Laser photoionization of Ho beams for charge-changing injection

The two-step charge-changing injection used in the Los Alamos Proton Storage Ring (PSR) requires stripping of H^- to H^o by high magnetic fields and subsequent stripping of H^o to H⁺ by a carbon foil. We consider single-and multiphoton laser ionization as alternatives to using a fragile foil. The multiphoton case is of possible interest for selection of practical lasers, which tend to have increased power output at higher wavelengths. The formulas derived express the necessary laser powers for ionization of monoenergetic H^o beams; they also hold for beams of particles other than atomic hydrogen. The numerical examples given are for the 800-MeV PSR beam with momentum spread taken into account. Additionally, we discuss selective stripping as an implication of the inherent energy selectivity of the photoionization process.