Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

TL;DR

This study reveals that nonlinear plasma structures hinder ion acceleration in laser-plasma interactions, and demonstrates control methods and experimental setups to optimize ion acceleration efficiency.

Contribution

It introduces a method to control plasma instabilities via density ramp tailoring and presents an experimental setup for studying isolated coherent structures.

Findings

Ion acceleration is suppressed by plasma instabilities and nonlinear structures.

Tailoring the plasma density ramp can control the onset of these instabilities.

A long pulse setup enables excitation of isolated coherent structures for further study.

Abstract

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.