Using the Continuous Electron Beam Accelerator Facility (CEBAF) at the Department of Energy's Jefferson Lab, a team of researchers has, for the first time, demonstrated a new technique for producing polarized positrons. The method could enable new research in advanced materials and offers a new avenue for producing polarized positron beams for a proposed International Linear Collider and an envisioned Electron-Ion Collider. http://phys.org/news/2016-06-electrons-yield-positrons.html Paper: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.214801
Article not clear on how even one positron can be created, without also creating an electron. Net / total amount of charge can not be changed.
Looks like electron>target 1>gamma ray>electron and positron. http://phys.org/news/2016-06-electrons-yield-positrons.html