Results 1 - 10 of 273
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[en] Experience using laser-wire beam profile measurement to perform transverse beam matching in the SNS superconducting linac is discussed. As the SNS beam power is ramped up to 1 MW, transverse beam matching becomes a concern to control beam loss and residual activation in the linac. In our experiments, however, beam loss is not very sensitive to the matching condition. In addition, we have encountered difficulties in performing a satisfactory transverse matching with the envelope model currently available in the XAL software framework. Offline data analysis from multi-particle tracking simulation shows that the accuracy of the current online model may not be sufficient for modeling the SC linac.
[en] A laser wire ion beam profile monitor system has been developed at the Spallation Neutron Source accelerator complex. The laser wire system uses a single laser source to measure the horizontal and vertical profiles of a pulsed hydrogen ion (H-) beam along a 230 m long superconducting linac, which accelerates H- from 200 MeV to 1 GeV. In this paper, we describe the laser optics requirement for the system, the performance of the profile measurement, and the effects of laser parameters on the measurement reliability. The result provides a practical guideline for the development of a large-scale, operational, laser-based diagnostics in accelerator facilities.
[en] Silver ions doping made enhancement of the photocatalytic activity of TiO2, which was determined by degradation of methyl orange (MO), a probe molecule, in an aqueous solution. X-ray diffraction (XRD) investigation demonstrated that the silver doping changed lattice parameters of TiO2, which should attribute to the O vacancies produced by the substitutional silver ion at lattice site. On above results, a doping mechanism of silver ions in TiO2 was also discussed
[en] Electron diffraction is used to investigate the average structure of microporous AlPO4-11 as well as the zero-frequency rigid unit mode (RUM) modes of distortion of the ideal AlPO4-11 tetrahedral framework. Direct experimental evidence (in the form of a highly structured, characteristic diffuse intensity distribution) has been found for the (presumably dynamic) excitation of numerous zero-frequency RUM modes of distortion. The lattice dynamic program CRUSH is used to confirm the existence of zero-frequency RUM modes of distortion with wave-vectors falling on the observed diffuse distribution. The simultaneous (presumably dynamic) excitation of such RUM modes of distortion needs to be taken into account in order for the local crystal chemistry of AlPO 4-11 to be understood
[en] A brief review on the emergent applications of laser technology to particle accelerators is provided. Important developments in laser technology that lead to the application are introduced. Advancements in laser technology have dramatically expanded the applications of lasers to particle accelerators. Today, lasers have been used for accelerators in a broad range from operational systems such as nonintrusive particle beam diagnostics instruments, to elaborate applications with high technical readiness levels including, for instance, photoinjectors, a laser assisted foil-less charge exchange injection scheme and Compton scattering-based light sources, and finally to exotic topics such as laser driven electron/ion accelerators. This talk reviews recent experimental results achieved in the above applications, their requirements on laser parameters and challenges that require future laser technology development. Important technical elements such as the femto-second pulse generation, the burstmode optical amplifiers, the beam combining from laser arrays, and the power enhancement optical cavity will be briefly described.
[en] A careful phase analysis study of cubic perovskite-related phases in the ternary SrO-CuO-Nb2O5 system has been carried out via the synthesis and compositional analysis of a range of specimens within the ternary SrO-CuO-Nb2O5 system. Powder XRD in conjunction with electron probe microanalysis (EPMA) has been used to determine whether the synthesized specimens are single phase or not and to determine the compositions of the various reaction products. Three quite distinct such solid solution phases have been found and their quite distinct electrical and diffraction characteristics investigated
[en] A careful TEM and XRD study of the (Ba1-xLax)2In2O5+x, 0≤x≤0.6, 'defect-perovskite'-type solid solution has been carried out. A well-defined structural phase transition is shown to occur between x=0.1 and 0.2 from the orthorhombic brownmillerite structure type on the low x side to a multiple twinned, tetragonal 1x1x2 perovskite-related superstructure phase on the high x side at x=0.2. This phase transition correlates with an important phase transition previously observed in electrical conductivity versus temperature measurements. The existence of additional satellite reflections close to the G±((1)/(2)) <001>p* regions of reciprocal space was found to be typical of all (Ba1-xLax)2In2O5+x specimens, although their intensity relative to the parent Bragg reflections systematically reduces as x increases. As x increases beyond 0.2, the G±((1)/(2)) <001>p*-type satellite reflections initially become weaker and rather more diffuse for x=0.3 before splitting into pairs of rather weak and somewhat diffuse incommensurate satellite reflections for x=0.4 and beyond. An interpretation in terms of oxygen vacancy ordering and associated structural relaxation is given. Additional structured diffuse scattering is also observed and a tentative explanation in terms of Ba/La ordering and associated local strain distortions put forward
[en] We construct explicit multisoliton complex solutions for multicomponent Bose–Einstein condensate systems with time- and spatial-coordinate-dependent atomic potentials and interactions. The exact solutions are used to analyze the important solitary matter wave properties such as the profiles of temporal and spatial multimode beams as well as focusing effects. Results demonstrate that soliton complexes can be controlled nonlinearly during the interaction by modulating the external potentials and nonlinearities. - Highlights: • An algebraic approach is proposed for the dynamics of multicomponent BECs. • External potentials and nonlinearities are time and space-dependent. • Analytical solutions are constructed. • Multisoliton complexes are predicted
[en] Full text: Properties and functions of materials are determined by the structure and its evolution on every relevant time, length, field and energy scale. To understand these, neutrons play a critical role in providing important insights into the structure of polar functional materials as it responds to stimuli. In this talk, I will present a summary of recent progress in neutron scattering studies of piezoelectric, anti/ferroelectric and multiferroic materials, with a special focus on the investigation of neutron diffraction conducted under different fields (e.g. temperature, magnetic/electrical field and pressure). I will also report structurally dynamic behaviours of zeolites and metal-organic frameworks (MOFs) investigated by using time-of-flight inelastic neutron scattering and comment on the role neutrons play in gaining new insights into the properties of a broad range of key materials for practical application. I will then discuss overcoming challenges and technical difficulties to attain precision neutron analyses, and give my personal perspective as a user on the continuous development of instruments and methods needed for neutron scattering studies in the future. (author)