Magnetic Shielding System Research Articles

Suppression of Nonuniform Magnetic Fields in Magnetic Shielding System for SERF Co-Magnetometer

Suppression of Nonuniform Magnetic Fields in Magnetic Shielding System for SERF Co-Magnetometer

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors.

Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM) is the root for progressing to the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter, some intriguing and yet unexplained phenomena occurred, such as a noticeable rise in the SC energy losses, and a local but not isotropic deformation of its magnetic flux density. These phenomena, which are in apparent contradiction with the most fundamental theory of electromagnetism for superconductivity, that is, the critical state theory (CST), have remained unexplained for about 20 years, given the acceptance of the controversial and yet paradigmatic existence of the so-called overcritical current densities. Therefore, aiming to resolve these long-standing problems, we extended the CST by incorporating a semi-analytical model for cylindrical monocore SC-SFM heterostructures, setting the standards for its validation with a variational approach of multipole functionals for the magnetic coupling between Sc and SFM materials. It is accompanied by a comprehensive numerical study for SFM sheaths of arbitrary dimensions and magnetic relative permeabilities , ranging from (NiZn ferrites) to = 350,000 (pure Iron), showing how the AC-losses of the SC-SFM metastructure radically changes as a function of the SC and the SFM radius for . Our numerical technique and simulations also revealed a good qualitative agreement with the magneto optical imaging observations that were questioning the CST validness, proving therefore that the reported phenomena for self-field SC-SFM heterostructures can be understood without including the ansatz of overcritical currents.

An actively compensated 8 nT-level magnetic shielding system for 10-m atom interferometer.

We design and develop a high-performance magnetic shielding system for a long baseline fountain-type atom interferometer. The shielding system is achieved by a combination of passive shielding using permalloy and active compensation with coils. An 11.4 m-long three-layer cylindrical shield is completed by the process of welding, local annealing, and entire annealing. The active compensations compress the residual magnetic field to 8.0 nT max-to-min and the corresponding gradient below 30 nT/m over 10m along the axial direction in which external compensation, internal compensation, and constant magnetic field (C-field) compensation reduce the inhomogeneities to 25.0, 12.6, and 1.7 nT (standard deviation) sequentially. We estimate that this system could reduce the systematic error of the quadratic Zeeman shift to the 10-13 level for the weak equivalence principle test with a simultaneous 85Rb-87Rb dual-species atom interferometer.

Development of the models of the magnetic shielding system for ITER neutral beam injectors

The paper is devoted to the development of the models of magnetic shielding system for the ITER neutral beam injectors. As the reactor operation is quasistationary, the magnetic field reduction system of the injectors combines a passive magnetic shield and a set of active correction coils. Due to the strict restrictions on the field inside the injectors, precision computations are required during the design stage. A special attention has been paid to possible gaps between steel panels of the passive magnetic shields due to manufacturing and assembly inaccuracies. A set of models with different levels of detail has been built for the convergence study. It was shown that the mesh needs to have tens of millions finite elements to provide the required computational accuracy.

Prospects for the Development of a Sensitive Atomic Interferometer Based on Cold Rubidium Atoms

An overview of the research results obtained at the All-Russia Research Institute of Physicotechnical and Radio Measurements when creating a fountain type clock is presented. The possibility of using the results obtained for the development of a sensitive atomic interferometer (gravimeter) based on cold rubidium atoms is analyzed. The relevance of the study lies in assessing the prospects for creating an interferometer (gravimeter) based on cold rubidium atoms for absolute measurements of the local value of the gravitational acceleration. The physical principles of operation of an atomic gravimeter are described. A comparison is made between an atomic gravimeter and a fountain-type frequency standard based on cold atoms. The technical solutions required for the creation of an atomic gravimeter with given values of the sensitivity for measuring the acceleration of gravity are proposed. To achieve a gravimeter sensitivity of the order of 1 μGal/Hz1/2, the phase noise of laser radiation, the pressure of residual gases in the vacuum system, and the parameters of the magnetic shield system are estimated.

The CLAS12 Central Time-of-Flight system

The Central Time-of-Flight system for the large-acceptance CLAS12 spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility is described. The system consists of a hermetic barrel of 48 scintillation counters at a radius of 25 cm from the beamline. The wedge-shaped counters are 3.4 cm wide, 3.0 cm thick, and 90 cm long, and span a range of polar angles relative to the center of the nominal target location from roughly 35∘ to 125∘. The counters reside in the 5-T field of the CLAS12 superconducting solenoid. The bars are read out via bent light guides 1 m long on the upstream end of the counters and 1.6 m long on the downstream end. The phototubes are shielded by a multi-layer dynamical magnetic shield system to reduce the local fringe fields in the range from 400 G to 1000 G down to the level of 0.2 G at the location of the photocathodes. The average effective time resolution of the counters is 80 ps.

