Simulation of beam steering phenomena in bent crystals

The simulation methods for the channeling phenomena in GeV/TeV energy range in ideal or distorted crystal lattices are discussed. Monte Carlo predictions for feed-out and feed-in rates, dislocation dechanneling, and deflection efficiencies of bent crystals are compared to the experimental data. The role of multiple interactions with crystal in circular accelerators ("multipass channeling") for the efficiency boost in the crystal-aided extraction experiments is analysed. Possible future applications of the crystal channeling technique are considered.Comment: 10pp. Presented at COSIRES 1998 (Okayama

Optimization of crystal extraction experiment

Using a computer model for the crystal extraction, we investigate the bent-crystal parameters optimal for the extraction experiment. The optimal crystal curvature is found to be near 1 GeV/cm (for pv/R), i.e. a factor of 2--3 higher than for the crystal application in beam lines. An influence of the accelerator optics on extraction is discussed. A possibility of using the high-Z crystals for extraction is considered. The simulations for the ongoing experiments at the CERN-SPS and the Fermilab Tevatron, and for the proposed extraction at LHC, are presented.Comment: 11 pages, 4 figure

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

Multiple Volume Reflection from Different Planes Inside One Bent Crystal

It is shown that multiple volume reflections from different planes of one bent crystal becomes possible when particles move at a small angle with respect to a crystal axis. Such a Multiple Volume Reflection makes it possible to increase the particle deflection angle inside one crystal by more than four times and can be used to increase the efficiency of beam extraction and collimation at the LHC and many other accelerators.Comment: 17 pages, 6 figure

The limits of volume reflection in bent crystals

We show that theory predictions for volume reflection in bent crystals agree with recent experimental data. This makes possible to predict volume reflection angle and efficiency in a broad range of energy for various crystals. A simple formula is proposed for volume reflection efficiency. We derive the physical limits for application of crystal reflection at high-energy accelerators where it may help beam collimation.Comment: 6 pages, 2 figure

OPTIMISATION OF THE DYNAMIC INDICATOR OF INTERACTION BETWEEN CHISELS AND THE WOOD OF THE CONICAL FACE MILLING CUTTERS (WITH SMALL NUMBER OF CHISELS) OF SAWING MACHINES

The work is related to the study and optimisation of the dynamic performance of interaction between chisels and the wood in the course of longitudinal milling using the conical face milling cutters (with small amount of chisels) of sawing machines. This dynamics is characterized by non-uniformity of the process load when using the specified milling cutters. It was quantitatively assessed by the indicator of non-uniformity of the technological load within the cycle of processing of logs and bars into sawn timbers and wood chips. For cutters with small number of chisels this dynamic indicator equals the ratio of the maximum total length of the cutting edges of the chisels to the average length of their cutting edges simultaneously involved in cutting throughout the cycle of wood processing (turn of the cutter). Conical face milling (conical) cutters with a small number of chisels were conventionally considered as a discrete set of square-shoulder mills, i.e. as a particular case of a cutter with many chisels. The process of interaction with between the chisels and wood within the processing cycle was divided into four zones (periods): I zone – period of cutting of all chisels into the timber; II zone - period of operation of all chisels of a group and subsequent extraction from timber; III zone – the period of gradual extraction of the group of chisels from the timber; IV zone – period of approaching the neighbouring group of chisels. The size and relative orientation of these zones in time in conditions of steady cutting define the different nature of interaction between chisels and the wood with the varying intensity of technological load. Author has obtained mathematical relationships between these zones, and taking them into account – determination of the index of uneven technological load per wood processing cycle; calculations were made and a number of parameters of cutters were substantiated. The author has determined the influence on the rate of non-uniformity of width, height of milling, as well as the angle of rotation of chisels in the centre plane of the cutter. The rational (optimal) location of double lip chisels (at two-row structure) on the milling cutter body is the following: the ratio of the width of a line of chisels with larger radius of cutting to the width of a line of chisels with smaller radius of cutting (at the calculated values of the milling process) is 1.25; the size of the non-covered area of the cutting edge at the smaller base of the cutter is 50 mm with a total width of 120 mm. This condition corresponds to the minimum maximum power of cutting along the length of the chips cut and the lowest indicator of uneven technological load per turn of the cutter

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

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