PROGRESS REPORT ON THE HIGH-CURRENT ION-SOURCE OF THE ZURICH AMS FACILITY

We developed a cesium (Cs) negative ion sputter source with the follow ing feature: the vacuum chamber of the ion source and the target casse tte are at ground potential. Batches of targets can be loaded and unlo aded without interrupting the operation of the source. All control sys tems for sample loading and automatic changing are also at ground pote ntial. The new ion source incorporates a spherical Cs surface ionizer to increase the negative ion currents. Extensive tests with this sourc e showed the difficulty of such a concept: the high electric field ins ide the vacuum chamber in an environment of high Cs vapour pressure te nds to cause discharges and sparks when not properly designed. Ion pro duction rate was measured for many elements. In general, beam currents have increased by a factor of 10 compared to the old ion source used at our laboratory which utilized a frit-type ionizer. The ion source h as undergone successful long-term tests and is currently being install ed on the AMS beam line.