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MQXAB: DECAY AND FIELD HARMONICS

FiDeL meeting, 26 th May 2009. MQXAB: DECAY AND FIELD HARMONICS. E. Todesco Magnets, Superconductors and Cryostats Group Technology Department, CERN. Ackowledgements : P. Schlabach , G. Velev. CONTENTS. Features and function in the machine, and available measurements for field harmonics

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MQXAB: DECAY AND FIELD HARMONICS

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  1. FiDeL meeting, 26th May 2009 MQXAB: DECAY AND FIELD HARMONICS E. Todesco Magnets, Superconductors and Cryostats Group Technology Department, CERN Ackowledgements: P. Schlabach, G. Velev

  2. CONTENTS • Features and function in the machine, and available measurements for field harmonics • Field harmonics • Allowed • Not allowed • Decay

  3. MQXB: FEATURES AND FUNCTION IN THE MACHINE • 16 magnets making 8 Q2, on each side of the four interaction points • Design and manufacturing made in the US • Two layer, four-blocks, graded coil • Free-standing collars • Currents: • Injection 716-776 A to give 13.2 – 14.3 T/m • Collision 5 TeV: 8120 A • Collision 7 TeV: 11380 A to give 205 T/m • Beam dynamics: • Negligible at injection, critical at high field after squeeze

  4. Field harmonics: AVAILABLE MEASUREMENTS • What do we have today ? • ‘Integral’ measurements: • For all magnets, for every cold mass • Values at 4 currents namely ~injection (669 A), 5460 A, ~collision at 7 TeV (11345 A), ultimate (11923 A). • Injection (716-776A) higher than what measured (669 A): good • To be checked: • Precycle • Waiting time before making the measurement • ‘Dcloop’ measurements: • More current values, only for transfer function • Other informations from papers

  5. CONTENTS • Features and function in the machine, and availablemeasurements for fieldharmonics • Field harmonics • Allowed • Not allowed • Decay

  6. Field harmonics: ALLOWED • The MQXB are critical after the squeeze • We propose to set the model at high field exactly on the measured values • Geometric set at value at 7 TeV • For the allowed b6, b10 • b6 at 7 TeV is smaller than 0.1 units – very well optimized ! • Negligible changes from 3.3 to 7 TeV: no need of different settings at 4-7 TeV • At injection, -1.5 unit of b6and a very small additional spread (0.2 units) • b10 always negligible

  7. Field harmonics: ALLOWED • Geometric: • One per magnet • Set at the value at 7 TeV • First 3 cold masses had a lower value b6, then a correction has been done through shims [G. Velev et al., IEEE Trans. Appl. Supercon. 17 (2007) 1109] • DC magnetization • Computed on the data averaged over all magnets: one generic, to take into account of about -1.5 units • m6=-1.24 • p6=0.3 • q6=2 • Iinj=750 A • Ic=13000 A

  8. Field harmonics: NOT ALLOWED • The MQXB are critical after the squeeze • We propose to set the geometric on the measured value at 7 TeV • For the not allowed • Small systematic b4 of about 0.1 units – could be relevant • All the other systematic are very close to zero ! • Spread at injection is the same as at high field – this is strange: in general the spread at high field is smaller than at injection • Slight difference with data presented in [G. Velev et al., IEEE Trans. Appl. Supercon. 17 (2007) 1109], where one has a systematic a4 of about 0.2 units Average and stdev of ‘Integral’ data as presented by G: Velev et al in IEEE Trans. Appl. Supercon. 17 (2007) 1109 Average and stdev of ‘Integral’ data

  9. CONTENTS • Features and function in the machine, and availablemeasurements for fieldharmonics • Field harmonics • Allowed • Not allowed • Decay

  10. DECAY • Measurements: • We have no data, and we base our analysis on the results reported by G. Velev et al. • In FNAL they used a two-parameter log fit • We used the listed parameters in Velev paper to reconstruct data • Average b6decay after 1200 s is 1.7 units with a 0.4 units spread • No info on the TF from that paper

  11. DECAY • FiDeL fit • We use a double exponential fit • The fit error is negligible (0.02 units) • The parameters d and t have a very small spread (the exp fit looks pretty solid!) • We propose to neglect this component

  12. CONCLUSIONS • Geometric: set on values at collision (about 7 TeV), one component per magnet • b6 very well optimized (shimming from the fourth magnet to correct 0.5 units, final average within 0.1 units) • Negligible difference from 5 to 7 TeV • Small systematic b4 (0.1 units) • Small systematic a4 (0.2 units) present in Velev papers, but not in our data – to be checked with FNAL colleagues • Persistent: about -1.5 unit on b6, taken into account by a persistent component, the same for every magnet • Decay: about 1.7 units on b6 • Fit for b6 has been computed as an excercise, but we propose to neglect it in FiDeL • Anyway, it would be good to recover warm measurements, Dcloop, and decay

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