Nina N. Skvortsova

Optimization of operation of a three-electrode gyrotron with the use of a flow-type calorimeter

Results are presented for measurements of microwave power of the Borets-75/0.8 gyrotron with recovery of residual electron energy, which were performed by a flow-type calorimeter. This gyrotron is a part of the ECR plasma heating complex put into operation in 2010 at the L-2M stellarator. The new calorimeter is capable of measuring microwave power up to 0.5 MW. Monitoring of the microwave power makes it possible to control the parameters of the gyrotron power supply unit (its voltage and current) and the magnetic field of the cryomagnet in order to optimize the gyrotron operation and arrive at maximum efficiency.

Microwave method for synthesis of micro- and nanostructures with controllable composition during gyrotron discharge

Abstract. We introduce an approach toward the synthesis of micro- and nanostructures under nonequilibrium microwave discharges within metal–dielectric powder mixtures induced by powerful microwave gyrotron radiation. A new plasma-chemical reactor capable of sustaining a discharge regime with an afterglow phase of an order of magnitude longer than the gyrotron pulse duration was constructed for these experiments. In the nonequilibrium conditions of such a discharge, plasma-induced exothermic chemical reactions leading to the synthesis of various compounds were initiated. The synthesized structures were deposited on the reactor walls and on the impurity particles within the reactor. This method was tested under gyrotron-initiated discharges within various metal–dielectric powder mixtures of titanium–boron, molybdenum–boron, titanium–silicon–boron, molybdenum–boron nitride, molybdenum–tungsten–boron nitride, and so on. Depending on the powder mixture composition, reactor atmosphere, and other parameters, micro- and nanosized particles of boron nitride, titanium diboride, molybdenum boride, titanium boride, molybdenum, and molybdenum oxide, were synthesized, detected, and analyzed.

On non-parametric methodology of the plasma turbulence research

A non-parametric approach to the estimation of plasma turbulence spectra is propesed in the paper. The basic model for description of the fine structure of stochastic processes is a finite location-scale normal mixture. The classical EM-algorithm is used for estimating the unknown parameters. The explanation of empirical results are given for the evolution of one-side Fourier spectra obtained in different modes of low-frequency plasma turbulence. Such kind of analysis allows to identify typical structures of processes forming plasma turbulence.

Effect of electron-cyclotron resonance plasma heating conditions on the low-frequency modulation of the gyrotron power at the L-2M stellarator

Low-frequency modulation of the gyrotron power at the L-2M stellarator was studied at different modes of plasma confinement. The plasma was heated at the second harmonic of the electron gyrofrequency. The effect of reflection of gyrotron radiation from the region of electron-cyclotron resonance plasma heating, as well as of backscattering of gyrotron radiation from fluctuations of the plasma density, on the modulation of the gyrotron power was investigated.

Collective backscattering of gyrotron radiation by small-scale plasma density fluctuations in large helical device.

A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (k(s) approximately 34 cm(-1)) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose.

On The Development Of An Information Technology For Plasma Turbulence Research.

The paper deals with an example of real information technology developed for the examination of specific structures of plasma turbulence by the spectral analysis. The mathematical basis is a probabilistic approach using a special simulation algorithm to construct sample for the probabilistic modeling. To describe the fine structure of stochastic processes, finite mixtures of various probability distributions are used. In the paper, the general structure of the developed information technology including mathematical models, algorithms and software realization is considered. Procedures for finding statistical estimators of the unknown parameters of model are based on modifications of EM algorithm. Examples of application of the developed technology in an important area of modern physics are presented.

On investigation of the fine structure of processes in low-frequency plasma turbulence

The paper presents methodology of the analysis of statistical characteristics of turbulent fluctuations based on the decomposition of processes into components using the method of moving separation of finite normal mixtures. To estimate the parameters, various modifications of the well-known EM algorithm are used. We analyze the changes in statistical characteristics for the case of variations in the conditions of microwave field excitation. The obtained results demonstrate good consistency with actually observed processes in turbulent plasma.