Status of crystal undulator experiment at IHEP

Yu.A.Chesnokov

for the collaboration ofInstitute for High Energy Physics, Protvino, Russia

INFN - Laboratori Nazionali di Frascati, Italy

Department of Physics and INFN, Ferrara, Italy

St. Petersburg Institute for Nuclear Physics, Russia

Aarhus University, Denmark

At present to researches in biology, medicine, material and many other areas of science and engineering intensive x-ray beams are applied. Conventional way for production of such beams (with the energy of few KeV and higher) is the use of special magnets – undulators in accelerators [1]. The energy of photons generated in undulator is proportional to a square of the gamma-factor of a particle and is reverse proportional to a period of an undulator (about several centimeters in usual electromagnetic undulator). Thus way at energy of a beam in accelerator about 1 GeV photons are produced with the energy of about 1 KeV. To increase the energy of photon beams is very important for several applications. The idea of creation of undulators on the basis of crystals, in which an intensive periodic electrical field is created by nature, was actively discussed in the last quarter of a century [2-9].

Idea of CU: to bent crystal like a snake

1. Beam Line, v. 32, no. 1 (2002).2. V.V. Kaplin, S.V. Plotnikov, and S.A. Vorobiev, Zh. Tekh.

Fiz. 50, 1079-1081 (1980).3. V.G. Baryshevsky, I.Ya. Dubovskaya, and A.O. Grubich,

Phys. Lett., 77A, 61-64 (1980).4. H. Ikezi, Y.R. Lin-Liu , and T. Ohkawa, Phys. Rev., B30,

1567-1568 (1984).5. S.A. Bogacz and J.B. Ketterson, J. Appl. Phys. 60, 177-

188 (1986). S.A. Bogacz, Particle Accelerators, 42 (1993) 181.

6. G.B. Dedkov, Phys.Stat.Sol.,(b)184, 535-542 (1994).7. A.V. Korol, A.V. Solovev, and W. Greiner, Intern. Journal

of Mod. Phys., 8, 49-100 (1999)8. U. Mikkelsen and E. Uggerhoj, Nucl. Instr. and Meth.,

B160, 435- 439 (2000). 9. R.O. Avakian, K.T. Avetyan, K.A. Ispirian and E.G.

Melikyan. Nucl. Instr. and Meth., A492, 11-13 (2002).

• S. Bellucci et al., Phys. Rev. Lett. 90 (2003) 034801.

• S. Bellucci et al., Phys. Rev. ST AB 7 (2004) 023501.

• A.Afonin et al NIMB-2005

• V.Baranov et al JETP Letters (2005) 562

Origins for our approach to CU at IHEP

The micro-photography of crystal end face with scratches (left) and image of the deflected by this crystal 70 GeV proton beam at distance of 1 m (right).

  

Angular distortion of crystal planes near a surface scratch

Scheme of realised crystalline undulator.

  

IHEP workshop: rough scratching by a diamond cutter. SEM image of one of our Si crystal undulators, showing 50 micron

grooves on the undulator surface, spaced by 200 micron.

IHEP workshop: rough scratching by a diamond cutter. Side view of the sample: micromachining produces periodical

deformations that propagate in the bulk of the crystal.

Ferrara group technologyFerrara group technology

A special diamond blade A special diamond blade scratched one or two faces of scratched one or two faces of silicon plate.silicon plate.

The scratches on crystal surface The scratches on crystal surface cause a deformation of the cause a deformation of the crystallographic planes.crystallographic planes.

Potential interest to realize an Potential interest to realize an undulator for positrons with undulator for positrons with submillimeter spasingsubmillimeter spasing

The CU samples were tested first by X ray at PNPI

Anode Spot

Collimator Slit Anode Slit

Si Plate underInvestigation

X-Ray Beam

X

Y

NaJ Detector

(width 40μm, height 2 mm)

Angle of reflection from unscratched surface of CU with 0.5 mm period

CU sample

A sample of CU mounted in a holder

(the holder can give compensation for global bending)

Scheme of extraction of circulating high-energy proton beam with bent undulator-type crystal.

  

Deflected beam profile and efficiency of extraction versus crystal orientation angle.

  

Scheme of CU radiation experiment at IHEP

• In experiment as this detector were used two calorimeters (not simultaneously): on the basis of crystals of YAlO3 and BGO. Yttrium detector was adapted for registration of photons in the field of 60 KeV up to 2 MeV energy.

