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MQXA: DECAY AND FIELD HARMONICS

This document presents comprehensive findings on decay behavior and field harmonics in MQXA magnets, derived from extensive measurements at various currents, including injection levels and high fields up to 7 TeV. Key insights into decay rates, measurement techniques, and implications for magnet performance are provided. We propose neglecting certain decay effects for the FiDeL project and emphasize the importance of setting field harmonics accurately at collision energies. This study contributes to the optimization of superconducting magnets for future high-energy physics experiments at CERN.

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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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