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At present, the method of current drive by means of lower hybrid waves is not applied to low-aspect-ratio tokamaks, because, in the traditional approach, it would be necessary to use waves with a very high slowing-down factor. However, studies of new transparency regions for waves in a nonuniform magnetized plasma, performed earlier at the Ioffe Physical Technical Institute, Russian Academy of Sciences, made it possible to develop an approach in which slow waves are excited in the poloidal (rather than toroidal) direction. In this approach, moderately slowed-down waves first propagate in the poloidal direction, but then turn in the toroidalal direction and get into the dense plasma. In this work, this approach is further developed using numerical methods. In particular, the influence of the density profile in the edge plasma on the efficiency of wave excitation for given antenna parameters is studied in detail. [ABSTRACT FROM AUTHOR]

In this paper, we study the convergence of time-dependent Euler-Maxwell equations to incompressible type Euler equations in a torus via the combined quasi-neutral and non-relativistic limit. For well prepared initial data, the local existence of smooth solutions to the limit equations is proved by an iterative scheme. Moreover, the convergences of solutions of the former to the solutions of the latter are justified rigorously by an analysis of asymptotic expansions and the symmetric hyperbolic property of the systems. [ABSTRACT FROM AUTHOR]

The reflection of probe radiation from a smooth inhomogeneity of characteristics of a medium that propagates with a relativistic velocity is analyzed. Equations that describe the propagation of forward and backward waves in an inhomogeneous medium are derived, conditions of occurrence of a Bragg resonance are formulated, and conditions for increasing the coefficient of reflection from the inhomogeneity are discussed. [ABSTRACT FROM AUTHOR]

The impedance of the coupling between the antenna and the plasma of the Globus-M2 tokamak with an increase in the toroidal magnetic field and profiles of HF power absorption by plasma components are calculated. The concept of an antenna for the input of fast magnetosonic waves into plasma is discussed. [ABSTRACT FROM AUTHOR]

It is found experimentally that the spectrum of waves forming a low-pressure RF discharge in a strong magnetic field broadens toward lower frequencies. Such an asymmetric broadening is explained by the scattering of the pump wave by the electron flows escaping from the discharge. A similar effect can take place during the formation of the spectrum of artificial RF radiation in the Earth's ionosphere. [ABSTRACT FROM AUTHOR]

A reflector plasma array antenna is investigated. A plasma array with a controlled pattern is created with the help of a discharge creeping over a dielectric surface. The scattering microwave radiation pattern is calculated for the vertical and horizontal polarizations of the radiation incident on the plasma array. [ABSTRACT FROM AUTHOR]

The influence of toroidal magnetic field on the energy confinement time τ in the ohmic H-mode has been studied in the TUMAN-3M tokamak with low magnetic field. The experiments were performed at a toroidal magnetic field of B = 0.68−1.0 T, which is about twice as large as that (0.25-0.5 T) studied in analogous experiments on the NSTX and MAST spherical tokamaks. The results are indicative of a strong dependence of the energy confinement time on toroidal magnetic field: τ ∝ B. This scaling is much stronger than that projected for the ITER (τ ∝ B), while being somewhat weaker than the scalings observed on the NSTX and MAST devices. The stronger (as compared to the ITER scaling) dependence of τ on B observed in these experiments should be taken into account in designing thermonuclear facilities with small aspect ratios and toroidal magnetic fields-in particular, fusion neutron sources. [ABSTRACT FROM AUTHOR]

The behavior of a geodesic acoustic mode (GAM) in the TUMAN-3M tokamak has been experimentally studied using the heavy-ion beam probing technique. Oscillations of the electric potential under the action of a GAM localized at the plasma periphery have been detected. The GAM was observed in the regime of low confinement (L-mode) with low plasma density (∼0.8 × 10 m) and disappeared upon the transition to a high confinement regime (H-mode). The possible role of GAM as a precursor of the improved confinement (LH-transition) is discussed. [ABSTRACT FROM AUTHOR]

This work is a continuation of our investigation into the properties of an electrical discharge in a condensed medium (water). The current characteristic of the discharge is determined. The initial phase of the discharge is found to consist of two stages. Comparison between the parameters of the discharge plasma in water and gas is made. The cost of HO molecule ionization is estimated. Experimental results are compared with published data. [ABSTRACT FROM AUTHOR]

