Detector

Again, we got similar problems as before with the temperature of the CryoTiger and the detector. It was suspected that the vacuum seals of the dewar were not made to precision, possibly leading to vacuum problems that causes the CryoTiger to no longer be able to maintain the temperature of the cold head as the required capacity increases, which in the long run also causes the detector temperature to rise.

The front flange, entrance window and ring, the mounting for the pressure sensor and the pressure valve, and the right-angled pipe connecting the valve to the main vessel were all dis-assembled. Some scratches were found under the O-rings which were polished, cleaned with acetone and baked in the oven. The vacuum connectors for the valve and sensor were modified such that they can no longer turn and the sensor was electrically isolated so it does not introduce pick-up noise. Despite all these changes no direct improvement was found in the dewar temperature reached by the CryoTiger though the detector did stabilise at its normal reference value. In the mean time the dewar temperature has dropped to close to -200 degrees Celsius which is the normal temperature to be reached by the CryoTiger, though a jump up by 5 degrees and later down by 5 degrees was also noted.

As part of our investigations some extra technical drawings of the FIES dewar were obtained from Copenhagen and additional photos were made of the detector, dis-assembled dewar, fiber-shutter train, and the fiber shaker (see above), and all were added to our documentation pages.