the strongly nonlocal regime, where the beam spot-size is much less than the plasma wavelength. This is done in the overdense regime, i.e., the beam density is much less than the plasma density. The beam is supposed to be sufficiently long to experience the adiabatic shielding by the plasma. In these conditions, we neglect the longitudinal beam dynamics and focus on the transverse one only. We derive the virial description (envelope description) from the 2D Vlasov-Poisson-type system of equations that governs the transverse self-consistent plasma wake field excitation. The resulting envelope equation is then reduced, in the aberration-less approximation, to a differential equation for the beam spot size, where the role of the ambient magnetic field is evaluated in both laboratory and astrophysical environments. An analysis of the beam envelope self-modulation is then carried out and the criteria for the occurrence of the instability are found.

The plasma wake field excitation: Recent developments from thermal to quantum regime

AbstractTo describe the transverse nonlinear and collective self-consistent interaction of a long relativistic electron or positron beam with an unmagnetized plasma, a pair of coupled nonlinear differential equations were proposed by Fedele and Shukla in 1992 (Fedele, R. and Shukla, P. K. 1992a Phys. Rev. A 45, 4045). They were obtained within the quantum-like description provided by the thermal wave model and the theory of plasma wake field excitation. The pair of equations comprises a 2D Schrödinger-like equation for a complex wave function (whose squared modulus is proportional to beam density) and a Poisson-like equation for the plasma wake potential. The dispersion coefficient of the Schrödinger-like equation is proportional to the beam thermal emittance. More recently, Fedele–Shukla equations have been further applied to magnetized plasmas, and solutions were found in the form of nonlinear vortex states and ring solitons. They have been also applied to plasma focusing problems and extended from thermal to quantum regimes. We present here a review of the original approach, and subsequent developments.

Self-modulation of a long externally injected relativistic charged-particle beam in a laser wake field acceleration scheme. A preliminary quantum-like investigation

Recent investigations indicate that sufficiently long beams of charged particles, travelling in a plasma, experience the phenomenon of self-modulation. The self-modulation is driven by the plasma wake field excitation due to the beam itself, and it may become unstable under certain conditions. A preliminary theoretical investigation of the self-modulation of a relativistic charged-particle beam in overdense plasma in the presence of a preformed plasma wave is carried out, within the quantum-like description of charged particle beams provided by the Thermal Wave Model. A simple physical model for the self-modulation is put forward, described by a nonlinear Schrödinger equation coupled with the Poisson-like equation for the plasma wake potential (so-called Fedele–Shukla equations). The physical mechanism is based on the interplay of three concomitant effects, the radial thermal dispersion (associated with the emittance ε), the radial ponderomotive effects of a preexisting plasma wave (which provides the guidance for the beam), and the self-interaction of the plasma wake field generated by the beam itself.

A plasma wakefield acceleration experiment using CLARA beam

We propose a Plasma Accelerator Research Station (PARS) based at proposed FEL test facility CLARA (Compact Linear Accelerator for Research and Applications) at Daresbury Laboratory. The idea is to use the relativistic electron beam from CLARA, to investigate some key issues in electron beam transport and in electron beam driven plasma wakefield acceleration, e.g. high gradient plasma wakefield excitation driven by a relativistic electron bunch, two bunch experiment for CLARA beam energy doubling, high transformer ratio, long bunch self-modulation and some other advanced beam dynamics issues. This paper presents the feasibility studies of electron beam transport to meet the requirements for beam driven wakefield acceleration and presents the plasma wakefield simulation results based on CLARA beam parameters. Other possible experiments which can be conducted at the PARS beam line are also discussed.

The quantum plasma lens concept: A preliminary investigation

AbstractRecently, a theoretical investigation of the collective and nonlocal quantum effects has been carried out within the framework of a quantum approach to the relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma. This has been done taking into account both the plasma wake field excitation and the quantum paraxial approximation. On the basis of this theory, here we carry out a preliminary study of the transverse effects experienced by a cold relativistic beam through a thin plasma slab (plasma lens). In the strongly nonlocal regime, in which the beam experiences a very strong focusing effect, the scheme of plasma lens is reviewed in terms of the wave description provided by the above quantum theory.

