Increase of probability of particle capture into the channeling regime Vincenzo Guidi, Andrea Mazzolari, University of Ferrara and INFN - Italy Alberto Carnera, Davide De Salvador, University of Padova and INFN - Italy and Victor Тikhоmirоv RINP, Minsk CERN, March 26, th 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. z1z1 z2z2 z 1 ~λ/12÷ λ/8 z 1 -z 2 ~λ/8÷ λ/6 λ: channeling oscillation period

Super-acceptance channeling II 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 and oxygen ions implantation Thermal annealing Thermal anneling at 1320 °C in O 2 /Ar atmosphere

SIMOX structure II Implementation of the method of the cut through a buried SiO 2 layer. Thermal annealing restores silicon cristalline quality and creates a buried SiO 2 layer. Interfaces between Si and SiO 2 are well terminated. Misalignment between silicon layers in available SIMOX structures: less than 0.7 Å/mm Si (device) SiO 2 (BOX) Si (Bulk)

Channeling in SIMOX structure I Focusing effect of BOX layer

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 x c = 0.15Å (dashed) and 0.20Å (solid). Below: optimal BOX layer coordinates vs proton energy.

SIMOX structure chanelling experiments RBS-channeling experiments with 6.1 MeV protons Divergence less than 0.01° (half angle) Crystal depth (μm) χ Si thickness: 231 nm BOX thickness: 377 nm SIMOX thickness: 500 μm

SIMOX structure -transmitted energy distribution Si Simox Transmitted energy distribution after a SIMOX 10 μm thin

SIMOX structure -transmitted angular distribution Left: for 400 MeV and z 1,2 = 150 nm, 560 nm, SIMOX thickness: 20 μm Right: for 7 MeV and z 1,2,3 =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 z 1 and z 2 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 nm BOX thickness: 377 nm SIMOX thickness: 500 μm Grazing incidence angle: 3° E = 400 GeV Θ (mrad) dN/dΘ (mrad)

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.