At Peking University (PKU), experimental research as well as theoretical study on how to produce high intense H+, H2+ or H3+ domain ion beams with a compact permanent magnet 2.45 GHz ECR ion source (PMECRIS) have been continuously carried out in the past decades.
With a so-called standard PKU PMECRIS, a 130 mA@50 keV pulsed (100 Hz/1 ms) H+ beam with H+ faction of 90% was obtained in 2016. A 50 mA@50 keV CW H+ beam with this PMECRIS has been run continuously for 300 hours without any beam-off, spark, beam drop. It proved that the availability and reliability of this standard PKU PMECRIS is nearly 100%. The root-mean-square (RMS) emittance of 50mA@50keV CW H+ is about 0.19 π.mm.mrad. Investigation on high intensity H2+ and H3+ ion domain beam generation has been also carried out since 10 years ago. In 2013, 40 mA H2+ and 20 mA H3+ beams were obtained with a source named as PKU PMECR II. The corresponding fractions of H2+ ion and H3+ ion within the total extracted beam are 47.7% and 43.2% respectively.
Recently, more attentions were paid on the understanding of hydrogen plasma to improve the performance of 2.45 GHz ECR hydrogen ion sources. Some hydrogen plasma parameters were acquired with method of optical emission spectroscopy (OES) in a 2.45 GHz ECR ion source. Meanwhile, a numerical model based on the particle population balance equations was developed for quantitative comprehension of electron cyclotron heated (ECH) hydrogen plasma. On these basis, working parameters of the source, wall material of the discharge chamber, and other factors have been optimized according to the calculated results. With these improvements, more than 42 mA H2+ ion beam with species fraction of 54% and 20 mA H3+ ion beam with species fraction of 55% were obtained with PKU PMECR II . Recently, a miniaturized ECR ion source was developed and a 52 mA hydrogen beam was extracted. Under the guidance of the model developed here on the ion species fraction selection, this miniaturized ECR ion source can easily produce either H+ or H2+ or H3+ domain beam. Measurement results with the miniaturized ECR ion source show that under different working parameters H+, H2+ and H3+ fraction can reach up to 88%, 80% and 82%, respectively.
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