Colliding Pulse Injection Research Articles

Electron beam acceleration using Colliding pulses injection in parabolic plasma channel

optical injection of electrons in laser wakefield accelerator scheme has been shown using the PIC simulation of colliding pulse injection method. Parameter scans like laser polarization, colliding angle, delay and injector pulse intensity have been carried out, to get the optimum values for the injection. To guide the laser pulse over many Rayleigh lengths a parabolic plasma channel is used. For a 45 fs laser pulse of intensity 9 × 1018 W/cm2 focused to spot size of 6 µm inside a plasma of density 4.0 × 1018 cm−3, a highly mono-energetic electron beam with 2.1 pC charge at 337 MeV was obtained.

Effects of slant angle of sharp plasma-vacuum boundary on electron injection in laser wakefield acceleration

Plasma wakefield acceleration driven by ultra short ultra intense laser pulse interacting with gas target has been studied for almost four decades. Monoenergetic electron beams with central energy of multi-giga electron-volt have been achieved in a centimeter-scale acceleration distance. Currently, the highest energy of electrons accelerated by laser wakefield is 8 GeV. In order to further improve the quality of such electrons, many kinds of electron injection schemes have been proposed such as density gradient injection, colliding pulse injection and ionization injection. Electrons under the suitable conditions can be trapped by the strong plasma wakefield. Those trapped electrons are then accelerated in the wakefield. In a nonlinear regime, the wakefield shows a “bubble” structure. Electrons with transverse momentum can oscillate in the wakefield and produce considerably betatron radiation in the ultraviolet and X-ray region. In this paper, we study the electron injection around the sharp plasma-vacuum boundary. The effects of the slant angle of the boundary on the final electron quality are investigated in detail. Our results show that with optimal slant density transition around the vacuum plasma boundary, both the beam quality and the injection charge in the second “bubble” can be improved. Two-dimensional particle-in-cell simulations show that the injection charge in the second wake bucket can be increased three times when an optimal slant angle is used compared with a vertical boundary. The driving pulse’s polarization also affects the injection charge. When the polarization is in the injection plane the injection charge in the first bucket can be triply increased compared with the case when the polarization is out of the plane. The reasons for the enhanced injection charge and transverse oscillation are found by tracing the initial injection positions and trajectories of the electrons. These studies would benefit the electron acceleration and its applications, such as compact betatron radiation source.

Controlled Betatron X-Ray Radiation from Tunable Optically Injected Electrons

The features of Betatron x-ray emission produced in a laser-plasma accelerator are closely linked to the properties of the relativistic electrons which are at the origin of the radiation. While in interaction regimes explored previously the source was by nature unstable, following the fluctuations of the electron beam, we demonstrate in this Letter the possibility to generate x-ray Betatron radiation with controlled and reproducible features, allowing fine studies of its properties. To do so, Betatron radiation is produced using monoenergetic electrons with tunable energies from a laser-plasma accelerator with colliding pulse injection [J. Faure et al., Nature (London) 444, 737 (2006)]. The presented study provides evidence of the correlations between electrons and x-rays, and the obtained results open significant perspectives toward the production of a stable and controlled femtosecond Betatron x-ray source in the keV range.

Injection and acceleration of quasimonoenergetic relativistic electron beams using density gradients at the edges of a plasma channel

The injection of quasimonoenergetic electron beams into a laser wakefield accelerator is demonstrated experimentally using density gradients at the edges of a plasma channel. In the experiment, two laser pulses are used; the main laser pulse drives a wakefield, while a second countercrossing laser beam produces a plasma whose expansion creates a channel with significant density gradients. Local injection of electrons in the wakefield is triggered by wave breaking in the density ramp. The injection is localized spatially and leads to the generation of collimated and narrow energy spread relativistic electron beams at the 100 MeV level, with charges in the range of 20–100 pC. The stability of this injection process is compared to the stability of the colliding pulse injection process and is found to be inferior for our experimental conditions. On the other hand, it is found that as the electron beam divergence is smaller in the case of gradient injection, the transverse emittance might be better.

Laser-driven accelerators by colliding pulses injection: A review of simulation and experimental results

A review of recent simulation and experimental studies of the colliding pulse injection scheme is presented. One dimensional particle in cell simulations show that when the colliding pulses have parallel polarizations, the dominant effects that have to be considered for modeling electron injection in plasma waves are (i) stochastic heating and (ii) wakefield inhibition at the collision. With cross polarized pulses, injection of an electron beam is still possible because stochastic heating still occurs. However, it is found numerically that the injection threshold is higher in this case. The simulations also underline the possibility of tuning the electron beam parameters by modifying the injection laser pulse. Experiments (i) validate these scenarios and show that stable and high quality electron beams are produced when two counterpropagating laser pulses collide in an underdense plasma and (ii) confirm very clearly the existence of a threshold for injection, which is higher with cross polarized pulses than with parallel polarized pulses.

Experiments and Simulations of the Colliding Pulse Injection of Electrons in Plasma Wakefields

In this paper, we report on recent experimental results on electron acceleration using two counterpropagating ultrashort and ultraintense laser pulses. We demonstrate that the use of a second laser pulse provides enhanced control over the injection and subsequent acceleration of electrons into plasma wakefields. The experimental results show that the electron beams obtained in this manner are collimated, monoenergetic, tuneable, and stable. Simulations of the process emphasize the crucial role of kinetic effects and the need for self-consistent models.

Clean beams from laser wake-field accelerators via optical injection with a cleanup pulse

Multiple colliding-pulse injection schemes have been proposed as means for trapping electrons in the ultrashort acceleration buckets of laser-generated wake fields. The primary goal of this paper is to present a parameter study to determine the beams that can be obtained through collisions of collinear laser pulses in uniform plasma. The parameter study is through fully self-consistent, two-dimensional, particle-in-cell simulations, as previous work used only test-particle computations. To remove the multiple beams that can commonly be generated in colliding pulse injection, we use a cleanup pulse, a trailing laser pulse that absorbs the wake. The wake then no longer exists in the region where the trailing beamlets would be, and so the trailing beamlets no longer form. A series of simulations predicts that with such one can obtain single, short (⩽10fs) beams with a bunch charge of order 10pC, normalized emittance of order 2πμm, and energy spread of the order of 10%. The parameters of the beams are insensitive to the amplitude of the backward pulse above normalized amplitudes of abw≈0.4.