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Deep geothermal drilling is a necessary technological stage to produce renewable energy by "enhanced geothermal systems" everywhere. However, the high cost and complexity of deep drilling through hard rock formations is a major barrier to its commercialization. One approach to reach affordability and reduce the cost of deep drilling is to use millimeter-wave (mmw) gyrotron radiation to melt or vaporize rocks. In this paper, the results of an experimental study of mmw radiation absorption by hard rocks are presented. Electromagnetic attenuation and reflection were measured in W-band at frequencies from 75 to 110 GHz in eight rock samples from six different geological formations originated in Israel. The results show that the mmw radiation absorption in hard rocks ranges from 90 to 99% per centimeter. The absorption varies slightly with rock type and is relatively independent of frequency but has reached higher values at the upper W band for all samples. The study suggests that high-power mmw radiation is a promising technology for deep geothermal drilling. The results of this experiment, attenuation, and reflection of W-band radiation in hard rocks provide valuable information for the design and optimization of mmw-based drilling systems, and will support the design and optimization of gyrotron based hard rock drilling equipment for geothermal applications. [ABSTRACT FROM AUTHOR]

The pulsed magnet can generate a high magnetic field (up to 100T), promoting the development of high-frequency high-power gyrotrons. In this article, a fast cooling and long lifetime 40 T pulsed magnet is developed for a 1 THz gyrotron. To address the various challenges in thermal and mechanical aspects, copper conductors and internal fibers have been combined to enhance mechanical strength and minimize temperature rise, prolonging the lifetime and the admissible duration of the magnet operation. Internal cooling channels are introduced to increase the cooling speed without compromising mechanical strength. Experimental results have demonstrated the magnet's reliability and repeatability in achieving a 40 T pulsed field for tens of milliseconds with a cooldown time of 6 min. It is estimated that the lifetime is about 20,000 shots at 40 T. Importantly, the magnet is capable of realizing a 40 T flat-top pulsed field (flat-top time 10 ms) with a cooldown period of 16 min. This can facilitate the long-pulsed quasi-steady operation of gyrotron operation, which is attractive for numerous high-power THz applications. [ABSTRACT FROM AUTHOR]

A 110 GHz quasi-optical ring resonator, designed for use with a 1 MW pulsed gyrotron, has been built and successfully tested using a 100 mW solid-state source. A low reflectance (2.4%) input coupler and a low-loss, four-mirror ring demonstrated a compression ratio, defined as the ratio of output to input power, of 36. The 6 ns output pulses were generated from the 2 m length ring using a silicon laser-driven semiconductor switch (LDSS). The quasi-optical ring resonator was designed with large waist sizes so that input pulses of up to 1 MW will stay under the 35 kV/cm electric field limit for ionization in ambient air. Maximum compression gain was achieved by matching the input coupling fraction to the round trip loss in the ring, achieving close to critical coupling. The experimental output pulse shape obtained after firing the LDSS was modeled using the reflectance, transmittance, and absorptance of the switch vs. time and vs. laser pulse fluence, with good agreement found with theory. The timing for the peak energy efficiency of 32% was found and the main loss mechanism limiting that efficiency was found to be the absorptance in the silicon wafer. [ABSTRACT FROM AUTHOR]

This paper presents an experimental setup of magnetic field taper variations to optimize the efficiency of a Ka-band pulsed gyrotron. Experimental optimization of the gyrotron's efficiency is presented. The efficiency dependence on three input parameters—beam current, magnetic field amplitude, and variations in the magnetic field taper profile—is studied. A gyrotron electron efficiency improvement from 25.4% for a non-tapered magnetic curve to 36.4% for a tapered magnetic curve is measured. The stability of the millimeter wave excitation in the cavity is also affected by the magnetic taper gradient. The magnetic taper is obtained by a practical modification of the solenoid that leads to an 11% electron efficiency improvement. Magnetic tapering can be combined with other types of efficiency enhancement concepts to obtain an overall improved efficiency that can be important for industrial applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of a new hybrid plasmatron scheme, which was used to realize a gas discharge at atmospheric pressure supported by continuous focused submillimeter radiation with a frequency of 263 GHz. The implemented design allowed organizing a self-consistent interaction between submillimeter radiation and the supercritical plasma in a localized area both in terms of gas flow and electrodynamic. It is experimentally shown that the gas discharge absorbs up to 80% of the introduced submillimeter radiation power. [ABSTRACT FROM AUTHOR]

