my magnet is possessed--concluded
David Vander Velde (dave@kunmr.chem.ukans.edu)
Thu, 4 Feb 1999 13:45:29 -0600 (CST)
The cause of a severe magnet vacuum problem I described earlier has turned
out to be blunt trauma. I have learned a couple of things en route, maybe
obvious in hindsight, but I think worth passing along.
It took a magnet engineer from Cryomag about two minutes to find the
problem--an impact point near the bottom of the magnet, something big and
heavy enough to chip the paint off the R2-D2 magnet, and more importantly,
enough to crack the aluminum outer shell and admit air into the vacuum
space. The spot was smaller than a match head. There were several more
small chipped paint spots in a trail leading down toward floor level, as
if the object had bounced a few times. There was no visible break in the
aluminum, but the helium leak detector left no doubt that that was the
spot. Presumably, this happened during some construction (removal of a
wall) right next to the magnet.
The Cryomag guy, Robert, mentioned a couple of things that I will
paraphrase as "Robert's Rules of Disorder (for magnets)":
1. If you are looking for magnet damage, look at the bottom. This was my
mistake; being tall, I minutely examined the top (where I was) as soon as
we saw the boiloff problem, but didn't crawl under the magnet to look
behind and underneath (where the problem was). If you picture your field
lines centering more than halfway down the magnet, and imagine e.g. a
crowbar moving under the combined influences of gravity and magnetism,
this is kind of obvious. Also, objects may bounce once off the floor and
then up to the bottom of the magnet.
2. You wouldn't believe how common it is for people to mess around with
magnets just for the fun of it. While I have no reason to believe that's
what happened to our magnet, when we looked at the damage on site, the
foreman of the remodeling crew (who was none too happy) commented, "That
would almost have to be deliberate." I chose not to respond ... but you
could imagine that your dire warnings about what the magnet can do could
inspire some people to try some informal crowbar, pipe wrench, etc.
levitation experiments when nobody was looking.
3. Whenever possible, be in the room when work is being done around the
magnet. This would have been a double challenge for me in this case,
because some of the work was asbestos abatement, and I was in San
Francisco at the time. But it's worth considering the idea that somebody,
even if it's not you, should be close enough to prevent either accidental
or deliberate approach to the magnet with ferromagnetic objects.
In this case, we were apparently fortunate enough to get the leak
fixed with a portable arc welder. And our facilities department is
picking up the entire repair bill, even though we could not prove it was
their fault.
Hope to see some of you at the ENC,
Dave Vander Velde, University of Kansas