Dewar

We have had recurring problems with the dewar warming up and losing vacuum. One of the problems is that we do not have a proper pressure sensor, and it is not easy to decide if the problem is a true loss of vacuum, or a problem with the cooling, leading to warming-up and increasing pressure. The dewar was refurbished from the vacuum point of view. Most of the O-rings were replaced. At the first try, the dewar could not hold the vacuum properly, so all the O-rings were cleaned and re-installed. When changing the O-rings, it was found that some of the O-rings were not the precise size as given in the documentation, so not all could be replaced. Proper O-rings were purchased, but have not been installed yet. It is still also not clear if the cooling system might have caused some of the problems, and a full cleaning of the cooling system with nitrogen gas, and a refill with the cooling gas might be needed if the dewar warms-up and losses vacuum again.