共查询到20条相似文献,搜索用时 0 毫秒
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Jun-Gao Zhu Kun Zhu Li Tao Xiao-Han Xu Chen Lin Wen-Jun Ma Hai-Yang Lu Yan-Ying Zhao Yuan-Rong Lu Jia-Er Chen Xue-Qing Yan 《中国物理C(英文版)》2017,41(9):097001-097001
Compared with conventional accelerators,laser plasma accelerators can generate high energy ions at a greatly reduced scale,due to their TV/m acceleration gradient.A compact laser plasma accelerator(CLAPA) has been built at the Institute of Heavy Ion Physics at Peking University.It will be used for applied research like biological irradiation,astrophysics simulations,etc.A beamline system with multiple quadrupoles and an analyzing magnet for laser-accelerated ions is proposed here.Since laser-accelerated ion beams have broad energy spectra and large angular divergence,the parameters(beam waist position in the Y direction,beam line layout,drift distance,magnet angles etc.) of the beamline system are carefully designed and optimised to obtain a radially symmetric proton distribution at the irradiation platform.Requirements of energy selection and differences in focusing or defocusing in application systems greatly influence the evolution of proton distributions.With optimal parameters,radially symmetric proton distributions can be achieved and protons with different energy spread within ±5% have similar transverse areas at the experiment target. 相似文献
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The temperature dependence of the sputter yield and the energy spectrum of sputtered atoms have been investigated on the basis of a standard model for thermal spikes. A high-temperature and a low-temperature regime have been identified in the temperature spectrum making up the evaporation yield. The high-temperature component of the yield as well as the associated energy spectrum are only very weakly dependent on ambient target temperature. The relative variation is the less pronounced the higher the spike temperature. The low-temperature component is associated with the long-time behavior of the spike, and measurable evaporation takes place over time intervals where spikes overlap. The importance of time constants for macroscopic heat transport is pointed out. The results are shown to provide a framework within which experimental results on the temperature dependence of the sputter yield of metals can be explained. The results are also consistent with measured temperature dependences in the sputter yield of insulators.On leave from Instytut Fizyki, Uniwersytet Jagiellonski, PL-30-059 Krakow, Poland 相似文献
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Møller SP Csete A Ichioka T Knudsen H Uggerhøj UI Andersen HH 《Physical review letters》2004,93(4):042502
The slowing-down process of pointlike charged particles in matter has been investigated by measuring the stopping power for antiprotons in materials of qualitatively very different nature. Whereas the velocity-proportional stopping power observed for metal-like targets such as aluminum over a wide energy range of 1-50 keV is in agreement with expectations, it is surprising that the same velocity dependence is seen for a large band-gap insulator such as LiF. The validity of these observations is supported by several measurements with protons and several checks of the target properties. The observations call for both a qualitative explanation and a quantitative theoretical model. 相似文献
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We report the first experimental demonstration of longitudinal compression of laser-accelerated electron pulses. Accelerated by a femtosecond laser pulse with an intensity of 101? W/cm2, an electron pulse with an energy of around 350 keV and a relative momentum spread of about 10?2 was compressed to a 500-fs pulse at a distance of about 50 cm from the electron source by using a magnetic pulse compressor. This pulse was used to generate a clear diffraction pattern of a gold crystal in a single shot. This method solves the space-charge problem in ultrafast electron diffraction. 相似文献
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Dynamics of wave packets formed by surface (edge) electronic states in topological insulators has been investigated. The spin and electron probability density, as well as zitterbewegung, of wave packets have been calculated analytically and numerically for various values of the Hamiltonian parameters. The effects of the main parameters (size and spin polarization) of the wave packets on a change in the packet shape and oscillations of their average velocity have been considered. 相似文献
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We have studied the photoexcited carrier relaxation dynamics in the Kondo insulator SmB6 and the heavy fermion metal YbAgCu4 as a function of temperature and excitation level. The dynamic response is found to be both strongly temperature dependent and nonlinear. The data are analyzed with a Rothwarf-Taylor bottleneck model, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The remarkable agreement with the model suggests that carrier relaxation in a broad class of heavy electron systems (both metals and insulators) is governed by the presence of a (weakly temperature dependent) hybridization gap. 相似文献
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Using the continual model of a semi-infinite three dimensional (3D) topological insulator (TI) we study the effect of the surface potential (SP) on the formation of helical topological states near the surface. The results reveal that spatial profile and spectrum of these states strongly depend on the SP type and strength. We pay special attention to the 3D TI substrate/non-magnetic insulating overlayer system to illustrate the principles of the topological near-surface states engineering. 相似文献
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Resta R 《Physical review letters》2006,96(13):137601
The ground-state fluctuation of polarization P is finite in insulators and divergent in metals, owing to the SWM sum rule [I. Souza, T. Wilkens, and R. M. Martin, Phys. Rev. B 62, 1666 (2000)]. This is a virtue of periodic (i.e., transverse) boundary conditions. I show that within any other boundary conditions the P fluctuation is finite even in metals, and a generalized sum rule applies. The boundary-condition dependence is a pure correlation effect, not present at the independent-particle level. In the longitudinal case inverted triangle x P = -rho, and one equivalently addresses charge fluctuations: the generalized sum rule reduces then to a well-known result of the many-body theory. 相似文献
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《Superlattices and Microstructures》1986,2(3):213-218
Analytical and numerical methods in the theory of quantum-mechanical propagation of electrons in parallel-geometry heterostructures, allowing for inhomogeneous effective mass and including interfaces, are presented: An algorithm for numerical computation of transmission probability, a treatment of the residual reflection probability in a graded structure, a discussion of resonant tunneling, and a general quantum-mechanical formulation of tunneling theory. 相似文献
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M. Noga 《Czechoslovak Journal of Physics》1988,38(2):210-223
Novel types of ground states associated with macroscopic formations of bilocal fields are derived for a subsystem of localized electrons with the Heisenberg exchange interaction. These ground states describe properties of heavy fermion systems both in their normal and superconducting states. The effective mass, Fermi energy, specific heat, Pauli susceptibility and critical temperature of heavy fermion systems are determined and compared with experimental data. The agreement with experimental quantities is reasonable. 相似文献
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The cross sections for inelastic scattering of electrons and X-rays in metals for fixed momentum transfer are proportional according to the Born approximation. This contradicts the experiments. For electrons multiple scattering is essential. This can be included in a weak coupling limit, which depends on the usual dynamic structure factor only. 相似文献
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Subir Sachdev 《Annals of Physics》2003,303(1):226-246
This paper surveys the physics of systems proximate to Mott insulators, and presents a classification using conventional and topological order parameters. This classification offers a valuable perspective on a variety of conducting correlated electron systems, from the cuprate superconductors to the heavy fermion compounds. Connections are drawn, and distinctions made, between collinear/non-collinear magnetic order, bond order, neutral spin 1/2 excitations in insulators, electron Fermi surfaces which violate Luttinger’s theorem, fractionalization of the electron, and the fractionalization of bosonic collective modes. Two distinct categories of Z2 gauge theories are used to describe the interplay of these orders. Experimental implications for the cuprates are briefly noted, but these appear in more detail in a companion review paper (S. Sachdev, cond-mat/0211005). 相似文献