Abstract
Laser-assisted charge exchange (LACE) is a novel scheme for injecting ${H}^{\ensuremath{-}}$ ions into proton rings. Lorentz stripping of ${H}^{\ensuremath{-}}$ 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 $<1\text{ }\text{ }\mathrm{MeV}$ for a $\ensuremath{\approx}1\text{ }\text{ }\mathrm{GeV}$ 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.
Highlights
Laser-assisted charge exchange (LACE) is a novel scheme for injecting H− into proton rings with the help of lasers
We demonstrated that the setup for LACE can be applied to measure proton beam energy
This extra application enhances the benefits of adopting LACE and its success is testimony to the growing impact of lasers in accelerators
Summary
Accurate knowledge of the beam energy is crucial to the operation of ion accelerators. Beam-induced signals along phase probes at different locations constitute a linear arrival time versus distance relation that gives the beam velocity This TOF technique is widely used in ion linacs for direct beam energy measurements [1,2,3,4,5]. We discuss how the system for laser-assisted charge exchange (LACE), a novel injection scheme into proton rings that makes use of lasers, can be directly employed to perform beam energy measurements Such an application enhances the benefit of adopting LACE and eliminates the need to construct a single-purpose laser system, as was done at LAMPF, for spectroscopy-based energy measurements. Since hydrogen atoms undergo negligible velocity change as LACE inverts their polarity, both the H− beam energy upstream and the proton beam energy downstream are measured by LACE simultaneously
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