1. G. G. Denisov, V. E. Zapevalov, A. G. Litvak, and V. E. Myasnikov, Radiophys. Quantum Electron., 46, No.10, 757 (2003).
2. M. Thumm, Plasma Phys. Control. Fusion, 45, A143 (2003).
3. B. M. Garin, in: Proc. Third Int.Conf. on Millimeter-Wave and Far-Infrared Science and Technology, China, 1994, p. 275.
4. R. Heidinger, in: 19th Int. Conf. on IR and MMW, Japan, 1994, p. 277.
5. R. Heidinger, J. Molla, and V.V. Parshin, in: 21st Int. Conf. on IR and MMW, Germany, 1996, p. AW8.