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18-01-2006, 11:07 AM posted to uk.rec.gardening

The message
from (Nick Maclaren) contains these words:
In article ,
Rusty Hinge 2 wrote:

For an even stronger effect, take several miles of niobium wire and wind
on a hollow core so as to produce an axial field.

Seal windings in a case, and introduce liquid nitrogen.

When the temperature of the windings has equalised with the liquid
nitrogen, their electrical resistance disappears, and a current can be
maintained by only overcoming the back-e.m.f. of the system.

Oh, really? I think that you have the wrong gas :-)

I don't *THINK* so, though it was a long time ago. I think we supplied
all the niobium for one accelerator - I'm not sure if it was linea or a
torus, but ISTR it was for the torus in Culham Laboratory.

It might have been liquid helium - can't unforget now.

Whatever it was, it was cold. (We 'made' helium, oxygen, nitrogen,
hydrogen etc too.)

High-temperature superconductivity hasn't yet reached the liquid
nitrogen stage - it will make a BIG difference if and when it does,
as the cost differential between liquid helium and liquid nitrogen
is large. Liquid hydrogen is intermediate, but a slight fire and
explosion risk ....

Don't I know it?

Not liquid hydrogen, but hydrogen generated in a big bank of NiFe
accumulators was used to feed our furnace. One day it blew back, and the
fuel was burning between the inside and outside skins, and I was in the
works fire brigade.

Bit of a brown trouser job really: the hydrogen couldn't be cut off
because the hydrogen/air ratio would have decreased until an explosive
mixture was reached, and in those conditions, i.e., rather hot, there's
nothing that will put burning hydrogen out except perhaps, steam. Our
fire chief decided that since our fire engine didn't carry steam hoses
there was only one thing for it: carbon dioxide.

While that is reduced by hydrogen to carbon monoxide, the plan was to
cool the interior by the sudden expansion of the gas, and this worked -
fortunately. Everyone donned asbestos suits and one at a time, we
entered the furnace, released as much carbon dioxide as possible for as
long as we could bear, (a matter of a few seconds - the temperature was
well into four figures centigrade) retreated, to be replaced by the next
one.

All the time we were expecting the thing to blow...

But, I'm living proof that it didn't.

--
Rusty
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