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
R. Assmann
Outline
• Functionality of the LHC collimator
• Performance estimates
• Set-up and optimization
• Conclusion
R. Assmann
The LHC Type Collimator
If we say collimator:
R. Assmann
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
R. Assmann
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
R. Assmann
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:
R. Assmann
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:
R. Assmann
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)
R. Assmann
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
R. Assmann
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
R. Assmann
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!
R. Assmann
Set-up of single collimator
BLM
Beam
BLM
R. Assmann
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.
R. Assmann
Set-up of single collimator
BLM
Beam
Shower
BLM
R. Assmann
Set-up of single collimator
BLM
Beam
Shower
BLM
R. Assmann
Set-up of single collimator
BLM
Beam
Shower
BLM
R. Assmann
Set-up of single collimator
BLM
Beam
Shower
BLM
R. Assmann
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...
R. Assmann
BLM
Advance procedures
Put all collimators to same normalized setting!
Assume we want to center gaps...
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
Advance procedures
Grow beam emittance...
Shower
R. Assmann
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!
R. Assmann
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?).
R. Assmann
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!
R. Assmann
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
R. Assmann
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...
R. Assmann