In the experiment, plasma–dust clouds were obtained from the substance of the Tsarev meteorite, a simulant of lunar regolith LMS-1D and ilmenite concentrate using a microwave discharge in powder media. For each of the samples, the dynamics of the development of the discharge and the formation of a plasma–dust cloud with subsequent relaxation after the end of the microwave pulse were recorded. From the emission spectra of the plasma and the surface of a solid body, the temperatures of the gas, electrons and surface were determined. A comparison of the phase and elemental composition of the initial samples and samples after exposure to plasma showed that there is no significant change in the composition. However, scanning electron microscopy results clearly indicate spheroidization of the original angular and irregularly shaped particles. The appearance of spherical particles is also observed, the dimensions of which are larger than the linear dimensions of the particles in the original sample. The results obtained indicate the possibility of using such experiments to study chemical and plasma-chemical processes of synthesis and modification of substances under conditions of plasma–dust clouds encountered in space phenomena. [ABSTRACT FROM AUTHOR]

The article describes simulation experiments of interaction of lunar dust with the surface of solar panels. The experiments are based on the creation of a dusty plasma cloud, when the radiation of a powerful pulsed gyrotron is exposed to a substance that simulates lunar dust. This approach was tested using a lunar regolith simulator. The analysis of the results of deposition of charged regolith particles on solar panels of different types and changes in their efficiency is presented. [ABSTRACT FROM AUTHOR]

Abstract—Experiments were carried out on the treatment of nanopowders of the W–C–Co system obtained by plasma-chemical synthesis in a microwave electromagnetic field with a frequency of 2.45 and 24 GHz in different gas media. The effect of treatment time, power input, and carbon content in the treated nanopowder on the yield of tungsten monocarbide WC was investigated. [ABSTRACT FROM AUTHOR]

[Introduction] In magnetic confinement fusion research, electron cyclotron heating (ECH) and current drive means are widely implemented for applications including, but not limited to, plasma initiation, heating, non-inductive current drive, and magnetohydrodynamic instability control. In recent years, ECH-related technologies have experienced significant development in response to the development needs of future fusion reactors, and ECH has become one of the main auxiliary heating means in magnetic confinement fusion devices. [Method] Firstly, the ECH system was introduced, and its components, characteristics and application status were described; then the development status and trends of ECH system-related technologies were discussed with emphasis on four aspects. [Result] Combined with the research status and application requirements of ECH-related technologies, the important and difficult points in developing each related technology are identified. [Conclusion] Based on the development status and trends of ECH-related technologies, the article forecasts future research directions and applications of ECH system-related technologies in diverse aspects, including high-frequency and multi-frequency gyrotrons (microwave sources), the intelligent control technology of ECH system, the high-efficiency current drive technology, and the gyrotron-based collective Thomson scattering technology.

Purpose. The article presents a new method for numerical simulation of quasi-eigenmode oscillations in open resonators of gyrotrons — powerful vacuum generators of electromagnetic waves in the millimeter and submillimeter ranges. The gyrotron cavity has the shape of a weakly inhomogeneous hollow circular metal waveguide. Methods. The proposed approach uses the inhomogeneous string equation with radiation boundary conditions to formulate a nonlinear spectral boundary value problem describing oscillations in a resonator, neglecting the couplings of waves with different radial indices. By linearizing with respect to frequency the radiation boundary conditions, the boundary value problem is reduced to a linear boundary value problem. To discretize this boundary value problem, the finite difference method is used and a linear generalized matrix eigenvalue problem is formulated. This problem is solved by the Arnoldi method with eigenvalues calculation in a shift-invert mode. An iterative algorithm is proposed that makes it possible to sequentially calculate a given number of frequencies and quality factors of quasi-eigenmodes of oscillations. Results. The computer program was developed written in the Wolfram Language and Fortran using the algorithms proposed in the work. The results of test calculations for real gyrotron resonators are presented, which demonstrate the high accuracy of the obtained values of frequencies, quality factors and field distributions of quasi-eigenmode oscillations in the studied resonators. Conclusion. The methods, algorithms and created program proposed in the article can significantly facilitate the process of developing gyrotrons intended for various practical applications and operating in new frequency ranges. The method of iterative refinement of boundary conditions can be generalized to the case of equations of the linear theory of a gyrotron and used to develop new methods for analyzing the starting conditions for the soft self-excitation in gyrotrons — generators.

