Baseline Scenario and Options for 3000 fb -1

Baseline Scenario and Options for 3000 fb-1

LHC Performance driversLHC Performance limitations and challengesOperation experience from 2010 and 2011HL GoalsUpgrade considerationsPotential HL-LHC Beam parameters

1O. BrüningHL-LHC Public meeting 18. November 2011

Luminosity (round beams):

1) maximize bunch intensity (brightness [Nb/en] if @ beam-beam limit)2) minimize beam size (constant beam power)3) maximize number of bunches4) compensate for ‘R’

Performance optimization for the LHC

2

Operation at performance limit choose parameters that allow higher than design performance leveling mechanisms for controlling performance during run

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O. BrüningHL-LHC Public meeting 18. November 2011

Performance Limitations & Challenges for the LHC

3

Bunch Intensity:

1) Beam-Beam interaction limit for beam brightness & crossing angle

2) Collective effects (e.g. TMCI) ca. 3.5 1011 ppb

3) e-cloud effect depends on bunch spacing and number of bunches see the

next 2 transparencies*:

1) Aperture interaction with WP3 of the HL-LHC

2) Chromatic aberrations novel correction mechanisms

3) Event pile up and bunch luminosity limit detectors upgrade


(e.g. ATS S. Fartoukh)

4

Number of bunches:

1) Operation with more than 150 bunches requires crossing angle; Operation with for 25ns bunch spacing and 2808 bunches implies ca. 30 long- range beam-beam interactions /IP 2) Electron cloud effect depends on bunch spacing (next transparency)

3) Total beam power and cleaning efficiency (limit on total beam power) fewer bunches more performing for

limited total current dedicated task in HL-LHC project

for now we assume a

limit of ca. 1 A per beam

5) Injector performance depends on bunch spacing (higher brightness for 50ns) maintain both bunch spacing options (25ns & 50ns)



25-ns bunch spacing 50-ns bunch spacing

H. Maury

e-cloud contribution acceptable for: 25ns and Nb = 2 1011 if dmax ≤ 1.2

50ns and Nb = 4 1011 if dmax ≤ 1.7

F. Zimmermann, Chamonix 2011

5

Electron cloud effect:



LHC Challenges: R

6

Geometric luminosity reduction factor:

large crossing angle: reduction of long range beam-beam interactions reduction of head-on beam-beam parameter

reduction of the mechanical aperture reduction of instantaneous luminosity

inefficient use of beam current (machine protection!)

opens the door for efficient luminosity leveling

effective cross sectionPiwinski angle


LHC Challenges: Beam-Beam Interaction

7

Tune spread due to head-on beam-beam interaction wo x-ing:

Werner Herr et al, LPN 416

Crossing angle configurations:Top Left: only head-onTop right: = 200mrad (≈ 7)Bottom left: = 285mrad (≈ 10)Bottom right = 400mrad (≈ 13)

DQ ≈ 0.01

Long range interactions:


LHC Challenges: Beam-Beam Interaction

8Werner Herr

DQy ≈ 0.01

DQx ≈ 0.01

Tune Footprint:Pacman bunches nominal beamsalternating crossing planes all insertions

Head-on &Long range


LHC Challenges: Resonances

9

LHC working point: n+m < 12

Qx = 64.31; Qy = 59.32total tune spread must besmaller than 0.018 (SppS experience) keep dQ = 8 10-3 for operation tolerances and coupling!

bunch intensity limited by beam-beam force:

Qy

Qx

3 head-on/bunch xbeam-beam< 3.3 10-3 N < 1.2 1011

2 head-on/bunch xbeam-beam< 5 10-3 N < 1.7 1011

3/10 1/32/7


Operation Experience in 2010 and 2011:

10

Leveling: successful for ALICE by parallel separation to be confirmed with long-range beam-beam!

beam-beam: able to collide beams with larger than nominal beam-beam parameters

Aperture better than expected (-beat, dispersion,tolerances)

ability to re-optimize beam parameters for higher performance smaller beam emittance and larger beam-beam parameter

Emittance able to operate the LHC with 50% smaller than nominal beam emittances (aperture & brightness)


