Em Emit ittance tance Gr Growth owth Dur uring ing the he LH - - PowerPoint PPT Presentation

LHC

Em Emit ittance tance Gr Growth

• wth Dur

uring ing the he LH LHC Ramp mp The he TRUE E Story

• ry
• M. Kuhn, G. Arduini, V. Kain, A. Langner, Y. Papaphilippou,
• M. Schaumann, R. Tomas

1

05/02/2014

LHC

• Overall average emittance blow-up through the LHC cycle:

− ~ 0.5 – 0.8 mm from injection to start of collision (convoluted e)

• Similar for ATLAS luminosity

Mo Motivati ivation:

• n: Em

Emit ittance tance Blo low-up up 2012 012

2

After TS3: Q20 optics in SPS and spare wire scanner system in LHC

Convoluted e:

• Collision values

from CMS bunch luminosity (nominal b*)

• Injection values

from LHC wire scanners (average of first 144 bunch batch), b from beta beat meas.

05/02/2014

LHC

Int ntrodu roducti ction

• n
• 2012 available transverse profile monitors through the cycle:

− ONLY WIRE SCANNERS!

• Could only measure low intensity test fills
• Problem with photomultiplier saturation during the ramp
• Conclusions from wire scanner measurements:

− Emittances are mainly growing during injection plateau and ramp − Sometimes shrinking emittances during the ramp − Sometimes large blow-up at the end of squeeze

• Sources of emittance blow-up:

− Injection: IBS and 50 Hz noise − Ramp: no clue so far − Squeeze: probably single bunch instabilities

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LHC

What’s New: LHC C Bet eta a Fct

• ct. Mea

easu surements ements

• The beta functions were measured through the ramp in 2012

− With turn-by-turn phase advance method at discrete energies

• at 0.45, 1.33, 2.3, 3.0, 3.8, 4.0 TeV for beam 1
• at 0.45, 1.29, 2.01, 2.62, 3.66, 4.0 TeV for beam 2

− Large uncertainties because of not optimal phase advance between the BPMs and problems with the algorithm

• Measured beta functions through the ramp could therefore not be

used for emittance determination in 2012

− Used linear interpolation between measured injection and flattop values from k-modulation

• Now: improvements of the algorithm

− re-calculated beta values through the ramp from AC dipole meas.

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LHC

Beta ta Fu Func ncti tions

• ns thr

hrough

• ugh LH

LHC Ramp mp

• Results obtained with new algorithm

− Measurements performed in October 2012 (MD3) − Beta functions during the LHC ramp at location of the wire scanners:

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Many thanks to A. Langer and R. Tomas! Note: large relative errors in B2H

LHC

Com

• mparison

parison of

• f Beta

ta Fu Func ncti tions

• ns

1. Interpolation of k-modulation values from injection to flattop 2. AC dipole measurements during the ramp + interpolation

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LHC

Wi Wire e Scan canner ner Me Measu asurements rements

• Comparison of emittances with different beta values

− K-modulation interpolation vs. AC dipole measurements − Example: Fill 3217, B1H (other planes look similar)

 Total growth through ramp reduced with new optics in ramp

But non-physical growth and shrinking still there!

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Beta beat values K-modulation values

LHC

Wh Where ere do

• the

he shri hrinki nking ng emit ittances tances com

• me

e from?

• m?

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LHC

• Growing- shrinking emittances due to non-monotonic changes of
• ptics at wire scanners (same for B1H)

− Not enough beta-measurements to remove all “non-physical” points

Emi mittance tance vs. . Beta ta Fu Func ncti tion

• n – B1

B1

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LHC

Emi mittance tance vs. . Beta ta Fu Func ncti tion

• n – B2

B2

• Monotonic growth of beta function at wire scanner (same for B2V)

 no shrinkage

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LHC

Résumé sumé – Non Non-Ph Phys ysical ical Emittance tance Evoluti ution

• n
• Most probable reason behind non-physical evolution of emittances

during the ramp in 2012

− Insufficient knowledge of beta function evolution at wire scanners during ramp − Still not enough beta measurement points to remove all “outliers” in emittance evolution for B1H and B1V

• Next: emittance measurement with new beta functions vs. IBS

simulations (MADX) during the ramp

− Using nominal optics − Measured bunch length through the ramp − Initial emittance at start of ramp from wire scans − CAVEAT: MADX algorithm assumes no coupling

• therefore predicts no growth in the vertical planes

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LHC

IBS S Sim imul ulati ations

• ns (1)
• Use input parameters from wire scans at the start of the ramp
• Simulate emittance blow-up due to IBS with MADX

