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On reproducibility. From several inputs of N. Sammut, S. Sanfilippo, W. Venturini Presented by L. Bottura LHCCWG - 4.10.2006. Geometric Proportional to conductor and iron positions and shapes - PowerPoint PPT Presentation
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On reproducibility
From several inputs of N. Sammut, S. Sanfilippo, W. Venturini
Presented by L. Bottura
LHCCWG - 4.10.2006
Components & reproducibility Geometric
Proportional to conductor and iron positions and shapes
May change from cycle to cycle (powering and thermal) due to conductor displacement because of the effect of Lorentz and thermal stresses
Persistent currents Depends on the integral of the
magnetic moments of each strand in the coil (including iron contribution)
May change from cycle to cycle (powering) due to the hysteretic nature of the magnetic moments
Saturation Depends on the shape and
characteristics of the iron yoke There is no physical
mechanism that could produce a relevant change during the magnet lifetime
Decay & Snapback Depends on the powering
history and on the cable characteristics
Different magnet to magnet Changes from cycle to cycle
55
Static – nominal current
GeometryEffect of repeated cycles
Data courtesy of N. Sammut
Six loadline measurements separated by 100 cycles
3.05
3.055
3.06
3.065
3.07
3.075
3.08
3.085
1 cycle 100 cycles 200 cycles 300 cycles 400 cycles 500 cycles
b3 geometric (units)
aperture 1
3.97
3.975
3.98
3.985
3.99
3.995
4
1 cycle 100 cycles 200 cycles 300 cycles 400 cycles 500 cycles
b3 geometric (units)
aperture 2
Standard deviation for both cycles is below 0.01 units for b3 which is lower than the measurement repeatability
55
0.00001
0.0001
0.001
0.01
0.1
1
10
b1 b2 a2 b3 a3 b4 a4 b5 a5
0.00001
0.0001
0.001
0.01
0.1
1
10
b1 b2 a2 b3 a3 b4 a4 b5 a5
harmonic (-)
aperture 1
aperture 2
Effect is small within measurement uncertainty but still larger than measurement repeatability
Static – nominal current
MB1017 - magnetic measurement in April 2003- magnetic measurement in September 2005
GeometryChanges over the magnet life
Data courtesy of N. Sammut
GeometrySummary of uncertainty
uncertainty estimated as 3 of multipoles repeatedly measured on the same magnet (few magnets tested)
after powering after training
u(b1)=2.8 units u(b3)=0.3 units @ 17 mm
55
Persistent currentsEffect of precycle - MB - 2
Data courtesy of N. Sammut, S. Sanfilippo
Differences in TF up to ≈ 1.5 units, on b3 up to ≈ 1 unit
55
Persistent currentsEffect of precycle - MQY
Data courtesy of W. Venturini
Differences in TF in the range of 10 units
Persistent currentsSummary of uncertainty
The effects are large (of the order of 10 units)
The variability associated with powering cycles is very large
MB (IFT 2 kA vs. nominal) u(b1) ≈ 1.5 units u(b3) ≈ 1 units @ 17 mm
MQY (Imin 50 vs. 200 A) u(b2) ≈ 10 units @ 17 mm
These values are relevant only if the pre-cycle is changed from run to run
55
Decay Effect of powering cycle
Data courtesy of N. Sammut
Large effects observed on harmonics
Main field dependency has larger randomAlso because it is more difficult to measure (range 1…2 units)
55
DecayModel of powering cycle
Courtesy of N. Sammut
b1 b3 b5
IFT 0.835 0.03 0.016
tFT - 0.02 -
tpreparation - 0.07 -
Median of the model error
57
DecayAperture difference - 1
Standard cycle (30’ flat-top), 1000 s injection
Negligible systematic difference
57
DecayAperture difference - 3
Influence of flat-top time, 1000 s injection
Influence of wiaiting time, 1000 s injection
57
t (s)
nominal current
injection current
I (A)
quench measurement 1 measurement 2 measurement 3 measurement 4
1.06
1.08
1.1
1.12
1.14
1.16
1.18
1.2
1.22
1.24
0 1 2 3 4 5Number of preceding LHC cycles
-0.137
-0.136
-0.135
-0.134
-0.133
-0.132
-0.131
-0.13
-0.129
-0.128
-0.127
0 1 2 3 4 5Number of preceding LHC cycles
b3 0.05 units
b5 0.004 units
Error is small and comparable to median of max scaling error for powering history
DecayEffect of repeated cycles
55
Change is comparable to the static and dynamic model error
0.001
0.01
0.1
1
b1 b3 b5harmonic (-)
decay amplitude difference (units)
aperture 1
aperture 2
MB1017 - magnetic measurement in April 2003- magnetic measurement in September 2005
Dynamic – decay amplitude
DecayChanges over the magnet life
DecaySummary of uncertainty
Although we have seen (much) better, we maintain that the empirical model (data fits) has a typical error that can amount to up to 20 % of the effect
Main source of uncertainty is from the modelling of powering history, all other effects (aperture differences, cycle details, ageing) are small and have negligible systematic
Why so cautious ? The sample of magnets used for the
data-fitting is limited (10 magnets) This adds an uncertainty in the
projection of the average
Uncertainty after correction
Values estimated for MB’s in July 2004, RMS rview
NOTE: variations of pre-cycle from the nominal one (e.g. due to limitations during commissioning or changes in optics) will cause an additional uncertainty that can be much larger than the above values
Open issues
We know what we know
and we know how well we know what we know
but
we do not know what we do not know
nor do we know how badly we do not know what we do not know
think we
think we
think we
think we
think we
think we
I think we
I think
Examplesa2 anomaly in Ansaldo-2 (2002)
The shape of the a2(I) has a strong anomaly in one aperture of on Ansaldo-2 (2002) reassembled
This data is real ! not a cable hysteresis measurements are OK as far
as we can tell a magnetic piece (protection
layer, shim,…) in the collared coils?
Observed in few other magnets
Depends linearly on maximum current reached