[en] This paper addresses the output characteristics of real electron bunches accelerated with ultra-intense laser pulse in vacuum by the capture and acceleration scenario (CAS) scheme (see, e.g., Phys. Rev. E66 (2002) 066501). Normally, the size of an electron bunch is much larger than that of a tightly focused and compressed laser pulse. We examine in detail the features of the intersection region, the distribution of electrons which can experience an intense laser field and be accelerated to high energy. Furthermore, the output properties of the accelerated CAS electrons, such as the energy spectra, the angular distributions, the energy-angle correlations, the acceleration gradient, the energy which can be reached with this scheme, the emittances of the outgoing electron bunches, and the dependence of the output properties on the incident electron beam qualities such as the emittance, focusing status, etc. were studied and explained. We found that with intense laser systems and electron beam technology currently available nowadays, the number of CAS electrons can reach 10⁴-10⁵, when the total number of incident electrons in the practical bunch reaches ∼10⁸. These results demonstrate that CAS is promising to become a novel mechanism of vacuum laser accelerators

[en] This paper studies the output properties of GeV electron bunches driven by ultra-intense lasers in vacuum based on the mechanism of capture and violent acceleration scenario [CAS, see e.g. J.X. Wang, et al., Phys. Rev. E 58 (1998) 6575]. We find that the output of the acceleration mechanism is a GeV electron macro-pulse which consists of many micro-pulses corresponding to the periodicity of the laser wave. The outgoing electrons can generally be divided into two groups. One spreads greatly in space and the other is a high-energy bunch with limited spread in space. Provided that the incoming electron bunch with comparable sizes as that of the laser pulse synchronously impinges on the laser pulse, the total fraction of CAS electrons can reach more than 20% of the incident electrons. These results demonstrate that the CAS is a pretty effective accelerator mechanism

[en] By taking account of the high-order corrections to the paraxial approximation of a Gaussian beam, it has been verified that for a focused laser beam propagating in vacuum, there indeed exists a subluminous wave phase velocity region surrounding the laser beam axis. The magnitude of the phase velocity scales as V_φm∼c(1+b/(kw₀)²), where V_φm is the phase velocity of the wave, c is the speed of light in vacuum, w₀ is the beam width at focus. This feature gives a reasonable explanation for the mechanism of capture and acceleration scenario

No abstract available

[en] The temperature dependence of the reflectance of the spin glass materials R₂Mo₂O_7-δ (R:Sm, Gd, and Ho) has been measured for frequencies from 40 to 40 000 cm^-1. The AC conductivity of Sm₂Mo₂O_7-δ derived from Kramers-Kronig analysis, indicates a Drude-like behaviour as the temperature is lowered. Between 150 and 40 K the scattering rate shows a sharp drop which is attributed to the scattering of conduction electrons by short-range ordered moments of the Mo ions. Below the spin glass transition temperature T_f (≅40 K) the scattering rate saturates due to the freezing of the moments. Gd₂Mo₂O_7-δ behaves like a poor metal at room temperature, but at low temperatures shows a linear increase in the conductivity for frequencies up to 400 cm¹ suggesting a localized hopping conductivity. The localization remains in the spin glass state for T< T_f (≅25 K). The conductivity of Ho₂Mo₂O_7-δ is semiconductor-like with a small and slightly temperature-dependent gap around 0.25 eV. Our optical results support a qualitative band model proposed by Sleight and Bouchard for the pyrochlore oxides. (author)

[en] The composition dependence of superconductivity and crystal structure in La(Ba_1-chiCa_chi)₂Cu₃O_7-y system was determined by the resistivity measurements and X-ray diffraction analysis. The superconducting transition temperature is raised with the increase of Ca content till chi=0.6, at which the zero resistance temperature of the sample is 81.5Κ. In the meanwhile, the crystal structure of the sample changed from tetragonal (chi=0) to orthorhombic structure (chi=0.2,0.4,0.6). With further increase of Ca content, the superconductivity decrease for the sample of chi=0.8 with mixed phases including the orthorhombic oxygen-deficient perovskite-like (ODP) structure and no superconducting transition is found at 4.2Κ for the sample of chi=1 without the ODP structure. A possible explanation of these experimental results is given

[en] Using three dimensional test particle simulations, the characteristics and essential conditions under which an electron, in a vacuum laser beam, can undergo a capture and acceleration scenario (CAS) have been examined. When a₀∼>100 the electron can be captured and violently accelerated to energies ∼>1 GeV, with an acceleration gradient ∼>10 GeV/cm, where a₀=eE₀/m_eωc is the normalized laser field amplitude. The physical mechanism behind the CAS is that diffraction of the focused laser beam leads to a slowing down of the effective wave phase velocity along the captured electron trajectory, such that the electron can be trapped in the acceleration phase of the wave for a longer time and thus gain significant energy from the field

[en] An acceleration channel has been found in the field of a focused laser beam propagating in vacuum, which shows similar characteristics to that of a wave guide tube of conventional accelerators: a subluminous wave phase velocity in conjunction with a strong longitudinal electric field component. Relativistic electrons injected into this channel can remain synchronous with the accelerating phase for sufficiently long time and receive considerable energy from the field. We call this acceleration scheme CAS (capture and acceleration scenario). The basic conditions for CAS to occur are examined and the output properties of electrons accelerated by this scheme are also presented in this paper

[en] It has been found that for a focused laser beam propagating in vacuum, there exist 'natural' channels for laser driven electron acceleration, which emerge just beyond the beam width and extend along the diffraction angle for a few Rayleigh lengths. These channels have the similar characteristics to that of a wave guide tube of conventional accelerators: a subluminous wave phase velocity in conjunction with a strong longitudinal acceleration electric field. Relativistic electrons injected into these channels can be captured in the acceleration phase of the wave for sufficiently long time and gain considerable net energy from the laser field. The basic conditions for this acceleration scheme to emerge are addressed here

[en] The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for the kinetic equation of the discrete velocity distribution function. We argue that for finite sets of discrete velocity models, such as LBM, the physical symmetry is necessary for obtaining the correct macroscopic Navier-Stokes equations. In contrast, the lattice symmetry and the Lagrangian nature of the scheme, which is often used in the lattice gas automaton method and the existing lattice Boltzmann methods and directly associated with the property of particle dynamics, is not necessary for recovering the correct macroscopic dynamics. By relaxing the lattice symmetry constraint and introducing other numerical discretization, one can also obtain correct hydrodynamics. In addition, numerical simulations for applications, such as nonuniform meshes and thermohydrodynamics can be easily carried out and numerical stability can be ensured by the Courant-Friedricks-Lewey condition and using the semi-implicit collision scheme. copyright 1997 The American Physical Society