Experimental determination of a species-dependent effect in the transverse emittances of sputter-generated negative-ion beams

We report experimental evidence of a previously unseen species-dependent effect in the transverse emittances of momentum-analyzed ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}_{}^{\mathrm{-}}{}_{}{}^{}$, ${}_{}{}^{58}{}_{}{}^{}$ ${\mathrm{Ni}}^{\mathrm{-}}$, and ${}_{}{}^{197}{}_{}{}^{}$ ${\mathrm{Au}}^{\mathrm{-}}$ negative-ion beams generated by cesium-ion sputtering. The differences in the emittances are found to be principally correlated with differences in the energy spreads in the respective ion beams, which have their origins in the sputter-ejection negative-ion formation process. The experimental equipment and techniques utilized for emittance data acquisition and analysis, and evidence for a species-dependent effect in the emittances and brightnesses of the subject ion beams, are presented in this paper.