arXiv subjects

Andrey V. Tyukhtin

Publications and source records attributed to Andrey V. Tyukhtin.

15 recordsLinked to original sources

arXiv2023

Radiation of a variable charge flying into medium

We study an electromagnetic radiation of a small bunch having a variable charge value and crossing a flat interface between two media. Both media are homogeneous, stationary, and isotropic. They may have frequency dispersion but no spatial dispersion. Cherenkov radiation can be generated in the second medium only. It is assumed that the bunch charge value decreases exponentially starting from some time moment after the charge enters the second medium. This means that we take into account the scatter of the particle path lengths, connected with a statistical nature of energy losses of particles. It is taken into account that the filamentous trace consisting of immobile charges is formed in the second medium. We obtain the general solution of the problem. The asymptotic study for the wave zone is carried out. We obtain expressions for the spherical wave as well as for the cylindrical wave generated in the second medium if the charge velocity is sufficiently high. The main properties of radiation are described. If the process of the bunch decay starts from the boundary between media, then the angular distribution of the radiation energy has the single maximum in each from two regions. In the second medium, the radiation, as a rule, is greater than in the vacuum area, and this difference increases with increasing the charge velocity. If the charge velocity is higher than the speed of light in the second medium, then, along with appearance of Cherenkov radiation, the properties of spherical wave change radically. In particular, the main maximum of the angular distribution of the radiation energy increases sharply. If the distance from the charge entry point to the region of the bunch decay is sufficiently large, then the complex interference pattern with many extrema take place.

physics.class-ph↗

arXiv2023

Radiation of a bunch in a waveguide having areas with deeply corrugated and smooth walls

We analyze radiation from a bunch that uniformly moves in a circular waveguide and crosses the boundary between two areas: with a corrugated wall and with a smooth wall. It is assumed that the corrugation period is much less than the wavelengths under consideration. However, in difference with our pervious works, the corrugation depth is of the same order as the wavelength. The influence of corrugation on the electromagnetic field is investigated using the method of equivalent boundary conditions. At first, we consider a regular corrugated waveguide. Then two cases of the waveguides with boundaries between the corrugated and smooth regions is studied: first, when the bunch flies out of the corrugated part into the smooth one, and second, when the bunch flies into the corrugated part from the smooth one. We obtain and analyze the analytical expressions for the field components in both areas and reveal the main physical peculiarities of the bunch radiation.

physics.acc-ph↗

arXiv2022

Radiation of Charge Moving along Face of Inverted Prism

Cherenkov radiation (CR) generated by a charge moving along one of the faces of a dielectric prism is analyzed. Unlike our previous papers, here we suppose that the charge moves from the the prism ``nose'' to its base. For CR analysis, we use the technique described in our previous papers and called the ``aperture method''. However, here we develop a new version of this technique which is suitable for objects with plane faces: it utilizes field expansion only over plane waves inside the object. This approach is especially convenient for objects having two or more plane interfaces on which the waves are reflected and/or refracted. Using this technique, we obtain the electromagnetic field distribution over the aperture and then apply Stratton-Chu formulas (aperture integrals). Further, the main attention is paid to the calculation of the radiation field in the Fraunhofer (far-field) area. It is notable that we obtain expressions for corresponding Fourier transforms in the form of single integrals. Using them, the series of typical angular diagrams are computed and physical conclusions are made.

physics.class-ph↗

arXiv2022

Radiation of a charge moving at an angle to the face of a dielectric prism

Cherenkov radiation which generates by a charge moving in presence of a dielectric prism from the base to the top is analyzed. Unlike our previous works, here we consider the case when the charge trajectory is not parallel to the prism face. We apply a new version of the aperture method which uses the expansion in terms of plane waves in the prism material and on the aperture. The integrals for the radiation field are calculated analytically in the Fraunhofer region where the field components are written as single integrals. The influence of the incline of the charge trajectory on the radiation characteristics is discussed.

physics.acc-ph↗

arXiv2021

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.

physics.class-ph↗

arXiv2021

Radiation of a Bunch Crossing a Boundary between a Vacuum and Cold Magnetized Plasma in a Waveguide

We analyze the electromagnetic field of a small bunch that uniformly moves in a circular waveguide and transverses a boundary between an area filled up with cold magnetized electron plasma and a vacuum area. The magnetic field is supposed to be strong but finite so the perturbation technique can be applied. Two cases are studied in detail: the bunch is flying out of the plasma into a vacuum, and, inversely, the bunch is flying into the plasma out of the vacuum area of waveguide. The investigation of the waveguide mode components is performed analytically with methods of the complex variable function theory. The main peculiarities of the bunch radiation in such situations are revealed.

physics.plasm-ph↗

arXiv2020

Energy loss reduction of a charge moving through an anisotropic plasma-like medium

We analyze radiation of a charge moving in a vacuum channel in an anisotropic non-gyrotropic medium with plasma-like components of the permittivity tensor. The expressions for field components are obtained and analyzed. It is shown that the field contains both the radiation field and the plasma oscillations. Most attention is focused on the energy loss of the charge per the unit path length. The dependencies of the loss on the charge velocity and the plasma frequencies are studied. The relative roles of radiation loss and polarization one are considered. The most interesting result is that the energy loss is negligible when one of the permittivity tensor components is equal to 1, and the charge velocity tends to the speed of light in vacuum. This effect can be promising for applying in collimators of ultrarelativistic bunches.

physics.acc-ph↗

arXiv2020

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.

physics.acc-ph↗

arXiv2020

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.

physics.acc-ph↗

arXiv2020

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.

physics.acc-ph↗

arXiv2020

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.

physics.acc-ph↗

arXiv2020

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.

physics.acc-ph↗

arXiv2019

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.

physics.acc-ph↗

arXiv2019

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.

physics.acc-ph↗

arXiv2018

Radiation of a Charge Exiting Open-Ended Waveguide with Dielectric Filling

We consider a semi-infinite open-ended cylindrical waveguide with uniform dielectric filling placed into collinear infinite vacuum waveguide with larger radius. Electromagnetic field produced by a point charge or Gaussian bunch moving along structure's axis from the dielectric waveguide into the vacuum one is investigated. We utilize the modified residue-calculus technique and obtain rigorous analytical solution of the problem by determining coefficients of mode excitation in each subarea of the structure. Numerical simulations in CST Particle Studio are also performed and an excellent agreement between analytical and simulated results is shown. The main attention is paid to analysis of Cherenkov radiation generated in the inner dielectric waveguide and penetrated into vacuum regions of the outer waveguide. The discussed structure can be used for generation of Terahertz radiation by modulated bunches (bunch trains) by means of high-order Cherenkov modes. In this case, numerical simulations becomes difficult while the developed analytical technique allows for efficient calculation of the radiation characteristics.

physics.acc-ph↗