The paper presents gyrotron-based system (developed by IAP RAS jointly with GYCOM Ltd.) for ECR plasma heating in the new T-15MD tokamak which is under construction in National Research Center "Kurchatov Institute". The first of a series (8 units) of microwave setups of a megawatt power level was developed and successfully tested. The setup includes a gyrotron, set of power supplies, a microwave radiation transmission line, and a fast protection system. 1 MW/82.6 GHz generation regime during 30 second pulse with an efficiency of 57% was experimentally demonstrated.
KEYWORDS: Terahertz radiation, Medium wave, Signal processing, Satellites, Particles, Optical simulations, Electron beams, VHF band, Extremely high frequency
We show that phase- and frequency-locking of a gyrotron with very-high-order operating mode TE56.24 by a relatively weak external monochromatic signal allows for MW-level power, high efficiency and high frequency- and phasestability of radiation in the terahertz frequencies region and broadens frequency tuning bandwith. Thus, significant enhancement of radiation parameters can be achieved. Such gyrotrons may be used in large complexes of coherently radiating gyrotrons for THz data and energy transmission and applied for electron cyclotron resonance heating and current drive (ECRH and CD) systems and for THz particles acceleration. We also show possibility of parametric 4-wave decay at the exit from the locking mode.
This report aims to bring together information about the most striking experimental results, new trends in gyrotron development, modern remarkable applications, new demands in parameter enhancement and future goals. The paper separated into two parts: first, related to progress in MW class gyrotron development for nuclear fusion and second, focused on the development of terahertz band gyrotrons. The data about pulsed and CW tubes, working in both specified frequencies ranges, are given. In particular, the series of 1MW/170 GHz/CW tubes with efficiency more than 50% has been developed successfully for ITER project. Same time, despite the requirement for strong magnetic fields, the problem of high ohmic losses and electron beam formation, the gyrotrons go through magic 1 THz mark with kW power level and demonstrate (in some specific combinations) operation at extremely low voltage and beam current, narrow frequency spectrum, wide frequency tuning. Novel schemes of high-frequency gyrotrons are analyzed. The novel quasioptical mode converters opened the possibility of phase-locking a number of tubes, which makes maximum power almost "unlimited"
This paper is devoted to theoretical and experimental investigations of high power microwave Cherenkov oscillators using of high current nanosecond electron beams. The influence of non synchronous waves and additional (non Cherenkov) resonance on the process of microwave generation in 3 cm relativistic BWO are discussed. Experimental data presented in this paper show that the efficiency of 3 cm relativistic BWO can achieve 40% and pulsed microwave power--500 MW. The enhancement of microwave power and efficiency of microwave generation was reached by creating of the non uniformity of the synchronous wave phase velocity and that of the coupling coefficient between the electrons and the electromagnetic wave. We experimentally studied the oversize Cherenkov oscillators in mm wavelength. One of them was 8 mm 120 MW orotron with TM13-mode of the circular waveguide. Another one was two stage two electron beams 8 mm Cherenkov oscillator. The maximum of microwave power in this experiment was 600 MW, pulse duration was 10 - 15 ns. All experiments were carried out by high current electron accelerators of type SINUS. The performance parameters of our accelerators are the following: electron energy from 100 to 2000 keV, beam current from 1 to 20 kA, pulse duration from 5 to 50 ns, repetition rate up to 200 - 300 pps.
A narrowly directed wavebeam injected into an oversized rectangular waveguide can bepresented as a sum of eigenwaves. Each of them is transmitted to the remote cross-section,where they form an image of the initial wavebeam. There are certain distances, where theinitial profile is repeated or split into a few beams with their amplitude profiles identical tothe initial one [11. Any initial profile is repeated at the distance i.----8a2,7,15 where a is widthof the waveguide., X is wavelength. The symmetrical profile is repeated at L i=a2/it, and splitinto n beams at Ln=a2/n2 (Fig. 1). Non-symmetrical input of a wavebeam results insplitting of the initial wavebeam into non-equal parts (Fig. 2). Similar effects can beformulated for linear-sectorial waveguides (Fig. 4).
KEYWORDS: Linear filtering, Applied physics, Plasma diagnostics, Waveguides, Diffraction gratings, Phase shifts, Mirrors, Signal attenuation, Infrared radiation, Extremely high frequency
A narrow frequency band (20...600 MHz) at frequencies 50...200 GHz and highsuppression (more than 40 dB) are the typical requirements for notch filters used in plasmadiagnostic during experiments with fusion installations. A very narrow frequency bandwidthAf/f=ia3...1a4 in the short millimeter wavelength range implies using of quasi-optical high- quality (Q ?_ 1(1') cavities as elementary cells that constitute a filter, and quasi-optical opentransmission line as a primary waveguide. We considered two possible ways to produce suchcavities (Fig. 1): 1) two-mirror cavity with a standing wave (a), 2) ring cavity with a travelingwave (b). For both cavities coupling is provided by a semi-transparent film or by diffractiongrating. In the first scheme there is a reflected wave, so phase shift (mutual position ofcavities) is important. The second scheme uses only a one-way wave and thus all cells areindependent.
One of the main factors, which limit duration of pulses and output powers of gyrotronsoperating in the short-wave part of the millimeter wavelength band in the quasi-continuousregime is heating of the gyrotron output window with microwave radiation, which in the longrun can lead to its destruction.
An universal method for highly efficient matching of an oversized waveguide with various types of open mirror lines is proposed. It is based on correlation of two different presentations of the field in an oversized waveguide: the first one presenting it as the superposition of waveguide modes, and the second one, as a set of geometric-optical rays.
For some years the main aim of investigations of gyrotrons is the creation of sources ECRH of fusion plasmas at frequenceies over 100 GHZ with outputs of 1 MW - level in pulses with duration of several seconds (up to CW). Nowadays the fabloration of gyrotrons with average output from 10 to 100 kW at frequencies ∼30 GHz and higher has been begun for technological applications. Nevertheless the basic investigation of cyrotrons are still bound with problems of increase in output power. Pulse duration and frequency.
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