Synthesis of Nitrogen Oxides in a Subthreshold Microwave Discharge in Air and in Air Mixtures with Methane

Plasma Physics Reports - A subthreshold discharge excited by a microwave beam in air at pressures close to atmospheric is studied as a plasmachemical method of nitrogen oxide (NOx) production. It...     

Toroidal inhomogeneity of plasma density fluctuations during ECR plasma heating in the L-2M stellarator

Correlation between short-wavelength (k_⊥ ≈ 20–30 cm^–1) and long-wavelength (k_⊥ ≈ 1–2 cm^–1) plasma density fluctuations in two poloidal cross sections of the stellarator chamber separated by 1/14 or 5/14 of the torus perimeter was studied using collective scattering of radiation of two 75-GHz gyrotrons and radiation of a 37-GHz Doppler reflectometer at an ECR heating power density of 1.6–3.2 MW/m³. It is found that excitation of turbulent fluctuations is bursty in character and that fluctuations excited in different L-2M cross sections are uncorrelated. It is shown that the energy of turbulent fluctuations is modulated by a low frequency of 5–20 kHz. An idea is put forward that anomalous transport is toroidally inhomogeneous.     

Reflection and backscattering of microwaves under doubling of the plasma density and displacement of the gyroresonance region during electron cyclotron resonance heating of plasma in the l-2M stellarator

Reflection and backscattering of high-power (400 kW) gyrotron radiation creating and heating plasma at the second harmonic of the electronic cyclotron frequency in the L-2M stellarator have been investigated experimentally. The effect of the displacement of the gyroresonance region from the axis of the plasma column under doubling of the plasma density on the processes of reflection and backscattering of microwave radiation has been examined. A near doubling of short-wavelength (k _⊥ ≈ 30 cm^–1) turbulent density fluctuations squared is observed. The change in the energy confinement time under variations of plasma parameters and characteristics of short-wavelength turbulence is discussed. A discrepancy between the measured values of the reflection coefficient from the electron cyclotron resonance heating region and predictions of the one-dimensional model is revealed.     

Energy Loss and Microturbulence under Multipulse ECR Plasma Heating at the L-2M Stellarator

Plasma Physics Reports - In experiments on multipulse on-axis electron cyclotron resonance heating (ECRH) of plasma by a series of microwave pulses at the L-2M stellarator, several phases of plasma...     

Application of microwave discharge for the synthesis of TiB2 and BN nano- and microcrystals in a mixture of Ti-B powders in a nitrogen atmosphere

Synthesis of titanium diboride and boron nitride nano- and microcrystals by means of a pulsed microwave discharge in a mixture of Ti-B powders in a nitrogen atmosphere is considered. For this purpose, a new type of reactor with a free surface of the powder mixture was used. The reactor design permits free expansion of the reaction products into the reactor volume and their deposition on the reactor walls. Conditions for the synthesis of TiB₂ and BN compounds were studied as functions of the energy input in the discharge, the powder component ratio, the rate of the nitrogen flow through the reactor, and the structure and phase composition of the compounds deposited on the reactor walls. The synthesis of boron nitride and titanium diboride in crystal structures is proven. An important role in the process of synthesis is played by the heating of the mixture due to the titanium diboride synthesis reaction, its behavior in the bulk of the reactor, and the titanium concentration in the powder mixture. It is also found that, as the number of discharges in the bulk of the reactor increases, a dust cloud forms. The luminescence of this cloud indicates that the initiated discharge proceeds not only on the powder surface and in the powder bulk, but also in the reactor volume.     

Plasmoid Generation behind the Front of a Subthreshold Discharge in Air under the Self-Action of a Microwave Beam

Plasma Physics Reports - Frames of a subthreshold microwave SNSS discharge were obtained in experiments. They showed that, behind the front of the head plasmoid with a fine-cell glow structure,...     

Characteristics of a Subthreshold Microwave Discharge in a Wave Beam in Air and the Efficiency of the Plasma-Chemical Reactor

Plasma Physics Reports - An analysis of a set of experiments on studying subthreshold microwave self/non-self-sustained (SNSS) discharges made it possible to estimate the volume of the active zone...     

Time–Space Evolution of the Parameters of Turbulent Density Fluctuations During Pulsed EC Heating of the Plasma at the L-2M Stellarator

Plasma Physics Reports - The study is continued of the temporal changes of the parameters of turbulent plasma density fluctuations during multi-pulse electron cyclotron (EC) heating of the plasma...     

Reaction of turbulence at the edge and in the center of the plasma column to pulsed impurity injection caused by the sputtering of the wall coating in L-2M stellarator

Impurity injection into plasma caused by the sputtering of the wall coating in the L-2M stellarator during auxiliary electron cyclotron resonance heating leads to a change in the level of plasma density fluctuations with frequencies above 0.25 MHz: suppression of long-wavelength (k _⊥ = 2 cm^–1) density fluctuations in the edge plasma, intensification of short-wavelength (k _⊥ = 30 cm^–1) and long-wavelength (k _⊥ = 1 cm^–1) fluctuations at the midradius of the plasma column, and intensification of short-wavelength fluctuations (k _⊥ = 20 cm^–1) in the plasma center (including the gyroresonance region). At the same time, the level of fluctuations with frequencies below 0.25 MHz remains unchanged. In the edge plasma, a decrease in the plasma potential and suppression of its fluctuations is observed during impurity injection, which also causes an increase in MHD activity.     

Spectra of low-frequency modulation of gyrotron radiation during electron-cyclotron resonance heating of plasma in the L-2M stellarator

Results from experimental studies of the modulation of the gyrotron power during electron cyclotron resonance heating of plasma L-2M stellarator are presented. It is shown that the modulation spectrum consists of separate spectral bands, among which a 20-kHz peak with a spectral density exceeding by one order of magnitude the spectral density of the other peaks is observed. This can be explained by the gyrotron operation being affected by the wave reflected from long-wavelength plasma fluctuations.