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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

Transcript of On reproducibility

  • On reproducibilityFrom several inputs of N. Sammut, S. Sanfilippo, W. Venturini

    Presented by L. Bottura

    LHCCWG - 4.10.2006

  • Components & reproducibilityGeometricProportional to conductor and iron positions and shapesMay change from cycle to cycle (powering and thermal) due to conductor displacement because of the effect of Lorentz and thermal stressesPersistent currentsDepends 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 momentsSaturationDepends on the shape and characteristics of the iron yokeThere is no physical mechanism that could produce a relevant change during the magnet lifetimeDecay & SnapbackDepends on the powering history and on the cable characteristicsDifferent magnet to magnetChanges from cycle to cycle

  • GeometryEffect of repeated cycles55Static nominal currentData courtesy of N. SammutSix loadline measurements separated by 100 cyclesStandard deviation for both cycles is below 0.01 units for b3 which is lower than the measurement repeatability

  • GeometryChanges over the magnet life55Effect is small within measurement uncertainty but still larger than measurement repeatabilityStatic nominal currentMB1017 - magnetic measurement in April 2003- magnetic measurement in September 2005Data courtesy of N. Sammut

  • GeometrySummary of uncertaintyuncertainty estimated as 3 of multipoles repeatedly measured on the same magnet (few magnets tested)after poweringafter training

    u(b1)=2.8 unitsu(b3)=0.3 units @ 17 mm

  • Persistent currentsEffect of precycle - MB - 155Data courtesy of N. Sammut, S. Sanfilippo

  • Persistent currentsEffect of precycle - MB - 255Data courtesy of N. Sammut, S. SanfilippoDifferences in TF up to 1.5 units, on b3 up to 1 unit

  • Persistent currentsEffect of precycle - MQY55Data courtesy of W. VenturiniDifferences in TF in the range of 10 units

  • Persistent currentsSummary of uncertaintyThe 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 unitsu(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

  • Decay Effect of powering cycle55Data courtesy of N. SammutLarge effects observed on harmonicsMain field dependency has larger randomAlso because it is more difficult to measure (range 12 units)

  • DecayModel of powering cycle55Courtesy of N. SammutMedian of the model error


  • DecayAperture difference - 157Standard cycle (30 flat-top), 1000 s injectionNegligible systematic difference

  • DecayAperture difference - 257Influence of flat-top current, 1000 s injection

  • DecayAperture difference - 357Influence of flat-top time, 1000 s injectionInfluence of wiaiting time, 1000 s injection

  • DecayEffect of repeated cycles57b3 0.05 unitsb5 0.004 unitsError is small and comparable to median of max scaling error for powering history

  • DecayChanges over the magnet life55Change is comparable to the static and dynamic model errorMB1017 - magnetic measurement in April 2003- magnetic measurement in September 2005Dynamic decay amplitude

  • DecaySummary of uncertaintyAlthough 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 effectMain source of uncertainty is from the modelling of powering history, all other effects (aperture differences, cycle details, ageing) are small and have negligible systematicWhy 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 correctionValues estimated for MBs in July 2004, RMS rviewNOTE: 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 issuesWe know what we know

    and we know how well we know what we know


    we do not know what we do not know

    nor do we know how badly we do not know what we do not know

  • Examplesa2 anomaly in Ansaldo-2 (2002)The shape of the a2(I) has a strong anomaly in one aperture of on Ansaldo-2 (2002) reassembledThis data is real !not a cable hysteresismeasurements are OK as far as we can tella magnetic piece (protection layer, shim,) in the collared coils?Observed in few other magnetsDepends linearly on maximum current reached

  • ExamplesEffect of precycle - MQT55Data courtesy of W. VenturiniThe effect low current cycling can be massive