Single-layer Coil Research Articles

Cylindrical induction coil to accurately imitate the ideal magnetic dipole

In this work, we optimize the geometry of a cylindrical induction coil in order to improve the imitation of the ideal dipole field. First, we analyze a single-layer coil and find that for an optimum length-to-diameter ratio ( L/ D) of 0.86:1 the imitation error, computed for a four radii distance from the coil’s center, is reduced by a factor of ∼12 (from 9.4 down to 0.73%) relative to a single-turn coil. Second, we analyze two different types of multilayer coils: one having for all the layers the same 0.86:1 optimum L/ D (a coil with a trapezoidal cross section of the winding); and another having for each layer a different L/ D (a coil with a rectangular cross section of the winding). The imitation error in this case is reduced by a factor of ∼22 and ∼33, correspondingly. We finally show that optimizing the multilayer coil makes the imitation error practically negligible (<0.28%) even at as short as four radii distances from the coil’s center. Employing such optimized coil allows one to use the simple dipole model with a high degree of accuracy. It also relieves the system of having to spend extra time for computing the exact values of the coil field.

Multilayer transverse gradient coil design

AbstractIn small, cylindrical gradient coils consisting of a single layer of wires, the limiting factor in achieving large magnetic field gradients is the rapid increase in coil resistance with efficiency. This behavior results from the decrease in the maximum usable wire diameter as the number of turns is increased. By adopting a multilayer design in which the coil wires are allowed to spread out into multiple layers wound at increasing radii, a more favorable scaling of resistance with efficiency is achieved, thus allowing the design of more powerful gradient coils with acceptable resistance values. By extending the theory used to design standard cylindrical gradient coils, mathematical expressions have been developed that allow the design of multilayer coils. These expressions have previously been applied to the design of a four‐layer z‐gradient coil. As a further development, the equations have now been modified to allow the design of multilayer transverse gradient coils. The variation in coil performance with the number of layers employed has been investigated for coils of a size suitable for use in NMR microscopy, and the effect of constructing the coil using wires or cuts in a continuous conducting surface has also been assessed. We find that at fixed resistance a small wire‐wound two‐layer coil offers an increase in efficiency of a factor of about 1.5 compared with a single‐layer coil. In addition, a two‐layer coil of 10‐mm inner diameter has been designed and built. This coil had an efficiency of 0.41 Tm−1 A−1, a resistance of 0.96 ± 0.01 Ω, and an inductance of 22.3 ± 0.2 μH. The coil produces a gradient that deviates from linearity by less than 5% over a central cylindrical region of interest of height and length 6.2 mm. © 2003 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 16: 38–46, 2003.

R&amp;D for a single-layer Nb/sub 3/Sn common coil dipole using the react-and-wind fabrication technique

A dipole magnet based on the common coil design, using prereacted Nb/sub 3/Sn superconductor, is under development at Fermilab, for a future Very Large Hadron Collider. This magnet has some innovative design and technological features such as single layer coils, a 22 mm wide 60-strand Rutherford type cable and stainless steel collars reinforced by horizontal bridges inserted between coil blocks. Both left and right coils are wound simultaneously into the collar structure and then impregnated with epoxy. In order to optimize the design and fabrication techniques an R&D program is underway. The production of cables with the required characteristics was shown possible. Collar laminations were produced, assembled and tested in order to check the effectiveness of the bridges and the validity of the mechanical design. A mechanical model consisting in a 165 mm long section of the magnet straight section was assembled and tested. This paper summarizes the status of the program, and reports the results of fabrication and test of cable, collars and the mechanical model.

Magnetic designs and field quality of Nb/sub 3/Sn accelerator magnets

This paper presents a new approach to accelerator magnet design, based on simple and robust single-layer coils with minimum number of turns arranged horizontally or vertically in a common iron yoke. Cos-theta and block type coil geometries as well as cold and warm iron yoke designs were studied. Coils and yokes were optimized for the maximum field, minimum field harmonics, and minimum sizes.

