V. I. Kotov

Crystal channeling and its application at high-energy accelerators

1. Channeling Phenomenon.- 2. Beam Deflection by Bent Crystals.- 3. Experimental Studies of High-Energy Channeling and Bending Phenomena in Crystals.- 4. Crystal Extraction.- 5. The Use of Crystal Deflectors in Beam Lines.- 6. Application of Crystal Channeling to Particle Physics Experiments.- Epilogue.- References.

Experimental study for the feasibility of a crystalline undulator

We present an idea for creation of a crystalline undulator and report its first realization. One face of a silicon crystal was given periodic microscratches (grooves) by means of a diamond blade. The x-ray tests of the crystal deformation due to a given periodic pattern of surface scratches have shown that a sinusoidal-like shape is observed on both the scratched surface and the opposite (unscratched) face of the crystal; that is, a periodic sinusoidal-like deformation goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in a crystalline undulator, a novel compact source of radiation.

High-efficiency multipass extraction of 70-GeV protons from an accelerator with a short bent crystal

Abstract Using channeling in a 5-mm crystal with a bending angle of 1.5 mrad, a radical increase in the efficiency of beam extraction from accelerator was achieved due to an increased number of particle encounters with crystal. The measured world-highest efficiency of crystal extraction, over 40%, is in good agreement with theory predictions. The extracted beam intensity of 6×1011 ppp was obtained, five orders of magnitude higher than previous results.

First results of experiments on high-efficiency single- crystal extraction of protons from the U-70 accelerator

A radical increase in the efficiency of beam extraction from an accelerator is achieved with a short (7 mm long) crystal bent by a small angle (1.7 mrad) by increasing the number of times particles pass through the crystal. A particle extraction efficiency of ~20%, in agreement with the prediction of the theory, was achieved experimentally. A record high intensity of the extracted beam 1.9×1011 protons per cycle, which is four orders of magnitude higher than previous results, is obtained.

First results from a study of a 70 GeV proton beam being focused by a bent crystal

Abstract The technique of beam focusing by a bent crystal is described and results from its application presented in this note. A 70 GeV 2 mm wide proton beam was deflected and focused into a narrow 200 μm wide strip.

Crystal deflector for highly efficient channeling extraction of a proton beam from accelerators

The design and manufacturing details of a new crystal deflector for proton beams are reported. The technique allows one to manufacture a very short deflector along the beam direction (2 mm). Thanks to that, multiple encounters of circulating particles with the crystal are possible with a reduced probability of multiple scattering and nuclear interactions per encounter. Thus, drastic increase in efficiency for particle extraction out of the accelerator was attained (85%) on a 70 GeV proton beam. We show the characteristics of the crystal deflector and the technology behind it.

On measuring 70 GeV proton dechanneling lengths in silicon crystals (110) and (111)

Abstract Measurements of 70 GeV proton dechanneling lengths in silicon crystals (110) and (111) are described. The agreement of the obtained results with the predictions of diffusion theory, Monte Carlo simulations and experimental data at other energies is shown.

First results of investigation of radiation from positrons in a crystalline undulator

Radiation emitted by positrons moving in a periodically deformed crystal has been experimentally observed for the first time. Radiation spectra have been measured in a wide energy range. Experimental evidence has been obtained for an undulator peak in a radiation spectrum, which is qualitatively consistent with calculations. Crystalline undulators ensure an equivalent magnetic field of 1000 T and a period in the submillimeter range and can therefore be used to generate x-ray and gamma radiation that is a hundred times harder than radiation in usual undulators.

Radiation of photons in process of charged particle volume reflection in bent monocrystal

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.

Crystal undulator as a novel compact source of radiation

A crystalline undulator (CU) with periodically deformed crystallographic planes is capable of deflecting charged particles with the same strength as an equivalent magnetic field of 1000 T and could provide quite a short period L in the sub-millimeter range. We present an idea for creation of a CU and report its first realization. One face of a silicon crystal was given periodic micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade. The X-ray tests of the crystal deformation have shown that a sinusoidal-like shape of crystalline planes goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in CU, a novel compact source of radiation. The first experiment on photon emission in CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV undulator photons.