Increase of probability of particle capture into the

channeling regimeVincenzo Guidi, Andrea Mazzolari,University of Ferrara and INFN - Italy

Alberto Carnera, Davide De Salvador, University of Padova and INFN - Italy

and Victor ТikhоmirоvRINP, Minsk

CERN, March 26, 2009

4th Crystal Channeling Workshop 2009

Outlook

Super acceptance channeling

SIMOX structure

Channeling in SIMOX structure

SIMOX structure channeling experiments

SIMOX structure-transmitted energy distribution

SIMOX structure-transmitted angular distribution

SIMOX structure-experiment at high energies

Conclusions

Super-acceptance channeling I

With a silicon lens it is possibile to reduce the number of dechanneled particles by focusing the proton beam onto the center of the potential well, with a precise cut in the crystal potential.

beam

cut

crystalz1

z2

z3

0

x

y z

z1

z2

z1 ~λ/12÷ λ/8z1-z2 ~λ/8÷ λ/6λ: channeling oscillation period

0 1 2 3 4 5 6 70

5

10

15

20

25

30

35

40

P

dech

, %

rms, rad

400 GeV

0,0 0,2 0,4 0,6 0,8 1,00

5

10

15

20

25

30

Pde

ch,

%

rms, rad

7 TeV

Super-acceptance channeling II

,1

,71

,17

3

2

1

cmz

mz

mz

,1

,14

,4

3

2

1

mmz

mz

mz

The cut decreases dechanneling probability to 1-2%Crystal can be realized using standard silicon micromachining tecniques

SIMOX structure I

Substrate heated at 650 °C andoxygen ions implantation

Thermalannealing

Thermal anneling at 1320 °C in

O2/Ar atmosphere

SIMOX structure IIImplementation of the method of the cut through a buried SiO2 layer.

Thermal annealing restores silicon cristalline quality and creates a buried SiO2 layer.Interfaces between Si and SiO2 are well terminated.

Misalignment between silicon layers in available SIMOX structures: less than 0.7 Å/mm

Si (device)

SiO2 (BOX)

Si (Bulk)

Channeling in SIMOX structure I

Focusing effect of BOX layer1

2

7

20

80

E MeV

z nm

z nm

Channeling in SIMOX structure II

Above: nonchanneling probability behind the BOX layers in a SIMOX structure (thick) and behind the entry face of a crystal (thin) vs proton energy simulated at xc = 0.15Å (dashed) and 0.20Å (solid). Below: optimal BOX layer coordinates vs proton energy.

SIMOX structure chanelling experiments

0 2 4 6 8 10 12 14 16 180,0

0,2

0,4

0,6

0,8

1,0

SiP110 - simulations SiMoxP110 - simulations Si, simulations SIMOX, z

1=20nm, z

2=60nm, simulations

Ch

i

microns

RBS-channeling experiments with 6.1 MeV protons

Divergence less than 0.01° (half angle)

Crystal depth (μm)

χ

Si thickness: 231 nmBOX thickness: 377 nmSIMOX thickness: 500 μm

SIMOX structure-transmitted energy distribution

6840 6880 6920 6960

dN

/d tr

, arb

itrar

y un

its

transmitted energy tr, keV

1/ 27 , 20 / 60E MeV z nm nm

SiSimox

Transmitted energy distribution after a SIMOX 10 μm thin

SIMOX structure-transmitted angular distribution

Left: for 400 MeV and z1,2= 150 nm, 560 nm, SIMOX thickness: 20 μmRight: for 7 MeV and z1,2,3 =20nm, 60nm, SIMOX thickness: 3 μm.

Transmitted angular distributions with (dashed) and without (solid) a BOX layer

SIMOX structure experiment at high energies I

Maximum z1 and z2 values for available SIMOX structures are respectively about 200 and 400 nm.

It is possible to use SIMOX crystal at high energies (400GeV) orienting the crystal at grazing incidence with respect to the beam

Beam

(110) planes

SIMOX structure experiment at high energies II

Si thickness: 231 nmBOX thickness: 377 nmSIMOX thickness: 500 μmGrazing incidence angle: 3°E = 400 GeV

Θ (mrad)

dN

/dΘ

(m

rad)

Conclusions

Crystal with cut may lead to deflection efficiency through planar channeling close to 100%

SIMOX crystal experiment at high or low energy is a good way to check the principle of crystal with cut.