Measurement of the first LINAC4 series PMQs

“Measurement of the first LINAC4 series PMQs ” [email protected] 15 February 2011

Page 1/29

Measurement of the first LINAC4 series PMQs

R. Beltron Mercadillo, M. Buzio, D. Cote, G. Golluccio, O. Dunkel,

L. Gaborit, D.Giloteaux, P. Galbraith, F. Mateo, L. Walckiers.

Contents:

1. Measurement instruments and method2. Summary of series test results3. Additional test results4. Conclusions and outlook

mailto:[email protected]

mailto:[email protected]


Page 2/29http://cern.ch/mm

Instrumentation and method

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Linac4 measurement bench

1:50 gearbox

viscous damper

stepper motor

demountable coupling

3-wheel demountable bearing

sliding supportsabsolute/incremental

through encoder

slip ring

coil head

electrolytic inclinometer

XY translation stage for coil calibration

• From September 2010 bench in I8 lab (ISR tunnel)• Better mechanical and thermal stability• Temporary magnet storage space (a cupboard)

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Multiple measurement configurations

main objectives:

- link the fiducial references on the magnet to the test bench references- Estimate systematic offsets (X,Y,α)

rectified pin rests

turn around longitudinal axis

flip around vertical axis

0

Base position Reference measurement (mandatory) { Cn = Bn + iAn}

1

Base + 180 around Z Measure X and Y offsets Check pin rests (recommended) Bn’= (-1)n Bn An’= (-1)n An (all odd harmonics change sign)

2

Base + 180 around Y Measure field direction offset (recommended) Bn’’= (-1)n Bn An’’= (-1)n-1 An (odd skew and even normal harmonics change sign)

3

Base + 180 around X (=Base + 180 around Y + 180 around Z) Cross-check 1.2 and 1.3 (recommended) Bn’’’= (-1)n-1 Bn An’’’= (-1)n An (odd normal and even skew harmonics change sign)

4

Base + 90 around Z Check Pin1 Pin2 (mandatory) Cn’’’’= ei (n-1)/2 Cn (odd normal and skew harmonics are swapped, harmonics 2 and 3, 6 and 7, etc. also change sign)

X

Z

X

Y Pin22 2

Y

Z X

Y

Pin 1

y Y

Z X Pin 1

y

Z X

Y

Pin 1

y

Z X

Y

Pin 1

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Field direction measurementY

X

x

y

ψ αPIN 1

XXX

ψ Field direction, measured field phase

α Angular offset between coil reference frame and magnet frame

220

220

B2

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Magnetic Axis Measurement

x,y Magnet axis (M)x0, y0 offset between magnet frame and coil frame (O)

y

xDz=Dx+iDy x`

y`

• Measured harmonics contain information about the magnetic axis• Assuming small offsets and one dominant harmonic, the center can be obtained by

feed-down:

• The computed ∆z is relative to the coil rotation axis → it must be transferred mechanically to the magnet references.

111

D

n

n

ref CC

nrz

xy

X

M (x,y)

O(x0 ,y0)

PIN 1

XXX

Y

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Z

Pin 2

Pin 1 beam direction

Field direction (roll)

ID tag

X

Y

+

PMQ reference system for harmonics, axis, field direction

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Polarity Convention-The beam enters into the screen.- the PINS are on the opposite face. -The By component grows for increasing x (normal quadrupole).- If a pin is inserted in PIN2 makes the quadrupole DEFOCUSING for a H- beam.

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Bench uncertainties

AverageValues

Repeatability(30 repetitions)

Reproducibility(10 rep. with coil and magnet replacement)

