A Polarity Checker for LHC Magnets

L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets”IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005

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A Polarity Checker for LHC MagnetsA Polarity Checker for LHC MagnetsL. Bottura, G. Brun, M. Buzio, G. Fievez, P. Galbraith, J. Garcia Perez, R. Lopez,

A. Masi, S. Russenschuck, N. Smirnov, F. Thierry, A. Tikhov

1.1. IntroductionIntroduction2.2. Measurement methodMeasurement method3.3. HardwareHardware4.4. SoftwareSoftware5.5. CharacterizationCharacterization6.6. Test resultsTest results7.7. Conclusions and outlookConclusions and outlook

ContentsContents

Ref: M Buzio et al, “Checking the Polarity of Superconducting Multipole LHC Magnets”, paper presented at MT-19


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the LHC will include about 1750 cryomagnet assemblies, up to almost 16 m long, housing a total of about 10000 superconducting magnets connected in 1612 electrical circuits

magnet connection errors are always detrimental and may be unacceptable in some cases, including esp. main dipoles and quadrupoles, insertion region magnets, skew and tuning quadrupole correctors

need to check systematically multipole order, type and polarity of all LHC magnetic elements automated, self-contained probe based on a rotating Hall sensor designed and built similar system used with success at BNL for RHIC and presented at IMMW XI, Brookhaven (A. Jain et

al.)

1.1 – Introduction: 1.1 – Introduction: Purpose of the systemPurpose of the system

1232 cryodipoles, including 3696 corrector spool pieces 360 arc Short Straight Sections, divided in 61 sub-types including 260 main quadrupolesand 1080 corrector magnets

~8000 total superconducting corrector magnets 106 Short Straight Sections for the insertion regions


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Specifications: - general-purpose system for any multipole order and type (normal or skew) - automatic, self-contained, fast- room temperature measurements, fit inside beam pipe (Ø 50 mm) - minimum field 60 T (~earth field !)

1.2 – Introduction: 1.2 – Introduction: SpecificationsSpecifications

MagnetType

T.F.[mT/A]

Imax

[A]Bmax

[mT]Diode

Main Dipole (MB) 0.66 5.0 3.32 YB1 arc Orbit Corrector (MCBV/H) 52.70 0.1 2.64B1 IR Orbit Corrector (MCBXH/V) 6.09 2.4 14.62Main Quadrupole (MQ) 0.29 3.0 0.88 YTuning Quadrupole (MQT) 0.10 3.0 0.31B3 Multipole Corrector (MCS) 0.05 3.0 0.15 YB3 Lattice Corrector (MS) 0.02 3.0 0.07B4 Multipole Corrector (MCO) 0.40 3.0 1.20 YB4 Lattice Corrector (MO) 0.56 1.0 0.56B5 Multipole Corrector (MCD) 0.18 3.0 0.55 YB6 Multipole Corrector (MCTX) 0.13 0.5 0.06


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Radial component (normal to Hall sensor)

Vector of N values sampled at regular intervals

DFT of the radial field vector

Inverse DFT of the radial field vector

2.1 – Measurement method: 2.1 – Measurement method: Harmonic analysis of radial fieldHarmonic analysis of radial field

1

)1(1

refr)iA(BB),(

n

nin

nnxy eriBrΒ

irR euBB B

)(

1-N to0j ,2 ),( jN

BB jjRR jj

1

0

21 N

j

ijkN

R eBN j

kβ

1

0

2N

k

ijkN

R eBj

kβ

*

1

n

nref

R

ri

nC

Tangential Hall plate

Stepwise Rotation Magnet Apertures

X

Y

Connection end

Y

X

B

BR R

1

1

12sin2cos

N

nnn

n

refR jn

NBjn

NA

rRB

j

Harmonic field coefficients as a function of the DFT of sampled values

* denotes complex conjugation

expand, equate term by term


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2.2 – Measurement method: 2.2 – Measurement method: Transfer functionTransfer function

Magnets without diode installed

Magnets with diode installed

For greater accuracy, polarity is determined on the basis of (approximate) transfer function rather than raw harmonic measurement

An arbitrary number of current points can be specified; minimum is two, of opposite sign if possible

