Plasma Wake Wave Research Articles

Laser driven wake wave in pair-ion electron plasma with inclusion of ion dynamics

The generation of laser driven plasma wake wave has been investigated in hydrogen pair-ion electron plasma. The consideration of dynamics of the positive and negative ion pair have been adopted. Inclusion of the ion motion has the effect of modifying the electric field and density profiles of the wake wave. This has been demonstrated by observing the variation of the electron density and electric field profiles with the change in positive ion/negative ion concentration. High density spikes and sawtooth like electric field profiles (indication of wave breaking) are observed to transform into sinusoidal electric field profile and low amplitude density profile when the positive ion density in the plasma system is kept higher. Furthermore, we observe the variation of the electric field amplitude of the wake wave with the laser pulse width. This feature is the indication of the possibility of hybrid acceleration (Direct Laser Acceleration and wake field acceleration) of accelerated beam. The results are quite relevant in laser plasma interaction field in experimental physics and also in planetary environment.

Beam current from downramp injection in electron-driven plasma wakefields

We study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser–wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimised by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density.

WAKE EXCITATION OF PLASMA AND ELECTROMAGNETIC OSCILLATIONS BY A RELATIVISTIC ELECTRON BUNCH IN A PLASMA RESONATOR

The process of the excitation of plasma and electromagnetic oscillations by a relativistic electron bunch in a plasma resonator is considered. It is shown that the potential electric field of plasma oscillations contains the field of a bulk wake plasma wave and the fields of two surface plasma oscillations. Surface plasma oscillations are localized in the vicinity of the input and output ends of the plasma resonator. In a plasma resonator, as a result of the effect of transition radiation at the ends of the resonator, the electron bunch will also excite eigen electromagnetic oscillations of the resonator. The spatio-temporal structure of the electromagnetic field of these oscillations has been studied.

Excitation of upper‐hybrid plasma wake wave by a low‐frequency extraordinary electromagnetic wave

AbstractThe excitation of upper‐hybrid wake electrostatic wave by interaction of an extraordinary Gaussian wave propagating perpendicular to the external magnetic field in a cold homogeneous plasma is investigated using magnetohydrodynamics theory. The plasma oscillations can be excited due to the charge separation appeared by the ponderomotive force of the electromagnetic wave whose frequency is considered in the lower pass band. By obtaining the equation governing the plasma wake, the dependency of the wake amplitude on the physical parameters is studied. It is observed that larger wake oscillation takes place when the pulse length is approximately close to 3λp/π and the X‐wave frequency is greater than ωp, which means that the phase velocity is less than the speed of light in vacuum (vp < c).

Generation of Multipetawatt Laser Pulses with a Small Number of Field Oscillations

We propose a method for two-stage compression of laser pulses, which makes it possible to shorten laser pulses of tens of picoseconds to an optical period with an energy efficiency of tens of percent. The method involves sequential use of the Raman compression (compression to a duration of tens of femtoseconds and the self-compression of the pulse to the field period when exciting the wake plasma wave. In this case, the seed pulse is focused to the input of the second gas jet to achieve the relativistic intensity required for the self-compression realization when exciting the plasma wave.

Acceleration of electrons in the interaction of a subterawatt laser pulse with a nonuniform plasma

We consider the effect of nonlinear self-focusing and self-modulation processes on the acceleration of electrons in the interaction of a subterawatt femtosecond laser pulse with a gas jet plasma. A three-dimensional particle-in-cell (3D PIC) simulation of the interaction of laser radiation with a low-density nonuniform plasma shows that laser pulse self-focusing that arises when the critical power of relativistic self-focusing determined by the local concentration of plasma electrons exceeds the pulse power results in efficient generation of a plasma wave. Due to a decrease in the phase velocity of the wake plasma wave generated via self-modulation of the laser pulse, electrons are trapped into the accelerating phase of the plasma wave and are accelerated to energies of ∼10 MeV. It is demonstrated that under the conditions for limiting the electrons’ acceleration region by the length of their dephasing, quasi-monoenergetic electron bunches with a characteristic energy of ∼9 MeV can be produced. The effective temperature of the accelerated electrons and their angular distribution, obtained by 3D PIC simulation, are in good agreement with those determined in the experiment.

