Collimators: Operations - Baseline Assumptions

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CollimatorsOperations - Baseline Assumptions
As indicated the collimators have to protect the
machine and experiments while were spraying beam
around at all stages of operations

• Types of losses
• Beams
• Operational cycle role of collimators
• Lifetime limits
• Collimator efficiency
• Operational constraints on beam parameters
• Annual losses
• LHC commissioning - phased approach

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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-beam
• Electron cloud
• IBS
• Collisions
• Longitudinal
• Touschek
• RF
• IBS

Other e.g. electron-capture by pair production
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Short Lifetime/Stable conditions
Required Beam Intensity
Operational cycle
Permitted beam loss
Acceptable Lifetimes
Collimator efficiency
Operational tolerances
Beam Instrumentation
Coming later
Abnormal losses
Collimator design
Other protection devices
Transfer Line collimation
Machine Protection
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Here to Protect

• 1. Damage
• Dangers clear and well enumerated.
• 2. Quenches
• For example, local transient loss of 4 107
  protons at 7 TeV

Nominal beam energy ?
One girl in a Porsche at 1600 mph
One British aircraft carrier at 11 knots
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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
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Nominal cycle
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Injection 450 GeV

• Pilot Intermediate beam to check adjust beam
  parameters, position collimators etc.
• 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

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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.

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Beam lifetimes
7 TeV - Physics
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
Plus Lifetime dips, background optimisation,
abort gap
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Emittance growth rates
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
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Minimum beam lifetimes
Mode T s ? h Rloss p/s Ploss kW
Injection continuous 1.0 0.8 x 1011 6
Injection 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
Top energy 10 0.2 4.3 x 1011 487
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Allowable Intensity in the LHC
Quench threshold (7.6 106 p/m/s _at_ 7 TeV)
Allowed intensity
Cleaning inefficiency Number of escaping p
(gt10s) Number of impacting p (6s)
Beam lifetime (e.g. 0.2 h minimum)
Dilution Length (50 m)
The nominal intensity of 3 1014 protons per
beam requires a collimation inefficiency of 2
10-5 m-1. Injection has less strict requirements.
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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.

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Operations - implications
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

• 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 gt 0.2 hours. Dump beam
  otherwise

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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

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Annual loss estimates Annual loss estimates 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
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Phased commissioning

• Initial commissioning
• Ending with Pilot physics 43 on 43 with 3 - 4 x
  1010 (if were lucky)
• Year one operation
• Lower beam intensity/luminosity
• Event pileup
• Electron cloud
• Phase 1 collimator impedance etc.
• Equipment restrictions
• Relaxed squeeze, lower intensities, 75 ns. bunch
  spacing

Initial commissioning of phase 1
Use this period to stage commissioning of
collimator systems to optimise cleaning
efficiency
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Phased commissioning
Parameter Tolerances for 50 increase in cleaning inefficiency Tolerances for 50 increase in cleaning inefficiency Tolerances for 50 increase in cleaning inefficiency
Parameter 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
R. Assmann, J.B. Jeanneret, E. Metral,
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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