X-ray characterization of self-standing bent Si crystal plates for Large Hadron Collider beam extraction

Abstract

Bent crystals can be used to deflect high‐energy charged particles for beam extraction and/or beam collimation at accelerator facilities, thanks to the channelling phenomenon. In the present paper, two perfect silicon mono‐crystals were bent using two different methods: sandblasting and the application of a carbon fibre composite. In particular, these samples were obtained for the realization of bent crystal prototypes to be used to steer the 7 TeV proton beam of the Large Hadron Collider in the context of the CRYSBEAM project. The two bending methods were selected since they allow a very homogeneous curvature of the crystals to be obtained, which is essential for high channelling efficiency. Moreover, the deformation obtained is self‐standing, i.e. there is no need for any external device to keep the samples bent. Self‐standing curvature can be useful because the presence of an external bender could be a severe limitation in the collider beam‐pipe. The curvature of the samples was measured through high‐energy X‐ray diffraction at the ID11 beamline of the European Synchrotron Radiation Facility in Grenoble, France. Since the diffraction efficiencies obtained were in good agreement with theoretical expectations, it follows that the manufacturing techniques did not damage the samples, i.e. the crystallographic quality was preserved. Finally, the crystal quality of the sandblasted sample was investigated in detail at the synchrotron source at Karlsruhe Institute of Technology by X‐ray white‐beam topography. The measurements showed no diffusion of defects from the machined surfaces to the crystal bulk.

Bent Crystal Design and Characterization for High-Energy Physics Experiments

“…This was the case for proton beam extraction in several accelerator such as the 8.4 GeV Synchrophasotron [15], 50 GeV U-70 [47], 450 GeV SPS [19] and 900 GeV Tevatron [48]. Primary curvature was taken in consideration as well for 7 TeV proton beam extraction of LHC beam halo, in the Crysbeam project [49]. Another application where primary curvature was successfully exploited is the spin precession of fast decaying particles during planar channeling.…”

“…Indeed, diffraction in a perfect flat crystal occurs only in a narrow angular range defined as Darwin width, while in a bent crystal such range is increased of the angle subtended by the lattice planes arc bathed by the X-rays beam. Optimal conditions to measure curvature with this method are found at synchrotron beamlines thanks to the intense and monochromatic hard X-rays beam available, featuring photons capable to penetrate the bulk of the crystal and diffract on the very bent planes that will be exploited during channeling [49]. The uniformity of the curvature can be estimated by the intensity of the diffracted beam during rotation of the sample.…”

Silicon crystals for steering high-intensity particle beams at ultrahigh-energy accelerators

“…Various approaches have been developed to achieve the needed deformation state: the most investigated are based on the action of a mechanical bender imparting the wanted deformation to the crystal. Alternative approaches are under investigation: they are based on the deposition of thin (few tens of nanometer thick) films generating stress in the crystal [91] or machining of a crystal surface to generate a superficially thin damaged layer under controlled conditions (ion implantation [92], sandblasting [93,94], grinding [95], surface grooving [96,97]). Independently from the method used to deform the crystal, it is important to avoid unwanted deformations of the crystal itself.…”

X-ray phase-contrast topography to measure the surface stress and bulk strain in a silicon crystal

“…No phase delay occurs in the transmissions. This is not true if the blade surfaces are differently stressed (Camattari et al, 2020;Ferrari et al, 2020). In this case, there is a strain gradient along the blade depth and the phase difference between the transmitted and reflected rays is set by the displacement field on the entrance surface (Mana & Palmisano, 2004;Apolloni et al, 2008).…”