P. N. Chirkov

Collimation of the circulating beam in the U-70 synchrotron by means of the reflection of particles in crystals with axial orientation

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 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.

Investigation of the focusing of a 50-GeV proton beam using a new crystal device

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.

Crystal-Assisted Beam Extraction and Collimation at the U-70 Circular Accelerator

New crystal devices—an array of bent strips and a fan-type reflector based on thin straight plates—have been used to study extraction and collimation of the beam circulating in the accelerator at energies of 50 and 1.3 GeV. It is shown that these devices allow high-efficiency beam steering in a wide energy range. For 50-GeV protons, the efficiency of beam extraction and collimation is ∼90%, which is the highest efficiency attained for this method to date. It has been observed that the use of different crystals causes the particle loss at the accelerator downstream of the absorber to decrease by a factor of 2–3 in comparison with the standard single-stage scheme of beam collimation by a steel absorber.

Focusing crystal device for deflecting a divergent 50-GeV proton beam

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.

A device based on a bent crystal with a variable curvature for controlling particle beams at accelerators

It has been recently proposed using a bent crystal with a declining curvature instead of a uniformly bent crystal in order to improve extraction and collimation of the circulating beam in the accelerator. Variable curvature crystal devices developed to implement this idea are described. Curvature values measured along the crystal plate are presented. It is shown that focusing of high energy beams can also be focused using the developed devices.

A study of collimation and extraction of the U-70 accelerator beam using an axially oriented crystal

Extraction and collimation of the 50-GeV proton beam with a bent silicon crystal at the U-70 accelerator of the Institute for High Energy Physics (Protvino, Russia) was investigated. Until recently, proton beam extraction (and collimation) from accelerators has been effected using crystals with the (111) or (110) plane orientation, when the beam propagates far from the crystal axes. In the described experiment, the silicon crystal was oriented so that the proton beam was incident on it near the 〈110〉 axis. Under these conditions, a part of the beam was deflected by the crystal owing to the dynamic chaos phenomenon. The maximum beam extraction efficiency was as high as ~80%.

Extraction of the carbon ion beam from the U-70 accelerator into beamline 4a using a bent single crystal

A beam of six-charged carbon ions with an energy of 24.8 GeV/nucleon is extracted from the U-70 synchrotron by means of a silicon crystal bent through 85 mrad. A total of 200000 particles are observed in beamline 4a upon forcing 109 circulating ions to the crystal. The geometrical parameters, timing structure, and composition of the beam have been measured. It has been shown for the first time that, using a bent single crystal, an ion beam with required parameters can be extracted from the accelerator ring and formed for regular use in physics experiments.

Crystal devices for beam steering in the IHEP accelerator

Different crystal devices are described, which provide an extraction and splitting of beams for a long period of time at the U-70 accelerator of IHEP. The modes of channeling and volume reflections in the bent crystals are used for these tasks. In regular accelerator runs crystals produce the particle beams in a wide range of intensity, from 106 up to 1012 particles in a cycle. Novel crystal techniques suitable for charged particle beams deflection and focus as well as photon generation are presented also.

Deflection of a 100-MeV positron beam by repeated reflections in thin crystals

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.

Focusing of a high-energy particle beam at an extremely short distance

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.