McLean, M. Cenede, J. Hori, M. Tranquille, G. JACoW Publishing Geneva, Switzerland 2673-5350 978-3-95450-230-1 10.18429/JACoW-IBIC2021-TUPP14 English 223-226 proton vacuum antiproton electron impedance Contribution to a conference proceedings 2021 2021-10 https://doi.org/10.18429/JACoW-IBIC2021-TUPP14 https://jacow.org/ibic2021/papers/tupp14.pdf ELENA is a compact ring for cooling and further deceleration of 5.3 MeV antiprotons delivered by the CERN Antiproton Decelerator. It decelerates antiprotons to a minimum energy of 100 keV, creating special challenges for the beam instrumentation. These challenges have been addressed by an extremely sensitive SEM-Grid monitor which is also compatible with the UHV requirements of ELENA. Since November 2019 ELENA’s H⁻ ion source has been used to test the SEM-Grid monitors and since July 2020 the monitors have been used to commission the ELENA transfer lines. In this paper a summary of the features of the SEM-Grid will be given, and an overview of the commissioning activities. A technique for testing the integrity of an inaccessible pickup wire will also be described.