Stengler, T. Aulenbacher, K. Hug, F. Kürzeder, T. Simon, D. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-MOPB101 English 297-300 MOPB101 ion cavity cryomodule operation experiment Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-MOPB101 http://jacow.org/srf2017/papers/mopb101.pdf At Johannes Gutenberg-Universität Mainz, the Institute for Nuclear Physics is currently building the multiturn ERL 'Mainz Energy-Recovering Superconducting Accelerator' MESA. The §I{1.3}{\giga\hertz} cryomodules are based on the ELBE modules at Helmholtz Center Dresden-Rossendorf (HZDR) but are modified to suit the high current, energy recovering purposes of MESA. With two 9-cell TESLA cavities each, they shall provide §I{50}{\mega\electronvolt} energy gain per turn. The design and fabrication was done by Research Instruments GmbH, Bergisch Gladbach, Germany. The current status of the cryomodules, the test set up at the Helmholtz-Institute Mainz, the cavity properties and their tests will be discussed.