Magnetic Coil Design Research Articles

Magnetic stimulation coil and circuit design.

A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation [1]. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

Shim coils for NMR and MRI solenoid magnets

The design of high-purity magnetic field shim coils for NMR and MRI laboratory solenoid magnets is discussed. The individual shim consists of several current carrying elements which have the form of a circle or circular arc. The influence of the needed connecting conductors can usually be neglected. The magnetic field components of the mentioned elements can be expressed in terms of spherical harmonics. The design is based on unique recursion relations for the coefficients of the most important expansion component. Using the Monte Carlo method, the procedure of optimizing the element positions is illustrated for an X-shim design. The results obtained by measuring the field of the implemented shim are compared with those of the theoretical evaluation.

Algorithm for the design of magnetic stimulation coils.

Algorithm for the design of magnetic stimulation coils.

Consideration of Optimal Magnet Coil Design for 1300 MWth Coal Combustion Magnetohydrodynamic Generator

In this paper, we discuss the effect of the cross-sectional shape of a magnet coil upon the reduction of the magnetohydrodynamic (MHD) channel length. Employing a coal-combustion plasma with semiperfect gaseous characteristics, the generator output performance of various magnet coil shapes are evaluated based on the 1-D gasdynamic model. The shape of a magnet coil cross section is optimized for a 1300 MWth supersonic Faraday-type MHD generator with a square inlet cross section. It is shown that the channel length can be shortened by 33% through optimization of the coil shape, in comparison with the case of the crescent-shaped coil producing a uniform magnetic field where the enthalpy extraction is effectively kept unchanged. Also, it is estimated that the capital cost for a stand-alone commercial MHD/steam combined plant can be decreased by more than 6% by means of this coil shape optimization.

Simple finite element calculations for the design and analysis of high field magnet coils

A simple algorithm is presented which solves the stress and strain components in the midplane of a coil. The algorithm was used to optimise the stress distribution in layer-by-layer reinforced copper coils. The deformation of the coil is related to the change in inductance.

The design of end magnetic system coils for 'AMBAL-M'

The end of the AMBAL-M tandem mirror plasma trap is an axially symmetric plug with a semicusp MHD (magnetohydrodynamic)-expander. The plug field is formed by a pair of coils, and the semicusp field is formed by another pair of anti-parallel coils. The axial dimension of the end magnet system is 3.2 m, and the middle diameters of the coils are from 0.6 to 1.1 m. The operation mode features a 24-kA current, a 1.5-s effective pulse time, and a repetition rate of 1 pulse per 15 min. The coil design is described. The coil is a packet of parallel modules whose conductor is a copper ribbon with a 500-mm/sup 2/ cross section, and water-cooled copper disks between them for heat removal. The heat calculation principles are given. The characteristics of the smaller semicusp coil with regard to its location in a vacuum are noted. Some manufacturing problems are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cryogenics: its influence on the selection of the ASTROMAG superconducting magnet coils

ASTROMAG, a particle astrophysics experimental facility proposed for running alongside a space station, has a large superconducting magnet to analyse particles coming from deep space. Several types of magnets were investigated for use in the ASTROMAG central facility. The factors which influence the selection of the magnet coil design include: 1, the upper limit of particle momentum resolved (proportional to the integrated field) as a function of solid angle; 2, cryogenic design and its effect on cryogen lifetime for a given central facility mass; and 3, the overall cost of the magnet coils and cryostat. Four magnet types are analysed in this paper. These include a simple two-coil solenoid (the baseline design), two disc coils at the ends of the helium tank, a two-coil toroid and a thin solenoid plus bucking coil. The superfluid helium cryogenic system must have a cryogen lifetime approaching four years without refilling. (Mechanical coolers on the outer shield may be used to extend this lifetime.) The baseline magnet and cryostat mass (including the helium) is set at 2000 kg. Coils which have extended surfaces will require more helium to keep them cold. Flat surfaces require more mass in the outer vacuum vessel or a greater distance between the coils and the detectors (hence a lower integrated field). A balance must be struck between cryostat lifetime, total mass and the integrated field through the detectors. This balance tends to favour coils which are in the same vacuum vessel as the cryogen. The trade-offs are examined for the four cases given previously.

Inverse magnetic separation coil design

A new method for the design of superconducting coils for magnetic separators is presented. It is based directly on the force-density requirement in the separation channel. The method is exemplified by means of an anadynamic field.

