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A multistage collimation system for the absorption of the growing halo of circulating beams is used at the Large Hadron Collider (LHC) to protect superconducting magnets and to ensure their reliable operation. A similar system is also planned for the Future Circular Collider (FCC). Studies for the improvement of the collimation system are performed prior to the operation of the LHC with a high luminosity. Studies have shown that one of the solutions to improve the beam collimation is the use of channeling in a short bent crystal, which serves as a primary collimator throwing particles deep into the secondary collimator by means of channeling. This system is very sensitive to the angular position of the crystal and various possible vibrations. In this work, another approach to beam collimation based on the bulk reflection of particles from bent crystal-lographic planes in a sequence of crystals has been proposed. Advantages of this scheme have been justified and a multistrip crystal device has been proposed to implement this scheme.

It has recently been realized that the focusing of high-energy particle beams at a distance of about 1 cm is promising. A new idea is proposed in this work to focus the beam at a short distance by using a bent plane–parallel silicon plate whose side edges are rotated at a small angle with respect to crystallographic planes. At the U-70 accelerator (IHEP, Protvino), a 50-GeV proton beam has been focused to a narrow line with a width of no more than 30 μm at a distance of 17 cm.

At large accelerators, bent crystals are employed to deflect weakly divergent proton beams at the stages of extraction and collimation. We demonstrate that a divergent particle beam may be efficiently deflected using a crystal with a focusing edge. A proton beam with divergence near 1 mrad, which exceeds the Lindhard angle by a factor of 30, has been experimentally deflected by 1.8 mrad with efficiency near 15%. The proposed focusing crystal may serve as an element of a novel optical system for secondary-particle beams in the TeV energy region.

The possibilities of the extraction and collimation of a circulating beam by a new method due to the reflection of particles in crystals with axial orientation were experimentally investigated in the Fall-2010 run at the U_70 synchrotron. Such crystals have positive features, because the axial potential is five times larger than the planar potential. It has been shown that the collimation efficiency can reach 90% due to axial effects in the crystal. Losses of the circulating beam on a collimator have been reduced by several times; this makes it possible to suppress the muon jet near the steel collimator of the circulating beam.

The efficiency of the deflection of 50-, 15-, and 1.3-GeV proton beams by means of planar channeling in a bent silicon crystal has been compared to that by means of the stochastic mechanism of the deflection of charged particles by the bent crystal. The deflection of protons at single passage through the crystal has been simulated. The results of the experiment on the deflection of a circulating beam at the U-70 accelerator (Institute for High Energy Physics, Protvino, Moscow region) are presented. It has been shown that the efficiency of the stochastic deflection mechanism increases with a decrease in the energy, whereas the efficiency of the planar channeling for deflection decreases.

The phenomenon of the deflection of a charged particle beam due to channeling in a bent crystal is thoroughly investigated and successfully applied for the extraction of the beam in high-energy accelerators, at the energies of about 10 GeV and higher. However, a big practical interest lies in the task of bending and extracting charged particles with energies below 1 GeV, for example, for the production of ultrastable beams of low emittance for medical and biological applications. That is why a novel crystal technique, namely thin straight crystal targets, is investigated in this article, using crystals as elements for extraction and collimation of the circulating beam in a ring accelerator. The advantages of reflection in straight crystals in comparison with bent crystal channeling consist in the small length of straight crystals along the beam that reduces the amount of nuclear interactions and improves the background. Experimental results were obtained for the bending of a 100 MeV positron beam with using five sequential straight crystals.

New crystalline equipment—an array of bent strips and fan reflector based on thin flat plates—has been used to investigate the extraction and collimation of a circulating beam in an accelerator with an energy of 50 and 1.3 GeV. It has been shown that new equipment can efficiently control the beam in a wide energy range. An extraction and collimation efficiency of 90%, which is a record for this method, has been achieved for 50-GeV protons.

The emission of photons in the motion of a 10-GeV positron beam in bent silicon crystals has been experimentally investigated. The experimental data are compared with the theoretical calculations.

Bent crystals are used at large accelerators to deflect particle beams for extraction and collimation. Not only the deflection but also the focusing of beams by bent crystals can be required for recently formulated proposals for investigations at the Large Hadron Collider (LHC) with a fixed target. The experimental results on the focusing of a 50-GeV proton beam with a new crystal device, which can be used in a circulating beam of a large accelerator such as the LHC, have been reported.

The measurements of the efficiency of the extraction of protons from the U-70 accelerator with the use of silicon crystals with bending angles of 36 and 64 mrad are reported. The data are confirmed by computer simulation. Proposals are made on the use of several crystals for the extraction of particles from the U-70 accelerator in the carbon ion acceleration mode.

We observe positron bending by a crystal lattice, presumably being guided by a channeling phenomenon, deflecting the beam by about 10 milliradian over a length of 1 mm of silicon. This technique may lead to the use of the channeling effect for steering particle beams at energies below 1 GeV, for the purpose of producing beams of low emittance with enhanced stability for medical and biological applications.