Comment on `Radiation from multi-GeV electrons and positrons in periodically bent silicon crystal'

TL;DR

This paper critiques a recent simulation study on electron and positron channeling in crystalline undulators, arguing that the claimed improvements and observed oscillations are not substantiated and contain errors.

Contribution

It provides a detailed comparison of two simulation approaches, challenging claims of increased accuracy and the observation of short-period undulator oscillations.

Findings

Both simulation methods show similar undulator oscillations.

The claimed 'more accurate' model has inconsistencies and errors.

Observed oscillations are not unique to the new approach.

Abstract

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) were repeated by V G Bezchastnov, A V Korol and A V Solov'yov (J. Phys. B: At. Mol. Opt. Phys. 47 (2014) 195401)for the same parameter set but using another computer code, MBN Explorer, which implements a different model of projectile scattering by crystal atoms. 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, the undulator oscillations become visible on trajectory segments which have a small amplitude of channelling oscillations. This is equally true for both approaches. The claim of Bezchastnov et al. that their model is "more accurate" is unfounded. Moreover, there are indications of severe mistakes in their calculations: the phases of undulator oscillations in the trajectories obtained with MBN Explorer are inconsistent with each other and with well established properties of forced oscillations.