Enhanced single-stage laser-driven electron acceleration by self-controlled ionization injection.

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• Particle Acceleration

Background:

• Laser wakefield acceleration (LWFA) is a promising technique for generating high-energy electron beams.
• Traditional LWFA often suffers from uncontrolled electron injection, leading to broad energy spreads and low charge.
• Ionization injection offers a potential pathway to improve LWFA performance.

Purpose of the Study:

• To investigate the enhancement of single-stage LWFA using ionization injection.
• To evaluate the impact of ultra-low nitrogen concentrations in helium gas on electron beam generation.
• To assess the controllability and quality of electron beams produced via this method.

Main Methods:

• Utilizing a 30-TW, 30-fs laser pulse interacting with a gas jet.
• Employing a gas mixture of 99.7% helium and 0.3% nitrogen.
• Analyzing electron beam parameters such as energy, charge, density, and energy spread.

Main Results:

• Generation of electron beams with energies exceeding 300 MeV at plasma densities of 3.3-8.5 × 10^18 cm^-3.
• Demonstration of self-controlled ionization injection due to ultra-low nitrogen concentrations.
• Achieved higher electron beam energies, increased charge, and a lower trapping density threshold compared to pure helium.
• Observed narrower energy spread, absence of dark current, and single electron bunch generation.

Conclusions:

• Ionization injection in a helium-nitrogen gas mixture significantly enhances LWFA performance.
• This method provides a self-controlled injection mechanism leading to superior electron beam quality.
• Further optimization could yield electron beams with 1% energy spread, suitable for driving ultra-compact free-electron lasers.