Error over 360 rotation (17 steps) Total

uncertainty Random Systematic

delta x [m] 3E-04 3E-07 1E-05 3E-05 1E-05 3E-05delta y [m] 4E-04 2E-07 3E-06 3E-05 4E-06 3E-05angle [rad] 2E-02 4E-05 7E-05 7E-05 0E+00 1E-04GdL [T] 2E+00 2E-04 3E-04 7E-04 2E-03 6E-03b3 [Units] 1.E+02 7E-02 2E-01 4E-01 6E+00 6E+00b4 [Units] -5.E+01 4E-02 5E-02 2E-01 2E+00 4E+00b5 [Units] 2.E+01 7E-02 4E-02 2E-01 7E-01 8E-01b6 [Units] 3.E+01 1E-01 1E-01 7E-02 2E-01 3E+00a3 [Units] -5.E+01 1E-01 3E-01 4E-01 1E+00 3E+00a4 [Units] 7.E+01 6E-02 2E-01 3E-01 2E+00 2E+00a5 [Units] -6.E+01 7E-02 2E-01 1E-01 8E-01 2E+00a6 [Units] 2.E+01 9E-02 5E-02 9E-02 2E-01 4E-01

Estimation done on R1 reference PMQall values RMS 1

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Stretched Wire for GdL calibration

A B C

y

dtVdzBxy D

x

dtVdzByx D

• Iterative XY centring of the wire until x=y =0• Reproducibility for 45 mm length, 2 Tm/m

magnet about ± 0.2 %• Measured GdL is used to calibrate the product

radius × area of the rotating coil• But: the measurement is affected by the error

induced by higher order harmonics …

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Uncertainty in GdL calibration with Single Stretched Wire• “doctored” Aster PMQ Ref2 used in 2010 as a mutual calibration reference (main worry at the

time: get the sextupole right)• detailed error analysis shows that GdL errors may add up to 0.5~1.0 %

Stretched Wire GdL measurement: 2×averages from 4× wire movements (stroke=D)

x-x

y

-y

(units @ 7.5 mm) b4 b6 b8

Aster Ref. 2 101 36 5Aster 121 19 -14 1

D

D

D

D

D

D

D

D

...104110

3110

211

...104110

3110

211

84

6

64

4

44

2

2

84

6

64

4

44

2

2

br

br

br

GdLGdL

br

br

br

GdLGdL

refrefref

yymeasy

refrefref

xxmeasx

Aster Ref. 2 0.5 % 0.2% 0.04 %Aster 121 0.08 % 0.07 % 0.01%

assuming: perfect initial centering and roll alignment

order or magnitude of expected errorsfor D=10 mm:

mitigating measures adopted from now on:- new 45 mm reference PMQ 121 one order of magnitude smaller errors- shorter wire stroke D=7.5 mm (S/N found still acceptable)- more frequent cross-checks SSW vs. rotating coil

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Summary of test results

- 16 PMQs of batch 3 (SSW + rotating coil)- 4 PMQs of batch 4 (SSW + rotating coil)

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GdL (SSW)

0.0

0.5

1.0

1.5

2.0

2.5

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122 20 126

137

104

T

Absolute integrated gradient

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GdL

-The integrated measured gradient is systematically 0.88 % lower than the specified values -the GdL measured by the coil after the latest calibration (reference = PMQ 121) agrees with the SSW within the uncertainties of the 2 systems (0.2 % SSW and 0.3 % Rotating coil @ 1)-There are no systematic discrepancies between rotating coil and SSW

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.410

6

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122 20 126

137

104

%

ERROR W.R.T SPECIFICATIONS AVERAGE: 0.88 %σ: 0.1 %

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-3

-2

-1

0

1

2

3

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

20 126

137

104mra

dField direction wrt Pin 1

Field directionAVERAGE: 0.06 mradσ: 1.5 mrad

Angular bench offsetAVERAGE: -3.2 mradσ: 0.1 mrad

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-3

-2

-1

0

1

2

3

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

20 126

137

104mra

d

Pin2-Pin1 orthogonality

AVERAGE: 1.05 mradσ: 0.9 mrad

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Pin orthogonality vs. field direction

no correlation

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

-3 -2 -1 0 1 2 3

Pin

orth

ogon

ality

[mar

d]

Field direction [mrad]

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-0.10

-0.05

0.00

0.05

0.10

-0.10

-0.05

0.00

0.05

0.10

106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 20 126 137 104

Xm [mm]

Ym [mm]

Magnet Axis (M)

Magnetic axis (mean ± ):X = 0.00 ± 0.03 mmY = -0.01 ± 0.03 mm

Bench offset (mean ± ):X0= -0.04 ± 0.01 mmY0= -0.15 ± 0.00 mm

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Magnet Axis (M)