Prospects of high sensitivity atomic interferometer development for current gravimetry

A review of the experimental results achieved in the process of atomic fountain clocks construction at “VNIIFTRI” is presented. A possibility of the application of achieved results to the development of a sensitive interferometer (gravimeter) based on cold rubidium atoms is analyzed. The relevance of the study is in the estimation of perspective of interferometer (gravimeter) based on cold atoms for absolute measurements of local free-falling constant development. Physical fundamentals of atomic gravimeter’s operation are described. A comparison between atomic gravimeter and atomic quantum frequency standard based on cold atoms is done. Engineering solutions, that are necessary for building atomic gravimeter with required sensitivity of free-falling acceleration measurement are suggested. In order to build a gravimeter with a sensitivity reaching 1 μGal/Hz1/2 the estimations of laser phase noise, residual gas pressure in vacuum system and magnetic shielding system’s parameters are made.

Experimental and theoretical approach to determination of heat evolution in electrically conductive aluminosilicates

Design of progressive building materials with increased utility value is the key issue for the development of reliable modern building structures. Compared to the conventional materials, progressive building materials are supposed to exhibit not just adequate mechanical, and thermal properties, but they are also supposed to be applicable in sophisticated solutions, such as in self-sensing, self-heating or magnetic-shielding systems. In terms of electric properties, the most of building materials are electric insulators which is the main limiting factor for their applicability in such sophisticated solutions. However, this deficiency can be solved by the addition of a proper amount of electrically conductive admixtures. Within the paper, electrically conductive alkali-activated aluminosilicate with 8.89 mass.% of carbon black admixture was designed and its materials properties necessary for calculations of heat evolution by the action of an electric source were experimentally determined. The electrical conductivity of such material equal to 5.57?10?2 S m?1 was sufficiently high to ensure self-heating ability. It was observed good agreement of experimentally determined data with those modeled by means of heat equation on sample with dimensions 40 ? 40 ? 10 mm. Finally, one- and two-layered large-scaled heating elements based on materials with experimentally determined properties were designed and calculations were conducted to determine the voltage level necessary for one-hour heating from 268.15 K and 273.15 K to 278.15 K in the middle-top point of the construction.

From international ophthalmology to space ophthalmology: the threats to vision on the way to Moon and Mars colonization.

To report the ophthalmological risks of space travel. The literature about the effect of microgravity and cosmic radiation on the human eye has been reviewed, focusing on the so-called "spaceflight related neuro-ocular syndrome (SANS)", and possible remedies. The eye is the major candidate to suffer from the adverse space conditions, so much so that SANS is the main concern of the National Aeronautics and Space Administration (NASA). SANS, that affects astronauts engaged in long-duration spaceflights, is characterized by optic nerve head swelling, flattening of the posterior region of the scleral shell, choroidal folds, retinal cotton wool spots, and hyperopic shift. Even if it seems related to an increased volume of the cerebrospinal fluid in the brain and the optic nerve sheaths, its pathogenesis is still unclear. In addition, cataract is related to the effect of galactic cosmic rays on the lens. Centrifuges, pressurizing chambers, and mechanical counter-pressure suits have been advanced to counteract the upward fluid shift responsible for the SANS syndrome. Shields with a high content of hydrogen, magnetic shielding systems, and wearable radiation shielding devices are under study to mitigate the exposure to galactic cosmic rays. Since 1961, the year of the first manned mission outside the Earth, history has shown that the human being may venture in space. Yet, visual impairment is the top health risk for long-duration spaceflight. Effective remediation is mandatory in anticipation of long space missions and Moon and Mars colonization.

Magnetic Shielding Capability of MgB2 Cup Made by Liquid Infiltration Process

With the development of weak magnetic detection methods, the sensors, like superconducting quantum interference device (SQUID), become more and more sensitive. The magnetic shielding takes a more important part in weak signal detection systems than before. Traditional magnetic shielding methods are expensive, not flexible, and hard to prevent the low-frequency magnetic field clearly. For the superconducting magnetic shield, the operating temperature of a low critical temperature superconducting magnetic shield has high demand on refrigerating system. The high critical temperature superconducting magnetic shielding would introduce thermal magnetic noise. Due to the excellent superconductive property, the medium-temperature superconductor MgB2 has a huge potential to build the magnetic shielding system. In this article, we fabricate an MgB2 superconducting magnetic shielding cup with Mg Liquid Infiltration method. The highest TC of the sample is 39.4 K. The highest JC is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K. The shielding effect of the cup has been tested at axial dc weak magnetic field and the shielding factor exceeds 2000.

