Abstract
Self-injection in a laser-plasma wakefield accelerator is usually achieved by increasing the laser intensity until the threshold for injection is exceeded. Alternatively, the velocity of the bubble accelerating structure can be controlled using plasma density ramps, reducing the electron velocity required for injection. We present a model describing self-injection in the short-bunch regime for arbitrary changes in the plasma density. We derive the threshold condition for injection due to a plasma density gradient, which is confirmed using particle-in-cell simulations that demonstrate injection of subfemtosecond bunches. It is shown that the bunch charge, bunch length, and separation of bunches in a bunch train can be controlled by tailoring the plasma density profile.
Highlights
Self-injection in a laser-plasma wakefield accelerator is usually achieved by increasing the laser intensity until the threshold for injection is exceeded
Considerable research effort is currently focused on the development of laser-plasma wakefield accelerators (LWFA) as sources of high-quality, ultrashort electron bunches [1–5] and as potential drivers of free-electron lasers (FELs) [6,7] and tabletop plasma-based light sources [8–13]
We show how arbitrary plasma density gradients give rise to changes in the phase velocity of the bubble that can lead to injection
Summary
Considerable research effort is currently focused on the development of laser-plasma wakefield accelerators (LWFA) as sources of high-quality, ultrashort electron bunches [1–5] and as potential drivers of free-electron lasers (FELs) [6,7] and tabletop plasma-based light sources [8–13]. Towards Attosecond High-Energy Electron Bunches: Controlling Self-Injection in Laser-Wakefield Accelerators Through Plasma-Density Modulation The velocity of the bubble accelerating structure can be controlled using plasma density ramps, reducing the electron velocity required for injection.
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