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