The COROT CCDs irradiation bench.
During the filght the CCDs are under radiation due to proton traped in the radiation belts. To measure the proton effects we planed to irradiate 3 chips at the Louvain synchroton facilities (Belgium). For that dutie we developped a specific test bench using the BCC2000 readout electronic.

Different characteristics are measured before and after the irradiation as : gain, dark current and quantum efficiency (relative pixel to pixel, the famous PRNU!!) and 4 different temperatures (-35°C, -20°C, 5°C and 25°C). During the irradiation on chip will be under working and so we will see the intantaneous effect of the proton hit (ionisation).

Long itegration time is needed to achieved high mesurment precision : better than 0.1% for both dark current and PRNU.

The CCD under test are the 4210 Marconi chip, a full frame 2k*0.5k pixel, backthinned and AIMO, comming from the flight model wafer.

Some pictures of the test bench installed near the photometric test bench, under the different sheats there're a CCD and optic stimuli!!

And here (left) a zoom on the most interesting part of the bench.

A box attached at one of the input port of the sphere contains LEDs to illuminated the CCD. We have 3 wavelenghts : 470, 640 et 880nm and a white LED (near blackbody spectrum).

The 4210 CCD has only one output (only one input at the front end electronic).

The 3 differents wavelenght are used to measure the PRNU in the blue, red and near IR part of the usefull optical bandwith.

The withe LED is used to measure the gain.

A mechanical shutter is hand installed to avoid stray light during long time exposure (dark measurement at low temperature).

And now the optical fiber path from the bench to the control/command center!!
The results of the 3 tested CCDs and the reference CCD (a 4280 measured in the 300K cryostat).
Acces to the results.

The first CCD named Reshep with the serial number 9234-06-01 ---> Results before and after.

The second CCD named Anhour with the serial number 9293-01-05 ---> Results before and after.

The third CCD named Mout with the serial number 9234-01-01 ---> Results before and after.

The reference CCD, Qadesh is a 4280 ---> No difference seen.

See proton hits here.

Synthesis of the results :

Experimental tests.

The following characteristics are measured before irradiation :

  • Working point at 20°C.
  • Gain at different temperatures.
  • Dark current at different temperatures (all pixels and binned mode readout).
  • PRNU at different temperatures for 3 wavelenghts.

At the Louvain synchotron facilities 3 CCDs have been irradiated under the following conditions :

  • Energy of the protons : windows with different thickness allow different proton energy (30, 40 and 60Mev).
  • Integrated dose : 4krad. Applied in four times with a flux of 107 protons/s/cm2, fluence of 109/3.109/5.109/10.109

All the CCDs were red during the test at normal rate (1 image / 17 seconds), two at ambient temperature (around 20°C) and one at -40°C. Dark images were taken before, during and after the different tests.

First CCD under test, Reshep : measured at ambient temperature, the total dose is applied in four times, readed during the irradiation. Image are taken after each dose application. Protons of : 30 and 60MeV.

Second CCD under test, Anhour : measured at ambient temperature, the total dose is applied in four times, readed during the irradiation. Image are taken after each dose application. Protons of : 40 and 60MeV.

Third CCD under test, Mout : measured at low temperature (-35°C) under vaccum, the total dose is applied in four times, readed during the irradiation. The proton flux is reduced to the minimum acheivable and some image are takend during the proton hits. After the test the CCD is thermaly cycling (-35°C to 20°C in different steps) to measure some improvement on the different defects at -35°C. Protons of : 30 and 50MeV.

The lower proton energy is always applied on the left part of the CCD.

After irradiation we will measured the modification (if there're!!) of the following characteristics :

  • Mean dark current and big defect occurence.
  • Gain, Full Well Capacity and CTE.
  • Working point (bias voltage shift).
  • PRNU at the three wavelenghts.
  • Time serie of dark pixel : Random Telegraph Signal.