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

We developed a cesium (Cs) negative ion sputter source with the following feature: the vacuum chamber of the ion source and the target cassette are at ground potential. Batches of targets can be loaded and unloaded without interrupting the operation of the source. All control systems for sample loading and automatic changing are also at ground potential. The new ion source incorporates a spherical Cs surface ionizer to increase the negative ion currents. Extensive tests with this source showed the difficulty of such a concept: the high electric field inside the vacuum chamber in an environment of high Cs vapour pressure tends to cause discharges and sparks when not properly designed. Ion production 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 has undergone successful long-term tests and is currently being installed on the AMS beam line.