Multistage Coupling of Laser-Wakefield Accelerators with Curved Plasma Channels

Multistage coupling of laser-wakefield accelerators is essential to overcome laser energy depletion for high-energy applications such as TeV-level electron-positron colliders. Current staging schemes feed subsequent laser pulses into stages using plasma mirrors while controlling electron beam focusing with plasma lenses. Here a more compact and efficient scheme is proposed to realize the simultaneous coupling of the electron beam and the laser pulse into a second stage. A partly curved channel, integrating a straight acceleration stage with a curved transition segment, is used to guide a fresh laser pulse into a subsequent straight channel, while the electrons continue straight. This scheme benefits from a shorter coupling distance and continuous guiding of the electrons in plasma while suppressing transverse beam dispersion. Particle-in-cell simulations demonstrate that the electron beam from a previous stage can be efficiently injected into a subsequent stage for further acceleration while maintaining high capture efficiency, stability, and beam quality.

Figure 1

Schematic diagram of coupling two LWFA acceleration stages via a curved plasma channel with trajectories of fresh lasers (red), depleted lasers (yellow), and electrons (green).

Figure 2

Centroid trajectories of a laser injected at different positions from a TDSE and PIC simulation in a curved plasma channel with a fixed curvature radius (a) and the proposed transition curvature (c) with ${\lambda }_l=0.8\mu \mathrm{m}$, $w_0=8\mu \mathrm{m}$, $R_0=10\mathrm{mm}$, and $n_0={10}^{-3}{n}_{\mathrm{cr}}$. Dashed lines represent the center of channels (black) and the laser equilibrium trajectory (red), respectively. A snapshot from a 2D PIC simulation in (b) shows the laser profile for injection into a straight channel. All results account for relativistic laser intensity effects, except the black solid line in (a).

Figure 3

2D PIC simulations of the multistage coupling scheme based on curved plasma channels. (a) Centroid trajectory of laser I (yellow), laser II (red), and the electron beam (green). Insets (b) and (c) show the electric field of laser II, plasma electron density, injected electrons (red points), and their charge distribution (red lines) at two propagation distances.

Figure 4

(a) Evolution of the injected electron beam energy (blue) and transverse momentum (red). (b) and (c) are, respectively, the initial (black points) and final (blue points) distributions of the electron beam longitudinal and transverse momentum and their Gaussian fitting curves (red). The injection ratio of finally accelerated electrons with different transverse (black) or longitudinal (red) offsets of initial electron beam position (d) and different preaccelerated electron beam energy (e).