Open Magnetic Shielding by Superconducting Technology

Until recently, a new type of open magnetic shielding system was realized by the combination of a series of closed high temperature superconductor coils. We experimentally confirmed that the shielding factor (SF) of the new shielding system can reach more than 40 dB in the frequency spectrum of 0.1-16 000 Hz. Because of its superior ability to resist alternating magnetic field, we named, the system Tesla-shielding (TS), to commemorate the father of alternating current, Nikola Tesla. In this paper, we will report the design and realization of a Helmholtz coil-based TS. The Helmholtz TS has many advantages over the previous planar TS. Especially, the Helmholtz TS has an engineering way of regulating the device for a better SF. We will introduce the design of the Helmholtz TS with the help of numerical simulation. The main electromagnetic properties of the TS, such as SF in the frequency spectrum and its shielding ability in the long duration measurement, are given in this paper.

Design of a neutron camera for the HL-2A tokamak

Abstract A new neutron camera, comprising nine individual photo-multiplier tubes coupled with liquid scintillators through light guides, was designed, constructed and installed on the HL-2A tokamak. Using the HL-2A tokamak as an example, the basic principles for designing a camera system in low fusion power tokamaks were illustrated in this paper. The 2” × 2” BC501A liquid scintillation detectors coupled with the gain stabilization system, were developed for neutron measurements and applied on the tokamak. A magnetic shielding system was designed, using the finite element method (FEM), to ensure excellent operation of detectors under a strong magnetic field. Energy calibration has been conducted and the light output function was compared with the PTB’s values. The reasons for discrepancy and variations in the results are analyzed and discussed in detail in the paper.

Multilayer Cylindrical Magnetic Shield for SERF Atomic Co-Magnetometer Application

This paper presents the development of a spin-exchange relaxation-free atomic co-magnetometer with a magnetic shielding system. The shielding system includes multiple cylindrical passive magnetic shield and active magnetic compensation coils. The multilayer shield, which adopts a structural style comprising a barrel body and end cover, is applied to attenuate the external magnetic field to less than 10 nT or ideally close to 0. For the purpose of degaussing, pumping, and probing light paths, several openings must be made on the magnetic shield. A hybrid approach combining theoretical calculations and the finite element method is proposed to analyze the shielding properties, considering the influence of openings. To evaluate the shielding properties of the magnetic shield, two different simplified finite element models are established and analyzed. The simulation results are compared with theoretical and experimental data, and the results are in good agreement. The modeled results show that the openings bear a considerable influence on the shielding performance, and thus, their effect cannot be ignored. The axial magnetic shielding factor with several openings is roughly $4.4\times 10^{4}$ , which is about 2 orders of magnitude lower than that without openings. Furthermore, a rotation sensitivity of $5.86\times 10^{-7}$ rad $\cdot \,\,\text{s}^{-1}\,\,\cdot $ Hz−1/2 is obtained with the open-hole magnetic shield. This sensitivity corresponds to a magnetic sensitivity of 27.8 fT/Hz1/2. Based on the results, possible improvements are suggested for future designs.

SERF Atomic Magnetometer–Recent Advances and Applications: A Review

This paper aims to review the technology, developments, and applications of spin exchange relaxation free (SERF) atomic magnetometers. The generalized comparisons between the SERF magnetometer and the other types of weak magnetic sensors are elaborated. Further, the fundamental composition and operational principle of the SERF atomic magnetometer are elucidated. The development history and recent technological developments with respect to several aspects, including the alkali metal vapor source, atom heating method, pump and probe lasers, and magnetic shielding system, are presented. The classification and respective advantages and disadvantages of these technologies are described in detail. Finally, the existing and potential applications, as well as the prospective future development trends are presented.

