-------- Original Message --------
Subject: RE: AMMRL: quench a horizontal magnet
From: "Hirschinger, Jerry D" <
jerryh56_at_purdue.edu>
Date: Wed, March 07, 2018 11:38 am
To: ammrl <
ammrl_at_ammrl.org>
Sorry Phil, but I beg to differ. Cracking the vacuum on a live magnet is NOT a good idea. Loss of vacuum results in masses of water condensing on the outside. Quenching will freeze that water, and can interfere with operation of the quench relief valves. Blocking the exhaust of a quenching magnet makes a bomb.
To speed up a dry quench, you must blow out the cryogens through a siphon tube. Thick-walled polyethylene tubing can reach the bottom of the LN2 can. The LHe transfer line, or the magnet L-tube can reach the bottom of the LHe can by way of the siphon cone. If they are sealed well, the boiloff pressure will push out the liquid, or you can use the appropriate pusher gas. Do NOT use N2 to push out LHe.
After the magnet quenches, then the vacuum can be released, but beware this will make a great wet mess in the lab from water condensation. The mess can be avoided by warming the magnet, using the same siphon tubes to inject warm gas into the bottom of the cans. Again, do NOT use N2 to warm the LHe can until the magnet temperature is above 77K.
Be SAFE out there! -Hirsch
Jerry Hirschinger, NMR Instrumentation Specialist
Purdue Interdepartmental NMR Facility
560 Oval Dr. West Lafayette, IN 47907-2084
Office: Wetherill 365A
Phone / Fax: (765) 494-5288 / 494-0239
Cellular: (765) 427-3034
-----Original Message-----
From: Philip Dennison [
mailto:dennison_at_uci.edu]
Sent: Tuesday, March 6, 2018 10:06 PM
To: Lingchao Zhu <
lzhu_at_chem.wisc.edu>; ammrl <
ammrl_at_ammrl.org>
Subject: Re: AMMRL: quench a horizontal magnet
On 20180306 11:41, Lingchao Zhu wrote:
> Hello AMMRL,
>
> We have an old Thermo LTQ FT Ultra Mass spectrometer waiting for its
> retirement. *(Model: Finnigan LTQ FT Serial No: SN06036F)* It has a
> horizontal Oxford magnet*(Part No: AJH0280)* and we are not going to
> reuse this magnet. We don't have any magnet book or charging rod of it.
> According to the student in the lab, it has 7T magnetic field.
>
> Without too much information from the lab, we decide to dry-quench
> this magnet, meaning we will let the cryogen boiloff itself to induce
> a quench. I have following questions to ask and would appreciate any
> input from AMMRL community:
>
> 1. Should we let the liquid nitrogen go dry completely first and then
> waiting for all liquid helium boiloff? Or we need to keep filling
> liquid nitrogen until the liquid helium level is low then stop filling
> liquid nitrogen? Which way is safer?
> 2. Please see the attached photo for top part of this magnet. It has
> helium exhaust port built on top of it so when quench happens all the
> helium gas will blow out through this big pipe. Anything we need to
> check before the quench happens?
> 3. Any other important notes before the quench? We will definitely
> block the lab room when the cryogen is low.
>
> Thank you.
>
> Lingchao
>
Hi Lingchao,
Do you have the ability to open the vacuum space of the magnet? If you can do that when the cryogens get low, a quench will happen fairly quickly. That way you can have some control over the quench timing.
If you have anyone interested in re-using the magnet, then dry nitrogen gas is the best way, otherwise it won't matter.
Regards,
Phil.
--
Dr Phil Dennison
NMR Facility Director (949)824-6010 (office)
Department of Chemistry (949)824-5649 (lab)
University of California (949)824-8571 (fax)
Irvine, CA 92697-2025
dennison_at_uci.edu
USA