Fabrication and tests of a rf cavity for a novel compact superconducting cyclotron for radioisotope production *

The AMIT cyclotron will be a 8.5 MeV, 10 μA, CW, H accelerator for radioisotope production, including a superconducting, weak focusing, 4 T magnet, allowing for a low extraction radius and a compact design. The cavity is a 60 MHz, quarter wave resonator powered by a modular 8 kW solid state amplifier. The design of the cavity dealed with challenging requirements: high electric fields required by a high voltage (60 kV) on a small gap, a small aperture of the magnet leading to high capacitances and thermal losses and a requirement for a low overall size of the cavity. The fabrication process included high precision machining, soft soldering, laser welding and careful metrologies, which are described together with other technical and practical aspects. The low power tests showed a good agreement with the simulations. The conditioning of the cavity was performed with a 1.1 T magnetic field applied on the central region. It was successfully finished regarding to maximum voltage reached, power losses and temperatures. The cavity was also tested at high power with a constant hydrogen flow injected in the central region (as expected in the cyclotron) with success.