One of the Research and Development projects
currently underway is the Bio-Med magnet.
Destined for use within the solenoidal field of an MRI, it is designed
for use where the subject, in this case a rat, must be tracked in order
to obtain an image. Typical MRIs require the subject to remain
stationary, and a rat will not normally oblige when it is awake. By
moving the composite field (MRI Solenoid plus Bio-Med dipole) to track
the rat, it is possible to allow the rat some freedom of motion, while
still imaging the brain functions.
For the rapid movement typical of a rat, the Bio-Med coil magnet must be
capable of very rapid changes in field. Superconducting magnets are
typically not designed to allow rapid field variations. To do so
typically causes the superconductor to quench, a condition which heats
the superconductors, ending the superconducting state and forcing the
magnet to be turned off.
One of the issues with such rapid field changes is the generation of
heat within metals subjected to such field changes. The rapidly changing
field is capable of generating kilowatts of heat within a stainless
support tube normally used to support the coil. For this reason, the
Bio-Med coils are manufactured on a G-10 composite tube. All associated
construction materials also need to be non-conducting for the same
reason. Figure 1 shows the first completed test coil set. The G-10 tube
is clearly visible.
Figure 1
Figure 2
To wind the coils, an 11 axis, computer controlled
winding machine is used. The machine affords the physicist the
flexibility of designing any coil pattern needed, and the manufacturing
techniques provide the rigidity necessary to combat the electromagnetic
forces that result when the magnet is powered. Figures 2 and 3 show the
Bio-Med coil being wound on the computer controlled winder. Also visible
is the end lead, which exits the coil at the pole. Figure 4 shows the
completed first dipole layer, still mounted to the wiring machine.
Figure 3
Figure 4
Presently, a dipole/skew dipole coil pair has been
fabricated and tested for function at high currents and moderate field
change rates. The next round of tests will be at 50 Hertz. So far, the
coils have followed predicted operation.
For more information contact
John Escallier
