Mirror-field magnet for stripped electron sweeping

Multi-turn injection of H- by foil stripping into an accumulator ring produces metastable neutrals that contribute to machine activation. Placing the foil in a magnetic field has been shown to greatly reduce such losses. However, the electrons associated with the H- repeatedly and destructively pass through the foil under the influence of the magnetic field. The electrons can be swept off the foil by a small circular coil placed on the surface of the injection dipole's pole face, centered on the electron's trajectory. The coil, in a magnetic-mirror configuration, will exert a downward force on the electrons causing them to be swept off the foil, limiting the electron foil interactions to one or two. Beam dynamics simulations indicate that such effects can be corrected by small correction magnets in the ring. As a test of this concept a full scale prototype has been fabricated and mapped in the magnetic-mirror configuration. The measured and calculated results were found to be in good agreement