MQW magnets: results from the measuring campaign (double aperture resistive quadrupoles for LHC)

1. MQW magnets: results from the measuring campaign(double aperture resistive quadrupoles for LHC) Didier Cornuet Jacques Dutour Miguel Silva

2. Topics to be presented: - ‘MQW magnet’ characteristics - Characteristics of the measurements - Measuring sequences - Results from the analysis of the measurements - Conclusions

3. MQW magnet characteristics: • -Quadrupole magnet:48 installed,4 reserve), 6 MQW quadrupoles • replace 1 superconducting quadrupole. • In cleaning insertions of LHC. • - Normal conducting (high radiation levels) • Two apertures in a common yoke (space constraints in the tunnel). • Two different power connections : DF (MQWA) and FF (MQWB). • Precision between pole profiles: 1x10-4m (over a length of 3.1m)

4. Characteristics of the measurements • -120 measurements MQWA,90 measurements in MQWB • 114 measurements in central position. • “Harmonic Coil” technique (using 5 coils in radial configuration) • “ Mole” (0.75 m) displaced manually with extension shafts (carbon fiber tube ) in 5 positions • along the magnet. • 3 measurements (forwards and backwards) in each position for all • the measuring currents. • DF measuring currents: 40A, 200A, 710A (nominal) and 810A • FF measuring currents: 40A, 200A and 600A (nominal) • - ‘Integrated field gradient’ measurement errors: ± 2 ‰ at 40A • (Gm.Lm) ± 1,5 ‰ at 200A • ± 1 ‰ at 600A • - Sextupolar component: ± 2 units • - Other harmonics: ± 10 %

5. Measuring sequences • Magnetic field lines DF configuration FF configuration • High saturation in some regions of the yoke, due to FF configuration, changes the quadrupole and sextupole components of the DF configuration. The values measured in DF1 at 40A, no longer correspond to real magnetic field values (2nd measuring sequence)

6. Measuring sequences • Influence of the FF configuration: • the measuring sequence had to be changed. • The magnets could be remeasured or we could introduce a correction • in the measured values: • -5 cycles not enough to fully magnetize (change ∫Gdl at low current). • -Start measurements at high currents and then at low currents • (remanent field stabilized, less change of ∫Gdl at low currents). • - Change demagnetization cycles (-Imax/3 => -2/3 Imax). • -FF mode before DF mode because of change ∫Gdl and sextupole • components even after demagnetization (memory of FF mode).

7. Measuring sequences • Improved demagnetization cycle

8. Analysis of the measurements • Harmonic coefficients • MQWA: nominal current

9. Analysis of the measurements • Harmonic coefficients • MQWA: nominal current R2=0.6924 R2=0.7843

10. Analysis of the measurements • Harmonic coefficients • MQWB: nominal current

11. Analysis of the measurements • Magnetic length • MQWA: • MQWB:

12. Analysis of the measurements • Main field gradient • MQWA: • MQWB:

13. Analysis of the measurements • Main field gradient

14. Analysis of the measurements • Magnetic centre drift • In horizontal plane • MQWA: • magnetic centres get • further from each other • MQWB: • magnetic centres get • closer to each other

15. Analysis of the measurements • Main field direction • Average values: AP1 = 0.03 mrad ; AP2 = -0.08 mrad • Values are within the expected precision: ± 2 mrad

16. Conclusions • The measured values are correct, within our expected errors: there’s • no need of corrections (MQW magnets in cluster of 5, average improved). • Each improvement made to get a better precision of the measurements, • resulted in a longer time needed for the same measurements. • -If 10 magnets were measured only in ‘FF configuration’ and the other • 42 magnets only in ‘DF configuration’ the measurement campaign time • would have been much reduced, but the flexibility for the selection • of the magnets would have been lost.