Longitudinal Ion Acceleration from High-Intensity Laser Interactions with Underdense Plasma

TL;DR

This study demonstrates that high-intensity laser interactions with helium gas jets can produce collimated, high-energy ion beams, with the acceleration mechanism influenced by plasma density and scale-length, supported by simulations.

Contribution

It provides new insights into the ion acceleration mechanism from underdense plasma using high-intensity lasers, highlighting the roles of magnetic fields and plasma scale-lengths.

Findings

Maximum He^2+ ion energy ~40 MeV

Ion beam collimated within 10 degrees

Plasma density and scale-length affect acceleration and collimation

Abstract

Longitudinal ion acceleration from high-intensity (I ~ 10^20 Wcm^-2) laser interactions with helium gas jet targets (n_e ~ 0.04 n_c) have been observed. The ion beam has a maximum energy for He^2+ of approximately 40 MeV and was directional along the laser propagation path, with the highest energy ions being collimated to a cone of less than 10 degrees. 2D particle-in-cell simulations have been used to investigate the acceleration mechanism. The time varying magnetic field associated with the fast electron current provides a contribution to the accelerating electric field as well as providing a collimating field for the ions. A strong correlation between the plasma density and the ion acceleration was found. A short plasma scale-length at the vacuum interface was observed to be beneficial for the maximum ion energies, but the collimation appears to be improved with longer scale-lengths due to enhanced magnetic fields in the ramp acceleration region.