The Cryogenic AntiCoincidence Detector for ATHENA X-IFU: Improvement of the Test Setup Toward the Demonstration Model

The ATHENA X-IFU development program foresees to build and characterize an instrument Demonstration Model (DM), in order to probe the system critical technologies before the mission adoption. In this respect, we are now developing the DM of the X-IFU Cryogenic Anticoincidence Detector (CryoAC), which will be delivered to the Focal Plane Assembly (FPA) development team for the integration with the TES array. Before the delivery, we will characterize and test the CryoAC DM in our CryoLab at INAF/IAPS. In this paper we report the main results of the activities performed to improve our cryogenic test setup, making it suitable for the DM integration. These activities mainly consist in the development of a mechanichal setup and a cryogenic magnetic shielding system, whose effectiveness has been assessed by FEM simulations and a measurement at warm. The preliminary performance test has been performed by means of the last CryoAC single pixel prototype, the AC-S8 pre-DM sample.

Low Noise Active Shield for SQUID-Based Magnetocardiography Systems

A light weight and low-cost active magnetic shield system is proposed for a single channel SQUID-based magnetocardiography system equipped for operating at liquid nitrogen temperature without passive magnetic shield. The developed active shield, using coils around the sensors, is a two-stage magnetic shielding system, each stage of which has been designed to compensate different frequency and dynamic ranges. The sensor part contains two high-Tc rf-SQUID magnetometers, capable of working stably under earth magnetic field, placed in an axial gradiometric arrangement with a baseline of 10 cm. The active shield setup is driven using two correlated proportional-integral-derivative closed loop systems. In the designed system, the coils are in the vicinity of the SQUIDs, resulting in coupling the coils to the SQUIDs as well as to the resonators. Hence, the impedance of the coils along with the phase of the feedback current is affected based on the configuration. In this paper, investigation of the shielding performance of our bi-stage magnetic shield as the active compensation, fed by the optimal feedback control system with all the above considerations, is reported. Using the designed shielding system, the disturbing magnetic signals could be attenuated such that the pico-Tesla signals could be obtained.

Development of Active Shielding-Type MI Gradiometer and Application for Magnetocardiography

We have developed an active magnetic shielding system for a magnetoimpedance (MI) gradiometer, in which a reference-type MI element output is fed back to a sensor head with a feedback coil to reduce the effect of environmental magnetic noise around the sensor head, and applied the device to magnetocardiography (MCG). This type of sensor reduced the 60 Hz noise related to the power source line by −40 dB and can operate in an unshielded environment and at room temperature with a noise amplitude of 100 pT. We simultaneously measured the electrocardiography (ECG) and MCG signals at a point on the chest surface near the pit of the stomach. In the output of the developed MI gradiometer, negative magnetic peaks were observed after average processing over 25 cycles, and these signals corresponded to the characteristics of the ECG waveform. The amplitude of the sharp magnetic peak corresponding to the R peak in the ECG was approximately 60 pT. This result corresponded to the value obtained by a low-Tc superconducting quantum interference device. Consequently, we considered the active magnetic shielding system to be effective for a very weak magnetic signal such as MCG.

MIグラジオメータ用アクティブ磁気シールドの環境磁界低減効果

We have developed the active magnetic shielding system, which a reference-type MI element output is fed back to a sensor-head with a feedback coil, to reduce the environmental magnetic noise around the sensor-head. Output properties of MI elements could keep linearity by adjusting the DC magnetic field in the feedback coil to less than 1 µT. Furthermore, the noise at 60 Hz related to the power source line was reduced by 1/10 with this system. We have measured a variation of magnetic field with a stainless steel metal ball (SUS304, 0.3 mm diameter) movement by using a new MI gradiometer with this system, and the magnetic signal of 700 pT was detected clearly compared with a previous MI gradiometer. Consequently, we considered that this type MI gradiometer is an effective method of a very weak magnetic measurement in the environmental magnetic noise.

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

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.

Decoupling and shielding numerical optimization of MRI phased-array coils

Receiver array coils in magnetic resonance imaging systems are used to pick up the signals emitted by the nuclei with high signal-to-noise ratio and a large region of sensitivity. Especially in low-field magnetic resonance systems, receiver coil performance plays a significant role in image quality. Moreover, since the magnetic resonance scanner shielding system strongly modifies resonance frequencies and field distribution, the array coils performance should be evaluated in dependence on the shield position.In this paper, we describe the use of a numerical solver based on finite-difference time-domain method to evaluate coil performances also considering the presence of radiofrequency shields.In particular, this paper deals with coupling and shielding in phased array coils at low field: we analyzed a classic two circular elements array and a novel two elements array coil both designed for the application in a 0.5T open magnetic resonance scanner. The prototypes of the arrays were tested by laboratory workbench in order to validate the simulated data and experiments were also done in real low field magnetic resonance scanner by using the novel coil.