Low power, 3.2-cm, efficient microwave electron cyclotron resonant ion source

Abstract

Design improvements in a microwave (2.45-GHz) plasma disk ion source have resulted in a compact, efficient, and low power ion source capable of delivering ion beam current densities in excess of 10 mA/cm2 . The ion source has been designed for a 3.2-cm-diam double graphite extraction grid set. Ion beam extraction was studied using argon and oxygen discharges with input gas flows of 1–5 standard cubic centimeters per minute (sccm) and input powers under 150 W. Ion beam currents of 20 to over 40 mA were obtained at extraction potentials of 1600 V. Double Langmuir probe measurements were made for argon, and by using a free-fall diffusion model, extracted beam current densities were shown to be consistent with measured discharge electron and ion densities. These experiments demonstrate the ability of microwave plasma technology to produce high beam current densities for both inert and chemically reactive gases. The compact electron cyclotron resonant microwave ion source shows significant improvements in efficiency, lifetime, and ion beam current densities over earlier designs and over similar size conventional broad beam dc and rf ion sources.