Gyrotrons with Shortened Cavities as Tunable Sources of Powerful Sub-Terahertz Radiation for Spectroscopic ApplicationsM.Yu. Glyavin, A.E. Fedotov, R.M. Rozental, I.V. Zotova, A.S. Zuev, V.N. Manuilov, M.Yu. Tretyakov and D.S. MakarovEPJ Web Conf., 195 (2018) 01012DOI: https://doi.org/10.1051/epjconf/201819501012