Some mechanisms for Joule dissipation of electric currents flowing in partially ionized hydrogen plasmas are analyzed in a three-fluid approximation. It is shown that ambipolar diffusion can be responsible for the annihilation of magnetic flux during collisions of ions with neutral atoms. The relative influences of the electron conductivity and the Cowling conductivity on the magnetic-field annihilation rate are examined in the frameworks of the Sweet-Parker reconnection model. The escape of plasma is an efficient mechanism for cooling current sheetswith thicknesses of hundreds of kilometers in the solar chromosphere. The origin of the solar chromospheric jets observed by the Hinode spacecraft is discussed. [ABSTRACT FROM AUTHOR]

Specific features of the linear interaction of ordinary and extraordinary electromagnetic waves in the electron cyclotron frequency range in a nonuniform plasma confined in a toroidal magnetic trap are considered. Reduced wave equations taking into account the curvature of the cut-off surfaces in toroidal geometry are formulated. Using these equations, the distributions of the wave fields in the coupling region are analyzed. A method for calculating quasi-optical beams passed through the region of linear wave interaction is proposed. [ABSTRACT FROM AUTHOR]

The breakdown of water in underwater discharge acoustic source (UDAS) is usually in the mode of electrothermal breakdown. The prominent characteristic of the electrothermal breakdown is the existence of prebreakdown-heating phase. In our experiment, the influences of salt concentration and water temperature on breakdown are tested. Three phenomena are observed: 1) The breakdown time obeys a “double peak” stochastic distribution; 2) the higher salt concentration in water leads to higher probability of nonbreakdown; and 3) the higher temperature of salty water also results in higher probability of nonbreakdown. In this paper, the mechanism of electrothermal breakdown is theoretically analyzed, and two conditions to realize electrothermal breakdown are concluded: 1) enough energy deposited to the gap to ensure “border boiling” and 2) enough remaining voltage on the gap at the moment of “border boiling.” Focused on the water temperature and gap voltage, a semiempirical model for prebreakdown-heating process is proposed. When two heating effects of both ionic current and radiation from the initial arc are taken into account, this semiempirical model provides preliminary explanations to the three phenomena observed in our experiment. Based on this model, a simulation code (CPH ) is developed which can numerically simulate the evolution of the gap voltage in prebreakdown-heating phase. The simulation reproduces the experimental phenomena under the same initial conditions. [ABSTRACT FROM PUBLISHER]

In the experiments carried out on the Globus-M tokamak in regimes with injection of 26-keV neutral beams with a power of 0.75-0.85 MW, two branches of instabilities excited by fast ions were observed in the early stage of a discharge: a low-frequency energetic particle mode (EPM) in the frequency range of 5-30 kHz and a high-frequency mode in the range of 50-200 kHz, identified as a toroidal Alfvén eigenmode (TAE). The TAE developed in the initial phase of the discharge at q(0) > 1 and terminated when sawtooth oscillations were excited at q(0) < 1. The spectrum and spatial localization of the mode agree with predictions of the linear theory. The modes observed in the Globus-M tokamak possess both properties common to other tokamaks and their own specific features. [ABSTRACT FROM AUTHOR]

We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot ( T ≳ 10 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier's classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier's law and anomalous heat conduction. [ABSTRACT FROM AUTHOR]

Experiments with the limiting density of a plasma generated in the Globus-M spherical tokamak operating in the ohmic heating regime show that, when the plasma density reaches a certain value at the center of the plasma filament, snake-type strong magnetohydrodynamic instability exciting the m/n = 1/1 mode arises. A further rise in the density causes an internal disruption of the plasma. Numerical simulation of the instability dynamics is performed, and the results of simulation are compared with experimental and theoretical data. Experimental and theoretical data are in good agreement. It is shown that the instability is associated with an increased amount of impurities in the plasma and that the limit in density is of a 'technological,' rather than of a fundamental, character. With the vacuum chamber cleaned more thoroughly, this limit disappears and the snake instability is not observed. Accordingly, a plasma filament density of 1 × 10 was attained with a Greenwald number as high as 95%. [ABSTRACT FROM AUTHOR]

