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The kinetic effects of thermal particles and fast ions on internal kink (IK) mode are numerically investigated by the MHD-kinetic hybrid code MARS-K. It is shown that either thermal particles or fast ions have stabilizing influence on IK. However, the former can not fully stabilize IK, and the later can suppress the IK. In addition, the synergistic effect from thermal particles and fast ions induces more stronger damping on IK. The kinetic effects from particles significantly raise the critical value of poloidal beta () for driving IK in the toroidal plasma. This implies a method of controlling IK or sawtooth in the high-βp discharge scenario of tokamak. It is noted that, at the q = 1 rational surface, mode structure becomes more sharp due to the self-consistent modification by particles' kinetic effect. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WEMM) has increasingly come to be recognized as a flexible and effective method for producing planar contour microfeatures. The machining performance of WEMM is significantly influenced by the mass transport rate in the machining gap. Recently, it has been found that the use of a wire electrode with surface microstructures further increases the mass transport rate. Nevertheless, the mechanism through which the microstructures on the wire surface affect the flow field in the machining gap has been poorly understood. In this paper, a simplified mathematical model taking account of the velocity slippage caused by hydrogen bubbles attached to the axially traveling wire surface is first established. The effects on the flow field distribution in the machining gap of surface hydrophilicity and microstructures on the wire surface are theoretically analyzed. The results show that the microstructures facilitate rapid detachment of hydrogen bubbles from the wire surface, resulting in a reduction in velocity slippage and increasing the mass transport rate. A series of comparative experiments on WEMM using both smooth wires and microstructured wires prepared by laser direct scanning machining are conducted. The results are in accordance with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Kinetic effects of both trapped thermal and energetic particles on the resistive wall mode (RWM) and on the fishbone-like mode (FLM) are investigated in theory. Here, the trapped thermal particles include both ions and electrons. The FLM is driven by trapped energetic particles. The results demonstrate that thermal particle collisions can either stabilize or destabilize the RWM, depending on the energetic particle pressure βh. Furthermore, the critical value of βh for triggering the FLM is increased when the thermal particle contribution is taken into account. The critical value sensitively depends on the plasma collision frequency. In addition, the plasma inertia is found to have a negligible influence on the FLM. [ABSTRACT FROM AUTHOR]

The neoclassical toroidal plasma viscosity torque and electromagnetic torque, generated by tearing mode (TM) in a toroidal plasma, are numerically investigated using the MARS-Q code [Liu et al., Phys. Plasmas 20, 042503 (2013)]. It is found that an initially unstable tearing mode can intrinsically drive a toroidal plasma flow resulting in a steady state solution, in the absence of the external momentum input and external magnetic field perturbation. The saturated flow is in the order of 0.5% ωA at the q=2 rational surface in the considered case, with q and ωA being the safety factor and the Alfven frequency at the magnetic axis, respectively. The generation of the toroidal flow is robust, being insensitive to the given amplitude of the perturbation at initial state. On the other hand, the flow amplitude increases with increasing the plasma resistivity. Furthermore, the initially unstable tearing mode is fully stabilized by non-linear interaction with the self-generated toroidal flow. [ABSTRACT FROM AUTHOR]

Electromagnetic effects of the kinetic geodesic acoustic modes (KGAMs) are numerically studied in low β(= plasma pressure/magnetic pressure) tokamak plasmas. The parallel component of the perturbed vector potential is considered along with the electrostatic potential perturbation. The finite Larmor radius and finite orbit width of the ions as well as electron parallel dynamics are all taken into account. Systematic harmonic and ordering analysis is performed for collisionless damping of the KGAMs, assuming β~(κρi)2, where κand ρiare the radial component of the KGAM wave vector and the Larmor radius of the ions, respectively. It is found that the electron parallel dynamics enhances the damping of the electrostatic KGAM modes when the safety factor q is high. In addition, the electromagnetic (finite β effect is revealed to enhance and weaken the damping of the modes in plasmas of low and high safety factor q~2.0 and 5.5, respectively. The harmonic features of the KGAMs are discussed as well. [ABSTRACT FROM AUTHOR]

