First-turn losses in the LAMPF Proton Storage Ring (PSR)

Beam-loss measurements protons injected into the PSR are lost during the first turn. We describe a plausible mechanism, involving field stripping of excited hydrogen atoms, for these losses. Protons are injected into the PSR by transporting a neutral hydrogen beam through a hole in the yoke of one ring bender and then through a carbon foil on the ring axis. The foil strips roughly 93% of the beam atoms to protons. Although the original PSR design assumed that all unstripped atoms would pass through a hole in the yoke of the next downstream bender and on to a beam stop, recent calculations indicate that about 6% of these unstripped atoms will emerge from the foil in an excited state with principle quantum number n≥23. These calculations also indicate that atoms in excited states with n≥3 will be stripped quickly to protons in the 1.2-Tesla field of the downstream bender. The trajectories of these protons will be outside the phase-space acceptance of the ring and will be quickly lost by collision with the beam pipe, thereby giving rise to first-turn losses. The estimated numbers of protons that would be lost by this mechanism are consistent with the observed first-turn loss rates. This mechanism has important consequences for the design of future storage rings that use neutral atom or negative ion stripping for injection