Article

Magnetic field calculations including the impact of persistent currents in superconducting filaments

CERN, Genève, Geneva, Switzerland
IEEE Transactions on Magnetics (Impact Factor: 1.39). 04/2002; 38(2):825 - 828. DOI: 10.1109/20.996213
Source: IEEE Xplore

ABSTRACT

The magnetic field in the coils of superconducting magnets induces
so-called persistent currents in the filaments. Persistent currents are
bipolar screening currents that do not decay due to the lack of
resistivity. The NbTi-filaments are type II superconductors and can be
described by the critical state model. This paper presents an analytical
hysteresis model of the filament magnetization due to persistent
currents which takes into account the changing magnetic induction inside
the filament. This model is combined with numerical field computation
methods, taking local saturation effects in the ferromagnetic yoke into
consideration

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Available from: Stephan Russenschuck, Dec 16, 2013
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    • "Adjacent resistances between neighboring strands are depicted in yellow and cross-over resistances in red. where with denoting the magnetic induction outside the filament, the filament radius , and the filling factor of filaments in a strand [6]. "
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    ABSTRACT: Fast-ramping superconducting (SC) accelerator magnets are the subject of R&D efforts at various laboratories. The simulation of field quality in fast-ramping magnets requires modifications of magnet design tools such as the CERN field computation program ROXIE. In this paper we present the efforts towards dynamic 2-D simulations of fast-ramping SC magnets. Models for persistent currents, inter-strand coupling currents, inter-filament coupling currents, and for eddy-currents in conducting coil-wedges are described and validated.
    Full-text · Article · Jul 2008 · IEEE Transactions on Applied Superconductivity
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    • "Wilson [4] applied the critical state model to a circular cylinder in a transverse field to describe persistent currents in filaments. Aleksa et al. [5] refined the Wilson model in order to account for the inhomogeneous critical current density inside one layer of shielding currents. The inhomogeneity is due to the fact that J c depends on the local magnetic induction. "
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    ABSTRACT: Fast-ramping superconducting (SC) accelerator magnets are the subject of R&D efforts by magnet designers at various laboratories. They require modifications of magnet design tools such as the ROXIE program at CERN, i.e. models of dynamic effects in superconductors need to be implemented and validated. In this paper we present the efforts towards a dynamic 2-D simulation of fast-ramping SC magnets with the ROXIE tool. Models are introduced and simulation results are compared to measurements of the GSI001 magnet of a GSI test magnet constructed and measured at BNL.
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    • "(q) reads dT 4 B 2 out − 2B out T (q) cos(α) + T (q) 2 = µ 0 F (B out )H dq, (7) where the geometrical factor H = 2r(1 − ln 2) = 0.614 r is explained in [1] "
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    ABSTRACT: Magnetic field changes in the coils of superconducting magnets are shielded from the filaments' core by so-called persistent currents which can be modeled by means of the critical state model. This paper presents a semianalytical two-dimensional model of the filament magnetization due to persistent currents for changes of the magnitude of the magnetic induction and its direction while taking the field dependence of the critical current density into account. The model is combined with numerical field computation for the calculation of field errors in superconducting magnets. The filament magnetization and the field errors in a nested orbit corrector magnet for the large hadron collider project at CERN have been calculated as an example.
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