Abstract
We propose a novel injection scheme for laser-driven wakefield acceleration in which controllable localized electron injection is obtained by inserting nanoparticles into a plasma medium. The nanoparticles provide a very confined electric field that triggers localized electron injection where nonlinear plasma waves are excited but not sufficient for background electrons self-injection. We present a theoretical model to describe the conditions and properties of the electron injection in the presence of nanoparticles. Multi-dimensional particle-in-cell (PIC) simulations demonstrate that the total charge of the injected electron beam can be controlled by the position, number, size, and density of the nanoparticles. The PIC simulation also indicates that a 5-GeV electron beam with an energy spread below 1% can be obtained with a 0.5-PW laser pulse by using the nanoparticle-assisted laser wakefield acceleration.
Highlights
Laser wakefield acceleration (LWFA) is a promising method to realize compact high-energy electron accelerators because of its significant acceleration field beyond 1 GV/cm[1]
From 3D PIC simulations, we obtained the energy spread of 14% when 50 nanoparticles were located within 10 μm with a background plasma density of 7 × 1018 cm−3, corresponding to the plasma wavelength of 12 μm, while it was 11% with a single nanoparticle placed on axis
We investigated the nanoparticle-assisted electron injection method by performing PIC simulations and formulating an analytical model for the injection characteristics
Summary
Laser wakefield acceleration (LWFA) is a promising method to realize compact high-energy electron accelerators because of its significant acceleration field beyond 1 GV/cm[1]. To overcome the limitations of self-injection, various electron injection methods have been proposed using colliding laser pulses[14,15,16,17], density gradients[7,18,19], inner-shell ionization[16,20,21], and external magnetic fields[22] These methods suffer from issues such as disturbed acceleration process, difficulties in controlling the charge and energy spread, and poor injection position stability. The plasma density should be higher than the threshold for self-injection at a given laser power, which limits the possible acceleration length This conflicting behavior between the electron injection and acceleration process restricts the enhancement of electron energy. When the attracted electrons reach the trailing part of the wakefield, as shown in Fig. 1c, the electrons with a sufficient momentum are injected into the plasma wave
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