A transformer coupled plasma ͑TCP͒ ion source has been tested in order to test its feasibility as a high brightness ion source for focused ion beam. When operating the TCP ion source with filter magnets in front of plasma electrode for a negative ion source, lower emittances are expected. Extracted beam emittances are measured with an Allison-type scanning device for various plasma parameters and extraction conditions. The normalized emittance has been measured to be around 0.2 ͑ mm mrad͒ with beam currents of up to 0.55 mA. In particular, noting that multicusp magnets have a role in decreasing the emittance as well as increasing plasma discharge efficiency, transverse magnetic field has been confirmed to be a useful tool for decreasing emittance via electron energy control.
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