Reduction of beam emittance by a tapered-foil technique

The transverse emittance of a particle beam can be reduced by means of a transverse energy gradient produced in a tapered energy-loss foil and by manipulation of the dispersion characteristics of the succeeding beam transport system. In spite of the multiple Coulomb scattering in the foil the area in one transverse phase plane can be substantially reduced provided that the incident beam is sufficiently mono-energetic. In the case of negligible multiple scattering the total six-dimensional phase-space volume occupied by the beam is not changed by this process. This paper discusses the method of reducing transverse emittance with and the effects of a tapered energy-loss foil on the phase-space distributions of a particle beam