Showing papers by "G. G. Denisov published in 2014"

Experimental Study of the Pulsed Terahertz Gyrotron with Record-Breaking Power and Efficiency Parameters

Abstract: We describe the results of studying experimentally a high-power (hundreds of kilowatts) pulsed (pulse duration of about 30 μs) subterahertz gyrotron with the generation frequency corresponding to one of the atmosphere transparency windows. The gyrotron with an operating frequency of 0.67 THz, a power of more than 200 kW and an efficiency of 20–25% was used in the experiments on ignition of a localized discharge in a plasma. The paper presents the data about measurements of the temperature field of the emitter, calorimetric measurements of the power and efficiency of the gyrotron, and the design of the quasioptical converter of radiation to a narrow wave beam. The first experiments with the terahertz discharge in a focused wave beam of the gyrotron are briefly described.

Frequency and phase stabilization of a multimode gyrotron with megawatt power by an external signal

Abstract: We have numerically studied capturing of the oscillation frequency and phase of the TE28.12 operating mode by an external monochromatic signal for a multimode gyrotron with a close to real regime of activation. It is shown that, even at a low external-signal power, in a wide range of the magnetic field and voltage, a highly efficient single-mode generating is set at the frequency of the external signal.

Development of Waveguide Semiconductor Switches of Microwave Radiation in the 70- and 260-ghz Ranges

Abstract: UDC 537.52 We have developed, manufactured, and studied experimentally prototypes of microwave switches operated in the 70- and 260-GHz frequency ranges and controlled by pulses of optical laser radiation. The results of their numerical simulation by the finite-difference time-domain (FDTD) method are presented, along with the design parameters of the prototypes. The switch speed is equal to 1 ns, and the microwave tuning frequency range amounts to about 10%. The process of switching with the use of a low-cost semiconductor optical laser (with a wavelength of 532 nm and a continuous-wave power of 200 MW) is demonstrated experimentally at a switched-radiation frequency of 266.68 GHz.

A traveling-wave ring resonator with Bragg deflectors in a two-stage terahertz free-electron laser

Abstract: We propose a scheme of a two-stage terahertz free-electron laser (FEL) based on a Bragg traveling-wave ring resonator and parallel ribbon relativistic electron beams. The first beam moves in the field of a planar undulator and generates a pumping wave in the millimeter range. At the second stage, this wave transforms into terahertz radiation in the course of intraresonator backscattering on the second parallel electron beam. The ring resonator consists of four Bragg deflectors, each deflecting radiation by 90° in the vicinity of Bragg resonance, thus closing the feedback ring of the low-frequency pumping generator and simultaneously providing effective transfer of the pumping wave to the scattering stage.

The development of gyrotrons and their applications for plasma science and material processing

Abstract: The data about gyrotron-based technological systems and THz-band gyrotrons for diagnostics of different media are presented. The possible improvements of selective excitation of the operating modes with allowance for the competition with lower harmonics are considered. Double-beam electron optics is developed for a THz- band gyrotron. A sheet gyrotron as a tool for combining a high output power and frequency tuning is discussed. Long-life cathodes with additional heating by reflected electrons are preliminarily tested. 3D calculation of gyrotron operation regimes is carried out and the azimuthal inhomogeneity effects are analyzed. The results of experimental tests of a pulsed 200-kW/670-GHz gyrotron used for the initiation of localized gas discharge are presented.

New results and new trends in development of gyrotrons for fusion

Abstract: 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 gyrotron development are studied: elaboration of gyrotrons at high frequencies (~300GHz) and investigation of the possibility to realize oscillations locking by means of external signal.

Operation and Upgrade of the ECRH System at ASDEX Upgrade

Abstract: The upgraded Electron Cyclotron Resonance Heating (ECRH) system at ASDEX Upgrade (AUG) has been routinely used in the last experimental campaign. A further upgrade will replace an existing system of four short-pulse (140 GHz, 2s, 500 kW) gyrotrons. The final goal is to have around 6.5-7 MW at 140 GHz (or 5.5 MW at 105 GHz) from 8 units available in the plasma during the whole AUG discharge (10 s).

New results of extra-powerful 1.5MW/170GHz gyrotron development

Abstract: Results of the continued work on 1.5-1.7 MW CW gyrotron development are presented. Last year 1.5-MW power was attained at 92 kV beam voltage and 52 A beam current. This year the gyrotron with modernized electron-optical system was tested yielding up to 1.5-MW power at 72-77 kV beam voltage and 64-70 A beam current.

Investigation of subterahertz gyrotron for DNP NMR spectroscopy at IAP RAS

Abstract: The present paper concerns the state of the art of the development and experimental investigations of subterahertz gyrotrons for spectroscopy applications at IAP RAS. The gyrotron with frequency of 258 GHz and power of 100 watts is successfully used for spectroscopy experiments and 80-time rising of sensitivity has been obtained. The fundamental harmonic gyrotron with an internal mode converter is under development now. The predicted efficiency is 20% at power about 100 W and frequency of 263 GHz. The same helium-free 10-T magnet and electron optics will be used for design of a second harmonic tube with operating frequency of 520 GHz.

Generation of powerful THz radiation by electron beams and its interaction with plasma and gases

Abstract: The main results of the IAP RAS activity at the powerful pulse THz gyrotrons are presented. The power about 200 kW at the frequency of 0.67 THz in single impulses with durations of 30 microseconds has been reached. This gyrotron is successfully used to initiate localized (characteristic size in the order about 1 mm) discharge in gases. The models describing the dynamics of discharge initiated by THz radiation are under development. New experimental facility for long pulse or CW gyrotrons in frequency band 0.28-0.52 THz has been build based on helium-free 10 T cryomagnet.