1. WSO/UV World Space Observatory / Ultraviolet Project
Detectors for the FCU
WSO/UV World Space Observatory / Ultraviolet Project
Michela Uslenghi
INAF/IASF Milano
WSO/UV Italian web site:

2. Outline Overview of the Field Camera Unit UVO Detector CCD FEE
NUV & FUV Detectors
Requirements
Selection process
Baseline architecture
MCP intensifier
Readout system
R&D
Leicester, December
WSO Detector Workshop

3. Imager requirements Large wavelength coverage (115-700 nm)
Large field of view
High spatial resolution
Morphological studies (e.g. planets, planetary nebulae, star formation regions, external galaxies)
High accuracy stellar photometry
High accuracy stellar astrometry
Resolve stars in crowded fields (e.g. in star clusters, external galaxies, star formation in AGNs)
High time resolution in the UV
Leicester, December
WSO Detector Workshop

4. Science requirements for the FCU camera
Parameter
Channel
Far-UV
Near-UV
UV-Optical
Spectral Range nm nm nm
Field of View
6.6’x6.6’
1’x1’
4.7’x4.7’
Scale
0.2”/pix
0.06”/pix
0.07”/pix
Pixel Size
20m
15m
Array Size
2kx2k
4kx4k
Detector
MCP (CsI)
MCP (CsTe)
CCD (UV optimized)
Leicester, December
WSO Detector Workshop

5. FCU Layout WSO Detector Workshop Leicester, December 3-5 2007
NUV Channel
FUV Channel
UVO Channel
Leicester, December
WSO Detector Workshop

6. Mechanical Design WSO Detector Workshop Leicester, December 3-5 2007
UVO Channel
Detector
UVO Filter Wheel
Baffles
Enclosure
Fore Optics
FCU Optical Bench
S/C Optical Bench
NUV Channel
Detector
NUV Filter Wheel
Baffle
Enclosure
Enclosure
FUV Filter Wheel
Detector
FUV Channel
Leicester, December
WSO Detector Workshop

7. Operational Modes Imaging (FUV, NUV, UVO)
Slitless spectroscopy (FUV, NUV, UVO)
Polarimetry (NUV, UVO)
Slitless spectro-polarimetry (NUV)
High Temporal Resolution Modes
Time Tag (MCP)
Windowing (CCD, MCP)
Leicester, December
WSO Detector Workshop

8. UVO Detector The UVO channel will extend from UV to visual wavelengths
The pixel scale of this channel is a compromise between the need of a large field of view and high spatial resolution.
Filters, dispersers and polarizers  narrow and broad band imaging, low resolution (R ~ ) slitless spectroscopy and imaging polarimetry.
Single CCD detector optimized for the UV wavelength range.
Leicester, December
WSO Detector Workshop

9. UVO CCD
CCD device back illuminated with AR coating optimized in the UV range.
4k  4k pixels
Pixel size will 15 m square
Exposures will be split in sub exposures with integration times ≤ minutes (due to cosmic ray contamination)  requirement on the dark current rate of 20 e–/pix/hr.
Leicester, December
WSO Detector Workshop

10. E2V CCD231-84 UVO channel CCD detector preliminary functional
Quantity
Required
Goal
Pixel size
15 x 15 microns
Array Size
4096 x 4096 pixels
Package size
70 mm x 70mm
65mm x 65mm
Surface Flatness (peak to valley)
 20
Dark current rate, e–/pixel/hour
 15
Readout 200 kHz (e– rms)
4.0
3.0
Linearity over 70% of full well capacity
1.0%
0.1%
Full Well Capacity (image area), electrons
Full Well Capacity (register area), electrons
275000
850000
350000
Wavelength Range
200 – 700 nm
200 – 900 nm
DQE Stability over 1 month (peak to peak)
5.0%
1.0%
Charge Transfer Efficiency (Parallel & Serial)  
Flat Field Non-uniformity Limit (1)
 5.0%
 3.0%
Flat Field Stability Limit, peak-to-peak over one month
0.5%
Black & White Spots (pixels)
800
400
Maximum number of Column Defects 5
Traps
10
Operating Temperature, C
–952
UVO channel CCD detector
preliminary functional
requirements
Leicester, December
WSO Detector Workshop

11. UVO detector package assembly (preliminary design)
Main components will be:
a baseplate.
a mounting support for the CCD
the CCD detector
a cover
a flat quartz window and optical baffles.
The baseplate will have holes for connectors and will host getter pumps to provide long term pumping against residual outgassing products.
There will be no FEE inside the package assembly. The FEE will be accommodated on the backside of the baseplate. Hermetic feedthroughs connectors will ensure electrical continuity between the CCD and the FEE PCB/ASIC.
Leicester, December
WSO Detector Workshop

12. Full Frame Readout Time (sec)
CCD Readout
Full Frame Readout Time (sec)
Outputs
100 kHz
200 kHz
500kHz 1
168 84 32 2 42 16 4 21 8
Operative modes:
Windowing: selection of a set of fixed sub-array apertures and user-defined sub-arrays
Binning: 2x2, 3x3, 4x4
Gain: to fully exploit the CCD well capacity the controller must allow the selection of different gains
Leicester, December
WSO Detector Workshop

13. UVO CCD electronics system
Timing Board: Commands CCD exposures. Generates TTL level clocks for the CCD timing pattern. Generates biases digital data.
Clock Driver: translate the TTL level clocks to CCD clock voltages and send them to the CCD.
Bias Generator / Analog Signal Processing: translate the biases digital data generating the bias voltages to operate the CCD. Digitize the signal from the CCD outputs to 16-bit accuracy.
Low Noise Preamps: receive the signal from each of the CCD outputs and send it to the analog signal processing board.
Leicester, December
WSO Detector Workshop

