Transcript The LHC Challenge on Beam Loss and Collimation R. Assmann, CERN/AB 16/08/2007 for the Collimation Team SLAC RWA, SLAC 8/07

The LHC Challenge on
Beam Loss and Collimation
R. Assmann, CERN/AB
16/08/2007
for the Collimation Team
SLAC
RWA, SLAC 8/07
Outline
1) Introduction: The LHC Challenge
2) LHC Collimation Basics
3) Collimator Hardware
4) Collimation Performance
5) Tunnel Installations
6) Collimator Beam Tests
7) Beyond Phase 1
8) Conclusions
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1) Introduction: The LHC Challenge
The Large Hadron Collider:
Circular particle physics collider with 27 km circumference.
Two colliding 7 TeV beams with each 3 × 1014 protons.
Super-conducting magnets for bending and focusing.
Start of beam commissioning: May 2008.
LHC nominal parameters
Particle physics reach defined from:
1) Center of mass energy

14 TeV
super-conducting dipoles
Number of bunches:
Bunch population:
Bunch spacing:
2808
1.15e11
25 ns
Top energy:
Proton energy:
Transv. beam size:
Bunch length:
Stored beam energy:
7 TeV
~ 0.2 mm
8.4 cm
360 MJ
Injection:
2) Luminosity
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1034 cm-2 s-1
Proton energy:
Transv. Beam size:
Bunch length:
450 GeV
~ 1 mm
18.6 cm
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LHC Luminosity
• Luminosity can be expressed as a function of transverse energy density
re in the beams at the collimators:
d = demagnification (bcoll/b*)
Np = protons per bunch
frev = revolution freq.
Eb = beam energy
• Various parameters fixed by design, for example:
– Tunnel fixes revolution frequency.
– Beam-beam limit fixes maximum bunch intensity.
– Machine layout and magnets fix possible demagnification.
– Physics goal fixes beam energy.
• Luminosity is increased via transverse energy density!
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Transverse Energy Density
1 GJ/mm2
1 MJ/mm2
Parameter for material damage:
re
LHC advancement:
Factor 7 in beam energy
Factor 1000
in re
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Stored Energy
 LHC stored energy corresponds to 80 kg TNT per beam! Dangerous beam!
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Proton Losses
• LHC high power beams:
– Ideally no power lost (protons stored with infinite lifetime).
• Collimators are the LHC defense against unavoidable losses:
– Irregular fast losses and failures: Passive protection.
– Slow losses: Cleaning and absorption of losses in super-conducting
environment.
– Radiation: Managed by collimators.
– Particle physics background: Minimized.
1% of beam over 10s peak loss
• Realistically:
– Slow losses:
0.5 – 1.0 MW onto collimators
– Fast losses:
up to 1 MJ in 200 ns into 0.2 mm2
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(up to 10 s)
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Preventing Quenches
• Shock beam impact: 2 MJ/mm2 in 200 ns
(0.5 kg TNT)
• Maximum beam loss at 7 TeV: 1% of beam over 10 s
500 kW
• Quench limit of
SC LHC magnet:
8.5 W/m
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Machine Protection
• There are a number of LHC failure scenarios which lead to beam loss.
• No discussion of machine protection details here. However, comments on
collimator role in machine protection.
• Slow failures:
– First losses after >50 turns appear at collimators as closest aperture
restrictions.
– Beam loss monitors detect abnormally high losses and dump the beam within
1-2 turns.
• Fast failures (dump and injection kicker related):
– Sensitive equipment must be passively protected by collimators.
• In all cases, the exposed collimators must survive the beam impact:
up to 2 MJ in 200 ns (0.5 kg TNT)
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The LHC Collimation Project
• 2002: Conclusion that the originally foreseen LHC collimation system
would not withstand the LHC intensities and not provide sufficient
cleaning and protection.
• 2003: Start of LHC collimation project to urgently provide:
– robust collimator hardware design.
– suffcient cleaning efficiency and protection.
– hardware R&D and prototyping.
