Gyrotron Complex Research Articles

A Method for non-destructive testing of resonant frequency in the W-band second harmonic gyrotron complex cavity

A Method for non-destructive testing of resonant frequency in the W-band second harmonic gyrotron complex cavity

Modernization of the filtration system for the Doppler reflectometry diagnostics of the L-2M stellarator for operation in regimes high-power ECR heating

The commissioning of the MIG-3 gyrotron complex at the L-2M stellarator has made it possible to reach a record power density input into plasma of 3.4 MW/m3 during the ECR heating of the plasma. This power input, however, resulted in noisy Doppler reflectometry signals (with a high-amplitude component at the gyrotron working frequency of 75.3 GHz), which could not be processed and analyzed. We modernized the filtering system of the Doppler reflectometry diagnostics, which had consisted of two pin-type band stop waveguide filters. Another pin-type filter was added to the filter system and a new compact bandstop filter was designed based on the Fabry-Perot resonator (BFFPR) to provide high suppression at the frequency of 75.3 GHz and low attenuation at the 30–40 GHz diagnostic frequency. We optimized the cavity length of the filter and calculated the characteristics of filters with different numbers of resonators by using numerical simulations. The filter layout was designed, and its characteristics were measured. The results of experimental measurements and numerical simulations have a good match. The redesigned filters were used to suppress the noise from the MIG-3 gyrotron complex.

A Subthreshold High-Pressure Discharge Excited by a Microwave Beam: Physical Basics and Applications

A new form of discharge excited by a microwave beam in a high-pressure (up to atmospheric and higher) gas in free space and in a closed chamber is discussed. For the first time, the discharge was implemented by means of a gyrotron with a pulse power of 200 ≤ P ≤ 600 kW, a pulse duration of 0.5 ≤ τ ≤ 20 ms, and a wavelength of λ = 0.4 cm. Under deeply subthreshold conditions in atmospheric-pressure air, a plasma column with a length of L = 50 cm was generated by a microwave beam formed with the help of a quasi-optical transmission line. With the use of the MIG-3 gyrotron complex with the above parameters, generation of a plasma column with a length of several meters is possible in principle. The parameters and structure of the formation of the plasma investigated make it possible to class it as a self-non-self-sustained (SNSS) discharge, discovered and described for the first time at the Prokhorov General Physics Institute, Russian Academy of Sciences. One of the important applications of this type of discharge is plasmachemical cleaning of the urban air environment of hazardous contaminants.

Status of the gyrotron complex for ITER: composition of the complex, manufacturing, obtained parameters, delivery conditions

Status of the gyrotron complex for ITER: composition of the complex, manufacturing, obtained parameters, delivery conditions

Advances in technology and high power performance of the ECH system on DIII-D

The gyrotron complex on DIII-D has been updated and consists of six gyrotrons installed and routinely operating reliably for injection of up to 3.6MW into the plasma. The eight sets of real time steerable mirrors that are installed on DIII-D inject the rf power from the tokamak low field side. The transmission line was upgraded with new rf power monitors at the last miter bend before the tokamak, which can measure wave polarization, mode content, and rf power reflected from the plasma. A new design depressed collector gyrotron in the 1.5MW class, operating at 117.5GHz, is expected to be installed in 2017. Plans call for an expansion of the ECH system to ten gyrotrons.

Millimeter-Wavelength Radiation Used to Sinter Radiotransparent MgAl2O4 Ceramics

We have developed a method for production of high-density MgAl2O4 ceramics characterized by low dielectric losses. The method is based on sintering of ultrafine, high-purity powder materials in the electromagnetic field of intense microwave radiation. The initial nanodimensional magnesium-aluminate powder was synthesized by the sol-gel method and sintered in a gyrotron complex operated at a frequency of 24 GHz. The results of studying the conditions and regimes of microwave sintering of MgAl2O4 ceramics are presented, along with its phase features, microstructural peculiarities, and mechanical and dielectric characteristics. The possibility of controlling the microstructure of the sintered material by varying the regime of RF heating is demonstrated.

The Multiple Gyrotron System on the DIII-D Tokamak

A major component of the versatile heating systems on the DIII-D tokamak is the gyrotron complex. This system routinely operates at 110 GHz with 4.7 MW-generated rf power for electron cyclotron heating and current drive. The complex is being upgraded with the addition of new depressed collector potential gyrotrons operating at 117.5 GHz and generating rf power in excess of 1.0 MW each. The long-term upgrade plan calls for 10 gyrotrons at the higher frequency being phased in as resources permit, for an injected power near 10 MW. This paper presents a summary of the current status of the DIII-D gyrotron complex, its performance, individual components, testing procedures, operational parameters, plans, and a brief summary of the experiments for which the system is currently being used.