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This paper aims to present some selected fundamentals of the theory of a broad class of gyro-devices in a systematic and consistent manner and with sufficient detail necessary for understanding the underlying physical principles of their operation. The focus of this work is on the derivation and analysis of important invariants (constants of motion), as well as on comments concerning their analytical power and the physical insights they provide. [ABSTRACT FROM AUTHOR]

In this paper we present a comprehensive overview of the theoretical and experimental studies on gyrotrons operating at harmonics of the electron cyclotron frequency. Besides the conventional (small-orbit) gyrotrons, three other types of such devices are considered, namely large-orbit gyrotrons (LOG), double-beam gyrotrons, and gyro-devices with a frequency multiplication. Based on a comparison between them and the devices that work on the fundamental resonances, both the advantages and disadvantages of the harmonic gyrotrons are critically examined. Such an analysis is helpful for choosing between different alternative concepts in the design process of appropriate radiation sources for various applications. [ABSTRACT FROM AUTHOR]

The article proposes a new method for estimating the number of particles in experiments on modeling the interaction of cosmic and lunar dust with the surface of spacecraft. The experiments are based on the creation of a dusty plasma cloud, when exposed to radiation from a powerful pulsed gyrotron on a substance simulating cosmic or lunar dust. This approach was tested using a lunar regolith simulator. The dynamics of particles in dust clouds obtained as a result of microwave discharge is analyzed using the ImageJ program. [ABSTRACT FROM AUTHOR]

The possibility of forming helical electron beams (HEBs) for multi-mirror and multi-barrel gyrotrons using systems with non-adiabatic injection of an electron beam into a magnetic field is analyzed. Systems where emission comes from circular arcs or from individual emission circles are considered. The possibility of implementing a HEB with a large (1.5–1.8) pitch factor, an acceptable velocity spread and a reduced influence of particles reflected from the magnetic mirror on the quality of the beam has been studied. [ABSTRACT FROM AUTHOR]

Calculations are made for a three-electrode magnetron-injector gun with a thermionic cathode for a relativistic gyrotron in the 300 GHz range. The gyrotron allows the formation of a helical beam with an energy of 250 keV, a current of 100–300 A, and a pitch factor of 1.1. The possibility of generating radiation with power of more than 8 MW in a gyrotron with a longitudinally slotted cavity is shown via three-dimensional PIC modeling. [ABSTRACT FROM AUTHOR]

Theoretical and experimental studies are performed of the generation of radiation in the mode of frequency multiplication at the third harmonic in a high-current Ka-band gyrotron. Three-dimensional PIC modeling shows that the coefficient of nonlinear transformation in the W-band can reach values of 0.5%. Experimental data are presented on recording radiation in this range. [ABSTRACT FROM AUTHOR]

We consider the possibilities of producing wideband chaotic terahertz-range radiation in gyrotrons with excitation of cyclotron harmonics. The transition to the chaotic generation mode in gyrotrons requires a significant excess of the operating current over the starting value, which excludes selective operation at cyclotron harmonics due to the intensification of mode competition. At the same time, it is attractive to use a competition-free frequency multiplication effect that arises due to the nonlinear properties of the electron beam. The implementation of the frequency multiplication regime is simplified when using low-energy electron beams. Based on the averaged model of electron-wave interaction, we simulate generation in a 250-GHz low-voltage gyrotron and demonstrate the regime of a double frequency multiplication providing 0.5 THz chaotic radiation with a bandwidth of about 20 GHz and an average power of 0.5 mW. A significant expansion of the spectrum is achieved through to additional resonant interaction at the intersection points of the dispersion characteristics of the operating mode and the electron beam at the second cyclotron harmonic. [ABSTRACT FROM AUTHOR]