Quantum ring solitons and nonlocal effects in plasma wake field excitations

A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (single-particle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poisson-like equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schrödinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of Laguerre-Gauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D Gross-Pitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatio-temporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent breathing, but it remains very stable for long time.

Plasma wakefield excitation with a 24 GeV proton beam

Proton driven plasma wakefield acceleration has recently been proposed as a means of generating high energy electron beams. In this paper, different options for a demonstration experiment with the CERN PS beam are considered. We review a possible magnetic compression of the PS bunches and resulting electric fields in the plasma. Results are then presented for self-modulation of the proton bunch for different plasma densities and lengths. It is found that the latter option offers interesting possibilities for a first experiment.

The optimum plasma density for plasma wakefield excitation in the blowout regime

The optimum plasma density for achieving the largest wakefield accelerating gradient in a plasma wakefield accelerator (PWFA) for a given electron beam driver parameters (fixed charge, spot size and duration) is analyzed. It is found that the peak beam current Ip (charge per unit time) plays an important role in determining the optimum density. We show that for narrow beams of low peak current (Ip≪IA≈17 kA and σr≪σz), the prediction from linear theory (Lu et al 2005 Phys. Plasma12 063101) that or np(cm−3)≈5.6×1019/σz2 (μm) for a bi-Gaussian bunch of length σz and spot size σr, works well for obtaining the maximum accelerating gradient. However, for narrow beams of high peak current (Ip≳IA and σr≪σz), the optimum density can be an order of magnitude larger than that predicted by linear theory. In this regime, we show that a new condition np∼nb0 should be used for 1≲σz/σr≲10, where nb0 is the peak beam density. Theoretical arguments for this new condition are given and the predictions are confirmed by particle-in-cell (PIC) simulations.

Basic concepts in plasma accelerators

In this article, we present the underlying physics and the present status of high gradient and high-energy plasma accelerators. With the development of compact short pulse high-brightness lasers and electron and positron beams, new areas of studies for laser/particle beam-matter interactions is opening up. A number of methods are being pursued vigorously to achieve ultra-high-acceleration gradients. These include the plasma beat wave accelerator (PBWA) mechanism which uses conventional long pulse ( approximately 100 ps) modest intensity lasers (I approximately 10(14)-10(16) W cm(-2)), the laser wakefield accelerator (LWFA) which uses the new breed of compact high-brightness lasers (<1 ps) and intensities >10(18) W cm(-2), self-modulated laser wakefield accelerator (SMLWFA) concept which combines elements of stimulated Raman forward scattering (SRFS) and electron acceleration by nonlinear plasma waves excited by relativistic electron and positron bunches the plasma wakefield accelerator. In the ultra-high intensity regime, laser/particle beam-plasma interactions are highly nonlinear and relativistic, leading to new phenomenon such as the plasma wakefield excitation for particle acceleration, relativistic self-focusing and guiding of laser beams, high-harmonic generation, acceleration of electrons, positrons, protons and photons. Fields greater than 1 GV cm(-1) have been generated with monoenergetic particle beams accelerated to about 100 MeV in millimetre distances recorded. Plasma wakefields driven by both electron and positron beams at the Stanford linear accelerator centre (SLAC) facility have accelerated the tail of the beams.

Charged particle acceleration by an intense wake-field excited in plasmas by either laser pulse or relativistic electron bunch

The results from theoretical and experimental studies, as well as from 2.5-dimensional (2.5-D) numerical simulation of plasma wake field excitation, by either relativistic electron bunch, laser pulse, and the charged particle wake field acceleration are discussed. The results of these investigations make it possible to evaluate the potentialities of the wake field acceleration method and to analyze whether it can serve as a basis for creating a new generation of devices capable of charged particle accelerating at substantially higher (on the order of two to three magnitudes) rates in comparison with those achievable in classical linear high-frequency (resonant) accelerators.