– prototype testing without and with beam.
– industrial production and installation.
• In view of technical challenge and short time available, implementation of
staged approach. Collaborative approach to include world-wide expertise.
• Total investment cost of ~28 M$ plus about 90 man-years CERN staff.
• Quite a strong effort over the last 4.5 years!
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The Collimation Team…
Collimation team:
About 60 CERN technicians,
engineers and physicists… in
various groups and
departments.
+ many friends in connected
areas (BLM’s, MP, …)
+ collaborators in various
laboratories (SLAC, FNAL,
BNL, Kurchatov, …)
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The Staged LHC Path
Energy density
at collimators
Stored energy
in beams
Number of
collimators
(nominal 7 TeV)
State-of-the-art in SC
colliders (TEVATRON,
1 MJ/mm2
2 MJ
Phase 1 LHC
Collimation
400 MJ/mm2
150 MJ
88
Nominal LHC
1 GJ/mm2
360 MJ
122
Ultimate & upgrade
scenarios
~4 GJ/mm2
~1.5 GJ
≤ 138
Limit (avoid
damage/quench)
~50 kJ/mm2
~10-30 mJ/cm3
HERA, …)
Factor
>1000
Equivalent 80 kg TNT explosive
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2) LHC Collimation Basics
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LHC Need for Collimation
• Ideally, stored proton beams would have infinite lifetime and no protons
would be lost.
• However, a multitude of physical processes will limit the lifetime of the
beams and unavoidable proton losses must be taken into account.
• Conditions for quenching the SC magnets:
– Transient loss of 10-9 fraction of beam (within 10 turns)
– Slow loss of 3×10-8 fraction of beam per s and per m (< 10000 h lifetime)
• Proton losses must be intercepted and absorbed by specifically
designed devices, namely collimators. These constrain the aperture.
• Multi-turn process: protons diffuse to limiting aperture bottleneck. Process
also called beam cleaning.
• 2 out of 8 straight sections in the LHC are dedicated to collimation!
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Multi-Stage Cleaning & Protection
Beam axis
Beam propagation
Impact
parameter
Core
Collimator
Particle
Unavoidable losses
CFC
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CFC
e
Absorber
e p
Shower
Secondary
collimator
Primary
collimator
Impact
parameter
≤ 1 mm
Secondary
p halo
p Shower
p
W/Cu
Tertiary halo
p
Superconducting
magnets
Absorber
Primary
halo (p)
SC magnets
and particle
physics exp.
W/Cu
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Diffusion Process & Impact Parameter
Slow loss:
Uniform “emittance”
blow-up
Beam lifetime: 0.2 h
Loss rate:
Loss in 10 s:
4.1e11
4.1e12
p/s
p
(1.4 %)
(~ 40 bunches)
Assume drift:
0.3
sig/s
5.3
nm/turn
(sigma = 200 micron)
Transverse impact
parameter
Almost all particles
impact with
y ≤ 0.2 mm
Surface
phenomenon!
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“Phase 1”
System Design
Momentum
Collimation
Betatron
Collimation
“Final” system:
Layount is 100%
frozen!
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C. Bracco
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LHC Collimator Gaps
Collimator settings:
5 - 6 s (primary)
6 - 9 s (secondary)
s ~ 1 mm (injection)
s ~ 0.2 mm (top)
Small gaps lead to:
1. Surface flatness
tolerance (40 mm).
2. Impedance
increase.
3. Mechanical
precision demands
(10 mm).
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Required Efficiency
Quench threshold
Allowed
intensity
(7.6 ×106 p/m/s @ 7 TeV)
Illustration of LHC dipole in tunnel
N
max
p
   Rq  Ldil /c
Cleaning inefficiency
=
Number of escaping p (>10s)
Number of impacting p (6s)
Beam lifetime
(e.g. 0.2 h minimum)
Dilution
length
(~10 m)
Collimation performance can limit the intensity and therefore
LHC luminosity.
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Intensity Versus Cleaning Efficiency
For a 0.2 h
minimum beam
lifetime during
the cycle.
