Laser-assisted charge exchange as an atomic yardstick for proton beam energy measurement and phase probe calibration

Abstract

Laser-assisted charge exchange (LACE) is a novel scheme for injecting H^{-} ions into proton rings. Lorentz stripping of H^{-} ions into bare protons in magnetic dipoles is enabled by laser excitation that reduces the electron binding energy. We show that such atomic transitions impose very precise requirements on ion and laser parameters which can be utilized to measure the ion velocity. At the LACE experimental station at the Spallation Neutron Source (SNS), proton beam energy has been measured via LACE to a precision of <1 MeV for a ≈1 GeV beam. To verify the results against the existing energy measurement method at the SNS which calculates revolution frequency in the accumulator ring, we discuss how knowledge of the beam energy can be employed to synchronize phase probes. Such beam-based calibration using energy measurements via both LACE and the SNS ring show that the two methods produce consistent results.