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Optimal beam loading in a nanocoulomb-class laser wakefield accelerator

Couperus, J. P.

Laser plasma wakefield accelerators have seen tremendous progress in the last years, now capable of producing electron beams in the GeV energy range. The inherent few-femtoseconds short bunch duration of these accelerators leads to ultra-high peak-currents. Reducing the energy spread found in these accelerators, while scaling their output to hundreds of kiloampere peak current would stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and -ray sources, compact free-electron lasers and laboratory-size beam-driven plasma accelerators. At such high currents, an accelerator operates in the beam loaded regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters. However, if appropriately controlled, the beam loading effect can be employed to improve the accelerator’s performance, specifically to reduce the energy spread.

In this thesis the beam-loading effect is systematically studied at a quasi-monoenergetic nanocoulomb-class laser wakefield accelerator. For this purpose, a tailored scheme of the self-truncated ionisation injection process is introduced for the non-linear bubble regime. This scheme facilitates stable and tunable injection of high-charge electron bunches within a short and limited time-frame, ensuring low energy spread right after injection. Employing a three millimetres gas-jet acceleration medium and a moderate 150 TW short pulse laser system as driver, unprecedented charges of up to 0.5 nC within a quasi-monoenergetic peak and energies of ~0.5 GeV are achieved. Studying the beam loading mechanism, it is demonstrated that at the optimal loading condition, i.e. at a specific amount of injected charge, performance of the accelerator is optimised with a minimisation of the energy spread. At a relative energy spread of only 15%, the associated peak current is around 10 kA, while scaling this scheme to operate with a petawatt driver laser promises peak-currents up to 100 kA.

Keywords: beam loading; plasma acceleration; electron acceleration; LWFA; laser wakefield acceleration; LPA

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-093 2018
    ISSN: 2191-8708, eISSN: 2191-8716
  • Lecture (Conference)
    Laser-Plasma Accelerator Workshop (LPAW) 2019, 05.-10.05.2019, Split, Republika Hrvatska

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Permalink: https://www.hzdr.de/publications/Publ-28080
Publ.-Id: 28080