Transcript (n)QPS LHC: past, present and future Mike Lamont for the LHC team 21-3-2011 LHC status.

(n)QPS
LHC: past, present and future
Mike Lamont
for the LHC team
21-3-2011
LHC status
1
2010 – main aims
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21-3-2011
Clear priority to lay the foundations for 2011 and
the delivery of 1 fb-1. Peak luminosity target
1x1032 cm-2s-1
Gain solid operational experience of injecting,
ramping, squeezing and establishing stable
beams
Steady running at or around 1 MJ for an
extended period
Perform a safe, phased increase in intensity with
validation and a running period at each step
LHC status
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Luminosity: 3 running periods
Performance
ramp-up
(368 bunches)
Nominal
bunch
operation
(up to 48)
Initial
luminosity
run
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Bunch
trains
Nominal bunch
commissioning
LHC status
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2010 parameters
2010
Nominal
3.5
7
beta* [m]
3.5, 3.5, 3.5, 3.5 m
0.55, 10, 0.55, 10
Emittance [microns]
2.0 – 3.5 start of fill
3.75
Transverse beam
size at IP [microns]
around 60
16.7
1.2e11
1.15e11
Number of bunches
368
348 collisions/IP
2808
Stored energy [MJ]
28
360
2e32
1e34
Energy [TeV]
Bunch current
Peak luminosity
[cm-2s-1]
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LHC status
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Overall LHC efficiency in 2010
65%
availability!
W. Venturini
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Physics operations
August
Technical stop/
HC
7%
Fault
27%
beam setup
31%
setup no beam
6%
Stable~30%
beams
29% beams!
Stable
W. Venturini
21-3-2011
LHC status
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2010 - records
Peak stable luminosity delivered
2.07 x 1032 cm-2s-1
Maximum luminosity delivered in one fill
6.3 pb-1
Maximum luminosity delivered in one day
5.98 pb-1
Maximum luminosity delivered in 7 days
24.6 pb-1
Maximum colliding bunches
348
Maximum average events per bunch crossing 3.78
Longest time in Stable Beams for one fill
30.3 hours
Longest time in Stable Beams for one day
22.8 hours (94.9%)
Longest time in Stable Beams for 7 days
69.9 hours (41.6%)
Fastest turnaround to Stable Beams
3.66 hours (protons)
Courtesy Atlas
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LHC status
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Status LHC Stored Energy
Stored energy reached at 3.5 TeV: 28.0 MJ
80 kg TNT
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LHC status
Ralph Assmann
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Ions
Protons
again
50 & 75 ns
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LHC status
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Lifetimes
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Excellent single beam before collisions ~200 - 300 hours
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Luminosity lifetime ~15 - 20 hours
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Intensity lifetime ~90 hours
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Luminosity burn, losses on collimators
Emittance growth (hor. ~ 30 hours, vert. ~ 20 to 40 hours)
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Reasonably well given by emittance growth and intensity decay
Minimal drifts in overlap – beams very stable
Intra Beam Scattering
and something else – at least sometimes “the hump”
LHC status
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Aperture
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LHC status
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Optics & magnetic machine
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Optics stunningly stable
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Machine magnetically and optically well understood
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Magnetically reproducible
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Excellent agreement with model and machine
Important because set-up remains valid from fill to fill
LHC status
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Measured Cleaning at 3.5 TeV
Momentum
Cleaning
IR2
Dump Protection Col.
Making sure the hierarchy is respected
(beam1, vertical beam loss, intermediate settings)
IR1
IR8
IR5
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LHC status
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LHC 2010 - summary
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Excellent single beam lifetime
Ramp & squeeze essentially without loss
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Optics close to model (and correctable)
Excellent reproducibility
Aperture as expected
Better than nominal from injectors
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No quenches with beam above 450 GeV
Excellent performance of Machine Protection
Emittances, bunch intensity
Beam-beam: can collide nominal bunch currents
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With smaller that nominal emittances
And surprisingly good availability…
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LHC status
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PROBLEMS – TWO OF THEM
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LHC status
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UFOs – unidentified falling objects
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Many sudden local losses have been recorded.
No quench, but preventive dumps
Rise time around of the order 1 ms.
Potential explanation: dust particles falling into beam
creating scatter losses and showers propagating
downstream
Distributed around the ring – arcs, inner triplets, IRs
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LHC status
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UFOs – a possible solution?
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More events at higher intensities
Only 1? event observed at 450GeV
Signal shortens, i.e. the losses are faster with intensity
Signal amplitude does not increase with intensity  
● Revision of thresholds on
superconducting magnets could
make the UFO effects
acceptable
● More detailed analysis needed
to understand discrepancies
with current simulations +
additional quench tests to
benchmark
B.Dehning, E. Holzer, A.Nordt, M.Sapinski
21-3-2011
LHC status
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Electron cloud
Reflection
Schematic of electron cloud build up in LHC arc beam pipe due to
photoemission and secondary emission [F. Ruggiero]
Secondary emission yield [SEY]
Very much dependent on bunch spacing:
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150 ns. – local signs in common beam pipe
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75 ns. – some first signs
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50 ns. – vacuum valves in
LHC status
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Electron cloud effects
Electron cloud effects occur both in the warm and cold regions.
