Snapback Analysis - Updates

1LHC magnets towards 7 TeV operationNicholas AquilinaTE-MSC-MDT

Acknowledgements:E. Todesco, P. Hagen, M. Giovannozzi, M. Lamont, S. Le Naour, J. WenningerCERN, LBOC meeting, 24th September 2013 2OverviewScope of this workSaturation componentDecay and snapback (for both tune and chromaticity)HysteresisPowering cyclesConclusions24/09/20133Scope of this workAfter the long shut down, the LHC energy will be pushed towards 7 TeVAt this energy, the main magnets (dipoles, quadrupoles and triplets) will enter a new regimeHere we study the issues in the field model (FiDeL) that can be critical at 7 TeV24/09/20134FiDeL componentsDepending on the operation current of the magnets, some components are more prominent than othersHysteresis and magnetization at low currentSaturation at high currentFiDeL model predicts each component with some level of uncertainty

24/09/20135

Saturation in MBs and MQsMBFrom 3 units to 60 units of saturation, so at 7 TeV we will have an uncertainty (2 sigma) of 4 units in the dipole fieldIs this a problem?MQFrom 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 fieldVery small, about 0.001 in tune no problem24/09/20136

Saturation in the tripletsMQXAFrom 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 correctionsMQXBFrom 70 units to 180 units of saturation so at 7 TeV we will have an uncertainty (2 sigma) of 14 unitsProbably to be compensated with beta beating corrections

24/09/20137

Saturation in IPDsMBXFrom 50 units to 580 units of saturation with an uncertainty (2 sigma) of 5 unitsOne of the highest saturation components uncertainty possibly underestimatedMBRSFrom 55 units to 620 units of saturation with an uncertainty (2 sigma) of 4 unitsOne of the highest saturation components uncertainty possibly underestimated24/09/20138

Saturation Magnet4 TeV7 TeV2 sigma (units)equivalent rad2 sigma (units)equivalent radMB0.260.133.71.85MBX (2,8)1.40.214.30.645MBRC (1,5)0.20.020.40.04MBRC (2,8)0.20.031.60.24MBRS (4)1.4*0.213.2*0.48MBRB (4)0.2*0.030.6*0.09MBW (3,7)0000MBXW (1,5)0.20.02222.224/09/20139Equivalent error of the dipoles in radThe 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 progressSaturation in correctorsMQT/MSFrom 5 units to 665 units of saturation with an uncertainty (2 sigma) of 65 unitsOne of the highest saturation components!!Should not be problem for tune/chroma feedback

24/09/201310

Saturation - multipolesMagnet4 TeV7 TeVCurrent (A)Average b3 (units)2 sigma (units)Current (A)Average b3 (units)2 sigma (units)MB6770-0.310.05118500.100.19MBX (2,8)3310-0.330.0258000.770MBRC (1,5)2510-0.030.6844000.150.62MBRC (2,8)34300.020.6660000.690.60MBRS (4)3350-0.390.06*5860-0.320.09*MBRB (4)35100.050.014*61500.620.06*24/09/201311Magnet4 TeV7 TeVCurrent (A)Average b6 (units)2 sigma (units)Current (A)Average b6 (units)2 sigma (units)MQ6780-0.100.0211870-0.020.01MQXA (1,5)3890-0.020.18680000.14MQXA (2,8)4100-0.020.18718000.14MQXB (1,5)6510-0.010.051140000.03MQXB (2,8)6830-0.010.051196000.03MQM @ 1.9 K3080-0.1705390-0.030MQM @ 4.5 K2460-0.2704310-0.070MQY2060-0.050.013610-0.010Saturation component with respect to the geometric in the sextupole componentSaturation component with respect to the geometric in the dodecapole componentno significant saturation for multipolesChromaticity decay24/09/201312

Measurement nameCommentsDescriptionDecay amplitude at infinity (units of b3)No. of measurementsSeries measurementsMagnetic measurements done before the magnets were installed in the tunnel before 2008dI/dt = 50 A/sIFT = 12 kA2.491654 TeV magnetic measurementsMagnetic measurements done during the operation of the LHC on spare magnets in SM18dI/dt = 10 A/sIFT = 6.8 kA0.4767 TeV magnetic measurementsMagnetic measurements done during the operation of the LHC on spare magnets in SM18dI/dt = 10 A/sIFT = 12 kA0.564Beam-based measurementsBeam-based measurements done during the 2011 to 2012 operation of the LHCdI/dt = 10 A/sIFT = 6.8 kA0.4060LSA settingsControl settings as used for 2012 operation0.39naDecay depends on the powering historyDecay was studied through a number of magnetic and beam-based measurementsDecay amplitude is expected to increase by 50% when compared to 2011/2012 operation

factor of 5factor of 1.5Chromaticity snapbackSnapback correlation factor gSB = 0.176 from magnetic measurementsgSB = 0.220 from beam-based measurementsWe are capable to model the chromaticity snapback, so even at 7 TeV the correction vs time should be ok24/09/201313

