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

An investigation on stochastic deflection of high-energy negatively charged particles in a bent crystal was carried out. On the basis of analytical calculation and numerical simulation it was shown that it exists a maximum angle at which most of the beam is deflected. The existence of a maximum, which is taken in the correspondence of the optimal radius of curvature, is a novelty with respect to the case of positively charged particles, for which the deflection angle can be freely increased by increasing the crystal length. This difference has to be ascribed to the stronger contribution of incoherent scattering affecting the dynamics of negative particles that move closer to atomic nuclei and electrons. We therefore identified the ideal parameters for the exploitation of axial confinement for negatively charged particle beam manipulation in future high-energy accelerators, e.g., ILC or muon colliders

Planar channeling and quasichanneling oscillations in a bent crystal

Particles passing through a crystal under planar channeling experience transverse oscillations in their motion. As channeled particles approach the atomic planes of a crystal, they are likely to be dechanneled. This effect was used in ion-beam analysis with MeV energy. We studied this effect in a bent crystal for positive and negative particles within a wide range of energies in sight of application of such crystals at accelerators. We found the conditions for the appearance or not of channeling oscillations. Indeed a new kind of oscillations, strictly related to the motion of over-barrier particles, i.e. quasichanneling particles, has been predicted. Such oscillations, named planar quasichanneling oscillations, possess a different nature than channeling oscillations. Through computer simulation, we studied this effect and provided a theoretical interpretation for them. We show that channeling oscillations can be observed only for positive particles while quasichanneling oscillations can exist for particles with either sign. The conditions for experimental observation of channeling and quasichanneling oscillations at existing accelerators with available crystal has been found and optimized.Comment: 25 pages, 11 figure

Horizontal Newton operators and high-order Minkowski formula

In this paper, we study the horizontal Newton transformations, which are nonlinear operators related to the natural splitting of the second fundamental form for hypersurfaces in a complex space form. These operators allow to prove the classical Minkowski formulas in the case of real space forms: Unlike the real case, the horizontal ones are not divergence-free. Here, we consider the highest order of nonlinearity and we will show how a Minkowski-type formula can be obtained in this case

New approaches to the crystal collimation

Possibilities of application of the effects of multiple volume reflection in one crystal and of the channeling efficiency increase by the crystal cut or buried oxide layer are applied for the first time to the problem of crystal collimation. It is demonstrated that both these effects decrease the nuclear reaction rate in the crystal scraper and increase the average impact parameter of collisions of deflected protons with an absorber. However the crystal cut is efficient at precise crystal orientation corresponding to the channeling conditions while the MVROC effect can be applied at relatively rough crystal alignment

Electromagnetic radiation accompanying multiple volume reflection in one crystal

An interpretation of the first experiment on gamma-radiation of 120 GeV positrons experiencing multiple volume reflection from planes of one bent crystal is given. An increase of radiation of 10–20 GeV gamma quanta by multiple reflection from skewed planes is demonstrated. Also a considerable influence of the axial field on both hard and soft parts of the positron radiation spectrum is revealed

How to make coherent bremsstrahlung circularly polarized

It is shown that if high energy positrons are moving in planar channeling conditions in a bent crystal at a small angle with respect to atomic strings which form the bent channeling planes, the hard part of the spectrum of gamma radiation emitted by the positrons will be highly circularly polarized. This Circularly Polarized String-of-Strings Radiation of Positrons Channeled in Bent Crystal (CPSOSRPCHBC) can be considered as a circularly polarized coherent bremsstrahlung manifesting itself efficiently from sub-GeV up to TeV and higher positron energies. The possibility to observe the CPSOSRPCHBC at the 500MeV positron beam of Frascati National Laboratory is considered

A model for the interaction of high-energy particles in straight and bent crystals implemented in Geant4

A model for the simulation of orientational effects in straight and bent periodic atomic structures is presented. The continuum potential approximation has been adopted.The model allows the manipulation of particle trajectories by means of straight and bent crystals and the scaling of the cross sections of hadronic and electromagnetic processes for channeled particles. Based on such a model, an extension of the Geant4 toolkit has been developed. The code has been validated against data from channeling experiments carried out at CERN

Thermal stability of a strip crystal for channeling of halo particles in the Large Hadron Collider

For possible application of a silicon bent crystal as a beam collimator in the Large Hadron Collider, the thermal stability of a strip-like crystal has been studied. The thermal power generated by the beam inside the crystal has been evaluated through a simulation and used as a source in the heat equation. The equation has been solved numerically with the semi-analytical method of lines to show the thermal stability of crystal-assisted collimation with the parameters currently being considered for its exploitation. The method we presented appears to be useful for calculation of the thermal load concerning any situation involving Crystal channeling