Production of WO3 tungsten oxide nanopowders by evaporation-condensation process using focused 24-GHz microwave radiation

Fabrication of WO3 tungsten oxide nanoparticles by evaporation of the initial oxide material with a focused beam of 24-GHz electromagnetic radiation generated in a 5-kW gyrotron complex at a design microwave power density of 10 kW/cm2 has been experimentally studied. Tungsten oxide powders consisting of particles, which sizes are in range of 20 nm up to 1 μm, have been obtained. The particles have different shapes, close to spherical or octahedral, suggesting their formation via both the “vapor-liquid-crystal” and the “vapor-crystal” mechanism. The maximal evaporation rate was 100 g/h. The feasibility of powder dispersity controlling by varying the flow rate of cooling air has been revealed.

Performance History and Upgrades for the DIII-D Gyrotron Complex

The gyrotron installation on the DIII-D tokamak has been in operation at the second harmonic of the electron cyclotron resonance since the mid-1990s. Prior to that a large installation of ten 60 GHz tubes was operated at the fundamental resonance. The system has been upgraded regularly and is an everyday tool for experiments on DIII-D.

Laser Ceramics Sintering by Millimeter-Wave Heating

Prospects for using microwave radiation to sinter optically transparent ceramics are stipulated by the absence of the heaters and screens contaminating the sintered material and the presence of the inverse temperature distribution in the product, which allows one to fabricate maximum-density ceramics. In this work, we present the results of studying the process of producing optically transparent Yb:YAG and Yb:(LaY)2O3 ceramics when the samples are sintered in the chamber of a gyrotron complex operated at a frequency of 24 GHz. The various-composition samples were manufactured by compaction of a mixture of commercially available powders (Yb:YAG ceramics) and the powders prepared by the self-propagating high-temperature synthesis (Yb:(LaY)2O3 ceramics). The sintering temperatures were varied in the interval 1700–1900°C, the sintering time was varied from 2 to 20 h, and the residual-air pressure in the working chamber was 10 Pa. Lasing was obtained for the samples of both compositions.

A new MIG-3 gyrotron complex for creation and heating of plasma in the L-2M stellarator and the first experimental results

The characteristics of a new MIG-3 gyrotron complex for creating and heating plasma in the L-2M stellarator are presented. The first experimental results using the complex are reported. The complex consists of two three-electrode GYCOM gyrotrons of the new generation with electron beam energy recuperation, a high-voltage modulator that enables both separate and simultaneous operation of the two gyrotrons, and a control/data-recording unit. The total specific power to be inserted into plasma reaches 5 MW/m3 when both gyrotrons in operation.

Specific features of the development of a high-stability continuous-wave gyrotron operated at the second harmonicwith a working frequency OF 258 GHz

We consider specific features of the development of a continuous-wave 258 GHz gyrotron operated at the second gyrofrequency harmonic, which are related to ensuring of high stability of its output parameters. The requirements to accuracy of manufacture of the cavity and adjustment of the electron beam are evaluated, as well as the necessary parameters of the power sources of the gyrotron complex, which should maintain the required level and stability of the generated power and frequency. The influence of the effect of spurious-mode reflection from the output window of the gyrotron is studied.

The Electron Cyclotron Resonant Heating System on the DIII-D Tokamak

In the DIII-D electron heating and current drive installation, up to six gyrotron microwave generators in the 1-MW class at pulse lengths up to 5 s have been operated simultaneously. The frequency for all the gyrotrons is 110 GHz, corresponding to the second harmonic of the electron gyrofrequency at 2 T. The peak generated power has been >4 MW with peak injected power slightly greater than 3 MW. The radio frequency (rf) generators are located remotely and are connected to the tokamak by up to 100 m of evacuated circular corrugated waveguide carrying the HE1,1 mode with overall transmission efficiency, including coupling to the waveguide, of up to 75%. Ancillary equipment for polarization control, beam switching, power monitoring, control of launch direction, and system protection has been developed.The system has been used to support a wide variety of physics experiments, including control of magnetohydrodynamic modes, current density profile modifications, basic plasma heating and current drive, transport studies, and rf-assisted start-up. The gyrotron complex is being upgraded by the acquisition of additional tubes with 5- to 10-s pulse length capability.