A.A. Tishchenko

Diffraction radiation from relativistic particles

Foreword Preface 1. Radiation from Relativistic Particles 2. General Properties of Diffraction Radiation 3. Diffraction Radiation at Optical and Lower Frequencies 4. Diffraction Radiation in the Ultraviolet and Soft X-Ray Regions 5. Diffraction Radiation at the Resonant Frequency 6. Diffraction Radiation from Media with Periodic Surfaces 7. Coherent Radiation Generated by Bunches of Charged Particles 8. Diffraction Radiation in the Pre-Wave (FRESNEL) Zone 9. Experimental Investigations of Diffraction Radiation Generated by Relativistic Electrons References

First experimental observation of the conical effect in Smith–Purcell radiation

The conical effect in Smith–Purcell radiation arising from electrons moving at non-zero angle to the direction of grating periodicity has been observed for the first time. It was found that the maximum of radiation intensity for ψ ≠ 0 shifts in both polar and azimuth angles. The experimental and theoretical results were compared, and the good agreement was shown. The experiment has been performed for 6 MeV electrons and at millimeter wavelengths.

Coherent effects in backward EUV and x-ray transition radiation of a bunch of electrons from thin wires

In this paper we consider X-Ray and EUV Transition radiation propagating in backward direction which is generated by the ultrarelativistic electron bunch crossing the target. The target consists of periodical set of thin wires with the rectangular cross-section. We obtain the analytical expressions for distribution of the energy of the transition radiation per solid angle and frequency. In high frequency region (X-Ray, EUV), where the wavelength of radiation is less than length of a beam, the main part of radiation is incoherent. In this case the radiation from electron bunches is described by the so called incoherent form-factor. We obtain and analyse the expression for incoherent form-factor. In this work we show that incoherent form-factor arises always when the size of a target is finite and that it depends on the ratio between the transversal size of the bunch and the production of wavelength and Lorentz-factor of the charged particles. The coherent effects of target and the electron bunch play an important role in increasing the intensity of radiation and also change the spatial distribution of radiation.

XUV Cherenkov and diffraction radiation from femtosecond electron bunch

Absorption in the medium, i.e. an imaginary part of the dielectric permittivity, can lead to arising of Cherenkov radiation at high frequencies – X-Ray and XUV. In this paper X-Ray Diffraction radiation from a bunch of ultra-relativistic electrons moving near an absorbing target is investigated theoretically. In these conditions the Cherenkov radiation arises even when trajectories of the particles does not cross the target. The spatial distribution of the radiation usually represents the cone with the axis in forward direction with thickness proportional to the imaginary part of dielectric permittivity. In this paper it is shown that taking into account the refraction and reflection of the waves at the surface of the target leads to essential changes in spatial distribution of radiation. We give analytical description of the XUV Cherenkov and diffraction radiation from the bunch of charged particles. We show that the spatial distribution of radiation is not symmetrical in relation to the top face of the target.

THz radiation under non-central propagation of electrons through periodical channel

Radiation from non-central electrons moving through channel with variable radius in the THz region is investigated using Particle In Cell (PIC) solver of the Computer Simulation Technology (CST) software package. Characteristics of radiation arising for non-central and central electrons propagation in the channel are compared, both for Smith-Purcell and Cherenkov kinds of radiation. It is demonstrated that the radiation is more intensive for the non-central propagation of electrons.

Experimental Investigations of Diffraction Radiation Generated by Relativistic Electrons

The theory of diffraction radiation was founded in the 1950s, but the first experimental investigation of the characteristics of diffraction radiation generated by relativistic electrons was carried out only in 1995 [1]. The scheme of the experiment is shown in Fig. 9.1. The measurements were performed with a 150-MeV electron beam consisting of bunches with a length of about 1 mm and a diameter of about 2.5 mm. The population of a bunch was 1.5·108e−. In the experiment, the spectrum of coherent diffraction radiation in a wavelength range of λ = 0.1−5 mm, as well as the angular distribution of forward and backward diffraction radiations, is measured. Discs with the hole diameters d=10,15,20 mm, as well as a transition radiation target (disc without hole), were used to generate coherent radiation.

Diffraction Radiation in the Pre-wave (Fresnel) Zone

The notion of the formation (coherence) length introduced in the early 1950s (see detailed references in [1,2]) was described in the framework of classical electrodynamics in Sects. 1.2 and 2.2 for bremsstrahlung and polarization radiation mechanisms, respectively. The quantum-mechanical consideration of this problem provides the identical result [2]. The notion of the formation length appeared to be useful for describing not only electromagnetic, but also strong interactions [3,4]. The main physical idea underlying the notion of the formation length for polarization emission mechanisms (including transition radiation and diffraction radiation) is the interference of the radiation fields emitted from different points of the emitting substance along particle trajectory (see Sect. 2.2). This concept is very close to the Fresnel zone widely known in optics.

Diffraction Radiation in the Ultraviolet and Soft X-Ray Regions

The majority of the problems on diffraction radiation that have been already studied theoretically were solved for ideally conducting targets. The perfect-conductivity model is applicable at large values of the imaginary part of the relative permittivity, i.e., for most metals at optical, infrared, and radio frequencies

Radiation from Relativistic Particles

It is well known that emission is the process of the formation of transverse electromagnetic waves by moving charged particles. Let us consider the emission process occurring when a relativistic charged particle moves according to the law

Coherent Radiation Generated by Bunches of Charged Particles

In one of the first works [1], where synchrotron radiation generated by an electron bunch containing N e electrons was considered, it was mentioned that, in the range of wavelengths comparable with the length of the electron bunch l B, radiation becomes coherent, i.e., the intensity of radiation generated by the bunch depends quadratically on the number of electrons in the bunch (on the “population” of the bunch).