Re: [AMMRL] Coil temp cooling too fast during LNâ‚‚ VT experiments

From: Michael Groves via groups.io <mgrovesnmr=yahoo.com_at_groups.io>
Date: Wed, 17 Dec 2025 14:21:11 +0000 (UTC)

Hi Lenny,

It is my understanding that the main concern at low temperatures is ice build-up,
so if you're blowing dry N2 gas around the shims you should be safe even if
the temperature drops lower than you'd like.  It's just at elevated
temperatures that the epoxy in the shim coil can soften and the shim coils
will tend to move around.  

On the newer Bruker spectrometers there's a ring that goes around the top of
the shim system that replaces the one on the older spectrometers--it's got
a port for a 6mm air line that is used to blow air down around the shim system. 
I'm not sure what your setup looks like but you could install one of those
if you've got one--that might improve the efficiency of the shim gas.  

One other consideration--that function is automatic on the newer Bruker systems
and it tends to use quite a bit of gas.  I don't believe an AVII has a
separate valve for that so you've likely got it set up manually. 
I would recommend cranking the flow up.  You don't want it going full
blast, but try increasing the flow.

That's what I've got.

Cheers,Mike
On Wednesday, December 17, 2025 at 04:19:34 AM MST, Lenny Haddad via groups.io wrote:


Dear all,

I’m running a low-temperature experiment on a Bruker Avance II with
a BBO probe, using LNâ‚‚ VT cooling.

During cooldown, I’m purging/aerating the shim stack with dry N₂
(instead of air) to avoid ice formation. However, the temperature around the
shims drops very quickly and gets down to about 5 °C well before the
sample reaches the target temperature of −70 °C. I’m
a bit concerned about overcooling the shim stack and nearby bore components.

I was wondering if you have any recommendations or best practices for keeping
the shim stack above 0 °C while running low-temperature experiments.

Thank you, 

Best regards, 

Lenny


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Received on Wed Dec 17 2025 - 06:35:51 MST