Snapback Analysis - Updates

Chromaticity decay and snapbackNicholas AquilinaTE-MSC-MDT

Acknowledgements:E. Todesco, M. Lamont, G. Papotti, EICsCERN, LBOC meeting, 17th April 2012 1OverviewChromaticity decay during injectionrecall of 2011 situation2012 beam measurementsanalysis and proposed model based on 2012 beam measurementsChromaticity snapbackChromaticity decay during flattop17/04/20122b3 decay and snapbackWe need to model and correct the b3 componentChromaticity depends on the b3 (1 unit b3 = 45 Q)

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decaysnapbackdecaysnapbackChromaticity decay during injection

17/04/20124Parameter Magnetic measurements2011 beam measurements2011 expectedat 4 TeV (s)2001000*-d'0.660.5-c'20 units16 units19 units*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 amplitude2012 beam measurements17/04/20125Fill no239524042406Date24/03/1225/03/1225/03/12Lattice sextupolesconstantconstantconstantSpool piecesconstant (no decay, no snapback correction)dynamic (decay and snapback correction)dynamic (decay and snapback correction)First data point after injection plateau500 s210 s50 stinj51 minutes90 minutes6 hoursPrevious cycletFT9 hours17 minutes17 minutestprep24 minutes24 minutes24 minutes

Fill 2395 the naked ramp17/04/20126decaysnapbackdecayFill 2406 (with dynamic correction)17/04/20127

FiDeL model was based on this measurement

2012 FiDeL model as obtained from Fill 2406 17/04/20128

2012 FiDeL model as obtained from Fill 2406 17/04/20129

2012 FiDeL model as obtained from Fill 2406 17/04/201210

2012 FiDeL model as obtained from Fill 2406 17/04/2012112012 FiDeL parameters17/04/201212*Decay amplitude for pre cycle is 17 units w.r.t. 19 units expected from scaling of 2011 beam measurementsFiDeL model based on Fill 2406previous IFT6740 Aprevious tFT17 minutesprevious tprep23 minutesc20 unitsd0.44tau600 sScaled for a pre-cycle case6740 A10 minutes20 minutes17 units*0.44600 susing powering history scaling law

2012 FiDeL model compared with Fill 2395 17/04/201213

2012 FiDeL model compared with Fill 2395 17/04/201214

2012 FiDeL model compared with Fill 2395 17/04/201215

2012 FiDeL model compared with Fill 2395 17/04/201216Implementation of new FiDeLThe new parameters have been used in the CCC since Friday 6th AprilWith new parameters chromaticity is kept within 1 unit (over a duration of 20 30 minutes)

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17/04/201218Fill 2478

17/04/201219Fill 2479

17/04/201220Fill 2480

Snapback analysis from Fill 239517/04/201221

SnapbackFitting parameters as obtained for the snapbackparameter b3 Qh b1b3 Qh b2b3 Qv b1b3 Qv b2b30.630.660.740.75I (A)119 1312gSB0.0570.0720.0570.061delta chroma28292929Parameters for snapback correction2012 gSB0.06this implies that the snapback is slower2011 gSB0.176based on series magnetic measurements but evidence from beam that correction was not perfect17/04/201222

b3ISnapback modelling17/04/201223

2012 FiDeL fit (red curve) versus beam measurements (fill 2395 the naked ramp)Decay during flattop at 4 TeVFitting parameters as obtained for the decay during flattop (Fill 2395)No asymmetry between the vertical and horizontal planeparameter Qh b1Qh b2Qv b1Qv b2c-4.95-4.735.084.36d0.430.510.650.49tau486319189vx-11.74-11.54-10.69-10.70Parameters for decay correctioncdtau4.780.52100 s17/04/201224Decay during flattop at 4 TeV17/04/201225

Decay during flattop at 4 TeV17/04/201226

Fill 245217/04/201227

Fill 246617/04/201228

ConclusionsDecay during injectiondecay amplitude increased by 5% from 2011 operationtime constant is around 600 s (more data was available during the first moments of injection)correction is in place and it is workingchromaticity decay is kept within 1 unitSnapbackgSB is found to be smaller, therefore slower snapbacknot implemented yetDecay during flattopa correction using the spool pieces is in place and active17/04/201229