A multisample, high‐intensity Cs sputter negative ion source for accelerator mass spectrometry applications

The development of a high‐intensity Cs sputter negative ion source has been completed. The source is equipped with a spherical tungsten ionizer and a target wheel with 18 sample positions. The wheel is separated from the hot sputter region by a gate valve in order to change the samples rapidly and reduce cross contamination. A drive system can push the selected sample into the sputter position and pull it back to the wheel. A metal‐ceramic bonded ring is used to support all the parts at sputter potential. The ring is protected from vapor depositions by a specially designed shielding structure, resulting in reliable insulation between the ionizer and the sputter samples. No insulation trouble has occurred during the work for over one year. Beams of 10‐μA BeO−, 5‐μA Al−, 4.5‐μA Fe−, and 350‐μA C−, etc. have been delivered. The normalized beam emittance ranges from (2–4) πmm mrad MeV1/2. The memory effect has been evaluated. More than 1000 and 500 times of attenuation for C− and BeO− are observed, respectively, in 10 min after a sample change. The ionization efficiency for 12C− is higher than 5.4% for a graphite sample.