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Now showing items 1 - 16 of 1639

  • The electrical behavior of Cu thin film induced by carbon ion irradiation

    Wang, P. P.   Liang, Y. X.   Xu, C.   Wang, X. J.   Zhang, Y.   Yan, X. Q.   Wang, Y. G.   Fu, E. G.  

    This study systematically investigates the influence of carbon ion irradiation on the electrical resistivity of single layer Cu films. Carbon ion irradiations with the energy of 3 MeV and the fluences of 5 x 10(13) ions/cm(2) and 5 x 10(14) ions/cm(2) were performed on the Cu films. The change of the resistivity and the temperature coefficient of resistivity before and after irradiation largely depends on the grain boundary. The amended model was proposed to describe the resistivity of ion-irradiated Cu films by considering the surface scattering, grain boundary scattering and the defects induced by ion irradiation. (C) 2019 Elsevier B.V. All rights reserved.
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  • Mechanism of abnormally slow crystal growth of CuZr alloy

    Yan, X. Q.   Lue, Y. J.  

    Crystal growth of the glass-forming CuZr alloy is shown to be abnormally slow, which suggests a new method to identify the good glass-forming alloys. The crystal growth of elemental Cu, Pd and binary NiAl, CuZr alloys is systematically studied with the aid of molecular dynamics simulations. The temperature dependence of the growth velocity indicates the different growth mechanisms between the elemental and the alloy systems. The high-speed growth featuring the elemental metals is dominated by the non-activated collision between liquid-like atoms and interface, and the low-speed growth for NiAl and CuZr is determined by the diffusion across the interface. We find that, in contrast to Cu, Pd, and NiAl, a strong stress layering arisen from the density and the local order layering forms in front of the liquid-crystal interface of CuZr alloy, which causes a slow diffusion zone. The formation of the slow diffusion zone suppresses the interface moving, resulting in much small growth velocity of CuZr alloy. We provide a direct evidence of this explanation by applying the compressive stress normal to the interface. The compression is shown to boost the stress layering in CuZr significantly, correspondingly enhancing the slow diffusion zone, and eventually slowing down the crystal growth of CuZr alloy immediately. In contrast, the growth of Cu, Pd, and NiAl is increased by the compression because the low diffusion zones in them are never well developed. (C) 2015 AIP Publishing LLC.
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  • Mechanism of abnormally slow crystal growth of CuZr alloy

    Yan, X. Q.   Lü, Y. J.  

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  • Beam experiments on the RFQ and SFRFQ combined accelerator system

    Kang, M. L.   Wang, Z.   Chen, J. E.   Lu, Y. R.   Zhu, K.   Gao, S. L.   Yan, X. Q.   Peng, S. X.   Zhao, J.   Ren, H. T.   Guo, Z. Y.  

    As an injector for the Separated Function RFQ (SFRFQ) accelerator, the Integral Split Ring Radio Frequency Quadrupole (ISR RFQ) accelerator was upgraded to achieve a higher beam current. The experiments on the RFQ accelerator indicated that the maximum accelerated O+ beam current could exceed 3.2 mA with an energy of 1.03 MeV and energy spread (EWHM) of 3.1%. The resultant beam is then transported through a 1-m-long magnetic triplet and finally accelerated to 1.654 MeV by the SFRFQ cavity. The beam conditions of the RFQ accelerator were carefully optimized to satisfy the requirements of the SFRFQ accelerator, and the combined accelerator was able to deliver 0.53 mA of O+ beam to the end of the beam line, which has sufficiently demonstrated the feasibility of the SFRFQ cavity. (C) 2012 Elsevier B.V. All rights reserved.
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  • Design of a CW high charge state heavy ion RFQ for SSC-LINAC

    Liu, G.   Lu, Y. R.   He, Y.   Wang, Z.   Xiao, C.   Gao, S. L.   Yang, Y. Q.   Zhu, K.   Yan, X. Q.   Chen, J. E.   Yuan, Y. J.   Zhao, H. W.  

