Progress with SNS fast beam chopper

The fast traveling-wave 2.5 MeV beam chopper for the Spallation Neutron Source (SNS) project has a new current structure based on the meander-folded notched stripline with separators. Measurements of the full-length structure prototype showed a good agreement with predictions of MAFIA electromagnetic modeling. The design of the final chopper units is completed, and they are being manufactured. Here we report on the final design of the chopper and on results of recent thermal and vacuum tests of the prototype chopper structure.