Production of highly charged ion beams from electron cyclotron resonance ion sources (invited)

Electron cyclotron resonance ion source (ECRIS) development has progressed with multiple-frequency plasma heating, higher mirror magnetic fields, and better technique to provide extra cold electrons. Such techniques greatly enhance the production of highly charged ions from ECRISs. So far at continuous wave (CW) mode operation, up to 300 eμA of ${\mathrm{O}}^{\mathrm{7+}}$ and 1.15 emA of ${\mathrm{O}}^{\mathrm{6+}},$ more than 100 eμA of intermediate heavy ions for charge states up to ${\mathrm{Ar}}^{\mathrm{13+}},$ ${\mathrm{Ca}}^{\mathrm{13+}},$ ${\mathrm{Fe}}^{\mathrm{13+}},$ ${\mathrm{Co}}^{\mathrm{14+}},$ and ${\mathrm{Kr}}^{\mathrm{18+}},$ and tens of eμA of heavy ions with charge states to ${\mathrm{Kr}}^{\mathrm{26+}},$ ${\mathrm{Xe}}^{\mathrm{28+}},$ ${\mathrm{Au}}^{\mathrm{35+}},$ ${\mathrm{Bi}}^{\mathrm{34+}},$ and ${\mathrm{U}}^{\mathrm{34+}}$ were produced from ECRISs. At an intensity of at least 1 eμA, the maximum charge state available for the heavy ions are ${\mathrm{Xe}}^{\mathrm{36+}},$ ${\mathrm{Au}}^{\mathrm{46+}},$ ${\mathrm{Bi}}^{\mathrm{47+}},$ and ${\mathrm{U}}^{\mathrm{48+}}.$ An order of magnitude enhancement for fully stripped argon ions $\text{(I⩾60\hspace{0.17em}}\mathrm{enA})$ were also achieved. This article will review the ECR ion source progress and discuss key requirement for ECRISs to produce the highly charged ion beams.