Transition Radiation Energy Research Articles

Резонансное взаимодействие переходного излучения заряженной частицы с периодически модулированным в пространстве анизотропным магнитодиэлектрическим заполнением волновода

The peculiarities of the interaction of the transition radiation of a charged particle with periodically modulated in space anisotropic magnetodielectric medium in the waveguide in the frequency region of the strong (resonant) interaction of the radiation with the modulated medium are considered. It is assumed that the charged particle moves with constant velocity perpendicular to the axis of the waveguide. Analytical expressions are obtained for the energy of transition radiation of transverse-electric (TE) and transverse-magnetic (TM) fields in the waveguide in the region of strong interaction with an accuracy of small modulation indexes in the first degree inclusive. Analytical expressions for the frequency and for the width of the frequency region of strong interaction are found. The possibility of the appearance of Cherenkov radiation in the region of strong interaction in the case of a rectangular waveguide is analyzed.

Transition radiation excited by a surface load that moves over the interface of two elastic layers

Transition radiation is emitted when a perturbation source such as an electric charge or mechanical load, which has no inherent frequency, moves along a straight line at constant velocity in or near an inhomogeneous medium. Transition radiation of elastic waves is emitted, for example, by the wheels of a train due to track inhomogeneities such as non-uniform subsoil. This type of radiation was analyzed in the framework of several 1-D and 2-D elastic systems, but very few studies focus on elastic continua. Here, we consider a continuum consisting of two elastic layers (i.e., waveguides) that are coupled at a vertical interface. Both layers are in plane strain, have a free surface and are fixed to a rigid bottom, while the load is assumed to move along the free surface and over the layer interface. The response in each layer consists of the stationary eigenfield that moves with the load and a free field that propagates independently. The latter is expanded into a set of propagating and evanescent guided modes, while all fields are coupled at the interface. Orthogonality relations are employed to find the modal coefficients. Results show that the transition radiation energy (i.e., the energy flux through a surface far away from the layer interface) becomes powerful for load velocities approaching the critical velocity or for high contrast in material parameters. Furthermore, the free-field contribution to the energy flux through a circular surface close to the layer interface exhibits peculiar directivities. Depending on the contrast in material parameters and the load velocity, it can be extreme along the free surface, along the layer interface or into the medium. The free-field contribution can dominate that of the eigenfield for high load velocities, as is the case for the transition radiation energy. To study the features of the generated wave field in pure form, we take the load velocity sub-critical throughout the paper, excluding other radiation effects. However, the adopted solution is not restricted to that and is expected to work also for layered media, even when connected to other elastic structures like beams.

Covariant formulation of the transition radiation energy spectrum of an electron beam at a normal angle of incidence onto a round metallic screen

In the formal expression of the transition radiation (TR) energy spectrum of an N electron bunch, the electron spatial coordinates leave the mark of the temporal causality and covariance constraints. In the case of normal incidence, the distribution of the N electron longitudinal coordinates determining indeed the temporal sequence of the N electron collisions onto the metallic screen rules the emission phases of the N single electron radiation field amplitudes from the metallic surface according to a causality constraint. The role of the N electron transverse coordinates goes beyond the determination of the relative phase distribution of the N electron field amplitudes at the observation point as a function of the transverse displacement of the N electrons with respect to the beam axis. The distribution of the transverse coordinates of the N electrons being a relativistic invariant under a Lorentz transformation with respect to the direction of motion of the beam is expected to leave a covariant mark on the radiation field amplitudes of the N single electrons and, consequently, on both the temporal coherent and incoherent parts of the TR energy spectrum. Compared to the ideal case of a single electron hitting an infinite metallic screen, the covariance of the TR energy spectrum is expected to manifest itself, with the decrease of the beam transverse size, as an asymptotic increase and broadening, respectively, of the radiation spectral intensity and of the corresponding angular distribution. In the case of a round metallic screen with an arbitrary radius, the formal expression of the TR energy spectrum will be derived and numerical results will be presented.

Transition radiation of elastic waves at the interface of two elastic half-planes

Radiation of elastic waves is studied that is emitted by a point load that crosses the interface of two elastic half-planes. It is assumed that the load has a constant magnitude, moves along a straight line normal to the interface, and has a constant speed that is smaller than the minimum shear wave speed in the half-planes. In this case the mechanism of excitation of elastic waves is conventionally referred to as transition radiation. The adopted model allows to obtain an analytical expression for the elastic field excited by the load in the frequency–wavenumber domain. Using this expression, the energy of transition radiation is derived in a closed form. It is shown that transition radiation of the body waves occurs at any non-zero velocity of the load. Additionally, transition radiation of interface waves may occur provided that parameters of the half-planes allow existence of Stoneley waves. A parametric analysis of the directivity diagram of radiated body waves is accomplished focusing on dependence of the diagram on the load speed, load direction, and parameters of the half-planes. Using parameters that allow radiation of interface waves, the energy of this radiation is compared to that of the body waves. It is shown that the energy of the interface waves is greater unless the load velocity is close to the lowest body wave velocity.

Transition radiation energy loss in inductively coupled argon plasma

This work studies the transition radiation energy loss in inductively coupled argon plasma. Energy loss channels due to ionization, momentum transfer, and radiation are investigated in argon plasma bounded by a cylindrical metal vessel. Radiation energy is calculated using the electron energy distribution function diagnosed by a Langmuir probe and the emission cross section. The measured electron energy is found to feature a Druyvesteyn-like distribution. Detailed emission lines and their relative intensity are investigated using high resolution optical emission spectroscopy. Radiation energy loss due to the blue lines (mainly 5p→4s transition) and red-IR lines (4p→4s transition) appears less prominent than that of the two ultraviolet emission lines originated from the transitions of the two lowest resonant levels to the ground state. Approximately 30% collisional energy loss is responsible for ionization, whereas only a few percent of the energy loss is attributed to elastic collision. Most energy loss is due to the transition radiation emission. These findings are remarkably important for controllable plasma aided materials processing.

X-ray transition radiation energy loss of relativistic charge in absorbing media

The theory of X-ray transition radiation is generalised to the case of absorbing media. The energy-angle distributions of the mean number of X-ray transition radiation photons produced by a relativistic charged particle crossing an interface between absorbing media are derived for different geometries. The models describing different practical radiators are implemented in the framework of the G EANT4 package. The calculations are in satisfactory agreement with experimental data for the energy loss distributions measured in gaseous proportional detectors.

Conceptual design of a charged particle beam energy spectrometer utilizing transition radiation grating

A new technique of measuring the energy spectrum of a charged particle beam using optical transition radiation is presented in this paper. The charged particle beam energy spectrum can be studied by analyzing the optical spectrum of the optical transition radiation produced in a multi-foil configuration. This type of energy spectrometer can have a very large energy acceptance which can not be matched by a simple conventional magnetic dipole spectrometer. The theory of transition radiation from a single boundary and from a foil with finite thickness are reviewed. Multi-foil transition radiation theory and its application for charged particle beam energy spectrum measurement are presented. The practical issues which may affect the performance of a multi-foil transition radiation energy spectrometer are discussed.

A Monte Carlo program to design a transition radiation detector

A Monte Carlo program to design a transition radiator detector is described. The program provides the possibility to calculate the X-ray yield from radiators of different materials and structures, and analyzes the transition radiation energy release in various gaseous detectors.