    The new linac injector SSC-LINAC has been proposed to replace the existing Separator Sector Cyclotron (SSC). This effort is to improve the beam efficiency of the Heavy Ion Research Facility of Lanzhou (HIRFL). As a key component of the linac, a continuous-wave (CW) mode high charge state heavy ion radio-frequency quadrupole (RFQ) accelerator has been designed. It accelerates ions with the ratio of mass to charge up to 7 from 3.728 keV/u to 143 keV/u. The requirements of CW mode operation and the transportation of intense beam have been considered as the greatest challenges. The design is based on U-238(34+) beams, whose current is 0.5 pmA (0.5 particle mili-ampere, which is the measured 17 emA electric current divided by charge state of heavy ions). It achieves the transmission efficiency of 94% with 2508.46 mm long vanes in simulation. To improve the transmission efficiency and quality of the beams, the phase advance has been taken into account to analyze the reasons of beam loss and emittance growth. Parametric resonance and beam mismatch have been carefully avoided by adjusting the structure parameters. The parameter-sensitivity of the design is checked by transportation simulations of various input beams. To verify the applicability of machining, the effects of different vane manufacturing methods on beam dynamics are presented in this paper. (C) 2012 Elsevier B.V. All rights reserved.
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  • Divergence of laser-driven ion beams from nanometer thick foils

    Bin, J. H.   Ma, W. J.   Allinger, K.   Wang, H. Y.   Kiefer, D.   Reinhardt, S.   Hilz, P.   Khrennikov, K.   Karsch, S.   Yan, X. Q.   Krausz, F.   Tajima, T.   Habs, D.   Schreiber, J.  

    We report on experimental studies of divergence of proton beams from nanometer thick diamond-like carbon (DLC) foils irradiated by an intense laser with high contrast. Proton beams with extremely small divergence (half angle) of 2 degrees are observed in addition with a remarkably well-collimated feature over the whole energy range, showing one order of magnitude reduction of the divergence angle in comparison to the results from mu m thick targets. We demonstrate that this reduction arises from a steep longitudinal electron density gradient and an exponentially decaying transverse profile at the rear side of the ultrathin foils. Agreements are found both in an analytical model and in particle-in-cell simulations. Those novel features make nm foils an attractive alternative for high flux experiments relevant for fundamental research in nuclear and warm dense matter physics.
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  • Brilliant GeV gamma-ray flash from inverse Compton scattering in the QED regime

    Gong, Z.   Hu, R. H.   Lu, H. Y.   Yu, J. Q.   Wang, D. H.   Fu, E. G.   Chen, C. E.   He, X. T.   Yan, X. Q.  

    An all-optical scheme is proposed for studying laser plasma based incoherent photon emission from inverse Compton scattering in the quantum electrodynamic regime. A theoretical model is presented to explain the coupling effects among radiation reaction trapping, the self-generated magnetic field and the spiral attractor in phase space, which guarantees the transfer of energy and angular momentum from electromagnetic fields to particles. Taking advantage of a prospective similar to 10(23) W cm(-2) laser facility, 3D particle-in-cell simulations show a gamma-ray flash with unprecedented multi-petawatt power and brightness of 1.7 x 10(23) photons s(-1) mm(-2) mrad(-2)/0.1% bandwidth (at 1 GeV). These results bode well for new research directions in particle physics and laboratory astrophysics exploring laser plasma interactions.
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  • On the small divergence of laser-driven ion beams from nanometer thick foils

    Bin, J. H.   Ma, W. J.   Allinger, K.   Wang, H. Y.   Kiefer, D.   Reinhardt, S.   Hilz, P.   Khrennikov, K.   Karsch, S.   Yan, X. Q.   Krausz, F.   Tajima, T.   Habs, D.   Schreiber, J.  

    We report on experimental studies of divergence of proton beams from nanometer thick diamond-like carbon foils irradiated by a linearly polarized intense laser with high contrast. Proton beams with extremely small divergence (half angle) of 2 degrees are observed in addition with a remarkably well-collimated feature over the whole energy range, showing one order of magnitude reduction of the divergence angle in comparison to the results from mu m thick targets. Similar features are reproduced in two-dimensional particle-in-cell simulations with parameters representing our experiments, indicating a strong influence from the electron density distribution on the divergence of protons. Our comprehensive experimental study reveals grand opportunities for using nm foils in experiments that require high ion flux and small divergence. (C) 2013 AIP Publishing LLC.
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  • Separated function RFQ beam dynamics design and commissioning

    Kang, M. L.   Lu, Y. R.   Chen, J. E.   Zhu, K.   Wang, Z.   Yan, X. Q.   Guo, Z. Y.   Gao, S. L.   Peng, S. X.   Fang, J. X.  

