Chromaticity decay correction during injection-dynamic correction

CERN, FiDeL meeting, 29th March 2011 Chromaticity decay correction during injection-dynamic correction Nicholas Aquilina TE-MSC-MDA Acknowledgements: E. Todesco, W. Venturini Delsolaro, M. Lamont, M. Strzelczyk EIC and operators

Contents • Correction of b3 in the LHC • Spool pieces • Lattice sextupoles • Static correction vs dynamic correction • Measurements of the first dynamic correction • Analysis and results • Conclusions

Correction of b3 in the LHC • Two circuits to correct/control b3 and therefore chromaticity • Spool pieces (RCS) • found after each dipole • correct for the b3hysteresis (baseline) and the decay and snapback • Lattice sextupoles (RSD/F) • found after each quadrupole • trims applied to control the chromaticity to a desired value Integrated and centered b3vs current [L. Deniau]

Static vs Dynamic correction during injection • Static correction • constant value according to the baseline • constant value to correct the decay (assuming a fixed injection time) 22nd February 2011 • Dynamic correction • constant value according to the baseline • varying value to correct the decay 18th March 2011

First dynamic correction - measurement • First injection with dynamic correction was done on 18th March @ 06h00 • Lattice sextupoles were used to trim the chromaticity (when a static correction is used, these are used to correct for the decay) • Spool pieces were used to correct for the decay (as it should be)

First dynamic correction – Analysis and results • Blue curve; the measured chroma with the lattice sextupoles trims removed (7.5 units of decay in 2520 seconds) • Green curve; the correction as applied by the spool pieces (15 units of decay in 2700 seconds) • Red curve; the corrected chromaticity (7.5 units of decay in 2520 seconds) N.B. the 2520 seconds range is from 600 to 3120 seconds, the length of available data

Conclusion • Spool pieces (not the lattice sextupoles) were used to correct for the b3 decay, as it should be • On analysing the static correction in the spool pieces it was found out that sometimes sectors 67 and/or 81 has no decay correction (during 2011) not even in the static case • A correction twice as much as that required was applied in this case • The time constant of the decay is inline with what we expect

Chromaticity decay correction during injection-dynamic correction