Yu.M. Ivanov

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.

Observation of the elastic quasi-mosaicity effect in bent silicon single crystals

A considerable elastic quasi-mosaicity effect has been observed upon the diffraction of x-rays on a bent silicon single-crystal plate. It has been shown that the effect depends on the choice of reflecting crystallographic planes and the orientation of the plate cut. The effect can be applied to improve the characteristics of silicon single-crystal monochromators of electromagnetic radiation and silicon single-crystal deflectors of charged-particle beams.

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.

Volume reflection of 1-GeV protons by a bent silicon crystal

The volume reflection of 1-GeV protons by a bent crystal has been observed. The crystal is made of single crystal silicon. The (111) atomic planes are bent owing to the elastic quasimosaicity effect, which makes it possible to reduce the crystal length for a beam to 30 µm. It is found that the probability of the reflection effect is higher than the probability of the channeling effect (0.71 vs. 0.63), and the deflection angle of the protons reflected inside the crystal is equal to 1.39 ± 0.04 in terms of the critical angle for channeling under the conditions of the experiment (170 µrad). The width of the reflected peak is equal to 1.76 ± 0.04 in the same units. The protons that are not involved in channeling at the angular position of maximum channeling undergo volume reflection and are deflected in the direction opposite to the channeled beam by the angle 1.01 ± 0.05 in terms of the critical angle for channeling. The width of the reflected peak is equal to 1.94 ± 0.08 in the same units.

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.

Low-energy-channeling surface analysis on silicon crystals designed for high-energy-channeling in accelerators

Channeling of relativistic particles in bent Si crystals is a powerful technique for use with accelerators. Its efficiency can be found to be highly dependent on the state of the surface of the crystal steering the particles. We investigated the morphology and structure of the surface of the samples that have been used with high efficiency for channeling in accelerators. Low-energy channeling of 2MeVα particles or protons was used as a probe. We found that mechanical treatment of the samples leads to a superficial damaged layer, which is correlated to efficiency limitations of the crystal in accelerators. In contrast, chemical etching, which was used to treat the surface of the most efficient crystals, leaves a surface with superior perfection.

Advances in the investigation of the extraction of a proton beam from the U-70 accelerator with the aid of bent single crystals

The efficiency of the extraction of a beam from an accelerator is radically improved owing to the application of short crystals of length up to 1.8 mm bent through a small angle of about 1 mrad. This success is due to an increase in the multiplicity of particle transmission through the crystal used. A record efficiency of the extraction of 70-GeV protons in excess of 80% is achieved experimentally, this result being in agreement with theoretical predictions. It is shown that the crystal can efficiently operate at the injection energy of 1.3 GeV.

Observation of multiple volume reflection by different planes in one bent silicon crystal for high-energy negative particles

Multiple volume reflection by different planes passing through the 〈111〉 axis in a bent silicon crystal was observed for the first time for 150 GeV/c negative particles, π- mesons, at one of the se ...

ACCELERATOR TESTS OF CRYSTAL UNDULATORS

A series of Silicon crystal undulator samples were produced based on the approach presented in PRL 90 (2003) 034801, with the periods of undulation from 0.1 mm to 1 mm, and the number of periods on the order of 10. The samples were characterized by X-rays, revealing the sine-like shape of the crystal lattice in the bulk. Next step in the characterization has been the channeling tests done with 70 GeV protons, where good channeling properties of the undulated Silicon lattice have been observed. The photon radiation tests of crystal undulators with high energy positrons are in progress on several locations: IHEP Protvino, LNF Frascati, and CERN SPS. The progress in the experimental activities and the predictions from detailed simulations are reported.

Progress in study of efficient crystal extraction and collimation at IHEP

The radical efficiency increase of accelerator beam extraction by means of bent crystals is reached by reducing the longitudinal dimension and bending angle of crystals. The usage of short crystals results in reduction of dechanneling losses and in increase of average number of crystal crossings by the particles. Both factors allowed an increased 70 GeV beam extraction efficiency of more than 80% which was proved experimentally and is in a good agreement with theoretical predictions. The feasibility of the crystal efficiency at injection energies (1.3 GeV) is demonstrated as well.