Could this be the result of the Z0 cryoshim quenching?
On Thu, Apr 11, 2024, 12:16 PM Platz Hirsch <ammrl_at_haessner.com> wrote:
> Hi,
>
> although retired since about 5 years, there are nice challenges from time
> to time.
>
> The recent one within my former university gave me some questions.
>
> ==========
> Equipment
> ==========
>
> unshielded 360 MHz magnet, discharged to 300 MHz about 10 years ago
> helium level (dipstick measured): about 80%
> AV III console
> Windows workstation running TopSpin 3.2
>
> ==========
> Magnet behaviour
> ==========
>
> Since about one year, the helium level meter always shows the same value.
>
> To make the story short, with very high probability a lot of air condensed
> within the magnet,
>
> maybe due to a broken sealing.
>
> Now the magnet began to drift with about 100 Hz/hour.
>
> Very bad, presumably an ice bridge between one of the joints and a warmer
> part of the cryostate, but, of course, I am not sure.
>
> But now the unexpected things began ...
>
> ==========
> Drift direction
> ==========
>
> The magnetic field increases! It was possible to get the spectrometer back
> to operation by increasing the base frequency by 100 MHz (from 300.13 to 300.23) using cf.
>
> ==========
> TopShim
> ==========
>
> After changing the base frequency the data sets have to be corrected using
> expinstall.
>
> This works perfect for nearly all data sets stored within
>
> .../exp/stan/nmr/par
>
> with the exception of topshim1d2H.
>
> This data set becomes *deleted*. Tried to manually install a copy from
> par.AVANCE, but running
>
> expinstall again to configure the parameters deletes this data set again.
> Only this one, nothing else.
> The data set for topshim1d1h is fine and produces the expected results.
> Didn't test the 3D data set.
>
> ==========
> user defined data sets
> ==========
>
> For ICON-NMR these are stored within
>
> .../exp/stan/nmr/par/user
>
> expinstall doesn't touch these data sets. I tried a dirty trick and moved
> one data set from
>
> .../par/user
>
> to
>
> .../par
>
> but even in this case the user defined data set remains unchanged doing
> expinstall.
>
> I fear, the magnet is lost. Nevertheless I am very interested to
> understand this unexpected drift behaviour.
>
> Greetings
>
> Rainer
>
>
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Received on Thu Apr 11 2024 - 10:52:11 MST