Detector

Again we have had problems with the vacuum of the FIES detector. This seems to be separate from the CryoTiger not always reaching its operating temperature at $\sim$-199$^{\circ}$C, and sometimes getting stuck at $\sim$-160$^{\circ}$C. Recently the detector lost vacuum on 3 consecutive occasions with only a few weeks in between. The sealing of the various fixtures (valve, pressure, CCD window) where improved. Also a problem with the functioning of the vacuum valve was found and it was replaced. These changes did not improve the vacuum behaviour. In was noted that the O-ring of the entrance window to the dewar was slightly too large. The proper size was not clear from the drawing we had, so a large set of O-rings of different size and thickness was purchased and after the last episode of loss of vacuum the ring was recently replaced with a properly fitting one. For the moment the system seems to behave better.

One of the main problems related to the loss of vacuum is that we have to enter the FIES room to install the vacuum pump. The pump generates a significant amount of heat where it takes many hours for the temperature to return to the set temperature and stabilise after we have stopped pumping. This means that although the FIES dewar is relatively small and can be pumped in a few hours, typically more than a day is needed before high-precision radial-velocity observations can be done. To avoid this situation, we are planning to extend the vacuum tube that leads from the pump to the dewar such that the pump can be installed outside of the FIES room, in the front room of the FIES building, avoiding heating up the FIES room. A special hole will be made between the two rooms so this tube can be installed permanently. We also are thinking of installing a remotely operable valve on the FIES dewar so there is no need to enter the FIES room at all when the dewar needs to be pumped

With respect to the bi-stability of the CryoTiger operating temperature, our automatic alarm system has been extended to provide separate warnings when the dewar temperature rises from either the lower or the higher stable temperature.

There has been an extended exchange with E2V about a possible replacement CCD for FIES, where the latest offer looks very attractive considering the price. One issue is the delivery time which is 10 month.