99.998 % per m efficiency
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The LHC Phase 1 Collimation
•
Low Z materials closest to the beam:
– Survival of materials with direct beam impact
– Improved cleaning efficiency
– High transparency: 95% of energy leaves jaw
•
Distributing losses over ~250 m long dedicated cleaning insertions:
– Average load ≤ 2.5 kW per m for a 500 kW loss.
– No risk of quenches in normal-conducting magnets.
– Hot spots protected by passive absorbers outside of vacuum.
•
Capturing residual energy flux by high Z absorbers:
– Preventing losses into super-conducting region after collimator insertions.
– Protecting expensive magnets against damage.
•
No shielding of collimators:
– As a result radiation spread more equally in tunnel.
– Lower peak doses.
– Fast and remote handling possible for low weight collimators.
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3) Collimator Hardware
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Hardware: Water Cooled Jaw
Up to 500 kW impacting on
a jaw (7 kW absorbed in jaw)…
Advanced material: Fiber-reinforced graphite (CFC)
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The LHC “TCSG” Collimator
1.2 m
3 mm beam passage with RF contacts for
guiding image currents
Designed for maximum robustness:
Advanced CC jaws with water cooling!
Other types: Mostly with different jaw
materials. Some very different with 2
beams!
360 MJ proton beam
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Other collimator features
• In-situ spare concept by moving the whole tank
(move to fresh surface if we scratch the surface
with beam)
• Direct measurements of jaw positions and
absolute gap (we always know where the jaws
are)
• Precision referencing system during production
• Measurements of jaw temperature
• Radiation impact optimization: Electrical and
water quick plug-ins, quick release flanges,
ceramic insulation of cables, ...
• RF contacts to avoid trapped modes or additional
impedance
C. Rathjen, AT/VAC
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Problem Collection I
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TS/MME analysis of problems
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Problem Collection II
TCS010 after bake-out (8 Sep 2006)
1.00E-07
9.00E-08
Partial Pressure [uncalibrated]
8.00E-08
7.00E-08
6.00E-08
5.00E-08
4.00E-08
3.00E-08
2.00E-08
1.00E-08
0.00E+00
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
Mass
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AT/VAC and TS/MME analysis of problems
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-06
06
-07
07
J an
-0 8
De
c-0
7
No
v-0
7
Oc
t-
Se
p- 0
7
Au
g- 0
7
J ul
J un
-0 7
Ma
y -0
7
Ap
r- 0
7
Ma
r- 0
7
Fe
b- 0
7
J an
-0 7
De
c-0
6
No
v-0
6
Oc
t-
Se
p- 0
6
Au
g- 0
6
J ul
J un
-0 6
Ma
y -0
6
Ap
r- 0
6
Ma
r- 0
6
# collimators
Production in Industry
110 collimators in industry
+ 26 collimators at CERN
spares
120
100
80
60
40
20
0
Date
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4) Collimation Performance
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Massive Computing: Performance
Simulations:
5 million halo protons
200 turns
realistic interactions in all collimator-like objects
LHC aperture model
 Multi-turn loss predictions
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Efficiency in Capturing Losses
Local inefficiency [1/m]
Beam1, 7 TeV
Efficiency
99.998 % per m
TCDQ
Betatron cleaning
Ideal performance
Quench limit
(nominal I, =0.2h)
Beam2, 7 TeV
Efficiency
99.998 % per m
TCDQ
Betatron cleaning
Ideal performance
Quench limit
(nominal I, =0.2h)
99.998 %
Local inefficiency: #p lost in 1 m over total #p lost = leakage rate
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Zoom Dispersion Suppressor IR7
Collimation team and FLUKA team
mW
Heat load showers
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Can We Run at the Quench Limit?
• BLM response depends on
where the protons are lost!
• Important shielding effect of
materials.
• Up to factor 10 different BLM
response for different
longitudinal locations!
• BLM threshold must protect
against quenches from all
different loss locations.
