Surface radiation of a charged particle bunch passing through a corrugated surface with a relatively small period

We investigate radiation of a charged particle bunch moving through a corrugated planar conductive surface. It is assumed that the corrugation period and depth are much less than the wavelengths under consideration. In this case, the corrugated structure can be replaced with some smooth surface on which the so-called equivalent boundary conditions (EBC) are fulfilled. Using the EBC method we obtain expressions for the electromagnetic field of the bunch which are presented in form of spectral integrals. It is demonstrated that the bunch generates surface waves propagating along the corrugations with the light velocity. Also we present results of numerical calculations for electromagnetic field components of surface waves depending on coordinates and show that these dependences can be used for determination of the bunch size

Reversed Cherenkov-transition radiation in a waveguide partly filled with an anisotropic dispersive medium

We analyze the electromagnetic field of a bunch that moves uniformly in a circular metal waveguide and crosses a boundary between a vacuum area and an area filled with an anisotropic dispersive nonmagnetic medium. The medium is characterized by the diagonal dielectric permittivity tensor with components possessing frequency dispersion of plasma types. The investigation of the waveguide mode components is performed with the methods of the complex variable function theory. It is shown that in compliance with the parameters of the medium, Cherenkov radiation (CR) generated in the filled area of the waveguide can have reversed direction in relation to the bunch motion. CR can penetrate into the vacuum area of the waveguide, that is, the intensive reversed Cherenkov-transition radiation (RCTR) can be generated. The main properties of this radiation are described, and essential differences from the RCTR in the case of isotropic left-handed medium are revealed

Radiation of a Charge in Dielectric Concentrator for Cherenkov Radiation: Off-Axis Charge Motion

A theoretical investigation of radiation field produced by a charge moving through the dielectric concentrator for Cherenkov radiation is performed for the general case where a charge trajectory is shifted with respect to the target axis. The idea of dielectric target with specific profile of the outer surface was presented and investigated in our previous papers for the symmetric case. Here we show how non-symmetric field components generated in the bulk of target affect field distribution near the focus where strong concentration of the energy occurs. Possible applications of this target are discussed. This version also contains corrections (Appendix C) made after publication.Comment: 13 pages, 8 figure

Radiation of a charge moving along a corrugated surface with a relatively small period

We consider electromagnetic radiation of a charged particle bunch moving uniformly along a corrugated planar metallic surface. It is assumed that the wavelengths under consideration are much larger than the period and the depth of corrugation. Using the method of the equivalent boundary conditions we obtain the Fourier-transform of the Hertz vector. It is demonstrated that the ultra-relativistic bunch excites the surface waves, whereas the volume radiation is absent. Fourier-transforms of the surface wave components and spectral density of energy losses are obtained and analyzed.Comment: 7 pages, 5 figure

Radiation of a Charge in Axicon-Based Dielectric Concentrator for Cherenkov Radiation

We propose a new type of axisymmetric dielectric target which effectively concentrates Cherenkov radiation (CR) generated in the bulk of the material into a small vicinity of focus point. It can be called the "axicon-based concentrator for CR". A theoretical investigation of radiation field produced by a charge moving through the discussed radiator is performed for the general case where a charge trajectory is shifted with respect to the structure axis. The idea of dielectric target with specific profile of the outer surface was presented and developed in our preceeding papers. However, contrary to the previous configuration of such a target (which was investigated for both centered and shifted charge trajectory), the current version allows efficient concentration of CR energy from relativistic particles, making this device extremely prospective for various applications.Comment: 7 pages, 4 figures. arXiv admin note: text overlap with arXiv:1904.0518

Cherenkov Radiation from a Hollow Conical Targets: Off-Axis Charge Motion

Cherenkov radiation (CR) generated by a charge moving through a hollow conical target made of dielectric material is analyzed. We consider two cases: the charge moves from the base of the cone to its top (``straight'' cone) or from the top to the base (``inverted'' cone). Unlike previous papers, a nonzero shift of the charge trajectory from the symmetry axis is taken into account which leads to generation of asymmetric CR. The most interesting effect is the phenomenon of ``Cherenkov spotlight'' which has been reported earlier for axially symmetric problems. This effect allows essential enhancement of the CR intensity in the far-field region by proper selection of the target's parameters and charge velocity. Here we describe the influence of charge shift on CR far-field patterns paying the main attention to the ``Cherenkov spotlight'' regime. Influence of variation of the charge speed on this phenomenon is also investigated

