Thomson scattering off a pair （electron-positron） plasma

Thomson scattering off a pair (electron--positron) plasma is theoretically investigated in the collisionless and collisional limits respectively. Our calculations show that the power spectrum of the Thomson scattering off a collisionless pair plasma is just proportional to the velocity distribution function of the particles in the plasma. Collective modes in the plasma do not have any effects on the Thomson scattering spectrum because of the correlation between the negatively- and positively-charged particles. In the collisional limit, the power spectrum of the Thomson scattering presents three spikes: two peaks correspond to two contra-propagating sound waves and one peak corresponds to an entropy wave.     

Spectral distributions of the scattered photons within an acceptance angle in Thomson scattering

In this paper, we present the analysis of the spectral distributions of the scattered photons within a certain acceptance angle in Thomson scattering, in which the beam divergence, energy spread and spatial distribution are all considered. The analytical results are compared with the simulation results, and good agreement between the two approaches is obtained.     

Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields

Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray,in which a high radiation power per solid angle as ～10~(11) a.u. can be obtained.     

Anomalously Strong Scattering of Spontaneously Produced Laser Radiation in the First Free-Electron Laser and Study of Free-Electron Two-Quantum Stark Lasing in an Electric Wiggler with Quantum-Wiggler Electrodynamics

We calculate the scattering cross section of an electron with respect to the spontaneously produced laser radiation in the first free-electron laser （FEL） with quantum-wiggler electrodynamics （QWD）. The cross section is 1016 times the Thomson cross section, confirming the result obtained by a previous analysis of the experimental data. A QWD calculation show that spontaneous emission in an FEL using only an electric wiggler can be very strong while amplification through net stimulated emission is practically negligible.     

Investigation on global positioning system signal scattering and propagation over the rough sea surface

This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system (GPS) scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation with using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern with using fast Fourier transform (FFT) is replaced by the GPS scattering field. And the propagation properties of GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform with taking into account the sea surface roughness.     

Simulation study of a photo-injector for brightness improvement in Thomson scattering X-ray source via ballistic bunching

Increasing the peak brightness is beneficial to various applications of the Thomson scattering X-ray source. A higher peak brightness of the scattered X-ray pulse demands a shorter scattering electron beam realized by beam compression in the electron beam-line. In this article, we study the possibility of compressing the electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve the peak brightness of the scattered x-ray pulse. Numerical optimization by ASTRA demonstrates that the peak current can increase from 50 A to > 300 A for a 500 pC, 10 ps FWHM electron pulse, while normalized transverse RMS emittance and RMS energy spread increases very little. Correspondingly, the peak brightness of the Thomson scattering X-ray source is estimated to increase about three times.     

Investigation on electromagnetic scattering from rough soil surface of layered medium using the small perturbation method

Electromagnetic scattering from a rough surface of layered medium is investigated, and the formulae of the scattering coefficients for different polarizations are derived using the small perturbation method. A rough surface with exponential correlation function is presented for describing a rough soil surface of layered medium, the formula of its scattering coefficient is derived by considering the spectrum of the rough surface with exponential correlation function; the curves of the bistatic scattering coefficient of HH polarization with variation of the scattering angle are obtained by numerical calculation. The influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the roughness surface parameters and the frequency of the incident wave on the blstatic scattering coefficient is discussed. Numerical results show that the influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the rms and the correlation length of the rough surface, and the frequency of the incident wave on the bistatic scattering coefficient is very complex.     

Sound scattering from partially water-filled elastic spherical shell with an internal elastic plate

According to the equation of motion in the elastic medium and integral equation of target scattering, the sound scattering from the partially water-filled elastic spherical shells with and without an inner plate is studied using the finite element and boundary element method, and the scattering normalized form functions of the shell filled with different volume of water are computed and the mechanism of resonance scattering is analyzed. The results show that the resonance of the shell with partially water-filled and without the plate is mainly related to the volume of water, and the resonance is produced by inner water and the spherical shell. The resonance characteristics of partially water-filled elastic shell with the plate are similar to that of empty structured elastic spherical shell, and the sound field in inner water is weaker which indicates the main resonance characteristics are decided by spherical shell and the plate. In addition, the scattering characteristics of spherical shell with plate and one side full water-filled are greatly different from the partially water-filled ones.     

Intermediate Energy Pion-~(20)Ne Elastic Scattering in the α+~(16)O Model of (20)~Ne

We present an analysis of π-20Ne elastic scattering at intermediate energy basing on the α+16O model of the20Ne nucleus and in the framework of Glauber multiple scattering theory. Satisfactory agreement with the general features of the experimental data of pion elastic scattering on the neighboring 4N-type nuclei is obtained without any free parameters. Compared with the experimental angular distributions of pion elastic scattering on12C,16O,24Mg,and28Si nuclei, the difractive patterns and the positions of the dips and peaks in the angular distributions of π-20Ne elastic scattering are reasonably predicted by the calculations.     

Calculation of three-dimensional acoustic scattering from Gaussian rough under-ice surface using the Kirchhoff approximation method with modified reflection coefficient

The Kirchhoff approximation with a modified reflection coefficient is used to calculate the three-dimensional acoustic scattering of a Gaussian rough under-ice surface.The concept of a local statistical average reflection coefficient of an under-ice surface is proposed in the calculation model.The scattered sound field of a two-dimensional Gaussian rough under-ice surface is divided into coherent scattering and incoherent scattering.A formula is derived for the scattering coefficient of each scattering component,and the three-dimensional scattering intensity is obtained.The relationships between the scattering intensity and(ⅰ) the root-meansquare height of the Gaussian rough under-ice surface,(ⅱ) the angle of incidence,and(ⅲ) the sound frequency are analyzed.The scattering intensity of a Gaussian rough under-ice surface is measured in a laboratory water tank,and the calculation results of the theoretical model are verified.The experimental results are compared with those of the theoretical model using(ⅰ) the present local statistical average reflection coefficient of an under-ice surface and(ⅱ) the mirror reflection coefficient of an under-ice surface from the literature.The calculation results of the model using the local statistical average reflection coefficient agree well with the experimental results.