Hi Rainer,
I have a couple of thoughts. Are any of the shims drifting significantly while
the main field is changing? There are several cryoshims that couple to the main
field and perhaps they are drifting and this is moving the main field higher as
a side effect. (Z2 maybe?)
And they measured the same helium level for a year? Hopefully they were still
filling at the usual intervals. Naively I would have expected them to do
something after a week or 2 of the level measuring the same. At this point if
it’s really been a year then I agree they’ve likely got plenty of ice.
This could just have been an o-ring that failed and if they had done something
early on they might have been able to fix the problem.
Regarding expinstall, the software thinks it’s smart and if it doesn’t
think you can do a specific experiment then it doesn’t keep it after converting
it. If your routing isn’t complete, and if in the RF routing in edprobe you
don’t have the 2H preamp connected to the 2H connector on the probe then
expinstall will erase those parameter sets. That’s most likely the cause
of that issue. And it doesn’t use the files in the par directory when it
does expinstall. It starts with the ones in par.avance and edits them and puts them
in par. Instead of using expinstall for user parameter sets use paracon. That will
let you point at the parameter sets you want to change and update them. Note—if
you run paracon it will set all the pulse powers to 0W because that’s a
“feature.”
Cheers,
Mike
> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of Platz Hirsch
> Sent: Thursday, April 11, 2024 8:39 AM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] Field drift /expinstall
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 - 10:57:57 MST