Material suited for fixing leakage in liquid nitrogen dewar

[Mikakadu]

0

I need to fix a leak on the inside of a liquid nitrogen dewar which acts as the coolant tank for a spectroscopy CCD camera. Due to the design of the camera, I unfortunately can only access the inside of the dewar via its bottleneck. Since the dewar is permanently connected to the camera body, the only idea I could come up with is spraying the inside with a material that hardens afterward, hoping to hit the leak in the process and therefore sealing it while also not depositing too much material. I roughly sketched the idea.

Let's suppose the dewar is made out of aluminum. Which material would be suitable to be sprayed onto the inside, adhering well to the aluminum after hardening and can be expected to withstand rapid temperature changes and low temperatures (-200 °C) over long periods of time?

Side note: I know this idea is sketchy, but we need to get this camera back running as soon as possible and are already working on replacing it in the near future.

 

[rb1957]

how big is the leak ? Can you live with it ?? (keep refilling the LN)

You can't see the leak ?? I'd've thought that a sizable leak would be readily apparent.
Is it leaking from the interface with the camera ??

If it's leaking from the body of the cylinder, can you patch with adhesive metal tape (like we have for car exhaust repairs) ?

If you spray "stuff" in the dewar, how do you keep it away from the camera ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[IRstuff]

I think the camera is technically outside of the Dewar interior like below. In general Dewars cannot be disassembled, since its mechanical integrity is what keeps the vacuum from leaking.

Have you vacuum leak tested the Dewar?

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[Mikakadu]

We don't know the size of the leak, but I suspect it to be more of a hairline crack. Since the dewar is permanently connected to the camera's casing, we can't take it out and our only access to the inside is via the bottleneck where we usually refill the nitrogen. Just refilling nitrogen does not help by the way because the dewar must be surrounded by a pressure < 7e-3 mbar. This means currently there is a vacuum pump attached to the camera pumping gases away between the dewar and the casing. With this crack, we can only maintain such a pressure for about 15 hours while continuously pumping. Without leakage, concurrent pumping would not be required. See image for more information on the camera's construction

 

[Mikakadu]

We have tested for leaks and all connections on the outside seemed to be functional. When we put the helium tube through the liquid nitrogen filler neck however, the pressure increased significantly

 

[IRstuff]

Have you contacted the manufacturer? Some have repair services.

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I can do absolutely anything. I'm an expert!

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[Mikakadu]

We try to quickly (even if not professionally) repair it ouselves because we already ordered a new one but need some more time until its integrated properly