-0.10

-0.05

0.00

0.05

0.10

-0.10 -0.05 0.00 0.05 0.10

mm

mmX

Y

no correlation

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Harmonics @ 7.5 mm - CERN vs. Aster

0.00

0.10

0.20

0.30

0.40

0.50

0.60

C3 C4 C5 C6 C7 C8 C9 C10

%Cn AsterCn CERN

BEST MAGNET: 107 Cumulative multipole field error <= 1.0 %

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

C3 C4 C5 C6 C7 C8 C9 C10

%

Cn AsterCn CERN

WORST MAGNET 113

Cumulative multipole field error <= 1.7 %

Harmonics @ 7.5 mm - CERN vs. Aster

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Harmonics @ 7.5 mmError bar 2σ

0.0

0.2

0.3

0.5

0.6

0.8

C3 C4 C5 C6 C7 C8 C9 C10

%

max

min

average

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Additional test results

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Comparison Ti/Steel yokes

0

10

20

30

40

50

60

70

C3 C4 C5 C6 C7 C8 C9 C10Mul

tipol

e no

rm (u

nits

@ 7

.5 m

m)

Harmonic order

Aster P3/P4 prototypes - 2.5 Tm/m

Ti yoke

Steel yoke

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Drift tube measurements• The test bench is equipped with a suitable support for DT measurements• Measurements done in 09/2010 on a DT prototype were affected by the rotating

coil (19 mm) scratching the DT bore• A new coil with reduced 18.5 mm is expected in 05.2010

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High gradients and Elytt PMQ prototypes

45 mm prototype

GdL Bx [T/m*m]

GdL By [T/m*m]

Difference % wrt SSW (x)

SSW 3.846 3.845 0.03 Linac4 bench 3.852 0.16 Linac2 bench 3.863 0.44

80 mm prototype

GdL Bx [T/m*m]

GdL By [T/m*m]

Difference % wrt SSW (x)

SSW 4.307 4.304 0.05 Linac4 bench 4.309 0.06 Linac2 bench 4.322 0.36

-30

-20

-10

0

10

20

30

40

50

60

3 4 5 6 7 8 9 10 11 12 13 14 15

Uni

ts @

7.5

mm

Harmonics

normal component

skew component

-30

-20

-10

0

10

20

30

40

50

3 4 5 6 7 8 9 10 11 12 13 14 15

Uni

ts @

7.5

mm

Harmonics

normal component

skew component

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• Vibrating wire system (FNAL system adapted at CERN): when AC current is passed through the wire, a Lorentz force is exerted by the magnetic field and excites a periodic oscillation . In the quad center no field, so no vibration.

• Unique method for very small aperture magnets (CLIC)• Novel development: integrated harmonics by stepwise scanning around a circular path• Preliminary results on 113 match very well harmonics obtained by rotating coil

(however: tests on other magnets are not consistent)• Further development: longitudinal axis localization in an assembled DTL tank (TBC)

Vibrating Stretched Wire Systems

Linac4 113 PMQ

wire

XY micrometric stages

XY optical wire position detectors

XY long-range translation stages

harmonic analysis

XY vibration amplitude = f()

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Conclusions• The GdL of the first 20 series PMQs is about 1% smaller than

specified due to a calibration error• Absolute GdL can from now on be guaranteed within ≤0.3%

uncertainty (including both manufacturing and measurement errors)

• Significant allowed and non-allowed multipole errors are found up to n=6, all well within tolerance individually

• About ½ of the PMQ exceed significantly the 1 mrad field direction tolerance

• About ½ of the PMQ exceed significantly the 1 mrad pin orthogonality tolerance

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Outlook• The remaining batch 4 PMQ shall be tested within the next few

weeks• Upcoming 80 mm PMQs: a good quality unit must be set aside

from the start as a calibration reference (Elytt prototype would be OK)

• A new rotating coil should enable more accurate measurements (better B1, B2 bucking immunity to mechanical errors) and prevent interference with DT

• Documents in preparation: test reports updated with the most recent GdL calibration + test method description

• Raw/intermediate data to be made available in: dfs:\Departments\TE\Groups\MSC\MM\Linac4\L + final results in existing Oracle database

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