The paper presents a review of the main results on the heating of plasma ions and behavior of fast ions in experiments on neutral beam injection (NBI) carried out in 2003-2010 on the Globus-M spherical tokamak. It is noticed that, along with significant success achieved in NBI plasma heating, there is experimental evidence indicating significant losses of the power injected into the plasma. Most probably, the power is lost due to so-called first-orbit losses, i.e., losses of fast ions that are produced in plasma after ionization of beam atoms and occur in unconfined trajectories. Until recently, the absence of appropriate diagnostic equipment did not allow one to verify this hypothesis. The use of the ACORD-M charge-exchange analyzer directed tangentially to the plasma column made it possible to measure the spectra of fast ions slowed down in plasma and confirm the assumption on the presence of substantial orbit losses of fast particles (∼25-50% of the beam power). In addition to the review of the experimental results, the paper presents analysis of orbit losses on the basis of 3D simulations of fast-ion trajectories in plasma. The results of experiments on studying the influence of the magnitude of the tokamak magnetic field on the confinement of fast ions are also presented. Along with computer simulations, these experiments made it possible to formulate recommendations on the reduction of orbit losses in the Globus-M tokamak. [ABSTRACT FROM AUTHOR]

We study the plasma conductivity within the framework of the magnetohydrodynamic approximation under conditions typical of the coronas of the Sun and stars of the late spectral classes. The problem of finding the elements of the plasma conductivity tensor is reduced to derivation of approximate formulas and numerical values. It is shown that two regimes of dissipation of the current running across the magnetic field can be realized in the corona, namely, one due to the friction of the ion and neutral plasma components (Cowling conductivity) and the other, due to the friction of two different ion components. The first regime is realized in the larger part of the lower corona, whereas the condition for realization of the second regime, i.e., B/ n < 10 G·cm, where B is the magnetic field and ne is the electron number density, can be satisfied in the base of the solar corona or in coronal streamers. In the second regime, the rate of the transverse-current dissipation increases tenfold compared with the hydrogen plasma. The longitudinal and Hall components of the conductivity tensor differ only slightly from their values for the electron-proton plasma. The paper draws attention to the fact that along with the momentum exchange due to the charge exchange, the momentum exchange due to ionization and recombination during electron collisions plays a significant part in the friction of neutral and ionized hydrogen atoms. [ABSTRACT FROM AUTHOR]

The physical properties of the process of heat transfer from a solar-flare's energy source (a high-temperature reconnecting current layer) to the surrounding plasma of the Sun's atmosphere are investigated. Major attention is given to consideration of the collisional relaxation of the heat flux and to analysis of its related effects. The physical meaning of this phenomenon is that the heat flux responds to a change in the spatial temperature distribution with a delay rather than immediately, as in the simplest approximation described by the classical Fourier's law. It is shown that this mechanism describes the heat transfer in flares better than classical and anomalous heat conduction (see Part 1). [ABSTRACT FROM AUTHOR]

In the context of the problem of energy transport in solar flares, simplified analytical models have been developed that describe plasma heating in the solar atmosphere by heat fluxes from the super-hot ( T ≳ 10 K) reconnecting current layer. It is shown that the applicability conditions of common heat conduction produced by Coulomb collisions of electrons in plasma are not fulfilled in solar flares. The heat flux calculated using the classical Fourier's law proves to be significantly higher than the real energy fluxes known from modern multi-wavelength observations of flares. The so called anomalous flux produced by interaction of free electrons with ion acoustic waves in a plasma is critically analyzed. The question of what the dominant mechanism of heat transfer in solar flares is requires additional consideration [1]. [ABSTRACT FROM AUTHOR]

Plasma can be used to create antennas: its conductivity is given by free electrons resulting from gas ionization. This process is obtained with the application of an intense electromagnetic field to a glass tube filled with a low pressure gas. The pump signal needed for ionization and gas discharge parameters have to be carefully chosen in order to optimize plasma antenna design and realization; in particular discharge working conditions have to be defined to obtain the desired antenna properties in terms of efficiency and effective length. For this purpose a self-consistent numerical model of a surface wave driven plasma column has been developed. This tool helps to understand the physical aspects involved in the problem and allows a parametric investigation to be carried out. [ABSTRACT FROM AUTHOR]

The model of the positive column (PC) of a moderate-pressure (5-30 Torr) glow discharge in a mixture of inert gases and chlorine under currents of up to 50 mA/cm extends the existing models of discharges in electronegative gases. The novelty of the model is the inclusion of radial nonuniformity in the gas temperature and dissociation of chlorine molecules into atoms, as well as allowance for heating of ions by the electric field and step ionization. As a result, the calculated radial profiles of charged particle concentrations are not only in qualitative agreement with earlier-developed theories of electronegative discharges, but also in quantitative agreement with experimental data. It is shown that allowance for dissociation of chlorine molecules and the effect of longitudinal field E on the ion temperatures is essential for this conformity in the model of the PC of a glow discharge in the mixture of inert gases and chlorine. However, radial field E can be disregarded in estimating the ion temperatures. The smallness of the contribution of the ion current to the total current of the discharge, which had earlier only been postulated, is demonstrated. It is shown that diffusion-aided removal is the predominant mechanism of perishing of electrons and positive ions; for this reason, electron-ion recombination (as well as ion-ion recombination in the balance of positive ions) can be disregarded. [ABSTRACT FROM AUTHOR]