HL-LHC Performance Goals

11

Preferred leveling mechanism: Crab Cavities

Reservations: technology & MP & noise

Supplementary tools for leveling: # crossing angle and Long-range and

beam-beam wire compensators # transverse offsets at IP# dynamic * squeeze

Operation at performance limit choose parameters that allow higher than design performance leveling mechanisms for controlling performance during run


Leveling by Crab Cavities

12


Piwinski angle


R(*)

*

Crab Cavities

13


CRAB cavity leveling is most effective for small *


HL-LHC Performance Goals

14

Integrated luminosity: 200 fb-1 to 300 fb-1 per year

Leveled peak luminosity: L = 5 1034 cm-2 sec-1

Total integrated luminosity: ca. 3000 fb-1

Virtual peak luminosity: L > 10 1034 cm-2 sec-1


For given luminosity teff scales with total beam current

levIP

toteff Ln

N

t

(=100 mbarn)

Upgrade Considerations: Beam LifetimeF. Zimmermann, Chamonix 2011

argument for HL-LHC scenarios with maximum beam currentteff = 13.9 hours for 5 1014 p/beam

15

levIPeff

tottot LnNdtdN

t

N(t) = (1-t/teff) Ntot


R. Assmann

R. Assman @ Chamonix 2010

16

Chamonix 2011

Lower Maximum Intensity of ca. 5 1014 p/beam

(TMCI limit f

or 50ns!)

Upper Maximum Intensity of 6.5 1014 p/beam

(e-cloud

limit f

or 25ns!)

Assume for n

ow beam current lim

it of ca. 1 A / b

eam!


Summary of LHC Intensity Limits (7 TeV)

Run length assuming leveled luminosity:

€

L ∝N

tot

2

nb

Upgrade Considerations: Beam Lifetime

virtual luminosity of k * 5 1034 cm-2 sec-1 Tlevel = (1-1/√k) * teff

Assuming: 1.8 1011 ppb @ 25ns & 3.5 1011 ppb @ 50ns ( ≈ 5 1014 p/beam)

teff = 13.9 hours for 5 1014 p/beam:

# k = 2: Tlevel = 4.1 h

# k = 3: Tlevel = 5.9 h

# k = 4: Tlevel = 7.0 h

17O. BrüningHL-LHC Public meeting 18. November 2011

Integrated luminosity: run with luminosity decay

Upgrade Considerations: Integrated Luminosity

Lint = ca 0.4 fb-1 over 3 h for a luminosity decay to 2.5 1034 cm-2 s-1

18

[Stephane Fartoukh]

assuming no emittance growth over the fill

the emittance growth due to IBS and beam-

beam is compensated by radiation damping


Integrated luminosity: leveling to constant luminosity Lint = Llevel * Tlevel


integrated luminosity directly proportional to total current

Lint = 0.4 + 0.73 fb-1 per fill for Ntot = 5 1014 ppb and k = 2

Lint = 0.4 + 1.25 fb-1 per fill for Ntot = 5 1014 ppb and k = 4 19

€

Lint = 1 − Llevel /Lvirt( )⋅N totnIPσ

(=100 mbarn)


LHC schedule 2011 v2.0 20

16-3

-201

1

Phase Days Comment

Commissioning 21Scrubbing run 105 MDs 22 4.5 days per slot

6 Technical stops 30 5 days (4 days TS plus 1 day recovery with beam)

Special requests10

TOTEM/ALPHAIntermediate energy runLuminosity scans

Intensity ramp up ~39 Total high intensity ~130Ion setup 4Ion physics 24TOTAL 290

M. Lamont March 2011


Assume ca. 150 days / yearfor HL-LHC operation

requires between 150 and 220 fills p

er year to reach 250 fb

-1 per year!

implies 1

to 1.5 fills

per day fo

r previous

scenario

(depending on virtual lu

minosity

reach) O. BrüningHL-LHC Public meeting 18. November 2011

HL-LHC running scenarios:


fill length between 7h and 10h for 5 1014 p/beam and ‘k’ = 2 4 Turnaround time of ca. 5 hours

total fill time of ca. 12 and 15 hours

1.5 fills (12h) per day (k = 2; virtual luminosity of 1035 cm-2 sec-1) requires 75% machine efficiency!

