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30/06/2004 LHC collimator review 1
Collimators:Operations - Baseline Assumptions
• Types of losses• Beams• Operational cycle & role of collimators• Lifetime limits• Collimator efficiency• Operational constraints on beam parameters• Annual losses• LHC commissioning - phased approach
As indicated the collimators have to protect the machine and experiments while we’re spraying beam around at all stages of operations
30/06/2004 LHC collimator review 2
Types of loss
• Abnormal (Fast & Ultra fast loss) Equipment malfunction etc.
• Short lifetimes Operator error Beam instabilities Parameter control challenges (persistent currents etc.)
• Stable Transverse
Beam gas
Nonlinearities Long range beam-beamElectron cloudIBSCollisions
LongitudinalTouschekRFIBS
Other: e.g. electron-capture by pair production
30/06/2004 LHC collimator review 3
Required Beam Intensity
Collimator efficiency
Operational tolerances
Acceptable Lifetimes
Abnormal losses
Other protection devicesTransfer Line collimation
Beam Instrumentation
Permitted beam loss
Operational cycle
Machine Protection
Collimator designComing later…
Short Lifetime/Stable conditions
30/06/2004 LHC collimator review 4
Here to Protect
• 1. Damage: Dangers clear and well enumerated.
• 2. Quenches For example, local transient loss of 4 × 107 protons at 7 TeV
One girl in a Porsche at 1600 mph
One British aircraft carrier at 11 knots
Nominal beam energy →
30/06/2004 LHC collimator review 5
Beams
Beam No. bunches
Protons/bunch
Total Intensity
Emittance
Pilot 1 5 – 10 x 109 5 – 10 x 109 1 – 3.75 µm
Intermediate
12 1.15 x 1011 1.4 x 1012 3.75 µm
Nominal 2808 1.15 x 1011 3.23 x 1014 3.75 µm
Ultimate 2808 1.67 x 1011 4.7 x 1014 3.75 µm
Ions 592 7 x 107 4.1 x 1010 1.5 µm
Totem 43/156 3 x 1010 1.3/4.4 x 1012 1.0 µm
30/06/2004 LHC collimator review 6
Nominal cycle
0
14000
-3000 -2000 -1000 0 1000 2000 3000
Time [s]
MB
cu
rre
nt
0
1
2
3
4
5
6
7
8
9
B [
T]
RAMP DOWNSTART RAMP
PHYSICS
PREPAREPHYSICS
BEAM DUMP
PREINJECTIONPLATEAU
INJECTION
T0 Tinj
SQUEEZE
PHYSICS
Ramp down 18 Mins
Pre-I njection Plateau 15 Mins
I njection 15 Mins
Ramp 28 MinsSqueeze 5 Mins
Prepare Physics 10 MinsPhysics 10 - 20 Hrs
30/06/2004 LHC collimator review 7
Injection – 450 GeV
1. Pilot & Intermediate beam to check & adjust beam parameters, position collimators etc.
2. 12 SPS batches per ring, 1 batch up to 288 bunches
• Big beams, lower dynamic aperture • Protection of cold aperture in arcs • Collimators to protect during:
Injection process (injection oscillations etc.) Accidents: kicker misfires, timing errors Inevitable lifetime dips
30/06/2004 LHC collimator review 8
Ramp & Squeeze
• Start ramp - out of bucket flash: ~5% total beam primarily onto the momentum collimators
• Start ramp - snapback: Tune, chromaticity, momentum, orbit, -beating. Lifetime.
• Ramp: Collimators stay (more-or-less) where they are. Beam
emittance shrinks. Still protecting arc cold aperture. Scraping at end of ramp?
• Squeeze: Aperture limit now becomes inner triplet [IR1 & 5].
Collimators need to move in before/during the squeeze to protect the insertion quadrupoles.
Tune, chromaticity, orbit, -beating. Lifetime.
