Description
Positron Annihilation Lifetime Spectroscopy (PALS) is a non-destructive technique for characterising defects in materials [1]. A key requirement for PALS is a high average positron flux with short bunch durations. Generating positrons at MeV energies, rather than conventional keV sources, enables deeper material probing. However, conventional positron sources are limited in flux, repetition rate or temporal resolution [2]. As a result, they are constrained in defect sensitivity, depth profiling and time-resolved studies.
A proof-of-principle experiment was conducted at Extreme Light Infrastructure – Attosecond Light Pulse Source (ELI-ALPS). This high-repetition-rate, laser-driven source enabled the demonstration and characterisation of positron production for PALS applications. A laser-wakefield accelerator driven by the kHz-class eSYLOS laser system generated high-energy electrons, producing 10^4 MeV-scale positrons per second with a bunch duration of ~90 ps through pair production.
Building on this experimental validation, we designed and optimised a positron beamline based on the parameters of a 100 Hz laser system, representative of that scheduled for operation at Queen’s University Belfast, with a pulse energy of 200 mJ and duration of 20 fs. Optimisation of a quadrupole triplet and magnetic dipole transport system in simulations of this system yielded an MeV-scale positron flux of 10^7 per second within a compact setup of ~50 cm achieving bunch durations of ~65 ps. These parameters enable improved time-resolved positron lifetime measurements. The dipole configuration allows for energy-selective positron extraction, while variation of the laser–plasma density provides a route to scaling the positron flux, broadening the range of potential applications. This emphasises the potential for compact table-top positron sources.
Such results position laser-driven positron sources as viable, compact alternatives to conventional facilities for advanced materials diagnostics. These advancements support the development of a dedicated positron beamline at ELI-Beamlines as part of the EuPRAXIA project [3].
[1] R. Krause-Rehberg and H. S. Leipner, Positron Annihilation in Solids: Defect Studies (Springer, 1999).
[2] T. L. Audet et al., “Ultrashort, MeV-scale laser-plasma positron source for positron annihilation lifetime spectroscopy,” Phys. Rev. Accel. Beams 24, 073402 (2021).
[3] R. W. Assmann et al., “EuPRAXIA Conceptual Design Report,” Eur. Phys. J. Spec. Top. 229, 3675–4284 (2020).