Relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal

Abstract

An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We identified a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We introduce the idea of using a short bent crystal, aligned with one of its main axis to the beam direction, as a beam steerer or a beam splitter with adjustable intensity in the field of particle accelerators. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels.

Influence of incoherent scattering on stochastic deflection of high-energy negative particle beams in bent crystals

“…This is the result of the strong contribution of incoherent scattering on thermal vibrations of atoms and scattering on electrons on particle dynamics in crystals for the case of negative particles. Conversely, for the case of positive particles (see [10]), l e grows with R 2 and hence α e grows with R. The same linear growth we see for the case of the above-barrier beam in the ideal crystal (dashed line in Fig. 5).…”

“…The result of simulation is displayed in Fig. 3-dashed curve, which show a parabolic dependence of l e from R, well representing the case of motion of over-barrier positive particles under stochastic deflection regime [10].…”

“…The third mechanism called stochastic deflection consists of the scattering of above-barrier particles in the field of bent crystal atomic strings. This mechanism was proposed in [8] and experimentally observed in [9][10][11] and [12] for positively and negatively charged particles, respectively. Recently, stochastic deflection was observed in the U-70 accelerator of the Institute for High Energy Physics (Protvino, Russia) [13].…”

“…In other words, for a crystal bent to a curvature radius R, the relaxation length l e determines the maximum crystal length for efficient steering of particles at the full bending angle. In [10], the dependence of l e vs. R was found for 400 GeV/c protons. This dependence To analyze the same dependence of l e from R for the case of negatively charged particles, we carried out numerical simulation of 150 GeV/c π − -mesons dynamics in the field bent atomic strings that are parallel to the 110 silicon crystal axis.…”

“…The Monte Carlo code was the same as in Refs. [10,19,20]. The code solves the equation of motion in the field of continuum atomic string potential through numerical integration and also takes into account the contribution of incoherent scattering on thermal vibrations of atoms and scattering on electrons.…”