1. On reproducibility
From several inputs of N. Sammut, S. Sanfilippo, W. Venturini
Presented by L. Bottura
LHCCWG

2. 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

3. Geometry Effect of repeated cycles
Data courtesy of N. Sammut
Geometry Effect of repeated cycles
Six loadline measurements separated by 100 cycles
Static – nominal current
Standard deviation for both cycles is below 0.01 units for b3 which is lower than the measurement repeatability 55

4. Geometry Changes over the magnet life
Data courtesy of N. Sammut
Geometry Changes over the magnet life
MB magnetic measurement in April 2003
- magnetic measurement in September 2005
Static – nominal current
Effect is small within measurement uncertainty but still larger than measurement repeatability 55

5. Geometry Summary 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)= mm

6. Persistent currents Effect of precycle - MB - 1
Data courtesy of N. Sammut, S. Sanfilippo
Persistent currents Effect of precycle - MB - 1 55

7. Persistent currents Effect of precycle - MB - 2
Data courtesy of N. Sammut, S. Sanfilippo
Persistent currents Effect of precycle - MB - 2
Differences in TF up to ≈ 1.5 units, on b3 up to ≈ 1 unit 55

8. Persistent currents Effect of precycle - MQY
Data courtesy of W. Venturini
Persistent currents Effect of precycle - MQY
Differences in TF in the range of 10 units 55

9. Persistent currents Summary 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 17 mm
MQY (Imin 50 vs. 200 A)
u(b2) ≈ mm
These values are relevant only if the
pre-cycle is changed from run to run

10. Decay Effect of powering cycle
Data courtesy of N. Sammut
Decay Effect of powering cycle
Large effects observed on harmonics
Main field dependency has larger random
Also because it is more difficult to measure (range 1…2 units) 55

11. Decay Model of powering cycle
Courtesy of N. Sammut
Decay Model of powering cycle
Median of the model error b1 b3 b5
IFT
0.835
0.03
0.016
tFT -
0.02
tpreparation
0.07 55

12. Decay Aperture difference - 1
Standard cycle (30’ flat-top), 1000 s injection
Negligible systematic difference 57

13. Decay Aperture difference - 2
Influence of flat-top current, 1000 s injection 57

14. Decay Aperture difference - 3
Influence of flat-top time, 1000 s injection
Influence of wiaiting time, 1000 s injection 57

15. Decay Effect of repeated cycles
Error is small and comparable to median of max scaling error for powering history
b3  0.05 units
b5  units 57

16. Decay Changes over the magnet life
MB magnetic measurement in April 2003
- magnetic measurement in September 2005
Dynamic – decay amplitude
Change is comparable to the static and dynamic model error 55

17. Decay Summary 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

18. 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

19. Open issues think we think we 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
I think we
I think

20. Examples a2 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

21. Examples Effect of precycle - MQT
Data courtesy of W. Venturini
Examples Effect of precycle - MQT
The effect low current cycling can be massive 55