Magnet Specifications

The rated field of each AMI magnet is the field at which the magnet can be operated continuously when immersed in liquid helium at a maximum temperature of 4.2K. Quench fields exceed the rated field in all cases. All standard magnets are tested by AMI in excess of the rated field. Warranted performance at lower temperatures and higher fields can be supplied on special order. Protection from damage in the event of a quench at fields up to and including the rated field is assured by the design and construction of the magnet. Each magnet is warranted against such damage by the standard AMI warranty.

All quoted currents are nominal and may vary slightly from the cited currents in the final magnet. The coil constant which specifies the magnetic field produced per ampere of current is supplied with each magnet. This constant is determined analytically for lower-homogeneity magnets, or by NMR measurements for high-homogeneity magnets.

Persistence of the magnetic field in the persistent mode varies with the inductance of the magnet and the conductor used in its construction. Guaranteed quotations can be provided upon request.

Homogeneities are specified as the maximum deviation from the central field at any point in the specified volume, and are usually quoted over a 1 cm diameter spherical volume. Where required, the homogeneity is verified using a 3 mm diameter NMR probe moved throughout the homogeneous volume.

Custom Magnets

Innovative research requires innovative magnet designs and AMI is noted for its cooperation with users in establishing such custom designs. Our customers frequently combine the functions of two types of magnets into one magnet (nuclear demagnetization and nuclear magnetic resonance), replace conventional magnets with superconducting magnets for increased performance or operational economy (bubble chambers and particle detectors for accelerators), or require special field profiles or configurations not attainable with conventional magnets (gyrotrons and open gradient magnetic separation).

Custom designs are a specialty of AMI and your inquiry is welcome.

Magnet Construction

AMI superconducting magnets are wound using conductors comprised of many filaments of a superconducting material embedded in a copper matrix and twisted along its axis to insure optimum performance of the superconductor. Electrical insulation is provided by the insulation on the wire and by the epoxy between each turn. All magnets are wet wound or vacuum impregnated with an epoxy to assure the absence of voids and to prohibit movement of the wire.

The former on which the magnet is wound is constructed of aluminum, brass, stainless steel, or other material as required for a particular magnet. Micarta end flanges are used on the magnets to provide a rugged, insulated mounting surface. Tapped brass inserts are screwed and epoxied into the end flange for supporting the magnet. Standard mounting holes are tapped for 10-32 threaded rods or screws. Current lugs, protective diodes, and persistent switches are mounted on one end of the magnet.

AMI magnets are overwrapped with a yellow cord to protect the windings from minor shock. The end flanges are painted dark blue and each magnet is stamped with a four digit serial number.

The construction materials and techniques have been employed and proven in hundreds of magnets constructed by AMI and used in applications worldwide.