Experiments with rf ovens in ECR ion sources

A 34 mm diameter radio frequency (rf) oven system previously developed on bench was inserted and tested into the Electron Cyclotron Resonance (ECR) Ion Source Alice, producing beams from natural copper and silver samples; charge range was typically i=10-13 for copper and i=10-19 for silver, which well compares to previous source yield for xenon (charges 11-20). Some issues of oven design, including wire section effects, and circuit matching, are discussed; taps on the coupling transformer improved the flexibility of rf matching to different crucible materials (tantalum or steel). Details of operating experience (cleaning the oven and replacing sample) are reported; sample duration was more than 100 h and temperature T-s in excess of 1750 K were demonstrated. The ion source operation depends on both the oven distance L-oe from ECR plasma and the bias voltage V-b of the sample. Best conditions were found for close (L(oe)congruent to70 mm) or preferably intermediate positions (L(oe)congruent to106 mm) and for sample negative respect to ECR chamber V-b<-400 V. Final results of current for silver [for example I(Ag-107(17+)) about 1000 nA] are well comparable to xenon case [for example I(Xe-129(18+)) about 500 nA] after correcting for isotopic abundance. Memory effect of metal ion generation was also important and is discussed as well as other time dependent effects and an empirical fit for the aggregate results of silver mass flow. New oven prototypes reached T(s)congruent to2250 K in development tests. (C) 2004 American Institute of Physics.