We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4 x 4 mu m(2)) at the sample position despite being exposed to ...
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We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4 x 4 mu m(2)) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm(2). raytracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator's central cone, which contains the usable photons but is considerably smaller than the angular power distribution. (C) 2008 American Institute of Physics.
Highly collimated betatron radiation from a laser wakefield accelerator is a promising tool for spectroscopic measurements. Therefore, there is a requirement to create spectrometers suited to the unique properties of ...
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Highly collimated betatron radiation from a laser wakefield accelerator is a promising tool for spectroscopic measurements. Therefore, there is a requirement to create spectrometers suited to the unique properties of such a source. We demonstrate a spectrometer which achieves an energy resolution of < 5 eV at 9 keV (E/Delta E > 1800) and is angularly resolving the x-ray emission allowing the reference and spectrum to be recorded at the same time. The single photon analysis is used to significantly reduce the background noise. Theoretical performance of various configurations of the spectrometer is calculated by a ray-tracing algorithm. The properties and performance of the spectrometer including the angular and spectral resolution are demonstrated experimentally on absorption above the K-edge of a Cu foil backlit by a laser-produced betatron radiation x-ray beam. Published by AIP Publishing.
Lateral penumbra of multileaf collimator plays an important role in radiotherapy treatment planning. Growing evidence has revealed that, for a single-focused multileaf collimator, lateral penumbra width is leaf positi...
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Lateral penumbra of multileaf collimator plays an important role in radiotherapy treatment planning. Growing evidence has revealed that, for a single-focused multileaf collimator, lateral penumbra width is leaf position dependent and largely attributed to the leaf end shape. In our study, an analytical method for leaf end induced lateral penumbra modelling is formulated using Tangent Secant Theory. Compared with Monte Carlo simulation and raytracing algorithm, our model serves well the purpose of cost-efficient penumbra evaluation. Leaf ends represented in parametric forms of circular arc, elliptical arc, Bezier curve, and B-spline are implemented. With biobjective function of penumbra mean and variance introduced, genetic algorithm is carried out for approximating the Pareto frontier. Results show that for circular arc leaf end objective function is convex and convergence to optimal solution is guaranteed using gradient based iterative method. It is found that optimal leaf end in the shape of Bezier curve achieves minimal standard deviation, while using B-spline minimum of penumbra mean is obtained. For treatment modalities in clinical application, optimized leaf ends are in close agreement with actual shapes. Taken together, the method that we propose can provide insight into leaf end shape design of multileaf collimator.
Even though a computer-aided design (CAD)-based geometry can be directly implemented in Geant4 as polygon-mesh using the G4TessellatedSolid class, the computation speed becomes very slow, especially when the geometry ...
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Even though a computer-aided design (CAD)-based geometry can be directly implemented in Geant4 as polygon-mesh using the G4TessellatedSolid class, the computation speed becomes very slow, especially when the geometry is composed of a large number of facets. To address this problem, in the present study, a new Geant4 solid class, named DagSolid, was developed based on the direct accelerated geometry for the Monte Carlo (DAGMC) library which provides the ray-tracing acceleration algorithm functions. To develop the DagSolid class, the new solid class was derived from the G4VSolid class, and its ray-tracing functions were linked to the corresponding functions of the DAGMC library. The results of this study show that the use of the DagSolid class drastically improves the computation speed. The improvement was more significant when there were more facets, meaning that the DagSolid class can be used more effectively for complicated geometries with many facets than for simple geometries. The maximum difference of computation speed was 1562 and 680 times for Geantino and ChargedGeantino, respectively. For real particles (gammas, electrons, neutrons, and protons), the difference of computation speed was less significant, but still was within the range of 53-685 times depending on the type of beam particles simulated.
There are two sun-tracking methods widely used for the heliostat, which are conventional Azimuth-Elevation and revolutionary Spinning-Elevation methods. Following the previous study to compare the range of motion, a c...
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There are two sun-tracking methods widely used for the heliostat, which are conventional Azimuth-Elevation and revolutionary Spinning-Elevation methods. Following the previous study to compare the range of motion, a comparison study in optical efficiency of heliostat field for the two methods is further explored in this paper. A special algorithm using ray-tracing technique has also been developed to simulate the optical efficiency of heliostat field for both sun-tracking methods in different latitudes. With the new algorithm, comprehensive analysis to compare the optical efficiency of individual heliostat and the overall heliostat field for the two sun-tracking methods has been carried out.
By actively distorting the cosmic microwave background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from...
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By actively distorting the cosmic microwave background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from the primordial type of non-Gaussianity requires calibration over synthetic full sky CMB maps, which until now had been numerically unachievable at the resolution of modern experiments. In this paper, we provide the first high resolution full sky CMB map of the temperature anisotropies induced by a network of cosmic strings since the recombination. The map has about 200 million subarcminute pixels in the healpix format which is the standard in use for CMB analyses (Nside=4096). This premiere required about 800 000 cpu-hours; it has been generated by using a massively parallel raytracing method piercing through thousands of state of art Nambu-Goto cosmic string numerical simulations which pave the comoving volume between the observer and the last scattering surface. We explicitly show how this map corrects previous results derived in the flat sky approximation, while remaining completely compatible at the smallest scales.
We develop an approach for constructing the Baxter Q-operators for generic sl(N) spin chains. The key element of our approach is the possibility of representing a solution of the Yang-Baxter equation in the factorized...
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We develop an approach for constructing the Baxter Q-operators for generic sl(N) spin chains. The key element of our approach is the possibility of representing a solution of the Yang-Baxter equation in the factorized form. We prove that such a representation holds for a generic sl(N) invariant R-operator and find the explicit expression for the factorizing operators. Taking trace of monodromy matrices constructed of the factorizing operators one defines a family of commuting (Baxter) operators on the quantum space of the model. We show that a generic transfer matrix factorizes into the product of N Baxter Q-operators and discuss an application of this representation for a derivation of functional relations for transfer matrices.
The current drive efficiency for the ITER reference scenario 2 has been calculated by the newly developed ray-tracing code TRAVIS for both the upper and the equatorial launchers. For comparison, two adjoint approach m...
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The current drive efficiency for the ITER reference scenario 2 has been calculated by the newly developed ray-tracing code TRAVIS for both the upper and the equatorial launchers. For comparison, two adjoint approach models are applied, the high-speed-limit model and a model with the parallel momentum conservation taken into account. It is shown that in the angle range expected as optimal launch angles the momentum conservation correction produces a non-negligible contribution in ECCD, leading to the necessity to revise the previous predictions carefully. Additionally, the scenario with reduced magnetic field is checked. It is shown that the ECCD efficiency (as well as the deposition profile) for the equatorial launcher may be significantly changed due to unwanted absorption at the higher (parasitic) harmonics.
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