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 1

LHC h=9 Beam from Injectors oAt SPS flattop: trans. emittance ~ 1  m, 1.1 x per bunch, 3 % scraping oIn the LHC: 1.1 x per bunch − Filling scheme: 6 nominal 50 ns + 32 h=9 50 ns 2 nom bunches h=9 bunches Distribution of bunch intensities in the LHC 1.1 x 10 11

LHC Emittance Evolution through Cycle oLow intensity ( # bunches = 38) → wire scanners − Soft interlock level reached at 4 x at 4 TeV → needed to get expert to increase threshold to 4.5 x → no measurements at flattop and during squeeze − Intensity limit at wire scanners changed to 2.7 x protons at injection and 5.8 x at 4 TeV oEvolution during squeeze from Enrico’s expert fast scan of BSRT. − 200 ms per bunch oWire scan measurements to compare with luminosity data oFollowing plots show average of 6 bunch batch and 32 bunch batch oMeasured beta functions are used − Preliminary K-modulation results at wire scanners oError bars include statistical error from averaging, beta function error 3

LHC oBunch-by-bunch emittance at injection – different performance of PSB rings − Larger emittances for vertical plane Emittance at injection 4 Small beams at injection  n = ±  n = 1.07 ±  n = ± 0.05  n = ± 0.039

LHC The Ramp oMD 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 oThis 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 5 Do not look at the values during the ramp

LHC Vertical Plane oNo measurable growth in vertical plane during injection plateau! oNo WS values available at flattop oCompare with data some time in collision already oGrowth injection – collision − < 0.2  m oNote also, growth during collisions: ~ 0.1  m in 10min 6 Beam [plane]Injection emittance [μm] Nom bunchesh=9 bunches B1 [V]1.891 ± ± 0.05 B2 [V]1.986 ± ± Collision emittance [μm] B1 [V] 1.83 ± ± B2 [V] ± ± 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 7 oStrong emittance blow-up during injection plateau –Beam 1: 0.22  m, beam 2: 0.16  m –Suspect IBS oRamp: compare injection with data after some time in collision –Contribution injection: 15 – 22 % –Contribution ramp/squeeze: 16 – 18 % Beam [plane]Injection emittance [μm] Nom bunchesh=9 bunches B1 [H]1.772 ± ± B2 [H]1.848 ± ± Collision emittance [μm] B1 [H] ± ± B2 [H] ± ± In total ~ 40 % blow- up in the horizontal plane ! (caveat: not measured straight after collision)

LHC Squeeze oNo significant blow-up during the squeeze oWithin measurement accuracy the beam sizes are constant during the squeeze oResults from earlier 2012 measurement not reproduced − B1 H emittance was blowing up ~ 15 % 8 Emittances conserved during squeeze

LHC Emittance from Luminosity oArriving with small emittances in collision oCompare with emittance from wire scanners (averaged over several profiles) oErrors large, but significant difference between wire scanner emittance and luminosity emittance: − ~ 20% → Working on trying to understand difference? oBlow-up from SPS → LHC collisions: ~ 50 % !!! − Convoluted emittance at LHC injection to collision :1.12  m → 1.7  m oCompare to nominal 50 ns (physics fills): ~ 40 % − Convoluted emittance LHC injection to collision: 1.7  m → 2.4  m 9 Wire scannersCMS luminosityATLAS luminosity Convoluted emittance [μm] ± ± ± 0.253

LHC Summary o1  m beams from the injectors with 1.1 x ppb successfully produced oSignificant blow-up in H while waiting at LHC injection plateau − ~ 19 % oSignificant blow-up during the ramp in H plane. − ~ 17 % oTotal blow-up until collision from LHC injection (using LHC luminosity emittances): − ~ 50 % oBut…doubt on emittance values from luminosity. oPerformance reach of h=9 beam (naïve approach – assume same filling scheme, shorter trains): − h=9: 1.1 x protons,  = 1.7  m − 50 ns nominal: 1.6 x protons,  = 2.4  m − h=9/50ns_nom ~ 60 % 10