Frequency Tunable sub-THz Gyrotrons for Spectroscopy Applications A. E. Fedotov, I. V. Zotova, M. Yu. Glyavin, R. M. Rozental, A. S. Zuev, N. S. Ginzburg, A. S. Sergeev and T. Idehara EPJ Web Conf., 187 (2018) 01025 Published online: 03 September 2018 DOI: 10.1051/epjconf/201818701025