Optical shaping of gas targets for laser–plasma ion sources

N P Dover,I Pogorelsky,M N Polyanskiy,N Cook,P Shkolnikov,Z Najmudin,C Maharjan,O Tresca,O Ettlinger

doi:10.1017/s002237781600012x

N P Dover, I Pogorelsky + Show 7 more

Open Access

PDF Available

https://doi.org/10.1017/s002237781600012x

Copy DOI

Export

Save

Cite

Abstract
Highlights/Summary
Full-Text PDF
Similar Papers

Abstract

Listen

We report on the experimental demonstration of a technique to generate steep density gradients in gas-jet targets of interest to laser–plasma ion acceleration. By using an intentional low-energy prepulse, we generated a hydrodynamic blast wave in the gas to shape the target prior to the arrival of an intense CO$_{2}$ (${\it\lambda}\approx 10~{\rm\mu}\text{m}$) drive pulse. This technique has been recently shown to facilitate the generation of ion beams by shockwave acceleration (Tresca et al., Phys. Rev. Lett., vol. 115 (9), 2015, 094802). Here, we discuss and introduce a model to understand the generation of these blast waves and discuss in depth the experimental realisation of the technique, supported by hydrodynamics simulations. With appropriate prepulse energy and timing, this blast wave can generate steepened density gradients as short as $l\approx 20~{\rm\mu}\text{m}$ ($1/e$), opening up new possibilities for laser–plasma studies with near-critical gaseous targets.

Highlights

Laser–plasma particle accelerators can generate bunches of energetic ions with energies 1 MeV and charge in excess of 10 nC (Daido, Nishiuchi & Pirozhkov 2012; Macchi, Borghesi & Passoni 2013)
FLASH simulations were performed for the 2 mm helium target, depositing energy in a cylindrical volume of length 400 μm and radius 70 μm, similar to the size of the beam waist and Rayleigh range as well as the size of the ionised region calculated from the data in figure 4
Axial density profiles from FLASH simulations using a typical gas density profile from Sylla et al (2012) with peak hydrogen density ni = 0.7 × 1021 cm3 are shown at various times for Eabs = 100 mJ deposited in a cylinder radius 50 μm and length 200 μm, centred 250 μm from peak density, demonstrating density profile steepening

Summary

Introduction

Laser–plasma particle accelerators can generate bunches of energetic ions with energies 1 MeV and charge in excess of 10 nC (Daido, Nishiuchi & Pirozhkov 2012; Macchi, Borghesi & Passoni 2013). 25 ns before the main intense pulse This prepulse is absorbed locally and heats a small region of gas, which subsequently expands and forms a blast wave. The resultant density profile, and support this with numerical hydrodynamic simulation to explain and predict the blast-wave properties We discuss briefly the effects of the density gradients on the laser–plasma interaction and propose an extension to blast-wave shaping of higher-density targets of interest to ion acceleration using higher-intensity near-IR lasers. 2. Modelling of prepulse-driven blast waves A tightly focussed laser pulse of sufficient intensity can induce breakdown of the target gas, forming a plasma which absorbs energy from the pulse.

Eabs ρ

Discussion