Collimators: Operations - Baseline Assumptions As indicated the collimators have to protect the machine and experiments while we’re 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 30/06/2004 LHC collimator review

Types of loss Abnormal (Fast & Ultra fast loss) Short lifetimes Stable 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 Other: e.g. electron-capture by pair production 30/06/2004 LHC collimator review

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 Transfer Line collimation Other protection devices Machine Protection 30/06/2004 LHC collimator review

Here to Protect 1. Damage: 2. Quenches Dangers clear and well enumerated. 2. Quenches For example, local transient loss of 4 × 107 protons at 7 TeV Nominal beam energy → One British aircraft carrier at 11 knots One girl in a Porsche at 1600 mph 30/06/2004 LHC collimator review

Beams Beam No. bunches Protons/bunch Total Intensity Emittance Pilot 1 5 – 10 x 109 1 – 3.75 µm Intermediate 12 1.15 x 1011 1.4 x 1012 3.75 µm Nominal 2808 3.23 x 1014 Ultimate 1.67 x 1011 4.7 x 1014 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

Nominal cycle 30/06/2004 LHC collimator review

Injection – 450 GeV Big beams, lower dynamic aperture 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 30/06/2004 LHC collimator review

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

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 30/06/2004 LHC collimator review

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 30/06/2004 LHC collimator review

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 97 0.2 4.3 x 1011 487 30/06/2004 LHC collimator review

Allowable Intensity in the LHC Allowed intensity Quench threshold (7.6 ×106 p/m/s @ 7 TeV) Cleaning inefficiency = Number of escaping p (>10s) 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. 30/06/2004 LHC collimator review

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

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 > 0.2 hours. Dump beam otherwise 30/06/2004 LHC collimator review

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

IR3 IR7 First Year - 1.3 x 1016 Nominal 8.0 x 1015 3.5 x 1016 Ultimate 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

Initial commissioning of phase 1 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 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 30/06/2004 LHC collimator review

Phased commissioning Parameter Tolerances for 50% increase in cleaning inefficiency Nominal Injection (6/7 ) Nominal Collisions Collisions (Relaxed *) (7/10.5 ) Beam size at colls. ≈ 1.2 mm ≈ 0.2 mm Orbit change 0.6  ≈ 0.7 mm 0.6  ≈ 0.12 mm 2.0  ≈ 0.4 mm Transient -beat 8% 80% Collinearity beam-jaw 50 µrad 75 µrad 30/06/2004 LHC collimator review R. Assmann, J.B. Jeanneret, E. Metral,

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… 30/06/2004 LHC collimator review