• Threshold at least factor 3
below quench limit (HERA factor
10).
• We cannot run at quench limit!
L. Ponce
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K. Tsoulou et al
Energy Deposition (FLUKA)
FLUKA team
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CERN Mechanical Simulations
Displacement analysis – Nominal conditions (100 kW) – Load Case 2
10s Transient (500 kW) – Loss rate 4x1011 p/s (Beam Lifetime 12min)
Initial loss 8e10p/s Max.
deflect. ~20mm
Transient loss 4e11p/s
during 10s
Max deflect. -108mm
Back to 8e10p/s situation!
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A. Bertarelli & A. Dallochio
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Kurchatov Studies on Shock Waves
One nominal p bunch impacts on the CFC collimator jaw: Evolution of shock wave…
X-axis:
Jaw length (0 to 150 cm)
Y-axis:
Pressure in 1012 erg/cm3
A. Ryazanov
Compression area
Relevant question:
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570 ms
110 ms
250 ns
Tensile area
Interference of shock waves from different bunches, including
reflections of shock waves at boundaries?
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Local Activation
•
Losses at collimators generate local heating and activation.
•
Local heating: On average 2.5 kW/m.
•
Activation: Up to 20 mSv/h on contact (better not touch it).
•
Fast handling implemented. Remote handling being developed.
Residual dose rates
One week of cooling
S. Roesler et al
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Kurchatov Collaboration Studies of CFC
Material Used in LHC Collimators
A. Ryazanov
 Working on understanding radiation damage to LHC collimators from 1016 impacting
protons of 7 TeV per year. Also with BNL/LARP…
… in addition shock wave models…
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Impedance Problem
• Several reviews of LHC collimator-induced impedance (originally not
thought to be a problem).
• Surprise in 2003: LHC impedance driven by collimators, even metallic
collimators.
• LHC will have an impedance that depends on the collimator settings!
• Strong effort to understand implications…
Third look at impedance in Feb 03
revealed a problem:
F. Ruggiero
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Transverse Impedance [MΩ/m]
First Impedance Estimates 2003
Typical collimator half gap
104
103
102
LHC impedance without collimators
10
1
10-1
0
2
4
6
Half Gap [mm]
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10
F. Ruggiero, L. Vos
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2006 Impedance Estimates
E. Metral
et al
 Limitation at about 40% of nominal intensity… (nominal b*, full octupoles)
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Important: Collimator impedance was measured in the SPS with LHC prototype collimator.
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Stability diagram (maximum octupoles) and collective tune shift for
the most unstable coupled-bunch mode and head-tail mode 0
(1.15e11 p/b at 7 TeV)
25 ns
Im Q 
Vertical plane
0.00005
UNSTABLE
0.00004
Effect of the
bunch spacing…
0.00003
50
STABLE
0.00002
75
150
Re  Q 
0.001
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Single bunch
0.00001
300
0.0008
900
0.0006
0.0004
0.0002
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Potential Solutions Impedance
•
Metallic secondary collimators (phase 2 design at SLAC and CERN)  lower
electrical resistivity of collimator “wall”.
•
Increased chromaticity  stabilize beams.
•
Low noise transverse feedback at 7 TeV  stabilize beams.
•
Larger collimator gaps:
–
Triplet upgrade with larger aperture. Collimator gaps at 7 TeV are a direct function
of the triplet aperture and the b*, if efficiency is good enough.
–
Crystal-based collimation with increased particle deflection  larger gaps for
secondary collimators, if efficiency good enough.
–
Non-linear collimation scheme  larger gaps for secondary collimators, if
efficiency good enough.
All approaches must be looked at, even if they now seem challenging!
LARP/SLAC takes first steps towards construction of phase 2 collimator.
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Opening Collimator Gaps
Power Deposition [W/m]
(dN/dt = 0.1% per s, lost at collimators, nominal intensity)
Quench Limit
TCP Setting [sigma]
C. Bracco et al
 Higher losses in SC magnets close to cleaning insertions.
