of main M Conclusions Introduction · PDF fileXII International Magnetic Measurement Workshop,...

XII International Magnetic Measurement Workshop, Grenoble, 1-4th October 2001 [email protected] (slide 1/24)

MMagneticagnetic alignment tests alignment tests of main of main LHC cryodipoles at CERNLHC cryodipoles at CERN

L Bottura, M Buzio, G Deferne, P Schnizer, P Sievers, N Smirnov

1.1. IntroductionIntroduction2.2. Field angle measurementsField angle measurements3.3. Alignment tests: motivations & strategyAlignment tests: motivations & strategy4.4. Definition of dipole axisDefinition of dipole axis5.5. Equipment & proceduresEquipment & procedures6.6. ConclusionsConclusions


1.1 Introduction1.1 Introduction

� 1232 dipoles + 430 quadrupoles to be cold tested at CERN upon reception(talk focused on dipoles, but equipment and procedures for quadrupoles are essentially similar – with tighter tolerances)

� cryogenic equipment for magnetic tests works @ room temperature inside an anticryostat⇒ cold mass not accessible to measurements

� all dipoles include sextupole corrector spool pieces at one end½ include combined octupole/decapole correctors at the other end

� Spool pieces are used to do quasi-local harmonic correction and are aligned mechanically upon installation

Background


1.2 Introduction1.2 Introduction LEICA laser tracker→

sextupole correctors

decapole/octupole correctors

dipole magnet

optical targets (fiducials)

additional central jack


1.3 Introduction1.3 Introduction

Main dipole alignment issues related to cryogenic tests

1) Dipole field angle: must be normal to beam orbit

2) Dipole harmonics:(field shape errors) must be expressed w.r.t. reference orbit

3) Corrector axis: must be aligned w.r.t. dipole ⇒ field errors can be corrected without generating spurious multipoles by feed-down


2.1 Field angle measurements2.1 Field angle measurements

Field angle measurementsField angle measurements

♦ Main dipole angle measured as the phase of the first harmonic

♦ Calibration done via a 0.5T reference dipole

♦ Precision required for the machine: ~ 0.5 mrad

♦ Measurement accuracy (1 σ):

0.25 mrad (local), 0.10 mrad (integrated)

MBP2O2 dipole angle

-2

-1

0

1

2

-8 -6 -4 -2 0 2 4 6 8z (m)

angl

e (m

rad)

A1 @ 11750AA2 @ 11750AA1 @ 760AA2 @ 760A

Connection (TRU) Lyre (CFU)


2.2 Field direction vs. central support jack 2.2 Field direction vs. central support jack Centre of Ap. 1 - MBP2O2 @ 11850A

y = -0.0451x - 0.0023

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

-1.000 -0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800 1.000

Increment of vertical sagitta at central jack (mm)

B1

angl

e in

crem

ent (

mra

d)

• dipole curvature ⇒ vertical displacement at central jack causes cold mass to rotate

• 3 magnets measured so far (results from A001 not fully consistent)

• upper bound:

• dipole curvature ⇒ vertical displacement at central jack causes cold mass to rotate

• 3 magnets measured so far (results from A001 not fully consistent)

• upper bound:

≤A 5000 @

mmmrad 07.0

A 11850 @mmmrad 05.0

_ jackcentralzdd

δα

(10 consecutive magnetic measurements at each position of the central jack)

cryostat

cold mass

support post

Central jack position is coupled to cold mass twist


3.1 Magnetic alignment tests3.1 Magnetic alignment tests

I. Magnetic axes are needed in nominal working conditions

II. Mechanical and magnetic axes seem to coincide within 0.1~0.2 mm1, but mechanical axes are measured are not accessible at 1.9K ⇒ unproved extrapolation from room to cryogenic conditions is necessary

III. Corrector leads accessible only after cold tests

IV. Cross-check with measurements1 in industry for absolute accuracy and effects due to transportation

1 see Juan’s talk

Motivations for alignment tests at CERN


3.2 Overall alignment test strategy3.2 Overall alignment test strategy

Cryogenic magnetic measurements with 15m shaft

The twin 15m coil shaft system measures dipole axis and field errors (multipoles) vs. excitation and powering history on the cryogenic test bench. The absolute position of the coil rotation axis is not known with precision.

twin 15m ceramic dipole coil shafts

xfield multipoles

magnetic axis(obtained by harmonic feed-down)

field reference system(centred on coil rotation axis)

B3

y // g

B2

B1



Cryogenic “cold mole” tests

The dipole is measured a second time with a traveling probe (“cold mole”), which detects the position of the magnetic axis of both dipole and correctors w.r.t. the standard {R,S,T} MAD dipole reference system (based on the reference beam orbit).

