* Thanks everyone. Here goes the summary.
*
*Carlos.
*
*
*
*Summary on Quenching a Superconducting Magnet *
The magnet that I quenched is a 26 years old Oxford 250 MHz Narrow bore.
The console was an AC250 Bruker with its computer upgraded 10 years ago
to a Tecmag DSPect system.
1)The first question I got from the Spinlanders was whether I was
planning on using the magnet again. If so, I should de-energize the
magnet instead of quenching it.
2)To de-energizing a magnet, if you know what you are doing, you can use
the charge rode, a battery and a bridge of diodes. Now, the problem is
that the operation is still risky, the magnet can quench. It actually
scares me more than the other options. I believe it needs to be
performed by someone with experience in this technique. Also, the Helium
reservoir must be full and then you need to wait for months for the
helium to evaporate.
3)The other two alternatives are: a) leave the magnet until it quenches
by itself or b) provoke the quenching of the magnet.
4)Case b): I thought it was a better to induce the quenching but I
ultimately didn’t feel confident doing it.
5)To induce the quenching: a) it is better if the magnet has no
nitrogen. b) take out the probe and shims stack. c) it is better to do
it when the Helium level is low to very low. d) use nitrogen to fill the
vacuum. e) do not leave exit ports open. Ice can build up and block the
exit ports.
6)Case a), what I did:
a) Until it was two weeks before the minimum filling time, as indicated
in the manual, I kept filling the magnet with nitrogen. The Helium level
gauge was not working, so I couldn’t know the actual He level.
b) I took out the probe and shims stack.
c) When it was two weeks before Helium filling time, I stop the nitrogen
fillings.
d) At this point, I didn’t allow access to the NMR lab. There is another
NMR system in the same room.
e) I put signs on the door. Communicate the issue to the NMR Users, to
the Dept. of Safety and to the people working on the same floor in
proximity to the NMR Lab, including the janitors.
f) I stuck a screw driver to the wall of the magnet in order to know
when the magnetic field was gone.
g) We checked the status of the magnet every day, through the window of
the door.
h) I didn’t notice a huge increase of the Helium flow rate after the
nitrogen reservoir was empty.
i) After two weeks, the magnet quenched. The process was very smooth.
There was frost formed on the top of the magnet, and the screw driver
was on the floor.
j) I noticed that even after the magnet quenched, Helium gas was still
coming out and took around 10 hours for the Helium flow to stop.
One important thing that I was worried about was how much Helium gas
would come out in short period of time. The main reason is that the
magnet is in an internal room without windows.
The way to know this is to compare the volume of the room with the
volume of He gas expected. He gas was calculated as 1 liter liquid ~ 740
L of gas. It turned out that in our case (assuming around 10 liters of
He), the He gas would only occupy less than 1 meter from the ceiling.
Also, I received the report “*Safe Operating Procedure (SOP): *Hazards,
Considerations, and Advice on the Decommissioning of a Superconducting
Magnet*.*Author:Ryan T. McKay and many others”. Although I got it a
little late, I browsed it (couldn’t read it carefully yet…). I think
that it is great. It has all you need to know and more about
decommissioning a magnet:**
Finally, I would like to thanks again all the Spinlanders that answered
my call. Ryan McKay, Simon Barrett, Clemens Anklin, Jerry Hirschinger,
EmericWasielewski, Neil Jacobsen, Robert Scott, Joseph Asta, Jay Shore,
Norman Chu, Phan Viet Minh Tan, Bob Berno, Jon Webb, Philip Dennison,
Jane Strouse.
Special thanks goes to Simon Barrett and Clemens Anklin for answering
all my questions, and to Ryan McKay for sending me the SOP report.
Received on Mon May 23 2016 - 10:21:27 MST