Summary and outcome of the 1st LIU-HL-LHC brainstorming meeting (24 th June 2011) Mike Lamont This event is jointly organized by the HL-LHC and LIU projects

Summary and outcome of the 1st LIU-HL-LHC brainstorming meeting (24th June

2011) Mike Lamont

This event is jointly organized by the HL-LHC and LIU projects (Lucio & Roland) to try and find solutions to the present discrepancy between the estimated needs of the LHC and the possibilities of the upgraded injectors.

Contributions

30/3/12

Beam characteristics at collision energies for the main HL-LHC scenarios: Fundamental reasons for each beam parameters

Oliver Bruning

Estimated beam characteristics from the upgraded injectors at 450 GeV: Fundamental limitations

Roland Garoby

Minimum turnaround time for the LHC at 7 TeV Mike Lamont

Impact on luminosity of Turn around time, Run time etc. Roland Garoby

Turnaround time in previous colliders (RHIC, TEVATRON, HERA) Oliver Bruning

Bunch spacing, pile up and all that Frank Zimmermann

Ideas from/for the SPS Brennan Goddard

Low transition energy optics Yannis Papaphilippou

Possible increase of bunch intensity in the SPS for HL-LHC Elena Chapochnikova

Single bunch intensity limit in the LHC Elias Metral

A few considerations Stephane Fartoukh

Warning – many updates since then…

Performance goals

30/3/12

Levelled peak luminosity 5 x 1034 cm-2s-1

Virtual peak luminosity > 10 x 1034 cm-2s-1

Integrated luminosity 200 to 300 fb-1 per year

Total integrated luminosity 3000 fb-1

Levelling

30/3/12

HL-LHC will use leveling• leveled luminosity is defined: 5x1034 cm-2s-1

• “ATS optics” solution for beta* < 30 cm

Level for Tlevel and then take another 3 hours

Illustration

30/3/12

k tLevel

[h]

Tdecay

[h]

Virtuallumi

Levelledlumi

Fill length[h]

Int lumi per fill [fb-1]

RequiredEfficiency

2 4.1 3 1e35 5e34 7.1 1.13 75%4 7.0 3 2e35 5e34 10 1.65 63%

Assuming: • 1.8 1011 ppb @ 25ns or 3.5 1011 ppb @ 50ns (≈ 5 1014 p/beam)• 3 hours after the end of levelling with natural luminosity decay• 2 high luminosity IPs• Only luminosity burn• Perfect levelling

Required overall efficiency to get 250 fb-1/year…

Operational efficiency• Assume 150 days/year

– Need 150 – 220 fills per year• 3 hour minimum turnaround and 5 hour average

turnaround - seem like reasonable numbers• Can play the usual games but will need high operational

efficiency (65 to 75%) and an average turnaround of the order of 5 hours.– Watch double counting

• Clear that pushing the total beam current and k is going to help– E.g. k = 5 with 6x1014 p/beam

• What k’s are within reach?

30/3/12

LHC 2011

30/3/12

Mean = 5.4 hours

Turn arounds elsewhere

30/3/12 OB

30/3/12

25 ns 50 ns

Protons per bunch 2.0e11 3.3e11Number of bunches 2808 1404

Protons per beam 5.6e14 4.6e14

Beam current [A] 1.02 0.84

X-angle [microrad] 475 520

Beam separation [s] 10 10

Beta* [m] 0.15 0.15

Norm. emittance 2.5 3.0Bunch length [cm] 7.5 7.5

Geom. reduction F 0.37 0.37

Peak lumi 7.4e34 8.4e34

Virtual peak 20e34 22.7e34

Levelled 5e34 5e34

k 4 4.5

Pile-up 95 190

HL baseline target

OB

Comments

• OK for HL goals with 25 ns• Stick numbers into the levelling formulae• Both scenarios with 60% efficiency on 150 day

year give 250 fb-1

• but we note the pile-up of 190 with 50 ns– Level at 2.5 x 1034 cm-2s-1 (OB)…

30/3/12

Pile-up

30/3/12

Experiments preparing for <mu> = 100(68% of bunch crossings will have between 100 +/- 10 events)

