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MQXA: DECAY AND FIELD HARMONICS

FiDeL meeting, 30 March 2009. MQXA: DECAY AND FIELD HARMONICS. E. Todesco Magnets, Superconductors and Cryostats Group Technology Department, CERN. CONTENTS. Decay Field harmonics Allowed Not allowed. DECAY. Measurements: Rotating coil, 600 mm long, In one central position,

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MQXA: DECAY AND FIELD HARMONICS

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  1. FiDeL meeting, 30 March 2009 MQXA: DECAY AND FIELD HARMONICS E. Todesco Magnets, Superconductors and Cryostats Group Technology Department, CERN

  2. CONTENTS • Decay • Field harmonics • Allowed • Not allowed

  3. DECAY • Measurements: • Rotating coil, 600 mm long, • In one central position, • Measurements taken every ~3.7 minutes for up to 6 hours • One close to injection (390 A) and one at high field (7149 A, i.e. ~ 7.3 TeV)

  4. TRANSFER FUNCTION DECAY • Decay from 1 to -4 units after 20 minutes, from 2 to -8 units after 200 minutes • We propose to neglect this effect in FiDeL

  5. B6 DECAY • Decay from 0.2 to 0.8 units after 20 minutes, from 0.4 to 1.3 units after 200 minutes

  6. B6 decay • The double exp fit works well • Time constants of about 500 s

  7. Decay OTHER HARMONICS • Other multipoles • All other multipoles are neglected • There is an unexplained systematic decay in a4

  8. CONTENTS • Decay • Field harmonics • Allowed • Not allowed

  9. Field harmonics: ALLOWED • The MQXA 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 • A persistent component can recover the 1.1 unit difference at injection • For the allowed b6, b10 • Small changes from 3.3 to 6.8 TeV • No need of different settings at 4-7 TeV • b10 always negligible

  10. Field harmonics: ALLOWED • Geometric: • One per magnet • Set at the value at 7 TeV • Persistent component • One per family, to take into account of about -1 units at injection • m6=-1 • p6=0.7 • Iinj=436 • Error of ~0.2 units at 2000-4000 A

  11. Field harmonics: NOT ALLOWED • The MQXA are critical after the squeeze • We propose to set the geometric on the measured value at 7 TeV • For the not allowed • Systematic b4 of about 1.3 units - relevant • Systematic a3 of 0.2 units – all the other systematic to zero • Offset at injection: all close to zero except a4, which has a systematic at injection of -1.3 units • Spread at injection much larger than at high field – to be added in the MAD model as a random component

  12. CONCLUSIONS • Geometric: set on values at collision (about 7 TeV), one component per magnet • Negligible difference from 5 to 7 TeV • Persistent: about -1 unit on b6, taken into account by a persistent component, the same for every magnet • Persistent: about 0.06 units in b10, neglected • For MAD: additional spreads from collision to injection given • Decay: negligible effect on TF, b6, b10 • Fit for b6 has been computed as an excercise

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