Development of a compact high current low emittance RF ion source

Abstract

A 13.56MHz inductively coupled plasma based RF ion source is developed for production of high brightness focused ion beams of heavy gaseous elements for high speed milling and light ions for high speed imaging. In order to obtain ion beams with low emittance, no magnetic field of any kind is used in the ion source. However, to achieve the high plasma density, the plasma chamber volume is reduced to couple RF power as high as 8–12W/cm3 to the plasma. Measurements show that the normalized rms emittance of 0.6mA Ar1+ beam to be as low as 0.0075mm-mrad while it is 0.004mm-mrad for 1.2mA of ion beam from hydrogen plasma. With a simple parallel plate extraction system with an aperture of 2mm diameter, 80mA/cm2 of ion beam from hydrogen plasma could be extracted at 3.5kV extraction potential and 300W of RF power. The ion source has been operated with other heavy gases and results show that more than 1mA of xenon and krypton ion beam could easily be extracted at 5kV extraction potential and 200W of RF power. In this article, the capability of the ion source to produce high current, low emittance heavy as well as light ion beams is presented.