Hi,
Recently we found a heavily damaged shim system of our 900 MHz system.
I am writing here, because the reason is very simple and I have the feeling the same
thing might happen anywhere else using high field magnets. Maybe it's a good idea
to have a closer look.
What happened?
Very simple. The inner bore of the magnet is cold. That's due to the fact, that the thermal
isolation is by no means as good as to the outer parts of the cryostate. Simply due to
the spatial restrictions.
Depending on the air conditions, water might condense there. Water drops down and
below is the base plate of the shim system. All the wires leading to the shim coils are welded
to this base plate. Water drops rinsing between the welding points cause electrolysis.
After a given time the copper changes to copper oxid and you loose the connection.
A repair seems to be senseless. We tried, but restoring one welding point destroyed two others,
which apparently were partially destroyed.
I believe it could be a good idea to have a look for water between the bottom of the magnet and
The base plate of the shim system.
Have a nice weekend
Rainer
Received on Fri Sep 21 2012 - 22:58:35 MST