Nondipolarity of axial channeling radiation at GeV beam energies

Abstract

We consider the nondipolarity of axial channeling radiation generated in a tungsten single crystal at electron-beam energies of several GeV. The calculations are based on the realistic axial continuous potential. It could be shown that, compared to the dipole approximation, the nondipole approximation results in a considerable variation of the channeling radiation spectrum. In a simulation of positron production via conversion of γ radiation into e þ e − pairs, the observed effect may play an important role.

New module for channeling radiation simulation in Geant4

“…The direct simulation of ChR in Geant4 would be very useful, e.g., for simulation of hybrid positron sources which might possibly be used in future electron-positron collider facilities. It has been demonstrated that the created module provides predictable results which coincide with those obtained by our former Mathematica ChR simulation codes [28,29,31,32] and available experimental data [13,47,56]. The newly created module simulates planar ChR applying the classical approach in dipole approximation.…”

“…Here we restrict to dipole ChR generated during planar channeling of electrons or positrons. A more detailed description of ChR, including dipole as well as nondipole approximations for both planar and axial channeling, is given in our previous works [27][28][29][30][31][32].…”

“…After choosing the ChR model (see diagram of class family in figure 2), one can start simulation of ChR. The simulation workflow is based on our proven codes originally worked out in Mathematica [28,29,31,32]. First one needs to calculate the continuous potential, then the particle trajectories, and finally, with the help of eq.…”

“…This approximation, however, starts to fail at particle energies of the order of 1 GeV [19][20][21][22]. Thus at higher energies, the classical treatment should account for the non-dipolarity of ChR, which is a consequence of the bound longitudinal and transverse motions [23][24][25][26][27][28][29][30][31][32].…”

“…are progressively developed, e.g. Mathematica [45] based codes [27][28][29][30][31], CRYSTRAD code based on CRYSTAL and RADCHARM ++ programs [43,46,47], or a new channeling simulation program using GPU for fast and accurate calculations [48]. The approach of combined calculations, however, extends simulation time and may also introduce additional uncertainties.…”