Calculations are presented for an electron-optical system that makes it possible to produce a helical electron beam with an energy of 250 keV, a current of 100 A, and a pitch factor of 1.1 for a 0.3 THz gyrotron with the operating mode of TE33.2. Based on averaged stationary equations with a non-fixed field structure, the cavity profile is optimized and the possibility of obtaining an output power of about 8 MW with an electronic efficiency of more than 30% is demonstrated. Within the framework of particle-in-cell three-dimensional simulation, the processes of establishing oscillations are considered. Besides, it is shown that in the range of magnetic fields from 14.7 to 15.1 T, selective excitation of oscillations in the operating mode with a maximum power of about 7 MW is possible. [ABSTRACT FROM AUTHOR]

This study presents the results of a complex physical modeling of a moderate power gyrotron operating at the 4-mm wavelength range. The characteristics of electrodes and magnetic coils in a four-stage recovery collector were optimized taking into account the coordinate and velocity distributions of electrons. These distributions were obtained through a trajectory analysis in the electron optical system and calculation of electron-wave interaction in the gyrotron cavity. To reduce parasitic effects of the bundles of a toroidal solenoid used to create an azimuthal magnetic field in the collector region, a sectioned electron beam was employed. The study demonstrated that the gyrotron's total efficiency of approximately 79 % could be achieved, being close to the maximum efficiency value achievable with separation of electron fractions with different energies, provided that the current of electrons reflected from a collector should not exceed 1% of the total current of an electron beam.

This paper aims to present some selected fundamentals of the theory of a broad class of gyro-devices in a systematic and consistent manner and with sufficient detail necessary for understanding the underlying physical principles of their operation. The focus of this work is on the derivation and analysis of important invariants (constants of motion), as well as on comments concerning their analytical power and the physical insights they provide.

We present the results of experimental studies of the intensity of vacuum ultraviolet self-radiation (VUV) of the discharge in hydrogen sustained in an open magnetic trap by the high-power radiation of a gyrotron (frequency f = 28 GHz and power Pgyr = 5 kW) under conditions of electron cyclotron resonance (ECR) in the continuous regime. The optimum system parameters were determined for the generation of VUV radiation by the plasma of the ECR discharge. It was shown that the radiation power in the wavelength range λ = 120–160 nm reaches W = 0.75 kW, which corresponds to an efficiency of η = 20%. [ABSTRACT FROM AUTHOR]

Making fusion power viable both technologically and commercially has been a challenge for decades due to the great complexity of the science and engineering challenges. In recent years, changes in both government policies and the emergence of private fusion companies have ushered a newfound push to accelerate fusion energy development. Kyoto Fusioneering (KF) is a privately funded fusion engineering start-up, founded to accelerate the development of high performance, commercially viable technologies that will be required for a fusion power plant, specifically those associated with heating and current drive systems, power generation, and the tritium fuel cycle. The company is focused on supporting the rapid expansion of the budding fusion industry. This paper provides a high-level description of some of the technical and industrial challenges it is tackling in developing a commercial fusion reactor, in particular in relation to: plasma heating with gyrotrons, tritium handling and breeding, energy conversion, and fusion materials. It provides an overview of KF's activities in finding solutions to challenges in each of these areas, including via its new testing facility now under construction, UNITY (Unique Integrated Testing Facility). KF’s core capabilities and areas of R&D focus are discussed, with reference to how they benefit the development of a new fusion industry as a whole and bring the technology closer to industrialisation, including via UNITY and through collaboration with external partners. The importance of industrialisation and subsequently commercialisation is also discussed, through KF’s assessment of the newly emerging fusion ecosystem, and where KF as a company sits within it. [ABSTRACT FROM AUTHOR]