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Fill 3217, batch 1 (6 bunches)

LHC

• Beam 2: relative emittance growth during the ramp fits very well

with IBS simulations

IBS S Sim imul ulati ations

• ns (2)

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LHC

IBS S Sim imul ulati ations

• ns (3)
• If it is ONLY IBS…why is it same growth for different initial e
• Fill 3217, all bunches (2 x 6):

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Bunch lengths and bunch intensities similar for both batches, but different initial emittances Almost same growth in IBS simulation

LHC

IBS S Sim imul ulati ations

• ns (4)
• Fill 3217, all bunches, relative emittance growth

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Smaller initial emittance (B2H batch 1) gives slightly larger growth ~ 5 % instead

• f ~ 4 %

BUT NOT MUCH DIFFERENCE!

LHC

Résumé sumé - IBS IBS and nd LH LHC Ramp mp

• Emittance growth in the horizontal plane during ramp probably
• nly from IBS

− For test fills ~ 3 - 5 % depending on initial beam parameters

• First guess for physics fills during ramp:

− Small would predict ~ 5 % ( ≤ 𝟏. 𝟐 mm) growth through the ramp

• Again dependent on initial beam parameters
• Prediction for physics fills before TS3: ~ 3 % (≤ 𝟏. 𝟏𝟔 mm)
• The what is the simulated IBS emittance growth through the LHC

cycle compared to measurements?

− For test Fill 3217 − For physics fills

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LHC

Em Emit ittance tance thr hrough

• ugh 2012

012 LH LHC Cycle cle

17

Fill 3217 (Oct. 2012, after octupole polarity switch), large growth during squeeze!

05/02/2014

LHC

Ex Exampl mple e IBS S dur uring ing the he Cycle cle – B2H

• Monotonic optics changes for B2H during the LHC cycle

− Therefore smooth emittance growth

• Full IBS simulation during the entire cycle compared to wire

scanner measurements

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IBS simulations and measurements for B2H very compatible!

LHC

IBS S dur uring ing the he LH LHC Cycle cle

• Estimates of mean horizontal emittance growth:
• IBS Simulations agree well with wire scanner measurements!

− Growth at flattop larger than expected! − But also some growth in the vertical plane (coupling for this fill)

• Total average growth of convoluted e through the LHC cycle

− For Fill 3217: 0.29 mm − For physics fills: ~ 0.5 mm – 0.8 mm

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Mean time [s] [s] Fill 3217 simula lated ted Fill 3217 measu sured ed Mean time [s] [s] physics ics fill simul ulated ted Injection 590 6 %, 0.09 mm 8 %, 0.12 mm ~ 900 5 – 10 % ≤ 𝟏. 𝟑 mm Ramp 770 4 %, 0.06 mm 3 %, 0.04 mm 770 3 – 5 % ≤ 𝟏. 𝟐 mm Flattop – start coll. 1500 5 %, 0.08 mm 9 % , 0.15 mm 1800 3 – 5 % ≤ 𝟏. 𝟐mm TOTAL 2860 (47 min) 15 %, 0.23 mm 21 %, 0.31 mm 3470 (58 min) ~ 10 – 20 % ≤ 𝟏. 𝟓 mm

 Why this large difference?

Additional meas. growth from 50 Hz noise

LHC

CAN WE WE TRUST ST WI WIRE RE SC SCANNER NNER ME MEASUREMENTS??? SUREMENTS??? Fi First t puz uzzle le: : dis iscrep crepancy ancy wire ire sca canne nner – ATLAS/C LAS/CMS lu lumi mino nosity ity and nd LH LHCb SMO MOG G me measure asurements ments

20

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LHC

ATL TLAS/ AS/CMS MS vs vs. . Wi Wire re Scanner anner

• Low intensity test fill in 2012 (Fill 3217):

− Injection values measured with wire scanners

• Beta function from AC dipole measurement

− Collision values measured with wire scanners and obtained from ATLAS and CMS luminosity − Average value of 6 colliding bunches (batch 2)

• Wire scan results much smaller than ATLAS/CMS results!

− Similar for other test fills measured in 2012

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Wire scanner ner ATLAS AS CMS CMS Emittance at injection [mm] 1.48 ± 0.06 Emittance at collision [mm] 1.77 ± 0.06 2.36 ± 0.35 2.63 ± 0.38 Emittance growth [mm] 0.29 ± 0.12 0.88 ± 0.41 1.15 ± 0.44 Relative growth 20 % 59 % 77 %

LHC

ATL TLAS/ AS/CMS MS vs vs. . Wi Wire re Scanner anner

• Low intensity test fill in 2012 (Fill 3217):

− Injection values measured with wire scanners WITH THOUT OUT CORE E FIT

• Beta function from AC dipole measurement

− Collision values measured with wire scanners and obtained from ATLAS and CMS luminosity − Average value of 6 colliding bunches (batch 2)

• Wire scan results much smaller than ATLAS/CMS results!

