Magnetic shielding of long paraboloid structures in the inhomogeneous magnetic field

Abstract: Shielding efficacy of the high-temperature superconducting (HTS) magnetic shields depends on the superconductor properties and on the orientation of the external magnetic field. For precise magnetic field measurements in areas with changing direction of magnetic noise it is important to reduce both the parallel and perpendicular components of the magnetic field. We have designed and fabricated magnetic shields of 25 cm long paraboloid shape with closed sides from second-generation HTS tapes. We have characterized HTS shields in DC and variable frequency AC magnetic fields at 77 K above a copper electromagnet acting as the source of inhomogeneous magnetic noise. The HTS magnetic shields reduce the magnetic field noise penetration and enhance the sensitivity of magnetic field sensors. The measurements were performed with the magnetic shield placed between the noise source and the sensor. 2D finite element analysis using Comsol model was generated and the results were compared with the experimental data of magnetic field dependences of the shielding factor (SF)

Measurements and calculations of transport AC loss in second generation high temperature superconducting pancake coils

Theoretical and experimental AC loss data on a superconducting pancake coil wound using second generation (2 G) conductors are presented. An anisotropic critical state model is used to calculate critical current and the AC losses of a superconducting pancake coil. In the coil there are two regions, the critical state region and the subcritical region. The model assumes that in the subcritical region the flux lines are parallel to the tape wide face. AC losses of the superconducting pancake coil are calculated using this model. Both calorimetric and electrical techniques were used to measure AC losses in the coil. The calorimetric method is based on measuring the boil-off rate of liquid nitrogen. The electric method used a compensation circuit to eliminate the inductive component to measure the loss voltage of the coil. The experimental results are consistent with the theoretical calculations thus validating the anisotropic critical state model for loss estimations in the superconducting pancake coil

Experimental and numerical study of a YBCO pancake coil with a magnetic substrate

A finite element model for a YBCO pancake coil with a magnetic substrate is developed in this paper. An axial symmetrical H formulation and the E-J power law are used to construct the model, with the magnetic substrate considered by introducing an extra time-dependent term in the formula. A pancake coil is made and tested. The measurement of critical current and transport loss is compared to the model result, showing good consistency. The influence of magnetic substrate in the condition of AC and DC current is studied. The AC loss decreases without a magnetic substrate. It is observed that when the applied DC current approaches the critical current the coil turn loss profile changes completely in the presence of magnetic substrate due to the change of magnetic field distribution. © 2012 IOP Publishing Ltd

Impact of experimental uncertainties on the reconstruction reliability for CCIC cable current

The determination of the current distribution in full-size cable-in-conduit conductor is a relevant research activity in the framework of the International Thermonuclear Experimental Reactor, aimed at optimizing the performance of the superconducting cables to be used for the machine magnets. The direct measurement of current in the cable is not possible, and inverse techniques must be used, providing only rough estimates due to the severe ill conditioning of the problem. The measurement of magnetic field in the neighbourhood of superconducting cables is the first step in the estimation of the current distribution inside them. Uncertainties in this early phase may very adversely impact the reliability of the problem solution. In this paper we study the impact on current reconstruction of possible errors in the measurement of magnetic field of superconducting cables of Cable in Conduit Conductor type, at low temperatures, close to 4.2 K, due to a number of physical and geometrical effects

Study of 2G high temperature superconducting coils: Influence of anisotropic characteristics

This paper focuses on the study of anisotropic characteristic of second generation high-temperature superconductors (HTS), and how it influences the performance of HTS coils. The critical current of 4 sections of a HTS coil is measured and compared. The sectional difference of critical current exists due to an HTS anisotropy. A numerical method is introduced to consider the HTS anisotropy using finite element method. The model shows good consistency with experimental results. The model demonstrates that the anisotropy changes the current distribution inside the coil, and the discrepancy of critical current in different sections is the joint-effect of the anisotropy and shielding current. The paper discusses the possibility to optimize the performance of HTS coils by changing the anisotropic characteristic. Based on the study, strategies to improve the performance of HTS coils are provided. © 2013 AIP Publishing LLC