A theoretical model for investigating the effect of the trapped energetic particles (EPs) on the resistive wall mode (RWM) instability is proposed. The results demonstrate that the trapped EPs have a dramatic stabilizing effect on the RWM because of resonant interaction between the mode and the magnetic precession drift motion of the trapped EPs. The results also show that the effect of the trapped EPs depends on the wall position. In addition, the stabilizing effect becomes stronger when the plasma rotation is taken into account. For sufficiently fast plasma rotation, the trapped EPs can lead to the complete stabilization of the RWM. Furthermore, the trapped EPs can induce a finite real frequency of the RWM in the absence of plasma rotation. [ABSTRACT FROM AUTHOR]

The linear behaviors of the double tearing mode (DTM) mediated by parallel electron viscosity in cylindrical plasmas with reversed magnetic shear and thus two resonant rational flux surfaces is numerically investigated. The distance between the two surfaces is found to play an important role for modes with poloidal mode number m>1. Two modes, one of which is centered at the inner rational surface and the other is located between the two surfaces, are simultaneously unstable and the growth rates show the standard single tearing mode (STM) scaling as γ∝R-1/3 when the distance is large (here, the Reynolds number R≡τυ/τh, τυ, and τh are, respectively, the viscosity penetration time of the magnetic field and the Alfvén time for a plasma sheet of width a). The latter is unstable only and the growth rate transits to the standard DTM scaling as γ∝R-1/5 for low-m (e.g., m<4) modes and keeps the STM scaling γ∝R-1/3 for high-m (e.g., m∼10) modes, which are found dominant, when the distance is decreased. In contrast, two unstable modes extending from plasma center to the two rational surfaces, respectively, coexist and the growth rates always show the scaling of γ∝R-1/5, independent of the distance, when the poloidal mode number m=1. The DTMs mediated by electron viscosity are enhanced by plasma resistivity of the range where the growth rate of the mode induced by the latter alone is comparable with that mediated by the former alone and vice versa. Otherwise, the growth rate of the mode is equal to the higher of the modes mediated by resistivity or electron viscosity alone when both of them are taken into account. [ABSTRACT FROM AUTHOR]

The internal kink (fishbone) modes, driven by barely passing energetic ions (EIs), are numerically studied with the spatial distribution of the EIs taking into account. It is found that the modes with frequencies comparable to the toroidal precession frequencies are excited by resonant interaction with the EIs. Positive and negative density gradient dominating cases, corresponding to off- and near-axis depositions of neutral beam injection (NBI), respectively, are analyzed in detail. The most interesting and important feature of the modes is that there exists a second stable regime in higher βh (=pressure of EIs/toroidal magnetic pressure) range, and the modes may only be excited by the barely passing EIs in a region of βth1<βh<βth2 (βth is threshold or critical beta of EIs). Besides, the unstable modes require minimum density gradients and minimum radial positions of NBI deposition. The physics mechanism for the existence of the second stable regime is discussed. The results may provide a means of reducing or even preventing the loss of NBI energetic ions and increasing the heating efficiency by adjusting the pitch angle and driving the system into the second stable regime fast enough. [ABSTRACT FROM AUTHOR]

An efficient approach for calculating the far field pattern of conformal phased array antennas mounted on cylindrical-shaped platforms is proposed. The array structure is taken into account by using an active element pattern technique, and the array is analyzed by using an element-by-element approach. The effects of all mutual couplings in the array environments are considered rigorously, and the efficiency of the proposed method is validated by using the commercial full-wave simulation software HFSS. Finally, a low side-lobe cylindrical phased array is designed for engineering by optimizing phases and amplitudes of port excitations. [ABSTRACT FROM AUTHOR]

The three-dimensional characteristics of the geodesic acoustic mode zonal flows (GAMZFs) and the ambient turbulence (AT) at the edge of the HuanLiuqi-2A tokamak [Y. Liu et al., Nucl. Fusion 45, S203 (2005)] are investigated with Langmuir probe arrays and the results are presented in detail. The toroidal and poloidal symmetries, and the radial scale of the GAMZFs are simultaneously identified. The envelopes of the high frequency components of the AT in the presence of the GAMZFs are analyzed. The GAM frequency components (GAMFCs) of the coherent envelopes are also shown to have poloidal and toroidal symmetries, and similar radial scales as the GAMZF does. The correlation between the GAMFCs of the envelopes and the GAMs is high, with phase shifts between π/2 to π, indicating that the GAMZFs may regulate the AT and the regulation is embodied in the envelopes. Three-wave coupling between GAM and AT is found to be a plausible formation mechanism for the former, which acts on the whole spectra of the latter within its scale length. The temporal evolutions of the total fluctuation power, the GAM and the AT powers show that the AT power decreases when GAM power increases and vice versa, indicating possible regulating effects of the latter on the former. [ABSTRACT FROM AUTHOR]