    Separated Function Radio Frequency Quadrupole (SFRFQ) accelerator is a new structure where diaphragms are loaded onto the quadrupole electrodes to form accelerating gaps, while the unmodu-lated RF quadrupole electric field provides transverse focusing. SFRFQ promises a higher accelerating efficiency than the conventional RFQ for heavy ions at low frequencies. In order to reduce reverse field and avoid RF sparking, an asymmetrical electrode and diaphragms designs were adopted. After simulation and RF design, a full scale SFRFQ prototype cavity with 14 beta lambda/2 cells has been constructed as a post-accelerator of the Peking University Integral Split Ring (ISR) RFQ. Beam commissioning was carried out to verify its feasibility. It accelerates O(+) beam from 64 to 103 keV/u with a beam current exceeding 0.53 mA and the experimental results agree well with the simulation predictions by SFRFQCODEV1.0 [Z. Wang, J.E. Chen, Y.R. Lu, et al., Nucl. Instr. and Meth. A, 572, (2007) 596]. (C) 2011 Elsevier B.V. All rights reserved.
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  • Single-Sensor Incipient Fault Detection

    Ren, L.   Xu, Z. Y.   Yan, X. Q.  

    This study presents a new detection method based on wavelet transform and kernel principal component analysis (KPCA) for single-sensor incipient faults. Wavelet transform is first utilized to extract the featured information of process noise while the single-sensor fault is analyzed by KPCA subsequently. The fault data from flow meter and pressure sensor on a process device as well as other disturbing factors which may lead to inaccuracy have also been analyzed in this study. The experimental results demonstrate the accuracy and effectiveness of the proposed method to cope with single-sensor incipient faults.
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  • Multiobjective Optimization Problem of Multireservoir System in Semiarid Areas

    Chen, Z. J.   Cheng, Z. J.   Yan, X. Q.  

    With the increasing scarcity of water resources, the growing importance of the optimization operation of the multireservoir system in water resources development, utilization, and management is increasingly evident. Some of the existing optimization methods are inadequate in applicability and effectiveness. Therefore, we need further research in how to enhance the applicability and effectiveness of the algorithm. On the basis of the research of the multireservoir system's operating parameters in the Urumqi River basin, we establish a multiobjective optimization problem (MOP) model of water resources development, which meets the requirements of water resources development. In the mathematical model, the domestic water consumption is the biggest, the production of industry and agricultural is the largest, the gross output value of industry and agricultural is the highest, and the investment of the water development is the minimum. We use the weighted variable-step shuffled frog leaping algorithm (SFLA) to resolve it, which satisfies the constraints. Through establishing the test function and performance metrics, we deduce the evolutionary algorithms, which suit for solving MOP of the scheduling, and realize the multiobjective optimization of the multireservoir system. After that, using the fuzzy theory, we convert the competitive multiobjective function into single objective problem of maximum satisfaction, which is the only solution. A feasible solution is provided to resolve the multiobjective scheduling optimization of multireservoir system in the Urumqi River basin. It is the significance of the layout of production, the regional protection of ecological environment, and the sufficient and rational use of natural resources, in Urumqi and the surrounding areas.
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  • Enhanced laser proton acceleration by target ablation on a femtosecond laser system

    Liao, Q.   Wu, M. J.   Gong, Z.   Geng, Y. X.   Xu, X. H.   Li, D. Y.   Shou, Y. R.   Zhu, J. G.   Li, C. C.   Yang, M.   Li, T. S.   Lu, H. Y.   Ma, W. J.   Zhao, Y. Y.   Lin, C.   Yan, X. Q.  

