Design and preliminary results of the microwave-driven proton ion source developed at the Center for Energy Research.

Abstract

A novel medium-current (up to 20 mA), low normalized beam emittance (<1 π mm mrad) electron cyclotron resonance microwave H+ ion source has been developed at the Center for Energy Research in Budapest, Hungary. This high-stability design targets an energy ripple below 1% while delivering a continuous or pulsed proton beam with adjustable pulse duration (0.1-10 ms) and frequency (0.01-40 Hz) at 35 keV beam energy. The design includes a microwave generator, a four-stub tuner, an E-bend, a DC break, a vacuum window, and a four-section matching transformer connected to a 90 mm diameter, 100 mm long cylindrical ionizing chamber. The magnetic field is generated by six axially aligned permanent magnet bars. Additionally, fifteen 4 mm-diameter holes allow discharge observation, pressure monitoring, and gas inlet placement. Magnetic simulations guided the layout of the permanent magnets and ferromagnetic components to shape the desired field. Beam simulations confirmed the feasibility of appropriate focusing. High-voltage insulators are mounted radially to minimize the gap between the extraction slit and ion optics. Experimental tests demonstrated stable beam extraction up to ∼6 mA at ∼250 W microwave power using a 2 mm aperture radius. A novel high-voltage beam chopper was also tested, achieving beam switch-off within ∼10 µs and enabling controlled time-structured beam operation. These results confirm the ion source's potential for integration into compact accelerator-based neutron generators, targeting applications such as boron neutron capture therapy and materials science investigations.