AXIAL CHANNELING OF RELATIVISTIC ELECTRONS IN CRYSTALS AS A SOURCE FOR POSITRON PRODUCTION

In the framework of studies of positron sources dedicated to linear co lliders, crystals are considered as photon radiators in association wi th thin amorphous converters or as compact positron sources where phot on production and pair creation occur in the same medium. The main fea tures of such sources in comparison with conventional amorphous source s are described. Taking linear collider requirements for such sources, a crystal converter suited for the Japanese Linear Collider (JLC) is considered. Limitations caused by radiation damage are mentioned and i ndications on critical fluences are given. A proof-of-principle experi ment has been undertaken in Orsay, observing radiation enhancement in a tungsten crystal oriented along the [111] axis and submitted to a 2 GeV electron beam. The main results are reported.