Orotrons and gyrodevices at terahertz waves

Summary form only given. Electron vacuum sources of coherent terahertz radiation are being now intensively developed at the Institute of Applied Physics (IAP). These devices are intended for wide-spread utilizing in many research and technical applications including spectroscopy, diagnostics of different media, communications, material processing etc. In this presentation, two types of promising THz electron oscillators, namely orotrons and gyrotrons, will be discussed. The orotrons have been realized at the IAP in collaboration with the Institute of Metrology for Time and Space and Institute of Spectroscopy. The operation of the orotron (or diffraction radiation generator) is based on the stimulated Smith-Purcell radiation of a rectilinear electron beam in a selective open cavity which has a periodic structure on one of its mirrors. At the moment, a series of the low-voltage (0.5-5 kV) orotrons developed generate in the frequency range of 0.1-0.4 THz with output power of 1.0-0.1 W and typical electrical-mechanical frequency tuning within an octave. Using same voltage, orotrons can enable higher power and frequency stability than BWOs that are most widespread devices within entire terahertz range. Orotrons with relativistic electron beams, which are studied at the IAP, are capable to provide significantly higher pulse THz power (up to MW level at ns pulse duration). Both conventional and large-orbit gyrotrons (LOGs) are also under development at the IAP The LOGs are based on the same mechanism of stimulated cyclotron radiation of electrons as conventional gyrotrons, but they are more selective when operating at higher cyclotron harmonics. Correspondingly, they work at lower magnetic fields. At the same time significantly more complicated electron guns are needed for the LOGs to provide appropriate axis-encircling electron beams. Such beams with electron energy 50-250 keV and very high compression have been obtained and powerful selective generation at 1st-5th cyclotron harmonics have been demonstrated in the IAP at millimeter and submillimeter waves. When operating at the third cyclotron harmonic generation with power level of 10-20 kW has been obtained in the range of 0.3-0.42 THz. Another prospective way for developing THz sources, that will be also presented, is realization of gyro-multipliers with self-exciting LF sections and HF sections operating at high cyclotron harmonics