[GreenKeys] Ebay Listing

[Jones, Douglas W]

On Jun 26, 2015, at 2:53 PM, Jeffrey D Angus wrote:

> I rather large program I worked on had a helium re-liquifier, several
> high pressure storage tanks and a low pressure recover storage tank.
> We were having problems with ice blockages in the re-liquifier.

If you're working with superconducting magnets, ice blockages
can be a significant safety hazard.  My dad had a large
superconducting magnet, with helium re-liquifier system to
keep the dewar cold.  It took about a day with an arc-welding
motor-generator to bring the magnet up to full current, but
once "charged" it could run forever, except ...

Occasionally, due to one or another fault, superconducting
magnets of that ear (early 1970s) would go normal -- that is,
they would cease to superconduct.  The faults typically
involve joints in the wire, as I understand things.

When a portion of the electrical circuit goes normal, it starts
to warm up by ohmic heating.  Warming a superconductor makes
it go normal, so once a spot of the circuit has gone normal,
you get a run-away effect, dumping all the stored energy in the
magnet in very short order.  The liquid helium boils extremely
quickly, and you need a safe place to put it -- typically a
safety valve leads to a large surge tank so you don't lose all
your helium when the magnet goes normal.

The problem my dat had was that the safety valve iced up.  Who
knows when it happened, but when the magnet went normal, the
dewar burst, and the experimental area was filled, rather
suddenly with helium.  The emergency call over the intercom
was made in a Donald Duck voice saying "Magnet went normal."
Fortunately, the only injury was a broken arm, suffered by the
person who released the winch that held the side of the building
closed -- the winch handle spun around and whacked his arm.

		Doug Jones
		jones at cs.uiowa.edu