Dabin, J. Adant, B. Cailliau, P. Ellis, K. Forton, E. Mandrillon, J. Ponter, T.S. Verbruggen, P. JACoW Publishing Geneva, Switzerland 978-3-95450-205-9 10.18429/JACoW-Cyclotrons2019-TUP009 English 169-172 TUP009 cavity cyclotron multipactoring vacuum electron Contribution to a conference proceedings 2020 2020-06 https://doi.org/10.18429/JACoW-Cyclotrons2019-TUP009 http://jacow.org/cyclotrons2019/papers/tup009.pdf In a cyclotron, RF cavities are usually among the most reliable subsystems, provided minimal care and maintenance. Nevertheless, several parameters may affect cavity performance after several years of operation. To name a few typical causes of degradation are: decreasing vacuum quality, various gas loads or gas qualities triggering adverse effects, deposition of highly emissive material on the cavity due to overheating of components like pass-through connectors, accidental use of chemicals or not-suitable greases. The cavity status can be monitored but, in the worst cases, the RF tuning may become difficult and it is important to apply methods in order to recover a better cavity Q-factor. In this paper, cases of cavity pollution will be shown, their potential root causes discussed and some recovery methods described.