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The paper describes recent results of theoretical and experimental studies of powerful relativistic masers based on linac LIU-3000. The key components of the oscillators are advanced Bragg resonators based on coupling of propagating and quasi-cutoff waves that possess high selectivity over transverse coordinates and allows establishment of narrow-band operating regime in strongly oversized system...
We demonstrate a novel approach to the problem of THz emission and detection by quantum Faraday effect that manifests itself in conductance of topological edge channels of silicon nanosandwich-structures.
The introduction of advanced Multistage Depressed Collectors (MDC) to high-power fusion gyrotrons will be the key to increase the gyrotron overall efficiency above 60 % as required for future DEMOnstration power plant. MDCs which base on the E×B drift concept might solve the fundamental issue of handling the secondary electrons. To consider the effect of secondary electrons in a stationary state,...
A second-harmonic frequency step-tuning gyrotron is under development. The oscillation frequencies are separated by approximately 15-GHz steps in a range from 270 to 420-GHz. The operation modes were selected to convert into Gaussian like radiations by one internal mode converter. A triode electron gun was designed in order to operate in a wide range of magnetic fields. The oscillation tests were...
A sheet beam traveling wave tube is designed, producing 231W at 94 GHz with a corresponding gain of 33.6 dB. A uniform longitudinal magnetic field of 0.9 T was used in the CST PIC simulation. The attenuator material is with a moderate loss tangent of 0.35 and a relative permittivity of 6.4. To get a stable operation of the tube, the reflectors for the input/output (I/O) structure are covered by attenuators...
The key to increase the gyrotron efficiency to a level significantly higher than 50% is the development of a highly efficient collector system for the recovery of the spent electron beam energy. In this context, a significant effort has been dedicated at KIT during the last years in order to design a reliable, robust and efficient multistage collector system. For this purpose several design approaches...
We demonstrate that gyrotrons operating in the regime of developed turbulence can sporadically emit “giant” spikes with intensities a factor of 100 ÷ 200 greater than the average radiation power and a factor of 4 ÷ 6 exceeding the power of a driving electron beam. Together with a long-tail pulse-height probability distribution, this allows the interpretation of generated spikes as microwave rogue...
A possibility of gyrotron operation at a very low voltage, 1.5–2 kV, is considered in the context of dynamic nuclear polarization (DNP) application. Simulations predict that a low-voltage device has some specific but useful features like efficiency operation at high axial modes and capability of wide-band frequency tuning.
To develop high harmonic terahertz gyrotron, gyrotron with quasi-optical confocal cavity has been studied. Theoretical studies show quasi-optical confocal cavity has good mode selectivity and could be adopted in high harmonic gyrotron. A 400 GHz second harmonic gyrotron with confocal cavity is designed and experimented. In initial experiment, 396GHz second harmonic output with 1.5 kW power is observed.
Using degenerate four-wave mixing (DFWM), we have investigated the coherent polarization between the lowest Landau levels in graphene under resonant excitation with narrowband THz pulses. A pronounced DFWM signal is observed and its dependence on THz field strength and magnetic field detuning is explored and compared with theoretical expectations.
The design of a W-band second harmonic gyrotron based on a 1.8 T continuous operation solenoid is presented. A compact triode MIG is designed to generate gyrating electron beam. The gyrotron operates at the TE0,2 mode with a conventional cylindrical cavity. And we designed a high efficiency quasi-optical mode converter with a dimpled wall laucher, the mode conversion efficiency is 97% and the Gaussian...
We performed a study of a range of (Cd1−xZnx)3As2 mixed crystals undergoing a transition from the Dirac semimetal phase to trivial semiconductor at variation of the composition x. We show that for the Dirac semimetal phase, the photoelectromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial semiconductor phase, it depends on the power in a laser...
Due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition, THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems. We have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic...
In this paper, we show that the terahertz photoconductivity and the magnetophotogalvanic effect in Hg1−xCdxTe films change the sign across the topological transition from the inverted to the trivial electron energy spectrum. Electron energy spectrum modification influenced by magnetic field and topological surface states formation are taken into account to discuss the observed photoelectric phenomena...
Bulk films and heterostructures based on HgCdTe compounds can be engineered to fabricate “gapped-at-will” structures. Therefore, 1D, 2D and even 3D massless particles can be observed in topological phase transitions driven by intrinsic (quantum well thickness, Cd content) and external (magnetic field, temperature, strain or hydrostatic pressure) physical parameters. In this work, we report on our...
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