Design of magnet coils for semi-continuous magnetic fields up to 60 T

Two constraints on semi-continuous magnet coils are the strength of the winding material, and the maximum power which the rectifier must deliver for a short time. Here we assume that for a 60-T coil wire of sufficient strength (about 100 kg/mm 2 is available. It was shown earlier that a single, homogeneous coil needs a power of nearly 150 MW, which calls for huge capital investments in power lines, transformers, switches and rectifiers. By using two nested coils, wound from wires with different strengths and current densities, and energized successively by the same rectifier, we can reduce the power to less than 50 MW.

A high-field air-cored magnet coil design for fast-field-cycling NMR

A mathematical formalism is described which allows the design of the most effective geometry for homogeneous, fast-switchable field-cycling magnets. The method minimizes the electric power needed to produce a flux density B subject to constraints on the homogeneity and effective volume. It was used to build a low-inductance 1.2 T coil for fast-field-cycling NMR experiments with protons at 50 MHz and with deuterons at 7.5 MHz. Driven by a 25 kW MOSFET switch the field turn-on and turn-off times can be adjusted to less than 0.4 ms. Data for a projected 2.4 T coil, which will extend the field-cycling range to Larmor frequencies of 100 and 15 MHz, respectively, are also given.

Harmonic Analysis of a Planar-Wound Toroidal Deflection Coil

We present analytical calculations to demonstrate how the mechanical constraints of the winding process limit the harmonic content of a planar-wound toroidal deflection coil and how one can change the various harmonics beyond this limitation by adding auxiliary turns to the coil. The results would be useful in application of theoretical knowledge about harmonics to the design of magnetic deflection coils.

Analytic theory of series field coil ion diodes

Ion diodes suited to inertially confined fusion research must conduct very high currents. The magnetic fields due to these currents are comparable to the fields used to provide magnetic insulation of electrons. Because these self-fields are necessarily high at the diode boundary where the power is applied, and are zero at some other part of the diode away from the power feed, these diodes have generally been treated theoretically by two-dimensional particle-in-cell computer simulations. There is a special class of ion diodes employing series magnetic field coils which can be described by a one-dimensional model. These diodes are highly amenable to treatment by analytic theory, and therefore are easily designed and scaled to multiterawatt systems. Many features of these diodes make them very attractive as drivers for inertial-confinement fusion research. Theoretical analysis of this class, including magnetic field configuration and field coil design, electron drifts, diode efficiency, and ion focusing, is presented. Also presented is analysis of a plasma-filled version which provides ion bunching and filtering of light ion species which might otherwise have detrimental effects on target experiments.

New formulas for the design and shimming of NMR magnetic field coils

New formulas for the design and shimming of NMR magnetic field coils

Radio frequency sputtering equipment: design considerations for the disc and annulus system

The basic equations important in the design of rf sputtering equipment are presented. Attention is restricted to the ‘disc and annulus’ system and simple techniques in lead-through fabrication and electrode shielding are described. Also rf power oscillator theory is used to derive the important parameters of power generation. Load coupling and power matching techniques are discussed. Problems of the magnetic field coil design are analysed and a value for the thermal conductivity of coils wound from polyurethane coated wire is given, namely κ = 0.64 W m −1 /°C −1 , permitting the steady state temperature distribution inside such coils to be predicted.

Design of High Field Magnet Coils for Long Pulses

Magnet coils are investigated which can produce magnetic fields of 15–40 MA/m (200–500 kOe) during working times of the order of 0.1 sec. These fields are suited for measurements in highly conducting materials. The coils are precooled to 20°K or 77°K and the Joule heat is not removed during the pulse. In Sec. I the thermal limitations of this method are reviewed. Plots are given for the optimum dimensions and current densities for coils producing a specified field during a specified time, minimizing the necessary power supply. Details of a magnet constructed along these lines are given. The maximum field produced by this coil, 16 MA/m (200 kOe) during 0.3 sec, however, proved to be determined by mechanical instabilities. These problems are reviewed in Sec. II. Calculations of the Lorentz force and the internal stresses resulting from it were carried out taking the elastic and plastic properties of copper and insulation into account. It is shown theoretically that a magnet stable to 35 MA/m (440 kOe) can be built from hard drawn copper if a reinforcing steel cylinder is used at a certain radius inside the coil.

Some basic concepts for magnet coil design

In the united States and abroad there is intensive activity in thermonuclear research.1 A major part of this effort is directed toward containment, in strong magnetic fields, of plasma of the necessary high-particle energies, corresponding to temperatures of hundreds of millions of degrees Kelvin. Magnetic field design in thermonuclear research has already been developed to a relatively broad field of electrical engineering.2 The purpose of this paper is to discuss some theorems which are of special interest for the design of large d-c magnet coils as used, for instance, in the DCX (d-c experiment) thermonuclear research program of the Oak Ridge National Laboratory.3