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Impedance and Chromaticity
E. Metral
et al
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5) Tunnel Installations
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Collimator General Layout
(vertical and skew shown)
Water
Connections
Vacuum pumping
Modules
Collimator
Tank (water cooled)
Quick connection
flanges
A. Bertarelli
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BLM
Beam 2
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Base Support and Lower Plug-In
Guides
Guides
Water plugs
Lower plug-in
Electrical plugs
Base support
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Support & Plug-In Installation
LSS5
Survey and
alignment done
with quick-plugin
supports and without
collimator (precise
reference from plugin and alignment
tool).
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Collimator Installation
Quick plug-in support (10 min installation)
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Collimator Transport Vehicle

Start of training for collimator installation with upgraded
vehicle (K. Kershaw et al).
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BLM’s for Observing Beam Loss
Every collimator has 2
dedicated BLM’s.
SEM:
0.05 charges per particle
Ionization chamber:
500 particles per particle
per cm traversal
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6) Collimator Beam Tests in SPS
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Collimator Controls
S. Redaelli et al
Collimator Beam-Based Alignment
Successful test of LHC collimator control architecture with SPS beam (low, middle, top level)
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Position Measurement and Reproducibility
LVDT Calibration Repeatability test (TT40)
36 repetitions
1.01
1.005
20 µm
1
Normalized position [mm]
0.995
0.99
0.985
0.98
0.975
~ 25 µm mechanical play
0.97
0.965
0.96
0.955
0.95
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
distance [mm]
•
Measured during test in TT40 (Oct. 31st) in remote!!!!
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R. Losito et al
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Typical beam loss signal for move of jaw
Observation of BLM signal tails:
BLM team:
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Up to 10-20 seconds in length
Many measurements  Beam related true signal!
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Loss Tails with Echo
12 s
Another example
Jaw movement
C. Bracco, T. Weiler et al
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Beam tails with long decay times (several 10 s) already shown in 2004!
This time observation of “echo” in beam loss tails…
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Collimator-Induced Tune Change
(Changing Collimator Gap)
Gap:
2.1
51 mm
M. Gasior, R. Jones et al
SPS tune depends on
collimator gap!
Expected tune change
observed within factor 2!
Impedance estimates are
strongly confirmed by
experiment!
F. Zimmermann et al
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2006 Impedance Measurement
Improved controls in 2006:
• Possibility of automatic
scan in collimator
position.
• Much more accurate
and complete data set in
2006 than in 2004!
R. Steinhagen et al
E. Metral et al
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Microphone
Robustness Test
C-C jaw
TED Dump
C jaw
450 GeV
3 1013 p
2 MJ
0.7 x 1.2 mm2
~ Tevatron beam
~ ½ kg TNT
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•
Jaw impact could be measured during all expected hits:
no change in jaw dimensions (nothing fell off)
•
Closure of two jaws to 1mm gap after test.
•
Took out collimator last week and inspected (two months
cooldown).
•
Microscopic analysis to be done.
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Jaws after Shock Impact
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Temperature Response
TT40 collimator temperature probes
65.0
60.0
Spikes correspond to 2 MJ
beam shock impact:
Possibility to detect
accidental beam impact!
Temperature [°C]
55.0
50.0
Temp Upstream [°C]
Temp Downstream [°C]
Temp Water Cooling [°C]
Temp Downstream [°C]
Temp Water Cooling [°C]
Temp Upstream [°C]
45.0
40.0
35.0
30.0
25.0
20.0
0:00
2:24
4:48
7:12
9:36
12:00
14:24
16:48
Time Elapsed [h:min]
P. Gander et al
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7) Beyond Phase 1
•
The phase 1 system is the best system we could get within the available 4-5
years.
•
Phase 1 is quite advanced and powerful already and should allow to go a factor
100 beyond HERA and TEVATRON.
•
Phase 2 R&D for advanced secondary collimators starts early to address
expected limitations of phase 1.
•
Phase 2 collimation project was approved and funded (CERN white paper). Starts
Jan 2008. Should aim at complementary design compared to SLAC.
