Nuttens, V. Cailliau, P. Flandroy, Q. Kleeven, W.J.G.M. Mandrillon, J. Velten, Ph. JACoW Publishing Geneva, Switzerland 2673-5482 978-3-95450-212-7 10.18429/JACoW-CYCLOTRONS2022-THPO009 English 317-320 vacuum cyclotron injection extraction hadrontherapy Contribution to a conference proceedings 2023 2023-10 https://doi.org/10.18429/JACoW-CYCLOTRONS2022-THPO009 https://jacow.org/cyclotrons2022/papers/thpo009.pdf Since 2020, NHa and IBA collaborate on the development of the C400 cyclotron dedicated to hadron therapy. This machine accelerates C⁶⁺ and He²⁺ up to 400 MeV/n and H²⁺ up to 260 MeV/n. The H²⁺ is extracted by stripping and the other particles by electrostatic extraction. Vacuum management in the injection line and in the cyclotron are of prime importance to avoid large beam losses. Indeed, C⁶⁺ ions are subjected to charge exchange during collision with the residual gas. On the opposite, H²⁺ will suffer from molecular binding break up. According to cross section data, the constraints on the residual gas pressure is driven by C⁶⁺ in the injection line and by H²⁺ in the cyclotron. An electrical equivalent model of the vacuum system of the cyclotron, its injection and extraction lines has been developed in LTSpice® software to determine the pressure along the particle path. Contributions from outgassing surfaces, O-ring outgassing and permeation are included and vacuum pump requirement could be obtained. The expected beam transmission is then evaluated based on cross sections available from the literature.