Channeling of particle beam in straight and bent single-wall nanotubes has been studied in computer simulations. We have found that the nanotubes should be sufficiently narrow in order to steer efficiently the particle beams, with preferred diameter in the order of 0.5-2 nm. Wider nanotubes, e.g. 10-50 nm, appear rather useless for channeling purpose because of high sensitivity of channeling to nanotube curvature. We have compared bent nanotubes with bent crystals as elements of beam steering technique, and found that narrow nanotubes have an efficiency of beam bending similar to that of crystals.
We present an idea for creation of a crystalline undulator and report its first realization. One face of a silicon crystal was given periodic micro-scratches (trenches) by means of a diamond blade. The X-ray tests of the crystal deformation due to given periodic pattern of surface scratches have shown that a sinusoidal shape is observed on both the scratched surface and the opposite (unscratched) face of the crystal, that is, a periodic sinusoidal deformation goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in crystalline undulator, a novel compact source of radiation. The wavelength λ of a photon emitted in an undulator is in proportion to the undulator period L and in inverse proportion to the square of the particle Lorentz factor γ. The minimal period L achieved presently with the electromagnetic undulators is limited to several millimeters [1], with respective restriction on the photon energy in the order of ћω=2πћγ 2 c/L. The crystalline undulators (CU) with periodically deformed crystallographic planes offer huge electromagnetic fields and could provide a quite short period L of an undulator in sub-millimeter range. This way one can also arrange for substantial amplitudes A of oscillation for the particles channeled through the undulator and thus increase the intensity of the radiation.Currently, bent crystals are largely used for channeling extraction of 70-GeV protons at IHEP (Protvino) with efficiency reaching 85% at intensity well over 10 12 particle With a strong world-wide attention to novel sources of radiation, there has been broad theoretical interest to compact crystalline undulators, with some approaches covering also nanotechnology to make use of nanotubes to guide radiating particles [4][5][6][7][8][9][10][11][12] In bent crystal channeling experiments at IHEP Protvino with 70-GeV protons, it was found that accidental micro-scratches on a crystal surface caused a deformation of the crystallographic planes to substantial depths, down to a few hundred microns as depicted in Fig. 1(a). The picture of the plane parallelism violation can be reconstructed through analysis of the profile data of 70-GeV protons channeled in crystals (ref.[15], p.120). This analysis shows that the protons in the vicinity of scratches are retained in channeling mode but do experience a substantial angular deviation following the deformation of the crystal planes. Therefore, this effect could be profitably used for creation of CU by making a periodic series of micro trenches on the crystal surface as shown on Fig. 1(b).For the first experimental proof of the method, a special diamond blade scratched one face of a silicon plate by a set of parallel trenches (grooves). A sample with dimensions of 50 x 17 x 0.48 mm 3 was prepared from commercial silicon wafer. The large polished faces of the sample were parallel to crystallographic planes (0 0 1), other faces were parallel to planes (0 1 1) and (0 1 -1). On one of the large faces of the sample, ...
Bent crystal channeling has been observed with protons and fully stripped gold ions in the Relativistic Heavy Ion Collider (RHIC). Prior to 2003, a bent crystal was installed in one ring of RHIC as the first stage of a two stage collimation system. The observed channeling efficiency was approximately 25%, less than half of original predictions. We show that this is due to a difference between the model and real Twiss parameters at the crystal location and our improved understanding of the beam halo. Collimation using the crystal was unsuccessful and raised background at the STAR detector by as much as a factor of 2 because of the low channeling efficiency. We give a report of our channeling studies in RHIC and describe our experience using the bent crystal as a collimator. The results are discussed and compared to simulations and theoretical predictions.
Abstract. IHEP Protvino has pioneered the wide practical use of bent crystals as optical elements in high-energy beams for beam extraction and deflection on permanent basis since 1989. In the course of IHEP experiments, crystal channeling has been developed into efficient instrument for particle steering at accelerators, working in predictable, reliable manner with beams of very high intensity over years. Crystal systems extract 70 GeV protons from IHEP main ring with efficiency of 85% at intensity of 10 12 , basing on multi-pass mechanism of channeling proposed theoretically and realised experimentally at IHEP. Today, six locations on the IHEP 70-GeV main ring of the accelerator facility are equipped by crystal extraction systems, serving mostly for routine applications rather than for research and allowing a simultaneous run of several particle physics experiments, thus significantly enriching the IHEP physics program. The long successful history of large-scale crystal exploitation at IHEP should help to incorporate channeling crystals into accelerator systems worldwide in order to create unique systems for beam delivery. We report recent results from the research and exploitation of crystal extraction systems at IHEP.
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