Quasimosaic crystals Yu.M.Ivanov

Elastic quasimosaic (Sumbaev) effect Studied by Sumbaev in 1957 Resulted in broadening of gamma-ray diffraction peaks from bent quartz plates Caused by bending of the reflecting atomic planes (initially flat and normal to large faces of plate) due to crystal anisotropy Depends on choice of crystallographic plane and orientation angle of plate cutting relative to a normal to the chosen crystallographic plane Figure from article: O.I.Sumbaev, Reflection of gamma-rays from bent quartz plates, Sov. JETP 32(1957)1276

Quasimosaic effect in silicon Calculations of deformed crystal plate done by V.M.Samsonov (Preprint No. 278, LIYaF AN SSSR, 1976). –Resulted in predictions of elastic quasimosaic effect for some other quartz and silicon plate orientations –Large elastic quasimosaicity for (011) plane of silicon predicted Zero result in the first experiments in 1999 New calculations using Samsonov approach and new measurements: - (111) plane, not (011) - published in JETP Letters 81, 99, 2005 Figure from article: V.M.Samsonov and E.G.Lapin, On some possibilities and pequliarities of a curved crystal use in crystal diffraction instruments, Preprint No. 587, LIYaF AN SSSR, 1980

Elastic quasimosaic in dependence on cut angle for Si (111) plane T – thickness of plate k 9 – deformation coefficient  = 2k 9 T, where Plate bending radius R = 1 m ( formula taken from V.M.Samsonov, E.G.Lapin, Preprint No. 587, LIYaF AN SSSR, 1980 )

Silicon cuts Cut without quasimosaic Cut with quasimosaic Oriented ingot φ

Rocking curves for Si plate with quasimosaic before and after bending. Quasimosaic effect in Si with X-rays Rocking curves for Si plate without quasimosaic before and after bending.

Shape of bent Si plate with elastic quasimosaic

Bending device

First quasimosaic silicon crystal prepared in 2002 for channeling experiment with 70 GeV protons

Layout of experiment at IHEP in April, 2002 Crystal 1 Magnets Crystal 2 Emulsion 1 S1 S2 S3 Background Channeled_1 30 m 35 m 4.6 m Collimator 1.3 m Emulsion 2 Channeled_2 70 GeV p-beam 5 m R=3 m

Profile of 70 GeV proton beam passed through the crystal measured with emulsion: superposition of channeling and volume reflection effects

Explanation of the observed picture on emulsions Proton trajectories crossing the crystal and emulsions in horizontal plane (top view)

Samples 0.3 mm and 2.7 mm with ~0.4 mrad bending angle

Sample 10 mm with ~100 μrad bending angle

Crystals for experiment on extraction of high entensive proton beam at IHEP Plane (111) Length along beam 2.65 mm Bending angle 400 μrad

Crystal station at IHEP ring

Crystal mounted on station

Result Beam in the U-70 ring 5.5∙10 12 p Intensity of extracted beam 4.0∙10 12 p Efficiency 70%

Experiment on observation of volume reflection effect with 1 GeV protons at PNPI, Gatchina Beam divergence ~ 160 μrad Beam size ~ 0.8 mm Critical angle for channeling ~ 170 μrad Crystal length along beam ~ 30 μm Bend angle of (111) planes ~ 380 μrad

One of unsuccessful attempts to bend a 30 μm crystal on 20 mm radius

Bent crystals in bending devices

Check of crystal shape with laser ~1m

Measurement of bending angle with X-rays

Collimator Crystal mounted on goniometer

Horizontal profiles of the p-beam vs. crystal angle measured with PPC p-beam reflection channeling p-beam Crystal angle, step 62.5 μrad Channel number, step 200  m

Channeling experiment with 400 GeV protons H8 beam line FAR_DETECTOR areaCRYSTAL area

QM2

Channeling angle (68.2  0.4) μrad Volume reflection deflection (12.7  0.6) μrad Volume capture ε (1.8  0.7) %

QM1

Channeling angle (77.0  0.4) μrad Volume reflection deflection (11.6  0.8) μrad Volume capture ε (2.6  0.8) %

QM2+QM1

Channeling angle Volume reflection deflection (23.4  0.7) μrad Volume capture ε (5  1) %

QM3

Channeling angle (72.7  0.8) μrad Volume reflection deflection (11.9  0.7) μrad Volume capture ε (5  1) %

QM4

Channeling angle (120.0  0.4) μrad Volume reflection deflection (12.7  0.5) μrad Volume capture ε (4.4  0.7) %

Design: sequence of quasimosaic crystals cut from a single initial plate p 1 Si plate 0.3 x 30 x 60 mm 3 12 Si plates 0.3 x 8 x 14 mm 3

Check of plate wedging with optical goniometer

Prototype assembly from 5 plates

Check with narrow X-ray beam ΔNΔN Δθ≈0.017x ΔN μrad Δθ < 40 μrad X, mm N, counts ΔXΔX N1N1 N2N2 Δθ ΔN=N 2 -N 1 ΔXΔX

Need to provide or to compensate plate wedging

Realization with evaporation technique Al-layer of 0.14 μm thickness Δθ = 0.14 μm / 12 mm = 12 μrad

Further steps to improve prototype assemly for experimental run in May’07 at CERN to prepare larger plates and assemble them for experiments at CERN and IHEP in the Fall’07