•
SLAC/LARP effort on rotatable collimator is a crucial contribution in our plans and
addresses several possible problems.
•
Goal is to be ready for collimation upgrade in shutdown 2011/12, if needed.
Base decision on phase 1 experience and results of phase 2 prototype tests.
•
We also revisit more advanced collimation schemes, like crystals, magnetic
collimators, non-linear schemes.
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Collimation Planning Phase 2
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The Staged LHC Path
Energy density
at collimators
Stored energy
in beams
Number of
collimators
(nominal 7 TeV)
State-of-the-art in SC
colliders (TEVATRON,
1 MJ/mm2
2 MJ
Phase 1 LHC
Collimation
400 MJ/mm2
150 MJ
88
Nominal LHC
1 GJ/mm2
360 MJ
122
Ultimate & upgrade
scenarios
~4 GJ/mm2
~1.5 GJ
≤ 138
Limit (avoid
damage/quench)
~50 kJ/mm2
~10-30 mJ/cm3
HERA, …)
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8) Conclusion
•
LHC advances the accelerator field into a new regime of high power beams
with unprecedented stored energy (and destructive potential).
•
The understanding of beam halo and collimation of losses at the 10-5 level will be
crucial for its success (high luminosity)!
•
LHC collimation will be a challenge and a learning experience!
•
Collimation is a surprisingly wide field: Accelerator physics, nuclear physics,
material science, precision engineering, production technology, radiation physics.
•
A staged collimation approach is being implemented, relying on the available
expertise in-house and in other labs.
•
The help from other labs, especially SLAC and LARP, is greatly appreciated. We
must be sure to get the best possible system implemented! Bid for support from
European Community (FP7).
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Supporting Slides
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Failure Impacts on Collimators
(for Cu)
Beam loss at the 10-5 level can damage components:
Pre-fire of one dump kicker module
(2.2 MJ)
Asynchronous beam dump (miss dump gap)
(0.5 MJ)
Impact from one full batch at injection
(2.3 MJ)
Slow case:
Impact during low beam lifetime (0.2 h to1 h)
(4.4 MJ in 10s)
Beam types:
Protons and ions
Full stored beam power:
360 MJ (7 TeV)
Fast cases (< 1 turn):
Energy to melt 1 kg Cu:
0.7 MJ
Observations:
•
We expect losses on the 0.1% - 1% level. Sufficient to melt several kg Cu.
•
The 2002 LHC collimation system (Al/Cu) would withstand only on the 0.001% level!
Note:
Only one primary per plane. Disturbed beam can bypass primary and hit secondary (1 turn).
Any collimator can be hit (don’t constrain LHC tune).
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Peak Beam Loss Specification
•
The collimation system should handle the following loss rates:
•
Loss rates based on experience. Not too conservative: Peak loss at 7 TeV is 1%
of beam in 10s!
•
Supported by Tevatron, HERA and RHIC experience!
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Collimation project
Resources/planning
R. Assmann, O. Brüning,
H. Schmickler, J. Lettry,
M. Mayer
Beam
aspects
R. Assmann,
LCWG
System design,
optics, efficiency,
impedance
(calculation,
measurement),
beam impact,
tolerances, diffusion,
beam loss, beam
tests, beam
commissioning,
operational
scenarios, support of
operation.
(R&D phase 1&2)
report to
Leader: R. Assmann
Project engineer: O. Aberle
Organization, schedule, budget,
milestones, progress monitoring,
design decisions
Energy
deposition,
radiation
Engineering,
production &
HW support
A. Ferrari
(collimator design,
ions)
SC/RP
(radiation impact)
FLUKA, Mars
studies for energy
deposition around
the rings. Activation
and handling
requirements.
(R&D phase 1&2)
O. Aberle (ring)
Y. Kadi (transfer
line)
Conceptual
collimator design,
hardware
commissioning,
support for beam
tests, series
production,
installation,
maintenance/repair.
