Shield Coil Research Articles

Evaluation of the Neutron and Gamma-Ray Heating in the Radiation Shielding and Magnet Coils of the VISTA Spacecraft

Basic nuclear data for a design concept with inertial fusion energy propulsion for manned or heavy cargo deep space missions beyond earth orbit have been evaluated. Fusion power deposited in the inertial confined fuel pellet debris delivers the rocket propulsion with the help of a magnetic nozzle.The superconducting magnets of the magnetic nozzle are protected against neutron and gamma-ray radiation by a massive shielding. Throughout the shielding, the nuclear heating, caused by neutrons and gamma rays has been calculated. As a critical issue for this design concept, special attention is paid to the nuclear heating in the superconducting magnet coils. The neutron and gamma-ray penetration into the coils is calculated using the Sn methods with a high angular resolution in r-z geometry in S16 P3 approximation by dividing the solid space angle in 160 sectors.Total peak nuclear heat generation density in the coils is calculated as 64.5 μW/cm3 by a fusion power of 17 500 MW. Peak neutron heating density is 30.8 μW/cm3, and peak gamma-ray heating density is 40.6 μW/cm3 (on a different point). However, volume-averaged heat generation in the coils is much lower, namely, 2.17, 8.49, and 10.66 μW/cm3 for neutron, gamma-ray, and total nuclear heating, respectively.A conically shaped frozen hydrogen expellant reduces the neutron streaming toward the spacecraft by a factor of ~12.5 via neutron scattering on hydrogen and deflection into vacuum, in addition to the geometric neutron flux attenuation in space by 1/r2. The results of these calculations can help to increase the credibility of the vehicle for interplanetary space transport applications design concept.

Caluculating Current Densities and Fields Produced by Shielded Magnetic Resonance Imaging Probes

A method is presented for computing the fields produced by radio frequency probes of the type used in magnetic resonance imaging. The effects of surrounding the probe with a shielding coil, intended to eliminate stray fields produced outside the probe, are included. An essential feature of these devices is the fact that the conducting rungs of the probe are of finite width relative to the coil radius, and it is therefore necessary to find the distribution of current within the conductors as part of the solution process. This is done here using a numerical method based on the inverse finite Hilbert transform, applied iteratively to the entire structure including its shielding coils. It is observed that the fields are influenced substantially by the width of the conducting rungs of the probe, since induced eddy currents within the rungs become more pronounced as their width is increased. The shield is also shown to have a significant effect on both the primary current density and the resultant fields. Quality factors are computed for these probes and compared with values measured experimentally.

Optimum sensitivity of an externally shielded cryogenic current comparator

The sensitivity of an overlapped-tube cryogenic current comparator (CCC) has been calculated including the effect of a cylindrical external shield. Dimensions of the shield, tube and pick-up coil can be optimized to give maximum sensitivity. The sensitivity in the case of a fixed radius shield has been numerically investigated and a CCC based on an optimized design has been constructed. A single sensitivity measurement indicates that the cylindrical-shield model is accurate to within about 20% of the measured value. This is a significant improvement compared with a simplified ring model of the shield or neglecting the shield entirely.

Pulsed gradient analysis using a dedicated magnetometer.

In magnetic resonance imaging and spectroscopy, knowledge of the magnetic field gradient behavior is very important. This work describes a simple way to characterize the temporal and spatial dependence of the main magnetic field when a gradient is switched. Records are performed with a home-built magnetometer. This device is controlled by a personal computer for recording and processing the NMR signals from an array of small probes spatially distributed and switched by the magnetometer. We present results of measurements on a 2-T superconducting magnet. These results show the residual defects of an active shielded gradient coils system.

Development and test results of the prototype active shield dipole magnets for the KEK B-Factory

A novel dipole magnet with an active shield coil has been developed as a candidate of the separation dipole in the interaction region of the KEK B-Factory. This is an iron-free magnet with an inner aperture of 113.8 mm diameter and a nominal field of 0.7 T. The main coil produces a field of 1.6 T, while the shield coil, which sits outside the main coil and has a current in the opposite direction produces a field of -0.9 T and suppresses the outside field to the level of 5 mT at a radius of 200 mm. Two prototype dipoles have been fabricated and tested. This paper summarizes the design, construction and test results of the dipoles.

Superconducting magnets in the interaction region of the KEK B-Factory

The interaction region of the KEK B-Factory requires four superconducting magnets (two dipoles and two quadrupoles). Due to their detrimental effect on the experimental detector, the leakage field of the magnets needs to be as small as possible. For achieving this smaller leakage field, we have designed special iron-free dipoles with an active shield coil. Due to the active shield method, the stray field of the magnets is suppressed to a level of 10 mT outside the radius of 0.25 m. The quadrupoles are also iron-free magnets, but have no shield coil. This paper presents the results of the two- and three-dimensional electromagnetic studies along with the structure of these magnets. >

Cross-Section Sensitivity Study for the Toroidal Field Coil Shielding Parameters in the ITER/OTR Design

