Mikhail Yu. Glyavin

A compact gyrotron scheme utilizing a nonuniform, high-gradient magnetic field is proposed and experimentally demonstrated in this letter. A high-gradient magnetic confinement profile is established from the cathode emission region to the interaction region within an axial distance of only 105 mm. Despite a steep local magnetic field gradient at the emitter and the absence of extended uniform-field sections, the electron beam undergoes adiabatic evolution, preserving beam quality and velocity spread during compression. This enables efficient beam–wave interaction in a compact cavity with a straight section of 65 mm, wherein the magnetic field uniformity is maintained within ±0.1% over 17.5 mm and ±0.5% over 37.5 mm. Experimental results confirm stable operation at 28.2 GHz, demonstrating a peak efficiency of 22.6% at an output power of 32.2 kW and a maximum output power of approximately 36 kW with an associated efficiency of 21.8%. These findings validate a viable pathway toward miniaturized, low-power consumption gyrotrons compatible with simplified magnetic topology for millimeter-wave applications.

Based on numerical simulation, the parameters of a megawatt gyrotron with operating frequency of 170 GHz and the operating mode TE25,10 were optimized to increase the output power up to 1.2 MW while maintaining an acceptable level of peak Ohmic loads on the cavity wall. This result is achieved by increasing the beam current while shortening the length of the regular part of the resonator. At the same time, the thermal load in the resonator remains at an acceptable level. The optimal relation between the resonator length and the operating current was found, taking into account the limitations of the cathode emission capacity. The obtained data can be used to implement a gyrotron with increased power, corresponding to the new requirements for the ITER plasma heating system, while maintaining the configuration of the cathode unit and quasi-optical converter.

Axis-encircling electron beams generated by cusp guns have been pivotal in advancing terahertz (THz) gyrotrons to high-harmonic operation due to its high mode selectivity. However, the presence of beam ripple weakens the coupling to the desired mode while simultaneously enhancing parasitic mode oscillations, thereby degrading mode selectivity and reintroducing mode competition. This study introduces an effective potential model based on the conservation of canonical angular momentum (CAM) to reveal the coupling mechanism between the electron’s guiding radius and its transverse velocity. We demonstrate that the key to forming low-ripple beams lies in preserving the minimum transverse energy state via trajectory control. To this end, an isolated, floating-bias internal electrode is introduced for active beam trajectory control and manufacturing error compensation, successfully maintaining the beam average guiding radius below $10~\mu $ m within a wide tolerance range. The proposed method will enable superior mode selectivity in high-frequency regimes, thereby promoting the development of high-harmonic THz gyrotrons.

We propose a gyrotron scheme with a two-mirror echelette-type resonator to obtain high-power continuous wave terahertz (THz) radiation, in which a corrugated profile applied to one of the mirrors is specified in the transverse plane (with respect to an electron's translation velocity). The gyrotron has been driven by a sheet helical electron beam (2 A/20 keV) with a pitch-factor of 1.2 and acceptable velocity spread formed by a planar magnetron-injection gun. The theoretical analysis was carried out both within the framework of a self-consistent theory and on the basis of 3D particle-in-cell simulations. The linear and nonlinear stages of electron–wave interaction were analyzed. Simulations demonstrate the operability of the proposed gyrotron circuit in the frequency range of 0.79 THz, operating at the second cyclotron harmonic with a magnetic field strength of 15 T at the high-order TE0,50,1 mode. The output power level in the steady-state single-mode oscillation regime reached several kilowatts with an Ohmic loss value of less than 20%. Proof-of-principle experiment was carried out to study the selective characteristics of a two-mirror echelette-type resonator in the G-band, demonstrating the feasibility of the proposed gyrotron design.

Sub-terahertz (THz) and THz devices are increasingly used across various industrial and technical applications. This article presents an experimental study of a 140-GHz gyrotron equipped with a multitip cold field emitter. The conditions for radiation generation were determined, and the feasibility of achieving an output power of approximately 13 W was demonstrated. The gyrotron’s electron gun provided a stable electron beam with currents of up to ~100 mA and operated reliably at typical technical vacuum pressures of 10^–7–10^–8 torr.

Микроволновый пиролиз древесины дуба: исследование процесса и характеристика продуктов

This article presents a comparison of theoretical and experimental results for a 170-GHz/1-MW gyrotron using injection locking by the signal from a 15-kW frequency-stabilized gyrotron driver. A significant increase in output power (by 11%) and tuning range (by a factor of 2.3) in the frequency-locked regime is observed in both theory and experiment. Numerical simulations of the system were performed in a self-consistent multimode model with a fixed axial field structure. The spread of electron velocities was taken into account. The zones of the magnetic field corresponding to the frequency locking and beating regimes of the operating mode were found.

Some applications require powerful multi-frequency sources in the centimeter and millimeter wavelength range. In particular, an additional signal is required in ECR sources of multiply charged ions to suppress cyclotron plasma instabilities. The paper proposes a concept of a double-beam technological gyrotron that provides two-frequencies output radiation at 28 GHz with a power of up to 10 kW for ECR plasma heating and at 14.4 GHz with a power of up to 6 kW for plasma stabilization. The possibility of radiation at two frequencies is realized by using an original electrodynamic system with nested cavities. This approach makes it possible to get a radiation source at close frequencies when operating at one cyclotron harmonic and/or at multiple frequencies when operating at different harmonics. Various combinations of electron-optical and electrodynamic gyrotron subsystems are possible in combination with standard or complex magnetic systems. Designs of a new type of gyrotron and concepts of a double-beam electron-optical system, double-beam EOS, are discussed. One of the promising concepts is an electron-optical system with counter-propagating electron beams, in which the first beam is formed by a standard magnetron-injection gun (MIG), and the second beam by an inverted MIG. Another promising modification is the introduction of several electron beams into one or each cavity for mode selection or multi-frequency operation. The EOS modifications with voltage regulation on electrodes are attractive for beam parameter control. In addition, separate heating of each emitter in some EOS concepts allows to independently switched on/off any of the beams during the operation. Promising modification for form of a two-frequency signal with almost any frequency ratio is the introduction of an additional solenoid, located in the bore of the main magnetic system. The considered gyrotron concepts require the use of magnetic systems with a large bore.

The paper presents the results of the first experiments on the investigation of an inverted gyrotron or a gyrotron rectifier, a device which, unlike a conventional gyrotron, converts incident microwave power into direct current (DC) power. In the experiment, by means of cyclotron-resonance interaction with a thin solid initially rectilinear 8.4 keV/0.54 A electron beam, microwave radiation at a frequency of about 34 GHz with a power of 13 kW is converted by it into a power of 15 kW of a 70-μs pulse current that flows through a 51.4 kΩ resistor connecting the device collector to ground. The achieved efficiency of microwave-to-DC power conversion, taking into account the power to drive the electron beam, is 80%.