Linear best fit to {Cn,I} pairs

0,nn

n CIIC

C

Cn

II1

I2

Cn

II1 I2 Transfer function [T/A @ 17 mm]

Remanent field [T @ 17 mm](+ Hall voltage offset)


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3.1 – Hardware:3.1 – Hardware: Probe (“mouse”) Probe (“mouse”)

Parameter ValueProbe length (mm) 768Probe external diameter (mm) 40Tube internal diameter (mm) 40 to 73Tilt sensor range 45°Tilt sensor resolution (mrad) 0.1Hall plate current (mA) 50 Hall plate sensitivity (mV/T) 233.8Hall plate radius (mm) 11Hall plate azimuthal offset (mrad) 10.5Hall plate max. field (mT) 30Hall plate min. field (mT) 0.01On-board Preamplifier gain 500Azimuthal resolution (mrad) 0.047

Functional block diagram

4+1 units in operation at CERN 24x256-stage stepping motor with

22:1 reduction gearbox electrolytic tilt sensor longitudinal transport motor not in

use (manual positioning)


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3.2 – Hardware: 3.2 – Hardware: DAQ systemDAQ system

Mobile rack

Power supplies for rack, DC motor, tilt sensor, stepping motorVoltmeter (tilt sensor)

50 mA Hall supply

Windows PC(+ DAC for Hall output acquisition)

Keithley 2001 multiplexer

DAQ electronics rack

Bipolar Kepco magnet power supply

Custom data switching unit


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3.3 – Hardware: 3.3 – Hardware: Connections to main cryoassembliesConnections to main cryoassemblies

Upstream (connection)

Downstream (lyre)

M1 M2 M1 M2

M3

Power supply

DSU

1 10 20 11 1 10 20 11

L R R L

J2 J3 J4

Upstream

(connection)

M1 M2

M3

Power supply

DSU

ES811 ES812 ES911 ES912

J5

J6

J7

ES8x1 ES8x2 ES831 ES832 ES9x1 ES9x2 ES931 ES932

Downstream (lyre)

L

R

L

R

Name J1 J2 J3 J4 J5 J6 J7 J8 Type Burndy Burndy Burndy Burndy Burndy Burndy Burndy Burndy Pins 4 4 28 28 8 12 5 12 Gender Male Female Female Male Female Female Female Female Output Channels - 1 2-9 2-9 1-2 3-6 7-8

MB SSS Used for Power

Supply MB MCS/MCDO Upstream

MCS/MCDO Downstream MQ Other

correctors MCBX MUX

standardized connections to cryodipoles and arc Short Straight Sections allow fully automatic sequential powering of the magnets

connections to magnets for the Insertion Regions are done manually (106 cryoassemblies, 16 types)

cryo

dipo

lesh

ort

stra

ight

sec

tion


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User panel, wizard-style interface

4.1 – Software: 4.1 – Software: LabView user interfaceLabView user interface

On-line assessment of results by cross-checkingwith expected values

Automatic generation of pdf

test report

Manual input of assembly/magnets to be tested


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4.2 – Software:4.2 – Software: Configuration files (examples) Configuration files (examples)

Magnet definition file

Magnet type Order R nominal

[Ohm]R protection[Ohm]

T.F. nominal[T/ A @ 17mm]

T.F. expected[T/ A @ 17mm]

Max. residual[T @ 17mm]

N. meas.

I1[A]

I2[A]

MB 1 6.00 100.00 7.0380E-04 6.6396E-04 1.0000E-03 2 2.00 5.00MCBV 1 11.50 inf 5.2700E-02 5.2700E-02 1.0000E-03 2 -0.05 0.05MCBH 1 11.50 inf 5.2700E-02 5.2700E-02 1.0000E-03 2 -0.05 0.05MQ 2 1.80 20.00 3.2000E-04 2.9358E-04 1.0000E-03 2 1.00 3.00MQT 2 12.00 0.34 3.8000E-03 1.0470E-04 1.0000E-03 2 -3.00 3.00MQS 2 12.00 0.34 3.8000E-03 1.0470E-04 1.0000E-03 2 -3.00 3.00MCS 3 0.20 0.01 8.5636E-04 4.8473E-05 1.0000E-03 2 1.00 3.00MS 3 21.00 0.22 2.3270E-03 2.4125E-05 1.0000E-03 2 -3.00 3.00