Effect of laser pulse self-focusing on plasma wave generation in the interaction of subterawatt laser pulse with a plasma jet

The wake plasma waves generated by high intensity laser pulses are of interest for acceleration of electrons to high energies. The aim of this work is to study the effect of self-focusing of a laser pulse on the plasma wakefields generation. Calculations were performed using the three-dimensional particle-in-cell method. When the laser pulse in the process of propagation in inhomogeneous plasma reaches the region where the pulse power exceeds a critical value for self-focusing, the laser pulse is self-focused and a steepening of the leading edge of the pulse increases. These processes lead to self-modulation instability and generation of a wake plasma wave.

Dependence of plasma wake wave amplitude on the shape of Gaussian chirped laser pulse propagating in a plasma channel

The generation of longitudinal electrostatic plasma waves (wakefields) due to the propagation of a chirped laser pulse through a parabolic plasma channel is studied. The wakes generated by a temporally symmetric Gaussian laser pulse are compared with those generated by asymmetric one. The main interest in this paper is to investigate the effects of a laser pulse shape with of sharp rising and slow falling time scales on the excited wakefield amplitude. Moreover, positive, negative and un-chirped laser pulses are employed in numerical codes to evaluate the influence of the initial chirp on wakefield excitation. Numerical results showed that for an appropriate laser pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced for a positively chirped asymmetric Gaussian laser pulse with a fast rise time.

Interference in multilayer relativistic mirrors

In this paper, reflection coefficient of a relativistic ultra-thin electron multilayer is calculated using electromagnetic interference procedures. The relativistic electron layers are assumed to be formed by nonlinear plasma wake waves that constitute the electron density cusps. It is shown that the interference between successive relativistic mirrors is restricted by the condition, τp≫(2γ0)5/2/ωp0, where τp is the laser pulse duration. The results showed that tailoring the pulse amplitude, incident wave frequency value, incidence angle, and plasma density leads to increasing reflection coefficient a few orders of magnitudes. This constructive interference condition can be used for increasing conversion efficiency in the reflected energy from relativistic mirrors for the purpose of generating ultra-short coherence pulses in the extreme ultraviolet and x-ray regions. We also performed reflection from relativistic thin electron layers using relativistic 1D3V electromagnetic particle-in-cell (PIC) simulation. It was found that the results of PIC simulation are in agreement with analytical considerations.

Photon acceleration in plasma wake wave

The photon acceleration effect in a laser wake field is investigated based on photon Hamiltonian dynamics. A test laser pulse is injected into a plasma wave at an incident angle θi, which could slow down the photon velocity along the propagating direction of the wake wave so as to increase the acceleration distance for the photons. The photon trapping condition is analyzed in detail, and the maximum frequency shift of the trapped photon is obtained. The acceleration gradient and dephasing length are emphatically studied. The compression of the test laser pulse is examined and used to interpret the acceleration process. The limit of finite transverse width of the wake wave on photon acceleration is also discussed.

Optimization of the regime of shortening of relativistically strong laser pulses in the process of excitation of a plasma wake wave

A detailed theoretical investigation is performed for the self-compression of relativistically strong laser pulses under plasma wake wave excitation conditions. An analytical expression is obtained for the characteristic length of laser pulse self-compression in the one-dimensional case. A good agreement between the theoretical and numerical calculation of the dependence of the wave-packet compression length on both amplitude and plasma concentration is demonstrated. The influence of the wave beam self-focusing radiation process on the rate of shortening of the laser pulse duration is considered.

Hose instability of relativistically strong femtosecond laser pulses with few field oscillations in a plasma under the excitation of a plasma wake wave

A detailed theoretical analysis is carried out of the hose instability of relativistically strong laser pulses propagating in a plasma, whose duration is less than the period of a plasma wake wave. An analytic expression is obtained for the displacement of the mass center of a wave pulse, and the effect of this instability on the modification of the spectrum of laser radiation is analyzed for a wide range of initial parameters. It is shown that the development of instability is characterized by a power-law (rather than exponential) time dependence along the propagation path and does not deteriorate the self-compression of laser pulses.

