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The results are presented from studies of the extraordinary wave (X-wave) absorption in plasma of the L-2M stellarator, as well as the power loss of microwave beam introduced into the plasma. The X-wave occurs as a result of splitting the linearly polarized gyrotron radiation, as it intersects the plasma boundary. Different electron cyclotron resonance heating (ECRH) regimes were studied: heating by a sequence of microwave pulses and heating that involves an auxiliary ECRH pulse. It was ascertained that for the X-wave, the single-pass absorption coefficient along the central chord of the plasma cross section is higher than 95%, and in the axial ECRH regime, the power losses correspond to the O-wave power. It was ascertained that the power loss of the beam inputted into the plasma increases up to 20–23% when the gyroresonance region was displaced towards the inner wall of the vacuum chamber and the ECRH pulse duration was increased. At the same time, the radiation loss drastically increased. It was hypothesized that an increase in the power loss is caused by a decrease in the X-wave absorption coefficient integrated over the beam cross section, which occurs due to a decrease in the electron temperature across the microwave beam cross section. In the regime with the auxiliary ECRH pulse, the pulsed sputtering of the vacuum chamber coating occurs, and the electron density and temperature change; nevertheless, the absorption coefficient along the central chord exceeds 90%.

A microwave beam (wavelength 4 mm, power 150–300 kW) generates an ionization wave in air in the subthreshold field in the shape of a conglomerate of thread-like channels that moves toward the beam. The periphery of the beam refracts in the plasma of the non-self-sustained discharge in the UV halo of the thread-like discharges and self-focuses in the recombining plasma behind the front of the plasmoid that consists of thread-like channels. The self-focusing of the peripheral regions of the wave beam causes local bursts of ionization behind the front of the leading plasmoid.

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 of self-sustained thread-like discharges resulting from the development of the ionization–overheating instability. It is shown that this volume is 0.04–0.1 of the wave beam volume. It is shown that in the processes of the plasma-chemical action of the SNSS discharge, mixing of the substance reacted in the active regions with the gas outside the active regions increases the cost of the plasma-chemical process. A decrease in the energy cost of plasma-chemical processes requires an increase in the ratio of the microwave beam volume to the plasma-chemical reactor volume. A scheme of a flow-through reactor with a multimode waveguide is proposed and the possible performance of such a design in the destruction of harmful impurities in gas mixtures is estimated.

Studies of the composition of the products of chemical reactions in the afterglow of a new type of atmospheric discharge, the microwave self-non-self-sustained discharge in air with admixtures of methane, were carried out. A detailed kinetic model was developed that describes the kinetics of reactions with polyatomic nitrogen oxides at the stage of intensive cooling of the discharge channel. It was found that the formation of nitrogen oxide NO depends on the percentage of the products of the methane molecule dissociation in the nitrogen–oxygen mixture that, initially, is atomic. The new discharge type can be used for the plasmachemical processing of gaseous media.

The subthreshold self-non-self-sustained discharge in air was studied as the basis of the system for cleaning urban air from ecologically harmful admixtures. A cycle of experiments was carried out and the efficiency of the destruction of small amounts of hydrogen sulfide mixed with air (about 8 ppm) introduced into the processed air volume was determined. Experiments demonstrated a relatively high degree of H2S decomposition (its concentration decreased 41.5 times at unit energy deposition of 8 J/cm3 in the SNSS discharge).

In the subthreshold microwave discharge (the wavelength of 4 mm) in argon at the pressure of 750 Torr at intensities of the wave beam from 3 to 7.8 kW/cm2, the velocity of the ionization front, measured from the phase change of the reflected wave, increases approximately as the intensity on the wave beam axis in the power of 3/2 from 0.5 × 105 to 2.9 × 105 cm/s. This velocity of the discharge front in argon is 20–30 times higher than the velocity of the discharge front in air at the same intensities in the microwave beam. The glow structure of the discharge at intensities higher than 3 kW/cm2 is similar to the glow structure in molecular gases. An even finer structure of the discharge is observed at glow intensities on the wave beam axis below 3 kW/cm2. The gas temperature in the discharge at radiation intensity of 6 kW/cm2 is 6 kK. It is concluded that the volume of high-temperature regions in the discharge is 0.01 of the volume of the discharge region. The problem of the mechanism of the argon ionization and the possibility of the development of ionization-overheating instability in a non-self-sustained microwave discharge in the UV halo of the discharge front are discussed.

