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An experimental study on the emission of THz-radiation from InP1−xAsx and Ga1−xInxAs crystals is reported. The semiconductor materials were grown by a hybrid vertical Bridgman and gradient freezing directional solidification process. A directly diode pumped Ytterbium — and a conventional Titanium-Sapphire femtosecond laser oscillator were used to stimulate the emission of THz radiation from the semiconductor...
In this paper, the simulation and design of a diode type magnetron injection gun (MIG) for a W-band CW gyrotron oscillator is presented. The simulation of the MIG, operating at the voltage of 55kV and the current of 4A, is finished with the help of a trajectory program EGUN. The simulation results indicate that the velocity ratio with velocity spread of less than 2.5% is 1.43.
A short pulse gyrotron was designed, fabricated and tested for 300 GHz oscillation. The oscillation mode is TE32, 18 and its neighborhoods and the power is output from the top of the gyrotron. The superconducting magnet has 110 mm room temperature bore diameter, and the maximum magnetic field is 13 T. In the preliminary experiment, the 300 kW power was obtained at ∼300 GHz.
During last years several new gyrotrons were developed at IAP/GYCOM. The main ITER requirements to a gyrotron have been demonstrated: 170 GHz frequency, 1MW power, 1000 seconds pulse duration, 53% efficiency. For a multi-frequency gyrotron a novel scheme for a tunable window was developed. Additionally some other new gyrotrons were developed for running plasma installations. New directions in the...
A U-shaped quasi-parallel-plate (QPP) slow wave structure (SWS) for 1 THz backward wave oscillator (BWO) has been investigated in this paper. The radio frequency characteristics and beam-wave interaction of the structure are calculated. The results show that such BWO can operated at a low voltage (< 10 kV), and potentially be used in THz wave radiation source.
A numerical procedure to implement non-reflecting radiation boundary conditions, based on the Laplace Transform, is described in details and tested successfully on a simple two frequencies test problem. The method is then implemented in the time-dependent gyrotron simulation code TWANG. In the case for which the code exhibits a multi-frequency spectrum with the same transverse mode, it is shown that...
We are studying resonant-tunneling diodes (RTDs) with strong back injection of electrons from collector into quantum well. Such RTDs exhibit large negative differential conductance and they operate up to 1.46 THz in oscillators.
The combination of a terahertz parametric oscillator and a large size surface-emitted injection-seeded terahertz parametric generator was used to generate nanosecond THz pulses. The obtained THz pulse energy at 1.74 THz was 6.5 µJ. This is the highest nanosecond THz pulse energy of the terahertz parametric sources.
Propagation of a pulse THz radiation through molecular gas mediums has series of features. In the paper three of them (giant light speed reduction, commensurate echoes, and non-Faraday rotation of polarization) are presented. The effects were measured directly in real time by a powerful pulse radiation of the Novosibirsk terahertz free-electron laser and our ultrafast detection technique.
Crystals KTiOPO4 and KTiOAsO4 are used in terahertz parametric oscillators. The transverse optical A1 mode associated with the stimulated polariton scattering for KTiOPO4 is 268.5 cm−1. The intermittently tunable THz wave from 3.17 THz to 6.13 THz is obtained. For KTiOAsO4, the transverse optical A1 mode is 233.8 cm−1 and the intermittently tunable range is from 3.59 THz to 6.43 THz. The appearance...
The effective cavity length of megawatt-class gyrotrons for thermonuclear fusion plasma heating with cavity quality factors in the range of 1000 to 2000 cannot be deduced just from the cavity field profile, since this has by far not a Gaussian contour. This report presents a novel method to determine the effective length of a high-power gyrotron cavity from the eigenvalue of the operating mode, the...
A novel slow wave structure (SWS) called sine ridge waveguide (SRWG) has been proposed for a wideband high-power terahertz radiation source. The cold bandwidth of the SRWG is similar to the sine waveguide structure. Meanwhile, the interaction impedance of the SRWG is about 70% higher than sine waveguide at 0.65THz with the same dimensional parameters. Furthermore, it possesses low ohmic losses and...
A high power 300 GHz band pulse gyrotron has been developed for use in the collective Thomson scattering (CTS) diagnostics in Large Helical Device. The design concept for stable and single mode oscillation was experimentally verified with a prototype tube of 295 GHz at the fundamental harmonic. A highest power approaching 250 kW was realized. Based on the results of the prototype tube, design of the...
We analyze a novel, phase-sensitive contribution to the oscillating magnetoresistance induced by the combined driving of two radiation fields having commensurate frequencies ω1 and ω2. This commensurate oscillating photoresistance not only depends on the frequencies and polarizations of both electromagnetic waves, but varies drastically when changing the relative phase of two incident radiation fields...
Future controlled fusion reactors require the development of MW-class gyrotrons at higher frequencies. To withstand the ohmic heating in the resonator walls, such gyrotrons should operate in higher order modes than the present-day tubes. This is why the analysis of stability of operation in such modes is of vital importance for future gyrotrons. In this paper, the stability of gyrotron operation is...
The new gyrotron simulation code TWANG-PIC, a Particle-In-Cell (PIC)-version of the code will be presented, which solves the slow-timescale self-consistent wave-particle interaction equations for a single transverse mode. This code represents a considerable improvement with respect to the previous trajectory-code by relaxing the approximation of a time-frozen electromagnetic (EM)-field during the...
We fabricated a novel resonant-tunneling-diode terahertz oscillator with high-frequency modulation structure for high-capacity terahertz communication and measured the frequency response using vector network analyzer. A very high cut-off frequency of 30 GHz in intensity modulation was obtained by the device oscillating at 350 GHz with reduced MIM capacitor of 0.7 pF.
Backward wave oscillation modes in a TE01 Gyro-TWT are researched by a nonlinear theory with consideration of electrons misalign. The results show the output power of most oscillation modes decreases with the increment of misaligns distance.
Sub-5-fs laser pulses and a photoconductive antenna are used to detect the frequency of continuous wave terahertz light sources at 0.1 and 0.6 THz. Both the frequency mixing in a photoconductive antenna and the heterodyne detection at the sub-harmonic mixer can detect the signals of the light source. By slightly changing the frequency of the light source, absolute frequency can be evaluated directly.
Gyrotron FU CW GV has been developed as a multiple-frequency gyrotron. The main mode is TE10, 6 and corresponding frequency is 265 GHz. More than ten modes oscillated and Gaussian beams were radiated for these modes. A double-disk window was adopted to maintain the transmittance through the window in high level for a wide range of frequency.
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