LHC performance with low-emittance h=9 beam Focus on emittance preservation

1. LHC performance with low-emittance h=9 beamFocus on emittance preservation M. Kuhn, H. Bartosik, B. Dehning, A. Guerrero Ollacarizqueta, V. Kain, F. Roncarolo, M. Sapinski, M. Schaumann, G. Trad

2. h=9 Beam from Injectors nom bunches h=9bunches 1.1 x 1011 Distribution of bunch intensities in the LHC • At SPS flattop: trans. emittance ~ 1 mm, 1.1 x 1011 per bunch, 3 % scraping • In the LHC: 1.1 x 1011 per bunch • Filling scheme: 6 nominal 50 ns + 32 h=9 50 ns

3. Emittance Evolution through Cycle • 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 • Evolution during squeeze from Enrico’s expert fast scan of BSRT. • 200 ms per bunch • Wire scan measurements to compare with luminosity data • Following plots show average of 6 bunch batch and 32 bunch batch • Measured beta functions are used • Preliminary K-modulation results at wire scanners • Error bars include statistical error from averaging, beta function error

4. Emittance at injection en = 1.005 ± 0.075 en = 1.169 ± 0.05 en = 1.252 ± 0.039 en = 1.07 ± 0.026 Small beams at injection • Bunch-by-bunch emittance at injection – different performance of PSB rings • Larger emittances for vertical plane

5. The Ramp Do not look at the values during the ramp • 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 mm for initial emittance of 2.1 mm • 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

6. Vertical Plane Non colliding bunches also grow Total emittance growth through cycle in vertical plane max. 10%, probably smaller. Nomeasurementright after startofcollisions. • No measurable growth in vertical plane during injection plateau! • No WS values available at flattop • Compare with data some time in collision already • Growth injection – collision • < 0.2 mm • Note also, growth during collisions: ~ 0.1 mm in 10min

7. Horizontal Plane • Strong emittance blow-up during injection plateau • Beam 1: 0.22 mm, beam 2: 0.16 mm • Suspect IBS • Ramp: compare injection with data after some time in collision • Contribution injection: 15 – 22 % • Contribution ramp/squeeze: 16 – 18 % In total ~ 40 % blow- up in the horizontal plane ! (caveat: not measured straight after collision)

8. Squeeze Emittances conserved during squeeze • No significant blow-up during the squeeze • Within measurement accuracy the beam sizes are constant during the squeeze • Results from earlier 2012 measurement not reproduced • B1 H emittance was blowing up ~ 15 %

9. Emittance from Luminosity • Arriving with small emittances in collision • Compare with emittance from wire scanners (averaged over several profiles) • Errors large, but significant difference between wire scanner emittance and luminosity emittance: • ~ 20% • Working on trying to understand difference? • Blow-up from SPS → LHC collisions: ~ 50 % !!! • Convoluted emittance at LHC injection to collision :1.12 mm →1.7 mm • Compare to nominal 50 ns (physics fills): ~ 40 % • Convoluted emittance LHC injection to collision: 1.7 mm →2.4 mm

10. Summary • 1 mm beams from the injectors with 1.1 x 1011 ppb successfully produced • Significant blow-up in H while waiting at LHC injection plateau • ~ 19 % • Significant blow-up during the ramp in H plane. • ~ 17 % • Total blow-up until collision from LHC injection (using LHC luminosity emittances): • ~ 50 % • But…doubt on emittance values from luminosity. • Performance reach of h=9 beam (naïve approach – assume same filling scheme, shorter trains): • h=9: 1.1 x 1011 protons, e = 1.7 mm • 50 ns nominal: 1.6 x 1011 protons, e = 2.4 mm • h=9/50ns_nom ~ 60 %