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 on the L-2M stellarator. The plasma density fluctuations with different wave vectors (k = 30, 20, 2, and 1 cm –1) in different spatial regions of the plasma column were recorded by the method of collective scattering of microwave radiation. The time dependence of plasma density fluctuations, which has a bursty shape, was analyzed, including the discharges in which the gyroresonance region was shifted by 3–4 cm from the center of the plasma column toward the inside of the torus. A comparison was made between the specificities of the evolution of plasma density fluctuations and the evolution of their statistical characteristics. It was found that the kurtosis (M4) of the scattering signals deviates from the value 3, which also occurs in bursts. During a EC heating pulse, three groups of different bursts (of signal intensity, its kurtosis and their increments) were observed. Autocorrelation analysis of density fluctuations and their increment was carried out and it showed that the half-width of the autocorrelation functions changes during multi-pulse EC heating. The probability of the initiation of bursty processes by perturbations in the near-wall plasma region is discussed.

Propagation velocity of a subthreshold microwave discharge in air and carbon dioxide is measured at various gas pressures and intensities of microwave radiation. At air pressures of 200, 390, and 738 Torr and carbon dioxide pressures of 390 and 750 Torr, the propagation velocity of the head part of the self-non-self-sustained discharge closely follows a quadratic power law as a function of microwave-beam intensity in the range from 4 to 16 kW/cm2, while decreasing directly proportional to the initial gas density. In the process, the discharge propagation velocities in carbon dioxide are twice lower that those in air at equal intensities of the microwave radiation. The temperature in the head part of the discharge in air reaches 3.5–5.5 kK, while that in carbon dioxide reaches 9–15 kK.

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 is shown that at the energy expenditure level (2–4) kW h/m3, it is possible to produce a nitrogen oxide concentration in pure air that exceeds the concentration in the initial gas by several orders of magnitude. At the same time, it is shown that it is possible to stop nitrogen oxide production almost completely by adding an admixture of methane (CH4) to the irradiated air, which makes the so-called self-non-self-sustained (SNSS) discharge much more promising for cleaning the gaseous exhausts from urban landfills from harmful admixtures (hydrogen sulfide, mercaptans, etc.).

In this article, results are presented of experiments on depositing charged particles, which imitate the levitating dust on the Moon, on stainless steel. Ensembles of particles are created above the surface of laboratory regolith whose composition and particle size distribution imitate the dust that covers the Moon’s surface. Under the action of the gyrotron radiation on regolith, non-linear physical-chemical processes develop (breakdown, chain plasmachemical reactions, and particle scattering by the Coulomb mechanism), which lead to the appearance of a levitating cloud of particles. The simulation experiment is based on the similarity between the processes that develop in the laboratory experiments with regolith and the processes that occur on the Moon during its bombardment by micrometeorites. The effect of the levitating cloud on stainless steel plates is studied and it is shown that regolith particles in the shape of spheroids of different sizes are deposited on the surface of the plates. The dimensions of the deposited particles and the density of their placement depend on the quality of treatment of the plate surface. It is shown that the laboratory-produced dusty plasma can be used in simulation experiments to study the modification of surfaces of different materials for space technology.

It is proposed to determine the propagation velocity of a self-sustained subthreshold microwave (SSM) discharge by measuring the beatings between the reflected radiation and the reference signal. It is shown that the velocity of the head part of the SSM discharge determined from the fundamental frequency harmonic of the beating signal coincides with the velocity of the front of UV discharge radiation. The proposed method allows one to measure the velocity of the head part of the discharge along the microwave beam path, variations in this velocity caused by changes in the microwave beam power, the reduction in the gas density along the beam path, and the time delay in the initiation of the burning wave in methane–air mixtures.

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 energy loss were observed: the short stage of low-energy loss, the stage of rapid increase in energy loss, the quasi-steady stage, and the relaxation stage between the heating pulses. In the stage of rapid increase in energy loss, the energy loss power is two or more times higher than that in the relaxation stage at the same energy of the plasma column. Short-wavelength plasma density fluctuations were measured using both the ordinary and extraordinary microwave collective scattering technique. It is found that, in the quasi-steady stage, the amplitude of density fluctuations is much lower than that in the preceding heating stages. The fluctuation amplitude lowers just after the restructuring of the density profile and establishment of a steady-state hollow density profile due to the density pump-out effect. The amplitude of large-scale density fluctuations at the plasma periphery recorded by a Doppler reflectometer remains unchanged during the ECRH pulses and in the time intervals between them. However, when the stage of rapid increase in energy loss begins, the shape of the density fluctuation spectrum changes significantly. The initially narrow spectrum with one peak near the zero frequency broadens, the amplitude of the central peak decreases, and two additional peaks at frequencies of 0.7 and −0.7 MHz appear.

