Detector

FIES documentation

- a new type of trouble was documented: condensation on the FIES CCD. This happened twice now, while pumping the CCD.

- 12 May 2014: the FIES dewar vacuum had been slowly and gradualy rising, and a pumping cycle was planned, also because the cryoTiger needs to be refurbished to allow the filter to be refreshed. GC+PB swapped the cryoTiger compressor for a brand new one. They also replaced a damaged supply hose.

It took some time and effort to get the new cryoTiger going, some flushing of the coolhead was done. Additionally, the vaccuum ducting of the pump was failing. The cryoTiger was finally working on 16/5.

Apparently, the above pumping trouble introduced condensation on the CCD. Similar to what was seen in the flatfields obtained after the Oct 2013 pumping, a much stronger pattern in the extracted flats was evident. The pattern does not change when looking at flats from day to day. A new warm pumping cycle was executed 26-28 May, after which the pattern was gone.

- A new chip has been ordered. This chip has 15-micron pixels and is physically 10% bigger then the current chip, which allows to sample the wavelength range of 370-830nm insteaf of currently 370-730nm. The chip is a low-fringing device and has high QE in the indicated band pass. The CCD awaits testing and assembly in and by Copenhaguen

- A new dewar for FIES is under construction in Copenhaguen. The new dewar is necessary to accompany the new CCD controller. With the new controller the read-out times should go down from 90 sec to about 30 sec per frame.

There were two occasions in which the FIES dewar needed to be pumped. Based on feedback from an observer, the first of these pumping introduced a fixed high-frequency ripple pattern clearly seen in the summed flat field frames. The ripple pattern resembled additional but constant-in-time spacial pixel-to-pixel response variations, and could be fully removed as part of a standard reduction. After the second time the dewar was pumped the ripple pattern had disappeared again.

The CryoTiger compressor used for the FIES detector has an inbuilt filter, and the compressor will need to be send back to the supplier to allow for a regular filter change. A spare compressor is available to cover this period.