(R&D phase 1&2)
(S. Myers, LTC)
LARP Collimation
SLAC, BNL, FNAL
Electronics,
sensors,
infrastructure
controls
R. Losito
(motors, sensors,
electronics,
infrastructure, low
level control)
M. Jonker
(control system and
middleware)
M. Lamont
(top level controls
application).
Mechanical
engineering
(TS)
Coord.: M. Mayer
Engin.: A. Bertarelli
Sen. designer:
R. Perret
Technical specification, mechanical
integration, thermomechanical
calculations and
tests, mechanical
design, prototype
production&testing,
drawings.
(R&D phase 1&2)
Installation & remote tools
Beam instrumentation
Dump/kickers/TL
K. Kershaw (TS)
B. Dehning
B. Goddard
Local feedback
Machine Protection
Electronics/radiation
J. Wenninger
R. Schmidt
T. Wijnands
RWA, SLAC 8/07
AB
department
Coll. vacuum
design &
production
(AT)
M. Jimenez
Vacuum design at
collimators, vacuum
performance,
vacuum
interconnects at
collimators (design,
production,
installation,
commissioning),
support for bake-out
equipment.
AT department
TS department
70
Collimator Sketch
A. Bertarelli, R. Perret et al
RWA, SLAC 8/07
71
Effect of Closed Orbit (Static)
Local inefficiency [1/m]
Quench limit
(nominal I, =0.2h)

Higher inefficiency (factor 2)  Less performance!

Impact on machine design: Allocation of ring BLM’s!
RWA, SLAC 8/07
72
Residual Dose Rates – TCP / TCSG /
TCAPA / TCAPC
One week of cooling
S. Roesler et al
LHC collimators and cleaning insertions optimized for radiation handling!
RWA, SLAC 8/07
73
Thermal expansion [mm/ºC]
CFC Material Properties (BNL tests)
Non-radiated
Radiated after
annealing
Radiated
Temperature [ºC]
N. Simos
 No change close to operating temperature in the LHC. Annealing…
RWA, SLAC 8/07
74
Required Collimator Openings
Aperture allowances: 3-4 mm for closed orbit, 4 mm for momentum offset, 1-2 mm for mechanical tolerances.
Energy
Location
a [m]
b [m]
anorm [m1/2]
anorm/e1/2
450 GeV
Arc
0.012
180
8.8 × 10-4
10
7 TeV
Triplet
0.015
4669
2.2 × 10-4
10
Collimator setting (prim) required for triplet protection from 7 TeV secondary halo:
~ 0.15
b coll
acoll  atriplet 
b triplet
~ 0.6
max
 Aprimary
  max
A
 secondary




Collimator gap must be 10 times
smaller than available triplet
aperture!
Collimator settings usually defined in sigma with nominal emittance!
RWA, SLAC 8/07
75
LHC Halo
Scattering in collimator jaws (at
6/7 s)
Transverse scattering angles
+ momentum loss
Halo at zero dispersion
Halo at max dispersion
Betatron collimators generate a
small off-momentum halo (singlediffractive scattering)!
RWA, SLAC 8/07
76
Single-Diffractive Scattering
Cross-section single-diffractive
scattering: Comparison FLUKA –
STRUCT – COLLTRACK/K2
LHC p collimation system was optimized until fundamental limitation was met:
•
Some protons experience single-diffractive scattering in primary betatron collimators: large
energy offset and small betatronic kick.
•
Betatron collimators generate off-momentum halo.
•
Most of newly off-momentum protons are lost in first place with high dispersion: downstream
dispersion suppressor.
RWA, SLAC 8/07
77
BNL/LARP Radiation Tests on CFC
Work done by N. Simos within LARP.
1020 p shot on CFC collimator material samples
(identical material).
Dose much higher than yearly dose on most
exposed LHC collimators (~1016 p/year).
Work in progress to extrapolate to LHC losses
(FLUKA team).
Serious DAMAGE of 2D CC after
heavy irradiation exposure
RWA, SLAC 8/07
78