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Lower hybrid current drive (LHCD) efficiency in H-mode plasmas, which was rarely reported, has been investigated. The experimental CD efficiency in quasi-steady-state H-mode plasmas is as high as ∼1.1 (1019 A/W/m2) with the line-averaged density around 3.1 × 1019 /m3. As the density increases beyond 3.1 × 1019/m3, the CD efficiency decreases slightly with increasing density. A CD efficiency of 0.9 (1019 A/W/m2) is obtained with density up to ∼5.4 × 1019/m3. The experimental results show a higher CD efficiency in H-mode plasmas compared to the L-mode with similar line-averaged plasma density. The main causes for the observed difference between L- and H-modes are identified and discussed. The methods to improve CD efficiency in H-mode are presented, including increasing the electron temperature by electron cyclotron (EC) and ion cyclotron (IC) power, and optimizing the plasma parameters in the edge by changing the magnetic field (Bt) directions. [ABSTRACT FROM AUTHOR]

We describe experimental measurements of energy modulation obtained using the Micro Accelerator Platform (MAP), a slab-symmetric dielectric laser accelerator based on a resonant structure, at the SLAC E-163 beamline. The structure is powered by a Ti:Sapphire laser side-coupled into a vacuum gap, where the MAP's periodicity and dimensions create a synchronous accelerating mode. The accelerating field experienced by the electron beam is greater than that in the incoming laser radiation by an enhancement factor on the order of 3 to 5, due to the resonant buildup of the cavity fields. Results presented here demonstrate acceleration in a resonant dielectric structure for the first time. Measured acceleration gradients are on the order of tens of MeV/m when the structure is illuminated with laser power well below breakdown limits. Careful comparison between simulation and experiment suggests that results depend sensitively on the degree of uniformity achieved in fabrication. Acceleration gradients of up to 1 GeV/m are possible within the breakdown limit of the structure. [ABSTRACT FROM AUTHOR]

Pneumatic-conveyed solid flows are common in many industrial processes. The flow speed may be high and varying. The density of solids may also change with time. The mass flow rate is usually difficult to quantify for such multphase flows. On the other hand, microwave Doppler radar has been used as a device for velocity measurement or motion detection. It would be feasible to use such a device for solid flow measurements. In this paper, the principle of using microwave Doppler radar for such an application is investigated. Experimental results obtained using a microwave Doppler velocimeter for different types of solid flows in a laboratory environment are presented. [ABSTRACT FROM AUTHOR]

Repeatable H-mode plasma in EAST is obtained with a local gas puffing near lower hybrid wave (LHW) antenna. The density modification in front of LHW grill during LHW mainly depends on the competition between ponderomotive force and ionization of neutral gas. Effects of edge localized mode (ELM) on LHW coupling are analyzed. Studies suggest that recycling plays an important role in determining LHW coupling. The burst of ELM enhances the density at the grill mouth, hence improving the coupling in low recycling, whereas such effect could decrease in high recycling. In addition, with anti-clockwise and clockwise toroidal magnetic fields (Bt), coupling experiments at LSN, DN and USN have been performed, indicating that flux induced by Er × Bt could lead to different coupling characteristics at different configurations. [ABSTRACT FROM AUTHOR]

A proof of principle fused-silica grating structure has been designed and fabricated for the purpose of direct laser acceleration of electrons. The optimal structure geometry was determined via 2D-FDTD and 3D-FEFD simulations to maximize the available acceleration gradient. The structure was fabricated with standard nanofabrication techniques, including optical lithography, reactive ion etching, and wafer bonding. Beam tests have been performed with the 60MeV beam at the Next Linear Collider Test Accelerator at SLAC, with successful demonstration of electron transmission through the micron-scale apertures. [ABSTRACT FROM AUTHOR]

Laser-driven acceleration in dielectric structures can provide gradients on the order of GeV/m. The small transverse dimension and tiny feature sizes introduce challenges in design, fabrication, and simulation studies of these structures. In this paper we present the results of beam dynamic simulation and short range longitudinal wakefield simulation of the double grating structure. We show the linear trend of acceleration in a dielectric accelerator design and calculate the maximum achievable gradient equal to 0.47E0 where E0 is maximum electric field of the laser excitation. On the other hand, using wakefield simulations, we show that the loss factor of the structure with 400nm gap size will be 0.12GV/m for a 10fC, 100as electron bunch which is an order of magnitude less than expected gradient near damage threshold of the device. [ABSTRACT FROM AUTHOR]

Two-proton emissions from the excited states of 17,18Ne and 28,29S were investigated by the radioactive beams bombarding on the 197Au target via the Coulomb excitation. The complete-kinematics measurements were actualized by the stacks of silicon-strip detectors and CsI+PIN array detectors. The invariant mass of final systems as well as the relative momentum, opening angle, and relative energy of the two emitted protons were reconstructed under the framework of relativistic kinematics. The mechanisms of two-proton emission were analyzed in a simple schematic model. With the help of Monte-Carlo simulations, the two protons emitted from the 6.15 MeV excited state of 18Ne and the excited states around 10 MeV of 29S, respectively, exhibit prominent features of 2He decay. While for the other states, no obvious diproton emissions were observed. [ABSTRACT FROM AUTHOR]

