Bias disk boost technique for pulsed-operation electron cyclotron resonance ion sources

A simple, effective technique to increase the intensity of multiply charged ions has been developed for pulsed-operation electron cyclotron resonance ion sources (ECRISs). The technique is realized simply by applying an additional boost voltage of about −1 kV to a negative constant voltage on the bias disk. The technique can be applied to general ECRISs by adding electric devices to the bias disk circuit, such as a high-voltage power supply, a fast high-voltage switch, and a diode. The effect of the technique depends on the ion species, and we obtained a maximum ion intensity increase of 66% for O${}^{6+}$ compared with the conventional bias disk method. In particular, the technique can be applied to the existing pulsed-operation ECRISs used at a heavy-ion cancer therapy facility where multi-ion treatment with multiply charged oxygen and neon ions is planned to be introduced.