A Cautionary Tale
RDUDLEY (rdudley@ARSERRC.Gov)
Wed, 30 Apr 1997 14:44:46 -0500 (EST)
Greetings,
We keep accurate records of Helium Fills and Nitrogen fills on our
magnets. Only one magnet lets us measure the 'actual' helium level, the others
require us to monitor gas flow levels. Recently we had a Preventative
Maintenance visit from the company that we have our service contract with.
When they asked if we had any problems, I mentioned that the helium hold time
appeared to be down. The field however did not appear to be drifting and the
shims appeared to be stable. We agreed that I should continue monitoring the
magnet.
Well, as you can guess the magnet quenched three weeks later.
Fortunately, or unfortunately, it occurred over the weekend. I am not sure
what could have been done to prevent the magnet quench but the important lesson
is that the magnet boil off rates and hold times should be carefully monitored.
Looking at our log we realized that the hold time had been slowly decreasing
for a number of months, but only during the past couple of months had it been
so dramatic as to be noticeable.
I have reviewed the logs of the other two magnets and they seem to be
behaving normally. The bottom line is that one should spend a few minutes
reviewing the log books for five or six months to determine if there are
problems with the magnets.
Bob Dudley
Proud Owner :-( of a quenched 300 widebore magnet.