Adiabatic matching section for plasma accelerated beams

An adiabatic matching section is discussed as option to control the divergence and emittance growth of a beam exiting a plasma channel. Based on a general analytical solution of a focusing channel with varying focusing strength, a focusing profile is proposed which allows for a fast expansion of the beam size while keeping the emittance growth minimal. The solution is also applicable to other cases, e. g., the matching of a positron source to the downstream accelerating section, which are, however, not discussed in this contribution.