Hi Lingchao,
Phil is right, it is better to have control over when the magnet quenches. That way you can ensure that the immediate area is safe when the quench happens. We quenched an identical magnet in Durham a couple of years ago without any problems. There are a few additional points I would make.
1) Make sure that the lab is clear of non-essential personnel. Despite the obvious attraction of the spectacle you don’t want the lab full of bystanders, just in case something unexpected happens and you want to get out of there quickly.
2) Make sure you have adequate ventilation. It looks like you have a quench tube installed (which is good) but you should still open as many windows as possible.
3) remove the top bungs (as though you were going to do a helium fill) immediately before you quench the magnet. That way, you are not relying on the bursting disk to let the helium gas out.
4) Check that the area that your quench tube vents into is suitable/unoccupied. You don’t want someone working next to the quench tube outlet when you quench the magnet! Keep in mind that the quench tube outlet has been there for years and (hopefully) never done anything, so people have become used to it and don’t expect anything to come out of it!
5) The best way to initiate the quench is to open the vacuum valve slightly (it is underneath the magnet) and bleed some helium gas into the vacuum space. You need to use helium gas because anything else will just freeze solid on the inner surface of the vacuum space. Once you have some helium gas in there, the helium boil-off rate will go up rapidly and when the level of liquid gets low enough, the magnet will quench. Given that you are scrapping the magnet, the nitrogen level is irrelevant.
Please note that the above comments are based on personal experience. They are not a foolproof, approved, guaranteed safe way of carrying out the procedure. So, if you are really not confident with what you are doing, you may want to see if you can get some assistance from a third party service organisation.
Good luck!
Alan
> On 7 Mar 2018, at 03:06, Philip Dennison <dennison_at_uci.edu> wrote:
>
> 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
>
Received on Tue Mar 06 2018 - 23:02:29 MST