Low-voltage extraction characteristics of ion beams and space potential measurements on ECRIS

We have been using an electron cyclotron resonance ion source (ECRIS) for ion beam production, and it is desirable to construct a universal ECRIS that can produce ions with a wide range of mass/charge ratios, e.g. from several to several thousand. We investigated the characteristics of ions with high mass/charge ratios, e.g., iron endohedral fullerenes production, which requires low voltage beam extraction. We investigated the characteristics of the ion beam extraction at low extraction voltage. It is found that the beam current almost obeyed the Child-Langmuir law for various ion species. The space potential of the plasma in the ion source can be obtained from the relation between the extraction voltage and the square of the magnetic field strength of the dipole magnet. It is found that space potential values are larger with large charge state of ions, in low gas pressure condition and in high microwave incident power. At the same time, the plasma space potential was measured by using a Langmuir probe and compared with the ion beam method. It is found that same trend is confirmed with probe method.