Investigation of Optically Grey Electron Cyclotron Harmonics in Wendelstein 7-XNeha Chaudhary, Johan W. Oosterbeek, Matthias Hirsch, Udo Höfel, Robert C. Wolf and W7-X TeamEPJ Web Conf., 203 (2019) 03005DOI: https://doi.org/10.1051/epjconf/201920303005