MCO 4 3.20 inf 4.0000E-04 4.0000E-04 1.0000E-03 2 1.00 3.00MO 4 11.50 inf 5.6300E-04 5.6300E-04 1.0000E-03 2 -1.00 1.00MCD 5 1.40 inf 1.8182E-04 1.8182E-04 1.0000E-03 2 1.00 3.00


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Assembly configuration file

4.3 – Software:4.3 – Software: Configuration files (examples) Configuration files (examples)

AssemblyType

N. of apertures

N. of magnets

Ap.1 Magnet

1

Ap.1 Magnet

2

Ap.1 Magnet

3

Ap.1 Magnet

4

Ap.1 Magnet

5

Ap.1 Magnet

6

Ap.1 Magnet

7

Ap.1 Magnet

8

Ap.2 Magnet

1

Ap.2 Magnet

2

Ap.2 Magnet

3

Ap.2 Magnet

4

Ap.2 Magnet

5

Ap.2 Magnet

6

Ap.2 Magnet

7

Ap.2 Magnet

8HCLMBBL 2 4 MB MCS MB MCSHCLMBBR 2 4 MB MCS MB MCSHCLMBAL 2 8 MCD MCO MB MCS MCD MCO MB MCSHCLMBAR 2 8 MCD MCO MB MCS MCD MCO MB MCSHCLQASA 2 4 MQS MQ MS MCBV MQS MQ MS MCBHHCLQASB 2 4 MQS MQ MS MCBV MQS MQ MS MCBHHCLQASC 2 4 MQS MQ MS MCBH MQS MQ MS MCBVHCLQASD 2 4 MQS MQ MS MCBH MQS MQ MS MCBVHCLQASE 2 4 MQS MQ MS MCBH MQS MQ MS MCBVHCLQASF 2 4 MQS MQ MS MCBH MQS MQ MS MCBVHCLQATA 2 4 MQT MQ MS MCBV MQT MQ MS MCBH

Magnet configuration file

Magnet Label (Type/ Assembly/ Aperture)

Magnet type

Insertfrom

Position[mm] Component Polarity

ExpectedPositive Terminal

MB_HCLMBA_1 MB Upstream 7500 N P AMB_HCLMBA_2 MB Upstream 7500 N N AMCS_HCLMBA_1 MCS Downstream 1500 N P AMCS_HCLMBA_2 MCS Downstream 1500 N P AMO_HCLQOAG_1 MO Upstream 259 N N AMO_HCLQOAG_2 MO Upstream 259 N N AMQ_HCLQOAG_1 MQ Upstream 2283 N N AMQ_HCLQOAG_2 MQ Upstream 2283 N N A

MCBV_HCLQOAG_1 MCBV Upstream 4803 S P AMCBH_HCLQOAG_2 MCBH Upstream 4803 N P A

MS_HCLQOAG_1 MS Upstream 4117 N P AMS_HCLQOAG_2 MS Upstream 4117 N P A

Expressed in the magnetic

measurement reference frame

(…) 4 types of cryodipoles, 61 + 16 types of short straight section in the arcs and insertions


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The calibration of the probe concerns mainly two parameters:

Voltage-to-field transfer function of the Hall plate + preamplifier combination (~8.5 mT/V):determined by measuring the loadline of a reference dipole and cross-checking with a Metrolab NMR teslameter

Angular offset between Hall plate and tilt sensor (~10 mrad):determined as the average of the field direction obtained from two harmonic measurements in a reference dipole, inserting the probe from both ends.

