A 263 GHz continuous-wave (CW) gyrotron was developed at the IAP RAS for future applications as a microwave power source in Dynamic Nuclear Polarization / Nuclear magnetic resonance (DNP/NMR) spectrometers. A new experimental facility with a computerized control was built to test this and subsequent gyrotrons. We obtained the maximum CW power up to 1 kW in the 15 kV/0.4 A operation regime. The power about 10 W, which is sufficient for many spectroscopic applications, was realized in the low current 14 kV/0.02 A regime. The possibility of frequency tuning by variation of the coolant temperature about 4 MHz/1 °C was demonstrated. The spectral width of the gyrotron radiation was about 10(-6).

The study of the gas discharge in quasioptical beams of electromagnetic radiation of the terahertz (THz) frequency band is attractive for fundamental and applied research. The study of this discharge was made possible by the emergence of unique and reliable sources of radiation of the THz frequency band. Electrovacuum radiation sources of THz band (gyrotrons) have been created at the Institute of Applied Physics (IAP RAS) (Nizhny Novgorod) with a power order of 100 kW in pulsed mode of operation (pulse duration ~ several dozens of µs) and a kilowatt in continuous mode, and investigations of gas discharge phenomena in various gases have been started. Even the first experimental studies of the discharge in noble gases (argon) showed a significant difference in the THz discharge from the discharge at lower frequencies, even in the dynamics of discharge glow. The maximum of the discharge glow was observed after the end of the THz pulse and the afterglow duration was hundreds of microseconds. This paper is devoted to the theoretical and experimental study of the breakdown thresholds of various gases by radiation at 263 and 670 GHz and the study of discharge dynamics in noble and molecular gases under the action of 670 GHz radiation.

A 250 GHz continuous-wave (CW) gyrotron has been developed at the IAP RAS jointly with GYCOM Ltd., as a prototype of the microwave source for the envisaged prospective nuclear fusion power plants (DEMO). The main applications of such a tube are electron cyclotron resonance heating and electron cyclotron resonance current drive of magnetically confined plasma as well as its diagnostics based on collective Thomson scattering in various reactors for controlled thermonuclear fusion (e.g., tokamaks and stellarators). The results of the preliminary experimental tests in a pulsed mode of operation are presented. The microwave power of up to 330 kW with an efficiency of 30% without collector depression was obtained. At an accelerating voltage of 55 kV and an electron beam current of 12.5 A (which corresponds to the design parameters for CW operation), the measured output power was about 200 kW. The TEM mode content evaluated at the tube output is not less than 98.6%.

Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10−4. Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 × 10−12 and 10−10, respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.