The paper describes the development and the experimental validation of a cryogenic magnetic shielding system for transition edge sensor based space detector arrays. The system consists of an outer mu-metal shield and an inner superconducting niobium shield. First, a basic comparison is made between thin-walled mu-metal and superconducting shields, giving an off-axis expression for the field inside a cup-shaped superconductor as a function of the transverse external field. Starting from these preliminary analytical considerations, the design of an adequate and realistic shielding configuration for future space flight applications (either X-IFU [D. Barret et al., e-print arXiv:1308.6784 [astro-ph.IM] (2013)] or SAFARI [B. Jackson et al., IEEE Trans. Terahertz Sci. Technol. 2, 12 (2012)]) is described in more detail. The numerical design and verification tools (static and dynamic finite element method (FEM) models) are discussed together with their required input, i.e., the magnetic-field dependent permeability data. Next, the actual manufacturing of the shields is described, including a method to create a superconducting joint between the two superconducting shield elements that avoid flux penetration through the seam. The final part of the paper presents the experimental verification of the model predictions and the validation of the shield's performance. The shields were cooled through the superconducting transition temperature of niobium in zero applied magnetic field (<10 nT) or in a DC field with magnitude ∼100 μT, applied either along the system's symmetry axis or perpendicular to it. After cool-down, DC trapped flux profiles were measured along the shield axis with a flux-gate magnetometer and the attenuation of externally applied AC fields (100 μT, 0.1 Hz, both axial and transverse) was verified along this axis with superconducting quantum interference device magnetometers. The system's measured on-axis shielding factor is greater than 106, well exceeding the requirement of the envisaged missions. Following field-cooling in an axial field of 85 μT, the residual internal DC field normal to the detector plane is less than 1 μT. The trapped field patterns are compared to the predictions of the dynamic FEM model, which describes them well in the region where the internal field exceeds 6 μT.

/pdf/design-and-validation-of-a-large-format-transition-edge-3kse0d7g6n.pdf

Design and validation of a large-format transition edge sensor array magnetic shielding system for space application.

Induced current in a Bi2Sr2CaCu2Ox superconductor tube

Magnetic shielding at liquid nitrogen temperature

Magnetic shielding from alternating magnetic field by a NbTi/Nb/Cu superconducting multilayer composite cylinder was investigated at liquid‐helium temperatures. The specimen employed in this study was a slender seamless cylinder about 15 mm in diameter and having an aspect ratio of 6. The frequency of the alternating magnetic field was in the range of 40–500 Hz, and the maximum amplitude was 1000 G rms at 40 and 50 Hz owing to the capacity of the ac generator. The magnetic shielding efficiency of this cylinder, defined as the ratio of the magnetic field strength with and without the cylinder, was found to be of the order of 10−4. It was also found that the magnetic shielding effect depends upon the frequency investigated in this study. These shielding effects were mainly due to the shielding current originating from the superconductivity, which turned out to give superior shielding effect than that of a Cu cylinder.

Magnetic shielding from alternating magnetic field by NbTi/Nb/Cu superconducting multilayer composite cylinder

This paper presents the magnetic shielding characteristics of a complex structure with multiple high-Tc superconductors (HTS) coaxially superposed and ferrite powder padding, and its effect on the critical current increase of a HTS current lead. A model HTS current lead is inserted into the complex structure and cooled by LN2. The magnetic flux density in the innermost HTS pipe with and without the ferrite powder, and the critical current of the current lead were measured and the various complex structures were evaluated. >

Magnetic shielding effect by complex structure with HTS pipes and ferrite powder on HTS current lead

The authors report the results of magnetic shielding measurements on pure YBa/sub 2/Cu/sub 3/O/sub 7- delta /, silver-doped YBa/sub 2/Cu/sub 3/O/sub 7- delta / packed powder, laser ablated thin film, and copper. The shielding factors of bulk ceramics were much higher than those of other materials and were not a function of frequency in the range from 10 Hz to 3000 Hz. Simply packed superconducting powder did not show any shielding. While polycrystalline ceramics were effective as shields, the thickness of the ceramic played a crucial role in shielding. The breakthrough field increased with thickness. The influence of DC fields on the shielding behavior depended on the magnitude of the fields. >

M. Sayer

Papers

High temperature superconductors for low frequency magnetic shielding