1. LHC LHC Wire Scanners: Updates on Measurement Accuracy Emittance Meeting 18 November 2015 Maria Kuhn – 18 November 2015 Many thanks to G. Baud, E. Bravin, B. Dehning, J. Emery, V. Kain, E. Piselli, G. Trad

2. LHC Outline Accuracy of LHC emittance measurements with wire scanners: oProblem: scan-to-scan beam size spread oSolution: new fitting method to reduce the position measurement uncertainty oUpdated scan-to-scan beam size spread oComparison with simulations oUnsolved: beam 2 vertical emittance fluctuations at 6.5 TeV 2 M. Kuhn - 18 November 2015

3. LHC Scan-to-Scan Emittance Spread oExample measurement with wire scanners at the beginning of the 2015 LHC proton run oLarge absolute emittance spread from scan to scan – WHY? − More emittance spread at higher energies 3 M. Kuhn - 18 November 2015

4. LHC Scan-to-Scan Beam Size Spread oAbsolute beam size spread larger at lower energies! − But in terms of emittance spread is larger at 6.5 TeV than at 450 GeV oRelative beam size spread ~ 10 % for all scanners and energies 4 M. Kuhn - 18 November 2015 ScannerB1H2B1V2B2H1B2V1 450 GeV  [  m] 8001108001200  [  m] 100  [  ] 139 8 6.5 TeV  [  m] 230310240330  [  m] 20  [  ] 9686

5. LHC Problem: Position Measurement oWire position measurement read out is noisy! 5 M. Kuhn - 18 November 2015 Why is the wire position more noisy at larger revolution number?

6. LHC New Fitting Method – from George 6 M. Kuhn - 18 November 2015 ScannerB1H2B1V2B2H1B2V1 450 GeV  [  m] 90012509001300  [  m] 25402040  [  ] 3323 6.5 TeV  [  m] 260310250360  [  m] 7102035  [  ] 33810 Problem in beam 2 remains! G. Trad

7. LHC Comparison with Simulations (1) oSimulated 40  m Gaussian distributed noise on wire position read out − For profile at 450 GeV (1000  m) and 6.5 TeV (300  m) 7 M. Kuhn - 18 November 2015

8. LHC Comparison with Simulations (2) oSimulated 40  m noise on wire position read out − For profile at 450 GeV (1000  m) and 6.5 TeV (300  m) oComputed statistical fluctuations for 1000 scans: − looking for 30  m spread at 450 GeV and 10  m spread (B1) at 6.5 TeV 8 M. Kuhn - 18 November 2015 Can simulate beam size spread for small , but not for large .

9. LHC Comparison with Simulations (3) oNeed to include Gaussian distributed scaling error on profile amplitude read out − Error gradually increases from profile centre 9 M. Kuhn - 18 November 2015 Position [mm]< -2-2-1.50+1+1.5+2> 2 Error0.050.040.03 0.02 0.030.040.05

10. LHC Comparison with Simulations (4) oNeed to include Gaussian distributed scaling error on profile amplitude read out − Error gradually increases from profile centre oComputed statistical fluctuations for 1000 scans: − looking for 30  m spread at 450 GeV and 10  m spread (B1) at 6.5 TeV 10 M. Kuhn - 18 November 2015 Can simulate beam size spread for small , but not for large .

11. LHC M. Kuhn - 18 November 2015 Wire Scanner B2V1 @ 6.5 TeV (1) oObserve large beam size fluctuations at flattop energy − Only for wire scanner B2V1 (on a smaller scale also for B2H1) 11

12. LHC M. Kuhn - 18 November 2015 Wire Scanner B2V1 @ 6.5 TeV (2) oObserve large emittance fluctuations at flattop energy − Visible over long periods of time − Not seen with BSRT 12 G. Trad BSRT bunch 1 BSRT bunch 2 WS bunch 1 WS bunch 2

13. LHC Summary oLarge beam size spread from scan to scan observed at all energies − More  spread for larger beam sizes oPartially due to wire position read out noise − When fitting the position measurement error could be reduced from 10 to 3 % in beam 1 − Beam 2 still shows large spread at flattop energy oSimulation cannot fully reproduce the picture − Even when including scaling error on profile amplitude read out oAlso observing large fluctuations of B2V1 beam size at 6.5 TeV − Very difficult to determine absolute emittance at flattop energy, for example to compare to OP scans 13 M. Kuhn - 18 November 2015