− Similar for other test fills measured in 2012

22

05/02/2014

Wire scanner ner ATLAS AS CMS CMS Emittance at injection [mm] 1.58 ± 0.06 Emittance at collision [mm] 1.84 ± 0.06 2.36 ± 0.35 2.63 ± 0.38 Emittance growth [mm] 0.25 ± 0.12 0.78 ± 0.41 1.05 ± 0.44 Relative growth 16 % 49 % 66 %

LHC

• Measurements during 30 min in stable beams with beam gas

interactions in LHCb (SMOG) and wire scanners

SMOG OG v

• vs. Wire

e Sca canner er

23

05/02/2014

LHCb e calculated with nominal b* = 3 m, WS e calculated with b from AC dipole meas., average e of 6 bunches per batch

Discrepancy up to 1 mm, but no systematic difference between wire scanner and LHCb emittances!

LHC

• Measurements during 30 min in stable beams with beam gas

interactions in LHCb (SMOG) and wire scanners

SMOG OG v

• vs. Wire

e Sca canner er

24

05/02/2014

LHCb e calculated with nominal b* = 3 m, WS e calculated with b from AC dipole meas., WITHO

THOUT UT CORE FIT, average e

• f 6 bunches per

batch

Discrepancy up to 0.8 mm, but no systematic difference between wire scanner and LHCb emittances!

LHC

Sum umma mary ry & Co Conc nclusi lusion

• n
• Measurements through the LHC cycle in 2012 only possible with

wire scanners

− Main blow-up occurs during injection and ramp − Sources of emittance growth at injection: IBS and 50 Hz noise

• NOW: new beta function analysis for values through the ramp

− Total growth through ramp reduced with new optics in ramp − Growing- shrinking emittances due to non-monotonic changes of

• ptics at wire scanners
• Comparison of wire scans and IBS Simulations:

− Emittance growth in the horizontal plane during ramp probably only from IBS − But large blow-up during squeeze that cannot be explained with IBS

• PUZZLE: discrepancy between wire scanner and

ALTAS/CMS/LHCb emittances at start of collisions

− ATLAS/CMS suggest larger total blow-up − LHCb measurements not fully compatible with wire scans

25

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LHC

Ou Outlo look

• k – Beams

ams Pos

• st

t LS LS1

• Emittance growth for high brightness beams post LS1

− With the following beam parameters for IBS simulations:

• 1.3 mm injected emittance
• Bunch intensity of 1.2 x 1011 ppb
• 1.25 ns bunch length

− 20 min ramp to 6.5 TeV

• assuming injection and flattop plateau length are same as in 2012
• Estimated emittance blow-up in the horizontal plane from injection

to start of collision: ~ 20 % (≤ 0.3 mm) only from IBS

− Similar as in 2012

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05/02/2014

Thank you for your attention!

LHC

Addit ditional ional Sli lides es

27

05/02/2014

LHC

Po Poss ssible e So Source rces s of Blow-Up Up Du During ng Ram amp

• Non Gaussian beam profiles
• Beam intensity losses
• Bunch length and longitudinal emittances instabilities
• Tune and beam lifetime
• BBQ amplitudes
• Transverse damper gain
• Dispersion
• Snapback
• Coupling – could cause emittance growth in the vertical planes
• IBS
• Noise
• Optics
• Chromaticity
• …

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05/02/2014

50 Hz noise and IBS cause emittance growth at the injection plateau

LHC

For r Completeness pleteness: : Optics ics Correction rrection Knob

• b vs.

Beta ta Function nction Evo volut ution ion

• Effect of optics correction knob on beta functions during the ramp

not obvious

29

05/02/2014

LHC

Wi Wire e Scan canner ner Me Measu asurements rements – B1V

 Total growth through ramp reduced with new optics in ramp

• But non-physical growth and shrinking still there!

30

05/02/2014

Beta beat values K-modulation values

LHC

Wi Wire e Sc Scan anner ner Me Measu asurements rements – B2H

 Total growth through ramp MUCH reduced with new optics in ramp

• (For completeness: continuing growth in B2H during flattop

correlates with large amplitudes in BBQ for that particular fill)

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05/02/2014

Beta beat values K-modulation values

LHC

Wi Wire e Scan canner ner Me Measu asurements rements – B2V

 Total growth through ramp reduced with new optics in ramp

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Beta beat values K-modulation values

LHC

Em Emit ittance tance vs. . Beta ta Fu Func ncti tion

• n – B1H

 Growing- shrinking emittances due to non-monotonic changes of

• ptics at wire scanners. Even more obvious for B1 V, next slide.

