L.Sh. Grigoryan

High power Cherenkov radiation from a relativistic particle rotating around a dielectric ball

Some characteristic features in the radiation from a relativistic electron uniformly rotating along an equatorial orbit around a dielectric ball have been studied. It was shown that at some harmonics, in case of weak absorption of radiation in the ball material, the electron may generate radiation field quanta exceeding in several dozens of times those generated by electron rotating in a continuous, infinite and transparent medium having the same real part of permittivity as the ball material. The rise of high power radiation is due to the fact that electromagnetic oscillations of Cherenkov radiation induced along the trajectory of particle are partially locked inside the ball and superimposed in nondestructive way.

Quantum-mechanical approach to planar positron channeling in a longitudinal hypersonic field

The wave function of a planar-channeled positron with energy MeV under the resonant influence of hypersound is calculated. It is found that the longitudinal hypersound changes the spectral distribution of the channeling radiation significantly. With decreasing wavelength λs of the hypersound, starting from λs=λE, where λE is the characteristic length related to one transverse oscillation of the channeled positron, a new type of radiative transition occurs. It is characterized by the stimulated enhancement of transverse energy of the positron at channeling (inverse radiative transition). When λs approaches λE/2 the inverse transitions show a resonant behaviour.

Radiation from a charged particle-in-flight from a laminated medium to vacuum

The radiation from a charged particle-in-flight from a semi-infinite laminated medium to vacuum and back,- from vacuum to the laminated medium, has been investigated. Expressions for the spectral-angular distribution of radiation energy in vacuum (at large distances from the boundary of laminated medium) were obtained for both the cases with no limitations on the amplitude and variation profile of the laminated medium permittivity. The results of appropriate numerical calculations are presented and possible applications of the obtained results are discussed.

Resonant influence of a longitudinal hypersonic field on the radiation from channeled electrons

Abstract The wave function of a planar/axially channeled electron with energy 10 MeV ⩽E≪1 GeV under the influence of a longitudinal hypersonic wave excited in a single crystal is calculated. Conditions for the resonant influence of the hypersonic wave on the quantum state of the channeled electron are deduced. Expressions for the wave function that are applicable in the case of resonance are obtained. Angular and spectral distributions of the radiation intensity from the planar/axially channeled electron are also calculated. The possibility of significant amplification of channeling radiation by a hypersonic wave is substantiated. It is found that the hypersound can excite inverse radiative transitions through which the transversal energy of the channeled electron is increased. These transitions have a resonant nature and can lead to a considerable intensification of the electron channeling radiation. In the case of axial channeling, the resonance radiation is sustained also by direct radiative transitions of the electron.

On features of the radiation from an electron moving along a helix inside a cylindrical hole in a homogeneous dielectric

Abstract The radiation from a charge moving along a helical trajectory inside a cylindrical hole in homogeneous dielectric medium is investigated. Prompted by availability of materials with large dielectric permittivity e and small absorption, we discuss the features of this type of radiation for media with e ≫ 1 . It is shown that there are high peaks in the angular distribution of radiation intensity at well-defined harmonics. The conditions are specified for the cavity-to-helix radii ratio, ρ 1 / ρ 0 , under which the angle-integrated radiation intensity on some harmonics exceeds that in the empty space. Though the amplification of radiation intensity increases with increasing e , the corresponding “resonant” values of ρ 1 / ρ 0 ratio are practically independent of the dielectric permittivity of surrounding medium. It is shown that an analogous amplification of radiation takes place essentially for the same values of ρ 1 / ρ 0 also for the radiation in a cylindrical waveguide with conducting walls. An explanation of this phenomenon is given.

Planar channeling radiation from electrons in quartz

The possibility to stimulate channeling radiation by external excitation of ultrasonic waves in a piezoelectric single crystal is predicted by theory. The experimental verification of this effect requires the knowledge of the undisturbed spectrum of channeling radiation. For the first time, planar channeling radiation from 17, 25 and 32 MeV electrons channeled in a quartz single crystal has been measured. The analysis performed bases on the application of the theory of channeling radiation. Real planar continuum potentials of a quartz single crystal, eigenvalues of channeling states and transition energies have been calculated and radiation intensities were evaluated. The corresponding calculations proved to be necessary for the unambiguous identification of the spectra of channeling radiation registered from this hexagonal crystal.

Planar channeled relativistic electrons and positrons in the field of resonant hypersonic wave

The wave function of a planar channeled relativistic particle (electron, positron) in a single crystal excited by longitudinal hypersonic vibrations (HVs) is determined. The obtained expression is valid for periodic (not necessarily harmonic) HV of desired profile and single crystals with an arbitrary periodic continuous potential. A revised formula for the wave number of HV that exert resonance influence on the state of a channeled particle was deduced to allow for non-linear effects due to the influence of HV.

On the amplification of radiant energy during channeling in acoustically excited single crystal

Abstract Numerical solutions of classical equations of motion and of total radiant energy from a relativistic electron/positron in planar channeling in a single crystal excited by longitudinal standing hypersonic (HS) wave are given. The limit on the radiant energy increase from the channeled particle at parametric resonance is determined by nonlinear effects and the amplitude of HS vibrations. The relative increase of radiant energy due to the transverse oscillations near the minima of potential energy of particle may reach ∼100% if HS vibrations are in phase with the instants of particle incidence on the crystal. For particles with energies E⩽100 MeV the achieved fit is only qualitative, because for description of channeling in this case the application of the methods of quantum theory is needed.

Radiation from an electron bunch flying over a surface wave

Abstract Radiation generated by the passage of a monoenergetic electron bunch above the surface wave excited in plane interface between homogeneous media with different dielectric constants is investigated. For the surface wave of general profile the radiation intensity is expressed via the radiated power from a single charge and bunch form factor. Various types of transverse and longitudinal distributions of electrons in the bunch have been considered including Gaussian, asymmetrical Gaussian, two Gaussian and rectangular distribution with asymmetrical exponential tails. Conditions are specified under which the coherent radiation essentially exceeds the incoherent part.

Radiation of Ultra Low Frequency Electromagnetic Waves from Atmosphere under the Influence of Strong Shock Waves

We present preliminary results from the experimental investigation of the response of the atmosphere due to the impact of powerful shock waves. The response is evidenced as ultra low frequency electromagnetic wave radiation at frequency of 2–5 kHz and in duration of 3–7 s. We hypothesize that this radiation appears due to the following process: the shock wave ionizes the neutral particles in the air and these charged and neutral particles continue their vertical motion, which forms in the trail of the shock wave. Such motion can cause the cyclotron-like radiation measured.