This Letter presents experimental confirmation of the presence of zonal flows in magnetically confined toroidal plasma using an advanced diagnostic system -dual heavy ion beam probes. The simultaneous observation of an electric field at two distant toroidal locations ( 1:5 m apart) in the high temperature ( 1 keV) plasma provides a fluctuation spectrum of electric field (or flow), a spatiotemporal structure of the zonal flows (characteristic radial length of 1:5 cm and lifetime of 1:5 ms), their long-range correlation with toroidal symmetry n 0 , and the difference in the zonal flow amplitude with and without a transport barrier. These constitute essential elements of turbulence-zonal flow systems, and illustrate one of the fundamental processes of structure formation in nature. Zonal flows-azimuthally symmetric bandlike shear flows-are ubiquitous phenomena in the Universe [1][2][3]; examples include Jovian belts and zones, the terrestrial atmospheric jet stream, the super-rotation of the Venusian atmosphere, and the rotation profile of the solar tachocline. Zonal flows have been expected to be present in magnetically confined toroidal plasmas [4] since the characteristics of drift wave turbulence in the plasmas are analogous to Rossby wave turbulence to cause the phenomena in the rotating planets. Recently, their crucial role in determining the turbulent level and resultant transport has been widely recognized, and the identification of the zonal flows becomes an urgent issue in the fusion research to enhance the prospect of plasma burning in the International Thermonuclear Experimental Reactor [5][6][7].In toroidal plasmas, the zonal flows emerge in electric field fluctuation symmetric m n 0 on magnetic flux surface with finite radial wave numbers (see for review, e.g., [8,9]). Two major branches of zonal flows are expected in magnetic confined toroidal plasmas, i.e., a residual flow of nearly zero frequency, and an oscillatory flow termed geodesic acoustic modes (GAMs) [10,11]. These zonal flows are driven exclusively by nonlinear interactions (or inverse cascade) through energy transfer from the microscopic drift waves. Inversely, the zonal flows regulate the drift wave turbulence and resultant transports. The time-varying E B shearing of zonal flows, similar to the mean flows [12], has a significant effect on plasma turbulence and transport.Direct nonlinear simulations have, in fact, confirmed the appearance of and generation processes for zonal flows [13][14][15][16][17][18][19][20], and their essential role in turbulence and transport of toroidal plasmas. In experiments, however, only indirect signs have been obtained for zonal flows and their role in confinement. Coherent oscillations presumed to be GAMs were detected in measurements with a heavy ion beam probe (HIBP) [21,22], with traditional probes [23,24], and with beam emission spectroscopy using a modified time-delayed-estimation analysis technique [25]. Bicoherence analysis showed an increase in nonlinear interaction between zonal flows and turbule...

A novel method to obtain the full neoclassical transport matrix for general toroidal plasmas by using the solution of the linearized drift kinetic equation with the pitch-angle-scattering collision operator is shown. In this method, the neoclassical coefficients for both poloidal and toroidal viscosities in toroidal helical systems can be obtained, and the neoclassical transport coefficients for the radial particle and heat fluxes and the bootstrap current with the nondiagonal coupling between unlike-species particles are derived from combining the viscosity-flow relations, the friction-flow relations, and the parallel momentum balance equations. Since the collisional momentum conservation is properly retained, the well-known intrinsic ambipolar condition of the neoclassical particle fluxes in symmetric systems is recovered. Thus, these resultant neoclassical diffusion and viscosity coefficients are applicable to evaluating accurately how the neoclassical transport in quasi-symmetric toroidal systems deviates from that in exactly symmetric systems.

We have investigated the influence of symmetry properties of toroidal magnetic configurations on the mechanisms used for determining the radial electric field such as the momentum balance and the ambipolar particle transport. Both neoclassical and anomalous transport of particles, heat and momentum in axisymmetric and nonaxisymmetric toroidal systems are taken into account. Generally, in nonaxisymmetric systems, the radial electric field is determined by the neoclassical ambipolarity condition. For axisymmetric systems with up-down symmetry and quasisymmetric systems with stellarator symmetry, it is shown using a novel parity transformation that the particle fluxes are automatically ambipolar up to O(δ 2 ) and the determination of the radial electric field E s requires solving the O(δ 3 ) momentum balance equations, where δ denotes the ratio of the thermal gyroradius to the characteristic equilibrium scale length. In axisymmetric systems with large E × B flows on the order of the ion thermal velocity v T i , the radial fluxes of particles, heat and toroidal momentum are dependent on E s and its radial derivative while the time evolution of the E s profile is governed by the O(δ 2 ) toroidal momentum balance equation. In nonaxisymmetric systems, E × B flows of O(v T i ) are not generally allowed even in the presence of quasisymmetry because the nonzero radial current is produced by the large flow term in the equilibrium force balance for which the Boozer and Hamada coordinates cannot be constructed.