The possibilities of two deterministic methods for describing the kinetics of high-energy runaway electrons (REs) are analyzed as alternatives to stochastic methods requiring unrealistically large computing resources in problems of numerical simulation of electric discharges in dense gases involving REs. One of the methods being developed in recent years is based on multigroup equations for the moments of the electron distribution function, while the second method, which is conventionally used to solve problems in gas discharges, is based on the diffusion-drift equation. The modern method of multigroup equations allows one to calculate the RE energy distribution and the spatial RE distribution along the electric force, which are close to these distributions obtained by the Monte Carlo method if the number N of energy groups is chosen properly. The diffusion-drift equation does not give the energy distribution, but its advantage is the possibility of obtaining spatial RE distributions using small computing resources not only along but also perpendicular to the electric force, which are close to those calculated by the Monte Carlo method. To simulate discharges by the method of multigroup equations, it is necessary to know a priori the number N of groups providing good accuracy, the characteristic RE multiplication time t, and the energy runaway threshold ɛ as functions of the electric-field overvoltage. The diffusion-drift equation requires the specification, along with t, of the directed RE velocity and longitudinal and transverse diffusion coefficients calculated by the Monte Carlo method. [ABSTRACT FROM AUTHOR]

The effect of viscosity on the evolution of an axisymmetric plasma column in a longitudinal magnetic field is considered. It is found that, under the action of viscosity, the plasma density profile tends to become Gaussian. [ABSTRACT FROM AUTHOR]

The efficiency of ethanol conversion into molecular hydrogen is studied in equilibrium and nonequilibrium plasmas, as applied to the problem of alternative fuel. It is shown that, under the same initial conditions (discharge current and voltage), glow-discharge plasma is more efficient than arc plasma. [ABSTRACT FROM AUTHOR]

Ion flows (ion drag forces) acting on macroscopic-size particles play a significant role in a plasma containing macroparticles. It is shown that ion drag forces can explain the magnetomechanical effect. The formula is derived for determining the dependence of the moment of the magnetomechanical effect on the type and pressure of the gas, tube radius, current, and magnetic field. This formula is in satisfactory agreement with experimental data for discharges in argon and neon with a relatively low magnetization of electron motion. For a high magnetization, the measured values of the moment of the magnetomechanical effect exceed the calculated values, which can be due to the effect of magnetic field nonuniformity and inhomogeneity of the plasma near the solenoid ends. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of the efficiency of lower hybrid current drive (LHCD) in the FT-2 tokamak. The dependence of the LHCD efficiency on the grill phasing Δφ and RF oscillator power was determined experimentally in a wide range of plasma densities. It is shown that, at high plasma currents (i.e., at sufficiently high electron temperatures), current drive is suppressed when the plasma density reaches its resonance value n for the pumping wave frequency, rather than when parametric decay comes into play (as was observed in regimes with lower plasma currents and, accordingly, lower electron temperatures T). In order to analyze the experimentally observed effect of LHCD and its dependence on the value and sign of the antenna phasing, the spectra of the excited LH waves, P( N), were calculated. Simulations using the FRTC code with allowance for the P( N) spectrum and the measured plasma parameters made it possible to calculate the value and direction of the LH-driven current, which are determined by the spectrum of the excited LH waves. It is shown that the synergetic effect caused by the interaction between different spectral components of the excited RF wave plays a decisive role in the bridging of the gap in the wave spectrum. [ABSTRACT FROM AUTHOR]

Plasma confinement in the vicinity of vacuum magnetic islands near the magnetic axis in the H-1NF heliac [S. M. Hamberger et al., Fusion Technol. 17, 123 (1990)] has been experimentally studied in a low temperature argon plasma. Experimental results indicate that, under favorable conditions, these low order (m=2) islands near the core of the plasma serve as “pockets” of higher electron density. This results in significant profile modifications including enhancement of the core radial electric field to a large positive value, possibly through an electron-root ambipolar condition. The characteristics of islands are found to be dependent on the plasma collisionality and island width. [ABSTRACT FROM AUTHOR]

