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M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 1 / 19
Uncertainty on magnetic measurements of the
LHC magnets at CERN
M. Gateau, L. Bottura, M.Buzio, S. Sanfilippo
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 2 / 19
Overview
Introduction
Uncertainty on magnetic field
Repeatability of measurements
Reproducibility of measurements
Summary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 3 / 19
Overview
Introduction
Uncertainty on magnetic fieldUncertainty on magnetic field
Repeatability of measurementsRepeatability of measurements
Reproducibility of measurementsReproducibility of measurements
Summary & ConclusionSummary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 4 / 19
The 3 magnetic measurement systemsused for cold characterization of LHC magnets (1)
Superconducting dipole on the cold test bench in SM18 equipped with
rotating coil system
A pair of shafts for measurements of 15-meter-
long dipoles
Field quality needs to be determined with high accuracy10-20% of the 1706 cryo-assemblies will be measured magnetically during cold series tests3 systems for magnetic measurements at cold
1) Rotating coils• Used for dipoles or Short Straight Sections (SSS) of
standard length• 12 sectors for dipoles & 6 for SSS’s over total
magnet length• Voltage integral vs. angular position is recorded• Field strength & multipoles for dipoles, quadrupoles
and associated correctors
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 5 / 19
The 3 magnetic measurement systemsused for cold characterization of LHC magnets (2)
Automated scanner installed on the special
SSS’s test bench in SM18
Installation of SSW for special SSS measurement
3) Single Stretched Wire (SSW)• Can be used on any length of magnet• 1 wire loop over total magnet length• Voltage integral vs. wire displacement in transversal plane• Integrated strength of quadrupoles and dipoles,
(field direction, magnetic axis)(See talk of G. Deferne, Fiducialisation/ Alignment / Axis, Today)
2) Automated scanner• Used for SSS & special SSS’s of variable
lengths• One 600mm-long rotating coil• Longitudinal scanning over magnet
length• Voltage integral vs. angular position• Integrated gradient & local multipoles of
quadrupoles, (axis)
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 6 / 19
Overview
IntroductionIntroduction
Uncertainty on magnetic field
Repeatability of measurementsRepeatability of measurements
Reproducibility of measurementsReproducibility of measurements
Summary & ConclusionSummary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 7 / 19
Uncertainty on magnetic field
To fulfil requirements of the beam dynamics, the main field should be known: better than 8 units of uncertainty for dipoles better than 10 units of uncertainty for quadrupoles
From cold measurements, we expect to reach less than 1 unit on main field random error for dipoles & quadrupole 0.1 units or better on higher harmonics random error few units on systematic error
Measurement uncertainty=
random error + systematic error
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 8 / 19
Overview
IntroductionIntroduction
Uncertainty on magnetic fieldUncertainty on magnetic field
Repeatability of measurements
Reproducibility of measurementsReproducibility of measurements
Summary & ConclusionSummary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 9 / 19
Rotating coils - Recent results on dipole field integral
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
shaft in ap1shaft in ap2
b1, (bn & an) normalised multipoles (n = 2 to 15)
(u
nits
)(b1)<1 unit
(bn&an)<0.02 units
MB3348 - Measurement repeatability on integrated field @ 11850A
Shafts are not identical: in this particular case, the rotating coil of aperture 1 gives higher accuracy for multipoles
Zero sensitivity for n = 12.5 due to measurement coil geometry
WITHIN EXPECTED LIMITS
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 10 / 19
Rotating coils - Noise study
per
bn
&an
(u
nits
)
0.E+00
1.E-01
2.E-01
3.E-01
4.E-01
0 2500 5000 7500 10000 12500
0.E+00
1.E-02
2.E-02
3.E-02
4.E-02
5.E-02
0 2500 5000 7500 10000 12500
Magnet current (A)MB1222 - Noise analysis on normalised multipoles vs. current
Noise signal is decreasing as magnet current is increasing ELECTRICAL NOISE
At high currents, noise signal is constant NOISE MECHANICAL COMPONENT
Current ripple not
compensated on b1
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 11 / 19
Rotating coils - Noise on integrator input