Tune decayTune decay was observed during operationTune 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 sThis accounts for only 40% of the tune decay observed during the operationAt 7 TeV a tune decay of -0.008 units at t=1000 s is expected (increase of 50%)

24/09/201314Tune snapbackSnapback is over in ~50 A, equivalent to 50 sTune 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 ok24/09/201315

Following the decay, tune snapback is also observedSnapback behavior follows the exponential decay similar to the chromaticity behavior

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 squeezeAn error twice as much as the hysteresis component is introduced as the model is on the wrong branchThe IPQs are the magnets which are mostly affected24/09/201316

errorHysteresis (2)Minimum * during squeeze at 6.5/7 TeV is expected to be 0.4/10/0.4/3Hysteresis start to be significantMQM magnets: currents less than 2700 AMQY magnets: currents less than 1800 AQ5 and Q6 are the IPQs which are mostly affectedOperation current go as low as 360 AAn error ranging from 10 to 25 unitsA trim will be implemented at the end of the squeeze to correct for this

24/09/201317Hysteresis (3)MagnetLocationCurrent (A)Error (units)ap1ap2ap1ap2MQYQ4.R11655na0.6naQ4.R51653na0.6naQ4.R8165814330.551.6MQMLQ5.R111321014427.4Q6.R13602546924Q8.L22229na4.2naQ6.L22372239843.9Q6.R2246124703.83.8Q8.R22611na3.7naQ6.L53614372524.8Q5.L5206614294.67.4Q5.R5144311327.410Q6.R54713622425Q8.L61970na4.8naQ8.R6na1951na4.9Q6.R8253925103.83.8Q6.L1na361na25Q5.L1143020687.44.6MQMQ6.L22372239843.9Q5.R2na2480na3.8Q6.R2246124703.83.8Q5.L82649na3.7naQ6.R8253925103.83.824/09/201318MagnetLocationCurrent (A)Error (units)ap1ap2ap1ap2MQYQ5.R8na1543na1.1MQMLQ5.R1121915539.16.7Q6.R13885052523Q8.L22400na3.9naQ6.L2255425823.73.7Q6.R2265026603.73.7Q6.L53894712524Q5.L5222515394.26.7Q5.R5155412196.79.1Q6.R550738922.825Q8.L62121na4.4naQ8.R6na2102na4.5Q6.L14723882425Q5.L1154022276.74.2MQMQ6.L2255425823.73.7Q5.R2na2670na3.7Q6.R2265026603.73.7IPQs which will be operating in the hysteresis region at 6.5 TeVIPQs which will be operating in the hysteresis region at 7 TeVPowering cycles (1)24/09/201319

Comparison of the pre-cycle and physics cycle of the MBs at 4 TeV and 7 TeV operation. Increase of 17 minutesComparison of the pre-cycle and physics cycle of the MQs at 4 TeV and 7 TeV operation. Increase of 17 minutesN.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.Powering cycles (2)24/09/201320

Slowest quadrupole is MQY left of point 5Comparison of the pre-cycle and physics cycle of the MBs at 4 TeV and 7 TeV operation. Increase of 10 minutesConclusionsSaturationOnce operating at 7TeV, all magnets will be operating in the saturation region of their transfer functionIn 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 snapbackDecay 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 7TeV is expected to increase by 50% when compared to the 4TeV operation. HysteresisThe present FiDeL model consists of the ramp up branch onlyQ5 and Q6 are the IPQs which are mostly affected, for these magnets an error between 10-25 units is expectedThis error will be compensated by adding opposite trims in the magnets showing this behaviour.Powering cycleIn the LHC current operational cycle, the linear ramp rate is limited to 10A/sAn increase of 17 minutes is expected for the main dipoles and the main quadrupoles An additional 10 minutes is expected for the slowest IPQ

24/09/20132122Tune decay24/09/201323FamilyAverage decay of TF after 1000sMeasurements conditionsMQ0.33dI/dt = 50A/s IFT = 11850AMQM-3.5dI/dt = 20 A/s IFT = 5390AMQY-1.7dI/dt = 5 A/s IFT = 2500 AMQXA-1.5dI/dt = 10A/sIFT = 7350 AMQXBNo dataFamilyAverage decay after 1000s at 4 TeVAverage decay after 1000s at 7 TeVTFtuneTFtuneMQ0.1610-40.170.001MQM-0.8-810-4-2-0.002MQY-3.4-0.001-3.4-0.001MQXA-0.75-4.510-4-1.5-910-4MQXBNo dataNo dataTotal-0.0016-0.0029Decay of the transfer function as observed during the magnetic measurementsDecay of the transfer function as expected at 4 TeV and 7 TeV operation based on magnetic measurements