The dynamics of electron heat transport at improved energy confinement during lower hybrid plasma heating in the FT-2 tokamak was studied experimentally. Evolution of the profiles of the electron temperature and density was thoroughly investigated under conditions of fast variation in the plasma parameters. The energy balance in the electron channel is calculated with the help of the ASTRA code by using the measured plasma parameters. Correlation is revealed between the dynamics of electron heat transport and the behavior of small-scale drift turbulence measured using the enhanced scattering correlation diagnostics. The suppression of heat transfer and turbulence agrees well with the increase in the shear of poloidal plasma rotation calculated from experimental data in the neoclassical approximation. [ABSTRACT FROM AUTHOR]

Results from experimental studies of multipactor discharges on the surfaces of various dielectrics placed in a high-Q cylindrical microwave cavity excited at the TE013 mode in the X-band are presented. The thresholds for the onset and maintenance of a multipactor discharge on quartz, polycrystalline diamond, lithium fluoride, and Teflon surfaces possessing different roughness are determined. It is shown that, in such a resonance system, a steady multipactor discharge can operate without transition into the stage of microwave breakdown of the desorbed gas. It is found that, due to long-term action of the discharge, a thin carbon-containing film is deposited on the dielectric surface, which leads to an increase in the breakdown threshold. [ABSTRACT FROM AUTHOR]

The stationary structure of an axisymmetric high-frequency discharge maintained by a given source in an external dc magnetic field is investigated. The source is assumed to be a current wave that travels over the discharge tube surface in the direction of the external magnetic field. The source current has a single azimuthal component and its frequency belongs to the lower hybrid range. The main emphasis is placed on the special case where the electron heat conduction length across the external magnetic field exceeds considerably the tube radius. The dependences of discharge plasma parameters on the current amplitude and propagation constant along the tube have been found for this case. The results of numerical calculations of the distributions of the field and the power of the Joule loss in a discharge are presented. [ABSTRACT FROM AUTHOR]

Basic experimental results on cyclotron heating of the ion plasma component in the Globus-M spherical tokamak obtained by means of the ACORD-12 charge-exchange ion analyzer are presented. A procedure for determining the maximum energy of fast ions confined in the plasma is described. The procedure was applied to estimate the limiting energy of hydrogen minority ions accelerated during ion cyclotron heating in the Globus-M tokamak. The experimental evaluation of the maximum hydrogen ion energy is confirmed by simulations of ion orbits. Recommendations for optimizing experiments on ion cyclotron heating in the Globus-M tokamak are formulated. [ABSTRACT FROM AUTHOR]

An expression is derived for the electric field strength near a wet hailstone in an approximation quadratic in the oscillation amplitude of a charged liquid layer on its surface. It is found that the electric field strength in a small neighborhood of the capillary wave crests grows with the number of a mode governing the initial deformation of the equilibrium (spherical) shape of the liquid layer. Even if the charge is small (when the Rayleigh parameter of the hailstone equals one-hundredth of the value critical for stability against the self-charge), the electric field near the hailstone is high enough for initiating a corona discharge in its vicinity. [ABSTRACT FROM AUTHOR]

A powerful millimeter-wave phase shifter switched by an electron beam is studied. The operation of the device is based on the phase change in a wave reflected from a microwave resonator, depending on whether this resonator is or is not turned to resonance. Numerical simulation of several designs of the phase shifter is carried out, and the feasibility of its low-power operation is experimentally demonstrated. In the experiments, the typical time of phase change in the electromagnetic wave is 30 ns. It is shown that not only the electron beam, but also the near-electrode plasma, significantly influences the amount and time of phase change in the reflected wave. [ABSTRACT FROM AUTHOR]

A plasma electron source (PES) based on a discharge in crossed E × H fields is developed and tested. The working gas is supplied to a quasi-closed PES discharge chamber, in which the conditions for effective ionization of the working gas in the axial magnetic field are created. The electron flow is formed by a positive-biased auxiliary electrode or the space charge from an ion source. Current-voltage and emission characteristics of the PES are obtained for various combinations of the cathode material (copper, titanium, and graphite) and the working gas (Ar and He). It is found that the discharge in the PES is stable when Cu and Ti are used as cathode materials with a working gas flow rate of 2–20 ml/min for Ar and 6–60 ml/min for He. The electron extraction efficiency for this type of PES attains unity in an Ar flow exceeding 6 ml/min for a Cu cathode insertion and for an Ar flow exceeding 8 ml/min for a Ti cathode insertion. The energy efficiency in a working gas (Ar) flow exceeding 10 ml/min is 4 mA/W for a Ti cathode and 2.56 mA/W for a Cu cathode. The low efficiency of this type of PES with He as the working gas is established. It is found that the appropriate choice of the working gas-cathode material pair ensuring higher values of the sputtering yield makes it possible to increase the PES efficiency. [ABSTRACT FROM AUTHOR]

