Collimators Operations Baseline Assumptions As indicated the collimators

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 1

Types of loss • Abnormal (Fast & Ultra fast loss) n Equipment malfunction etc. • Short lifetimes n n n Operator error Beam instabilities Parameter control challenges (persistent currents etc. ) • Stable n Transverse Beam gas Nonlinearities Long range beam-beam Electron cloud IBS Collisions n Longitudinal Touschek RF IBS 30/06/2004 Other: e. g. electron-capture by pair production LHC collimator review 2

Short Lifetime/Stable conditions Required Beam Intensity Operational cycle Permitted beam loss Acceptable Lifetimes Collimator efficiency Operational tolerances Coming later… Transfer Line collimation 30/06/2004 Beam Instrumentation Abnormal losses Other protection devices LHC collimator review Collimator design Machine Protection 3

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

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 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 5

Nominal cycle 30/06/2004 LHC collimator review 6

Injection – 450 Ge. V 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: n n n 30/06/2004 Injection process (injection oscillations etc. ) Accidents: kicker misfires, timing errors Inevitable lifetime dips LHC collimator review 7

Ramp & Squeeze • Start ramp - out of bucket flash: n ~5% total beam primarily onto the momentum collimators • Start ramp - snapback: n Tune, chromaticity, momentum, orbit, -beating. Lifetime. • Ramp: n n Collimators stay (more-or-less) where they are. Beam emittance shrinks. Still protecting arc cold aperture. Scraping at end of ramp? • Squeeze: n n 30/06/2004 Aperture limit now becomes inner triplet [IR 1 & 5]. Collimators need to move in before/during the squeeze to protect the insertion quadrupoles. Tune, chromaticity, orbit, -beating. Lifetime. LHC collimator review 8

Beam lifetimes 7 Te. V - 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 9

Emittance growth rates Plus random power supply noise, ground motion, RF noise, electron cloud, nonlinearities. Small contribution to beam lifetime at 7 Te. V especially given the presence of synchrotron radiation damping 30/06/2004 LHC collimator review 10

Minimum beam lifetimes Mode T [s] [h] Rloss [p/s] Ploss [k. W] continuous 1. 0 0. 8 x 1011 6 10 0. 1 8. 6 x 1011 63 ≈1 0. 006 1. 6 x 1013 1200 continuous 1. 0 0. 8 x 1011 97 10 0. 2 4. 3 x 1011 487 Injection Ramp Top energy 30/06/2004 LHC collimator review 11

Allowable Intensity in the LHC Allowed intensity Quench threshold (7. 6 × 106 p/m/s @ 7 Te. V) Cleaning inefficiency = Number of escaping p (>10 ) Number of impacting p (6 ) 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 12

Operations • Limitations on the allowed minimal collimator gap: n n n 30/06/2004 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 Te. V. Operational and mechanical tolerances are specified for this offset. LHC collimator review 13

Operations - implications The settings n 1, n 2 and n 3 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 n n Max. -beating ≈ 20% Max. orbit deviation ≈ 4 mm. • Transient changes in orbit and -beating under control (tune & orbit feedback, etc. ) n n Max. transient -beating ≈ 8% Max. orbit shift ≈ 0. 6 • Nominal beam loss rates established n 30/06/2004 Min. beam lifetime > 0. 2 hours. Dump beam otherwise LHC collimator review 14

Annual Doses • Take: assumed operational efficiency, number of days of operation, turn around → number of fills • For a fill, estimate: n n n n 30/06/2004 Injection oscillation losses, lifetime at 450 Ge. V, scale to 7 Te. V 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 LHC collimator review 15

Annual loss estimates 30/06/2004 IR 3 IR 7 First Year - 1. 3 x 1016 Nominal 8. 0 x 1015 3. 5 x 1016 Ultimate 1. 1 x 1016 7. 3 x 1016 LHC collimator review 16

Phased commissioning • Initial commissioning: n Ending with Pilot physics: 43 on 43 with 3 - 4 x 1010 (if we’re lucky) Initial commissioning of phase 1 • Year one[+] operation: n Lower beam intensity/luminosity: Event pileup Electron cloud Phase 1 collimator impedance etc. Equipment restrictions n Relaxed squeeze, lower intensities, 75 ns. bunch spacing Use this period to stage commissioning of collimator systems & to optimise cleaning efficiency 30/06/2004 LHC collimator review 17

Phased commissioning Tolerances for 50% increase in cleaning inefficiency Parameter Beam size at colls. Orbit change Transient -beat Collinearity beam-jaw 30/06/2004 Nominal Injection Nominal Collisions (6/7 ) Collisions (Relaxed *) (7/10. 5 ) ≈ 1. 2 mm ≈ 0. 2 mm 0. 6 ≈ 0. 7 mm 0. 6 ≈ 0. 12 mm 2. 0 ≈ 0. 4 mm 8% 8% 80% 50 µrad 75 µrad LHC collimator review R. Assmann, J. B. Jeanneret, E. Metral, 18

Conclusions • Difficult beams, potential for quenches/damage high • Operational cycle will include challenges n 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 IR 3 & IR 7 • Phased commissioning foreseen Acknowledgements… 30/06/2004 LHC collimator review 19