Measuring Beam Emittance for High-Energy H- Accelerators

A novel technique is presented for measuring the six-dimensional beam emittance for high-energy H- accelerators in real time. This techniuqe uses the single charge exchange cross section from thin and narrow foils (intercepting 1-3% of the beam) as a line source for measuring the divergence and momentum spectra for operating H- accelerator beams. By scanning the foil across the beam, X, θ, and p beam density spectra and emittance can be determined. The introduction of a second foil provides the Y-ϕ emittance. Operational experience of this low cost emittance measuring device has been obtained from the 50-MeV H- linear accelerator at Argonne National Laboratory, simultaneously with its use as an injector into the Rapid Cycling Synchrotron (RCS).