The glow-to-arc transition of the positive column of a dc discharge in argon in the course of constriction has been investigated on the basis of a self-consistent 1-D axisymmetric fluid model. The model adopts the nonlocal moment method, i.e., the system of balance equations resulting from the moments of the radially dependent Boltzmann equation is solved. The electron transport and rate coefficients are applied in dependence on the mean energy of the electrons, the gas temperature, and the ionization degree. Investigations have been performed for currents from 0.6 to 70 mA and pressures from 100 to 500 torr. The model predictions are compared with experimental and other available modeling results, and they show good agreement with these data in general. The pronounced nonlocal features of the mean electron energy balance are found, and their influence on the constricted argon positive column is analyzed. Different assumptions concerning the electron velocity distribution function have been considered in the present model. In particular, the impact of using a Maxwellian distribution instead of solutions of the steady-state spatially homogeneous electron Boltzmann equation is discussed where the assumption of a Maxwellian distribution for the electrons was found to be inappropriate for describing the constriction effect. [ABSTRACT FROM AUTHOR]

Research on neutral particle diagnostics of thermonuclear plasmas that has been carried out in recent years at the Ioffe Physicotechnical Institute of the Russian Academy of Sciences (St. Petersburg, Russia) is reviewed. Work on the creation and improvement of neutral atom analyzers was done in two directions: for potential applications (in particular, on the International Thermonuclear Experimental Reactor, which is now under construction at Cadarache in France) and for investigation of the ion plasma component in various devices (in particular, in the largest tokamaks, such as JET, TFTR, and JT-60). Neutral atom analyzers are the main tool for studying the behavior of hydrogen ions and isotopes in magnetic confinement systems. They make it possible to determine energy spectra, to perform the isotope analysis of atom fluxes from the plasma, to measure the absolute intensity of the fluxes, and to record how these parameters vary with time. A comparative description of the analyzers developed in recent years at the Ioffe Institute is given. These are ACORD-12/24 analyzers for recording 0.2–100-keV hydrogen and deuterium atoms with a tunable range of simultaneously measured energies, CNPA compact analyzers for a fixed energy gain in the ranges 80–1000 eV and 0.8–100 keV, an ISEP analyzer for simultaneously recording the atoms of all the three hydrogen isotopes (H, D, and T) in the energy range 5–700 keV, and GEMMA analyzers for recording atom fluxes of hydrogen and helium isotopes in the range 0.1–4 MeV. The scintillating detectors of the ISEP and GEMMA analyzers have a lowered sensitivity to neutrons and thus can operate without additional shielding in neutron fields of up to 109 n/(cm2 s). These two types of analyzers, intended to operate under deuterium-tritium plasma conditions, are prototypes of atom analyzers created at the Ioffe Institute for use in the International Thermonuclear Experimental Reactor. With these analyzers, a number of new results have been obtained in recent years in various devices. Some results are presented from investigation of ions in the Globus-M spherical tokamak, the W7-AS stellarator, and the JET tokamak by means of the analyzers developed at the Ioffe Institute. Challenges and opportunities for applying these diagnostics in the International Thermonuclear Experimental Reactor project are discussed. [ABSTRACT FROM AUTHOR]

A power-series method for solving the kinetic equation is proposed. A simple procedure for deriving equations for arbitrary moments of the distribution function is described. An analysis of wave propagation in a stationary uniform hot magnetoactive plasma shows that allowance for tensors of ranks up to n and omission of higher rank tensors in the equations of tensor magnetohydrodynamics corresponds to taking into account waves at cyclotron harmonics with numbers up to n inclusive and ignoring higher harmonics. Thus, from the standpoint of accuracy and complexity of plasma description, tensor magnetohydrodynamics occupies an intermediate position between the kinetic approach and the conventional magnetohydrodynamics with a scalar pressure. [ABSTRACT FROM AUTHOR]

