CryoTigers

We still experience occasional problems with the CryoTigers. We had recurrent problems with the FIES detector heating up and losing vacuum. As described in the last report, we tried various things with the dewar of the FIES detector to improve its holding time. In the end it was found that replacing the compressor of the CryoTiger solved the problems, with the dewar temperature and pressure staying at significantly lower values than before. For StanCam we also saw some episodes where both the detector temperature and pressure would go up (we do not have dewar temperature reading), but after some time (a few hours at most) the temperature and pressure would go down again. As the vacuum can not recuperate by itself we concluded it is actually the dewar temperature that rises and falls. Again, this pointed to the CryoTiger where the idea was that the cold head would occasionally get blocked. The cold head was cleaned by reversing the flow of the cooling gas for a few hours simply swapping the hoses. Since that time the detector temperature and pressure have behaved normally.

It was noted that the StanCam CryoTiger is aging while the FIES CryoTiger has already been partly replaced and we are looking at the option to replace some broken parts, or buy a full new system as a complete spare.