A study of multipacting effects in large cyclotron cavities by means of fully 3-dimensional simulations*

Field emission model and secondary emission models, as well as 3D boundary geometry handling capabilities, are needed to efficiently and precisely simulate multipacting phenomena. These models have been implemented in OPAL, a parallel framework for charged particle optics in accelerator structures and beam lines. The models and their implementation are carefully benchmarked against a non-stationary multipacting theory. A dedicated multipacting experiment with nanosecond time resolution for the classic parallel plate geometry has also shown the validity of the OPAL model. Multipacting phenomena, in the CYCIAE-100 cyclotron, under construction at the China Institute of Atomic Energy, are expected to be more severe during the RF conditioning process than in separate-sector cyclotrons. This is because the magnetic stray fields in the valley are stronger, which may make the impact electrons easier to reach energies that lead to larger multipacting probabilities. We report on simulation results for CYCIAE-100, which gives us an insight view of the multipacting process and help to develop cures to suppress these phenomena.