A converter of focused optical radiation into electric current is considered on the basis of the photovoltaic effect in plasmas. The converter model is based on analysis of asymmetric spatial distributions of charge particle number density and ambipolar potential in the photoplasma produced by external optical radiation focused in a heat pipe filled with a mixture of alkali vapor and a heavy inert gas. Energy balance in the plasma photoelectric converter is analyzed. The conditions in which the external radiation energy is effectively absorbed in the converter are indicated. The plasma parameters for which the energy of absorbed optical radiation is mainly spent on sustaining the ambipolar field in the plasma are determined. It is shown that the plasma photoelectric converter makes it possible to attain a high conversion efficiency for focused solar radiation. [ABSTRACT FROM AUTHOR]

We analyze the properties of the electric-current distribution over the cross sections of fairly dense coronal magnetic flux tubes in which the plasma pressure exceeds the magnetic pressure, so that the equilibrium is maintained by the ambient magnetic field. If the plasma is fully ionized, the distributions of the longitudinal and azimuthal currents over the cross section of the loop have the same spatial scale as the pressure distribution. However, even a small number of neutral atoms in the corona (with a mass fraction of the order of 10−5, taking into account the partial ionization of helium) substantially modifies the current distribution over the tube cross section: in this case, a considerable fraction of the full current flowing along the tube is concentrated in a thin region near the axis with a radius of the order of (10−2–10−3) r0 (where r0 is the characteristic scale of the plasma-pressure distribution over the tube), thus forming a sort of a jet current. This comes about because the pattern of the conductivity anisotropy is substantially modified in the presence of ion-atom collisions in the magnetoactive plasma of the tube, and the Cowling conductivity dominates over the Hall and Pedersen conductivities. The high current density near the axis of the tube can ensure heating of the plasma to coronal temperatures via Joule dissipation. [ABSTRACT FROM AUTHOR]

The oblique wave propagation in helicon-sustained plasma accounting for the effect of the radial electron density gradient is investigated. It is shown that the conditions for the conversion of electrostatic and electromagnetic modes may change drastically in strongly nonuniform helicon plasma due to modification of the wave dispersion branches. Furthermore, the densities at which mode conversion occurs can be considerably lower if the density gradient is steep enough. This result contrasts with the common mode conversion theory neglecting density gradient effects and predicting mode conversion in the central plasma region at very high electron densities. [ABSTRACT FROM AUTHOR]

The stimulated scattering of a whistler wave beam forming an extended discharge channel in a magnetic mirror trap is discovered and investigated experimentally. It is shown that the beam is scattered by relaxaction oscillations of the lattice of plasma inhomogeneities excited by the beam field. The spectrum of the pump field in the RF discharge plasma is found to broaden considerably and to contain individual modulation peaks corresponding to lattice oscillations. The peaks are observed at working gas pressures at which the electron mean free path is close to the wavelength of the standing wave forming the discharge channel. A physical model describing the phenomena observed is developed. [ABSTRACT FROM AUTHOR]

A 3.7 GHz system, which is meant for LHCD experiments on ADITYA tokamak, is used for producing ECR discharge. The ECR discharge is produced by setting the appropriate resonance magnetic field of 0.13 T, with hydrogen at a fill pressure of about 5x10-5 Torr. The RF power, up to 10 kW (of which !~50% is reflected back), with a typical pulse length of 50 ms, is injected into the vacuum chamber of the ADITYA tokamak by a LHCD grill antenna and is used for plasma formation. The average coupled RF power density (the RF power/a typical volume of the plasma) is estimated to be ~5 kW/m3. When the ECR appears inside the tokamak chamber for the given pumping frequency (f = 3:7 GHz) a plasma with a density (ne) ~ 4x1016 m-3 and electron temperature ~8 eV is produced. The density and temperature during the RF pulse are measured by sets of Langmuir probes, located toroidally, on either side of the antenna. Hα signals are also monitored to detect ionization. An estimate of density and temperature based on simple theoretical calculation agrees well with our experimental measurements. The plasma produced by the above mechanism is further used to characterize the ECR-assisted low voltage Ohmic start-up discharges. During this part of the experiments, Ohmic plasma is formed using capacitor banks. The plasma loop voltage is gradually decreased, till the discharge ceases to form. The same is repeated in the presence of ECR-formed plasma (RF pre-ionization), formed 10 ms prior to the loop voltage. We have observed that (with LHCD-induced) ECR-assisted Ohmic start-up discharges is reliably and repeatedly obtained with reduced loop voltage requirement and breakdown time decreases substantially. The current ramp-up rates also decrease with reduced loop voltage operation. These studies established that ECR plasma formed with LHCD system exhibits similar characteristics as reported earlier by dedicated ECR systems. This experiment also addresses the issue of whether ECR plasma formed with grill antenna exhibits similar behavior as that formed by single waveguide ECR antenna. Our experimental observations suggest that the characteristics of (LHCD system-induced) ECR-assisted Ohmic start-up discharges show similar properties, reported earlier with normal ECR-assisted Ohmic start-up discharges and hence LHCD system may be used as ECR system at reduced toroidal magnetic field for other applications like wall conditioning. [ABSTRACT FROM AUTHOR]

