G. I. Britvich

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.

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.

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.

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.

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.

Fast neutron detector based on surface-barrier VPE GaAs structures

Surface-barrier structures based on thin high-purity GaAs epilayers with a polyethylene converter were studied as fast neutron detectors. A continuous Schottky barrier with a large area of 5 × 5 mm2 to the high-purity GaAs epilayers was fabricated using a Pt/TiN/Au metallization system. Results of measurement of electric parameters and α-particle spectra are presented. The fast neutron spectra from the 241Am-Be source measured by the recoil proton method for various thicknesses of the polyethylene converter and various operating biases are shown as well. The proposed detectors have shown high neutron detection efficiency of 1.3010−3 puls./neutr. and an acceptable signal-to-background ratio (at level of 50) as well as the capability to operate efficiently without any external bias.

Investigation of the efficiency of the extraction of a 50-GeV proton beam from a ring accelerator with the use of silicon crystals bent at various angles

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.

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.

The main characteristics of polystyrene scintillators produced at the institute of high-energy physics and detectors on their basis

The results of measurements of the main characteristics of polystyrene scintillators, which were developed using new technologies at the Institute of High-Energy Physics (IHEP), are presented. Scintillators are used in a number of experiments both on the IHEP accelerator and on facilities of foreign physical centers (CERN, FNAL, BNL, DESY). Specific features of the operation of detectors that use “scintillator-wavelength shifting fiber” systems are considered. The efficiencies of various reflecting surfaces, the light yield, and the time resolution of scintillation detectors were measured.

Investigation of the emission of photons induced in the volume reflection of 10-GeV positrons in a bent silicon single crystal

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.