Transcript Презентация PowerPoint - LHC Collimation

Crystal collimation for LHC
Valery Biryukov
IHEP Protvino
Vincenzo Guidi
Ferrara University and INFN
Walter Scandale
CERN
CERN, Geneva, 24 April 2003
Borrowed from Ray Fliller’s talk at Paris EPAC 2002
Crystal Channeling
Beam line (70 m long) made of 3 crystals, IHEP
• Beam focusing by
crystal
Crystal design as used at IHEP Protvino and RHIC
Crystal is 3 to 5 mm along the beam
Crystal
Beam Direction
5mm
Crystal Courtesy of IHEP, Protvino
New crystal design (“strip”) gave 85% efficiency at IHEP
Typical beam phase space at crystal location, IHEP
1- circulating beam, 2- extracted beam, IHEP
Crystal extraction efficiency as measured since Dec 1997.
85% is measured even when all stored beam is dumped onto crystal
Deflected (left) and incident (right) beams as seen
downstream of the crystal
• Prior to the test, the crystal
was exposed in the ring to
50-ms pulses of very
intense beam (about 1014
proton hits per pulse).
• No damage of crystal was
seen in the test, after this
extreme exposure.
Beam profile at collimator face with NO crystal, 70 GeV
Misaligned x
Crystal collimation
Effy vs Energy
45 GeV
12 GeV
Crystal lifetime is order of 5*1020 proton/cm2
RHIC Crystal Collimator
Setup
8 Upstream PIN diodes
4 Downstream PIN diodes
Data fill focus on upstream PIN diodes
Layout of RHIC experiment on crystal collimation
RHIC measurements, EPAC 2002
Simulations of LHC crystal collimation
LHC crystal collimation (0.2 mrad)
1
0,8
450 GeV
0,6
7 TeV
0,4
0,2
Length (mm)
15
.
13
.
11
.
9.
7.
5.
3.
0
1.
channeling efficiency
1,2
Simulations with smaller bending, 0.1 mrad
LHC crystal collimation (0.1 mrad)
1
0,8
450 GeV
0,6
7 TeV
0,4
0,2
Length (mm)
15
.
13
.
11
.
9.
7.
5.
3.
0
1.
channeling efficiency
1,2
Two bending options compared: 0.2 and 0.1 mrad
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
0.2 mrad
Length (mm)
.
15
.
13
.
11
9.
7.
5.
0.1 mrad
3.
1.
channeling efficiency
LHC crystal collimation (7 TeV)
Efficiency vs bending angle
Crystal collimation at 7 TeV
channeling efficiency
1
0,95
0,9
0,85
0,8
0,75
.
.05
.
.1
.
bending (mrad)
.15
.
.2
Background suppression factor vs crystal bending
Background reduction, 1/(1-F)
reduction factor
25
20
15
10
5
0
.
.05
.
.1
.
bending (mrad)
.15
.
.2
FNAL simulations for Tevatron crystal scraping, PAC 1999
Conclusion
• Simulations and experiments promise
10-fold improvement in backgrounds
at TeV accelerators if bent crystal is used as
primary scraper.
• No problems with high intensity or lifetime.
Extraction parameters
Extraction efficiency vs.
crystal length at 70 GeV
• Protons
• 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
Structure of the bending crystal
2
0.5
• Dimensions 0.5250mm3
• 1/R is the curvature
experienced by channelled
protons
50
z
y
x
Bending device
• Bending exploits
anticlastic effects due
to anysotropy of
crystalline Si
• For the (111) direction
the sample takes the
shape of a saddle
Preparation of the Si samples I
• Starting material is prime-grade, (111) oriented
525-m-thick silicon wafer
• In previous runs there came out that a surface
layer as thick as 30 m was rich in scratches,
dislocations, line defects and anomalies that would
reduce channelling efficiency
• Such a layer originated in the mechanical cutting
for manufacturing the samples
• Thus we attempted removal of the layer
Preparation of the Si samples II
• Preliminary cleaning to organic and metallic
impurities from the surface of the wafers by H2O2,
NH4OH, HF, HCl,...
• Coverage of the largest surfaces by Apiezon wax
• Cutting of the samples by a diamond-blade saw
avoiding alignment with major crystalline axes.
• Planar etching (HF, HNO3 and CH3COOH,
2:15:5) with a timing set for 30 m thinning.
More info in Rev. Sci. Instrum. 73 (2002) 3170-3173
CRYSTAL
S1
EM S3 S4
S2
VACUUM PIPE
7 meter
Images of the beam
deflected through
mechanically treated
(left) and chemically
polished crystals (right)