• The BGO detector could register photons with energies from 2 MeV to few GeV.

The vacuum box with CU and cleaning magnet (IHEP setup)

  

The photon spectrometer (1) and scintillator trigger (2) mounted on mechanical drivers.

  

Data acquisition system

• The specific character of this radiation experiment is included in unusual geometry of the source. It has the small sizes in transversal direction ( ~0.3 mm ) and significant extent along the beam, few mm, as it is required about ten undulator periods with 0.5 mm step and 100 Å amplitude. Earlier the experiments on radiation from crystals were carried out with short targets, less than 1 mm.

Therefore the first problem consists in identification of a source, as only the small fraction of beam particles cross a crystal (~1/500). We used thin scintillator S1, 500 microns  in width as a trigger, and remotely moved a crystal across a beam, therefore have easily found out the source of radiation. Orientation curve that is dependence of a signal on crystal alignment, shown on fig. 3, proves, that the source of radiation is exactly crystal.

The number of registered photons versus orientation of a crystal. Ten bins correspond to 1 microradian

angle.

. The gamma spectrum in oriented (white dots), disoriented

crystal(black dots) and background without crystal( square

points) measured by BGO detector.

• The second feature, connected with large extent of crystal, resulted in multiple production of photons, deforming measured spectra.

• At the energy of positrons 10 GeV the average number of irradiated in crystal photons is about 5, appreciably exceeding by 1 (so called multiplicity factor), thus way most part of undulator events are accomplished by few another photons and registered with distortions.

. Spectra of irradiated power from oriented (white dots) and disoriented crystal (black dots) measured by yttrium detector. Two right bins show up 2 MeV signals (oriented/disoriented

case) and these bins are decreased 50 times in scale.

Selection of events with small energy transfer

Observation of undulator effect

Comparison with theory

Future plans: modernization of the setup:

installation of gamma-collimator, application of new-type calorimeters,

testing of 3 undulator samples with an account of theoretical recommendations

New proposal for collaboration:creation of

Multilayered crystal mirror for steering of TeV-energy particle

beams.

A.M.Taratin and S.A.Vorobiev,

Phys.Lett. A119 (1987) 425

and

A.M.Taratin and S.A.Vorobiev,

NIM in PR B26 (1987) 512

Reflected

Channeled

d

U

Mini workshop on crystal channeling (December 2005)

Prediction of beam reflection in bent crystal

A.M.Taratin and S.A.Vorobiev,

Sov. Journal of Technical Physics, v.55, p.1598, 1985 (in Russian)

Mini workshop on crystal channeling (December 2005)

O.I.Sumbaev,

The theory of volume capture by a curved crystal in the channeling regime, Preprint LIYaF-1201, 1986 (in Russian)

Prediction of beam reflection in bent crystal

Scheme of experiment crystal extraction at IHEP with 70 GeV

protons 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 GeVp-beam

5 m

R=3 m

Mini workshop on crystal channeling (December 2005)

Exposure of emulsions 1 and 2 made at IHEP in 2002

Mini workshop on crystal channeling (December 2005)

Interpretation of the IHEP results

Incident Emulsion 1

Channelled

Reflected

Emulsion 2

1

2

3

4

5

6

Mini workshop on crystal channeling (December 2005)

1 TeV Channeling at the Tevatron, October 5, 2005

Not volume capture, but volume reflection !

Mini workshop on crystal channeling (December 2005)

The observed tail beside the channeling peak is most likely induced by beam reflection into the crystal itself

Creation of multilayered crystal mirror

Scattering and reflection in 1mm long silicon bent crystal

Accelerator Energy

70 GeVU-70

450 GeVSPS

1 TeVTevatron

7 TeVLHC

Reflection2c, µrad

50 20 12 5

Scattering1500/p, µrad

20 3.5 1.5 0.2

Scattering and reflection in serial of 10 silicon bent crystals

Accelerator energy

70 GeVU-70

450 GeVSPS

1 TeVTevatron

7 TeVLHC

Reflection10×2c, µrad

500 200 120 50

Scattering√10×1500/p, µrad

65 11 5 0.6

CU sample

A sample of CU mounted in a holder

(the holder can give compensation for global bending)

Different multilayered strips.