Numerical Study of the Shielding properties of Macroscopic Hybrid Ferromagnetic/Superconductor Hollow Cylinders

in IEEE Transactions on Applied Superconductivity (2010), 20(1), 33

We study the magnetic shielding properties of hybrid ferromagnetic/superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material.We use an axisymmetric finite-element ... [more ▼]

We study the magnetic shielding properties of hybrid ferromagnetic/superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material.We use an axisymmetric finite-element model in which the electrical properties of the superconducting tube are modeled by a nonlinear E-J power law with a magnetic-field-dependent critical current density whereas the magnetic properties of the ferromagnetic material take saturation into account. We study and compare the penetration of a uniform axial magnetic field in two cases: 1) a ferromagnetic tube placed inside a larger superconducting tube (Ferro-In configuration) and 2) a ferromagnetic tube placed outside the superconducting one (Ferro-Out configuration). In both cases, we assess how the ferromagnetic tube improves the shielding properties of the sole superconducting tube. The influence of the geometrical parameters of the ferromagnetic tube is also studied: It is shown that, upon an optimal choice of the geometrical parameters, the range of magnetic fields that are efficiently shielded by the hightemperature superconductor tube alone can be increased by a factor of up to 7 (2) in a Ferro-Out (Ferro-In) configuration. The optimal configuration uses a 1020 carbon steel with a thickness of 2 mm and a height that is half that of the superconducting cylinder (80 mm). [less ▲]

Magnetic shielding properties of high- Tc superconducting hollow cylinders: model combining experimental data for axial and transverse magnetic field configurations

in Superconductor Science and Technology (2009), 22(10), 10500210

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The ... [more ▼]

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77 K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10 uT s[?]1 and 10 mT s[?]1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n', is found between Blim and dBapp/dt. The values of n' are nearly the same for both configurations. We show that the main features of the curves Bin(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)[?]1). In particular, a linear relationship between the measured n'-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields. [less ▲]

Characterization of the magnetic flux propagation in a drilled YBCO single‐crystal during a pulsed‐field excitation

Poster (2009, September)

Article associé : Pulsed-field magnetization of drilled bulk high-temperature superconductors: flux front propagation in the volume and on the surface

Numerical simulation of the magnetization of high-temperature superconductors: a 3D finite element method using a single time-step iteration

in Superconductor Science and Technology (2009), 22

In this paper, we report progress towards a 3D finite element model for the magnetization of a high-temperature superconductor (HTS): we suggest a method that takes into account a power law conductivity ... [more ▼]

In this paper, we report progress towards a 3D finite element model for the magnetization of a high-temperature superconductor (HTS): we suggest a method that takes into account a power law conductivity and demagnetization effects, while neglecting the effects associated with currents that are not perpendicular to the local magnetic induction. We consider samples that are subjected to a uniform magnetic field varying linearly with time. Their magnetization is calculated by means of a weak formulation in the magnetostatic approximation of the Maxwell equations (A–φ formulation). An implicit method is used for the temporal resolution (backward Euler scheme) and is solved with the open source solver GetDP. Fixed point iterations are used to deal with the power law conductivity of HTS. The finite element formulation is validated for an HTS tube with large n value by comparing with results obtained with other well-established methods. We show that carrying out the calculations with a single time-step (as opposed to many small time-steps) produces results with excellent accuracy in a drastically reduced simulation time. The numerical method is extended to the study of the trapped magnetization of cylinders that are drilled with different arrays of columnar holes arranged parallel to the cylinder axis. [less ▲]

Modeling of ferromagnetic/high‐Tc superconductor structures for shielding applications

Poster (2008, August)

Backward Euler method for single time step finite element simulation of the magnetization of high-temperature bulk superconductors with non linear conductivity

Conference (2008, May)

We consider a three dimensional (3D) finite element modeling of high temperature superconductors (HTS) submitted to a uniform magnetic field varying linearly with time. HTS are characterized by a non ... [more ▼]

We consider a three dimensional (3D) finite element modeling of high temperature superconductors (HTS) submitted to a uniform magnetic field varying linearly with time. HTS are characterized by a non linear conductivity described by a power law with the critical exponent, n. We implement an A- phi weak formulation into the opensource solver GetDP. Backward Euler method is used for the temporal resolution and is coupled to a non linear Picard iteration scheme for dealing with the non linear resistivity of HTS.We consider single- and multiple-time step methods and show that the single time step method produces an accurate result in a drastically reduced calculation time for HTS with large pinning strength (or similarly, with large values of n). The finite element formulation is validated by comparing the magnetization of a HTS tube calculated either with our finite element formulation or with other well-known techniques. The numerical method is then applied for comparing the magnetization of cylinders that are drilled by different periodic arrangements of columnar holes parallel to the cylinder axis. [less ▲]

Hole lattice influence on the magnetization of drilled superconductors

Poster (2007, September)

Article associé : Bulk high-Tc superconductors with drilled holes: how to arrange the holes to maximize the trapped magnetic flux?

Schottky-Barrier height lowering by an increase of the substrate doping in PtSi Schottky barrier source/drain FETs

in IEEE Electron Device Letters (2007), 28(2), 123-125

In this letter, the Schottky-barrier height (SBH) lowering in Pt silicide/n-Si junctions and its implications to Schottky-barrier source/drain p-field-effect transistors (p-SBFETs) are studied ... [more ▼]

In this letter, the Schottky-barrier height (SBH) lowering in Pt silicide/n-Si junctions and its implications to Schottky-barrier source/drain p-field-effect transistors (p-SBFETs) are studied experimentally and numerically. We demonstrate that the increase of the n-Si substrate doping is responsible for a larger hole SBH lowering through an image-force mechanism, which leads to a substantial gain of the drive current in the long-channel bulk p-SBFETs. Numerical simulations. show that the channel doping concentration is also critical for short-channel p/n-silicon-on-insulator SBFET performance. [less ▲]

Experimental and simulation study of the Schottky barrier lowering by substrate doping variation for PtSi Source/Drain SBFETs

in Proceedings of ESSDERC 2006 (2006, September)

In this paper, the authors study experimentally and numerically the Schottky barrier height (SBH) lowering of Pt silicide/n-Si diodes and its implications to Schottky-barrier (SB) source/drain p-FETs. The ... [more ▼]

In this paper, the authors study experimentally and numerically the Schottky barrier height (SBH) lowering of Pt silicide/n-Si diodes and its implications to Schottky-barrier (SB) source/drain p-FETs. The authors demonstrate that hole SBH can be lowered through an image-force mechanism by increasing the n-Si substrate doping, which leads to a substantial gain of the drive current in the long-channel bulk p-SBFETs. Numerical simulations show that the channel doping concentration is also critical for short-channel n- & p-SOI SBFETs performance [less ▲]