American Magnetics AMI Superconducting Magnets User Manual
EXCELLENCE IN MAGNETICS AND CRYOGENICS
A
MI
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 tha t is permane ntly instal led into a cryo stat, the se instruct ions 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 it s axis to insur e optimu m performanc e of the su percon ductor. Elect rical
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 ma gnet is w ound is c onstruct ed of aluminum, br ass, sta inless
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.
1
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 a nd t he magnet can be charged or discharged. After re ach ing 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.
2
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 Magn et Spec ification 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
3
Specifications
Magnet Specification Sheet
magnetic resonance (NMR) tests at 4.2K or by calculation if NMR checks are
not possible.
Rated Current
2.
the rated field.
Maximum Test Field @4.2K
3.
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.
Field-to-Current Ratio
4.
the magnetic fiel d produc ed per amp of magn et curr ent. It is specif i ed in uni ts
of gauss per amp and is generally determined by NMR measurement
techniques.
- The rated current is the magnet current required to achieve
- The maximum test field is the maximum field
- The field-to-current ratio is a number defined to be
Homogeneity
5.
field specified over a specific length or volume.
Measured Inductance
6.
magnet testing using the relationship L = E(
Charging Voltage (used in test)
7.
voltage developed across the magnet during testing at AMI.
Clear Bore
8.
Radial Access
9.
temperature. (Split coil systems only).
Overall Length (flange to flange)
10.
including the end flanges. This dimension excludes the persistent switch and
current lugs if applicable.
Maximum Outside Diameter
11.
Weight
12.
Recommended Persistent Switch Heater Current
13.
persistent swit ch heater current is t he a m ount of current required to gua rantee
the persistent switch is in the resistive state.
- Homogeneity is the maximum field deviation from the rated
- The inductance of the magnet is determined during
- The charging voltage is the maximum
- The minimu m magnet bore diameter at operati ng temperature.
- The minimum magnet radial access diameter at operating
- The measured overall length of the coil
- Maximum outside diameter of the magnet.
- Magnet weight.
dt
/dI).
- The recommended
Persistent Switch He ater Nominal Resistance
14.
nominal resistance is the room temperature resistance of the switch heater.
4
- The persisten t switch heater
Specifications
Magnet Specification Sheet
Magnet Resistance in Parallel with Switch
15.
with switch is the room temperature resistance of the magnet windings and
the switch in parallel.
Mounting Holes
16.
method and geometry.
- Magnet resistance in parallel
- The mounting hole specification is the magnet mounting
5
Specifications
Magnet Specification Sheet
6
Table of Contents
Specifications........................................................................................ 3
1 Installation............................................................................................9
Unpack the magnet..........................................................................................9
Setup ................................................................................................................9
Cooldown.......................................................................................................12
Instrumentation and control check.................................................................13
System setup..................................................................................................14
2 Operation............................................................................................15
Energizing the magnet...................................................................................15
Magnet persistent operation (if applicable)...................................................16
Returning from persistent operation..............................................................1 6
Deenergizing the magnet...............................................................................17
System shutdown...........................................................................................17
3 Troubleshooting.................................................................................19
Magnet not charging............................................................................19
Voltage developed across magnet but magnet field less
than predicted..........................................................................20
Magnet discharges when attempting to enter persistent mode ............20
Magnet quenches lower than rated field..............................................20
4 Warranty/Return Authorization......................................................21
Return Authorization.....................................................................................21
Index....................................................................................................23
7
Loading...