It has been shown that grating based x-ray phase contrast imaging (GPI) can be performed on x-ray tubes and therefore has a great potential for a wide application in many fields. So far to extract and to separate the phase information from other contributions, a phase-stepping approach is normally adopted. One of the gratings is scanned transversely to the incident beam while acquiring multiple projections of the sample. However, during the grating scanning, the sample is supposed to be static, and the resulting poor time resolution is one of the major drawbacks of this method. It is clear that a method that would extract the phase information without the need of multiple stepping would be a breakthrough enabling fast, highly sensitive (phase-contrast) x-ray imaging. According to the similar physics and mathematics between diffraction enhanced imaging (DEI) and GPI, here we report how the DEI methods can be generalized for GPI and how GPI can use the same acquisition procedure as the conventional absorption CT without grating scanning. [ABSTRACT FROM AUTHOR]

The investigation on the performance of a traveling-wave thermoacoustic refrigerator driven by a self-made linear compressor is presented in this paper. The linear compressor is of moving-coil type, which has a moving coil, a piston with about 100 square centimeters cross section area, and a flexure bearing unit for piston support. The operating frequency can be adjusted to achieve a resonant status in order that the compressor can work with high electroacoustic efficiency. The thermoacoustic refrigerator operates on traveling-wave mode with acoustic power recovery. In the experiments, influence of different working frequencies on electroacoustic efficiency, lowest temperature, cooling power and COP is investigated. So far in the experiment with helium as working fluid, a lowest temperature of -29 °C is obtained, when the mean and oscillating pressures are 1.0MPa and 0.042MPa respectively and the temperature of room-temperature heat exchanger is kept around 15°C. And a maximum cooling power of about 28.5W@0°C is achieved under 1.5MPa mean pressure and 0.049MPa oscillating pressure. Besides, the performance of the linear compressor itself is also investigated, which is important for a reasonable evaluation of the refrigerator performance. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Here we discuss origin of pre-edge features in the K-edge absorption spectra of transition metal atoms in octahedral coordination, in oxides and sulphides. We provide a unifying interpretation on the basis of multiple scattering simulations performed with different cluster models. We find that the pre-edge features arise due to hybridisation of the orbitals belonging to the central atom with the higher-shell metal orbitals. The results are obtained by performing multiple scattering simulations with cluster of size equal to the cation-cation plus the cation-anion bond lengths in order to ensure that the higher-shell metal atoms remain in the octahedral coordination. Within this framework, we are able to identify the electronic structure of the metal atoms and the ligand-field characters looking at position, shape and intensity of the different features observed in the XANES spectra. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy at the C K edge has been perforated on carbon nanotubes to demonstrate the capability of the technique to investigate the electronic structure of these systems. We compare and discuss the experimental results achieved on both graphite and nanotubes trying also to determine the relationship between multiple scattering structures and different topology and surface structure of the samples. [ABSTRACT FROM AUTHOR]

Based on the experimental setup of a thermoacoustically driven pulse tube refrigeration system, by which a lowest refrigeration temperature of 138K was achieved in 1999, several improvements have been made to the heating and water cooling system of the thermoacoustic driver and the pulse tube refrigerator, as well as the connection between the driver and the pulse tube. Minimum temperatures of 119.7K and 117.6K have been obtained from the recent experiments with helium and helium-argon mixture filling of 2.0MPa as the working fluids, respectively. It is a significant progress for the present standing wave machine and provides the possibility of liquefying natural gas of 0.2MPa. [ABSTRACT FROM AUTHOR]

X-ray absorption near edge structure (XANES) spectroscopy has been used to investigate local lattice and electronic structure of the intermetallic La[sub 1−x]Ce[sub x]Ru[sub 2] system. Origin of different features is explored by one electron multiple scattering calculations. The experimental and theoretical analysis demonstrate that the Ce doping in La[sub 1−Ce[sub x]Ru[sub 2] has direct influence on the states at the Fermi level and hence the hybridization between the f and d states induced by doping. [ABSTRACT FROM AUTHOR]

The CeRu[sub 2] and the LaRu[sub 2] compounds represent valuable, still not understood, exceptions to the magnetic behaviors of standard BCS superconductor materials. To understand the anomalous behavior of these superconductors we investigated the solid dilution La[sub 1−x]Ce[sub x]Ru[sub 2] by both X-ray absorption spectroscopy and thermodynamic experiments. Among the large class of REM[sub 2] type C15 Friauf-Laves phase compounds, this series offers a good opportunity to investigate the correlation between structural and electronic modifications associated to the interstitial doping. Moreover the understanding of the structural, electronic and magnetic properties of intermetallic rare earth (RE) and the 4d transition metal (M) compounds addresses a large amount of research triggered by technological applications. These experiments have been performed to compare the results obtained by a local spectroscopy with thermodynamic data. Comparative and theoretical analysis demonstrate the large influence of the doping on the electronic and structural behavior of these systems. [ABSTRACT FROM AUTHOR]