R

T-g

αααα

reference beam orbit

magnetic axis

cold mole

harmonic coil

mole parking + reference bench



Room-temperature “warm mole" tests

For most dipoles there will be no time to carry out mole measurements on the cryogenic test bench. Instead, the magnetic axis will be measured with a simpler room-temperature probe and extrapolated via a suitable warm/cold correlation.

R

T-g

αααα



Result

The measurements are finally combined via harmonic feed-down to get the desired multipoles (along with corrector axes)

referred to the beam orbit.

R

TCryogenic magnetic tests with 15m shaft

(100% of dipoles)

Cryogenic “cold mole” tests(100% of pre-series dipoles,10% of full series production)

Room-temperature “warm mole” tests(100% of dipoles)

Warm-cold correlation


4.1 Definition of dipole axis4.1 Definition of dipole axis

How to define a dipole axis ?How to define a dipole axis ?

♦ A perfect dipole has no axis, but a conventional one can be defined based on field errors.

♦ Axes based on high-order harmonics (defined by zeroing e.g. C10 C12 C14, which can be assumed to be generated by feed-down from strong C11, C13 and C15) lie close to the mechanical axis but correlate poorly in different magnets.

♦ Note that the axes of the harmonics needing corrections (C3, C4, C5) are ill-defined (they move with dynamic effects)


4.2 Definition of dipole axis4.2 Definition of dipole axis

QCD dipole axis QCD dipole axis

The Quadrupole-Configured Dipole (QCD) is obtained by feeding opposite current in each half-coil through the voltage taps.

QCD axis has been chosen as the most convenient reference because of the following advantages:

♦Depends on the global coil shape (represents the geometry of the cold mass ⇒ long term stability)

♦Close (<200 µm) to cold bore geometrical axis (to be confirmed on a statistical basis)

♦Easy to measure with precision from feed-down even at extremely low current (<10 µm @ ±0.5A)


5.1 Cold mole: test bench5.1 Cold mole: test bench• fully automatic motorized travelling probe

• 750 mm × ∅ 20 mm coil for QCD and harmonic measurements

• telescope+CCD camera transversal coil position sensor (same as for warm mole)

• operating in a vacuum for high optical accuracy despite large thermal gradients

• absolute coil position is recovered at external reference quadrupoles via laser tracker survey

• not optimised for mechanical axis measurement

• no on-board tilt sensor ⇒ cannot be used to measure field direction

• 1 unit only in production at Fraunhofer IPT, expected Q4 2001

• fully automatic motorized travelling probe

• 750 mm × ∅ 20 mm coil for QCD and harmonic measurements

• telescope+CCD camera transversal coil position sensor (same as for warm mole)

• operating in a vacuum for high optical accuracy despite large thermal gradients

• absolute coil position is recovered at external reference quadrupoles via laser tracker survey


• no on-board tilt sensor ⇒ cannot be used to measure field direction

• 1 unit only in production at Fraunhofer IPT, expected Q4 2001

mole

longitudinal transportation

sliding support to access both magnet apertures

cable receptacle

harmonic coil(dipole, quadrupole or higher-orders)


5.2 Optical position sensor5.2 Optical position sensor

Note: the same system is used for warm/cold dipole moles & quadrupole scanning machine

• telescope+CCD camera transversal coil optical position sensor

• common to warm and cold MB moles + SSS scanning system

• LED light-spot generated in the front of the probe optically projected into coil centre (follows probe pitch and yaw)

• Range: XY up to ±7 mm @ 3 m distance – distance<20 m

• absolute accuracy:

20 µm @ 3 m distance (air)60 µm @ 20 m distance (air)30 µm @ 20 m distance (vacuum)

• telescope+CCD camera transversal coil optical position sensor

• common to warm and cold MB moles + SSS scanning system

• LED light-spot generated in the front of the probe optically projected into coil centre (follows probe pitch and yaw)

