Hello Lenny,
I have 28 years old Bruker Ultrashield magnet (11,7 T) and Avance IIIHD console
after DRX. It was quite common that the shim temperature was around 0 C
(even slightly below). I am using dry air (dew point ~ -30 C) for the “shimcool”
and I do not see any reason to waste LN2. Since there is the temperature
sensor on the shim stack, I would be calm, if temperature is more or less
close to the magnet specs (check it, they may differ).
The shimcool gas flow is controlled by BCU and I suppose that default settings
are more or less OK – it significantly increases flow at extreme
temperatures.
The shim and sample temperature are different since the gas around sample is
taking a complicated way + it is passing the heater as well. This also depends
on the probehead construction.
Well, since I was also feeling uncertain, I bought a heated hose with its own
temperature controller in order deliver warm shimcool gas. But after all, it
has never been tested. And there are definitely some risks of overheating
the shims (with the heated hose) in case of the VT gas cooling failure, etc..
Best regards,
Jan
> From: main_at_ammrl.groups.io On Behalf Of Lenny Haddad via groups.io
> Sent: Wednesday, December 17, 2025 11:19 AM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] Coil temp cooling too fast during LN₂ VT experiments
Dear all,
I’m running a low-temperature experiment on a Bruker Avance II with
a BBO probe, using LN₂ 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 - 07:45:04 MST