Characterization of Laser-Wakefield Produced Positron Beams

A laboratory-based source of positron-electron pair jets is necessary for scaled relativistic astrophysics studies. Most prominently, such a platform could test the microphysics of particle acceleration from Weibel-mediated relativistic shocks, mimicking environments found in gamma-ray bursts, active galactic nuclei, or pulsar wind nebulae. Recent attention has been paid to LWFA-generated pairs due to claims of charge neutrality [1], incredibly high densities (>10¹⁶/cm³), and near-collimation (5 mrad) [2]. These results have not been reproduced using similar LWFA electron sources [3] where simulations suggested the divergences are an order of magnitude larger than estimated in Ref. [1,2] due to Coulomb scattering in mm-to-cm-scale targets. We explore these discrepancies, present new measurements of positron beam emittance, and examine the fundamental limitations to laser-produced pair plasmas for scaled astrophysical studies.

[1] G. Sarri, et al. Nat. Commun., 6, 04 2015

[3] G. Sarri, et al. Phys. Rev. Lett., 110:255002, Jun 2013

[4] G. J. Williams, et. al. Phys. Plasmas, 22(9):093115, 2015