Positron production at CLIC

The CLIC positron source is based on the conventional scheme, using a metal converter target and an Adiabatic Matching Device (AMD) composed of a Flux Concentrator and a DC magnetic field along the e+ Pre-Injector linac. Positrons are accelerated with L-band RF structures. In this paper extensive beam dynamics simulations are described for the e+ production in the target and for the e+ capture in the matching and focusing sections. The distribution of the energy deposition in the target is studied with the EGS4 code. The AMD acceptance is expressed by analytic formulae. The dependence of the e+ yield on several parameters (incident beam radius, target thickness, aperture radius, longitudinal acceptance, accelerating field) is studied and optimized. With these new parameters, detailed particle tracking simulations are performed. Based on the analysis of the results, the transverse and longitudinal acceptances of the capture system and of the e+ Pre-Damping Ring are derived. Finally a new set of design parameters is proposed for the CLIC e+ production.