Observation of a periodic pattern in the persistent-current fields of the superconducting HERA magnets

Brück, H.; Gall, D.; Krzywiński, J.; Meinke, R.; Preissner, H.; Halemeyer, M.; Schmüser, Peter; Stolzenburg, C.; Stiening, R.; Avest, D. ter; Klundert, L.J.M. van de

doi:10.1109/pac.1991.164895

Cited by 21 publications

(12 citation statements)

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“…However, evidence was gradually collected that flux creep could not be the only mechanism behind the time dependence of field harmonics at low current [2]. An alternative explanation refers to the current imbalances inside the Rutherford cable, which are also the source of a time dependent spatially periodic flux pattern along the magnet bore [3]. The modulation of the cable internal field influences the magnetization of superconducting filaments [4].…”

mentioning

confidence: 99%

Degaussing and decay reduction in the short superconducting dipole models for the LHC

Delsolaro

Bottura

Haverkamp

et al. 2002

IEEE Trans. Appl. Supercond.

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Abstract-The time decay of field harmonics during current plateaus is a known drawback of superconducting accelerator magnets. The present understanding of this phenomenon refers to a combination of flux creep and of the interaction between the redistribution of currents in Rutherford cables and the filament magnetization. Current cycles of decreasing amplitude, called here degaussing, were found to reduce significantly the decay observed in accelerator magnets. This paper reports on the measured reduction of decay obtained in short dipole models for the LHC and on one experiment with a single LHC strand.Index Terms-Degaussing, field decay and snapback, superconducting magnets, superconductor magnetization.

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mentioning

confidence: 99%

Degaussing and decay reduction in the short superconducting dipole models for the LHC

Delsolaro

Bottura

Haverkamp

et al. 2002

IEEE Trans. Appl. Supercond.

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“…As already known [8][9][10] the local field exhibits variations on the length scale of a cable twist pitch. These local variations are most probably due to the current distribution in the strands of each cable.…”

Section: Current Distribution and Operating Temperaturementioning

confidence: 67%

“…In addition, each strand sees a changing external field which rotates along the cable with period equal to the cable twist pitch Lp, similar to what is measured in the aperture [8][9][10]. The direction of the field change is therefore not necessarily parallel to the initial magnetic moment M of the filament.…”

Section: The Decay Mechanismmentioning

confidence: 84%

Field errors decay and "snap-back" in LHC model dipoles

Bottura

Walckiers

Wolf

1997

IEEE Trans. Appl. Supercond.

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The magnetic field in accelerator magnets decays when the current is kept constant during the particles injection phase, and returns quickly (snaps back) to the original values as soon as ramping is restarted. Here we show results of measurements of the decay of the field errors in 10 m long LHC model dipole magnets. In accordance with previous findings, precycles and stops at intermediate current levels influence the decay. We discuss a possible mechanism causing the decay and snap-back, based on the internal field change in the cable.

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“…Sinusoidal variations in the axial direction of the magnet have been observed for the first time in HERA magnets 23 . Since the amplitude and the phase depend strongly on the actual and preceding excitation cycles but not on dB/dt and its direction, induction is not responsible for the field oscillation.…”

Section: A Field Errorsmentioning

confidence: 82%

Review on Boundary-Induced Coupling Currents

Verweij

1998

Advances in Cryogenic Engineering Materials

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* LHC DivisionPresented at CEC/ICMC '97, Portland Boundary-Induced Coupling Currents (BICCs) are generated in multistrand superconducting cables during a field sweep if a) the field sweep and/or b) the electrical contacts between the strands of the cable vary along the cable. Typical parts in a coil which cause large BICCs are the connections between two cables in or outside a coil and the coil ends of racetrack magnets.In the first part of the paper several approaches for describing and calculating BICCs are reviewed. Attention is paid on the steady-state as well as the time dependent solutions.In the second part of the paper the consequences of BICCs on the behaviour of magnets are discussed. These are additional field variations along the magnet length, additional coupling losses and a non-uniform distribution of coupling losses and current among the strands, resulting in a reduced stability. Several effects are illustrated by means of measurements on model dipole magnets. It is shown how the additive effect of all the BICCs in a coil is rather unpredictable so that similar coils can have rather different BICC related behaviour.2

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Observation of a periodic pattern in the persistent-current fields of the superconducting HERA magnets

Cited by 21 publications

References 0 publications

Degaussing and decay reduction in the short superconducting dipole models for the LHC

Degaussing and decay reduction in the short superconducting dipole models for the LHC

Field errors decay and "snap-back" in LHC model dipoles

Review on Boundary-Induced Coupling Currents

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