Test results of a demonstration HTS magnet for minesweeping

American Superconductor completed building a demonstration HTS minesweeping magnet for airborne superconducting mine countermeasure system in December 1999, The demonstration magnet consisted of a single-layer HTS coil wound on a 457-mm G-10 mandrel, and housed in a 560 mm diameter by 1.5-m long stainless steel vacuum vessel. It is conduction cooled with a two-stage cryocooler. It has a magnetic moment of 15 kAm/sup 2/. The magnet was successfully ramped up to 400 A at /spl sim/35 K. The magnet current was kept at 400 A for six hours without any voltage run-away. The magnet was also successfully tested for 50% AC modulation (200 A to 400 A) with a trapezoidal current waveform. Experimental data from these tests are presented.

ＩＴＥＲ‐ＣＳモデル・コイルとＣＳインサート・コイルの実験結果 ＩＴＥＲ‐ＣＳインサート・コイルのクエンチ特性

The Central Solenoid (CS) insert coil and the CS model coil (CSMC) have been developed in the Engineering Design Activity (EDA) for the International Thermonuclear Experimental Reactor (ITER). They are wound with the ITER CS conductor. The CSMC is composed of 18 layer windings, whose most important object is to generate 13-T magnetic field at 46-kA current, so the coil does not have instrumentation in winding. The CS insert coil is a single layer coil and was tested under a field generated by CSMC. This coil was fabricated to study its performance when wound with the ITER CS conductor, so the coil has much instrumentation in winding. Both coils are very stable and achieved their rated condition without quench. To study the quench characteristics, we made artificial quenches by heating the coils. Many data about quench behavior of CS insert coil were obtained from the experiment. The results of quench property, propagation velocity, pressure rise, and temperature rise are reported and compared with the calculation results.

単層だ円形コイルの自己インダクタンスの計算式

単層だ円形コイルの自己インダクタンスの計算式

100 T magnet developed in Osaka

A non-destructive pulsed magnet for 100 T has been developed to carry out precise magnetic measurements at extremely low temperatures and under high pressures. Our record magnet has generated 80.3 T in a 10 mm bore with 7 ms pulse duration and then is called a 80 T magnet. The 80 T magnet consists of inner and outer coils, both of these are made by winding with Cu–Ag wire and reinforced by maraging steel. The inner coil is a single-layer coil backed up with a thin maraging pipe and the outer coil is made with nine layers reinforced by a thick maraging ring. Magnetization and magnetoresistance measurements at 1.3 K have been carried out up to 70 T in the 80 T magnet. The outer coil of the 80 T magnet has an 18 mm bore and can generate 71.3 T as a record and then is called a 70 T magnet. The 18 mm bore of the 70 T magnet is a useful space for introducing an extremely low temperature into high magnetic field; this was used to carry out both magnetization and magnetoresistance measurements at 80 mK up to 60 T. We have examined the lifetime of the 70 T magnet at various maximum fields in ordinary use. The results show that about 100 shots can be made with 60 T and 500 shots at 55 T. We have developed another 70 T magnet with longer pulse duration of about 20 ms for magnetization measurements under high pressure up to 10 kbar. The 70 T magnet for high-pressure experiments has an 18 mm bore and an inductance of about 3 mH. The magnet consists of an inner five-layer coil backed up with a thick maraging steel pipe and the outer has 11 layers and a maraging ring. As the pressure cell used for the measurement is made of Be–Cu, a longer pulse is necessary to allow penetration of the pulsed field into the cell. Magnetization measurements under high pressure have been carried out successfully up to 55 T although the pulse duration is not long enough to keep the temperatures very low. A new pulsed magnet with higher field and longer pulse duration is proposed.

単層ひし形コイルの自己インダクタンスの計算式

単層ひし形コイルの自己インダクタンスの計算式

Circuit theory of video delay lines

Electromagnetic slow waves guided by single-layer coils and video delay lines are studied from the point of view of circuit theory. The main idea is to introduce into the model the mutual inductance that exists between nearby coil turns. This concept leads to finite-difference, finite-sum equations which pass in the limit into a partial differential equation and an integro-differential equation. The capacitance between adjacent wire turns is taken into account. The decrease of inductance at high frequencies, as computed from the integro-differential equations, is compared with prior computations based on electromagnetic field theory. In this respect agreement between the two theories is complete. A comparison with experiment is made, from which a novel parameter of the coil, termed the series capacitance parameter and measured in Fm, is determined.

