  Recently, the use of $\mathrm{H}_2^+$ ions instead of protons to overcome
space charge challenges in compact cyclotrons has received much attention. This
technique has the potential to increase the available beam current from compact
cyclotrons by an order of magnitude, paving the way for applications in energy
research, medical isotope production, and particle physics, e.g. a decisive
search for sterile neutrinos through the IsoDAR experiment. For IsoDAR we go a
step beyond just using $\mathrm{H}_2^+$ and add pre-bunching through a
Radio-Frequency Quadrupole (RFQ) embedded in the cyclotron yoke. This puts beam
purity and beam quality constraints on the ion source that no published ion
source has simultaneously demonstrated so far. Here, we report results from a
new multicusp ion source (MIST-1) that produces the world's highest
steady-state current of $\mathrm{H}_2^+$ from this type of ion source (1 mA),
with exceptionally low emittance (0.05 $\pi$-mm-mrad, RMS, normalized) and high
purity (80% $\mathrm{H}_2^+$). This result shows the feasibility of using a
multicusp ion source for IsoDAR and the RFQ direct injection prototype, and
paves the way to record breaking continuous wave (cw) beam currents of 5 mA
$\mathrm{H}_2^+$ (equivalent to 10 mA protons) from compact cyclotrons, ideal
for underground installation. This represents a significant advance, with
impact on neutrino physics specifically and high power cyclotron design in
general.
