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Energy calibration of fast alkali beams obtained from charge-exchange sources

The authors present an experimental method to determine the true energy of alkali beams obtained from charge-exchange sources in the energy region up to 400 eV. Using an alkali-noble-gas scattering experiment, the shift of a particle structure in the energy spectra of inelastically-scattered particles is studied as a function of the alkali-beam intensity. This shift is attributed to a decrease in beam energy due to intensity-dependent space-charge effects. Extrapolation to zero intensity allows calibration of the beam energy. Space-charge related energy deficits of about 6 eV have been found at beam energies around 300 eV. The results can be qualitatively understood with a simple model for the space-charge distribution in the source.