Transport characteristics of space charge-dominated multi-species deuterium beam in electrostatic low-energy beam line

The transport characteristics of a space charge-dominated multi-species deuterium beam consisting of $D_1^{+}$, $D_2^{+}$, and $D_3^{+}$ particles in an electrostatic low-energy beam line are studied. First, the envelope equations of the primary $D_1^{+}$ beam are derived considering the space charge effects caused by all particles. Second, the evolution of the envelope of the multi-species deuterium beam is simulated using the PIC code TRACK, with the results showing a significant effect of the unwanted beam on the transport of the primary beam. Finally, different injected beam parameters are used to study beam matching, and a new beam extraction system for the existing duoplasmatron source is designed to obtain the ideal injected beam parameters that allow a $D_1^{+}$ beam of up to 50 mA to pass unobstructed through the electrostatic low-energy beam transport line in the presence of an unwanted ($D_2^{+}$, $D_3^{+}$) beam of 20 mA; at the same time, distortions of the beam emittance and particle distributions are observed.