Papers by Sergey Galyamin
arXiv (Cornell University), May 7, 2023
We investigate the diffraction of a slow symmetric TM mode by an openended corrugated cylindrical... more We investigate the diffraction of a slow symmetric TM mode by an openended corrugated cylindrical waveguide with a flange. This mode can be generated, in particular, by a charged particle bunch moving along the waveguide axis. We analyze the so-called "longwave" range when the wavelengths and the waveguide radius are much greater than the corrugation period. In this case, the corrugated waveguide wall can be replaced with a smooth one on which the so-called equivalent boundary conditions (EBC) are fulfilled. Here, we also assume that the wall is deeply corrugated, i.e. the corrugation depth is of the same order as an inverse wavenumber. The approach applied uses the solution of the corresponding Wiener-Hopf-Fock equation. This solution is in turn utilized to construct an infinite linear system for reflection coefficients which can be solved numerically using the reduction technique.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Feb 1, 2018
A transverse laser-shaping optical setup using microlens arrays (MLAs), previously developed and ... more A transverse laser-shaping optical setup using microlens arrays (MLAs), previously developed and employed at Argonne Wakefield Accelerator (AWA), allows the formation of both highly uniform and modulated (patterned) beams. In the latter case, transverse modulation is imposed in the sub-millimeter scale. In the present study, we report the simulations of backward coherent transition radiation (CTR) emitted from a transversely modulated beam. We compare the case of a uniform round beam against different transverse modulation wavelengths by generating CTR on a steel target and measuring the autocorrelation function of the resulting radiation with an interferometer. We particularly focus on the differences between round and patterned beam distributions and discuss possible future applications of this setup in THz radiation generation. 1 Additionally, an analytical expression for a TR EM-field in case of a finite metallic plane can be found in [12].
7th International Particle Accelerator Conference (IPAC'16), Busan, Korea, May 8-13, 2016, Jun 1, 2016
7th International Particle Accelerator Conference (IPAC'16), Busan, Korea, May 8-13, 2016, Jun 1, 2016
* The work is supported by the Grant of the President of Russian Federation (No. 6765.2015.2) and... more * The work is supported by the Grant of the President of Russian Federation (No. 6765.2015.2) and the Grants from Russian Foundation for Basic Research (No. 15-32-20985, 15-02-03913).
IEEE Transactions on Microwave Theory and Techniques, 2022
A rigorous approach for solving canonical circular open-ended dielectric-lined waveguide diffract... more A rigorous approach for solving canonical circular open-ended dielectric-lined waveguide diffraction problems is presented. This is continuation of our recent paper [1] where a simpler case of uniform dielectric filling has been considered. Here we deal with the case of an open-ended circular waveguide with layered dielectric filling which is closer to potential applications. The presented method 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 the described waveguide is considered. A series of such modes forms the wakefield (Cherenkov radiation field) generated by a charged particle bunch during its passage along the vacuum channel axis. Calculated S-parameters were compared with those obtained from COMSOL simulation and an excellent agreement was 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.
We consider a semi-infinite open-ended cylindrical waveguide with uniform dielectric filling plac... more 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.
Physical review, Mar 29, 2017
This study analyzes the radiation produced by a point charge intersecting the interface between a... more This study analyzes the radiation produced by a point charge intersecting the interface between a vacuum and a chiral isotropic medium. We deduce analytical expressions for the Fourier components of an electromagnetic field in both vacuum and medium for arbitrary charge velocity. The main focus is on investigating the far field in a vacuum. The distinguishing feature of the interface with a chiral isotropic medium is that the field in the vacuum area contains both copolarization (coinciding with the polarization of the self-field of a charge) and cross-polarization (orthogonal to the polarization of the self-field). Using a saddle-point approach, we obtain asymptotic representations for the field components in the far-field zone for typical frequency ranges of the Condon model of the chiral medium. We note that a so-called lateral wave is generated in a vacuum for certain parameters. The main contribution to the radiation at large distances is presented by two (co-and cross-) spherical waves of transition radiation. These waves are coherent and result in a total spherical wave with elliptical polarization, with the polarization coefficient being determined by the chirality of the medium. We present typical radiation patterns and ellipses of polarization.
Physical review, Nov 18, 2020
Radiation generated by a charge moving through a vacuum channel in a dielectric cone is analyzed.... more 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.
IEEE Transactions on Microwave Theory and Techniques, May 1, 2018
We consider a charged particle bunch passing along the axis of a semi-infinite open-ended circula... more We consider a charged particle bunch passing along the axis of a semi-infinite open-ended circular vacuum waveguide placed into a collinear infinite waveguide with larger radius. The rigorous solution of this problem is constructed using residue-calculus technique. Analytical expressions for the Fourier harmonics of the field components are obtained in each domain of the structure. Numerical integration over frequency is also performed and time-domain field dependencies are obtained. The analytical results are compared with the results of the numerical simulation and an excellent agreement is observed. In particular, we report on the effect of a "bunch image," a radiation pulse is generated in the coaxial area and has the form of the transverse electric field correlating with the longitudinal charge distribution within the bunch.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Jul 1, 2017
Recently we have reported on axisymmetric dielectric concentrator for Cherenkov radiation that fo... more Recently we have reported on axisymmetric dielectric concentrator for Cherenkov radiation that focuses almost the whole radiation in the vicinity of the given point (focus) located on the trajectory of the charge. Here we continue investigation of this concentrating target and analyze in more detail the field in the focal spot depending on parameters of the target. We also discuss how the concentrating properties of this device depend on variations in velocity of a moving charge.
