Transcript Slide 1

Collimator Functionality,
Performance and First View
on Set-up and Optimization
R. Assmann
AB/ABP, CERN
Part of discussions on commissioning of machine protection related system:
B. Dehning, B. Goddard, M. Lamont, J. Wenninger, R. Schmidt
External Review of the LHC Collimation Project
June 30th - July 2nd 2004
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Outline
• Functionality of the LHC collimator
• Performance estimates
• Set-up and optimization
• Conclusion
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The LHC Type Collimator
If we say collimator:
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We mean a collimator with two parallel jaws!
Each jaw controllable in position and angle!
Functionality
Side view at one end
Calibration:
Inside vs outside gap etc
Microphonic
sensor
Temperature sensor
Reference
Reference
Motor
Motor
Gap opening (LVDT)
Resolver
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Resolver
Gap position (LVDT)
Not shown: IN, OUT, ANTI-COLL switches!
Functionality
Side view at one end
Calibration:
Inside vs outside gap etc
Microphonic
sensor
Temperature sensor
Reference
Reference
Motor
Motor
Gap opening (LVDT)
Resolver
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Gap position (LVDT)
Resolver
Basic control in-/output
Basic input:
Motor setting: jaw position at each end

Readings:
Control position and angle of each
jaw independently!
For each motor:

Local resolver reading
For each end of the jaw:


Monitoring:
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Gap width
Gap position
Temperature, switches, micro-phonic sensors
For set-up
We can guarantee a gap in mm to several 10’s of mm!
However, we must set to beam s, e.g. 6 s for primary
collimators!
Understand beta function at collimator! Must be known to 20% anyway
for aperture before serious commissioning  J. Wenninger!

Collimator gaps can be set to better ± 0.6 s from
basic aperture tolerances!
Major task for collimation set-up:

