Investigation of Optically Grey Electron Cyclotron Harmonics in Wendelstein 7-X Neha Chaudhary, Johan W. Oosterbeek, Matthias Hirsch, Udo Höfel, Robert C. Wolf and W7-X Team EPJ Web Conf., 203 (2019) 03005 Published online: 25 March 2019 DOI: 10.1051/epjconf/201920303005