    Proton acceleration during the interaction of an ultraintense (6 x 10(19) W/cm(2)) femtosecond (fs) laser pulse with a thin (2.5 mu m) foil target pre-ablated by a picosecond (ps) pulse is experimentally and numerically investigated. Enhancements in both proton cut-off energy and charge are observed with the target ablation due to a large number of energetic electrons generated from the preformed preplasma in front of the target. The enhanced proton beams are successfully collected at 4-9 MeV with +/- 4% energy spread and then transported to the irradiating platform. The results show that for the interaction between fs laser pulse and mu m-thickness target, proton energy and charge can be enhanced by target ablation using a ps laser pulse, which is valuable for application like cancer radiotherapy. Published by AIP Publishing.
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  • High-quality proton bunch from laser interaction with a gas-filled cone target

    Wang, H. Y.   Lin, C.   Zheng, F. L.   Lu, Y. R.   Guo, Z. Y.   He, X. T.   Chen, J. E.   Yan, X. Q.  

    Generation of high-energy proton bunch from interaction of an intense short circularly polarized (CP) laser pulse with a gas-filled cone target (GCT) is investigated using two-dimensional particle-in-cell simulation. The GCT target consists of a hollow cone filled with near-critical gas-plasma and a thin foil attached to the tip of the cone. It is observed that as the laser pulse propagates in the gas-plasma, the nonlinear focusing will result in an enhancement of the laser pulse intensity. It is shown that a large number of energetic electrons are generated from the gas-plasma and accelerated by the self-focused laser pulse. The energetic electrons then transports through the foil, forming a backside sheath field which is stronger than that produced by a simple planar target. A quasi-monoenergetic proton beam with maximum energy of 181 MeV is produced from this GCT target irradiated by a CP laser pulse at an intensity of 2.6 x 10(20) W/cm(2), which is nearly three times higher compared to simple planar target (67 MeV). (C) 2011 American Institute of Physics. [doi:10.1063/1.3630930]
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  • Collimated proton acceleration in light sail regime with a tailored pinhole target

    Wang, H. Y.   Yan, X. Q.   Zepf, M.  

    A scheme for producing collimated protons from laser interactions with a diamond-like-carbon + pinhole target is proposed. The process is based on radiation pressure acceleration in the multi-species light-sail regime [B. Qiao et al., Phys. Rev. Lett. 105, 155002 (2010); T. P. Yu et al., Phys. Rev. Lett. 105, 065002 (2010)]. Particle-in-cell simulations demonstrate that transverse quasistatic electric field at TV/m level can be generated in the pinhole. The transverse electric field suppresses the transverse expansion of protons effectively, resulting in a higher density and more collimated proton beam compared with a single foil target. The dependence of the proton beam divergence on the parameters of the pinhole is also investigated. (C) 2014 AIP Publishing LLC.
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  • Design and measurements of SFRFQ cavity

    Wang, Z.   Chen, J. E.   Lu, Y. R.   Zhu, K.   Kang, M. L.   Yan, X. Q.   Guo, Z. Y.   Gao, S. L.   Fang, J. X.  

    Separated Function Radio Frequency Quadrupoles (SFRFQ) structure is a new post accelerator of RFQ, the higher accelerating efficiency and transmission make it become a proper choice for the post acceleration after the integral split ring RFQ(ISR RFQ)-1000 accelerator at Peking University [Y.R. Lu, J.F. Guo, W.G. Li, et al., Nucl. Instr. and Meth. A 420 (1999) 2]. A novel design strategy is proposed in this paper to avoid the sparking problem and decrease the energy spread at the exit of SFRFQ. Correspondingly, a code SFRFQCODEV1.0 was developed specially for beam dynamic simulations and error studies. A prototype cavity with 14 accelerating gaps has been constructed and tested at low and high RF power successfully. The operating energy region of SFRFQ structure and the results of error study are presented. Crown Copyright (C) 2009 Published by Elsevier B.V. Ail rights reserved.
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  • Yan\r et?al.\r Reply:

    Yan, X. Q.   Lin, C.   Sheng, Z. M.   Guo, Z. Y.   Liu, B. C.   Lu, Y. R.   Fang, J. X.   Chen, J. E.  

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