Observation of laser plasma accelerated electrons with transverse momentum spread below the thermal level

TL;DR

This paper reports the experimental creation of high-quality, relativistic electron beams with transverse momentum spread below thermal levels, achieved through plasma density tailoring in laser-plasma accelerators, enhancing beam quality and control.

Contribution

It demonstrates the first experimental observation of electron beams with sub-thermal transverse momentum spread controlled by plasma density tailoring.

Findings

Transverse momentum spread of 0.2 mec achieved

Electron beams with 190 MeV energy and 1.9% energy spread produced

Numerical simulations reveal momentum spread reduction in plasma tail

Abstract

Achieving high-quality electron beams from laser-plasma 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 3D shaping, in transverse momentum and longitudinal phase space, controlled by plasma density tailoring in a gas cell. It leads to relativistic electron beams with a transverse momentum spread of 0.2 mec, below the thermal level imprinted by the process of ionization injection in a laser-driven wakefield accelerator. These beams have a charge of 40 pC at an energy of 190 MeV with 1.9% energy spread and an rms divergence of 0.54 mrad, resulting in single-peak spectra with a brightness of up to 8 pC/MeV/mrad. Using numerical simulations, we show that the decrease in transverse momentum spread starts in the downramp and continues in a 10 mm long plasma tail at the exit of the gas cell, where it is accompanied by energy dechirping.