22-LF-01 (english)

Generation of laser-driven GeV-scale high-quality positron beams
Gianluca SARRI (QUB, UK) 14 March – 8 April 2022


Following extensive numerical work and promising experimental results at lower energy performed by our group using the Astra-Gemini laser hosted by the Rutherford Appleton Laboratory and the UHI100 laser hosted by CEA-LIDYL, we propose here to generate and fully characterise, for the first time, laser-driven GeV positron beams with unique characteristics, including ultra-short duration (~10 fs), high current (~kA), and low geometrical emittance (sub-micron).
The beams will be generated during the interaction of high-charge and broad spectrum electron beams, accelerated using the laser-wakefield mechanism, with a mm-scale high-Z converter target. Numerical simulations [A. Alejo et al., Scientific Reports 9, 5729 (2019)], which have been experimentally validated by our group up to a positron energy of 500 MeV, indicate that a high charge >GeV electron beam can produce pC-scale positron beams with a maximum energy in the GeV range, a duration comparable to that of the primary electron beam, and a sub-micron geometrical emittance. These positron beams will represent a fundamental milestone towards the demonstration of plasma-based acceleration of positron beams, since they will provide an ideal and rather unique witness beam for this class of experiments, both for beam-driven and laser-driven wakefield acceleration. The importance of this area of experimental research is internationally recognised by its inclusion in several national and international strategic roadmaps (see, for instance, arXiv:1901.08436 and http://pwasc.org.uk) and it is proposed as one of the five user areas for EuPRAXIA [Eur. Phys. J. Special Topics 229,3675 (2020)].
The second main objective of the proposal is to generate high-density neutral electron-positron beams following a virtually identical experimental configuration, with the only exception of using a thicker converter target (~ 2 – 2.5 cm). Previous work carried out at lower energy by our group has already demonstrated the possibility of generating neutral electron positron beams and of studying their dynamics [Nat. Comm. 6, 6747 (2015) and Phys. Rev. Lett. 119, 185002 (2017)]. Extending these results to higher electron energies will allow reaching much higher neutral beam densities, paving the way for the laboratory study of novel and exciting plasma phenomena of direct interest to astrophysics and fundamental plasma physics.

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