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CCD Contamination

Status, February 22nd, 2005

The Imager CCD camera is now back at Siding Spring and was used for
observing on the 16th, 17th and 18th February. The data has yet to
be inspected but a cursory glance indicates there may well be some
residual cleaning marks, most easily seen in U and B frames.
These appear as low level, vertical, 'streaky' marks and should
be removed during flat-field exposure processing. All other Detector
characteritics are nominal.

The new GAIN option has now been added to the Cicada release as
a menu option. This permits the observer to change from the default
2.4e/adu to 1.1e/adu system gain - if so required. The noise performance
at each of these settings is about the same, 4e rms.

Status, February 7th, 2005

The Imager Science detector is now operational in the science camera
Early tests indicate that the device has survived in-tact after the
clean at E2V in January. 2 spot QE tests performed last Friday
at 400 and 500 nm show a responsivity of about 90%, indicating that
the AR coating has not been damaged. Similarly a noise test performed
on the detector using the Bias frames from the QE test showed a
read-out noise of about 4.5e rms. Further tests will be performed this
week then the Imager will go back to Siding Spring for observer's use.

The image 'glitching' problem has now also been resolved. The source of
this was due to a routine (IDLE) which is run be default all the time the
detector is being operated - and this routine resulted in a varying amount
of data (CCD lines) being shifted out of the detector after the shutter is closed
and before the CCD READ operation took place. This rountine has been disabled
as it is not required for the E2V CCDs.

Pre and Post-clean images from the E2V CCD

The 1st of the following 2 images was taken just after the contamination occured
and clearly shows the 'spattered' material on the CCD surface. The Images are
zero exposure frames, with the intrenal dewar LEDs illuminated for 80ms, after the
CCD is cleared and just before the CCD is read-out.

JPEG Image showing contamination FITS Image showing contamination

JPEG Image showing Clean surface FITS Image showing Clean surface

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Status, January 31st 2005

The E2V CCD has now arrived back at RSAA and is ready to be mounted in the Imager.
This will happen later this week after the work to seek out the cause of
the current image glitching, i.e. image moving within the frame between exposures,
has been found. Current suspect is related to whether the user requests a
frame to be 'pre-flushed' i.e. cleared of charge, before the exposure takes
place. The problem doesn't occur if the CCD is NOT 'pre-flushed'... Strange...!!!

Status, January 24th 2005

The Imager CCD was DC tested on Friday and passed the room Temp. (RT) test. Paul Jorden is
sending the device back to us today (Monday 24th) and I hope it will arrive late this week -
or early next week. The successful RT DC test almost certainly indicates that the CCD will
image properly. This will be checked out when it arrives here before transport to SS
With this prompt return of the detector - there seems little point in delivering the Imager
to SS with the Engineering CCD - so the head will remain here - pending a re-fit of the
science detector.... -:))

Status, January 21st 2005

The E2V Imager CCD has been DC tested at room temp - and was working ok when it
arrived at E2V. It was cleaned yesterday (Thurs 20th) and then baked out to remove
any water vapour contamination etc. It is due to be room temperature, DC tested again
today - so we should know by Monday whether the CCD has survived the process. If it is
still operational it will be immediately returned to us - so we should have it back by
late next week, or early the following week
Imaging tests will then be performed and the the Dewar returned to SSO as soon as possible
after completion of these tests.

Status, January 19th 2005

The CCD has now reached E2V - but not Paul Jorden. He has stated that once he receives the
device, it will be DC tested (at room temperature), inspected and if possible, with our approval,
cleaned. After this the device will be DC tested (again at RT) - this should confirm the device's
operational state. It will then be returned to us. This should take between 3-4 weeks

The CCD will then have to be installed in the Imager dewar and some imaging tests performed
with the CCD at operating temperature. If all this goes well, the camera can then be returned
to Siding Spring and put back into operational use for observing.
In the meantime, the E2V Engineering CCD is now in the newly cleaned Imager dewar - this is to
be checked out over the next week or so and then a decision made as to whether it is worthwhile
returning the head with the Eng. CCD in it, or to wait return of the Science device

Pictures of Rebuild of E2V Imager Dewar

1. Front of Imager dewar after cleaning.

2. Superinsulation laid out ready to roll onto LN2 can.

3. Superinsulation - 14 layers being rolled onto LN2 can.

4. Final layer of Superinsulation rolled onto LN2 can.

5. Finished LN2 can ready to be installed in Imager dewar body.
Test dewar is stood next to Imager with the Eng grade E2V CCD mounted inside.

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Status, January 11th 2005

A report from Mike Dopita has alerted me to tha fact that the 2.3m Imager dewar has
been subject to some contamination of the CCD.
Small patches of material could be seen in images taken at the 2.3, in a run just before Xmas
This was investiagted and the most likely cause was deemed to be material which has reached the
surface of the CCD from over-driving the getter (molecular sieve) heater at the rear of the dewar
which resulted in the resistor getting too hot and buring both the sieve material and pcb onto
which the getter is mounted.

The 2.3m E2V CCD Imager dewar was therefore returned to RSAA on the 4th January - for inspection.

The dewar was found to be contaminated with material from the getter unit (used to maintain
good vacuum performance. The material in this unit was found to have been severely over-heated
ands has caused a yellow material to be deposied on the internal surfaces in the Dewar.
In consequence, the whole of the dewar will have to be dis-mantled and cleaned in the
Ultra-sonic Iso-proponol bath, to remove all traces of this material, before the original
or another detector is installed

The E2V 4240 CCD was removed from the Imager Dewar on the 6th January and placed in a carton
to be sent back to E2V in the UK. They are going to inspect and cleaning the device - at OUR risk.
The chip will then be returned to RSAA for installation back into the science camera. This will
take a few weeks, at the very least.

In the meantime, the Engineering grade CCD is being characterised, using the new test dewar

Test Dewar on pump.

Close-up of above.

There will be a first cool-down today (11th January) and characterised after which, if found
suitable, will be pressed into service until the science chip is returned.

Pictures of Getter - Rear of E2V Imager Dewar

1. Rear - E2V dewar showing yellow contamination on surfaces.

2. Close-up of above.

3. Getter unit dis-mounted.

4. Close-up of Getter and rear dewar plate.

5. Getter unit being dismantled.

6. Getter material partially burnt.

7. Heater resistor and temp sensor.

8. Close-up of above.

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Enquiries about the E2V Contamination Issue?
detman@mso.anu.edu.au

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