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

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

[email protected]

20 September 2005 IMMW-14 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…


Q2 initial alignment


Scope of work

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

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!

Measurements During Fabrication

Measurements at Test Facility

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


Magnets in various stages of assembly


Completed Q1


Alignment measurements

Single Stretched Wire System


Single (100m) wire stretched between precision x-y stages with 1m 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

SSW technique

• 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.


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)


Main quads resolutions

AlignmentParameter typical limit typical limit typical limitx-center (m) 5 10 50 100 50 100y-center (m) 25 50 50 100 60 120z position (m) 5000 10000 50 100 5000 10000roll (rad) 50 100 25 50 75 150pitch (rad) 20 40 10 20 25 50yaw (rad) 10 20 10 20 15 30

SSW Survey/Transfer Total

Summary table for RMS errors (single measurements)

“Total” refers to the error present as encoded in fiducial position data. Mechanical stability is assumed.


Resolutions

Warm AC measurement noise floor ~5 nVs


Removing sag - vibration technique

yz2

2

w

T

kw

T

g

4 f2 L w2

f1

2 L w

Tg

w

1/T subject to stretching and tension gauge errors.

Better to use 1/f 2


Vibration measurement


Removing sag - vibration technique

Recent improvement in determining frequency – Lomb Transform – can obtain frequency to better than 0.1%

f=7.951


Corrector measurements

Use ‘rotating wire’ – find center from feed-down as with rotating coil. Roll angle given wrt stages (leveled to gravity)

Sextupole Corr.

Dodecapole corr.


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 50m


Finding axial z center

cnp

Gradient, g measured with rotating coil

Integrated gradient, gdl measured with SSW

Lw

Lm = gdl/g

a b

Flux measured counter-directional depends on Z-position of magnet with respect to wire stages.D

a1

4 g D2 L m

L w2 2 g D2

L m

L w

2 g D2L m

2

L w2

2

33 D

L w2

g L m g D2 L m

3 6 cn L w

2

Meas. Q2A/B distancecoil 6526

mech 6523ssw 6523

Consistent within meas. uncertainties of few mm from tape meas.


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.


Strength measurements

Results of 6 LQXB magnets at various currents

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

0 2000 4000 6000 8000 10000 12000 14000

Current (A)

Variation from average strength at each current (units)


Changes with thermal cycles


Warm-Warm average change

-0.700

-0.600

-0.500

-0.400

-0.300

-0.200

-0.100

0.000

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Magnet sequence number

Average vertical change warm-warm (mm)

1TC

2TC

3TC


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.


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


Lug adjustments

Before

After


Other problems


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.


Wire susceptibility for ‘best wire’

Same wire at 669A, 11345A


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.


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.

Documents

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