30/06/2004 LHC collimator review 9
Beam lifetimes
Proton loss rate 7 TeV [hours] Ending up Beam lifetime from residual gas interactions - Inelastic (Nuclear)
7.5e8 120 around ring
Beam lifetime from residual gas interactions - Elastic (Coulomb)
3.2e8 280 betatron cleaning
Touschek effect 7.2e7 1246 momentum cleaning Collisions – inelastic – one high luminosity IP 6.0e8 150 triplet Collisions - single diffractive – one high luminosity IP
2.4e7 3738 dispersion
suppressors Collisions - single diffractive – one high luminosity IP
9.6e7 935 momentum cleaning
Collisions - elastic– one high luminosity IP 4.0e8 224 betatron cleaning Gas + IBS + long range beam-beam (assume matched by synchrotron radiation damping)
- 150 -
Machine imperfections 1.65e9 54 betatron cleaning
The contributions for collisions have to be doubled up to get an estimate for an intensity lifetime of around 17.8 hours. NB figures preliminary
7 TeV - Physics
Plus: Lifetime dips, background optimisation, abort gap
30/06/2004 LHC collimator review 10
Emittance growth rates
Growth rate 7 TeV [hours]
Residual gas interactions(small angle scattering) 500
Transverse IBS 80
Longitudinal IBS 61
Long range beam-beam Cuts in above 6 Synchrotron radiation – longitudinal emittance damping 13
Synchrotron radiation – transverse emittance damping 26
Plus random power supply noise, ground motion, RF noise, electron cloud, nonlinearities . Small contribution to beam lifetime at 7 TeV
especially given the presence of synchrotron radiation damping
30/06/2004 LHC collimator review 11
Minimum beam lifetimes
Mode T [s] [h] Rloss [p/s] Ploss [kW]
Injection
continuous
1.0 0.8 x 1011 6
10 0.1 8.6 x 1011 63
Ramp ≈ 1 0.006 1.6 x 1013 1200
Top energy
continuous
1.0 0.8 x 1011 97
10 0.2 4.3 x 1011 487
30/06/2004 LHC collimator review 12
Allowable Intensity in the LHC
cdilqp LRN /max
Allowed
intensity
Quench threshold
(7.6 ×106 p/m/s @ 7 TeV)
Dilution
Length
(50 m)
Cleaning inefficiency
=Number of escaping p (>10)
Number of impacting p (6)
Beam lifetime
(e.g. 0.2 h
minimum)
The nominal intensity of 3 × 1014 protons per beam
requires a collimation inefficiency of 2 × 10-5 m-1.
Injection has less strict requirements.
30/06/2004 LHC collimator review 13
Operations
• Limitations on the allowed minimal collimator gap:
The beam core must not be scraped by collimation, usually requiring collimator settings above 4-5 .
The collimator gap must be wide enough to avoid excessive impedance from the collimators and to maintain beam stability.
The two-stage functionality of the collimation system must be maintained during the whole operational cycle, e.g. the primary collimators must always remain primary and the secondary must always remain secondary collimators. Usually a relative offset of 1 nominal sigma is required, corresponding to about 200 µm at 7 TeV. Operational and mechanical tolerances are specified for this offset.
30/06/2004 LHC collimator review 14
Operations - implications
• Design aperture must be established Max. -beating ≈ 20% Max. orbit deviation ≈ 4 mm.
• Transient changes in orbit and -beating under control (tune & orbit feedback, etc.)
