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EXCELLENCE IN MAGNETICS AND CRYOGENICS
AMI
AMI SUPERCONDUCTING MAGNETS
INSTALLATION, OPERATION, AND
MAINTENANCE INSTRUCTIONS
American Magnetics, Inc.
PO Box 2509, 112 Flint Road, Oak Ridge, TN 37831-2509, Tel: 865 482-1056, Fax: 865 482-5472
Rev. 4, September 1996
Introduction
These instructions are written to be generic and apply to most of the various types of magnets supplied by AMI. Some sections and data may or may not apply to the system you have purchased. It is recommended that you carefully read these instructions prior to the installation and operation of your magnet system. If you have purchased a magnet that is permanently installed into a cryostat, these instructions will generally be supplemented by operating instructions provided by the cryostat manufacturer.
Magnet Construction
AMI superconducting magnets are typically 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 typically used on the magnets to provide a rugged, insulated mounting surface. When required, tapped brass inserts are screwed and epoxied into the end flange for supporting the magnet. Standard mounting holes are tapped for threaded rods or screws. Current lugs, protective diodes, and a persistent switch are typically mounted on one end of the magnet.
AMI magnets are typically over-wrapped with a yellow cord to protect the windings from minor shock. The end flanges are painted dark blue and each magnet is labeled with a unique four digit serial number.
Specifications
A Magnet Specification Sheet is provided with each magnet after it has been tested at AMI. All stated currents are nominal and may vary slightly from the cited currents in the final magnet application. The coil constant which specifies the magnetic field produced per ampere of current is supplied with each magnet.
Magnet Protection
All AMI magnets are designed and constructed such that in the unlikely event of a quench at fields up to and including the rated field, damage will not occur to the magnet. Each magnet is warranted against such damage by the standard AMI warranty. AMI magnets are not warranted if operated above the rated field.
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Introduction
Persistent Mode
After it has been energized, a superconducting magnet can be operated in the persistent mode by short circuiting the magnet with a superconductor. This is accomplished by connecting a section of superconducting wire contained in the persistent switch across the terminals of the magnet. This section of superconductor can be heated to drive it into the resistive state so a voltage can be established across the terminals and the magnet can be charged or discharged. After reaching the desired field, the heater is turned off and the magnet is shorted by the switch.
Maintenance
AMI magnets are designed and constructed so as to provide years of useful service and require no maintenance if installed and operated in accordance with these instructions.
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Specifications
The above diagram is an example of a typical Magnet Specification Sheet. The specifications for the magnet are mailed to the customer and a copy is included with the magnet shipment.
The following is an explanation of typical magnet specification parameters as they appear on the Magnet Specification Sheet. Some specifications are unique to a particular magnet type and the data may not appear on your sheet or additional data may be added as appropriate.
1.Rated Field @4.2K - The rated field is the maximum field the magnet is guaranteed to achieve and be protected. The rated field is verified by nuclear
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Specifications
Magnet Specification Sheet
magnetic resonance (NMR) tests at 4.2K or by calculation if NMR checks are not possible.
2.Rated Current - The rated current is the magnet current required to achieve the rated field.
3.Maximum Test Field @4.2K - The maximum test field is the maximum field achieved during AMI testing. The magnet is not warranted for operation at the maximum test field. AMI performs the test to insure the magnet is of good design and construction and will operate properly at rated field.
Caution
!
AMI magnets are not warranted for operation above rated field.
4.Field-to-Current Ratio - The field-to-current ratio is a number defined to be the magnetic field produced per amp of magnet current. It is specified in units of gauss per amp and is generally determined by NMR measurement techniques.
5.Homogeneity - Homogeneity is the maximum field deviation from the rated field specified over a specific length or volume.
6.Measured Inductance - The inductance of the magnet is determined during magnet testing using the relationship L = E(dt/dI).
7.Charging Voltage (used in test) - The charging voltage is the maximum voltage developed across the magnet during testing at AMI.
8.Clear Bore - The minimum magnet bore diameter at operating temperature.
9.Radial Access - The minimum magnet radial access diameter at operating temperature. (Split coil systems only).
10.Overall Length (flange to flange) - The measured overall length of the coil including the end flanges. This dimension excludes the persistent switch and current lugs if applicable.
11.Maximum Outside Diameter - Maximum outside diameter of the magnet.
12.Weight - Magnet weight.
13.Recommended Persistent Switch Heater Current - The recommended persistent switch heater current is the amount of current required to guarantee the persistent switch is in the resistive state.
14.Persistent Switch Heater Nominal Resistance - The persistent switch heater nominal resistance is the room temperature resistance of the switch heater.
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Specifications
Magnet Specification Sheet
15.Magnet Resistance in Parallel with Switch - Magnet resistance in parallel with switch is the room temperature resistance of the magnet windings and the switch in parallel.
16.Mounting Holes - The mounting hole specification is the magnet mounting method and geometry.
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Specifications
Magnet Specification Sheet
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Table of Contents |
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|
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Specifications ........................................................................................ |
3 |
1 |
Installation ............................................................................................ |
9 |
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Unpack the magnet .......................................................................................... |
9 |
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Setup ................................................................................................................ |
9 |
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Cooldown....................................................................................................... |
12 |
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Instrumentation and control check................................................................. |
13 |
|
System setup .................................................................................................. |
14 |
2 |
Operation ............................................................................................ |
15 |
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Energizing the magnet ................................................................................... |
15 |
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Magnet persistent operation (if applicable) ................................................... |
16 |
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Returning from persistent operation .............................................................. |
16 |
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Deenergizing the magnet ............................................................................... |
17 |
|
System shutdown ........................................................................................... |
17 |
3 |
Troubleshooting ................................................................................. |
19 |
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Magnet not charging ............................................................................ |
19 |
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Voltage developed across magnet but magnet field less |
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than predicted.......................................................................... |
20 |
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Magnet discharges when attempting to enter persistent mode ............ |
20 |
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Magnet quenches lower than rated field .............................................. |
20 |
4 |
Warranty/Return Authorization ...................................................... |
21 |
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Return Authorization ..................................................................................... |
21 |
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Index.................................................................................................... |
23 |
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