Other systematic and random factors affecting the measurement that were neglected include:- roll/pitch angle error of the Hall plate ( pick-up of tangential/longitudinal field component)- error R in the radial position R of the Hall plate ( error (n-1)R/R in the field coefficients)- planar effect - temperature drift

5.1 – Characterization:5.1 – Characterization: Calibration Calibration

Hall probe linearity error

-0.20-0.15-0.10-0.050.000.050.100.150.200.25

-100 -50 0 50 100Field (NMR) [mT]

Field

erro

r (Ha

ll pro

be) [

mT]

linearity error of the Hall sensor:<3% for all cases of interest


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5.2 – Characterization:5.2 – Characterization: Validation (1) Validation (1)

results were consistent in both cases

The polarity of Hall sensor output was verified with two methods:1) deformation of current-carrying wire from right-hand rule: F = I × B2) commercial 3D Hall probe teslameter (Metrolab THM7025)

N

S

B

magneticfield

force

current

+ -

http://www.metrolab.ch/7025/7025.html


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5.3 – Characterization:5.3 – Characterization: Validation (2) Validation (2)A systematic verification procedure was carried out on magnets of order n=1 to 5 (total = 5x4x2 measurements):

1) Install magnet so that field is normal positive2) Check polarity with commercial Hall teslameter 3) Verify multipole order, magnet type and polarity with the Polarity Checker in four cases: { current, insertion from connection or non-connection end} polarity must reverse with the current (always) and with insertion side (only n=2,4)4) Turn magnet by -/n to make it skew, repeat step 3)

e.g. Normal negative quadrupole

Rotating Hall probe measurement

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 50 100 150 200 250 300 350 400Angle (deg)

Radi

al F

ield

(mT)

results were conforming to expectations in all cases

expected Br()

measured Br()


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5.4 – Characterization:5.4 – Characterization: Repeatability tests Repeatability tests

Repeatability test result

-30-25-20-15-10-505

10

1 2 3 4 5Magnet order

Main

field

[mT]

Field direction(mrad)

Avg. s s

1 -25.58 0.0240 1.792 8.60 0.0104 1.703 0.10 0.0013 4.194 -0.85 0.0010 7.555 0.42 0.0009 2.04

Main Field(mT)

Magnet Order

(1=dipole)

repeatability of the main field: better than ~1% in all tested casesrepeatability of field direction: between 2 and 8 mrad

The repeatability of the system was checked by running 60 consecutive measurements in the reference magnets.

affected by errors in the dynamic readout of the electrolytic tilt sensor + feed-forward control of the

stepper motor


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5.5 – Characterization:5.5 – Characterization: Overall performance Overall performance

Quantity Estimatedaccuracy Unit

Main field amplitude 5% mTMain field direction 3 degMain harmonic order error-freeMain harmonic polarity error-free

Main harmonic type error-free

main field accuracy: depends on repeatability + linearity error field direction accuracy: depends on repeatability + main field error time required for

- single acquisition: 0.75 s (motor must be switched off)- harmonic measurement: 90 s- full standard cryomagnet: ~1 hour

10% rejection threshold on the difference between measured and expected T.F.

inadequate for field direction measurements

main field accuracy << amplitude of other harmonic components

field direction accuracy << threshold to discriminate phase of main component (worst case=dodecapole=15°)

no errors reasonably expected for the target measurement results


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6 – Test results:6 – Test results: Summary of results of first 505 cryoassemblies Summary of results of first 505 cryoassemblies

Magnet Type Tested Faults Type Cryodipoles 330 3 Any - Main dipoles (MB) 330 0 - - Spool piece correctors 990 3 Polarity Short Straight Sections 175 34 Any - Main Quadrupoles (MQ) 175 0 -

- Dipole Correctors (MCB) 175 3 Polarity 28 Aperture

- Tuning Quadrupoles 71 0 - - Skew Quadrupoles (MQS) 1 0 - - Sextupole Correctors 175 8 Polarity 28 Aperture - Octupole Correctors (MO) 103 2 Polarity 2 Aperture Total Cryoassemblies 505 37 Any Total magnets 2020 61 Any

1% of faults in cryodipoles, 20% in Short Straight Sectionsnon-critical errors, all easily rectified at CERN


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7 – 7 – Conclusions and outlookConclusions and outlook

• 4 units built and in use at CERN, proved reliable and easy to use• 505 cryoassemblies tested, 1200 to go before end 2006• Automated test procedures for cryodipoles and short straight sections fully

established: inner-region insertion quadrupoles/correctors being finalized now

• Possible further developments (not really necessary for series tests) include:- improving the mechanics of the longitudinal transport system - characterization of neglected error sources

A Polarity Checker for LHC Magnets

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