• Range: XY up to ±7 mm @ 3 m distance – distance<20 m

• absolute accuracy:

20 µm @ 3 m distance (air)60 µm @ 20 m distance (air)30 µm @ 20 m distance (vacuum)

(in the transversal plane)

XY

travelling probe (mole)

LED light spot(optically projected in the centre of the coil)

telescope CCD camera + DSP XY measurement


5.3 cold mole: axis transfer overview5.3 cold mole: axis transfer overview

Telescope coordinate frame

Magnet coordinate frame

Dipole

Reference quadrupole

Telescope

Alignment target (fiducial)

Magnetic axisLED light-spot

(≅coil rotation axis)

Laser tracker

S

T

Anticryostat under vacuum

Quartz glass window


5.4 cold mole: axis transfer detail5.4 cold mole: axis transfer detail

Telescope reference framex

y Magnet coordinate frame

Laser Tracker

Reference quadrupole (see G. Deferne’s talk)

QCD magnetic axis

LED light-spot(≡ search coil rotation axis)

Optical alignment targets (fiducials)

QCD Axis w.r.t. magnet frame →→→→ XY telescope measurement→→→→ harmonic measurement→ laser tracker →→→→ fiducialisation (EST/SU)→→→→ magnetic calibration

end result

→→→→ XY telescope measurement→→→→ harmonic measurement→ laser tracker →→→→ fiducialisation (EST/SU)→→→→ magnetic calibration

end result

R

T


5.5 Cold mole: summary5.5 Cold mole: summary

Main benefits of cold mole measurementsMain benefits of cold mole measurements

1) Indispensable tool to transport axes and multipoles to the reference orbit frame.

2) Cold magnetic axes (of both dipole and correctors) can be given directly w.r.t. magnet fiducials, bypassing mechanical extrapolations used to define the cold reference orbit

3) Relative alignment between dipole and correctors can be verified directly with one instrument (bypassing the transformations to the fiducial and to the reference orbit frames)


5.6 warm mole5.6 warm mole

warm mole


• 750 mm × 400 turns dipole-compensated harmonic coil

• telescope+CCD camera transversal coil position sensor

• absolute coil position recovered at external reference marbles via laser tracker survey


• 1 unit operational + 1 expected Q1 2002


• 750 mm × 400 turns dipole-compensated harmonic coil

• telescope+CCD camera transversal coil position sensor

• absolute coil position recovered at external reference marbles via laser tracker survey


• 1 unit operational + 1 expected Q1 2002

Front reference marble (transportation)

Back reference marble (optical system)


5.7 warm mole: axis transfer overview5.7 warm mole: axis transfer overview

Telescope coordinate frame

Magnet coordinate frame

Dipole

Reference support

Telescope

Alignment target (fiducial)

Magnetic axisLED light-spot

(≅coil rotation axis)

Laser tracker

T

S


5.8 warm mole: axis transfer detail5.8 warm mole: axis transfer detail

Telescope reference framex

y Magnet coordinate frame

Laser Tracker

Mole sitting on rest positionon reference marble

QCD magnetic axis

LED light-spot(≡ search coil rotation axis)

Optical alignment targets (fiducials)

QCD Axis w.r.t. magnet frame→→→→ XY telescope measurement→→→→ harmonic measurement→ laser tracker →→→→ fiducialisation (EST/SU)→→→→ mechanical calibration

end result

→→→→ XY telescope measurement→→→→ harmonic measurement→ laser tracker →→→→ fiducialisation (EST/SU)→→→→ mechanical calibration

end result

R

T


5.9 warm mole: results5.9 warm mole: resultsPre-series Noell 1 dipole magnetic axis (QCD)

wrt harmonic coil rotation axis

-1.400

-1.200

-1.000

-0.800

-0.600

-0.400

-0.200

0.000

0.200

0.400

0.600

0.800

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

longitudinal position (mm)

axis

offs

et (m

m)

External aperture (radial)

Internal aperture (radial)

External aperture (vertical)

Internal aperture (vertical)


3800

3900

4000

4100

4200

4300

4400

4500

4600

4700

-20000 -15000 -10000 -5000 0 5000 10000 15000

longitudinal (mm)

radi

al (m

m)

