Andriy Kostyuk

Planar channelling of 855 MeV electrons in silicon: Monte Carlo simulations

A new Monte Carlo code for the simulation of the channeling of ultrarelativistic charged projectiles in single crystals is presented. A detailed description of the underlying physical model and the computation algorithm is given. First results obtained with the code for the channeling of 855 MeV electrons in Silicon crystal are presented. The dechanneling lengths for (100), (110) and (111) crystallographic planes are estimated. In order to verify the code, the dependence of the intensity of the channeling radiation on the crystal dimension along the beam direction is calculated. A good agreement of the obtained results with recent experimental data is observed.

The High ET Drop of J/ to Drell-Yan Ratio from the Statistical cCoalescence Model

The dependence of the J/ψ yield on the transverse energy ET in heavy ion collisions is considered within the statistical c coalescence model. The model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the high-ET region (ET 100 GeV). Here ET fluctuations and ET losses in the dimuon event sample naturally create the celebrated drop in the J/ψ to Drell–Yan ratio.

The influence of the structure imperfectness of a crystalline undulator on the emission spectrum

We study the influence of an imperfect structure of a crystalline undulator on the spectrum of the undulator radiation. The main attention is paid to the undulators in which the periodic bending in the bulk appears as a result of a regular (periodic) surface deformations. We demonstrate that this method of preparation of a crystalline undulator inevitably leads to a variation of the bending amplitude over the crystal thickness and to the presence of the subharmonics with smaller bending period. Both of these features noticeably influence the monochromatic pattern of the undulator radiation.

Stable propagation of a modulated positron beam in a bent crystal channel

The propagation of a modulated positron beam in a planar crystal channel is investigated. It is demonstrated that the beam preserves its modulation at sufficiently large penetration depths, which opens the prospect of using a crystalline undulator as a coherent source of hard x-rays. This finding is a crucial milestone in developing a new type of laser radiating in the hard x-ray and gamma-ray range.

A One-dimensional model of a gamma klystron

A new scheme for amplification of coherent gamma rays is proposed. The key elements are crystalline undulators—single crystals with periodically bent crystallographic planes exposed to a high-energy beam of charged particles undergoing channeling inside the crystals. The scheme consists of two such crystals separated by a vacuum gap. The beam passes the crystals successively. The particles perform undulator motion inside the crystals following the periodic shape of the crystallographic planes. Gamma rays passing the crystals parallel to the beam get amplified due to interaction with the particles inside the crystals. The term gamma klystron is proposed for the scheme because its operational principles are similar to those of the optical klystron. A more simple one-crystal scheme is considered as well for the sake of comparison. It is shown that the gamma ray amplification in the klystron scheme can be reached at considerably lower particle densities than in the one-crystal scheme, provided that the gap between the crystals is sufficiently large.Communicated by Professor J Aichelin

Comment on ‘Radiation from multi-GeV electrons and positrons in periodically bent silicon crystal’

Simulations of electron and positron channelling in a crystalline undulator with a small amplitude and a short period (A Kostyuk, Phys. Rev. Lett. 110 (2013) 115503) have been repeated by V G Bezchastnov, A V Korol and A V Solovyov (J. Phys. B: At. Mol. Opt. Phys. 47 (2014) 195401) for exactly the same parameter set but using a different model of projectile scattering by crystal atoms implemented in another computer code. The authors of the latter paper claim that their approach, in contrast to the one of the former paper, allows them to observe short-period undulator oscillations in plots of simulated trajectories. In fact, both approaches can be shown to give the same amplitude of the undulator oscillations. In both cases, the undulator oscillations become visible on trajectory segments having small amplitude of channelling oscillations. The claim of Bezchastnov et al. that their model is more accurate is unfounded. In fact, there are indications of severe mistakes in their calculations.

Demodulation of a positron beam in a bent crystal channel

Abstract The evolution of a modulated positron beam in a planar crystal channel is investigated within the diffusion approach. A detailed description of the formalism is given. A new parameter, the demodulation length, is introduced, representing the quantitative measure of the depth at which the channelling beam preserves its modulation in the crystal. It is demonstrated that there exist crystal channels with the demodulation length sufficiently large for using the crystalline undulator as a coherent source of hard X-rays. This finding is a crucial milestone in developing a new type of lasers radiating in the hard X- and gamma-ray range.