The generation frequency is ω ≈ kωн in classical gyrotrons, where ωн = еB0/m is the electron cyclotron rotation frequency in a uniform longitudinal magnetic field with induction B0, e is the electron charge, m is the electron mass, k = 1, 2, 3… is the cyclotron frequency working harmonic number. Thus, the generation frequency ω being tuned is possible only by changing B0. This way is very inconvenient. It’s necessary a solenoid additional (control) winding. That difficulty can be eliminated in gyrotrons with crossed fields - electric 0 and magnetic 0, here 0 ⊥ 0. The frequency can be tuned by changing E0. This possibility can be realized at least two ways: a gyrotron based on a coaxial resonator with radial field E0; a four-mirror gyrotron on traveling Т-waves with transverse in respect the traveling wave direction to uniform crossed fields – electric 0 and magnetic 0. The single-screw electron flow has a rotation frequency , for the first gyrotron type, where , , ΔV is the potential difference between the inner (radius b1) and outer (radius b2) coaxial conductors, r0 is the electron flow rotation radius. Thus, the generation frequency ω ≈ kωн is determined by both B0 and ΔV. Moreover, at ΔV = 0 the device becomes a classical high-orbit gyrotron, at B0 = 0 a classical helitron. Therefore, at B0 ≠ 0 and ΔV ≠ 0 it should be called a gyrohelitron, the generation frequency of which is tuned electrically - by changing ΔV. The article presents the design schemes of a gyrohelitron and a two-beam four-mirror gyrotron. In both cases, piezoelectric devices realize synchronous tuning of the frequency, just it allows the devices becoming fully electrically controllable. The following results were obtained for the gyrohelitron. Resonator field – H211, interaction on the second harmonic ωs; a) narrow-band tuning 10 %: maximum efficiency – 55 %, minimum efficiency – 25 %; β0 = v0/c = 0.27; q = v0⊥/v|| = 2; b) broadband tuning 58 %: maximum efficiency – 18 %, minimum efficiency – 14 %; β0 = v0/c = 0.2; q = v0⊥/v|| = 2. The given results for the gyrohelitron indicate that it is promising to use electrical frequency tuning in a coaxial gyro-BWT and the amplification band in a gyro-TWT, since these devices do not require piezoelectric tuning of electrodynamic structures.

The measurement and manipulation of the microwave polarization emitted from a frequency-agile 198 GHz gyrotron for dynamic nuclear polarization (DNP) are demonstrated. In general, gyrotrons emit linearly polarized radiation, yet in this case elliptical polarization is observed from the 198 GHz gyrotron window. Indeed, half of the microwave power is circularly polarized while the other half is linearly polarized with a polarization of 60∘ with respect to the horizontal plane. For optimal use of microwave power for DNP experiments, the elliptical polarization from the gyrotron is converted into circular polarization with a Martin-Puplett interferometer (MPI). The dependence of the DNP enhancement on the microwave polarization was investigated by modifying the microwave polarization with the MPI. In addition, the MPI can generate a linearly polarized beam, which holds promise for future development of induction-mode electron spin detected experiments. [ABSTRACT FROM AUTHOR]

In this work we investigated the scattering parameters and mode conversion of axisymmetric TE modes in smooth cylindrical waveguides with wedge-shaped azimuthal corrugations. In particular, we studied the effect of the length of the corrugated region on the scattering parameters and on the mode conversion. The field distribution was derived by the FDTD code COCHLEA and further post-processed using the COPP code. Results showed that the incident mode is converted to an ensemble of modes, the azimuthal indices of which are given by the SHM criterion. Azimuthal corrugated waveguides are usually employed in the gyrotron beam-tunnel to enhance the suppression of the parasitic modes. [ABSTRACT FROM AUTHOR]

The electron beam current of high-power, long-pulse gyrotrons for fusion devices is typically controlled to remain constant by adjusting the power to the cathode heater by using a pre-programmed waveform. However, this pre-programmed waveform is usually developed through a time-consuming trial and error process and its precision is low. Therefore, a system to automatically control electron beam current was developed and its performance was tested with one of the JADA/QST-manufactured gyrotrons for ITER. The control system automatically adjusted beam current to a target value of 47 A within ±0.5% for 900 s. This high-precision beam current control can maintain an output power of 1 MW and, being automated, it is useful for power on/off modulation operations. If the operation is switched from continuous to modulated, the beam current can be changed to compensate for the decrease in emission cooling of the cathode. This automatic control system demonstrates the quick recovery of a stable beam current in modulation operations.