Propagation of ultra-short, intense laser pulses in air

Recent theoretical, computational, and experimental work carried out at the Naval Research Laboratory on the propagation of ultra-short laser pulses in air is presented. Fully time-dependent, three-dimensional, nonlinear equations describing the propagation of laser pulses in air under the influence of diffraction, group velocity dispersion, Kerr nonlinearity, stimulated Raman scattering, ionization, and plasma wakefield excitation are presented and analyzed. The propagation code, HELCAP [P. Sprangle, J. R. Peñano, and B. Hafizi, Phys. Rev. E 66, 046418 (2002)], is used to simulate the propagation of laser pulses in air under the influence of the physical processes mentioned above. Simulations of laser filamentation together with experimental measurements are used to confirm that the filamentation process is dependent on pulse duration. An equilibrium configuration for optical and plasma filaments in air is derived and the dynamic guiding and spectral broadening of a laser pulse is modeled. The effect of atmospheric turbulence on nonlinear self-focusing is demonstrated. Simulations of a recent electromagnetic pulse (EMP) generation experiment are also presented and the efficiency of EMP generation is determined and found to be extremely small.

Plasma wake-field excitation by relativistic electron bunches and charged particle acceleration in the presence of external magnetic field

High-amplitude plasma wake waves are excited by high-density relativistic electron bunches (REB) moving in a plasma. The wake-fields can be used to accelerate charged particles, to serve as electrostatic wigglers in plasma free-electron lasers (FEL), and also can find many other applications. The electromagnetic fields in the region occupied by the bunch control the dynamics of the bunch itself. This paper presents the results of 2.5-dimensional numerical simulation of the modulation of a long REB in a plasma, the excitation of wake-fields by bunches in a plasma, in particular, in magnetoactive plasma. The previous one-dimensional study has shown that the density-profile modulation of a long bunch moving in plasma results in the growth of the coherent wake-wave amplitude. The bunch modulation occurs at the plasma frequency. The present study is concerned with the REB motion, taking into account the plasma and REB nonlinearities. It is demonstrated that the nonlinear REB/plasma dynamics exerts primary effect on both the REB self-modulation and the wake-field excitation by the bunches formed. We have demonstrated that a multiple excess of the accelerated bunch energy εmax over the energy of the exciting REB is possible in a magnetoactive plasma for a certain relationship between the parameters of the “plasma–bunch–magnetic field” system (owing to a hybrid volume–surface character of REB-excited wake-fields).

Plasma-wakefield acceleration of a positron beam.

Plasma-wakefield excitation by positron beams is examined in a regime for which the plasma dynamics are highly nonlinear. Three dimensional particle-in-cell simulations and physical models are presented. In the nonlinear wake regime known as the blowout regime for electrons, positron wakes exhibit an analogous "suck-in" behavior. Although analogous, the two wakefield cases are quite different in terms of their amplitudes, wavelengths, waveforms, transverse profiles, and plasma density dependence. In a homogenous plasma, nonlinear positron wakes are smaller than those of the corresponding electron case. However, hollow channels are shown to enhance the amplitude of the positron wakes.

Dynamic effects in plasma wakefield excitation

We have used 2D cylindrically symmetric particle-in-cell simulations to investigate the dynamics of a high energy electron beam propagating through an underdense plasma. The simulation parameters are relevant to a recent plasma wakefield experiment conducted at the Stanford Linear Accelerator Center [R. Assmann et al., Stanford Linear Accelerator Center Proposal, 1997]. We model the dynamic development of the beam and wakefield excitation over meters of propagation length. To most clearly illustrate the dynamics of both the beam and the wakefield, a video of the simulation data is presented. The main observation is that the beam dynamics, i.e., its betatron motion in the resulting ion channel, agree well with the theoretical predictions while the plasma wake remains almost invariant over the entire propagation distance. The video illustrates subtle details regarding the interplay between the beam dynamics and wakefield generation. The results presented here complement results published separately [S. Lee et al., Phys. Rev. E 61, 7014 (2000)].