Helical Undulator Based Production of Polarized Positrons and Status of the E166 Experiment

This paper describes the status of the E166 experiment. The experiment is dedicated to test the helical-undulator-based polarized positron source for the international linear collider. The physics motivation for having both electrons and positrons polarized in collision is crucial and a demonstration experiment for the undulator-based production of polarized positrons is summarized. The E166 experiment uses a 1 meter long helical undulator in the 50 GeV Final Focus Test Beam at SLAC to provide MeV photons with circular polarization. These photons are then converted in a thin (0.5 radiation length X₀) target into positrons (and electrons) with about 50% degree of longitudinal polarization. In this experiment, the polarization of both photons and positrons is measured simultaneously using photon transmission polarimetry.