Ion beam acceleration by an RFQ with an LC resonance circuit

Abstract

For the development of a high current MeV implanter, ion beam acceleration using a variable energy RFQ system has been studied. The RFQ system consisted of an LC resonance circuit and conventional RFQ electrodes of 1.3 m in length. The output energy could be continuously varied by changing the resonance frequency of the circuit. The electrodes were designed to accelerate nitrogen ion beams (N +) from 10 keV to 270 keV in order to investigate fundamental acceleration characteristics of the system. The designed intervane voltage was 26 kV. By improving the LC resonance circuit to generate a high voltage of radio frequency, a shunt impedance of over 70 kΩ was obtained, which was sufficient for MeV-range acceleration. Experimental results showed that N + beams were accelerated to 265 keV and Ar 2+ beams to 740 keV. Energy was varied by changing the frequency, in agreement with the calculated value. It was concluded that the RFQ system driven by the LC circuit should be very useful for MeV ion implantation in semiconductor device fabrication.