− Not enough beta-measurements to remove all “non-physical” points

33

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LHC

Emi mittance tance vs. . Beta ta Fu Func ncti tion

• n – B2V

2V

• Monotonic growth of beta function at wire scanner

 no shrinkage

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LHC

Fi Fill ll 268 2687 7 wit ith h Ramp mp Betas tas

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LHC

Fi Fill ll 272 2722 2 wit ith h Ramp mp Betas tas

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LHC

Fi Fill ll 301 3014 4 wit ith h Ramp mp Betas tas

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LHC

Beam eam Pa Parameters rameters 2012 012 Test st Cycl cles es

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Fill ll Beam Bunch length [ns] Bunch intensity [1011 ppb] 𝜻𝒚 [𝝂𝒏] 𝜻𝒛 [𝝂𝒏] 2687 (batch 2: 12 bunches) 1 1.2 1.4 1.92 1.73 2 1.18 1.4 1.68 1.80 2722 (batch 1: 12 bunches) 1 1.23 1.35 1.92 1.73 2 1.27 1.4 1.68 1.92 3014 (batch 1: 6 bunches) 1 1.17 1.55 1.92 1.78 2 1.17 1.6 1.92 1.97 3217 (batch 1: 6 bunches) 1 1.2 1.55 1.51 1.42 2 1.15 1.6 1.52 1.49 3217 (batch 2: 6 bunches) 1 1.15 1.55 1.51 1.44 2 1.15 1.65 1.68 1.65

LHC

Fi Fill ll 268 2687 7 IBS S Si Simu mula lati tions

• ns
• Fill 2687, batch 2, 12 bunches

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LHC

Fill Fill 2722 722 IBS S Si Simu mula lati tions

• ns
• Fill 2722, batch 1, 12 bunches

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LHC

Fill Fill 3014 014 IBS S Si Simu mula lati tions

• ns
• Fill 3014, batch 1, 6 bunches

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LHC

Fi Fill ll 321 3217 7 ATLAS/ LAS/CMS CMS Lu Lumi mino nosit sity

• Rather large discrepancy between ATLAS and CMS emittance

values from luminosity

• Closer look at specific luminosity reveals different results for

ATLAS and CMS

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Fill 3217 6 bunches (batch 2) colliding. Black line indicates peak luminosity taken for emittance calculation.

LHC

MD MD3 3 Fi Fill ll 316 3160 0 – LH LHC Cycle cle

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LHC

• Measurements during 30 min in stable beams: batch 1 and 2

SMOG OG v

• vs. Wire

e Sca canner er (1 (1)

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05/02/2014

LHCb emittances calculated with nominal b* = 3 m, l WS emittances calculated with b from beta beat meas. Average e of 6 bunches per batch

Measurements in the vertical plane agree best. No systematic difference between WS and LHCb emittances visible.

LHC

• Measurements during 30 min in stable beams: batch 3 and 4

SMOG OG v

• vs. Wire

e Sca canner er (2 (2)

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Measurements in the horizontal plane agree best.

LHCb emittances calculated with nominal b* = 3 m, l WS emittances calculated with b from beta beat meas. Average e of 6 bunches per batch

LHC

Fi Fill ll 316 3160 0 SMO MOG G Data ta Ana nalysis lysis

• Some observations:

− We had 2 hours of SMOG operation. − The true beam width at LHCb varies between 35 and 70 mu, leading to a systematic uncertainty of 0.7 - 0.8 mu. − The bunches had different intensities leading to a beam-gas rate of 10 to 45 Hz. We can reach about 0.7 micron statistical uncertainty in 5 minutes, but this vary with the bunch intensity. − The resolution deconvolution is made assuming a simple Gaussian beam which is reasonable for this fill. A double Gaussian analysis might help on some bunches, but most fit chi^2 are close to 1. − The beam width given is 1 sigma of a Gaussian distribution. − The statistical and systematic uncertainties are provided. It is therefore possible to average multiple time bins to reduce the statistical error, however, the systematic error should only be averaged and can not be reduced by averaging. − 𝜏𝑓𝑠𝑠 = ∆𝜏𝑡𝑧𝑡

2 + ∆𝜏𝑡𝑢𝑏𝑢 2

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