Optimizing the beam purity of the MIST-1 ion source

The Isotope Decay-at-Rest (IsoDAR) experiment seeks to place a high-intensity, proton-driven source adjacent to a kiloton-scale scintillator detector to investigate beyond standard model physics. This novel concept brings an accelerator near a large detector underground into a very low background environment. To provide the high number of required protons on target, IsoDAR will build a 60 MeV/10 mA proton driver cyclotron. To reduce space-charge effects, IsoDAR will accelerate H2+ instead of H+. MIST-1, a multicusp ion source, will provide the H2+ beam. It uses permanent magnets to create a multicusp field to confine a hydrogen plasma which is created in a discharge facilitated by a hot tungsten filament. Atomic processes inside the plasma include ionization-, dissociation-, and recombination processes leading to protons, H2+ and H3+ contributions to the beam. The rates of these processes depend on parameters such as magnet type and arrangement, filament shape and position, heating current, discharge voltage, and H2 gas inflow. MIST-1 has already demonstrated record currents for this type of source and an H2+ fraction of 80%, however, further optimization is ongoing. Here, we present MIST-1's performance at combinations of these parameters in order to maximize the H2+ fraction.