Reminded of limits

30/3/12 RA

30/3/12

25 ns 50 ns

Protons per bunch 1.7e11 2.5e11

Number of bunches 2808 1404

Protons per beam 4.8e14 3.5e14

Beam current [A] 0.86 0.64

X-angle [microrad] 480 520

Beam separation [s] 10 10

Beta* [m] 0.15 0.15

Norm. emittance 2.5 3.5

Bunch length [cm] 7.5 7.5

Geom. reduction F 0.37 0.4

Peak lumi 5.3e34 5.2e34

Virtual peak 14e34 11e34

Levelled 5e34 5e34

k 2.8 2.5

Pile-up 95 190

APPROXIMATE LIU BASELINE AS OF LAST JULY (OB & RG)

OB

LIU baseline

• 25 ns short of HL goals – 60% efficiency on 150 days gives 225 fb-1

• 50ns requires > 80% machine efficiency to even get close

30/3/12

Could take this set as the lower limits of acceptable parameters and rely on the ingenuity of LHC personnel to push peak performance and operational efficiency

Oliver’s conclusions• CRAB cavities are a vital ingredient for HL-LHC. Without them

we will fall short of 250 pb-1 goal (k ≥ 4). – CC are the best tool for compensating geometric reduction factor

(LRBB wires perhaps partially) (flat beams [SF])• Given equal bunch parameters, 25 ns case is clearly better than

50 ns (assuming there is no electron cloud limit for 25ns!)• If LHC is limited by total beam current, 50 ns offers larger

performance reach (higher virtual luminosity for equal lifetime)– 50ns schemes benefit from double batch injection & higher

brightness• Rather then lowering the bar for project goals, I would stick to

challenging (ideal) goals [while underlining that there is a risk associated to it (like CC & Nb3Sn for HL)] and to pursue novel schemes (e.g. feedback systems etc.)

30/3/12

Frank’s conclusions

• No beam-beam limit• Limit on total beam current in LHC [& SPS] due to several

systems (RF, dump, vacuum, collimator robustness, machine protection, RP, …) at ultimate value

• Single bunches > 3e11 ppb with 2.5 micron emittance have been accelerated in the SPS

• We can get a factor 2 higher peak luminosity with 50 ns spacing at the same current

• In addition we may get smaller emittance at 50 ns– additional gain in peak luminosity?– pile up replaces beam-beam as HL-LHC constraint

• Leveling works! 30/3/12

LIUEstimated beam characteristics from the upgraded injectors

30/3/12

Strategy

• Increased brightness:– LINAC4– Booster injection energy– PS injection energy– Higher brightness measures in PSB, PS and SPS

• Emittance conservation– Measurements, understanding, low gamma T

• Consolidate for reliability and longevity

30/3/12

Estimates

• NB: Numbers refer to injection into LHC• Assume all necessary improvements in injectors

are made and work as foreseen• Budget - assumptions made:

– PSB inj-extr: 5% emittance blowup, 5% beam loss– PS inj-extr: 5% emittance blowup, 5% beam loss– SPS inj-extr: 10% emittance blowup, 10% beam loss

(including scraping)– LHC inj-flat top: 10% emittance blowup, 10% beam

loss

30/3/12

R.G. 20 Brainstorming – 24/06/2011

Beam parameters at LHC injection [50 ns]

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Emitt

ance

[mm

.mra

d]

Intensity/bunch [x 1E11]

Sterbini (LHC CC10)

Fartoukh (Chamonix11)

Bruning (Chamonix11)

Zimmermann (Chamonix11)

BeamParametersat 7 TeV

Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]

SPS 2.7 1.6PS 3.0 1.5PSB 3.2 1.5


SPS 2.5 3.5PS 2.8 3.3PSB 2.9 3.2

? ?

H/V

tran

sver

se e

mitt

ance

s [m

m.m

rad]

Bunch intensity within constant longitudinal emittance [x1011 p/b]

Nominal performance

Baseline(estimated limit of SPS)

Stretched:(estimated limit of

SPS injectors)



0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Emitt

ance

[mm

.mra

d]


Sterbini (LHC CC10)






SPS 2.7 1.6PS 3.0 1.5PSB 3.2 1.5


SPS 2.5 3.5PS 2.8 3.3PSB 2.9 3.2

? ?

