Funnel cavities for 4-MW upgrade of Spallation Neutron Source

The Spallation Neutron Source (SNS) project includes a future upgrade option to 4 MW of beam power. The upgrade scenario stipulates adding a second front end and drift-tube linac, and then merging two 402.5-MHz beams from the parallel legs by interlacing them into a single 805-MHz beam at the entrance to the main linac. The funnel energy is chosen to be 20 MeV. The beam funnel section requires two types of rather special cavities: the two-beam buncher and the RF-deflector. The design options of the funnel cavities and some results of their 3-D electromagnetic modeling with MAFIA are presented. These results show feasibility of the beam funneling for the SNS upgrade.