Merger system optimization in BNL's high current R&D ERL

A super-conducting RF R&D energy recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL). This ERL will be used as a test facility to study issues relevant to high-current, high-brightness beams. One of the goals is to demonstrate an electron beam with high charge per bunch (˜ 5 nC) and extremely low normalized emittance (˜ 5 mm-mrad) at an energy of 20 MeV. In contrast with operational high-brightness linear electron accelerators, all presently operating ERLs have order of magnitude larger emittances for the same charge per bunch. One reason for this emittance growth is that the merger system mixes transverse and longitudinal degrees of freedom, and consequently violates emittance compensation conditions. A merger system based on zigzag scheme resolves this problem. In this paper we discuss performance of the present design of the BNL R&D ERL injector with a zigzag merger.