Development of Negative Heavy Ion Sources for Plasma Potential Measurement

"A plasma sputter negative ion source was studied for its applicability to the potential measurement of a fusion plasma. Both the beam current density and the beam energy spread are key issues. Energy spectra of a self extracted Au^- beam from the source were measured under the condition of a constant work function of the production surface. The FWHM increases from 3 eV to 9 eV monotonically as the target voltage increases from 50 V to 300 V, independently from the target surface work function of 2.2 - 3 eV.