The degradation of the critical current density in a Nb3Sn tape conductor due to parallel and transversal strain

In order to investigate the influence of mechanical strain on the intrinsic critical density, a tape conductor is selected as a simple two-dimensional model. In a tape geometry a homogeneous strain distribution can be generated with an external load. A new experimental setup is designed to maintain two different components of the strain tensor (transverse and axial) in a superconducting tape. In this experiment the effects of the distortional and the volume strain are separated. The dependence of the direction of the magnetic field on the strain-current relation is measured by changing the orientation of the sample and the press inside the magnet bore. Preliminary three different sample materials (all Nb3Sn) are investigated with an axial strain inside the superconductor

Modeling the current distribution in HTS tapes with transport current and applied magnetic field

A numerical model is developed for the current distribution in a high temperature superconducting (HTS) tape, (Bi,Pb)2Sr2 Ca2Cu3Ox-Ag, subjected to a combination of a transport current and an applied magnetic field. This analysis is based on a two-dimensional formulation of Maxwell's equations in terms of an integral equation for the current density J. The finite thickness of the conductor and an arbitrary voltage-current relation (e.g. n-power relation, magnetic field dependency) for the conductor are included in the model. Another important feature is that the model also covers an applied magnetic field in arbitrary directions and a rotating field perpendicular to the conductor, which is of great interest for analyzing the AC loss of HTS (transformer) coils or three-phase electric power cables. A comparison is made with transport current loss measurements on an HTS tape with an AC applied fiel

Interaction between current imbalance and magnetization in LHC cables

The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents ¿I, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection the authors performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyze

Improved depth sensitivity by separation of excitation and detection coils

A laparoscopic probe for magnetic sentinel node biopsy has been developed. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as a tracer. They are selectively detected by Differential Magnetometry (DiffMag). Excitation and detection coils are separated. To make this possible, we developed active compensation, which removes influence of the excitation field. Separation of coils leads to improved depth sensitivity, from 20 mm with our handheld probe to 80 mm with our novel laparoscopic probe. As stated by Biot-Savart law, we win a factor distance to the third power by separating the excitation and detection part of the system

Separation of excitation and detection coils to locate superparamagnetic iron oxide nanoparticles in vivo

The aim of this study is to develop a novel laparoscopic probe for sentinel node biopsy. The latter is a procedure to analyze the lymph node status of cancer patients [1], enabling personalized patient care