Nonlinear plasma wave in magnetized plasmas

Nonlinear axisymmetric cylindrical plasma oscillations in magnetized collisionless plasmas are a model for the electron fluid collapse on the axis behind an ultrashort relativisically intense laser pulse exciting a plasma wake wave. We present an analytical description of the strongly nonlinear oscillations showing that the magnetic field prevents closing of the cavity formed behind the laser pulse. This effect is demonstrated with 3D PIC simulations of the laser-plasma interaction. An analysis of the betatron oscillations of fast electrons in the presence of the magnetic field reveals a characteristic “Four-Ray Star” pattern.

Excitation of large amplitude wake electron oscillations in adiabatic plasma

AbstractElectron plasma waves excited and/or modified by finite objects such as laser and charged particle pulses are investigated nonperturbatively using a simple model where the driver is unaffected by the interaction. It is shown that smooth as well as sharply peaked electron plasma wake waves of large amplitude can exist. In particular, two charged pulses moving in tandem can excite a highly localized electron plasma wave without producing the expected long wake wave, a configuration that should be particularly useful for efficient trapping and acceleration of electrons to high energies.

Self-compression of relativistically strong femtosecond laser pulses during the excitation of a plasma wake wave

A new concept of the development of plasma compressor for generation of extremely short, relativistically strong femtosecond pulses at a petawatt power level is proposed. The considered compression mechanism is based on the non-stationary self-focusing of a spatially confined wave packet in transparent plasma during the excitation of a plasma wake wave with a period exceeding the laser pulse duration. It is shown that by using appropriately shaped, strong short laser pulses even shorter pulses (with durations up to one optical cycle of the field) can be generated with intensities much greater (>10 times) than the incident pulse with a significant fraction (∼25%) of incident pulse energy.

Optimum conditions of the plasma density for the generation of the maximum bunch charge in a laser wakefield accelerator

The effects of plasma density on the bunch charge in a laser wakefield accelerator were investigated by using experiments and simulations. We used an energy spectrometer and Integrating Current Transformer (ICT) to measure the energy and the charge of a quasi-monoenergetic electron bunch. Also, the plasma density was measured using a biprism interferometer. The measured electron energy showed that the electron energy decreased with increasing plasma density due to the dephasing effect. The results of the bunch charge measurement showed that the effect of the plasma density on the bunch charge could be separated into two different density regions. In the low-density region (cτ/λp 2), the bunch charge decreased with increasing plasma density. Thus, an optimum plasma density to generate a high bunch charge exists. Particle-in-cell simulations show that multi-cavitation of the plasma wake wave results in maximum generation of the bunch charge in a laser wakefield accelerator.

Feasibility study of the plasma electron density measurement by electromagnetic radiation from the laser-driven plasma wave

When an intense laser beam is focused in a plasma, a plasma wake wave is generated and the oscillatary motion of the plasma electrons produces a strong electromagnetic wave by a Cherenkov-like process. Spectrum of the genetated electromagnetic wave has dependence on the plasma density. In this paper, we propose to use the emitted electromagnetic radiation for plasma diagnostic, which may provide an accurate information for local electron densities of the plasma and will be very useful for three-dimensional plasma density profiles by changing the focal point location of the laser beam. Two-dimensional (2-D) particle-in-cell (PIC) simulation is used to study the correlation between the spectrum of the emitted radiation and plasma density, and the results demonstrate that this method is promising for the electron density measurement in the plasma.

Quasistationary wake plasma wave excited by a comoving charged pulse

Fully nonlinear quasistationary wake plasma waves excited by and comoving with a charged pulses are investigated. The characteristics of the excited plasma wave depend on a (nonlinear) resonance between the wave and the pulse. With two comoving driver pulses, localized wake structures without the long wakes can be produced.

Propagation of the high power laser pulse in multicomponent cluster targets

We present the results of 3D PIC and 2D PIC simulations of the ultra short high irradiance laser pulse interaction with targets where the plasma containing multicomponent cluster targets and multicluster cloud is imbedded in an underdense plasma. In both cases the laser radiation expels the electrons from the clusters and ejects them into the wake plasma wave generated by the ultrashort laser pulse in the underdense plasma. This provides a novel mechanism for the electron injection into the wake field for acceleration.

Demonstration of Laser-Frequency Upshift by Electron-Density Modulations in a Plasma Wakefield

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counterpropagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counterpropagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 114) was detected in our experiment.