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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. Scope of work.
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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
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
Q2 initial alignment IMMW-14
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
Completed Q1 IMMW-14
Alignment measurements • Single Stretched Wire System IMMW-14
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
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
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
Resolutions • Warm AC measurement noise floor ~5 nVs IMMW-14
Removing sag - vibration technique 1/T subject to stretching and tension gauge errors. Better to use 1/f 2 IMMW-14
Vibration measurement IMMW-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
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
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
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
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
Strength measurements • Results of 6 LQXB magnets at various currents Variation from average strength at each current (units) Current (A) IMMW-14
Changes with thermal cycles IMMW-14
Warm-Warm average change Magnet sequence number 1TC Average vertical change warm-warm (mm) 2TC 3TC IMMW-14
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
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
Lug adjustments Before After IMMW-14
Other problems IMMW-14
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
Wire susceptibility for ‘best wire’ Same wire at 669A, 11345A IMMW-14
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
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