A 2.45 GHz microwave ion source for carbon positive-ion mass spectrometry

Abstract

Carbon positive-ion mass spectrometry (C-PIMS) is a two stage mass spectrometer by producing high charge state carbon ions (C2+/C3+) directly in the ion source to eliminate molecular interferences and by converting the beam (C2+/C3+) to C− ions in a charge exchange cell to eliminate 14N interference. It has been proven that C-PIMS is an effective method for the detection of radiocarbon at low levels. This article will focus on the multiply charged carbon ion generation. Based on the fact that a C-PIMS system is usually equipped with high frequency electron cyclotron resonance (ECR) ion sources. It is significant to investigate if the simple and low-cost 2.45 GHz ECR ion source is an optional choice for the C-PIMS. At Peking University (PKU), a 2.45 GHz microwave ion source with minimum-B magnetic field configuration is designed for the production of intense C2+ beam. Preliminary experiments have proved that the 2.45 GHz microwave ion source can produce up to 40 μA@40 keV C2+ beam. In addition, it was found that argon could increase the decomposition efficiency of CO2, which can eliminate CO2+ ions of the extracted beam.