D. Bruce Montgomery

A new magnet system for 'intravascular navigation'.

Channels such as blood vessels may provide a valuable means of access to parts of the body otherwise inaccessible except by major surgery. The system described here uses the field gradient to a large, movable electromagnet to propel and guide a small permanent magnet through such channels. The permanent magnet may incorporate or tow any of a number of minute diagnostic or therapeutic devices. A flexible catheter may be attached to conduct fluids to or from the tip and to provide additional control.SommaireLes vaisseaux sanguins se présentent comme des voies d’accès possibles à certaines parties du corps inaccessibles autrement que par une intervention chirurgicale importante. Le système décrit ici utilise le champ d’un grand électro-aimant convenablement orienté, guidant un petit aimant permanent, à travers les vaisseaux sanguines. L’aimant permanent peut être tracteur ou porteur d’un certain nombre d’éléments de diagnostic ou de thérapeutique. On peut y attacher un cathéter flexible qui facilite le guidage et permet l’injection de liquide.ZusammenfassungKanäle wie die Blutgefäße können eine wertvolle Möglichkeit bieten, Körperteile zu erreichen, die sonst nur durch große Chirurgie zu erreichen sind. Das hier beschriebene System benutzt den Feldgradienten eines großen, geeignet befestigten Elektromagneten, un einen kleinen Dauermagneten duchr derartige Kanäle zu führen. Der Dauermagnet kann hinter sich (oder kann selbst eingebaut werden in) jede gewünschte Zahl kleinster diagnosticher oder therapeutischer Geräte tragen. Ein flexibler Katheter kann befestigt werden, wenn Flüssigkeiten an die Spitze geleitet werden sollen, und wenn zusätzliche Führung gewünscht ist.

The generation of high magnetic fields

The generation of high magnetic fields by means of water-cooled magnets, iron magnets, pulsed magnets, cryogenic magnets and superconducting magnets is discussed. Relationships between currents, fields, power, magnetic stresses, cooling requirements and field homogeneity are presented in detail. Fabrication techniques, power supplies and specific magnet constructions are discussed. Reference is made to nearly 100 papers giving more detail on specific subjects.

Magnetic Forces for Medical Applications

The force that a magnetic field gradient can exert on a ferromagnetic material can be utilized in a number of medical applications. This force is proportional to the spatial gradient of the ambient magnetic field times the magnetic moment of the material; the magnetic moment is a function of the magnitude of the ambient field and the geometry and material used. This paper discusses the importance of each of these factors and discusses methods for calculating magnetic fields and gradients produced by permanent magnets, electromagnets, and superconducting magnets. Examples of an electromagnet and a superconducting magnet for medical applications are presented.

CURRENT-CARRYING CAPACITY OF SUPERCONDUCTING Nb-Zr SOLENOIDS

Explanation of the discrepancy between Nb -- Zr short sample tests and solenoid performance and prediction of the current carrying capacity of Nb -- Zr solenoids are based on the mechanism of induced persistent-eddy currents. Study of residual fields following reduction of magnetic field strength to zero leads to assumptions permitting calculations of circulating current magnitudes. Data are presented graphically, and generation of the same field using less material is found to result from spreading out layers or turns. (D.C.W.)

Generation of Intense Magnetic Fields

The advent of high‐field superconducting magnets has made magnetic fields above 30 kG available to the entire scientific community. Small diameter coils to 60 kG cost considerably less than conventional 12‐in. iron magnet systems. Fields to 80 kG, and in a few recent instances to 100 kG, even in multicentimeter bores, are now economically within the reach of most research budgets. The current and future status of superconducting magnets, their economic advantages and associated problems are presented. Other methods of generating fields, such as water‐cooled continuous magnets, millisecond pulse magnets, and long‐pulse cryogenic magnets, will find their principal use in reaching even higher fields, supplementing superconducting magnets, or in circumventing problems which preclude the use of superconductors. Pulse magnets are presented as a relatively simple and inexpensive method of producing millisecond fields up to 500 kG and long pulses to 250 kG. Relationships between energy, time, and volume are given...

Insulator flashover mechanism in vacuum insulated cryocables

This paper describes research on vacuum insulated cryocables for underground power transmission. It deals particularly with the flashover mechanism observed on solid dielectric conductor supports in vacuum. The insulators were protected by ion shields. The work revealed the important role played by gas and vapor absorbed on dielectric surfaces bridging the high voltage gap. Photographic evidence proved that an early link in the chain of breakdown events is a gas discharge (short mean free path) in the absorbed layer. Gas layer breakdown also offers explanations for the beneficial effects of ion shields with regard to breakdown voltage and protection against arc damage. With the help of high voltage capacitors it has been established that ion shielded, inorganic insulators will survive the discharge of all electrostatically stored energy in a long cable. This is an important requirement for high voltage conditioning. The paper contains the first published photograph of a Lichtenberg discharge in vacuum.

The generation of continuous fields: Future prospects

Abstract It is presently possible to generate a continuous field of 30 T by combining an outer superconducting coil with a 10 MW inner water-cooled coil. Using superconductors alone it has been possible to generate 17.5 T and a 20 T coil has been proposed for construction in the nearterm future. Far beyond these accomplishments lie the measured upper-critical fields of the yet untried superconductors, some in excess of 50 T. This paper examines what we may expect in the future for superconducting and hybrid systems, and compares these truly continuous field systems with systems generating quasi-continuous long pulses.

High-strength conductors for supermagnets

With the introduction of powerful magnets such as the National Magnet Laboratorys 225-kG device that recently went into continuous operation, it has become necessary to consider the structural problems that arise because of the high stresses-and high temperatures-involved in generating these high fields. Primarily, a magnet material must be provided that possesses strength as well as porosity. Various combinations of ETP copper, steel, beryllium-copper, and zirconium-copper have proved effective. Also, it is pointed out that stresses can be reduced by proper arrangement of the coils, and that there is an advantage to using high-strength materials in stress-limited magnets despite their increased resistivity.

High power vacuum insulated LN 2 cryocable loop

Economic studies1 have indicated that vacuum insulated, liquid nitrogen cooled, underground transmission lines have the best prospect of becoming competitive with overhead transmission. The cost comparison shown in Figure 1 has been prepared from these data.