Hi,
I second your warning. Many systems already have ports to which nitrogen or
dry gas can be used to purge the bore area of moist air. In the absence of
anything better, try hooking up the LN2 blowoff with a rubber line to the
shim purge port see if that's enough to eliminate moisture if you find any.
Regards - Gerry
From: Rainer Haessner [mailto:rainer.haessner_at_tum.de]
Sent: Saturday, September 22, 2012 2:59 AM
To: ammrl_at_ammrl.org
Subject: AMMRL: shim systems of high field magnets
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 Mon Sep 24 2012 - 09:37:20 MST