Application of quasi-steady-state plasma streams for simulation of ITER transient heat loads

The paper presents experimental investigation of energy characteristics of the plasma streams generated with quasi—steady—state plasma accelerator QSPA Kh-50 and adjustment of plasma paramenters from the point of view its applicability for simulation of transient plasma heat loads expected for ITER disruptions and type I ELMs. Possibility of generation of high-power magnetized plasma streams with ion impact energy up to 0.6 keV, pulse length 0.25 ms and heat loads varied in wide range from 0.5 to 30 MJ/m² has been demonstrated and some features of plasma interaction with tungsten targets in dependence on plasma heat loads are discussed.     

Radial electric fields and confinement in the TJ-II stellarator

Radial plasma potential profiles have been obtained in the TJ-II by the Heavy Ion Beam Probing (HIBP) diagnostics. Results show that the potential increases up to 1 kV near the magnetic axis in ECRH low-density plasmas. The secondary ion current profiles, which directly reflect the plasma density, are hollow. In low-density ECRH operation, radial electric fields are found to be positive in the plasma core, however, a reduction in these fields is observed with increasing density. Radial plasma potential profiles show evidence of structures in configurations with low-order rational surfaces. In particular, HIBP measurements have permitted characterization of the plasma potential profile during e-ITB formation. Experiments in TJ-II have shown that it is possible to modify the global confinement and edge plasma parameters with limiter biasing, illustrating the direct impact of radial electric fields on confinement properties. Plasma potential measurements by the HIBP diagnostic show a strong impact of heating method (ECRH versus NBI) on radial electric fields.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

Conservative finite-difference scheme for the problem of propagation of a femtosecond pulse in a nonlinear photonic crystal with nonreflecting boundary conditions

Conservative finite-difference schemes are constructed for the problems of self-action of a femtosecond laser pulse and of second-harmonic generation in a one-dimensional nonlinear photonic crystal with nonreflecting boundary conditions. The invariants of the governing equations are found taking into account these conditions. Nonreflecting conditions substantially improve the efficiency of conservative finite-difference schemes used in the modeling of complex nonlinear effects in photonic crystals, which require much smaller steps in space and time than those used in the case of linear propagation. The numerical experiments performed show that the boundary reflects no more than 0.01% of the transmitted energy, which corresponds to the truncation error in the boundary conditions. The amplitude of the reflected pulse is less than that of the pulse transmitted through the boundary by two (and more) orders of magnitude. The simulation is based on the approach proposed by the authors for the given class of problems.     

An all-optical switch based on a one-dimensional layered structure with defocusing nonlinearity

The feasibility of an optical switch of femtosecond range controlled by a femtosecond light pulse acting on a nonlinear one-dimensional photonic crystal (a layered one-dimensional periodic structure) is demonstrated by computer simulation. The crystal comprises linear and weakly defocusing layers. It is shown that switching occurs when the peak intensity of the initial pulse exceeds a certain threshold value due to the dependence of the transmission-reflection bands of the photonic crystal on the nonlinearity of the medium.     

Modeling of supramolecular ordering and physicochemical properties in cyclohexane-ethanol mixtures

The quasichemical model of the nonideal associated solution (QCNAS) was used to analyze the excess thermodynamic functions and permittivity of cyclohexane-ethanol mixtures in the entire range of compositions and in a wide temperature range. A new model of supramolecular organization was substantiated, taking into account chain and cyclic aggregation of alcohol with the formation of chain aggregates of arbitrary size, which describes a set of physicochemical properties of this mixture with complicated behavior of both thermodynamic and dielectric properties. Equilibrium constants and thermodynamic parameters of H bonding having cooperative character and integral and differential characteristics of aggregation and the structural parameters of aggregates were determined. It was established that the role of nonpolar cyclic structures increases as alcohol concentration decreases. The model describes the permittivity of solutions in the entire range of compositions and reproduces a minimum of the dipolar correlation factor in the range of dilute alcohol solutions. The new data obtained on the supramolecular ordering characterized by the long-range molecular correlations due to H bonding are discussed in detail.     

On the nature of phase separation of polymer solutions at high extension rates

Experiments with stretching moderately concentrated polymer solutions have been carried out. Model experiments were carried out for poly(acrylonitrile) solutions in dimethyl siloxane. Just the choice of concentrated solutions allowed for a clear demonstration of a demixing effect with the formation of two separate phases—an oriented polymer fiber and solvent drops sitting on its surface. An original experimental device for following all subsequent stages in the demixing process was built. It combined two light beams, one transverse to the fiber and a second directed along (inside) the fiber, the latter played the role of an optical line. This gives a unique opportunity to observe processes occurring inside a fiber. The process of demixing starts from the volume phase separation across the whole cross section of a fiber at some critical deformation and the propagation of the front of demixing along the fiber. Then a solvent cylindrical skin appears which transforms into a system of separate droplets. New experimental data are discussed based on a comparison of the current different points of view on the phenomenon of deformation‐induced phase separation: thermodynamic shift of the equilibrium phase transition temperature, growth of stress‐induced concentration fluctuations in two‐component fluids, and mechanically pressing a solvent out from a polymer network. The general belief is that a rather specific (so‐called “beads‐on‐a‐string”) structure of a filament is realized in stretching dilute solutions: beads of a polymer solution connected by oriented polymer bridges forming a single object. The situation in stretching moderately concentrated solutions appears quite different: real phase separation was observed. So, the alternative phenomenon to the formation of the “beads‐on‐a‐string” structure has been experimentally proven. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 559–565     

On determination of elastic limits by dissipative heating of materials

This paper considers a method for determining the conventional elastic limit by dissipative heating of materials and the results of experimental investigation of these characteristics during periodic asymmetric loading of steel and alloy.     

Modeling of Supramolecular Structure and Physicochemical Properties of the Propanone–Methanol Mixture

The results on modeling of the supramolecular organization and physicochemical properties of the propanone-methanol mixture are presented. An analysis of the excess thermodynamic functions (Gibbs energy, enthalpy, and entropy) and the permittivity of mixtures have been performed in the whole range of compositions and temperatures. It has been demonstrated that the model of supramolecular structure, taking into account the chain and cyclic association of methanol molecules and complexation of alcohol aggregates with propanone, describes the properties of the mixture. It established that both specific and universal interactions contribute to the positive deviations from the thermodynamic ideal solution behavior. Positive deviation of the dipole correlation factor from unity is due to a predominantly parallel orientation of the dipoles of the molecules in methanol aggregates and their complexes with propanone. The thermodynamic parameters of aggregation and structural parameters of aggregates have been determined. The cooperativity of H bonding was established. Distribution functions of the aggregate, according to size and structure, are presented. The manifestations of the supramolecular ordering on the physicochemical properties of the mixture are discussed.