Plasma Generation and Beam Extraction on Reentrant-Cavity-Type Electron Cyclotron Resonance Ion Source

An electron cyclotron resonance (ECR) ion source 8 cm in diameter using a reentrant coaxial cavity and a ring cusp magnetic field was developed to improve plasma uniformity and operational reliability. The reentrant coaxial cavity is utilized to achieve electrical breakdown easily, to tune in variable electromagnetic fields and to introduce microwaves into plasma from an annular window of a discharge chamber sidewall. Microwaves are resonantly absorbed by the ECR magnetic field. Above 10 sccm flow rate for Ar, uniform and overdense plasmas were obtained in an area 4 cm in diameter from the center axis. The maximum plasma density of 1.26×1011 cm-3 was achieved on the center axis at 20 sccm. However, plasma densities for N2 and O2 were lower than the cutoff density. The maximum ion beam current density of 1.26 mA/cm2 was obtained at a forward power of 304 W for Ar.