Abstract
Laser wakefield accelerators rely on relativistically moving micron-sized plasma cavities that provide extremely high electric field >100GV/m. Here, we demonstrate transverse shaping of the plasma cavity to produce controlled sub-GeV electron beams, adopting laser pulses with an axially rotatable ellipse-shaped focal spot. We showed the control capability on electron self-injection, charge, and transverse profile of the electron beam by rotating the focal spot. We observed that the effect of the elliptical focal spot was imprinted in the profiles of the electron beams and the electron energy increased, as compared to the case of a circular focal spot. We performed 3D particle-in-cell (PIC) simulations which reproduced the experimental results and revealed dynamics of a new asymmetric self-injection process. This simple scheme offers a novel control method on laser wakefield acceleration to produce tailored electron beams and x-rays for various applications.
Highlights
The laser wakefield acceleration (LWFA) has attracted attention intensively since its conception [1,2,3] as a potential alternative to the conventional technology for developing a compact TeV electron-positron collider [4] and ultrashort bright x-ray sources [5]
We report here demonstration of stable sub-GeV quasimonoenergetic electron beams with enhanced energy and tailored transverse profile from LWFA driven by a laser pulse with an ellipse-shaped focal spot
The LWFA experiment was initially carried out without the elliptic aperture and reproducible electron beams were obtained from self-injected LWFA at plasma density, ne ≈ 1 × 1019 cm−3 from 2.3 ± 0.1-mm-long plasma channel
Summary
The laser wakefield acceleration (LWFA) has attracted attention intensively since its conception [1,2,3] as a potential alternative to the conventional technology for developing a compact TeV electron-positron collider [4] and ultrashort bright x-ray sources [5]. Nearly 10-GeV electron beams have been demonstrated through LWFA from 10cm scale plasma with a petawatt laser pulse [6,7]. LWFA exploits strong wakefields ( 100 GV/m) in plasma excited by the ponderomotive force (Fp) of an intense laser pulse. The ponderomotive force (Fp ∝ −∇IL, where IL is laser intensity) of a focused short-pulse laser displaces plasma electrons in all directions, while heavier ions stay behind. At sufficiently high intensity the laser pulse induces nonlinear plasma wave breaking which causes self-injection of elec-
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