A subthreshold microwave discharge in atmospheric-pressure air is used to process mixtures of mercaptans (thiols) with air and with air and methane. It is found that, at microwave intensities of ~10 kW/cm2 and pulse durations of 1–3 ms, the mercaptan concentration decreases 100-fold in mixtures with air and 20-fold in mixtures with air and methane. It is shown that, at an average specific energy deposition in a single discharge of ~0.4 J/cm3, the specific microwave energy spent on mercaptan decomposition is ~10 J/cm3. It is concluded that the active zone of the discharge with high specific energy deposition occupies less than 5% of the microwave beam volume.

Ionization−overheating instability of a non-self-sustained discharge in air in a subthreshold microwave field creates a self-sustained discharge with a fine cellular structure, whose UV radiation, in turn, generates a new non-self-sustained discharge on the microwave beam path, where ionization−overheating instability arises again. It is shown that, at microwave intensities in the range of 3–18 kW/cm2, the propagation velocity of the ionization wave, including the region of the self-sustained discharge and the forward region of the non-self-sustained discharge developing in its UV halo, is proportional to the third power of the microwave field strength, while the maximum temperature in the discharge is inversely proportional to the microwave field strength.

The propagation velocities of a subthreshold discharge excited in air at atmospheric pressure by a pulsed microwave beam with a Gaussian field distribution, a wavelength of 4 mm, and an intensity up to 30 kW/cm2 have been measured by means of optical and microwave diagnostics. It has been shown that the motion of a discharge front along the path of the beam toward the region of an increasing microwave field is accompanied by an increase in the velocity from subsonic (~10–4 cm/s) to supersonic (~(6–8) × 104 cm/s). At the same time, motion toward the decreasing field region is accompanied by a decrease in the velocity from supersonic to subsonic. It has been found that the maximum temperature of the gas in the discharge at velocities of ~104 cm/s reaches ~5.3 kK.

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.

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.

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.

We show the possibility of creating a metal microcrystalline relief (micro- and nanosized) on molybdenum plates in a plasma gas-phase discharge initiated by gyrotron radiation in molybdenum–dielectric powder mixtures.

This paper describes the reaction of a gyrotron oscillator when a very small fraction of its radiation, extracted from the main beam, is phase-modulated in a controlled way and is finally redirected back to the gyrotron. The gyrotron may exhibit a 10 % modulation of its total power even if the reflected power is lower than 1 %. Moreover, radial probing of the beam power distribution shows that the amplitude of the power modulation differs at different radial positions across the beam.

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.

Fluctuations of the density in a transient process at electron-cyclotron heating have been measured by the methods of backscattering and small-angle scattering of gyrotron radiation by fluctuations of the plasma density. Estimates have indicated the increase and decrease in the turbulent heat fluxes at the switch-on and switch-off of additional electron-cyclotron heating, respectively. The possibility of excitation of vortices of drift waves and their relation with fast anomalous heat transport at electron-cyclotron heating has been discussed.

Reflection of the heating extraordinary microwave incident obliquely onto the surface of the electron cyclotron resonance (ECR) at the second harmonic of the electron gyrofrequency in the 3D magnetic configuration of the L-2M stellarator was studied experimentally. The plasma was heated using two gyrotrons with a total power of 600–700 kW, the specific heating power being 2.4–2.8 MW/m3. The displacement of the ECR region in the course of heating was monitored by measuring the phase of the reflected extraordinary wave. It is found that the growth of the plasma density is accompanied by the displacement of the ECR heating region from the center of the plasma column toward its periphery. The coefficient of reflection of the heating microwave beam from the ECR region was measured. The spectra of short-wavelength (k s ≈ 30 cm−1) plasma density fluctuations were explored by analyzing backscattered microwave radiation. A tenfold increase in the energy of short-wavelength density fluctuations and the growth of the spectral density of fluctuations in the frequency range of 0.3–1.5 MHz were observed.

Changes in the energy spectra of short-wavelength (ks ≈ 35 cm−1) plasma density fluctuations in the local region of the plasma column (r/a = 0.5–0.6) of the L-2M stellarator were studied by the method of collective scattering of 150-GHz radiation. The plasma was heated at the second harmonic of the electron gyrofrequency, the microwave heating power being in the range of 90–170 kW. A sector limiter was introduced in the peripheral plasma (r/a ≥ 0.8), and the Shafranov shift of the magnetic axis was varied by varying the vertical magnetic field. The results of measurements were averaged over 9–16 discharges. It is found that an increase in the heating power and/or the introduction of the sector limiter in the plasma lead to an increase in the energy of density fluctuations, which correlates with a decrease in the plasma energy lifetime. In the spectra of fluctuations, a broad spectral band in the range of 3–50 kHz was observed in which the spectral density was one order of magnitude higher than in the rest of the spectrum. Analysis of the Fourier spectra showed that the introduction of the sector limiter in the plasma resulted in an increase in both the spectral density of fluctuations in the range of 3–50 kHz and the fraction of quasi-coherent structures in turbulent density fluctuations.

