Radiation pressure acceleration of high-quality ion beams using ultrashort laser pulses

Letter
Open Access

Radiation pressure acceleration of high-quality ion beams using ultrashort laser pulses

H.-G. Jason Chou, A. Grassi, S. H. Glenzer, and F. Fiuza

Phys. Rev. Research 4, L022056 – Published 10 June 2022

Abstract

The generation of compact, high-energy ion beams is one of the most promising applications of intense laser-matter interactions, but the control of the beam spectral quality remains an outstanding challenge. We show that in radiation pressure acceleration of a thin solid target the onset of electron heating is determined by the growth of the Rayleigh-Taylor-like instability at the front surface and must be controlled to produce ion beams with high spectral quality in the light sail regime. The growth rate of the instability imposes an upper limit on the laser pulse duration and intensity to achieve high spectral beam quality and we demonstrate that under this optimal regime, the maximum peak ion beam energy per nucleon is independent of target density, composition, and laser energy (transverse spot size). Our predictions are validated by two- and three-dimensional particle-in-cell simulations, which indicate that for recent and upcoming experimental facilities using ultrashort ( $≲$ 25 fs) laser pulses it is possible to produce $100 - 300$ MeV proton beams with $\approx 30 %$ energy spread and high laser-to-proton energy conversion efficiency.

Received 4 December 2021
Accepted 16 May 2022

DOI:https://doi.org/10.1103/PhysRevResearch.4.L022056

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

High-energy-density plasmas Laser driven ion acceleration Laser-plasma interactions Plasma instabilities Radiation pressure acceleration

Particle-in-cell methods

Accelerators & BeamsPlasma Physics

Authors & Affiliations

H.-G. Jason Chou ^1,2,*, A. Grassi¹, S. H. Glenzer¹, and F. Fiuza ^1,†

¹High Energy Density Science Division, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
²Department of Physics, Stanford University, Stanford, California 94305, USA

^*jasonhc@slac.stanford.edu
^†fiuza@slac.stanford.edu

Article Text

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Issue

Vol. 4, Iss. 2 — June - August 2022

Subject Areas

Plasma Physics

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Images

Figure 1
Results of 2D PIC simulation of the interaction of an intense Gaussian CP laser pulse with a thin target. (a) Longitudinal (top) electron and (middle) ion phase spaces and (bottom) ion density profile for a laser with pulse duration $τ_{0} = 105 ω_{0}^{- 1}$ . (b) Temporal evolution of $T_{e}$ (blue, left axis), ion beam energy spread $Δ ε / ε_{0}$ (black, right black axis) within a $10^{\circ}$ opening angle from the laser propagation direction, and $n_{e} / (γ n_{c})$ (red, rightmost axis). The time $t = 0$ is defined as $τ_{0} / 2$ before the laser peak intensity reaches the target.
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Figure 2
(a) Development of surface corrugations in ion density at $t = 90 ω_{0}^{- 1}$ . (b) Evolution of Fourier modes at the relativistic critical surface of the corrugation amplitudes ${\tilde{n}}_{i} (k_{x_{2}})$ . The inset shows the growth rate of the $k_{x_{2}} = k_{0}$ mode and its linear fit. (c) Scaling of the measured growth rate of the $k_{x_{2}} = k_{0}$ mode of the surface corrugations. (d) Strong correlation between the electron heating time $τ_{heating}$ and the growth time of the RTI. Colored symbols are measurements from 2D PIC simulations.
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Figure 3
(a) Electron temperature $T_{e}$ and (b) ion beam energy spread $Δ ε / ε_{0}$ measured from 2D PIC simulations of a 1- $μ m$ wavelength Gaussian laser pulse with duration $τ_{0}$ and spot size $w_{0} = 7.6$ $μ m$ interacting with a thin solid target with $n_{0} = 250 n_{c}$ and $l_{0} = l_{opt}$ . $T_{e}$ is measured at the end of the laser interaction when the maximum is observed. $Δ ε / ε_{0}$ is measured for protons within a $10^{\circ}$ opening angle at $t ≃ 2 τ_{0}$ . The black curve corresponds to the prediction of Eq. (1) and the white dots denote the parameters sampled by the simulations.
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Figure 4
(a) Peak proton beam energy $ε_{0}$ as a function of laser duration $τ_{0}$ in high-quality regime of LS acceleration. Colored symbols are measurements from 3D PIC simulations, the solid line is the prediction of Eq. (3), and the gray shaded area above the solid line indicates the parameter space outside the high-quality acceleration regime. (b) Proton spectra from 3D PIC simulations with $a_{0} = {\hat{a}}_{0}$ and $τ_{0} = {\hat{τ}}_{0}$ (solid lines), $a_{0} = {\hat{a}}_{0}$ and $τ_{0} = 2 {\hat{τ}}_{0}$ (dotted), and $a_{0} ≃ 3 \hat{a_{0}}$ and $τ_{0} = {\hat{τ}}_{0}$ (dashed). The spectra are measured within a $10^{\circ}$ opening angle from the laser propagation direction at $t ≃ 2 τ_{0}$ .
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Figure 5
Comparison between the short- (left) and long-pulse (right) simulations in Fig. 1. Top: ion density; bottom: local electron temperature. All plots are shown at $t = 70 ω_{0}^{- 1}$ , which is approximately both $τ_{heating}$ for the long-pulse ( $τ_{0} = 105 ω_{0}^{- 1}$ ) case and the end of interaction time for the short-pulse ( $τ_{0} = 40 ω_{0}^{- 1}$ ) case.
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Figure 6
Evolution of electron temperature for different transverse simulation domain sizes (black, left axis). The solid black curve corresponds to the simulation in Figs. 2 and 2 with a transverse box size of $40 λ_{0}$ and for this case the growth of the $k_{x_{2}} = k_{0}$ (solid) and $k_{x_{2}} = k_{max}$ (dotted) modes are shown (blue, right axis).
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