Life with MC-SNICS. Part II: Further ion source development at the Keck carbon cycle AMS facility

We report on an ongoing program of improvements to the National Electrostatics (NEC) MC-SNICS ion source at the KCCAMS laboratory at UC Irvine. Recent work has focused on vacuum improvements and on increasing the source output and efficiency. We replaced the extractor and preacceleration assemblies for a threefold improvement in pumping conductance, leading to lower source pressures and quicker startup after sample wheel changes. A switch to spherical ionizers caused a marked improvement in the focusing of the Cs beam, leading to major gains in ion source efficiency and negative ion beam quality. Better confinement of Cs within the new ionizer assembly resulted in lower Cs consumption and a significant reduction in arcing problems.