The resistive wall mode (RWM) instability is numerically investigated for a toroidal resistive plasma, with results compared to those of an analytic cylindrical model. The full toroidal code MARS-F [Liu et al., Phys. Plasmas 7, 3681 (2000)] is applied for a computational study. The results indicate that there are two branches of unstable RWMs, when the toroidal favorable average curvature effect (the GGJ effect) is taken into account in the resistive layer. In addition, the GGJ physics not only directly affects the mode growth rate, but also indirectly modifies the mode stability by changing the continuum damping through modifying the mode frequency in the plasma frame. Furthermore, the plasma resistivity can either stabilize or destabilize the RWM, depending on the regime of key plasma parameters (e.g., the plasma rotation). Similarly, the plasma rotation can stabilize or destabilize the RWM, depending on the plasma resistivity. These numerical results from MARS-F are qualitatively confirmed by an analytic theory model which includes the GGJ effect. [ABSTRACT FROM AUTHOR]

This article presents laser interference lithography, a preferred method to achieve periodic structures in a large area with fast speed and low cost. Simulations and experiments for two-beam interference lithography with single exposure and double exposure were expressed. In the experiments, patterns on photoresist were transferred to a silicon substrate by wet etching. The experimental results were consistent with the simulative results. The one-dimensional nanogrooves were obtained by single exposure, and different widths of nanogrooves during the same period were fabricated on silicon substrates by varying exposure time. In addition, two-dimensional grid patterns were obtained by double exposure. With the increasing of exposure time, the grid pattern changed from a nanoholes array to a nanodots array. The results showed that laser interference lithography is an efficient method to fabricate nanostructures with various geometrical parameters by controlling exposure time, which has a promising application in the study of nanotextured surface properties, such as wetting, adhesion and friction. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the imaging performance characteristics of four multidetector-row helical computed tomography (CT) and assess improvement in volume coverage speed over that with single multidetector-row helical CT., Materials and Methods: The section-sensitivity profile and image noise of a four multidetector-row scanner were measured with phantom scans and compared with predictions from theoretic models. Nominal section thickness ranged from 1.25 to 10.00 mm, beam collimation from 1.25 to 5.00 mm, and table speed from 3.75 to 30.00 mm per rotation. Image artifacts with four and single multidetector-row helical CT were compared in both a phantom study and a subjective rating analysis of clinical images., Results: Compared with single multidetector-row helical CT, the volume coverage speed of four multidetector-row helical CT (range, 3.75-30.00 mm per rotation) is at least twice as fast as that with single multidetector-row helical CT (1.0-10.0 mm per rotation) with fully comparable image quality or, in many cases, three times as fast with diagnostically comparable image quality., Conclusion: Compared with single multidetector-row helical CT, four multidetector-row helical CT provides a two- to threefold improvement in volume coverage speed with comparable diagnostic image quality.

Progress in helical CT acquisition and processing over the last 5 years has lead to new applications and new requirements. Recent progress to meet these requirements is discussed in this article. The potential of future acquisition developments and their potential to further import application are explored.

Platelet aggregation and thromboxane B2 (TXB2) production induced by arachidonic acid (AA) or Adenosine diphosphate (ADP) were studied by turbidimetry and radioimmunoassay in rabbits. 3,4,5-tri-hydroxystibene-3-beta-mono-D-glucoside (PD) 6.7-107.2 mumol/L inhibited platelet aggregation and the production of TXB2 as well. The inhibitions by PD were dose-dependent: 48-90% (AA-induced) and 43-69% (ADP-induced) for platelet aggregation; 50-87% (AA-induced) and 43-68% (ADP-induced) for TXB2. There were positive correlations between the inhibition of platelet aggregation and production of TXB2.