Simulation of CRYSTAL, the Bent Crystal Based Collimation Experiment in the SPS

Crystal collimation is a possible variant of the two-stage collimation systems used in modern accelerators, by which the collimation efficiency may be strongly enhanced. An experiment is proposed in the CERN-SPS to check the improved performance on crystal collimation. Here we present the experiment layout and we perform simulations showing in quantitative manner the expected behavior of crystal collimation in the SPS

Radiation of photons in process of charge particle volume reflection in bent single crystal

New type of radiation in crystals is predicted and investigated in computer simulation. It is shown that process of volume reflection of electrons and positrons in bent crystals is accomplished with high-power radiation of photons. Volume reflection radiation has intensity comparable with known channeling radiation, but it is less sensitive to entrance angle and sign of charge of a particle. Simulated spectra of radiation power are presented for 10 GeV and 200GeV particles.Comment: Latex, 8 pages, 4 fig

The influence of the dechanneling process on the photon emission by an ultra-relativistc positron channeling in a periodically bent crystal

We investigate, both analytically and numerically, the influence of the dechanneling process on the parameters of undulator radiation generated by ultra-relativistic positron channelling along a crystal plane, which is periodically bent. The bending might be due either to the propagation of a transverse acoustic wave through the crystal, or due to the static strain as it occurs in superlattices. In either case the periodically bent crystal serves as an undulator which allows to generate X-ray and gamma-radiation. We propose the scheme for accurate quantitative treatment of the radiation in presence of the dechanneling. The scheme includes (i) the analytic expression for spectral-angular distribution which contains, as a parameter, the dechanneling length, (ii) the simulation procedure of the dechanneling process of a positron in periodically bent crystals. Using these we calculate the dechanneling lengths of 5 GeV positrons channeling in Si, Ge and W crystals, and the spectral-angular and spectral distributions of the undulator over broad ranges of the photons. The calculations are performed for various parameters of the channel bending.Comment: published in J. Phys. G: Nucl. Part. Phys. 27 (2001) 95-125, http://www.iop.or

Total spectrum of photon emission by an ultra-relativistic positron channeling in a periodically bent crystal

We present the results of numerical calculations of the channelling and undulator radiation generated by an ultra-relativistic positron channelling along a crystal plane, which is periodically bent. The bending might be due either to the propagation of a transverse acoustic wave through the crystal, or due to the static strain as it occurs in superlattices. The periodically bent crystal serves as an undulator. We investigate the dependence of the intensities of both the ordinary channelling and the undulator radiations on the parameters of the periodically bent channel with simultaneous account for the dechannelling effect of the positrons. We demonstrate that there is a range of parameters in which the undulator radiation dominates over the channelling one and the characteristic frequencies of both types of radiation are well separated. This result is important, because the undulator radiation can be used to create a tunable source of X-ray and gamma-radiation.Comment: published in J. Phys. G: Nucl. Part. Phys. 26 (2000) L87-L95, http://www.iop.org ; 12 pages, 4 figures, LaTe

Deflection of high-energy negative particles in a bent crystal through axial channeling and multiple volume reflection stimulated by doughnut scattering

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First observation of the deflection of a 33 TeV Pb ion beam in a bent silicon crystal

For the first time, the deflection of an ultra-relativistic, fully stripped Pb82+ ion beam in a bent silicon crystal has been observed. The ions were provided by the CERN-SPS in the H4 beam at a momentum of 400 GeV/c per unit of charge. A 60 mm long silicon crystal, bent over 50 mm to give a 4 mrad deflection angle, was used in this experiment. The measured Pb ion deflection efficiency is comparable to the one obtained with protons at an equivalent ratio of momentum per charge, and is found to be about 15\% for a beam with a divergence of 35 microradians (FWHM). The interaction rate observed in a background counter is found to drop when the crystal is well aligned with the beam. This corroborates further the channeling model, which predicts that channeled ions are steered away from regions of high electron densities as well as the nuclei in the crystal

The UA9 experimental layout

The UA9 experimental equipment was installed in the CERN-SPS in March '09 with the aim of investigating crystal assisted collimation in coasting mode. Its basic layout comprises silicon bent crystals acting as primary collimators mounted inside two vacuum vessels. A movable 60 cm long block of tungsten located downstream at about 90 degrees phase advance intercepts the deflected beam. Scintillators, Gas Electron Multiplier chambers and other beam loss monitors measure nuclear loss rates induced by the interaction of the beam halo in the crystal. Roman pots are installed in the path of the deflected particles and are equipped with a Medipix detector to reconstruct the transverse distribution of the impinging beam. Finally UA9 takes advantage of an LHC-collimator prototype installed close to the Roman pot to help in setting the beam conditions and to analyze the efficiency to deflect the beam. This paper describes in details the hardware installed to study the crystal collimation during 2010.Comment: 15pages, 11 figure, submitted to JINS

Deflection and extraction of Pb ions up to 33 TeV/c by a bent silicon crystal

The first results from an experiment to deflect a beam of fully stripped, ulta-relativistic Pb ions of 400 GeV/c per unit of charge, equivalent to 33 TeV/c, by means of a bent crystal are reported. Deflection efficiencies are as high as 14%, in agreement with theoretical predictions. In a second experiment a bent crsytal was used to extract 270 GeV/c per charge Pb82+ (22 TeV/c) ions from a coasting beam in the CERN-SPS, and a high extraction efficiency of up to 10% was found. These represent the first measurements to demonstrate applications of bent crystals in high energy heavy ion beams