Hi Tianzhi,
actually the liquid nitrogen doesn't flow upward in these Oxford dual-helium
reservoir (2 K/4 K) magnets: The actual nitrogen dewar is only located in the
lower half of the magnet (with the 2 K helium dewar inside) and the upper 4K
refill dewar has only a shield tube thermally attached to the nitrogen vessel
below. So the liquid nitrogen goes "down" like in other magnets from these
tilted refill necks. In the same way the nitrogen exhaust also exits upwards
from the same point half-way up the magnet.
What still may make a removal of ice blocks difficult though is that the nitrogen
neck has a flexible tube inside (to which then an approx. 20 cm straight tube is
welded which is then attached to the refill neck). This flexible section then
bends down by an about 45 degree angle and is welded to the nitrogen dewar at
that angle. You should definitely not remove an ice blockage by mechanical means
(poking with a stick)!! Always use a thin tube to flow warm nitrogen gas onto
the ice blockage until it melts and flies out in form of droplets.
Best regards
Bert
> Am 03.04.2026 um 22:33 schrieb Wang, Tianzhi via groups.io:
>
> Hi, Luke
>
> Thank you for your helpful suggestions.
>
> In our system, the nitrogen filling and vent port are located in the middle
> of the magnet (see attached picture), rather than at the top. As I understand
> it, liquid nitrogen flows upward into the nitrogen vessel through the fill
> line, while nitrogen gas returns through the top and exits via the middle port.
>
> Because of this configuration, it is very difficult to remove a possible ice
> blockage using conventional approaches.
>
> I would greatly appreciate any further advice or shared experience on how to
> safely address this type of blockage in such a setup.
>
> Best,
> Tianzhi
> <image.png>
> -------------------------------------------------------------------
> Tianzhi Wang, Ph. D.
> NMR Manager
> Sealy center for Structural Biology & Molecular Biophysics
> University of Texas Medical Branch,
> 301 University Bvld, NMR dockside building, Rom 1.104
> Galveston, TX 77555-1157
> Email: tiawang_at_utmb.edu <mailto:tiawang_at_utmb.edu>
> (409)7476821 (O)
>
Selling & buying used NMR equipment (all vendors)
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Received on Sat Apr 18 2026 - 17:48:43 MST