5.10 warm mole: results5.10 warm mole: results

Pre-series Noell 2 @ 300K - beam pipe geometry survey with MTA mole radial offset from theoretical cold mass geometry (2 arcs R=2812360 mm, distance=194 mm)

-2

-1

0

1

2

-10000 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 10000

longitudinal position (mm)

rad

ial o

ffse

t (m

m)

Aperture 1

Aperture 2

Nominal bending radius @ 300K R=2812.36 m

nominal distance between magnet apertures d=194 mm

reference beam orbit arcs positioned via least-squares best fit w.r.t.

measured points

nnecd

Residuals from best-fitting theoretical arcs


5.11 random axis error summary5.11 random axis error summary

155155162162155155163163170170167167σσσσσσσσ RMSRMS

115115

6565

4646

3333

4040

ColdColdvac. 1Avac. 1A

Dipole (QCD)Dipole (QCD)

115115

6161

5050

6161

1010

WarmWarmair 1Aair 1A

115115

6565

4646

3232

55

ColdColdvac. vac. ≤≤≤≤≤≤≤≤550A550A

MCD (bMCD (b55≡≡≡≡≡≡≡≡00))

115115

6161

5050

6161

2020

WarmWarmair 0.5Aair 0.5A

MCS (bMCS (b33≡≡≡≡≡≡≡≡00))values in µm

61616565Coil rotation axis to telescopeCoil rotation axis to telescope((×× 2) (2) (at reference positions)at reference positions)

61613232Coil rotation axis to telescopeCoil rotation axis to telescope(mech. (mech. toltol., CCD+camera precision, thermal effects)., CCD+camera precision, thermal effects)

50504646Reference Reference fiducialsfiducials to coil rotation axis to coil rotation axis ((×× 2)2)

115115115115Reference Reference fiducialsfiducials to magnet to magnet fiducialsfiducials(survey, overall stability)(survey, overall stability)

20201010Magnetic axis to coil rotation axisMagnetic axis to coil rotation axis(feed(feed--down calculation)down calculation)

WarmWarmair 0.5Aair 0.5A

ColdColdvac. vac. ≤≤≤≤≤≤≤≤550A550A

Standard deviation (1 Standard deviation (1 σσσσσσσσ) of magnetic axis w.r.t. magnet ) of magnetic axis w.r.t. magnet fiducialfiducial coordinate system coordinate system (conservative estimates based on (conservative estimates based on reproducibility of reproducibility of preliminary measurements)preliminary measurements)


6.1 conclusions6.1 conclusions♦♦ Outlook Outlook

alignment test equipment needed for detailed study of pre-series dipole fully available as of end 2001

critical measurements will be cross-calibrated with multiple systems and cross-checked with results from other groups (LHC/MMS, EST/SU)

estimated accuracy in line with requirements and with comparable results in other superconducting accelerators

♦♦ Issues still to be assessed Issues still to be assessed

reproducibility of warm-cold QCD correlation dependence of axis deformation and field rotation upon thermal cycling, central jack position,

magnet current etc.. cross-talk between apertures in QCD mode ⇒ radial shift of QCD axis


Magnetic axis vs. central support jackMagnetic axis vs. central support jack

• Problem: zCENTRAL JACK on test benches ≠ than in the tunnel ⇒ QCD axis is incorrect

• Assumption: QCD axis follows mechanical axis during a bending deformation

• Mechanical model: standard linear beam theory, uniform load, 3×simple supports

• Result: QCD axis deformation is parameterised in the difference δzCENTRAL JACK:

• Problem: zCENTRAL JACK on test benches ≠ than in the tunnel ⇒ QCD axis is incorrect

• Assumption: QCD axis follows mechanical axis during a bending deformation

• Mechanical model: standard linear beam theory, uniform load, 3×simple supports

• Result: QCD axis deformation is parameterised in the difference δzCENTRAL JACK:

≤<

−−

≤

−−=∆

�xaax

axxaax

zz jackcentral

123

3231

·3

2

_δ

Mechanical axis vs. δδδδzCENTRAL JACK (vertical coordinate, normalized plot)

z

x

Mechanical axis deformation ∆∆∆∆z (vertical coordinate, normalized plot)

z

x

z

2�

2a

q (own weight)

x

cold foot

cold mass

δδδδzCENTRAL JACK

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