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The results of measuring the longitudinal electric current excited in the toroidal plasma of the L-2M stellarator as a result of powerful pulsed microwave heating (power up to 600 kW, pulse duration up to 20 ms) are presented. In the experi-ments, to create and heat plasma in the stellarator, microwave radiation of gyro-trons with a frequency of 75 GHz, equal to the frequency of the 2nd harmonic of electron cyclotron resonance for a magnetic field with induction B = 1.34 T at the center of the plasma column, was used. To measure the currents in the plasma, di-agnostic systems of the stellarator were used, designed to record changes in time of the transverse and poloidal magnetic fields. It is shown that the presence of an ohmic heating iron transformer in the stellarator design significantly affects the temporal development of equilibrium currents due to the significant inductance of the toroidal plasma. When compensating the inductance of these devices, the ex-pected value of the current excited in the plasma can reach a value of about 7 kA.

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.

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).

D-shaped tokamak T-15MD is nowunder construction in the NRC "Kurchatov Institute". Heavy ion beam probing (HIBP) is an important part of T-15MD diagnostic system. Calculations of the probing ions trajectories show that the beam will pass through the plasma about 1.0…1.5 m, which can lead to its significant attenuation. HIBP operation requires obtaininga high-current long-focus probing beam of Tl+ ions (I = 200…400 μA, f = 4…6 m, d ≤ 10 mm). A high voltage (300 keV) test-benchto test such beams is being created now. Numerical modeling shows the possibility of a beam formation with a current of 300 μA and diameter 12 mm at 6 m from the ion emitter.

The goal of the research is to expand the capabilities of the heavy ion beam probing (HIBP) diagnostic. HIBP is a unique diagnostic, capable to measure plasma potential, density and their fluctuations, as well as the poloidal magnetic field fluctuations in the core and edge plasmas. The sensitivity of the diagnostic is determined by the level of the output signal related to the instrumental noise. The level of the probing beam current should be as high as possible, especially for measurements at the periphery with low output signal due to low plasma density, and in the core, where the beam is attenuated due to the high plasma density. Optimization experiments have shown the possibility of ion beam forming in the current range from 40 to 800 µA.

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.).

The results are presented from measurements of the power absorbed in plasma of the L-2M stellarator in experiments on the electron cyclotron resonance (ECR) plasma heating at the second harmonic of the gyrofrequency. Hydrogen plasma was created and heated in the stellarator vacuum chamber as a result of the resonance absorption of microwave power supplied by the gyrotrons in the pulse-periodic operation regime. The total energy of the toroidal plasma column and the absorbed power were measured using the diamagnetic diagnostics. The shielding effect of the metal vacuum chamber on the diamagnetic signal measurements was taken into account. It was ascertained that, during the axial ECR heating, up to 90% of the inputted gyrotron power is absorbed in the plasma that is consistent with the theoretical estimates.

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.

Advanced heavy ion beam probe (HIBP) operates on the T-10 tokamak with 20–130 μ A T l + beam accelerated up to 330 keV. The HIBP has a unique capability to measure the mean value of the core plasma potential, and the oscillations in potential φ , density n e and poloidal magnetic field simultaneously in 5 spatially separated sample volumes for OH and ECRH plasmas with n ¯ e = ( 0.3 − 5 ) × 1 0 19 m − 3 , 100 I p l 330 kA . Time evolution of local plasma parameters and/or radial profiles can be measured in a single shot. The profile in the range 0.25 ρ 1 is available shot by shot for B 0 2.2 T . The paper describes main elements of hardware: injector, beamlines, control systems, analyzer, power supplies, and software for HIBP. Physical examples show that HIBP can measure the cross-phase of density oscillations, the poloidal phase velocity of turbulence rotation, the poloidal electric field and the radial turbulent particle flux. Spectral analysis allows us to distinguish various types of turbulence, such as broadband (

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.

Local fluctuations of electrostatic potential, poloidal electric field, magnetic potential and electron density are simultaneously measured in the T-10 tokamak by a heavy ion beam probe (HIBP) having a five-slit energy analyser, which allows an estimate of the turbulent particle flux and $\boldsymbol {E}\times \boldsymbol {B}$ rotation velocity in the off-minor-axis gradient zone of the toroidal plasma column. The high spatial and temporal resolution of the modern multichannel HIBP makes it an effective tool to study plasma oscillations. Motivated by previous work that has documented time-resolved interactions between measured plasma parameters using correlation analysis (coherence of $E_{\textrm {pol}}$ and density $n_e$ , and cross-phase), a new result from bicorrelation analysis (bicoherence of magnetic potential $A_\zeta$ and density $n_e$ , and biphase) is reported for documenting the evidence of wave–wave coupling and energy transfer associated with the interaction between geodesic acoustic modes (GAM) and broadband, quasi-coherent modes.

