Observation of channeling and volume reflection in bent crystals for high-energy negative particles

Abstract

Deflection due to planar channeling and volume reflection in short bent silicon crystals was observed for the first time for 150 GeV/c negative particles, pi(-) mesons, at one of the secondary beams of the CERN SPS. The deflection efficiency was about 30% for channeling and higher than 80% for volume reflection. Volume reflection occurs, in spite of the attractive character of the forces acting between the particles and the crystal planes, in a wide angular range of the crystal orientations determined by the crystal bend angle

Manufacturing and characterization of bent silicon crystals for studies of coherent interactions with negatively charged particles beams

“…The key factors which lead to spread of this technology in worldwide accelerators were the increasing of channeling efficiency and the discovery of the VR effect, both achieved thanks to the advent of innovative crystal manufacturing processes [12][13][14] and geometries [15][16][17]. A high steering efficiency, both with channeling ($80%) and VR (more than 95%), was obtained with positive particles [18,19], while, comparatively, very little has been achieved concerning steering of negatively charged particle beams in bent crystals [20][21][22][23][24]. In fact, since positive particles are repulsed by the nuclei, whose repulsive effect is only partially screened by core electrons, the trajectories of channeled positive particles are bounded far from the region with the highest atomic density, therefore they do not significantly suffer collisions on them.…”

The experimental setup of the Interaction in Crystals for Emission of RADiation collaboration at Mainzer Mikrotron: Design, commissioning, and tests

“…1,6 With the aim of developing innovative crystal-based solutions for beam extraction, collimation, and steering, several experiments were performed in the last decades leading to an increase of the CH and VR efficiencies: thanks to the advent of new solutions for the crystal geometries 7 and the fabrication methods, 8,9 high deflection efficiency values (up to 80% and 97% in the CH and VR regimes, respectively) have been obtained with positive particles in the 10-400 GeV energy range. 1,6,10 By contrast, very little has been achieved concerning the steering of negative particle beams in bent crystals; 11,12 negative particles are in fact "captured" around the crystal planes/axes and in turn are more subjected to the so-called DeChanneling (DC) effect (i.e., the particle release from the CH condition caused by the scattering with the crystalline medium 1 ). This results in a shorter dechanneling length (L DC ) for negative particles with respect to the one for positive particles in the same conditions (beam energy and used crystal) 1 and the situation becomes worse decreasing the particle energy.…”

Channeling efficiency dependence on bending radius and thermal vibration amplitude of the model for the channeling of high-energy particles in straight and bent crystals implemented in Geant4

“…For this purpose, the usage of orientational effect in curved crystal [1,2] was proposed as a realistic solution. The usage of bent crystals proved the capability to steering both positively [3,4] and negatively [5,6] charged particle beams. In particular, the usage of bent crystals as a primary collimator proved to reduce the beam losses for the SPS proton synchrotron at CERN [7][8][9], leading to the installation of two bent crystals in the LHC collider for a collimation experiment in 2015.…”