Max. transient -beating ≈ 8% Max. orbit shift ≈ 0.6
• Nominal beam loss rates established Min. beam lifetime > 0.2 hours. Dump beam otherwise
The settings n1, n2 and n3 of primary, secondary and tertiary collimators must be carefully adjusted in order to minimize the leakage rates of the cleaning
insertions → tight demands on beam optics and stability. To go to significant intensity therefore:
30/06/2004 LHC collimator review 15
Annual Doses
• Take: assumed operational efficiency, number of days of operation, turn around → number of fills
• For a fill, estimate: Injection oscillation losses, lifetime at 450 GeV, scale to 7 TeV Start ramp: out of bucket flash, snapback Lifetime in ramp Squeeze: lifetime, lifetime dips Physics: lifetimes (plus lifetime evolution) - halo versus luminosity
etc. Dump Plus some lost fills
30/06/2004 LHC collimator review 16
DAYS OF PHYSICS 200 timeOPERATION EFFICIENCY 0.6 1
2NUMBER BUNCHES 2808 3BUNCH CURRENT 1.15E+11 4
3.23E+14 56
INITIAL BEAM CURRENT 0.85 7INITIAL NUMBER OF PARTICLE 3.23E+14 8INITIAL LUMINOSITY 1.00E+34 9
10LUMINOSITY LIFETIME 13.9 15
2025
Assume fill length 10 12 15 20Assume turnaround 3 5 5 10
Number of fills 221.5 169.4 144 96
injection oscillations - 2% 6.46E+12
On injection plateau - 20 minutes at 10 hours lifetime 1.05E+13
INJECTION TOTAL - SCALED BY GAMMA 1.09E+12
Start ramp - at 450 GeV 2% of total 6.46E+12Scale by gamma 4.14E+11
Ramp - 20 minutes at 10 hours lifetime 1.05E+13
Scale by gamma/2 1.31E+12
Squeeze - lets say 10 minutes at 1 hour lifetime 5.05E+13
Squeeze - 2*10s at 0.2 hour lifetime 8.92E+12
total beam lost during physics (assume 5% loss during inj,ramp & squeeze) 5.37E+13 7.82E+13 8.28E+13 8.68E+13Physics - how much do we loose on the collimators at IR7 1.74E+13 2.54E+13 2.69E+13 2.82E+13
DUMPED 2.66E+14 2.41E+14 2.36E+14 2.32E+14
TOTAL LOST IN IR7 PER FILL 7.97E+13 8.76E+13 8.91E+13 9.04E+13PERCENTAGE LOSS PER FILL 2.47E-01 2.71E-01 2.76E-01 2.80E-01
TOTAL PER YEAR PER BEAM 1.76E+16 1.48E+16 1.28E+16 8.68E+15
TOTAL 3.53E+16 2.97E+16 2.57E+16 1.74E+16
Lifetime limits at 7 TeV
cont 1.0 hr 0.8 ×10^11 10s 0.2 hr 4.3 ×10^11
Annual loss estimates
IR3 IR7
First Year - 1.3 x 1016
Nominal 8.0 x 1015 3.5 x 1016
Ultimate 1.1 x 1016 7.3 x 1016
30/06/2004 LHC collimator review 17
Phased commissioning
• Initial commissioning: Ending with Pilot physics: 43 on 43 with 3 - 4 x 1010 (if we’re lucky)
• Year one[+] operation: Lower beam intensity/luminosity:
Event pileup Electron cloudPhase 1 collimator impedance etc. Equipment restrictions
Relaxed squeeze, lower intensities, 75 ns. bunch spacing
Use this period to stage commissioning of collimator systems & to optimise cleaning efficiency
Initial commissioning of phase 1
30/06/2004 LHC collimator review 18
Parameter
Tolerances for 50% increase in cleaning inefficiency
Nominal Injection(6/7 )
Nominal Collisions
(6/7 )
Collisions (Relaxed *)
(7/10.5 )
Beam size at colls. ≈ 1.2 mm ≈ 0.2 mm ≈ 0.2 mm
Orbit change 0.6 ≈ 0.7 mm
0.6 ≈ 0.12 mm
2.0 ≈ 0.4 mm
Transient -beat 8% 8% 80%
Collinearity beam-jaw
50 µrad 50 µrad 75 µrad
Phased commissioning
R. Assmann, J.B. Jeanneret, E. Metral,
30/06/2004 LHC collimator review 19
Conclusions
• Difficult beams, potential for quenches/damage high
• Operational cycle will include challenges effective collimation essential at all stages
• Reasonable limits on lifetimes assumed• Tight limits on collimator settings• Tight limits on operational beam parameters
to ensure required collimator efficiency• Annual dose estimates for IR3 & IR7• Phased commissioning foreseen
Acknowledgements…