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.

Physics-Uspekhi (Advances in Physical Sciences) is the English edition of the Russian monthly journal Uspekhi Fizicheskikh Nauk (UFN) journal.

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 TEM₀₀ mode content evaluated at the tube output is not less than 98.6%.

We explore the possibility of a significant increase in the sensitivity of high-resolution molecular spectroscopy in the subTHz range by the method of radio-acoustic detection of radiation absorption using the gyrotron as a source of high-power, continuous, frequency-tunable, highly stable radiation source. We demonstrate that the sensitivity increases in direct proportion to the radiation power until the molecular line saturation is reached. For unsaturated lines corresponding to rotational transitions of methane, a sensitivity of the order of $\alpha;_{\rm min}\approx 10^{-11}{\rm cm}^{-1}$ is achieved for a power level of about 20 W, which was limited in this work by technical reasons. Examples of spectral line records of other light molecules such as SO $_2$ , OCS and CH $_3$ OH are given. These records permit one to examine the spectral content of gyrotron radiation. The presence of high harmonics without any external frequency multiplier is revealed and evaluated for the first time. Prospects for a further increase in the sensitivity of the method by increasing the radiation power by one or two orders of magnitude are discussed.

To cover the so-called terahertz gap in powerful sources of coherent electromagnetic waves, a second-harmonic gyrotron operating in a 10 T liquid helium-free superconducting magnet has been designed, manufactured, and tested. With an operating voltage of 15 kV and a beam current of 0.6 A, the gyrotron generated coherent continuous-wave radiation at a frequency of 0.526 Terahertz with an output power of 250 Watts and an efficiency of 2.7%.