Reduction of Beam Emittance by a Tapered-Foil Technique

The use of a tapered energy-loss foil plus dispersion and optical matching in the succeeding beam transport system can reduce the emittance of a particle beam in one transverse phase plane at the expense of increasing it in the longitudinal plane. Multiple Coulomb scattering in the foil increases the emittance in both transverse planes but can be acceptable provided that the incident beam is sufficiently mono-energetic and is tightly focussed at the foil. This technique can be applied to advantage in typical non-relativistic proton beams from RF linacs and to high-emittance, high-intensity, low-energyspread electron beams from induction linacs, but multiple scattering effects make unprofitable for typical electron beams from RF linacs, unless the energy spread can be appreciably reduced. Claud Bovet6 has previously emittance-reducing properties of arrangement. His report includes sults of this paper.