LHC

LHC performance with low-emittance h=9 beam

Focus on emittance preservation

M. Kuhn, H. Bartosik, B. Dehning, A. Guerrero Ollacarizqueta, V. Kain, F. Roncarolo, M. Sapinski, M. Schaumann, G. Trad

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LHC

h=9 Beam from Injectorso At SPS flattop: trans. emittance ~ 1 m, 1.1 x 1011 per bunch, 3 % scraping

o In the LHC: 1.1 x 1011 per bunch

− Filling scheme: 6 nominal 50 ns

+ 32 h=9 50 ns

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nom bunches

h=9 bunches

Distribution of bunch intensities in the LHC

1.1 x 1011

LHC

Emittance Evolution through Cycle

o Low intensity ( # bunches = 38) → wire scanners

− Soft interlock level reached at 4 x 1012 at 4 TeV

→ needed to get expert to increase threshold to 4.5 x 1012

→ no measurements at flattop and during squeeze

− Intensity limit at wire scanners changed to 2.7 x 1013 protons at injection and 5.8 x 1012 at 4 TeV

o Evolution during squeeze from Enrico’s expert fast scan of BSRT.

− 200 ms per bunch

o Wire scan measurements to compare with luminosity data

o Following plots show average of 6 bunch batch and 32 bunch batch

o Measured beta functions are used

− Preliminary K-modulation results at wire scanners

o Error bars include statistical error from averaging, beta function error3

LHC

o Bunch-by-bunch emittance at injection – different performance of PSB rings

− Larger emittances for vertical plane

Emittance at injection

4Small beams at injection

n = 1.005 ± 0.075

n = 1.07 ± 0.026

n = 1.169 ± 0.05

n = 1.252 ± 0.039

LHC

The Rampo MD data suggests:

− MDs with single bunches

→ No “measurable” growth for vertical plane during ramp

→ Beams are growing in the horizontal plane

− More for beam 2 than for beam 1

− Beam 2 ~ 0.5 m for initial emittance of 2.1 m

o This year issues with understanding optics:

− Initial results indicated non-physically smaller normalized emittances at flattop versus injection

− No beta measurements during ramp, do not use data

− Only compare injection data with flattop

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Do not look at the values during the ramp

LHC

Vertical Planeo No measurable growth in vertical

plane during injection plateau!

o No WS values available at flattop

o Compare with data some time in collision already

o Growth injection – collision

− < 0.2 m

o Note also, growth during collisions: ~ 0.1 m in 10min

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Beam [plane] Injection emittance [μm]

Nom bunches h=9 bunches

B1 [V] 1.891 ± 0.078 1.169 ± 0.05

B2 [V] 1.986 ± 0.056 1.252 ± 0.039

Collision emittance [μm]

B1 [V] 1.83 ± 0.095 1.274 ± 0.087

B2 [V] 2.148 ± 0.119 1.398 ± 0.086

Total emittance growth through cycle in vertical plane max. 10%, probably smaller. No measurement right after start of collisions.

Non colliding bunches also grow

LHC

Horizontal Plane

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o Strong emittance blow-up during injection plateau

– Beam 1: 0.22 m, beam 2: 0.16 m

– Suspect IBS

o Ramp: compare injection with data after some time in collision

– Contribution injection: 15 – 22 %

– Contribution ramp/squeeze: 16 – 18 %

Beam [plane] Injection emittance [μm]

Nom bunches h=9 bunches

B1 [H] 1.772 ± 0.135 1.005 ± 0.075

B2 [H] 1.848 ± 0.006 1.07 ± 0.026

Collision emittance [μm]

B1 [H] 2.159 ± 0.113 1.43 ± 0.072

B2 [H] 2.286 ± 0.185 1.454 ± 0.166

In total ~ 40 % blow- up in the horizontal plane ! (caveat: not measured straight after collision)

LHC

Squeezeo No significant blow-up during the squeeze

o Within measurement accuracy the beam sizes are constant during the squeeze

o Results from earlier 2012 measurement not reproduced

− B1 H emittance was blowing up ~ 15 %

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Emittances conserved during squeeze

LHC

Emittance from Luminosityo Arriving with small emittances in collision

o Compare with emittance from wire scanners (averaged over several profiles)

o Errors large, but significant difference between wire scanner emittance and luminosity emittance:

− ~ 20%

→ Working on trying to understand difference?

o Blow-up from SPS → LHC collisions: ~ 50 % !!!− Convoluted emittance at LHC injection to collision :1.12 m → 1.7 m

o Compare to nominal 50 ns (physics fills): ~ 40 %

− Convoluted emittance LHC injection to collision: 1.7 m → 2.4 m

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Wire scanners CMS luminosity ATLAS luminosity

Convoluted emittance [μm]

1.388 ± 0.102 1.751 ± 0.263 1.686 ± 0.253

LHC

Summaryo 1 m beams from the injectors with 1.1 x 1011 ppb successfully produced

o Significant blow-up in H while waiting at LHC injection plateau

− ~ 19 %

o Significant blow-up during the ramp in H plane.

− ~ 17 %

o Total blow-up until collision from LHC injection (using LHC luminosity emittances):

− ~ 50 %

o But…doubt on emittance values from luminosity.

o Performance reach of h=9 beam (naïve approach – assume same filling scheme, shorter trains):

− h=9: 1.1 x 1011 protons, = 1.7 m

− 50 ns nominal: 1.6 x 1011 protons, = 2.4 m

− h=9/50ns_nom ~ 60 %

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