A. Mazzolari

Shaping of silicon crystals for channelling experiments through anisotropic chemical etching

We present an idea and its development to realize crystals for channelling experiments, which result in significant improvement of the crystal quality with respect to the traditional methods of fabrication. The technique relies on non-conventional usage of the established technique of the anisotropic etching of silicon in micro-machining. Morphological and structural analyses were carried out through electron and scanning-probe microscopy to show that the crystal exhibited flat surfaces with atomically sharp termination, i.e. no appreciable surface damage was induced by the preparation. Thereby, the crystal meets the stringent requirements that are demanded for operation with high-energy beams and in particular for halo collimation in modern hadron colliders.

Optimal crystal surface for efficient channeling in the new generation of hadron machines

The new generation of hadron machines may profitably take advantage of channeling for steering and collimation of high-energy particle beams. In that case, the requirements on the quality of the crystal surface are rather stringent in terms of both lattice perfection and roughness. Here, the authors show the structural and morphological characterizations of crystals fabricated through a method to achieve a surface that fulfills all needed specifications for application in hadron machines.

High diffraction efficiency with hard X-rays through a thick silicon crystal bent by carbon fiber deposition

The diffraction capability of two crystalline silicon plates bent by carbon fiber deposition has been studied. The performed treatment induced a permanent curvature in the samples, resulting in an increase of the diffraction efficiency. The obtained efficiencies are constant over a wide angular range and close to the theoretical expectations, meaning that the curvatures were homogeneous. Most importantly, the bending technique allowed the manufacture of bent samples up to 5 mm thick and with a radius of curvature down to 30 m. With such a technique, the fabrication of crystals for the realization of a hard X-ray concentrator (Laue lens) for astrophysical purposes is enabled.

Apparatus to study crystal channeling and volume reflection phenomena at the SPS H8 beamline

A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeV/c protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 murad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeV/c protons proved true with a deflection angle of (10.4+/-0.5) murad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam.

Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal

A crystalline undulator consists of a crystal with a periodic deformation in which channeled particles undergo oscillations and emit coherent undulator radiation. Patterning by an alternate series of tensile Si3N4 strips on a Si crystal is shown to be a tractable method to construct a crystalline undulator. The method allows periodic deformation of the crystal with the parameters suitable for implementation of a crystalline undulator. The resulting periodic deformation is present in the bulk of the Si crystal with an essentially uniform amplitude, making the entire volume of the crystal available for channeling and in turn for emission of undulator radiation.

Note: Rigid holder to host and bend a crystal for multiple volume reflection of a particle beam

A holder to lodge and bend a silicon crystal to excite multivolume reflection of a high-energy particle beam has been designed and fabricated. A mechanically robust and stable structure fastens a crystal at best condition for experiments. The holder has allowed the observation of 12-time repeated volume reflection with very high efficiency. We detail the most important features behind the construction of the holder together with the characterization of the crystal being bent by the holder.

Experimental evidence of independence of nuclear de-channeling length on the particle charge sign

Under coherent interactions, particles undergo correlated collisions with the crystal lattice and their motion result in confinement in the fields of atomic planes, i.e. particle channeling. Other than coherently interacting with the lattice, particles also suffer incoherent interactions with individual nuclei and may leave their bounded motion, i.e., they de-channel. The latter is the main limiting factor for applications of coherent interactions in crystal-assisted particle steering. We experimentally investigated the nature of de-channeling of 120 GeV/c

Steering of an ultrarelativistic proton beam by a bent germanium crystal

e^{-}