Longitudinal tapering in meter-scale gas jets for increased efficiency of laser plasma accelerators

TL;DR

This paper demonstrates that longitudinal tapering of gas density profiles in meter-scale gas jets can significantly enhance the energy and charge of electron beams in laser plasma accelerators, enabling higher energy gains with current laser systems.

Contribution

The study introduces a method to control plasma density profiles via jet geometry adjustments, validated through simulations and experiments, to improve laser plasma accelerator performance.

Findings

Density control achieved by adjusting jet throat width and angle

Tapering increases electron energy from ~9 GeV to >12 GeV

Accelerated charge increased by an order of magnitude

Abstract

Modern laser plasma accelerators (LPAs) often require plasma waveguides tens of cm long to propagate a high-intensity drive laser pulse. Tapering the longitudinal gas density profile in 10 cm scale gas jets could allow for single stage laser plasma acceleration well beyond 10 GeV with current petawatt-class laser systems. Via simulation and interferometry measurements, we show density control by longitudinally adjusting the throat width and jet angle. Density profiles appropriate for tapering were calculated analytically and via particle-in-cell (PIC) simulations, and were matched experimentally. These simulations show that tapering can increase electron beam energy using 19 J laser energy from ~9 GeV to >12 GeV in a 30 cm plasma, and the accelerated charge by an order of magnitude. This paper was published in Review of Scientific Instruments on April 11, 2025 DOI: https://doi.org/10.1063/5.0250698