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

Overview Chromaticity decay during injection Chromaticity snapback recall of 2011 situation 2012 beam measurements analysis and proposed model based on 2012 beam measurements Chromaticity snapback Chromaticity decay during flattop 17/04/2012

b3 decay and snapback We need to model and correct the b3 component Chromaticity depends on the b3 (1 unit b3 = 45 Q’) decay snapback snapback decay 17/04/2012

Chromaticity decay during injection Parameter Magnetic measurements 2011 beam measurements 2011 expected at 4 TeV τ‘ (s) 200 1000* - d' 0.66 0.5 c' 20 units 16 units 19 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 amplitude 17/04/2012

2012 beam measurements Fill no 2395 2404 2406 Date 24/03/12 25/03/12 Lattice sextupoles constant Spool pieces constant (no decay, no snapback correction) dynamic (decay and snapback correction) First data point after injection plateau 500 s 210 s 50 s tinj 51 minutes 90 minutes 6 hours Previous cycle tFT 9 hours 17 minutes tprep 24 minutes 17/04/2012

Fill 2395 – the “naked” ramp decay decay snapback 17/04/2012

Fill 2406 (with dynamic correction) 17/04/2012 FiDeL model was based on this measurement

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

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

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

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

FiDeL model based on Fill 2406 Scaled for a pre-cycle case 2012 FiDeL parameters FiDeL model based on Fill 2406 previous IFT 6740 A previous tFT 17 minutes previous tprep 23 minutes c 20 units d 0.44 tau 600 s Scaled for a pre-cycle case 6740 A 10 minutes 20 minutes 17 units* 0.44 600 s 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 17/04/2012

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

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

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

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

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) 17/04/2012

Fill 2478 17/04/2012

Fill 2479 17/04/2012

Fill 2480 17/04/2012

Snapback analysis from Fill 2395 17/04/2012

Snapback Parameters for snapback correction Fitting parameters as obtained for the snapback parameter b3 Qh’ b1 b3 Qh’ b2 b3 Qv’ b1 b3 Qv’ b2 ∆b3 0.63 0.66 0.74 0.75 ∆I (A) 11 9 13 12 gSB 0.057 0.072 0.061 delta chroma 28 29 Parameters for snapback correction 2012 gSB 0.06 this implies that the snapback is slower 2011 gSB 0.176 based on series magnetic measurements – but evidence from beam that correction was not perfect 17/04/2012

Snapback modelling 2012 FiDeL fit (red curve) versus beam measurements (fill 2395 – the « naked ramp ») 17/04/2012

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 parameter Qh’ b1 Qh’ b2 Qv’ b1 Qv’ b2 c -4.95 -4.73 5.08 4.36 d 0.43 0.51 0.65 0.49 tau 48 63 191 89 vx -11.74 -11.54 -10.69 -10.70 Parameters for decay correction c d tau 4.78 0.52 100 s 17/04/2012

Decay during flattop at 4 TeV 17/04/2012

Decay during flattop at 4 TeV 17/04/2012

Fill 2452 17/04/2012

Fill 2466 17/04/2012

Conclusions Decay during injection Snapback Decay during flattop 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 17/04/2012