High-current H₂ ⁺ beams from a filament-driven multicusp ion source

We report the results from a new multicusp ion source (MIST-1) that produces record steady-state currents of H₂ ⁺ (1 mA) from this type of ion source with high purity (80% H₂ ⁺). We built MIST-1 to fulfill the stringent beam purity and beam quality requirements for IsoDAR, a proposed discovery-level neutrino experiment, requiring a 10 mA, 60 MeV/amu continuous wave (cw) proton beam on the target. IsoDAR will use a cyclotron accelerating H₂ ⁺ ions and using a novel radio frequency quadrupole (RFQ) direct injection method. Systematic measurements, varying discharge voltage, discharge current, and gas pressure, indicate that the ideal operating regime is at low pressure, high discharge current, and high discharge voltage. We have measured the combined species emittance after the source extraction to be <0.05 π-mm-mrad (rms, normalized) for a 0.95 mA beam. Beyond showing high currents and high H₂ ⁺ fraction, our measurements agree well with high fidelity simulations. These results show the feasibility of using a multicusp ion source for IsoDAR and the RFQ direct injection prototype and paves the way to record breaking cw beam currents of 5 mA H₂ ⁺ (equivalent to 10 mA protons) from compact cyclotrons, ideal for underground installation.