Physical review accelerators and beams, Apr 10, 2019
We analyze the electromagnetic field (EMF) of a small bunch that moves uniformly in a circular me... more We analyze the electromagnetic field (EMF) of a small bunch that moves uniformly in a circular metal waveguide and crosses the boundary between two areas: a vacuum area and an area loaded with an anisotropic homogeneous nondispersive dielectric characterized by a diagonal permittivity tensor. Two cases are studied in detail: the bunch flies from a vacuum into the dielectric and, inversely, from the dielectric into a vacuum. In the second case, so-called Cherenkov-transition radiation (CTR) can be generated in the vacuum area of the waveguide. Exact expressions for the EMF components are obtained and investigated. A comparison between the present problems and the analogous problems in the case of an isotropic dielectric is performed. We discuss some benefits occurring from using the anisotropic dielectric. For example, anisotropic dielectric allows more efficient generation of radiation compared to the isotropic dielectric for the same bunch and geometry parameters.
Physical review accelerators and beams, Aug 6, 2019
A theoretical investigation of radiation field produced by a charge moving through the dielectric... more 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.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Jul 1, 2017
Terahertz radiation is considered as a promising tool for a number of applications. One possible ... more Terahertz radiation is considered as a promising tool for a number of applications. One possible way to emit THz waves is to pass short electron bunch through a waveguide structure loaded with dielectric [1]. In our previous papers, we have analyzed this problem in both approximate [2] and rigorous [3] formulation. However, we have encountered certain difficulties with calculations. In the present report, we are starting to develop another rigorous approach based on modematching technique and modified residue-calculus technique [4]. We consider the radiation from the openended dielectrically loaded cylindrical waveguide placed inside regular cylindrical waveguide with larger radius. We present structure of reflected and transmitted modes and typical radiation patterns from the open end of larger radius waveguide.
Physical review, Feb 6, 2019
Radiation generated by a charge moving in a vacuum channel through a dielectric cone is analyzed.... more Radiation generated by a charge moving in a vacuum channel through a dielectric cone is analyzed. The size of the conical target is assumed to be much greater than the wavelengths under consideration. We calculate the wave field outside the target using Stratton-Chu formulas ("aperture integrals"). This work focuses mainly on investigation of the electromagnetic field in the far-field area (Fraunhofer area). We calculate representative radiation patterns and show that typically the maximal radiation is generated in the direction of one of the refracted rays. However, in the specific case where the refracted ray is parallel to the symmetry axis, the maximal radiation is observed at some small (but nonzero) angle with respect to this axis. The maximum radiation in this case is much more intensive compared to all other situations. This phenomenon can be referred to as the "Cherenkov spotlight."
Journal of Instrumentation, Feb 21, 2018
Journal of The Optical Society of America B-optical Physics, Mar 19, 2015
The radiation of a charge moving in the presence of a large (compared with the wavelengths under ... more The radiation of a charge moving in the presence of a large (compared with the wavelengths under consideration) dielectric prism of two different configurations is studied: case (I), a charge moving in the channel, and case (II), a charge moving along the prism's face. The approximate method that combines an exact solution of certain "key problems" (without the external boundaries of the object) and the ray-optics technique for the field outside the prism is used. A general analytical solution of the problems is obtained, a particular case of small angles is considered, and an algorithm for computation of the radiation field is developed. The computed results are visualized in plots of the spectral density of radiation on the plane parallel to the external face of the prism. In case (I), the radiation is found to be more intensive and has a single maximum in the central plane. In case (II), the radiation can have a single maximum in the central plane (for relatively low velocities) or two lateral maxima (for an ultrarelativistic velocity).
Journal of Instrumentation, May 18, 2020
Radiation of charged particles moving in the presence of dielectric targets is of significant int... more 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.
arXiv (Cornell University), May 2, 2020
We analyze radiation of a charge moving in a vacuum channel in an anisotropic non-gyrotropic medi... more 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.
Journal of physics, Jun 1, 2010
We present a new approach to the analysis of the field of a uniformly moving charge in medium wit... more We present a new approach to the analysis of the field of a uniformly moving charge in medium with frequency dispersion. This is based on methods of complex function theory. First, we give the deduction of expressions for the field components directly from the causality principle. Second, the properties of integrands and integrals for the field components in the complex plane are discussed. Further, we use our approach for the case of a left-handed medium. The charge's field is presented as the sum of different components having clear physical interpretation: the quasi-Coulomb field, the wave field, and the plasma trace. An efficient method for computing the field is developed. Additionally, the case of a boundary between an ordinary medium and a left-handed one is considered. The phenomenon of reversed Cherenkov-transition radiation is described.
Physical Review E, Jul 29, 2013
We analyze the electromagnetic field generated by a point charge moving with a constant velocity ... more We analyze the electromagnetic field generated by a point charge moving with a constant velocity in an isotropic chiral medium. We work in the frame of the Condon dispersion model for the weak chirality and ultrarelativistic motion of the charge. We show that the field of a moving charge contains two low-frequency wave processes with right- and left-hand circular polarizations and a high-frequency wave process with a right-hand polarization. The low-frequency wave field exists at an arbitrary charge velocity and oscillates at a frequency of the order of the resonant frequency of the medium. This effect is of most importance near the charge trajectory. The high-frequency wave field arises at an ultrahigh velocity and is essential near the plane of charge dislocation for a sufficiently large offset from the trajectory. This wave field oscillates at a frequency that is considerably greater (up to several orders) than the resonant frequency of the medium. Intriguingly, both of these phenomena exist in the domain in front of the charge, thus producing the low- and high-frequency wave forerunners correspondingly.
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Papers by Sergey Galyamin