LHC IR Quadrupole Alignment Experience at Fermilab

1. LHC IR Quadrupole Alignment Experience at Fermilab T. Beale, J. DiMarco, J. Nogiec, P. Schlabach, C. Sylvester, J. Tompkins, G. Velev 28 September 2005 dimarco@fnal.gov

2. Scope of work • Final focus quad triplets for the LHC are supplied by Fermilab and KEK. Fermilab manufactures the Q2 – two 5.5m long 215 T/m magnets (Q2a/Q2b) housed in a single cryostat. KEK manufactures the Q1 and Q3 cold masses (6.3m long, also 215 T/m), then ships them to Fermilab for cryostatting. Nine magnets of each flavor Q1, through Q3 are needed. • Final alignment of all 27 magnets rests with FNAL. Only the nine Q2 magnets are cold tested within their cryostat along with a single Q1. The rest had cold test at KEK as a cold-mass, and final alignment is done warm. Try to understand warm/cold so that can predict what happens for Q1/Q3 elements not cold tested. • Could not rely on tooling for alignment during production as was hoped. Had to measure at each production step and adjust as needed – fairly large measurement load… IMMW-14

3. Q2 initial alignment IMMW-14

4. Scope of work Measurements During Fabrication Measurements at Test Facility • Q2a/b alignment measurements • Initial Q2a to Q2b relative alignment and roll angles (Q2a, Q2b powered separately) • Alignment after interconnect tube welding • Beam tube flange alignment • Q1/Q3 alignment measurements • Initial establishment of roll angle • Beam tube flange alignment • Individual alignment of 3 corrector packages to main quadrupole • Final alignment of main quadrupole and measurement of 8 corrector elements • Q2a/b alignment measurements • Mounting on test stand and lug adjustment for Q2a/Q2b relative alignment • Warm alignment before cold test • Cold alignment • Cold strength measurements • Warm alignment after cold test • Additional round of lug adjustment based on warm /cold alignment change • Final alignment Note that all fabrication alignments (except final alignment) as well as lug adjustment alignments at test facility are an iterative loop with mechanical adjustments between! IMMW-14

5. Magnets in various stages of assembly IMMW-14

6. Completed Q1 IMMW-14

7. Alignment measurements • Single Stretched Wire System IMMW-14

8. SSW technique • Single (100mm) wire stretched between precision x-y stages with 1mm accuracy linear encoders. • Integrator measures flux change from wire motion or AC field. For quadrupole, use wire motions in horizontal and vertical planes. The flux change is the same for +/- motions when wire centered. • Stages have laser tracker target fiducial mounts referenced to wire. • Adjustable wire tensioning for removal of effects from sag • J. DiMarco et al., “Field alignment of quadrupole magnets for the LHC interaction regions”, IEEE Trans. Appl. Supercond., Vol. 10, No. 1, March 2000. • J. DiMarco, J. Krzywinski, “MTF Single Stretched Wire System”, MTF-96-001, 1996. IMMW-14

9. What’s measured • 6-axis alignment (X, Y, Z, Roll, Pitch, Yaw) of the one-element (Q1, Q3) and two-element (Q2a, Q2b) magnet assemblies • X, Y, and Roll of their corrector packages • Integrated strength • X, Y are obtained by stages moving Co-directionally +/- • Pitch, Yaw are obtained by including Counter-directional stage • Roll obtained from measurements of X-offset as function of Y • Z (discussed later) IMMW-14

10. Main quads resolutions • Summary table for RMS errors (single measurements) “Total” refers to the error present as encoded in fiducial position data. Mechanical stability is assumed. IMMW-14

11. Resolutions • Warm AC measurement noise floor ~5 nVs IMMW-14

12. Removing sag - vibration technique 1/T subject to stretching and tension gauge errors. Better to use 1/f 2 IMMW-14

13. Vibration measurement IMMW-14

14. f=7.951 Removing sag - vibration technique • Recent improvement in determining frequency – Lomb Transform – can obtain frequency to better than 0.1% IMMW-14

15. Corrector measurements • Use ‘rotating wire’ – find center from feed-down as with rotating coil. Roll angle given wrt stages (leveled to gravity) Dodecapolecorr. Sextupole Corr. IMMW-14

16. Corrector Meas. Resolution • Importance of field strength ( current, rot. wire radius) • Q3’s have 8 correctors – tested warm 15-20mm radius, 40V AC power supply  ~0.5-2A on magnet • Angles typically found to ~0.1-0.2mrad, centers to 50mm IMMW-14

17. Lm = gdl/g a b Lw Gradient, gmeasured with rotating coil Integrated gradient, gdl measured with SSW Finding axial z center Flux measured counter-directional depends on Z-position of magnet with respect to wire stages. D Consistent within meas. uncertainties of few mm from tape meas. IMMW-14

18. Longitudinal axis centering • Mechanical (tape measure) studies with yoked magnet in production  SSW vs mechanical same to 2-3mm (~accuracy of tape results) (3 magnets) • Some geometry dependence observed – better signal if stages are not equal distance from magnet ends. • Better results if don’t use AC current normalization (current only good to 1e-04) • Signal weak – better in production than on cold test stands (no warm bore or end cans to limit wire travel) • Some systematic difference with nominal (mechanical) distances observed (3-4mm average) – still being looked into. IMMW-14

19. Strength measurements • Results of 6 LQXB magnets at various currents Variation from average strength at each current (units) Current (A) IMMW-14

20. Changes with thermal cycles IMMW-14

21. Warm-Warm average change Magnet sequence number 1TC Average vertical change warm-warm (mm) 2TC 3TC IMMW-14

22. Survey issues • Need fixed points in building measured with level scope to get plane of gravity right • With 2-in-1 (Q2a/b), if magnet changed benches (fabrication area to test area) fiducial plane would change (tables not equally level wrt center. IMMW-14

23. Magnet specific issues • Long magnets – need to get magnet on test stand right so have best aperture as possible (sometimes constrained to 5mm – tough). • Two-magnet system – • Warm/cold changes – goes where it wants to. • Positions need to be monitored and adjusted after fabrication and testing IMMW-14

24. Lug adjustments Before After IMMW-14

25. Other problems IMMW-14

26. Other problems… • Finding good wire • Ordering ‘same wire’ from a company can have very different properties. Not controlled at the level we’re interested in. • Had wire that was very susceptible and appear to saturate (?) (very strange 1/T dependence) • Had wire that is paramagnetic/diamagnetic depending on current (turns out that was best case – low susceptibility even at 220T/m over 11m !) • (Strong wire susceptibility/saturation affects strength but not center much) • Best spool was from California Fine Wire – but seemed ‘one-of-a kind’. Goodfellow pretty good to ~110T/m (5x worse at 220T/m than ‘best spool’). • Will also try additional vendors. IMMW-14

27. Wire susceptibility for ‘best wire’ Same wire at 669A, 11345A IMMW-14

28. Other problems (continued) • Motion Controllers reliability problems (fail with power surges/failures, disconnection of stages) – (have now located a replacement vendor). • Speed (basic measurement took 15min for XY) - measurements now 5x faster on new computers • Error handling in software – new EMS software “almost ready” • Mechanical, electrical noise on high field strength measurements. IMMW-14

29. Summary of Experience • Alignment needs to be measured during production • 2- magnet systems are tough – changeable, need to adjust • SSW was able to handle all the alignment load; cold strengths as well. • Some practical and ‘interesting’ problems with wire variability, understanding axial centering, equipment issues – need for spares – should have planned for additional system (and technicians) for production load. IMMW-14