Diffraction at the Open-Ended Dielectric-Loaded Circular Waveguide: Rigorous Approach

An elegant and convenient rigorous approach for solving circular open-ended dielectric-loaded waveguide diffraction problems is presented. It uses the solution of corresponding Wiener-Hopf-Fock equation and leads to an infinite linear system for reflection coefficients (S-parameters) of the waveguide, the latter can be efficiently solved numerically using the reducing technique. As a specific example directly applicable to beam-driven radiation sources based on dielectric-lined capillaries, diffraction of a slow TM symmetrical mode at the open end of a circular waveguide with uniform dielectric filling is considered. A series of such modes forms the wakefield (Cherenkov radiation field) generated by a charged particle bunch during its passage along the waveguide axis. Calculated S-parameters were compared with those obtained from COMSOL simulation and an excellent agreement is shown. This method is expected to be very convenient for analytical investigation of various electromagnetic interactions of Terahertz (THz) waves (both free and guided) and charged particle bunches with slow-wave structures prospective in context of modern beam-driven THz emitters, THz accererators and THz-based bunch manipulation and bunch diagnostic systems.Comment: 5 pages, 2 figure

Radiation of charge moving through a dielectric spherical target: ray optics and aperture methods

Radiation of charged particles moving in the presence of dielectric targets is of significant interest for various applications in the accelerator and beam physics. The size of these targets is typically much larger than the wavelengths under consideration. This fact gives us an obvious small parameter of the problem and allows developing approximate methods for analysis. We develop two methods, which are called the "ray optics method" and the "aperture method". In the present paper, we apply these methods to analysis of Cherenkov radiation from a charge moving through a vacuum channel in a solid dielectric sphere. We present the main analytical results and describe the physical effects. In particular, it is shown that the radiation field possesses an expressed maximum at a certain distance from the sphere at the Cherenkov angle. Additionally, we perform simulations in COMSOL Multiphysics and show a good agreement between numerical and analytical results.Comment: 8 pages, 4 figures. The XIII International Symposium "Radiation from Relativistic Electrons in Periodic Structures", September 16-20, 2019. Belgorod, Russian Federatio

Cherenkov Radiation of a Charge Flying through the "Inverted" Conical Target

Radiation generated by a charge moving through a vacuum channel in a dielectric cone is analyzed. It is assumed that the charge moves through the cone from the apex side to the base side (the case of "inverted" cone). The cone size is supposed to be much larger than the wavelengths under consideration. We calculate the wave field outside the target using the "aperture method" developed in our previous papers. Contrary to the problems considered earlier, here the wave which incidences directly on the aperture is not the main wave, while the wave once reflected from the lateral surface is much more important. The general formulas for the radiation field are obtained, and the particular cases of the ray optics area and the Fraunhofer area are analyzed. Significant physical effects including the phenomenon of "Cherenkov spotlight" are discussed. In particular it is shown that this phenomenon allows reaching essential enhancement of the radiation intensity in the far-field region at certain selection of the problem parameters. Owing to the "inverted" cone geometry, this effect can be realized for arbitrary charge velocity, including the ultra relativistic case, by proper selection of the cone material and the apex angle. Typical radiation patterns in the far-field area are demonstrated.Comment: 12 pages, 5 figure

Radiation of a charge intersecting the boundary between a homogeneous area and bilayer one in a circular waveguide

The problem of the electromagnetic field of a charge moving along the cylindrical waveguide axis is considered. The charge flies from the homogeneously filled area to the area composed of a dielectric layer and a channel. The solution is performed by representing the electromagnetic field in each waveguide area as a sum of known “forced” field (the source field in an infinite regular waveguide) and a “free” field conditioned by the transverse boundary influence. The free field is written in the form of eigenfunction expansion for corresponding waveguide area. Shown that the problem is reduced to solving an infinite system of linear algebraic equations for the free field mode amplitude. Expressions for the components of the free field “cherenkov” part are obtained using the methods of complex variable theory. It is shown that there is a compensation effect between cherenkov part of the free filed and wakefield. It leads to the decreasing of the number of the “total Cherenkov field” modes with increasing distance from the charge. The generation area border for each cherenkov mode is determined by the its group velocity. The wakefield formation process is demonstrated using the original numerical algorithm. Refs 17. Figs 2.Работа выполнена при поддержке РФФИ, грант № 15-02-03913