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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
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
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)
R.G. 21 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
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
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]
Bunch intensity within constant longitudinal emittance [x1011 p/b]
Q2/2011
Nominal performance
Baseline(estimated limit of SPS)
Stretched:(estimated limit of
SPS injectors)
R.G. 22 Brainstorming – 24/06/2011
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]
Intensity/bunch [x 1E11]
Sterbini (LHC CC10)
Fartoukh (Chamonix11)
Bruning (Chamonix11)
Zimmermann (Chamonix11)
Beam parameters at LHC injection [25 ns]
BeamParametersat 7 TeV
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
SPS 1.8 2.5PS 2.0 2.4PSB 2.1 2.3
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
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]
Bunch intensity within constant longitudinal emittance [x1011 p/b]
Nominal performance
Baseline(estimated limit of SPS)
Stretched:(estimated limit of
SPS injectors)
R.G. 23 Brainstorming – 24/06/2011
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]
Intensity/bunch [x 1E11]
Sterbini (LHC CC10)
Fartoukh (Chamonix11)
Bruning (Chamonix11)
Zimmermann (Chamonix11)
Beam parameters at LHC injection [25 ns]
BeamParametersat 7 TeV
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
SPS 1.8 2.5PS 2.0 2.4PSB 2.1 2.3
Intensity/bunch Transverse emittances[x 1E11] [mm.mrad rms]
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]
Bunch intensity within constant longitudinal emittance [x1011 p/b]
MD: single bunch with low gt
Nominal performance
Baseline(estimated limit of SPS)
Stretched:(estimated limit of
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)
30/3/12 Brennan at Chamonix
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
30/3/12 Brennan at Chamonix
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