An extensive analysis of the sensitivity of the fast neutron flux in the superconductor, the dose to the electrical insulator, and the number of displacements per atom in the copper stabilizer to variations of the neutron cross sections for the International Thermonuclear Experimental Reactor (ITER/OTR) inboard region (first wall/blanket/shield/vacuum vessel) was carried out. All of the nuclides with a significant concentration in the ITER/OTR inboard region were investigated, namely, iron, chromium, nickel, lead, oxygen, hydrogen, boron, copper, [sup 6]Li and [sup 7]Li. The integrated total sensitivities of iron, lead, hydrogen, and oxygen were compared with the results for the OTR and Next European Torus (NET) sensitivity analyses. The integrated total sensitivity of both the fast neutron flux and the dose to variation of lead cross sections for the ITER/OTR was much higher than that for the OTR, namely, 3.5 and 1.2, respectively. The difference in the integrated total sensitivities of the inboard toroidal field coil responses to a one standard deviation variation of the iron, hydrogen, and oxygen neutron cross sections was <30%. The most important energy regions and the types of neutron cross sections for shield calculations were identified. The uncertainty of the neutron cross sections in the important more » energy regions needs to be decreased to<10% to decrease the uncertainty of the calculated neutron dose and fast flux behind the ITER/OR inboard shield to <15 to 30%. 36 refs., 15 figs., 1 tab. « less

Numerical analysis of magnetic field in superconducting magnetic energy storage

Fit designs of magnetic shielding of the solenoidal-type superconducting magnetic energy storage (SMES) for reduction of magnetic fields in a living environment are discussed. When some superconducting shielding coils are over the main storage coil, the magnetic field is reduced significantly over the case of unshielded coils. The calculated results of the magnetic field are obtained by the finite-element method. The toroidal-type SMES is studied. The leakage magnetic field is lower than in the solenoid-type SMES, but the electromagnetic force of the coil is very strong. A numerical analysis of magnetic field in the toroidal-type SMES is described by analytical calculation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Next European Torus Basic Machine

The basic features of the Next European Torus are described. This includes the cryostat and biological shield, the toroidal and poloidal field coils, the vacuum vessel, and the bulk shield. In addi...

A 60 cm bore 2.0 tesla high homogeneity magnet for magnetic resonance imaging

A 60 cm warm bore imaging and spectroscopy magnet has been constructed and placed in operation at the Francis Bitter National Magnet Laboratory (FBNML). The magnet achieved its design central field of 2.0 T but is currently being operated at 1.5 T. It operates in the persistent mode with a measured decay rate of less than 0.03 ppm/hr. Employment of both 10 superconducting shims and small ferromagnetic shims located close to the warm bore has resulted in a homogencity of better than 3 ppm throughout the 25 cm diameter spherical volume (DSV). Room temperature shim coils have not been incorporated into the system. A novel form of compact shielded pulsed gradient coil system has been designed, constructed and tested. In such a system, appropriate configuration of an external shield coil results in cancellation of external flux without the introduction of impurity harmonics that degrade the linearity of the gradients. Six sets (X, Y, Z coils, and X, Y, Z shields) have been incorporated into a unit of 6 cm build. The all aluminum cryostat employs a 77 K nitrogen recondenser and a shield cooler operating at less than 20 K. Steady state helium consumption is about 50 ml/hour. The system is currently being used for both high resolution, in-vivo <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> P-NMR spectroscopy and a variety of MRI experiments including <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup> Na imaging of eyes.

Shield Optimization Study for Choke Coil of Tandem Mirror Fusion Reactor "GAMMA R"

In summary, shield optimization calculations have been carried out for the choke coil shield of the GAMMA R. We could obtained the shield distribution in which an expensive material, tungsten, is effectively used to protect the choke coil. This optimal distribution could not have been obtained by varying the homogenized composition parametrically. Such an optimized distribution can decrease the amount of tungsten by 40% compared to the original homogeneous shield, while retaining the same dpa rate in the SC coil. These results provide the basic information for further study of the choke coil design for the GAMMA R.

Neutron streaming analysis for helical geometry system, heliotron-H fusion power reactor.

Nuclear analysis was carried out for the Heliotron-H reactor. Due to the helical geometry of the system, 14 MeV neutron streaming inherent in the reactor exists; some of source neutrons generated in the plasma region can see the coil shield surface in a direct line-of-sight manner and stream through blanket regions without collisions. With an appropriate coordinate transformation from the helical geometry, analysis on the neutron streaming was made possible by a method coupling the three-dimensional Monte Carlo code and two-dimensional discrete-ordinates transport code. For each radiation response parameter in the helical magnet, the streaming neutrons contribute 40–50%. This fact strongly suggests the need of taking account of the contribution from the streaming neutrons to provide an adequate shielding for the helical magnet.

