Experimental study of coherent transition radiation from relativistic electrons in a dihedral angle

Angular intensity distributions for transition radiation excited by a beam of relativistic electrons in the emitter in the form of a dihedral angle are measured in the millimeter range. The angle is formed by the intersection of two conducting planes. The source of radiation is a microtron with an electron energy of 7.4 MeV. We analyze the effect of the magnitude of the dihedral angle of the emitter, the position of the electron transition point on the surface of the angle, and the direction of motion of electrons on the angular distribution of radiation intensity. It is shown that the spectral and angular distributions of radiation intensity in the dihedral angle substantially differ from analogous distributions for a particle intersecting a planar conducting surface. The possibility of using radiation to measure the energy, spatial position, and direction of motion of charges is considered.     

Transition radiation in a dihedral angle formed by perfectly conducting planes

The spatial distribution of the field of transition radiation generated by a relativistic particle flying into a dihedral angle formed by perfectly conducting plane surfaces is determined. The cases when particles are injected from the edge and from a plane of the dihedral angle are considered. The angular distributions of radiation intensity in dihedral angles of different values are calculated.     

Peculiarities of the spectral-angular distribution of transition radiation from a relativistic particle in a dihedral angle

The spatial distributions of transition radiation from relativistic particles entering and exiting the edge of a dihedral angle formed by perfectly conducting flat surfaces have been investigated. The angular distributions of the radiation intensity in dihedral angles with various opening angles have been calculated. The angular distributions of forward radiation (when the particle exits the dihedral angle) and backward radiation (when the particle enters the dihedral angle) are shown to differ significantly.     

Spatial distribution of transition radiation of relativistic particles in the dihedral angle formed by perfectly conductive planes

Spatial distributions of transition radiation intensity of particles entering the dihedral angle and escaping from it are calculated. It was shown that radiation of escaping charge at any opening of the dihedral angle ?? is concentrated near the motion direction. If the particle enters the angle, the radiation distribution is defined by the opening angle. At opening angles ?? = ??/n, radiation is concentrated near the direction of actual charge motion when n is an even number and near the direction of image charge motion when n is an odd number. At other opening angles, the spatial distribution of entering particle radiation has two maxima whose positions are defined by the injection angle.     

Transient radiation of particles in dihedral and trihedral angles

The image method is used for determining the field of transient radiation emitted by a charged particle intersecting a dihedral angle formed by ideally conducting charged planes. The spectral-angular distributions of radiation intensity in a dihedral angle with different corner angles are calculated. The effect of the direction of motion of the particle and of the position of the point at which the particle intersects the plane on radiation parameters is considered. Transient radiation distributions in a trihedral angle are also obtained.     

Experimental study of coherent transition radiation from relativistic electron bunches entering a dihedral angle

The angular distributions of the intensity of transition radiation from a bunch of relativistic electrons entering a dihedral angle between two conducting planes have been measured in a millimeter wavelength range. A microtron with a particle energy of 7.4 MeV is used as a source of electrons. The effect of the particle injection direction and the magnitude of the dihedral angle on the angular distribution of the radiation intensity has been analyzed. The measurements show that the character of the distribution of radiation from a charge entering the dihedral angle significantly differs from that for a charge escaping the angle. A comparatively small change in the magnitude of the dihedral angle can lead to qualitative changes in the angular distribution of radiation from a charge entering the dihedral angle.     

The study of surface polaritons by transition radiation

An experimental method for the study of surface polaritons by the use of of transition radiation is proposed. It is found that the placement of a prism close to the surface of a crystal allows one to study the decaying surface modes that are excited by a geam of charged particles travelling perpendicular to the surface of the crystal. Analytic and numerical results for the energy radiated per unit solid angle per unit frequency interval by a single charged particle over its complete trajectory are presented for the phonon form of the dielectric onstant for the crystal GaP. It is found that the predicted effects should be observable experimentally.     

Transition radiation generated by a particle passing through the apex of a conducting cone

The spatial field distribution is determined for the transition radiation generated by a particle passing through the apex of a cone along its axis. Expressions for the angular distribution of the radiation intensity are obtained for apex angles between 0 and π. Characteristics of transition radiation emitted into a “funnel” and a dihedral angle are compared.     

