A two-beam RFQ for ion beam funneling

The front end of a spallation source linac, e.g. for the European Spallation Source (ESS) and also a Heavy Ion Inertial Fusion (HIIF) driver injector has to provide a high current and small emittance ion beam which cannot be provided by one single ion source. The space charge forces at the low energy part of the linac are the strongest current limitations. For these reasons the required beam will be reached by several funneling stages, where two identically bunched ion beams are combined into a single beam with twice the frequency, current and brightness. For the most critical first funneling stage a two-beam RFQ, where two beams are bunched and accelerated in a single RF cavity and a novel scheme for an RF funneling deflector operating at low voltages has been developed. With the use of convergent incoming beams, the funneling structure will be placed around the beam crossing position. The experimental setup of combination of a two-beam RFQ with such a deflector for funneling of two He/sup +/-beams at low energies will be presented.