1 fill (15h) per day (k = 4; virtual luminosity of 2 1035 cm-2 sec-1) requires 60% machine efficiency

42% of time in stable beams with physics (= best performance in 2011)!

21

What virtual performance levels (‘k’) are within

reach for

5 1014 p/beam and 6 1014 p/beam?


Upgrade Considerations: Minimum * values:

22

HL LHC Upgrade: New scheme (ATS) for optics:-* of 0.15m accessible for round beams @ 7 TeV

implies -functions of > 20km inside triplet magnets!

limit of Field Quality and aperture

-* of 0.3m / 0.075m accessible for flat beams @ 7 TeV

Limitations for * at 7 TeV: Aperture & Chromatic aberrations

S. Fartoukh

Aperture at 7 TeV: interaction with WP3 of the HL-LHC current aperture goals are consistent with * of 0.15m and

10 separation


23

Bunch Intensity:

1) Collective effects (e.g. single bunch TMCI) ca. 3.5 1011 ppb

2) e-cloud effect depends on bunch spacing

2.2 1011 ppb at 25ns requires: dsec < 1.3 and IR cryo upgrade

TMCI intensity limit for 50ns compatible with: dsec > 1.7 and IR cryo upgrade

3) Maximum bunch intensity always linked to beam emittance Injector

complex performance after LIU

Upgrade Considerations: Maximum Bunch Intensity:


Beam-Beam: limits maximum beam by brightness

DQ = 0.02 – 0.03 seems feasible based on 2010 - 2011 experience maximum acceptable PA? Q>2?(sync-betatron resonances)

Three experiments with head on collisions: x = 7.7 10-3

assuming the same geometric reduction factor for x as for L (0.35 with alternating crossing) and assuming negligible contribution from long range:

en ≥ 2 mm for Nbunch = 3.5 1011 (50ns bunch spacing)

en ≥ 1 mm for Nbunch = 2.2 1011 (25ns bunch spacing)

24

Upgrade Considerations: Maximum Brightness


HL-LHC Performance Estimates

25

Parameter nominal 25ns 50nsN 1.15E+11 2.0E+11 3.3E+11nb 2808 2808 1404beam current [A] 0.58 1.02 0.84x-ing angle [mrad] 300 475 520beam separation [] 10 10 10* [m] 0.55 0.15 0.15en [mm] 3.75 2.5 3.0eL [eVs] 2.51 2.5 2.5energy spread 1.00E-04 1.00E-04 1.00E-04bunch length [m] 7.50E-02 7.50E-02 7.50E-02IBS horizontal [h] 80 -> 106 25 17IBS longitudinal [h] 61 -> 60 21 16Piwinski parameter 0.68 2.5 2.5geom. reduction 0.83 0.37 0.37beam-beam / IP 3.10E-03 3.9E-03 5.0E-03Peak Luminosity 1 1034 7.4 1034 8.4 1034

minimum *

(Leveled to 5 1034 cm-2 s-1)

nominal bunch length and minimum *: ‘HL-LHC Kickoff+’

Events / crossing 19 141 257 95 190

5.6 1014 and 4.6 1014

p/beam sufficient room for leveling with Crab Cavities:

Virtual luminosity for 25ns:L = 7.4 / 0.37 1034 cm-2 s-1

= 20 1034 cm-2 s-1 (‘k’ = 4)

Virtual luminosity for 50ns:L = 8.4 / 0.37 1034 cm-2 s-1

= 22.7 1034 cm-2 s-1 (‘k’ = 4.5)


Defines HL-LHC parameters for physics operation

still need to elaborate required margins for losses during acceleration and squeeze

LIU requires specifications for LHC injection!

OK for HL goals (‘k’ = 4)

(Even better if emittances can be further reduced:still a factor 1.2 to 2.5 wrt beam-beam limit)

Baseline Scenario and Options for 3000 fb -1

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