71 research outputs found
Geometrical optics method in the theory of channeling of high energy particles in crystals
The process of scattering of fast charged particles in thin crystals is
considered in the transitional range of thicknesses, between those at which the
channeling phenomenon is not developed and those at which it is realized. The
possibility is shown of application of the methods of geometrical optics for
description of the scattering process. The dependence is studied of the total
scattering cross-section of ultrarelativistic positrons on target thickness in
this range of crystal thicknesses. In the case of ultrarelativistic particles
channeling the possibility is shown of the existence of an effect analogical to
the Ramsauer-Townsend effect of conversion into zero of the total scattering
cross-section at some values of crystal thickness. The important role is
outlined of the Morse-Maslov index that enters into the wave function
expression in the geometrical optics method.Comment: 6 pages, 2 figure
Transition radiation on semi-infinite plate and Smith-Purcell effect
The Smith-Purcell radiation is usually measured when an electron passes over
the grating of metallic stripes. However, for high frequencies (exceeding the
plasma frequency of the grating material) none material could be treated as a
conductor, but ought to be considered as a dielectric with plasma-like
permittivity. So for describing Smith-Purcell radiation in the range of high
frequencies new theoretical approaches are needed. In the present paper we
apply the simple variant of eikonal approximation developed earlier to the case
of radiation on the set of parallel semi-infinite dielectric plates. The
formulae obtained describe the radiation generated by the particles both
passing through the plates (traditionally referred as "transition radiation")
and moving in vacuum over the grating formed by the edges of the plates
(traditionally referred as "diffraction radiation", and, taking into account
the periodicity of the plates arrangement, as Smith-Purcell radiation).Comment: Submitted to Journal of Physics: Conference Serie
On spectral method in the axial channeling theory
The quantization of the transverse motion energy in the continuous potentials
of atomic strings and planes can take place under passage of fast charged
particles through crystals. The energy levels for electron moving in axial
channeling regime in a system of parallel atomic strings (for instance, [110]
strings of a silicon crystal) are found in this work for the electron energy of
order of several tens of MeV, when a total number of energy levels becomes
large (up to several hundreds). High resolution of the spectral method used for
energy level search has been demonstrated. Hence this method could be useful
for investigation of quantum chaos problem.Comment: 11 pages, 4 figures, presented on the conference "Channeling-2012",
23-28 September 2012 Alghero, Sardegna, Italy; accepted for publication in
Nuclear Instruments and Methods
On the analogies between the processes of coherent radiation at collisions of relativistic particles with bunches of relativistic particles and crystals
At scattering of relativistic bunches of charged particles the effect of a significant amplification of radiation in the region of low radiated frequencies, when the spectral density is proportional to the square number of particles in the bunch, is possible. This effect holds both for head-scattered bunches, and bunches which scattered at a small angle between their axes of motion. At the same time with an
increasing number of the particles in bunches the radiation is almost independent of the number of particles. The analogy of these effects and the effects of radiation at the passage of charged particles in matter is discussed. The analogy of the mechanisms of these radiation processes not only for coherent, but also for incoherent radiation, is shown. The possibility of usage of the coherent effect in radiation for monitoring charged particle beams is noted
On quantum spreading of a localized stationary flow of high energy particles
The study addresses the quantum spreading of a localized stationary flow of
high energy particles. Results demonstrate that as particle energy increases,
the spreading speed of the particle wave packet diminishes rapidly.
Concurrently, increasing the energies stabilizes the initially localized
packet, preserving its transverse form in a vacuum over extended distances.
This allows substantial simplifications when using various approximate methods
to calculate the wave function in an external field
Contribution of incoherent effects to the orientation dependence of bremsstrahlung from rapid electrons in crystal
The bremsstrahlung cross section for relativistic electrons in a crystal is
split into the sum of coherent and incoherent parts (the last is due to a
thermal motion of atoms in the crystal). Although the spectrum of incoherent
radiation in crystal is similar to one in amorphous medium, the incoherent
radiation intensity could demonstrate substantial dependence on the crystal
orientation due to the electrons' flux redistribution in the crystal. In the
present paper we apply our method of the incoherent bremsstrahlung simulation
developed earlier to interpretation of some recent experimental results
obtained at the Mainz Microtron MAMI.Comment: VIII International Symposium "Radiation from Relativistic Electrons
in Periodic Structures" (RREPS-09) Zvenigorod, Russia, September 7-11, 200
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