2D plasma potential ϕ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of the TJ-II stellarator with the heavy ion beam probe for the whole radial range and wide area of the poloidal angle, and supported by Langmuir probe data at the edge. The whole operation domain for the on-axis ECRH was explored ( n ˉ e = 0.45–0.8 ×1019 m−3, P EC = 220–470 kW), in addition, NBI plasmas with n ˉ e = 0.9–1.3 × 1019 m−3 and P NBI = 510 kW were studied. In ECRH plasmas the density ramp-up is accompanied by the evolution of the potential from the bell-like to the Mexican hat profile, while the density profiles were flat or slightly hollow. The potential has the positive peak at the centre, and LFS-HFS (low field—high field sides) and up-down symmetry. Equipotential lines are consistent with vacuum magnetic flux surfaces. In the high-density NBI scenario, the ϕ profile was fully negative with a minimum up to −300 V at the centre, while at low-density ECRH plasma, ϕ has a maximum up to +0.9 kV at the centre. Fluctuations of potential and density are stronger in low-density scenarios and not poloidally symmetric. At the mid-radius (area of the maximum density), root mean square (RMS) of fluctuations were up to ϕ ∼ 15 V at LFS vs ∼20 V at HFS; RMS n e ∼ 2% at LFS vs ∼3% at HFS. In the NBI plasmas with the density rise, the asymmetry decreases and finally vanishing at n ˉ e = 1.2 × 1019 m−3. 2D distribution of the NBI-induced Alfvén eigenmodes (AEs) shows asymmetric ballooning structure: contrary to broadband turbulence, AE-associated potential perturbation dominates in the LFS with a factor up to 1.7 respect to the HFS. The electrostatic mode, excited in ECRH plasmas by suprathermal electrons also shows asymmetric structures: density perturbation dominates in the top-bottom direction compared to LFS-HFS direction.

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.

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.

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.

We study Alfven eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from fAE ∼ 30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one.

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.

A dusty plasma formed in chain exothermal reactions initiated by radiation of a high-power gyrotron in mixtures of metal and dielectric powders has been described. An oscillatory character of such chain reactions, as well as the appearance of dust particles at the first (explosive) stage, has been detected. The tracks, velocities, and sizes of dust particles have been measured. It has been revealed that ensembles of dust particles appear in a reactor after switching-off of the gyrotron against the background of development of chemical reactions. The time of existence of these ensembles is three or four orders of magnitude larger than the duration of a microwave radiation pulse. The quasistationary state of the low-temperature plasma with charged macroparticles appears because of both the chemical heating of the mixture in the reactor and thermophoresis. It has been shown that dust particles are necessary as crystallization nuclei for the creation (or deposition) of complex composites of nano- and micromaterials produced in secondary plasma chemical synthesis.

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.

In this paper, we analyze the impact of electron cyclotron resonance heating and electron cyclotron current drive on the Alfvénic instabilities driven by neutral beam injection observed in the TJ-II stellarator. An MHD stability analysis of driven Alfvén eigenmodes compatible with the experimental plasma parameters is carried out in order to compare with the data provided by magnetic coils, radiation monitors, and heavy ion beam probes. To this end, the vacuum magnetic configuration modified by the different levels of plasma current, the thermal plasma parameters and the fast ion pressure profiles generated by the co-injected neutral beam, are entered in the FAR3d gyro-fluid code in order to follow the linear evolution of the destabilized plasma equilibrium. Linear growth rates and radial location of the dominant predicted modes coincident in frequency with the observed fluctuations are presented. Despite the uncertainties related to the estimation of the rotational transform profile, the code predictions agree within reasonable accuracy with the experimental results.

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.

2D poloidal contour plots of plasma potential, plasma density, and their fluctuations have been measured in low density plasmas sustained by Electron Cyclotron Resonance Heating using a heavy ion beam probe (HIBP) system in the TJ-II stellarator. A HIBP has been used in the new energy scanning mode to obtain the measurements for a 2D poloidal cross section of the stellarator. The 2D map for the absolute plasma potential shows a local maximum in the plasma core as expected in low density plasma scenarios. Fluctuations in the HIBP secondary ion current, as a proxy of plasma density fluctuations, appear both in positive and negative density gradient regions, with a normalized level of density fluctuations higher in the negative density gradient region. The TJ-II innovative experimental setup developed using a dual HIBP diagnostic paves the way for model validation on core plasma potential asymmetries and particle transport and fluctuations under positive and negative density gradient scenarios.

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.

Геодезические акустические моды (ГАМ) рассматриваются в качестве механизма самостабилизации турбулентности. На токамаке Т-10 ГАМ на электростатическом потенциале и флуктуации плотности одновременно исследовались с помощью зондирования пучком тяжёлых ионов (ЗПТИ) и корреляционной рефлектометрии (КР). Изучались режимы с омическим и электронноциклотронным (ЭЦ) нагревом. ГАМ более выражены во время ЭЦ-нагрева, при этом их типичные частоты лежат в узкой полосе 22—27 кГц для основного пика и 25—30 кГц для более высокочастотного сателлита. Локальные значения электрического потенциала и флуктуаций демонстрируют заметную когерентность и постоянный фазовый сдвиг в диапазоне частот ГАМ. Существование дальних пространственных (1/4 тора) корреляций потенциала и плотности для ГАМ означает, что ГАМ является глобальной модой, что впервые показано на токамаке.

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 conceptual design of the heavy ion beam probe (HIBP) for T-15MD tokamak (R = 1.5 m, a = 0.67 m, Bt = 2 T, Ipl = 2 MA) is presented. The location of the HIBP injection and detection points is chosen based on the probing beam trajectory calculations. Observation area covers the whole radial interval 0 < r < a for Bt = 1 T, Ipl = 1 MA with the beam energy Eb

The paper presents the recent results from the quasi-coherent (QC) mode studies performed in the ohmic plasma of the T-10 tokamak (R = 1.5 m. a = 0.3 m, B 0 = 2.2 T, I pl = 230 kA, and n e ≈ 1⋅1019 m−3) using Heavy Ion Beam Probe diagnostics (HIBP). The radial distribution of the amplitude of the density perturbations caused by the QC-mode has two pronounced peaks (approximately 5 and 1.5 % at radii of 25–30 and 8–14 cm, respectively) with an intermediate zone of lower amplitude in between them (

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.