The extraction of both positive and negative ions from a volume cusp H- ion source

The TRIUMF licensed H- ion source is known to produce 15 mA of H- ions, but some applications, such as cyclotrons, require the injection of both positive and negative ions. Furthermore, when using a tandem accelerator, there would be a benefit in using an ion source that can directly extract H- and He+. A charge exchange chamber would only have to be used with the He+ beam for the production of He-. In this paper, we present the conversion of the H- ion source to allow for the extraction of both positive (He+, H+, H-2(+) and H-3(+)) and negative (H- and D-) ions. In the modified design, up to 3 mA of protons and 2 mA of He+ can be extracted when using positive extraction power supplies and up to 5 mA of H- can be extracted when the polarity of the power supplies switched to negative extraction. We study how the ion source parameters affect the proton fraction and we look at the influence of the magnetic filter field in the plasma chamber.