This paper presents the study of a gyrotron magnetic system with a field intensity of 2.45 T and a triode magnetron injection gun system to achieve electron trajectories into the cavity operating zone to generate a 60 GHz radiofrequency used in electron cyclotron resonance heating applications. The operating mode of the gyrotron is TE4,3. A copper coil system arrangement of four solenoids with a stationary current of 750 A and a magnetic compression of 16.53 with a magnetic field homogeneity of 0.10% over a length of 56 mm in the operating zone was designed. A very good approximation of the magnetic field profile of the copper coil system was obtained using a novel formulation derived from the geometry of the coils. The magnetron injection gun parameters were obtained applying the trade-off equations, resulting in a cathode radius of 13.5 mm. The helicoidal and laminar trajectories of the electrons with a transverse-velocity of 1.175 are obtained from the magnetic and gun systems. The resulting trajectories are generated using the 2-D EGUN code. The study represents an effort to create an Experimental Theoretical Fusion Platform of the High Magnetic Field Program at the Autonomous University of Nuevo León (UANL). [ABSTRACT FROM AUTHOR]

Experimental results are presented on deposition of charged particles that imitate the levitating dust of regolith (dusty plasma) on the Moon on metal plates. The experiment was based on the analogy between the physical–chemical properties of the processes that develop in regolith during microwave discharge excited by the radiation of a powerful gyrotron in the powder of regolith (lunar dust) and the processes that occur on the Moon during the bombardment of its surface by micrometeorites. The action is studied of the levitating dust cloud on plates made from molybdenum and tantalum with a size of 10 × 40 mm. The results are compared with the experiment on deposition of lunar dust on plates from stainless steel. It is shown that dust particles in the shape of spheroids of different sizes are deposited on the plates. The size distribution of these particles and their chemical composition are those of lunar regolith. It is found that the uniformity of dust deposition can be controlled by preliminary processing of the metal plates by the low-temperature plasma of a direct piezodischarge. It is shown that the levitating dust obtained under laboratory conditions (ensembles of charged regolith particles) can be used in imitation experiments on surface modification of different materials and in the development of methods for cleaning the space equipment during Moon missions. [ABSTRACT FROM AUTHOR]

The features of the use of carborane as a catalyst in the synthesis of particles of micro- and nano sizes in processes initiated by radiation of a gyrotron in mixtures of titanium and boron nitride powders (with hexagonal and cubic structure) are considered. The threshold conditions for the development of processes and the mass and composition of the obtained substances are determined. [ABSTRACT FROM AUTHOR]

Using a simplified approach, a self-consistent modeling of beam–wave interaction in a complex cavity is performed to evaluate the performance of the complex cavity second-harmonic 0.4-THz gyrotron developed at the University of Fukui. For this gyrotron, the quantitative analysis of an adverse effect of small manufacturing errors of the complex cavity on mode selection, output power, and output mode purity is done. To improve the robustness of gyrotron operation to manufacturing errors, a novel complex cavity formed by coupled smooth-walled and corrugated cylindrical resonators is considered. The novel cavity is a hybrid between conventional cylindrical and standard complex cavities and therefore offers the benefit of a tradeoff between engineering tolerance and mode selection. [ABSTRACT FROM AUTHOR]