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Vacuum pressure rise (background in experiments)
Single-bunch instability
Multi-bunch instability
Incoherent emittance growth
Heat load in cold arcs (quenches in the limit)
Perturbation of beam diagnostics
Well understood, very well studied
(other machines, simulations…)
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LHC status
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Experience in 2010
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Vacuum activity started off in regions with common
beam pipe at 450 GeV as we pushed up the number of
bunches with 150 ns spacing
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Test solenoids cured problem – electron cloud
Tried 50 ns bunch spacing
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Things really kicked off
High vacuum activity in warm regions (single beam pipe)
Significant heat load in cold regions
Instabilities and beam size growth observed
Surface conditioning (‘scrubbing’) observed
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Situation a lot cleaner with 75 ns
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Gas desorption rates and SEY drop
Time constant < 1 day
incoherent effects seen – emittance blow-up
800+ bunches injected into both beams
LHC status
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Scrubbing strategy for 2011
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2010 observations are certainly due to ~ 2 < SEY < 2.5,
whereas 1.7 was usually the max value studied in the
past
Expect to be able to reach 200-300 b with 75 ns without
scrubbing
Scrubbing with large emittance (>3.5 mm), high intensity
(>1.2e11), 4x36b of 50 ns beam
Time
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2-3 days needed to setup 50 ns at injection
7 days of scrubbing
1 day for validation and scrubbing result evaluation
Lots of wire wrapped around warm bits during the
technical stop (solenoids)
LHC status
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Solenoids between DFBX and D1 in IR1R
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2011
Energy – stick at 3.5 TeV – we still worry about the splices
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2011: main goals
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Motivation is clear!
fast, secure and far-reaching
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1 fb-1 delivered to each of IP1, IP5 and IP8 at 3.5 TeV
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It will be a challenge to deliver 1 fb-1 to IP8
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Can probably do better for IP1 and IP5
Maximum luminosity : from 2e32 to 3e32 cm-2 s-1
Luminosity leveling via separation required to get close
Alice
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pp run: 5e29 < L < 5e30 cm-2 s-1, µ < 0.05
Decided on beta* = 1.5 m in Atlas, CMS; 3 m in LHCb; 10 m in Alice
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LHC status
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Baseline scenario
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Beam commissioning: 3 weeks
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Ramp-up to ~200 bunches (75 ns): 2 weeks
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Multi-bunch injection commissioning continued
Stable beams
Technical Stop: 4+1 days
Scrubbing run: 10 days including 50 ns injection comm.
[Intermediate energy run – 5 days]
Resume 75 ns operation and increase no. bunches: 3
weeks
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Exit - stable beams with low number of bunches
300 – 400 – 600 – 800 – 930 - MPS and OP qualification
Physics operation 75 ns: ~930 bunches
(50 ns. remains an option if things look good)
LHC status
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2011 LHC schedule Q1/Q2
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2011 Q3/Q4
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Estimated Peak and Integrated Luminosity
Energy
3.5 TeV
Beta*
1.5 m
Bunch spacing
75 ns
Bunch intensity
1.2 x 1011
Stored beam energy
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75 MJ
Days at peak luminosity
135
Hübner factor
0.2
Emittance
[mm.mrad]
Beam-beam
parameter
Peak
Luminosity
[cm-2 s-1]
Integrated
Luminosity
[fb-1]
2.5
0.006
1.3 x 1033
~2.7
2.0
0.007
1.6 x 1033
~3.3
LHC status
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2011 – progress so far
19th February
First beam, circulating beams established.
3rd March
First collisions at 3.5 TeV, beta*=1.5 m. with pilot beams
5th March
Nominal bunches at 3.5 TeV, start collimator set-up, injection
and beam dump set-up & validation
13th March
First stable beams, 3 bunches per beam, initial luminosity
1.6e30 cm-2s-1
18th March
32 bunches per beam, initial luminosity ~3e31 cm-2s-1
19th March
64 bunches per beam, initial luminosity ~6e31 cm-2s-1
20th March
75ns_136b+4small_138_102_105_24bpi11inj
1.45e32 cm-2s-1
Impressive re-commissioning, improvements across the board.
Operation cycle now well optimized: faster ramp & squeeze, much fewer
manual actions required by shift crews
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Machine still beautiful
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Conclusions 1/2
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Injection, ramp and squeeze fully operational
LHC magnetic model & optics excellent
Beam instrumentation in good shape.
Beam cleaning and collimation works reliably
with predicted efficiency.
Machine protection excellent performance
Machine aperture looks good
Performance with beam (losses, lifetimes,
luminosity, emittance growth etc.) is very
encouraging
We have a beautiful machine on our hands!
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Conclusions 2/2
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Machine availability is excellent – the hard work of
numerous teams
There are problems
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2011 – another long year ahead…
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75 ns. bunch spacing – up to 930 bunches
Nominal intensities, beta* 1.5 m in Atlas and CMS
Should be good for 5 to 10 x 1032 cm-2s-1 and 1 to 3 fb-1
Progress so far is good…
Will run in 2012
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UFOs somewhat worrying
Electron cloud well understood – measures prepared
Attempt to measure splice resistance in 2011/2012 might open
the way to 4 TeV or higher
LHC status
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