Polarized Positrons At A Future Linear Collider And The Final Focus Test Beam

Polarized positrons in addition to polarized electrons are a highly desirable feature of future linear e(+)e(-) colliders. The motivation for polarized positrons, and a demonstration experiment for the undulator-based production of polarized positrons are reviewed. This experiment ('E-166') uses the 50 GeV Final Focus Test electron beam at SLAC with a 1 m-long helical undulator to make approximate to 10MeV polarized photons. These photons are then converted in a thin (approximate to 0.5 radiation length) target into positrons (and electrons) with about 50% polarization.