CHARACTERISTICS OF SUPERCONDUCTING SYNCHRONOUS GENERATOR WITH ELECTROMAGNETIC SHIELD COIL CONTROL

Abstract A new type of control concept for the superconducting generator with electromagnetic shield coil instead of damper shells is proposed to avoid field current variations and improve the dynamic performance during transients This concept comprises both a field forcing system and a controller on the electromagnetic shield coil, which should be adjusted according to a specific control principle Comparisons are made, in the dynamic performance, when employing the field forcing alone and when the shield coil control is added to it.

Low Activation Fusion Reactor Design Studies

A design study for a low activation tokamak fusion reactor based on the STARFIRE baseline design has been done. The major components of limiter, first wall, blanket, shield and toroidal field coils have all been designed with very low activation materials and the designs appear technically achievable. The result provides a fusion power reactor with a high degree of direct personnel access for maintenance and repair, with a large reduction in safety and environmental impact, and with much reduced waste disposal problems. This low activation design also appears economically attractive and is expected to have a high degree of public acceptance.

EBT-P Gamma Ray Shielding Analysis

First, a one-dimensional scoping study was performed for the gamma-ray shield of the ELMO Bumpy Torus proof-of-principle device to define appropriate shielding material and determine the required shielding thickness. The dose-equivalent results are analyzed as a function of the radiation-shield thickness for different shielding options. A sensitivity analysis for the pessimistic case is given. The recommended shielding option based on the performance and cost is discussed. Next, a three-dimensional scoping study for the coil shield was performed for four different shielding options to define the heat load for each component and check the compliance with the design criterion of 10 watts maximum heat load per coil from the gamma-ray sources. Also, a detailed biological-dose survey was performed which included: (a) the dose equivalent inside and outside the building, (b) the dose equivalent from the two mazes of the building, and (c) the skyshine contribution to the dose equivalent.

Characteristics of a 200 kJ shielded superconductive coil for pulsed energy storage

The first model of the shielded pulse superconductive energy storage was constructed and tested. The model which has the stored energy of 200 kJ is composed of a superconductive coil made by a commercially available monolithic wire and a shield coil by a copper cable. The shield coil is divided into 12 blocks which are distributed appropriately arround the superconductive coil. The accuracy of the shield coil distribution was confirmed by measuring the leakage magnetic field on the superconductive coil. The experiment of the pulse operation has been performed to test the effectiveness of the shield coil. The results shows that the pulse current in the superconductive coil could be suppressed and the good performance of this method was confirmed.

On the electrodynamics of coil shielding

Coil shielding is resorted to in many electronic applications in order to prevent undesirable coupling. The paper deals with such a shield and the results obtained may be used as an indication of the overall field pattern as established due to the presence of an external screen.

Hybrid Bundle Divertor Design

A hybrid bundle divertor design is presented that produces <0.3% magnetic ripple at the center of the plasma while providing adequate space for the coil shielding and structure for a tokamak fusion test reactor similar to the International Tokamak Reactor and the Engineering Test Facility (with R = 5 m, B = 5 T, and a /SUB wall/ = 1.5 m, in particular). This hybrid divertor consists of a set of quadrupole ''wing'' coils running tangent to the tokamak plasma on either side of a bundle divertor. The wing coils by themselves pull the edge of the plasma out 1.5 m and spread the thickness of the scrape-off layer from 0.1 to 0.7 m at the midplane. The clear aperture of the bundle divertor throat is 1.0 m high and 1.8 m wide. For maintenance or replacement, the hybrid divertor can be disassembled into three parts, with the bundle divertor part pulling straight out between toroidal field coils and the wing coils then sliding out through the same opening.

One-Dimensional Gamma-Ray and Photoneutron Shielding Calculations for the Elmo Bumpy Torus Proof of Principle Device

One-dimensional radiation transport calculations have been performed to obtain estimates of the nuclear heat loads and biological dose rates due to bremsstrahlung gamma rays and photoneutrons in the ELMO Bumpy Torus proof of principle device. The bremsstrahlung gamma rays arise because of electron impingement on the magnetic coil assemblies, and these gamma rays in turn produce photoneutrons through interactions in the high-Z shielding materials. For a 1-MW electron power loss, /sup 238/U and tungsten coil shield thicknesses of 22.5 and 27.3 mm, respectively, were found sufficient to limit the nuclear heat load on a single superconducting coil to 10 W. The estimated lead and concrete primary shield thicknesses required to reduce the biological dose rate due to bremsstrahlung gamma rays to 2.5 mrem/h were calculated to be 0.318 and 1.92 m, respectively. Because of photoneutron production, however, lead by itself was not found to be an acceptable biological shield.

The first model of the shielded pulsed superconductive energy storage

The first model of the shielded pulsed energy storage was designed and constructed to test the effectiveness, the construction problems, and the scaling problems. The stored energy is 200 kJ, and its available energy is designed as 50 kJ at the transfer time less than 50 ms. The shield coil is distributed arround the superconductive coil in a simple form for easy construction. The measurement of the leakage field showed that the simplified distribution of the shield coil was available. The dewar was constructed to have a wall as thin as possible with small heat leak by using GFRP supports. The design value of heat leak agreed well with the measurement. The current of 80 % of the design value was obtained by the first preliminary test with three quenchings.