MD: single bunch with low gt

MD: double PSB batch

H/V

tran

sver

se e

mitt

ance

s [m

m.m

rad]


Q2/2011

Nominal performance



SPS injectors)


0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3

Emitt

ance

[mm

.mra

d]


Sterbini (LHC CC10)







SPS 1.8 2.5PS 2.0 2.4PSB 2.1 2.3


SPS 2.1 2.2PS 2.3 2.1PSB 2.4 2.0

? ?H/V

tran

sver

se e

mitt

ance

s [m

m.m

rad]


Nominal performance



SPS injectors)


0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3

Emitt

ance

[mm

.mra

d]


Sterbini (LHC CC10)







SPS 1.8 2.5PS 2.0 2.4PSB 2.1 2.3


SPS 2.1 2.2PS 2.3 2.1PSB 2.4 2.0

? ?

MD: double PSB batch

H/V

tran

sver

se e

mitt

ance

s [m

m.m

rad]


MD: single bunch with low gt

Nominal performance



SPS injectors)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Emitt

ance

(x+y

)/2

[um

]

Bunch Intensity [e11]

SPS 450 GeV 25 ns

SPS

RF p

ower

Long

itudi

nal i

nsab

ilitie

s

PS R

F po

wer

Long

itudi

nal i

nsab

ilitie

s

HL-LHC

25 ns after LIU upgrade

• Fundamental limit: space charge in PS

• Limit is 2.3e11 p+/b in 3.6 um at SPS extraction (1.6e11 in 2.3 um)

30/3/12 Brennan at Chamonix

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Emitt

ance

(x+y

)/2

[um

]

Bunch Intensity [e11]

SPS 450 GeV 50 ns

SPS

Long

itudi

nal i

nsab

ilitie

s

PSLo

ngitu

dina

l ins

abili

ties

SPS

TMCI

lim

it

HL-LHC

50 ns after LIU upgrade

• Limited by longitudinal instabilities in PS and SPS, and by brightness in SPS

• Limit is 2.7e11 p+/b in 2.7 um at SPS extraction (closer to HL-LHC requirement)


Table of dreams?25 ns Ib [e11] Exy [um] scaled Ib^2/Exy

HL-LHC target (LHC flat-top) 2.0 2.5 1.00LIU scenario (SPS extraction) LIU baseline (>LS2) 2.3 3.6 0.92 + "stretch" blowup/losses (>LS3) 2.3 3.3 1.00+ PS DQ to -0.32, PSB DQ to -0.31 (>LS3) 2.1 2.3 1.20

50 ns I [e11] Exy [um] scaled Ib^2/ExyHL-LHC target (LHC flat-top) 3.3 3.0 1.00LIU scenario (SPS extraction) LIU baseline (>LS2) 2.7 2.7 0.74 + "stretch" blowup/losses (>LS3) 2.8 2.5 0.86+ PS longitudinal stability 3.7e11 (>LS3) 3.4 3.2 1.00+ SPS DQ to -0.17 (>LS3) 3.4 2.8 1.14


Stretching

• “A number of optimistic assumptions are necessary for reaching the HL-LHC figures, concerning the success of measures against space charge, instabilities, e-cloud and to minimize beam loss and emittance growth.”

30/3/12

Invitation to further reading• Momentum slip stacking - Elena• Low gamma T optics in SPS – Yannis• Exotic SPS scrubbing• Longer bunches at SPS2LHC transfer• Bunch merging in SPS/LHC• Different working points in SPS• Low gamma T: increase instability thresholds...still many issues to address

(multi-bunch, RF volts, longitudinal transfer to LHC, ...)• Alternative filling patterns for LHC if limited by total SPS current• What about halving the bunch length in the LHC? (SF)• Pacman versus micro-batches (SF)• What to do at the beginning of the coast if natural peak > levelled

luminosity value? (SF)

30/3/12

Conclusions

• Posted HL parameters are outside: LIU baseline and LHC intensity limits - but not ridiculously so…

• 250 fb-1/year is challenging– Requires high availability and efficient operation– Very effective levelling is implied

• Push k - stretch LIU…

30/3/12

Documents

Summary and outcome of the 1st LIU-HL-LHC brainstorming meeting (24 th June 2011) Mike Lamont This event is jointly organized by the HL-LHC and LIU projects