Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams

TL;DR

This paper analyzes the harmonic components of irradiation asymmetry in cylindrical implosions driven by high-frequency rotating ion beams, proposing methods to optimize beam parameters for improved symmetry and stability.

Contribution

It introduces a Fourier analysis of irradiation asymmetry and identifies specific beam parameters that enhance symmetry in cylindrical implosions.

Findings

Fourier components of irradiation are exactly expressed via the Fourier transform of the beam profile.

Identification of 'magic products' ΩT that cancel the first harmonic, improving symmetry.

Provides a framework linking beam temporal profile to irradiation asymmetry control.

Abstract

Cylindrical implosions driven by intense heavy ions beams should be instrumental in a near future to study High Energy Density Matter. By rotating the beam by means of a high frequency wobbler, it should be possible to deposit energy in the outer layers of a cylinder, compressing the material deposited in its core. The beam temporal profile should however generate an inevitable irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI) during the implosion phase. In this paper, we compute the Fourier components of the target irradiation in order to make the junction with previous works on RTI performed in this setting. Implementing a 1D and 2D beam models, we find these components can be expressed exactly in terms of the Fourier transform of the temporal beam profile. If $T$ is the beam duration and $\Omega$ its rotation frequency, "magic products" $\Omega T$ can be identified which cancel the first harmonic of the deposited density, resulting in an improved irradiation symmetry.