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Centering of gap around the beam!
Inefficiency and Allowable Intensity
Allowed
intensity
Quench threshold
(7.6 ×106 p/m/s @ 7 TeV)
N pmax    Rq  Ldil /c
Beam lifetime
(e.g. 0.2 h
minimum)
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Dilution
Length
(50 m)
(Luminosity)
Cleaning inefficiency
=
Number of escaping p (>10s)
Number of impacting p (6s)
How to get collimators going for phase 1
Start at low intensity:
 Need for less cleaning efficiency!
No collimation
Pilot bunch
Single-stage collimation
~ 500 bunches (inj)
~ 20 bunches (top)
b-cleaning: 2 primary coll.
momentum cleaning: 1 primary coll.
Help with local tertiary coll.
Limited two-stage collimation Intermediate intensities
Bring on secondary coll.
b-cleaning: ~ 7 TCS
momentum cleaning: ~ 4 TCS
Full two-stage cleaning
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Up to 50% of nom. intensity
b-cleaning: 11 TCS
momentum cleaning: 4 TCS
Components for the Collimation System (Phase 1)
Label
Number
per beam
Material
Jaw length
[m]
Collimators
Primary betatron
Secondary betatron
TCP
TCSG
3
11
CC
CC
0.2
1.0
Primary momentum
Secondary momentum
TCP
TCSG
1
4
CC
CC
0.2
1.0
TCT
6
Cu/W
1.0
TCHS
TCHS
2
1
tbd
tbd
tbd
tbd
TCLI
TCLP
TCLA
2
2
(8)
CC
Cu/W
Cu/W
1.0
1.0
1.0
Tertiary triplets
Focus of review
Most difficult!
Number of objects:
80 + 13 spares
Scrapers
Betatron
Momentum
Absorbers
Injection errors
Luminosity debris
Cleaning showers
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Per beam:
25 collimators
3 scrapers
12 absorbers
Collimators / Scrapers / Absorbers
Components of the collimation system are distinguished by their
function:
Collimators:
Elastic and inelastic interactions of beam protons.
Precise devices with two jaws, used for efficient beam
cleaning. Small gaps and stringent tolerances.
Scrapers:
Used for beam shaping and diagnostics.
Thin one-sided objects.
Absorbers:
Absorb mis-kicked beam or products of proton-induced
showers.
Movable absorbers can be quite similar in design to
collimators, but mostly with high-Z jaws. Larger gaps and
relaxed tolerances.
Precise set-up and optimization in first line affects collimators!
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Set-up of single collimator
BLM
Beam
BLM
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Set-up of single collimator
1-by-1 procedure:
1. Lower intensity  1 stage cleaning is sufficient.
2. Scraping of beam to ~ 3 s
3. Move in single jaw. One edge after the other.
4. Second jaw the same way.
5. Collimator to reference position (record) and then out.
6. Next collimator…
 No problem of cross-talk (do both beams at same time).
 Need good BLM system (B. Dehning, B. Holzer)
adjusted to set-up.
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Set-up of single collimator
BLM
Beam
Shower
BLM
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Set-up of single collimator
BLM
Beam
Shower
BLM
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Set-up of single collimator
BLM
Beam
Shower
BLM
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Set-up of single collimator
BLM
Beam
Shower
BLM
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Set-up of single collimator
BLM
Beam
Calibrated center and width of gap, if beam
extension is known (e.g. after scraping).
Advance with experience! Rely on good BLM
system...
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BLM
Advance procedures
Put all collimators to same normalized setting!
Assume we want to center gaps...
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Advance procedures
 Grow beam emittance...
Shower
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Advance procedures
 Grow beam emittance...
Shower
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Advance procedures
 Grow beam emittance...
Shower
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Advance procedures
 Grow beam emittance...
Shower
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Advance procedures
 Grow beam emittance...
Shower
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Advance procedures
 Grow beam emittance...
Shower
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Advanced procedures
• In principle we could optimize many collimators at once.
• Efficient procedures should be prepared!
• Can also imagine long orbit bumps through collimation
insertions with equal settings  similar to emiitance growth
procedure!
• Do at lower intensity, where one-stage cleaning is sufficient
(20 nom. bunches at 7 TeV, more at injection).
• Maybe less for machine protection!?
• Detailed simulations for these set-up procedures will be
done
 required and achievable tolerances (~0.1s or 20 mm)!?
• SPS: Test for single collimator set-up!
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Fine tuning of performance
• Best cleaning efficiency to avoid quenches!
• Look at places where losses are highest!
 Critical BLM’s!
• Use critical BLM’s for empirical optimization of collimator
settings (within limits):
 Trial and error procedure!
• Similar to regular machine tuining (orbit, ...). Just watch
out not to get the collimators damaged:
 Limits on tuning range (several s?).
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Loss Maps Around the Ring: Injection
Tertiary halo
Aperture model for 27,000 m
LHC with 0.1 m longitudinal
resolution: ~ 270,000 loss
points!
 S. Redaelli
G. Robert-Demolaize
Q6 downstream of betatron
cleaning: first SC magnet
Acceptable!? Understand effect of azimuth on
quench. Help further with absorbers in IR7!
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Loss Maps Around the Ring: Collision
Peaks in all
triplets:
Tertiary halo
Cure with tertiary
collimators!
Work is ongoing...
Massive computing effort:
9 × 106 p tracked over
100 turns through each
LHC element!
27,000 loss points
checked in aperture!
So far only tertiary halo:
Include also secondary
halo.
IR8: Initial optics with b* = 1 m
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Future data generated
from SIXTRACK!
Conclusion
• Preliminary thoughts on set-up and optimization.
• Evolutionary process: no collimation – 1 stage – limited 2
stage – full 2 stage. Help by tertiary collimators!
• Time scale of months/years  not all collimators needed for
day 1. Learn while the LHC performance is being pushed!
• Set-up of single collimator: Standard procedure exists and is
used successfully at other laboratories (adjust position and
angle)! Test with LHC collimator in the LHC!
• Advanced procedures: Should work to efficiently set up
many collimators!
• All of this will be simulated in detail!
• Goal: Procedures ready and implemented for LHC start-up in
2007! Then make them work...
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