First measurement of a 2.5 MeV RFQ output emittance with 1 part-per-million dynamic range

Accurate characterization and prediction of beam halo has been historically prohibited by an inability to measure beam phase distributions with the required sensitivity level. To address this limitation, a system for measuring transverse beam emittance with very high dynamic range is developed at the Spallation Neutron Source Beam Test Facility. An emittance of a 20 mA H- beam is measured at the 2.5 MeV RFQ exit with the dynamic range larger than 1-part-per-million for the first time. Though no obvious halo is observed within this dynamic range for this particular configuration, the measurement demonstrates a capability to resolve beam distributions at the level required for inspection and characterization of beam halo.