Novel additive technology of the Chemical Metallization of Photopolymer-based Structures (CMPS) is under active elaboration currently at the IAP RAS (Nizhny Novgorod). The use of this technology has made it possible to implement components of electron–optical and electrodynamic systems for high-power microwave vacuum tubes, such as a gyrotron and a relativistic Cherenkov maser, the design and experimental studies of which are described in this paper. Within the framework of the gyrotron developments, we carried out a simulation of the distribution of the heat load on the collector of high-power technological gyrotron taking into account secondary emission. The prospect of a significant reduction in the maximum power density of the deposited electron beam was shown. The experimental study of the gyrotron collector module manufactured using CMPS technology demonstrated high potential for its further implementation. Recent results of theoretical and experimental studies of a spatially extended Ka-band Cherenkov maser are presented. In this oscillator, the 2D-periodical slow-wave structure made by the proposed technology was applied and a narrow-band generation regime was observed with a sub-GW power level. The design and simulations of a novel selective electrodynamic system for a high-harmonic gyrotron with the planned application of the CMPS technology are discussed. [ABSTRACT FROM AUTHOR]

Physical engineering technology using far-infrared radiation has been gathering attention in chemical, biological, and material research fields. In particular, the high-power radiation at the terahertz region can give remarkable effects on biological materials distinct from a simple thermal treatment. Self-assembly of biological molecules such as amyloid proteins and cellulose fiber plays various roles in medical and biomaterials fields. A common characteristic of those biomolecular aggregates is a sheet-like fibrous structure that is rigid and insoluble in water, and it is often hard to manipulate the stacking conformation without heating, organic solvents, or chemical reagents. We discovered that those fibrous formats can be conformationally regulated by means of intense far-infrared radiations from a free-electron laser and gyrotron. In this review, we would like to show the latest and the past studies on the effects of far-infrared radiation on the fibrous biomaterials and to suggest the potential use of the far-infrared radiation for regulation of the biomolecular self-assembly. [ABSTRACT FROM AUTHOR]

In this article, the experimental investigations on a 263-GHz gyrotron are presented. With the change of the operating magnetic field and the beam energy, the operating frequency is adjusted and the output power is also varied. It is found that when the operating magnetic field changes from 9.59 to 9.82 T at a fixed operating voltage of 20 kV and a beam current of 0.8 A, the operating frequency increases from 263.39 to 264.84 GHz, the frequency-tuning range is about 1.45 GHz, and the output power is from 26 to 463 W. When the operating voltage increases from 14.4 to 22.2 kV at a fixed operating magnetic field of 9.65 T, the operating frequency decreases from 263.68 to 263.40 GHz, the frequency-tuning range is 0.28 GHz, and the output power changes from 52 to 424 W. When the operating magnetic field is fixed at 9.65 T and the operating voltage is fixed at 20 kV, but the beam current increases from 120 to 880 mA, the output power increases from 21 to 277 W, the operating frequency increases from 263.396 to 263.425 GHz, and the frequency-tunable range is 0.029 GHz. The effects of the axial position of the gyrotron in the superconducting magnet system on the operating frequency, the frequency-tuning range, and the output power are also investigated experimentally. When the beam current is increased, the nonstationary phenomenon is observed. [ABSTRACT FROM AUTHOR]

We report the design and initial experimental results of an 800-GHz second harmonic gyrotron prototype, in which a 15-T pulsed magnet is applied. This gyrotron prototype is developed at the Wuhan National High Magnetic Field Center (WHMFC). An in-house software for analyzing and designing terahertz gyrotrons and an experimental research platform are developed. In addition, alignment adjustments, eddy current effects, and radiation tests are discussed. The initial experimental results show that the prototype gyrotron can irradiate ~40 W at fundamental harmonic 383.7-GHz (TE1,4) waves at 14.14 T and a few milliwatts at second harmonic 0.8-THz (TE8,5) waves at 14.86 T. [ABSTRACT FROM AUTHOR]

We describe the small-signal theory of a backward-wave gyro-oscillator with a sectioned quasi-optical system with the zigzag path of the operating wave beam. This theory explains peculiarities (namely, a piecewise character) of changing the operating frequency and power of the output signal in the process of the broadband frequency tuning provided by changing the operating magnetic field. [ABSTRACT FROM AUTHOR]

