Proton acceleration with intense twisted laser light

Open Access

Proton acceleration with intense twisted laser light

Camilla Willim, Jorge Vieira, Victor Malka, and Luís O. Silva

Phys. Rev. Research 5, 023083 – Published 9 May 2023

Abstract

An efficient approach that considers a high-intensity twisted laser of moderate energy (few J) is proposed to generate collimated proton bunches with multi-10 MeV energies from a double-layer hydrogen target. Three-dimensional particle-in-cell simulations demonstrate the formation of a highly collimated and energetic ( $\sim 40$ MeV) proton bunch, whose divergence is $\sim 6.5$ times smaller compared to the proton bunch driven by a Gaussian laser containing the same energy. Supported by theoretical modeling of relativistic self-focusing in near-critical plasma, we establish a regime that allows for consistent acceleration of high-energetic proton bunches with low divergence under experimentally feasible conditions for twisted drivers.

Received 29 June 2022
Accepted 10 February 2023
Corrected 5 October 2023

DOI:https://doi.org/10.1103/PhysRevResearch.5.023083

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)

Angular momentum of light Laser driven electron acceleration Laser driven ion acceleration Particle acceleration in plasmas Radiation pressure acceleration Self-focusing & filamentation in plasmas Structured light Target normal sheath acceleration

Laser dynamics Near-critical & underdense plasmas

Accelerators & BeamsPlasma PhysicsParticles & FieldsNuclear Physics

Corrections

5 October 2023

Correction: The omission of additional support information has been fixed.

Authors & Affiliations

Camilla Willim ¹, Jorge Vieira ¹, Victor Malka ², and Luís O. Silva¹

¹GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
²Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel

Article Text

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References

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Issue

Vol. 5, Iss. 2 — May - July 2023

Subject Areas

Plasma Physics

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Images

Figure 1
Laser pulse at four consecutive time steps at the relative propagated position, demonstrating the differences in relativistic self-focusing between Gaussian and OAM pulses. The near-critical plasma layer starts at $- 100 c / ω_{0}$ and ends at $125 c / ω_{0}$ . The laser electric field component of OAM and Gaussian lasers are in (a) Vacuum, (c) Near-critical plasma and (b) Vacuum, (d) Near-critical plasma, respectively, and above the corresponding inverse of the relativistic transparency factor $1 / \bar{n} = γ n_{c r} / n_{e}$ for OAM (green) and Gaussian (purple) vector potentials. The superimposed dashed line corresponds to the analytical solution of the beam waist evolution, calculated with Eqs. (1) and (2).
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Figure 2
Averaged time evolution of the cumulative sum of the work components $W = \int p_{j} (t) / (γ m_{i}) E_{j} (t) d t$ acting on selected protons after irradiation with Gaussian (purple) and OAM (green) drivers with (a) the longitudinal work component $W_{∥} = p_{1} E_{1}$ , and (b) the transverse work components $W_{⊥} = p_{⊥} E_{⊥}$ , where $p_{2} E_{2}$ corresponds to the laser polarization direction. In the OAM scenario, the transverse work acting on the protons is significantly smaller.
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Figure 3
Properties of proton bunches $\sim 93$ fs ( $520 1 / ω_{0}$ ) after Gaussian (purple) and OAM (green) drivers reached the overdense plasma layer, show significantly smaller divergence in the OAM case and a similar longitudinal charge distribution. (a) $p_{2} - p_{1}$ momentum space of forward accelerated protons. Dashed line marks the cutoff at $0.01 %$ of the maximum of the integrated charge function $f (p_{1})$ . (b) Corresponding integrated charge over transverse momentum $f (p_{1})$ (left axis: area plots) and divergence (right axis: lines). The arrows indicate the value of divergence at the cutoff ( $p_{1} \approx 0.3 m_{i} c$ ).
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Figure 4
Dependence on the laser pulse energy of Gaussian and OAM drivers of: (a) the proton bunch divergence at the cutoff energy where the dashed line highlights the maximum values of 0.04 (OAM) and 0.16 (Gaussian), (b) the corresponding proton energy at cutoff where the cross relates to simulation results and the line to a fit function $E_{cutoff} \propto a_{0} log (n_{1})$ . In each simulation the plasma densities ( $n_{1}, n_{2}$ ) of the double-layer target increase by the same factor as the the laser amplitude $a_{0}$ . The cutoff energy $E_{cutoff}$ is measured at $0.01 %$ of the maximum of the integrated charge function $f (p_{1})$ .
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Figure 5
Relativistic self-focusing of laser with OAM is less sensitive to adjustments in electron density $n_{e}$ or laser amplitude $a_{0}$ but responds more to shifts of the focus than Gaussian laser. Three different scenarios are considered, in (a) the electron density $n_{e}$ is doubled, in (b) the laser amplitude $a_{0}$ is doubled, and in (c) the position of the focus is moved to the beginning of the near-critical plasma layer, i.e., $z_{0} = 0$ , and to the end of the plasma layer, i.e., $z_{0} \approx 220 c / ω_{0}$ , with reference to the parameters from the initial simulation case.
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