Installation of a 134-sample MC-SNICS ion source at NOSAMS and first results

In April 1999, the National Ocean Sciences AMS (NOSAMS) facility received t he shipment of a 134-sample MC-SNICS ion source from the National Electrost atics Corporation (NEC). It replaced one of the two 59-sample spherical ion izer sources (US-AMS Model 3090A, HVEE Model 846). In this paper, we will d escribe the adaptation of the NEC ion source to the US-AMS/HVEE recombinato r injector at NOSAMS. This is the first lime that the two leading sputter i on source designs are directly comparable on the same system. We will prese nt ion beam optics calculations for both in comparison with measured result s. Once fully operational, the new ion source will assume all of the sputte r sample measurements at NOSAMS, while the remaining 59-sample source will be replaced by the newly developed microwave gas ion source. One of the mos t desirable features of the MC-SNICS design is the smaller cathode geometry . At comparable extracted currents, the surface diameter of the pressed sam ples is reduced from 1.5 to 1 mm. A new, automatic sample pressing procedur e is being developed for this design. This will improve the capability for preparing and analyzing smaller sputter samples (carbon weight <100 <mu>g). Our US-AMS cathodes showed considerable reduction in the extracted current s when the sample diameter was reduced to 1 mm, even with samples of normal size (>200 mug C). (C) 2000 Elsevier Science B.V. All rights reserved.