Results from experimental studies on the injection of high-energy neutral hydrogen beams into the plasma of the Globus-M spherical tokamak are reviewed. In the Introduction, the importance of these studies for implementing the controlled fusion research program and constructing the ITER tokamak is proved. Some problems related to the use of neutral beam injection in small and low-aspect-ratio tokamaks is analyzed. Results are presented from numerical simulations of the experiment by using the ASTRA transport code. It is shown that the use of neutral beam injection in the Globus-M tokamak ensures efficient ion heating and increases the plasma stored energy. The greater part of the review is devoted to the survey of experiments on the injection of 22-to 30-keV hydrogen and deuterium beams with a power of 0.4–0.8 MW into the plasma of the Globus-M spherical tokamak in a wide range of plasma currents and densities. The experimental results are analyzed and compared with the results of numerical simulations. The achievement of top plasma parameters is highlighted. [ABSTRACT FROM AUTHOR]

The spatial evolution of a Langmuir wave excited by external sources in a weakly inhomogeneous electron plasma in a longitudinal electrostatic field is considered. It is shown that, in a longitudinal electrostatic field, a Langmuir wave can only be amplified in an inhomogeneous plasma provided that the current of trapped electrons exceeds that of untrapped electrons. In this case, as the wave propagates through the inhomogeneous region where its phase velocity increases, some untrapped electrons become trapped in the wave potential wells. As a result, the current of trapped electrons increases and the wave is amplified. Moreover, in the regions where the bulk electrons are localized, the minima of the wave are amplified to a greater extent than its maxima. [ABSTRACT FROM AUTHOR]

The application of resonant light pressure in the presence of nonuniform bichromatic laser fields for the localization and control of ultracold electron-ion plasma in which the quantum transitions of ions are resonant with respect to the laser radiation is analyzed. It is demonstrated that the so-called rectified radiation forces that selectively act upon plasma ions and give rise to a dissipative optical superlattice (for ultracold plasma) whose period is significantly greater than the radiation wavelength can be used for this purpose. [ABSTRACT FROM AUTHOR]

The formation of dusty plasma structures has been experimentally investigated in a cylindrical dc discharge in axial magnetic fields up to 2500 G. The rotation of the dusty plasma structures about the discharge symmetry axis with a frequency depending on the magnetic field has been observed. When the field increases to 700 G, the displacement of dust particles from the axial region of the discharge to the periphery, along with the continuation of the rotation, has been observed. The kinetic temperatures of the dust particles, the diffusion coefficients, and the effective nonideality parameter have been determined for various magnetic fields. The explanation of the features in the behavior of the dust particles in the discharge in the magnetic field has been proposed on the basis of the analysis of ambipolar diffusion in the magnetized plasma. The maximum magnetic field at which the levitation of the dust particles in the discharge is possible has been estimated. [ABSTRACT FROM AUTHOR]

A simplified model describing the steady state of a helicon discharge in a low-pressure plasma is considered. The electron Langmuir frequency of the plasma produced by the discharge is shown to be much higher than the electron gyrofrequency. It is found that the gas medium is ionized and the electrons are heated primarily by the extraordinary mode. The calculated electron density depends nonmonotonically on the magnetic field, in agreement with the results of numerous experiments. [ABSTRACT FROM AUTHOR]

Results are presented from experimental and theoretical studies of the heating of a hydrogen plasma with a lithium admixture at the fundamental ion-cyclotron frequency of hydrogen in the T-11M tokamak. It is found experimentally that the action of RF radiation on a hydrogen plasma containing a small amount (less than 4%) of lithium increases the duration of the discharge current pulse. The effect of the increase in the discharge current pulse under the action of RF radiation is simulated numerically. [ABSTRACT FROM AUTHOR]

It is shown that the process of magnetic field penetration into the plasma bridge in a plasma opening switch is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the bridge. This transport is due to the field being “frozen in” to the flow of plasma behind the front of a shock wave, which is formed in the plasma accelerated by the magnetic field pressure. [ABSTRACT FROM AUTHOR]