Possibility of generating H+, or H2+, or H3+ dominated ion beams with a 2.45 GHz permanent magnet ECR ion source

Abstract

At Peking University (PKU), experimental research as well as theoretical study on how to produce high intense H+, H2+, or H3+ dominated ion beams with a compact permanent magnet 2.45 GHz electron cyclotron resonance (PMECR) ion source have been continuously carried out in the past few decades. Based on the comprehension of hydrogen plasma processes inside a 2.45 GHz PMECR discharge chamber, a three-phase diagram of ion fraction dominant regions that illustrates the relationship between the H+, H2+, and H3+ ion species and working parameters was presented. Meanwhile, a numerical model based on the particle population balance equations was developed for quantitative comprehension of electron cyclotron heated hydrogen plasma. Calculated results of H+, H2+, and H3+ fractions against gas pressure, microwave density, and wall material obtained with this numerical model agree well with the measured ones. Recently, a miniaturized ECR ion source has been developed, and a 52 mA hydrogen beam was extracted. Under the guidance of the model, H+, H2+, and H3+ beams with a fraction of 88%, 80%, and 82%, respectively, were obtained with this miniaturized ECR ion source under suitable working parameters. A PMECR ion source for a proton therapy facility has been built at PKU recently. A 34 mA beam H+ fraction of 91% was obtained at the first attempt.