Transition radiation in a system of two cascaded gratings

Transition radiation that arises when a charged particle passes through two consecutive plane gratings is considered. The gratings are made up of parallel metal wires. The planes of the gratings are parallel to each other and perpendicular to the direction of motion of the particle. The conductors of one of the gratings are perpendicular to the conductors of the other. It is shown that the generated transition radiation has elliptic polarization; the ellipticity and the sign of rotation depend on the angle of radiation, the distance between the gratings, and the velocity of the charged particle.     

Transition radiation detectors with a dihedral angle or a cone as a radiator

The spectral and angular distributions of the transition radiation produced by a charge crossing an interface shaped like a dihedral angle or a cone are considered. The effects of the variation in the dihedral angle and cone angle, the location of the crossing point on the interface, and the direction of the charge motion on the spatial distribution of the radiation are discussed. The radiation characteristics of the particles that are incident on the interface and those leaving it are given. The features of transition-radiation detectors with dihedral-angle or cone radiators and detectors with plane-surface radiators are compared.     

Equilibrium configurations of the conducting liquid surface in a nonuniform electric field

Possible equilibrium configurations of the free surface of a conducting liquid deformed by a nonuniform external electric field are investigated. The liquid rests on an electrode that has the shape of a dihedral angle formed by two intersecting equipotential half-planes (conducting wedge). It is assumed that the problem has plane symmetry: the surface is invariant under shift along the edge of the dihedral angle. A one-parametric family of exact solutions for the shape of the surface is found in which the opening angle of the region above the wedge serves as a parameter. The solutions are valid when the pressure difference between the inside and outside of the liquid is zero. For an arbitrary pressure difference, approximate solutions to the problem are constructed and it is demonstrated the approximation error is small. It is found that, when the potential difference exceeds a certain threshold value, equilibrium solutions are absent. In this case, the region occupied by the liquid disintegrates, the disintegration scenario depending on the opening angle.     

Transition radiation from relativistic electrons crossing a perfectly conducting conical surface: Calculation and experiment

The angular distributions of the transition radiation intensity when a charged particle passes through the vertex of a perfectly conducting conical surface have been calculated. The radiation generated both when the particle exits the conductor and when it falls on the conductor has been considered. The angular distributions of the intensity of the transition radiation generated by a bunch of relativistic electrons have been measured in the millimeter wavelength range. A microtron with a particle energy of 7.4 MeV was the source of electrons. The influence of the particle injection direction and the conical-surface opening angle on the angular distribution of the radiation intensity has been studied. The measurements have shown that the distribution of the radiation generated by a charge when it enters the horn differs significantly in pattern from the distribution when it exits the horn.     

On the theory of diffraction radiation

A macroscopic theory of diffraction radiation emerging when a charged point particle moves in the vicinity of a perfectly conducting screen is developed. The integral equations derived for radiation fields form the basis for analyzing the similarity and difference of diffraction of electromagnetic radiation and diffraction radiation from a charged particle. It is shown that in the case considered here, the widely used model in which the radiation field can be represented as the field of surface current has more stringent limits of application as compared to the classical theory of diffraction. This considerably restricts the applicability of the results obtained earlier using the double-layer method to only ultrarelativistic energies and to transit angles of particles close to the direction of the normal to the screen surface. The method developed here is used for analyzing familiar problems of diffraction radiation, such as radiation emerging during normal transit of a particle along the axis of a circular aperture in the screen, radiation emitted during oblique transit near a perfectly conducting half-plane, and radiation emitted during oblique transit of a particle through a rectangular slit in an infinitely large screen. In the latter case, the results obtained after the limiting transition to zero width of the slit completely coincide with the theory of transition radiation for arbitrary energies of the particle and its angle of incidence to the screen.     

混浊介质中后向单次漫散射米勒矩阵特征

采用斯托克斯(Stokes)矢量形式,推导出当无限窄的连续光束垂直入射到混浊介质表面时,后向单次漫散射米勒(Mueller)矩阵的解析表达式。基于米氏(Mie)散射模式,详细分析了单次散射米勒矩阵元素的分布模式,以及与介质粒子数密度,粒子尺寸参量之间的关系。研究表明:单次散射米勒矩阵的方位变化随粒子数密度的增加,逐渐消失,而矩阵元素m22,m33,m23,m32随粒子数密度的变化,具有更显著的方位变化特征。矩阵元素m22,m33在方位角=45°时的值随尺寸参量的变化有一定的规律性,当尺寸参量小于某一特征参量时,其值呈下降趋势,反之则呈波动上升趋势。当介质粒子数密度以及粒子尺寸参量改变时,米勒矩阵元素强度的径向分布模式不变,即在任何方位,强度随径向距离都近似成指数规律衰减,方位变化呈周期性。     

