Plasma dechirper and lens for electron beams from laser wakefield acceleration in a tailored density profile

TL;DR

This paper demonstrates how plasma density tailoring in laser wakefield accelerators enables control over electron beam quality, including acceleration, shaping, and dechirping, resulting in high-brightness electron beams.

Contribution

First experimental observation of electron beam shaping and dechirping via plasma density tailoring in a gas cell for laser wakefield acceleration.

Findings

Electron beams with 40 pC charge at 190 MeV energy were produced.

Plasma density tailoring enabled control over transverse momentum and energy spread.

Simulations confirmed the role of plasma down-ramps and tails in beam dechirping.

Abstract

Achieving high-quality electron beams from laser wakefield accelerators critically relies on density tailoring to control electron dynamics during injection, acceleration, and extraction. We report on the experimental observation of electron beam acceleration and shaping, in transverse momentum and longitudinal phase space, controlled by plasma density tailoring in a gas cell. Electron beams with a FWHM charge of 40 pC at an energy of 190 MeV, 3.4\% energy spread and an rms divergence of 0.46 mrad, corresponding to a transverse momentum spread of 0.2 $m_e c$, have been measured. These beams have a peak spectral brightness of up to 8 pC/MeV/mrad. Simulations using experimental parameters as input show that acceleration in the plasma plateau leads to chirped electron beams which then undergo transverse momentum spread reduction in a plasma down-ramp followed by dechirping in a 10~mm long plasma tail, leading to the measured peaked spectra. %\textcolor{blue}{A control experiment with and without the LPT confirms these results.} The comparison of experimental results with and without long plasma tail confirms this analysis.