A compact, resonant cavity, five centimeter, multicusp, ECR broad-beam ion source

Researchers in many industrial and scientific activities desire a physically compact, long-life ion source that can produce high-current density broad-beams in chemically reactive gases such as CF4 and O2. Earlier studies of a multicusp-ECR microwave-cavity ion source concept have demonstrated that a 5-cm-diam discharge can produce high beam current densities for broad-beam applications. More recently, this ion source concept has been redesigned to compact its size and to improve its operation and lifetime. In particular the physical size of the cylindrical microwave-cavity has been reduced to an outer diameter of 3.75 in. and an inner diameter of 3.5 in. Improved water and air cooling and permanent magnet arrangement allows the instrument to be operated continuously with powers greater than 200 W. The microwave cavity operates in the TE111 mode at 2.45 GHz and is self-starting in Ar, O2, and N2 gases at discharge pressures necessary for beam extraction (<5 mTorr). Ion densities of 1011/cm3–1012/cm3 have been achieved with input powers less than 200 W. These ion densities produce ion current densities in excess of 10 mA/cm2 which may be extracted by either single- or multiple-grid extraction optics. The operation, diagnostics and performance of this new ion source is reviewed.