Dependence of the temperature behaviour of the sputtering ratio on the channelled fraction of the ion beam

A method of calculation is presented for the yield of an electron excitation process by a channelled particle in a single encounter with an atomic row or plane in a crystal. It is shown that, if ψ is the initial angle between the ion trajectory and the row or plane, the number of inner-shell electrons excited is an increasing function of ψ whereas the number of outer electrons excited may decrease with increasing ψ.     

Kinetic effects in an optically excited gas

A resonance transition in a one-dimensional layer of gas contained between transparent parallel plates and optically excited by external radiation has been treated using kinetic theory. A perturbation method has been used to obtain the “first scattering” results for the velocity distribution and number density of excited atoms and the intensity of radiation at any point in the gas. Two special cases are discussed in detail: broad band excitation with inhomogeneous broadening and monochromatic excitation with homogeneous broadening. The effects of particle streaming and wall quenching are shown to produce boundary layer behavior in the excited level density which scales with the particle mean free path. In addition, line reversal of the radiation reemited from the gas is shown to occur and to be a direct result of particle streaming. Numerical and asymptotic results are presented which show these effects. These results should be pertinent to many laboratory and industrial devices in which the particle and photon mean free paths are comparable and to diagnostic techniques which use resonance fluorescence to infer excited level densities.     

Dynamics and mechanism of the Crystal II → smecticG phase transition in TB7A by a temperature‐dependent micro‐Raman study and DFT calculations

The solid to smecticG (SmG) phase transition in a Schiff base liquid crystalline compound, terepthal‐bis‐heptylaniline (TB7A), is monitored in situ by temperature‐dependent Raman microspectroscopy, using the band of a C H in‐plane bending mode as a marker. Contrary to the earlier report of a sudden wavenumber shift, the in situ measurement shows very clearly that a new Raman band at ∼1160 cm⁻¹ appears at the Crystal II → SmG transition. The dynamics of this phase transition is discussed in terms of a triple well potential below 210 K and a double well potential above 210 K. The phase transition essentially takes place as a result of intra‐molecular rotation about the long molecular axis. The optimization energy at various fixed dihedral angles, ( C C CN ) are calculated using density functional theory (DFT) at the B3LYP/6‐31G* level of theory. The relative energy at each dihedral angle is calculated relative to optimization energy obtained without any constraints and plotted as a function of dihedral angle (Φ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Features of the acoustic field of angle surface-wave transducers

The influence of process features in the fabrication of angle transducers (deviation from uniform distribution of mechanical stresses/strains over their transmitting/receiving surface) on the acoustic field of excited surface waves has been investigated. Calculation was carried out within the parabolic approximation by replacing a real angle transducer of surface waves with a linear source located on the surface of a waveguide (control object) with a nonuniform (cosine) distribution of stress amplitudes. The expressions for the stress (strains) at an arbitrary observation point for a point receiver (reflector) and for the stress averaged over the receiver plane are obtained in complex form. The coordinate dependences of the stress amplitudes and phases have been calculated for typical technological modes; the calculation results are presented as plots. It is shown that the effect of deviations from uniform distribution is strongest in the transition (from the near-to far-field) zone, where nonuniformity of displacements of 10–15% at the edges of a piezoelectric cell causes a change in their amplitude by 15–30% in comparison with uniform distribution; this must be taken into account when estimating diffraction corrections. The possibilities of experimentally verifying the degree of nonuniformity of the stress distribution over the angle-transducer surface are discussed.     

Surface-plasmon assisted Auger transitions in grazing collisions of ions with simple metal surfaces

The dependence of surface-plasmon assisted decay of excited atomic p-levels to s-levels in front of simple metal surfaces on the particle velocity parallel to the surface plane is studied within a dielectric linear-response theory. This non-radiative de-excitation channel can be rather likely, provided the atomic transition energy is close to the surface-plasmon energy. Furthermore, a strong orientational effect of this damping process on the mean orbital angular momentum of the atom is found as a consequence of the particle motion parallel to the surface plane.

The reverse process, that is, surface-plasmon assisted excitation is also discussed.