Characteristics Improvement of A. C. Machines by Single Layer Winding with Short Pitch Effect

Armature winding of a small sized three-phase a. c. machine is preferably used with a single-layered and full pitched coils, in order to reduce manufacturing cost. But, this winding produces a great deal of the higher harmonic components of the magnetic field and causes stray losses, magnetic noises and parasitic torques.This paper proposes the equivalent short pitch winding for the single-layered coils and the characteristics improvement.

Fully integrated magnetically actuated micromachined relays

A fully integrated magnetically actuated micromachined relay has been successfully fabricated and tested. This particular device uses a single-layer coil to actuate a movable upper magnetically responsive platform. The minimum current for actuation was 180 mA, resulting in an actuation power of 33 mW. Devices have been tested which can make and break 1.2 A of current through the relay contacts when the relay is electromagnetically switched. Operational lifetimes in excess of 850000 operations have been observed. Contact resistances as low as 22.4 m/spl Omega/ have been observed under electromagnetic actuation. Magnetic and structural finite-element (FE) simulations have been performed using ANSYS to calculate both the actuation and contact forces.

Circuit properties of coils

Measurements conducted on cylindrical single-layer coils reveal some of their high-frequency properties. A set of measured resonance and antiresonance frequencies is used to determine a series of partial inductances and partial capacitances of a coil, based on Foster&apos;s first form of two-terminal LC networks. Although the procedure departs from most general properties of LC coils, the system of partial capacitances and inductances at low frequencies reduces to coil inductance and self-capacitance. In cases when a coil is operated with one end free, the standard procedure of self-capacitance determination has to be modified accordingly, to take into account the top capacitance of the coil.

Shielding of Low-Frequency Magnetic Interference in Weak-Field MRI by a Single-Layer Cylindrical Coil

Shielding of detection coil from low-frequency magnetic-field interference is one of the main problems in weak-field MRI methods that utilize cycling of main magnetic field (MRI in the Earth's magnetic field, for example). In such cases, the best solution is usually to shield the detection coil by shorting one of the resistive coils of the system, typically the magnetization coil. The optimization of this shielding method has been done by studying the total magnetic field on the axis of a shorted single-layer cylindrical coil placed in a homogeneous oscillating magnetic field parallel to the coil axis. The results are generalized for the case when series impedance is added to the shielding coil. The optimal added impedance that gives the largest shielding factor in the center of the coil is calculated. Because the theoretical treatment is confined to the coil axis, the results are in simple form ready to use in applications. The results of the calculation are verified experimentally and implemented in Earth's field MRI system.

AC losses in multifilamentary Bi-2223/Ag superconducting tapes

In this study we examined AC losses in a multifilamentary Bi-2223/Ag superconducting tape carrying AC transport current. The tape consisting of 85 filaments was helically wound to a single-layer coil. The losses were measured at 77 K in the frequency range from 1 Hz up to 250 Hz. Current amplitudes I/sub p/ were ranging from l=I/sub p//I/sub c/=0.6 to 1.5, critical current I/sub c/=15.4 A determined by the standard 1 /spl mu/V/cm static electric field criterion. The roles of special loss components were considered: hysteresis, flux-creep, coupling and eddy current losses. Hysteresis losses due to the self-field of the AC transport current were found to dominate when l/spl les/1.1. Resistive losses dominated when l>1.2. In the hysteretic regime, the higher the frequency, the smaller the losses per cycle.

