CHARGE-EXCHANGE ATOMS AND ION-SOURCE DIVERGENCE IN A 20 TW APPLIED-B ION DIODE

Space- and time-resolved spectroscopy is used to measure properties of several-keV Li atoms in a 20 TW ion diode. These measurements but in the diode anode-cathode gap are used in a charge-exchange model for th e Li atom production in order to obtain the Li+ beam angular divergenc e within 50 mu m of the LiF-coated anode surface. This ion divergence near the surface is surprisingly large, and accounts for about half th e typical 25 mrad final accelerated-beam divergence. The measurements provide constraints for models attempting to explain highly diverging ion emission from thin alkali-halide films in similar to 10 MV/cm appl ied fields.