Optimization of the plasma-sputter-type negative ion source

A study is being made to increase the beam current of the negative ions extracted from a plasma-sputter-type ion source operated with Cs. The result of the mass analysis showed that polyatomic carbon negative ions such as C₃^-, C₄^- and C ₅^- were extracted from the source with C^- and C₂^ons. The percentages of the sum of C^- and C₂^- currents to the total current increased by the Cs supply from 40% to 90%. To investigate the loss of negative carbon ions in the ion source plasma, the dependence of the ion beam currents on the gas pressure was measured. The C₂^- ion beam current took the maximum at 0.06 Pa ion source pressure with Ar plasma. The effective cross sections for electron detachment of C₂^- in Ar, Ne and He plasmas with electron density of 10¹¹-10¹² cm^-3 and electron temperature of 2-6 eV were measured. They were 1.5±0.1×10^-15 cm², 1.8±0.1×10^-15 cm² and 1.4±0.1×10^-15 cm², for Ar, Ne and He respectively