Electric field and losses in BSCCO-2223/Ag tapes carrying AC transport current

Electric field and losses in single layer coils wound of 0.75 m long multifilamentary BSCCO-2223/Ag tapes carrying AC transport current have been studied at both 4.2 K and 77 K in the frequency range from 0.01 Hz up to 100 Hz, with the main effort at 50 Hz. Current amplitudes (I/sub p/) ranged from i=I/sub p//I/sub c/=0.5 to 1.3, critical current (I/sub c/) determined by the standard 1 /spl mu/V/cm static electric field criterion. I/sub c/ of coil 1 was 15 A at 4.2 K and 3 A at 77 K. Losses due to the wide resistive transition of the coils were found to dominate over self-field losses even well below i=1. Therefore the total losses in the whole applicable i range could not be described well by equations based on the critical state model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Test of eight superconducting arc quadrupoles for RHIC

Test results from a group of eight superconducting quadrupoles made at Brookhaven National Laboratory are presented. The magnets have been designed for use in the arc regions of the Relativistic Heavy Ion Collider now under construction at Brookhaven. Novel features of the design include a single-layer coil, the use of injection-molded phenolic for the pole spacers, and a yoke that also serves as a collar. This R&D series has been used to verify the magnet quench performance and field quality prior to the start of the production run in industry.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The fabrication of Bi-based superconductor tape by electrophoretic deposition and melt-texturing techniques

A processing technique has been developed for the fabrication of high-current Bi-2212 superconductor tapes. The technique comprises three steps: (i) treating the particulate ceramic superconductor with trichloroacetic acid in 2-butanol to generate a negative charge on the particle surface; (ii) electrophoretic deposition of the particulate ceramic onto an Ag-based substrate and (iii) melt-texturing of the deposit to form a superconductor coating on the substrate. It has been found that the 2212 superconductor can only be melt textured on an Ag substrate in a narrow temperature window around 885 degrees C. Slow cooling from the molten state not only allows the development of superconductor phase texture, but also suffers from the growth of Ca-Cu-O oxides. These oxides can be transformed into 2212 phase by annealing at 850 degrees C. However, the 2212 grains formed from the Ca-Cu-O precipitates are invariably oriented at right angles to the 2212 phase formed in the course of solidification. The presence of such large-angle grain boundaries is detrimental to the superconductor properties. An optimal processing procedure has been proposed and some important processing parameters discussed. A pilot plant has been set up and semi-continuous tape of Bi-2212 superconductor on Ag has been produced. Critical currents as high as 155 A have been measured over a length of 1 m of multilayer coil at 4.2 K. The performance corresponds to a critical current density of about 70000 A cm-2 in the superconductor layer in a self-field up to about 64 mT. The uniformity of Jc measured on adjacent 10 cm lengths in the multilayer coil is much better than that in a single layer coil, about 30% variation in the former compared with 80% in the latter. The results show that electrophoretic tapes have a promising future for integration into small magnet windings.

Study of power coil resonance phenomena based on traveling wave theory

New measurement capabilities allow greater in-depth investigations of the propagation of guided electromagnetic waves inside a coil. Based on numerous measurements of the frequency-dependent conductance and susceptance of various arrangements of cylindrical and disc-type single-layer air-core coils, resonance phenomena of such arrangements, and the main influencing factors, are investigated. The results show dependencies which can be quantified by the application of the theory of traveling waves to the propagation of guided waves in coils. A single method, which is based on the interpretation of real physical phenomena, enables the prediction of the resonance frequencies of all orders. >

Design and optimization of hydrogen cooled pulsed storage inductors for electromagnetic launchers

Experimental results are reported on hydrogen-cooled aluminum cryoresistive coils operating at frequencies greater than 1 Hz. It is shown that eddy current losses due to pulsing are minimized by using single-layer coils. Higher losses of cabled conductors and multilayer coils are caused by self-shielding of each conductor or layer from the AC fields from the other conductors. I/sup 2/R losses for cable is low if the wire size is much smaller than the skin depth (d<<2 mm). High-purity aluminum inductors pulsed at 1 Hz for a few minutes have storage efficiencies greater than 95%. High-modulus-low-density structural materials are required to limit conductor strain and resistivity degradation. Optimization of energy stored per unit mass is discussed, and conceptual designs of 300-MJ hydrogen cooled cryoresistive toroids and solenoids are examined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>