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LHC magnets towards 7 TeV operation

CERN, LBOC meeting, 24 th September 2013 . LHC magnets towards 7 TeV operation. Nicholas Aquilina TE-MSC-MDT Acknowledgements: E. Todesco, P. Hagen, M. Giovannozzi, M. Lamont, S. Le Naour, J. Wenninger. Overview. Scope of this work Saturation component

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LHC magnets towards 7 TeV operation

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  1. CERN, LBOC meeting, 24thSeptember 2013 LHC magnets towards 7 TeV operation Nicholas Aquilina TE-MSC-MDT Acknowledgements: E. Todesco, P. Hagen, M. Giovannozzi, M. Lamont, S. Le Naour, J. Wenninger

  2. Overview • Scope of this work • Saturation component • Decay and snapback (for both tune and chromaticity) • Hysteresis • Powering cycles • Conclusions

  3. Scope of this work • After the long shut down, the LHC energy will be pushed towards 7 TeV • At this energy, the main magnets (dipoles, quadrupoles and triplets) will enter a new regime • Here we study the issues in the field model (FiDeL) that can be critical at 7 TeV

  4. FiDeL components • Depending on the operation current of the magnets, some components are more prominent than others • Hysteresis and magnetization at low current • Saturation at high current • FiDeLmodel predicts each component with some level of uncertainty

  5. Saturation in MBs and MQs • MB • From 3 units to 60 units of saturation, so at 7 TeV we will have an uncertainty (2 sigma) of 4 units in the dipole field • Is this a problem? • MQ • From 1 unit to 13 units of saturation , so at 7 TeV we will have an uncertainty (2 sigma) of 0.2 units in the quadrupole field • Very small, about 0.001 in tune – no problem

  6. Saturation in the triplets • MQXA • From 80 units to 450 units of saturation so at 7 TeV we will have an uncertainty (2 sigma) of 10 units • Probably to be compensated with beta beating corrections • MQXB • From 70 units to 180 units of saturation so at 7 TeV we will have an uncertainty (2 sigma) of 14 units • Probably to be compensated with beta beating corrections

  7. Saturation in IPDs • MBX • From 50 units to 580 units of saturation with an uncertainty (2 sigma) of 5units • One of the highest saturation components – uncertainty possibly underestimated • MBRS • From 55 units to 620 units of saturation with an uncertainty (2 sigma) of 4 units • One of the highest saturation components – uncertainty possibly underestimated

  8. Saturation The uncertainty in the model of saturation gives an error in the kick We are checking if the correctors are strong enough to compensate this – work in progress Equivalent error of the dipoles in μrad

  9. Saturation in correctors • MQT/MS • From 5 units to 665 units of saturation with an uncertainty (2 sigma) of 65 units • One of the highest saturation components!! • Should not be problem for tune/chroma feedback

  10. Saturation - multipoles Saturation component with respect to the geometric in the sextupole component no significant saturation for multipoles Saturation component with respect to the geometric in the dodecapole component

  11. Chromaticity decay • Decay depends on the powering history • Decay was studied through a number of magnetic and beam-based measurements • Decay amplitude is expected to increase by 50% when compared to 2011/2012 operation factor of 5 factor of 1.5

  12. Chromaticity snapback • Snapback correlation factor gSB = 0.176 from magnetic measurements • gSB = 0.220 from beam-based measurements • We are capable to model the chromaticitysnapback, so even at 7 TeV the correction vs time should be ok

  13. Tune decay • Tune decay was observed during operation • Tune decay of -0.005 units at t=1000 s, (-0.022 units as t→∞) • Tune decay measured during magnetic measurements • @ 4 TeV: tune decay of 0.0016 at t=1000 s • @ 7 TeV: tune decay of 0.003 at t=1000 s • This accounts for only 40% of the tune decay observed during the operation • At 7 TeV a tune decay of -0.008 units at t=1000 s is expected (increase of 50%)

  14. Tune snapback • Following the decay, tune snapback is also observed • Snapback behavior follows the exponential decay similar to the chromaticity behavior • Snapback is over in ~50 A, equivalent to 50 s • Tune snapback correction not implemented in LSA • But if needed we are capable to model the tune snapback, so even at 7 TeV the correction vs time should be ok

  15. Hysteresis (1) • FiDeL model only consist of the ramp-up branch of the hysteresis (blue) • This induce an error for those magnets who have to ramp down, e.g. during the squeeze • An error twice as much as the hysteresis component is introduced as the model is on the wrong branch • The IPQs are the magnets which are mostly affected error

  16. Hysteresis (2) • Minimum β* during squeeze at 6.5/7 TeV is expected to be 0.4/10/0.4/3 • Hysteresis start to be significant • MQM magnets: currents less than 2700 A • MQY magnets: currents less than 1800 A • Q5 and Q6 are the IPQs which are mostly affected • Operation current go as low as 360 A • An error ranging from 10 to 25 units • A trim will be implemented at the end of the squeeze to correct for this

  17. Hysteresis (3) IPQs which will be operating in the hysteresis region at 6.5 TeV IPQs which will be operating in the hysteresis region at 7 TeV

  18. Powering cycles (1) Comparison of the pre-cycle and physics cycle of the MQs at 4 TeV and 7 TeV operation. Increase of 17 minutes Comparison of the pre-cycle and physics cycle of the MBs at 4 TeV and 7 TeV operation. Increase of 17 minutes N.B. The power converter for the quadrupoles cannot ramp down the current, so one has an exponential decay with the time constant of the cirucit. This is different for each quadrupole, the worst case is taken in these cases.

  19. Powering cycles (2) • Slowest quadrupole is MQY left of point 5 • Comparison of the pre-cycle and physics cycle of the MBs at 4 TeV and 7 TeV operation. Increase of 10 minutes

  20. Conclusions • Saturation • Once operating at 7 TeV, all magnets will be operating in the saturation region of their transfer function • In principle the associated uncertainty, which can be of the order of 10-50 units, should be corrected by feedback system (orbit, tune) and beta beating measurements (triplets and IPQ). • Decay and snapback • Decay and snapback were observed in both tune (due to the b2 component) and chromaticity (due to the b3 component). • In case of the chromaticity, the decay amplitude at 7 TeV is expected to increase by 50% when compared to the 4 TeV operation. • Hysteresis • The present FiDeL model consists of the ramp up branch only • Q5 and Q6 are the IPQs which are mostly affected, for these magnets an error between 10-25 units is expected • This error will be compensated by adding opposite trims in the magnets showing this behaviour. • Powering cycle • In the LHC current operational cycle, the linear ramp rate is limited to 10 A/s • An increase of 17 minutes is expected for the main dipoles and the main quadrupoles • An additional 10 minutes is expected for the slowest IPQ

  21. Tune decay Decay of the transfer function as expected at 4 TeV and 7 TeV operation based on magnetic measurements Decay of the transfer function as observed during the magnetic measurements

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