GFA Accelerator Seminars

Laser-driven generation of high-charge and ultra-relativistic positron beams

by Dr Gianluca Sarri (University Belfast)




Plasma-based electron acceleration is arguably one of the most promising alternatives to more conventional radio-frequency acceleration techniques. Several landmark results have already been obtained, including accelerating fields exceeding 100 GV/m [1], charge-coupling in a multi-stage accelerator [2], and the laser-driven acceleration of electrons up to 8 GeV in only
20 cm of plasma [3]. Due to the intrinsic asymmetry in the plasma-based accelerating fields, the acceleration of positrons is far more complex, requiring seed positron beams with rather challenging characteristics, including sub-micron emittance and ultra-short longitudinal length
(1 to 10s of microns).

Our group has recently demonstrated that positron beams with such characteristics can be generated in a fully laser-driven configuration [4-6], opening up the possibility for the extensive experimental study of plasma-based acceleration of positrons, with the long-term goal of working towards a plasma-based collider [7]. Numerical work carried out by our group [8] has
demonstrated that fs-scale positron beams containing ~pC of charge in a 5% energy slice at the GeV level can be generated using the upcoming next generation of laser facilities, currently either under construction or commissioning. For instance, a dedicated positron beam line based
on a plasma source of this kind has been designed for the EuPRAXIA facility [9], currently being reviewed by ESFRI.

In this seminar, preliminary experimental work at the sub-GeV level [10,11] will be presented, confirming the numerical predictions reported in [8] and demonstrating the possibility of measuring, simultaneously and in a non-invasive manner, all the main positron beam characteristics, including spectrum, overall charge, energy-resolved emittance, and
source size.

[1] J. Liu et al., Phys. Rev. Lett. 107, 035001 (2011).
[2] S. Steinke S et al Nature 530, 190 (2016).
[3] A. Gonsalves et al., Phys. Rev. Lett. 122, 084801 (2019).
[4] G. Sarri et al., Phys. Rev. Lett. 110, 255002 (2013).
[5] G. Sarri et al., Nat. Commun. 6, 6747 (2015).
[6] G. Sarri et al., Plasma Phys. Contr. F. 59, 014015 (2016).
[7] E. Adli E et al., arXiv:1901.10370 (2019).
[8] A. Alejo, R. Walczak and G. Sarri, Sci. Rep. 9, 5279 (2019).
[9] R. Assman et al., Eur. Phys. J. Special Topics 229,3675 (2020).
[10] A. Alejo, et al., Plasma Phys. Contr. F. 62, 055013 (2020).
[11] M. Streeter et al., in preparation (2021).