Here we provide some information that may be useful for MR laboratory managers during the restrictions imposed by the Covid-19 pandemic (we are grateful to Bruker Biospin for providing this information)
Recommendations regarding Magnet Maintenance Activities during the COVID-19 Pandemic (Bruker UK)
We understand that during the coming weeks many of our customers may have significant concerns relating to their ability to maintain their spectrometers particularly with regards to Cryogen refills and especially where Site Closure or Access Restrictions are being considered.
We are maintaining close communication with our Helium suppliers and have been assured that at present no difficulties with the provision of deliveries is foreseen. Regular updates are being made with regard to the changing situation. We would advise all our customers to maintain contact with their Helium and Nitrogen supplier throughout the coming period.
If restricted access is being considered at your installation site we strongly recommend that arrangements are considered to provide essential maintenance refill activities for your spectrometers with respect to both Liquid Nitrogen and Helium Refill. Please discuss the situation directly with your site management or facilities provider to ensure that these tasks can be completed. We would recommend all customers consider any upcoming Nitrogen and Helium refill requirements and plan accordingly.
If the magnet cannot be filled with Liquid N2 due to lack of supply or access, the magnet will eventually run dry. Because of this, the Liquid He boil-off will subsequently increase, and when this happens there may be seen condensation on the helium towers.
The Liquid Helium boil-off rate in this situation cannot be quantified as there are many factors that control this, however it will be abnormally high and once the Liquid Helium level reaches the minimum allowed level an uncontrolled quench is very likely to occur.
Therefore, it is essential to do everything possible to maintain an adequate Liquid N2 level. Most magnets will have a two week hold time, some even longer. Although we would normally recommend a weekly fill this can be extended in unusual circumstances to the maximum hold time (please consult the manual supplied with your magnet).
An uncontrolled quench is not a situation that is recommended, because although there are protection components built into the magnet, there is always a small possibility of damage to the magnet in this event. It is therefore imperative to maintain adequate Nitrogen and Helium levels within the magnet
If it is envisaged that a Liquid Nitrogen or Helium level cannot be maintained, a controlled de-energisation of the magnet performed by a trained Bruker engineer should be considered (see further notes below). In this circumstance the magnet would be de-energised and left under vacuum, ready for re-installation at some later date. Please bear in mind that to safely de-energise the magnet it would need to be at least 80% full of Liquid Helium (please consult the manual supplied with your magnet to obtain a precise ‘minimum allowed level for (de)-energising’).
Our engineering team remain available during the coming period and can be reached via our Helpdesk in case of need for further advice or concern (email : service.bbio.uk@bruker.com, phone: 02476 855333).
Magnet de-energising or potential for quench
The following information has been provided by Carl Bridge (Bruker UK) regarding procedures to follow should you be faced with a potential magnet quench, or indeed if a magnet is de-energised in a controlled fashion.
"If anyone is actually considering leaving their systems unattended for any particular lengthy period of time (i.e weeks), whether energised or de-energised they should consider removing the lower shimcoil and probe from the magnet. Should a quench occur and/or the cryogens eventually boil away the magnet bore will ice as the vacuum becomes soft (some condensation will also form on the outer dewar of the magnet but that is not really a problem).
This bore ice will eventually melt and obviously that is not good for the shimcoil and probe. Leaving a plastic bucket or waste paper bin or suchlike under the magnet bore will collect any water and prevent carpet tile staining or a slip hazard etc...if the magnet is energised, obviously don't use a metal receptacle!
For an energised magnet, they should consider closing the lower magnet bore opening with a large rubber bung or similar in order to prevent anything magnetic ending up in the bore. Other people have used a square of sturdy thick plastic gaffa taped to the underside over the opening as an alternative. Obviously the bung or taped plastic should not seal the bore. Water should be capable of draining out of the bore. Do not tape the whole edges of the plastic sheet and/or consider drilling several small holes into the sheet prior to mounting. If using a rubber bung, cut a few small channels into the sides of the bung to allow water to escape.
The idea of the bung or plastic is to prevent larger items such as screwdrivers, spanners etc from being pulled into the bore. Holes in the plastic or channels in the bungs should not be made to a size that would be big enough to allow for example a 1/2” screw or paper clip to pass through.
If people do find small items have been pulled in like this it is not such a major issue but a spanner or screwdriver most definitely is.
I guess a lot of people will then ask how to remove the shimcoil........hopefully most forum members can answer that (3 screw's at the top of upper shimcoil etc). But one thing to mention is that newer shimcoils that have demountable cables...cables should removed after powering down the BSMS (if not done as part of powering off the console).
Another question might arise due to the lower shim clamp (same colour as the shimcoil base).....this should be loosened (horizontal allen screws) if there is a tight fit, prior to sliding the shim coil down partially to allow access to the screws that retain the clamp on the magnet (vertical allen screws) and then removing the coil and clamp as one (this is the safest way to do it without potentially damaging the coil) - if the clamp is not loosened and is still a little tight it can be that the upper end of the coil which is slightly wider goes tighter in the clamp and then some people might try to twist the coil out of the clamp to extract it further (that is not good - don't do it!)
Systems with cryoprobes have a slightly different arrangement due to the mounting hardware. You will notice that the front side of the horizontal part of the mounting hardware is capable of being loosened (again there are allen screws)
There should be non-magnetic allen keys provided with every system (check blue spares boxes etc.....)
If they are in any doubt about removing the shimcoil they should at least be removing the probe and the shimcoil can be left but bear in mind damage to the shimcoil could occur if ice forms and it is not recommended to leave it mounted.
Never, ever, ever attempt to undo the allen bolts on the black plates that surround the magnet bore - don't be confused! - that will release the magnet vacuum!"
