Collimators: Operations - Baseline Assumptions

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


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


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


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 →


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


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


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


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.


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


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


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


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.


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.


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:


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


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


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


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,


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…

Collimators: Operations - Baseline Assumptions

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