SynopsisHot ductility in steels was studied. Special emphases were placed on the effects of thermal history, strain rate and fracture mode in order to clarify the sensitivity of surface cracking during both continuous casting operation and direct hot rolling.There exist three temperature regions where typical embrittlement is noticed, i.e., Tm.'1200°C (I), 1200 N 900°C (II), and 900' 600°C (III). The cause of the embrittlement in the region I is the existence of residual liquid film along the dendritic interfaces. The ductility is found to be independent of the strain rate. In the region II, the precipitation of finely distributed oxy-sulfides at the austenite grain boundary weakens the boundary strength, and thus overaging treatments such as slow cooling, holding for certain time, or slow rate of straining result in good ductility. On the other hand, the embrittlement in the III region is manifested by the slower strain rate of test. Controlling factors of this embrittlement are precipitation of oxides, sulfides and nitrides, precipitation of proeutectoid ferrite film along austenite grain boundary as well as grain boundary sliding. Detailed mechanism is discussed. I. IntroductionIncreasing importance is being attached to the study of cracking in continuously cast slabs and of their hot workability during hot rolling, in order to increase the continuous casting ratio and accomplish hot direct rolling as means for reducing the consumption of energy and the number of processes involved in the manufacture of steel products. Laboratory approaches to the cracking in continuously cast slabs are represented by analysis of deformation characteristics by hot-stage tensile tests and theoretical analysis of thermal stresses. However, complete solutions to the cracks encountered in actual operations have not been obtained. Two of the reasons are that experiments which simulate the thermal history to which continuously cast slabs are subjected are difficult to perform and that the deformation mechanism and embrittlement factors of steels in a high-temperature region are not fully understood. In a metallurgical view of the continuous casting process, the process starts with the solidification of liquid steel. As soon as the solidified shell is formed, the segregation and precipitation of solute atoms proceed. Thermal stresses set up during the intervening time combine with mechanical stresses as from ferrostatic pressure of liquid steel and misalignment of guide rolls, causing surface and internal cracks in the slab being cast. A better clarification of these problems calls for study on basic matters, such as the temperature region where embrittlement occurs, the factors that govern embrittlement and the strain rate dependence of embrittlement.The works which have investigated the deformation behavior of steel in the high-temperature region

One of the major advantages of polymeric materials over inorganic ones such as metals or ceramics is their lower specific gravity. Substitution of the latter by the former is promoted not only by economic reasons but also from an environmental point of view. To improve the inferior mechanical and thermal properties of the polymeric materials, compounding with inorganic fillers and fibers has been carried out. 1 However, when the inorganic additives were increased, the specific gravity also increased while better performance could be achieved. Compounding on the order of nanometers, socalled nanocomposites, is expected to avoid such a conflict. Many studies on polymer-clay nanocomposites have demonstrated that the low inorganic content of a few weight percent can result in significant improvements in stiffness, strength, thermal stability, and gas barrier properties and fire retardance. [2][3][4][5][6] Poly(ethylene terephthalate) (PET) has found a variety of applications such as fibers, bottles, films, and engineering plastics for automobiles and electronics because of its low cost and high performance. 7 The primary objective of the development of PET-clay nanocomposites was to improve the gas barrier property that is required for beverage and food packagings. 8 Another expectation for PET-clay nanocomposites is to be an alternative to the glass-fiber reinforced PET. Recently, several researchers reported PET-clay nanocomposites. Ke et al. dispersed organically modified * To whom correspondence should be addressed.

The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System ͑CHS͒ ͓K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 ͑International Atomic Energy Agency, Vienna, 1989͒, Vol. 2, p. 411͔. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied.

A low-aspect-ratio quasi-axisymmetric stellarator CHS-qa was designed. An optimization code was used to design a magnetic field configuration with evaluations of physical quantities of quasi-axisymmetry, rotational transform, MHD stability and alpha particle collisionless confinement. It is shown that the electron neoclassical diffusion coefficient is similar to tokamaks for the low collisional regime. A self-consistent equilibrium with bootstrap current confirms the global mode stability up to 130 kA for R = 1.5 m and Bt = 1.5 T device. The evaluation of plasma rotation viscosity is greatly suppressed compared with conventional stellarators. Engineering design was completed with 20 main modular coils and auxiliary coils which provide flexibility of configuration study for confinement improvement and MHD stability.

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