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.

In experiments on electron cyclotron resonance (ECR) heating of plasma at the second harmonic of the electron gyrofrequency in the L-2M stellarator, the effect of partial reflection of high-power gyrotron radiation from the ECR heating region located in the center of the plasma column was revealed. The reflection coefficient is found to be on the order of 10−3. The coefficient of reflection of an extraordinary wave from the second-harmonic ECR region is calculated in the one-dimensional full-wave model. The calculated and measured values of the reflection coefficient are found to coincide in order of magnitude.

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.

Backscattering of gyrotron radiation (θ = π) by short-wavelength density fluctuations (k ⊥ = 30 cm−1) in the plasma of the L-2M stellarator was studied under conditions of electron cyclotron resonance (ECR) plasma heating at the second harmonic of the electron gyrofrequency (75 GHz). The scattering of the O-wave emerging due to the splitting of the linearly polarized gyrotron radiation into the X- and O-waves was analyzed. The signal obtained after homodyne detection of scattered radiation is a result of interference of the reference signal, the quasi-steady component, and the fast oscillating component. The coefficients of reflection of the quasi-steady component, R = 2 (Y), and fast oscillating component, R ∼ 2 (Y), of scattered radiation are estimated. The growth of the R ∼ 2 (Y) coefficient from 3.7 × 10−4 to 5.2 × 10−4 with increasing ECR heating power from 190 to 430 kW is found to correlate with the decrease in the energy lifetime from 1.9 to 1.46 ms. The relative density of short-wavelength fluctuations is estimated to be 〈n ∼ 2 〉/〈n 2 〉 = 3 × 10−7. It is shown that the frequencies of short-wavelength fluctuations are in the range 10–150 kHz. The recorded short-wavelength fluctuations can be interpreted as structural turbulence, the energy of which comprises ∼10% of the total fluctuations energy. Simulations of transport processes show that neoclassical heat fluxes are much smaller than anomalous ones. It is suggested that short-wavelength turbulence plays a decisive role in the anomalous heat transport.

Results of testing of a possible method for location of water microleakages in the cooling system of the first wall and vacuum chamber of ITER are presented. The method consists in spectroscopic detection of the emission lines of atoms and ions of the Xe additive dissolved in water. These lines are excited when the water with dissolved Xe contacts the plasma. The high electron cyclotron resonance heating (ECRH) power deposited in a relatively small plasma volume in the L-2M stellarator (P = 0.5 MW, V = 0.24 m3, and the specific heating power ∼2 MW/m3) makes it possible to achieve plasma parameters close to those in the edge plasma of ITER for different operating modes, including the H-mode with an edge transport barrier. In test experiments, several lines of Xe ions were revealed suitable for detection of xenon in plasma with parameters close to those in the edge plasma of ITER at leakage rates at a level of ∼10−6 Pa m3 s−1 and spatial resolution of ∼0.5 cm.

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.

In studying the high-temperature plasma physics, the researcher is faced with the need to process large amounts of semi-structured data. Dozens of multi-channel diagnostics, the results of which are multi-million ensembles of time samples of plasma signals, are usually installed at the same time in thermonuclear devices. These samples contain information necessary to understand the mechanisms of relation between plasma macroparameters (plasma density and temperature, plasma current, magnetic field, auxiliary heating power, etc) and plasma microparameters determined by turbulence (energy, spectral composition, amplitude density distribution, etc). The methods of analysis of plasma signals based on the processing of a single time realization of turbulence cannot be used as a basis for comparison with macroparameters and identification of new patterns of plasma containment in a magnetic trap. The main objective of this work is to obtain information about the relationship between the macro- and microparameters of the plasma based on the structuring of the acquired data and its multi-parameter processing using the modern software and hardware.

The results of experiments on plasma confinement at ECRH power density up to 1.5 MW/m3 are reported. It is shown that the results of measurements of the diamagnetism and poloidal rotation velocity of the plasma in the peripheral region agree with numerical calculations using a neoclassical model with allowance for anomalous losses. The correlation has been found between the low-frequency modulation of the gyrotron power radiation and the modulation of the radiation scattered by the turbulent plasma density fluctuations.