Crystal Channeling Study (experiment to study and apply channeling to HEP)

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Crystal Channeling Study(experiment to study and
apply channeling to HEP)

• Vincenzo Guidi
• University of Ferrara and INFN

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Channeling in crystals
Trapping of charged particles in the inter-planar
potential well (20 eV in Si)
Critical angle
A bent crystal can be used to steer particles
through channeling
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Applications to HEP

• Halo cleaning in the LHC
• Diffractive physics (TOTEM experiment)
• In-situ calibration of the calorimeters in LHC
  experiments

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Two-stage collimation
The number of secondary collimators grows quickly
when background or machine protection
requirements are strict and a high collimation
efficiency is required.
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Crystal collimation
Use a bent crystal to channel halo away from the
beam core, intercept with a scraper downstream.
Number of secondary collimators can be greatly
reduced.
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Optimal design for the LHC
Optimal size of the silicon crystal for
collimation is about 10 mm for 0.1 mrad (7 TeV).
NIM B 234 (2005) 23
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The RD-22 experiment

• Large channelling efficiency measured for the
  first time in extraction mode
• Consistent with simulation expectation for high
  energy beams
• Experimental proof of multi-turn effect
  (channelling after multi-traversals)
• Definition of a reliable procedure to measure the
  channelling efficiency

The RD22 Collaboration, CERN DRDC 94-11
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Intas projects

• Energy at 1.3-70 GeV
• Intensity 1012 protons in spills of 2 s duration
• Efficiency greater than 85
• Equivalent to 1000 T dipole magnetic field

Extraction efficiency vs. crystal length at 70
GeV
PRL 87 (2001) 094802
PRL 90 (2003) 034801
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Novel crystal configuration
0.5?2?50 mm3
Bending exploits anticlastic effects due to
anysotropy of crystalline Si
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Novel crystal preparation

• Dicing of the samples by a diamond-blade saw
  avoiding alignment with major crystalline axes.
• Defects are induced by the dicing saw (a
  surface layer estimated to be as thick as 30?m is
  rich in stratches, dislocations, line defects and
  anomalies).
• Planar etching removes crystalline planes one by
  one

RSI 73 (2002) 3170
Removal of such layer by wet planar etching
(HF,HNO3,CH3COOH).
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Mechanical vs. chemical treatments
Images of the beam deflected through
mechanically treated (left) and chemically
polished crystals (right)
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NTA-HCCC project
Chemical etching
As diced
As diced
Chemical etching
Chemical polishing enhances standard roughness
(Ra)
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Surface analysis
30??m
APL 87 (2005) 094102
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Recent achievements (FNAL)
FNAL results (2005)
Crystal Collimator in E0 to replace a Tungsten
Target
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Recent achievements (IHEP)
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Anomalous effects
Exposure of emulsions 1 and 2 made at IHEP in 2002
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Interpretation
Particle reflection has been indicated as an
interpretation for experimental evidences.
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Interpretation
First evidence for reflection in a crystal,
theoretically predicted in Sov. J. Tech. 55
(1985) 1598
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Reconsidering FNAL experiments
1 TeV Channeling at the Tevatron, October 5, 2005
Not volume capture, but volume reflection !
The observed tail beside the channeling peak is
most likely induced by beam reflection into the
crystal itself
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CCS an experiment to study and apply channeling
to HEP

• Continuous upgrading of performance of crystals
  boosted new achievements and new prospects.
• Need for a newly conceived experiment to
  investigate novel phenomena.
• Three-weeks machine time (external line H8, SPS)
  has been requested in 2006 and decision will be
  taken soon.

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Basic idea of the experiment
Bent beam
10 ?rad
Line H8 - SPS
Crystal
Primary proton beam
100 ?rad
Unbent beam
20 ?rad

• 400 GeV/c
• 105 p/spill
• 5 mm in diameter
• 3 ?rad divergence

10 ?rad
Reflected beam
The idea is to track the trajectoriesof the
particles and to determine the cross sections
for each branch
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Layout of the experiment
Goniometers with crystal holders
Line H8
S2
S3
S1
vacuum
vacuum
p
Si microstrips with 10 ?m resolution (AMS type)
1 m
34 m
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Collaboration

• CERN infrastructure of the experiment
• IHEP lattice design, simulations (INTAS)
• PNPI crystals (INTAS)
• JINR simulation, DAQ (INTAS)
• FNAL mutual participation in experimental runs
• FE crystals, construction of the apparatus
  (CCS-NTA)
• LNL goniometers (CCS-NTA)
• PG Si microstrips (CCS)
• Participation of persons from PI and TO

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Details of the experiment CCS
Duration 3 years INFN personnel FE (4 FTE),
PG (2.5 FTE), LNL (4 FTE), TO, PI Cost in
2006 150 kEuro for construction of detectors
(AMS type) and implementation at CERN