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
0 2500 5000 7500 10000 12500
Magnet current (A)
p
er fl
ux n
(V
.s)
MB1222 - Noise analysis on flux
|∆n|=N.L.2sin(n/2).rn/rrefn-1..T.|∆Cn|/(n-1).G with integration period T = 7 ms
Noise on flux is of the order of noise limit of VFC (Voltage to Frequency Converter) integrators we use
For higher frequency integration, R&D with A/D converters has started(see talk of A. Masi, Fast devices, Tuesday)
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 12 / 19
Rotating coils - No degradation with time
On b1(units)
On higherorders
Current(A)
Bench Other info
MB3348 0.57 10e-3 11850 F2 With PGAs
MBP201 0.14 > 10e-3 5000 A2 Without PGAs
MB1017 0.13 NA 5000 A2 Without PGAs
MB1017 0.13 NA 5000 A2 With PGAs
MB1022 0.27 10e-3 5000 F2 With PGAs
In year 2000
Standard deviation averaged on 12 sectors of different magnets Factor affecting repeatability:
Noise on current Mechanical noise (rotation) Electrical noise (cabling of bench) Integrators offset adjustment Measurement environment (temperature, humidity)
STILL WITHIN EXPECTED TOLERANCES
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 13 / 19
Overview
IntroductionIntroduction
Uncertainty on magnetic fieldUncertainty on magnetic field
Repeatability of measurementsRepeatability of measurements
Reproducibility of measurements
Summary & ConclusionSummary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 14 / 19
Rotating coils - Same magnet measured with 2 different coils (1)
Position of the 12 measurement coil center on magnet length (mm)
B1
(T
)
MB1222 - Main field @ 11850A measured with 2 different coils
8.310
8.315
8.320
8.325
63
0
18
90
31
50
44
10
56
70
69
30
81
90
94
50
10
71
0
11
97
0
13
23
0
13
86
0
reference position1 sector shifted position
Confirmation of reliable and stable coil calibration(see talk of O. Dunkel, Coils, Tuesday)
Average systematic error on B1 between the 2 measurements = 2.34 units
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 15 / 19
Rotating coils - Same magnet measured with 2 different coils (2)
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01b1, (bn & an) normalised multipoles per sector (n = 2 to 15)
Diff
ere
nce
be
twe
en
the
2 p
osi
tion
s (u
nits
)
b1≈2.34 units bn&an<0.2 units
Cross-check on rotating coils system gives very conclusive results
WITHIN TOLERANCES
MB1222 - Field difference @ 11850A measured with 2 different coils
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 16 / 19
SSW & rotating coils - result comparison
0
1
2
3
4
5
6
MB
10
09
Ap
1
Ap
2
MB
10
14
Ap
1
Ap
2
MB
10
15
Ap
1
Ap
2
MB
10
19
Ap
1
Ap
2
MB
30
05
Ap
1
Ap
2
MB
30
11
Ap
1
Ap
2
MB
33
33
Ap
1
Ap
2
Diff
ere
nce
b
etw
ee
n th
e 2
sy
stem
s o
n b
1 (u
nits
)
Magnet & magnet apertureField difference on B1 @ 11850A measured with 2 different systems
Comparison between SSW & rotating coils gives a difference of 5.5 units at maximum (1.98 units in average)
The difference between the 2 systems is within expectations
WITHIN TOLERANCES
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 17 / 19
SSW & automated scanner - result comparison
Warm data: Courtesy of P.Hagen & E.Todesco, CERN
Warm mole TF (T/kA)
Co
ld T
F (
T/k
A)
58.2
58.3
58.4
58.5
58.6
57.9 58.0 58.1 58.2 58.3
SSWAutomated scannerScanner ideal fitSSW ideal fit
17 units
W/C correlation of the field gradient transfer function using 2 systems of measurements at cold
The 17 unit offset correlate with the calibration uncertainty of 15 m on rotation radius (coil radial position should be known better than 8 m)
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 18 / 19
Overview
IntroductionIntroduction
Uncertainty on magnetic fieldUncertainty on magnetic field
Repeatability of measurementsRepeatability of measurements
Reproducibility of measurementsReproducibility of measurements
Summary & Conclusion
M. GateauCERN – Geneva – CH
14th International Magnetic Measurement Workshop26-29 September 2005, Geneva, Switzerland 19 / 19
Summary & Conclusion
Courtesy of L. Bottura, CERN
Un
cert
ain
ty(u
nits
@ 1
7m
m)
Uncertainty on the 3 systems
0.01
0.1
1
Long shaft Automatedscanner
SSW
bn&an
8 units on B1
1
10
100
Long shaft Automatedscanner
SSW
B1B2
10 units on B2
Uncertainty on the dipole main field is of the order of 3 to 5 units for all systems used and sufficient for LHC requirements
Uncertainty on the quadrupole main gradient of 5 (SSW) to 35 units (coils) has a large variability from system to system:SSW is at present our reference system