Beam optics study on high-intensity beam extraction methods for a Q/A=1/2 K100 compact cyclotron

High-current beam acceleration of compact cyclotrons can be limited by extraction efficiency since fractional beam losses at the extraction can severely activate cyclotron components. We have designed a high-current Q/A = 1/2 K100 compact cyclotron, where Q is the charge state, A is the mass number, and K is a maximum kinetic energy in MeV/u when multiplied by (Q/A)2, to accelerate H2+, D+, and He2+ for medical isotope and neutron productions, and light heavy-ions such as 14N7+ and 36Ar18+ for space radiation effects and radiobiology studies. The beam energy is fixed at 25 MeV/u, and the maximum proton current is expected to be higher than 2 mA. An extraction efficiency of over 99.8% is required at a beam power of 50 kW to allow routine hands-on maintenance. Beam optics simulation with realistic emittance shows that high efficiency can be achieved using an electrostatic deflector with four RF dees at a voltage of 100 kV with the last-turn separation of roughly 0.9 cm. We have also explored a magnetic extraction method often called self-extraction, with a groove on the pole tip, locally reducing the sector magnetic field along the extracted orbit. Charge-stripping extraction is studied for an H2+ beam to enable energy variability for protons at around 10 MeV, and simultaneous extraction of remaining H2+ is feasible at 25 MeV/u.