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Chromaticity decay and snapback

CERN, LBOC meeting, 17 th April 2012 . Chromaticity decay and snapback. Nicholas Aquilina TE-MSC-MDT Acknowledgements: E. Todesco, M. Lamont, G. Papotti , EICs. Overview. Chromaticity decay during injection recall of 2011 situation 2012 beam measurements

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Chromaticity decay and snapback

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  1. CERN, LBOC meeting, 17th April 2012 Chromaticity decay and snapback Nicholas Aquilina TE-MSC-MDT Acknowledgements: E. Todesco, M. Lamont, G. Papotti, EICs

  2. Overview • Chromaticity decay during injection • recall of 2011 situation • 2012 beam measurements • analysis and proposed model based on 2012 beam measurements • Chromaticity snapback • Chromaticity decay during flattop

  3. b3 decay and snapback • We need to model and correct the b3 component • Chromaticity depends on the b3 (1 unit b3 = 45 Q’) snapback decay snapback decay

  4. Chromaticity decay during injection *First data points were after 15 minutes @ injection For 2012 operation, energy has been increased from 3.5 to 4 TeV, an increase of 20% is expected in the decay amplitude

  5. 2012 beam measurements

  6. Fill 2395 – the “naked” ramp decay decay snapback

  7. Fill 2406 (with dynamic correction) FiDeL model was based on this measurement

  8. 2012 FiDeL model as obtained from Fill 2406

  9. 2012 FiDeL model as obtained from Fill 2406

  10. 2012 FiDeL model as obtained from Fill 2406

  11. 2012 FiDeL model as obtained from Fill 2406

  12. 2012 FiDeL parameters using powering history scaling law *Decay amplitude for pre cycle is 17 units w.r.t. 19 units expected from scaling of 2011 beam measurements

  13. 2012 FiDeL model compared with Fill 2395

  14. 2012 FiDeL model compared with Fill 2395

  15. 2012 FiDeL model compared with Fill 2395

  16. 2012 FiDeL model compared with Fill 2395

  17. Implementation of new FiDeL • The new parameters have been used in the CCC since Friday 6th April • With new parameters chromaticity is kept within 1 unit (over a duration of 20 – 30 minutes)

  18. Fill 2478

  19. Fill 2479

  20. Fill 2480

  21. Snapback analysis from Fill 2395

  22. Snapback ∆b3 ∆I • Fitting parameters as obtained for the snapback • Parameters for snapback correction

  23. Snapback modelling 2012 FiDeL fit (redcurve) versus beammeasurements (fill 2395 – the « nakedramp »)

  24. Decay during flattop at 4 TeV • Fitting parameters as obtained for the decay during flattop (Fill 2395) • No asymmetry between the vertical and horizontal plane • Parameters for decay correction

  25. Decay during flattop at 4 TeV

  26. Decay during flattop at 4 TeV

  27. Fill 2452

  28. Fill 2466

  29. Conclusions • Decay during injection • decay amplitude increased by 5% from 2011 operation • time constant is around 600 s (more data was available during the first moments of injection) • correction is in place and it is working • chromaticity decay is kept within 1 unit • Snapback • gSB is found to be smaller, therefore slower snapback • not implemented yet • Decay during flattop • a correction using the spool pieces is in place and active

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