Topic. The paper is devoted to the study of synchronization of a gyrotron by an external harmonic signal. A theoretical study of gyrotron synchronization processes by means of a computational experiment based on certain traditional models of microwave electronics does not provide a complete description of the synchronization pattern. Therefore, the goal of the paper is to develop a modified quasi-linear model based on an approximation of the electron susceptibility by rational functions. Methods. The developed model allows for bifurcation analysis of synchronization processes. On its basis, stationary states are determined and their stability analysis is carried out. The results are in good agreement with numerical simulation based on the non-stationary theory of a gyrotron with a fixed Gaussian high-frequency field structure. Results and discussion. Resonance curves and synchronization bounds are built on the plane of parameters “amplitude – frequency of external signal”. The case where the gyrotron is in the hard excitation mode is considered, since the maximum efficiency is usually achieved in the hard excitation mode. In general, the results are in qualitative agreement with the picture described earlier for a simpler quasi-linear model of a oscillator with hard excitation, in the case of a sufficiently strong phase nonlinearity.

In the paper, a 3D trajectory analysis taking into account the surface roughness of the thermionic cathode and thermal effects caused by its heating has been performed in the electron-optical system of a gyrotron with a frequency of 74,2 GHz and an output power of approximately 100 kW. A new approach based on the use of standard settings available in the 3D simulation software when the model parameters of thermionic emission being given, was used for consideration of the micron-sized cathode surface roughness. A comparison between the calculated and experimental data made it possible to clarify the regularities of the influence of the initial velocity spread and the change of geometry of the cathode assembly caused by its heating on the parameters of the electron beam formed in the electron-optical gyrotron system.

We propose a new type of a gyrotron cavity comprising the external and internal cylindrical resonators with azimuthally periodical axial slits. A theory of such a cavity is presented together with the eigenmode computation, which confirms its high mode selectivity. In 3D simulations using the particle-in-cells method, we compare the output characteristics of 0.5 THz gyrotrons with 0.1 to 1 kW output power. We demonstrate that as compared to a conventional solid wall cavity, the use of the novel-type cavity allows the smooth frequency tuning band to be increased by an order of magnitude and more. [ABSTRACT FROM AUTHOR]

At the specific power of electron cyclotron resonance (ECR) heating of 3.2 MW m–3 (plasma density of 2 × 1019 m–3, electron temperature of 0.6 keV), an increase in the plasma energy lifetime by not less than 30% is accompanied by a two-time-decrease in the level of short-wave turbulent density fluctuations. In such a shot, before the beginning of the quasi-stationary confinement stage, the turbulent state of density fluctuations is characterized by the stronger deviation from zero of the coefficient of excess of fluctuation increments than it is in shots without transport transitions. This indicates the stronger deviation of the probability distribution function of density fluctuation increments from the normal law in shots with transport transitions. Based on the analysis of increments of short-wave fluctuations using the special method for separating the continuous components in stochastic processes, a qualitative difference was established between the behaviors of the structural components forming the plasma turbulence in shots with and without transport transitions. In addition, for shots with transport transitions, a change in the shape of the approximating finite mixture of normal distributions and parameters of its component densities is demonstrated. [ABSTRACT FROM AUTHOR]

Gyrotrons are used as high-power sources of coherent radiation operating in pulsed and CW regimes in many scientific and technological fields. In this paper, we discuss two of their numerous applications. The first one is in gyrotron-powered electromagnetic wigglers and undulators. The second one is for driving high-gradient accelerating structures in compact particle accelerators. The comparison, between the requirements imposed by these two concepts on the radiation sources on one hand and the output parameters of the currently available high-performance gyrotrons on the other hand, show that they match each other to a high degree. We consider this as a manifestation of the feasibility and potential of these concepts. It is believed that after the first successful proof-of-principle experiments they will find more wide usage in the advanced FEL and particle accelerators. [ABSTRACT FROM AUTHOR]

Simulation of gyrotrons using the particle-in-cell method predominantly requires 3D calculations. At large oversize factors of the interaction space, it leads to lengthy calculation times. We show that under certain conditions, the dimensionality of the problem can be reduced and 2.5D PIC simulations can be applied. Using the example of a 170 GHz gyrotron with TE28,12 operating mode, we study the influence of the external signal on the noise level in the output radiation under conditions of fluctuations of the accelerating voltage. [ABSTRACT FROM AUTHOR]