Development of a Negative Ion Beam Apparatus

Primary design and construction tasks have been completed for a new negative ion beam apparatus for laser photodetachment experiments. A cesium sputtered negative ion source produces 10-20 keV ions which are formed into a beam and mass selected. Projects included installation of a new ultrahigh vacuum chamber, tuning of a 90$^{^{\circ}}$ mass separating magnet and associated beam optics, and construction of a photon-ion interaction region with neutral particle separation and detection. Working pressures of 1.0x10$^{-9}$ torr have been achieved in the analysis chamber, and successful detection of photodetached neutrals from multiple ion species has been demonstrated. Isotopic identification of Pt$^{-}$ has been used to determine the mass resolution to be $\sim $1 in 330 amu. Use of a limited sputter angle CeO$_{2}$ cathode in the source permitted production of $^{140}$Ce$^{-}$ beams of $\sim $70 pA with a cathode life up to 76 hours without deterioration of ion source performance.