14. Requirements for NUV&FUV detectors
Parameter
FUV
NUV
Array size
2048x2048
Active area 
40 mm
Pixel size
20 µm
Spectral range nm nm QE
> nm
> nm
Time resolution
≤20 ms
LDR
≥20 counts/s
GDR
≥2*105 counts/s
Leicester, December
WSO Detector Workshop

15. Some considerations on detector choice
Directions from the science team: the more important characteristic is the spatial resolution (in particular for the NUV)
Very short WSO schedule: no R&D
Looking for something available now. Delivery time should fit the schedule
Avoid (if possible) ITAR
Leicester, December
WSO Detector Workshop

16. Baseline configuration of the UV detectors
PC-ICCD
Photocathode
2-3 stages MCP intensifier
Phosphor screen
Fiber Optic taper
High speed CCD camera
Real time digital electronics unit
Leicester, December
WSO Detector Workshop

17. FUV & NUV Detectors
FUV & NUV Channel: MCP-based detector in sealed configuration
Format: 2kx2k (40mm)
Read-out system: CCD
Photocathodes: CsI (FUV), Cs2Te (NUV)
Leicester, December
WSO Detector Workshop

18. Photek 40 mm
Leicester, December
WSO Detector Workshop

19. MCP intensifier MCP 2-stages (Chevron) Diameter 40 mm
Pore size m (12 m)
L/D I 50:1
II 80:1
Gain 5•105 e-
Pulse Height Distribution (PHD) <125% FWHM
PHD spatial variation <10% peak-to-peak
Dark 20C <1 counts/cm2s
Photocathode CsTe/CsI
Window MgF2
Phosphor screen P46
Sealed configuration
Leicester, December
WSO Detector Workshop

20. Photocathodes
Leicester, December
WSO Detector Workshop

21. CsI Photocathode DQE for the CsI coated ACS SBC MCP Photek data
Semitrasparent vs opaque photocathode
Leicester, December
WSO Detector Workshop

22. CCD Readout sensor Sarnoff VCCD-512 Format 512 x 512 pixels
Pixel size 18 x 18 m2
Architecture Splitted FT
Full well 240,000 e-
Fill factor 100%
N. of output Ampl. 16
Readout frequency 10 MHz (per amplifier)
Frame rate frames/s
Require:
4x centroid subpixel resolution
Leicester, December
WSO Detector Workshop

23. PC-ICCD Electronics Overview
The detector electronics include two main blocks:
an Analog Front-End Electronics (AFEE), an high speed front-end CCD electronics
a Digital Front-End Electronics (DFEE) with a real time data processing unit, which will acquire the data from the CCD camera, search for the photon events and computes the coordinates of the detected photons with sub-pixel accuracy
Filters for the High Voltage Power Supply should also be located close to the detectors.
ICU
Leicester, December
WSO Detector Workshop

24. DFEE: data processing and centroiding
The DFEE will acquire serially the CCD digitized output signals + sync signals (frame, line and pixel sync), reorder them (if required), and subdivide the frame in sub-regions to be analyzed by parallel processors, each one implementing the following tasks:
through a proper system of delays, the processor will generate 33 pixel windows that sweep dynamically the whole matrix to be analyzed at the pace of the pixel clock;
on each window:
check, according to appropriate discrimination and pile-up rejection criteria, for the presence of a charge distribution representing a photon event;
compute the centroid coordinates with a centre of gravity algorithm to the charge distribution in the current window and correcting for systematic errors.
All the operations should be done in real time  no limits should be introduced by the electronics on the dynamic range
 implementation in FPGA, adopting a pipeline architecture in order to process the data at the rate they are generated by the sensor
Leicester, December
WSO Detector Workshop

25. System Overview
Leicester, December
WSO Detector Workshop

26. Local Dynamic Range
Leicester, December
WSO Detector Workshop

27. LDR translated to magnitudes …
Low limit:
High limit:
V Johnson
Range: 8.9 magnitudes
Leicester, December
WSO Detector Workshop

28. UV detectors data flux SDMU
The DFEE produces a 32-bit word for each detected photon, with the x,y,t coordinates (plus “amplitude”, used for monitoring). These words are sent, via Spacewire interface to the ICU. Operative mode (science + calibration) are (software) implemented in the ICU
At least two operative modes (+windowing) will be implemented for science observations:
time tag mode: photon list {x,y,t} is sent to the SDCU and then to ground. Data rate depends on the flux of incoming photons (which in turn depends on filters and sources in the field)
accumulation mode: before sending them to the SDCU, counts are accumulated by the ICU in an array in which each element correspond to a pixel, eventually producing a CCD-like image  limit data rate by loosing time information, allowing exposures with high count rate.
Leicester, December
WSO Detector Workshop

29. Model Philosophy (Moscow)
Our proposal:
Bread Boards (not deliverable)
Structural Thermal Model (deliverable, should be returned)
Optical Bench
Mass dummies
Thermal dummies
Engineering Model (deliverable)
Mock-up optics and detectors
Functional representative of the flight model at Bus functional I/F level
Optical Bench: Initially could be a plate to be replaced by OB when performing EMC tests or bus mechanical/functional integration tests.
Flight Model (deliverable)
WSO-UV plans
Full Scale Model – MSM (May 2008)
Mass Model + Structural Model
Thermal Equivalent – TM (Jan 2009)
Technological Model – EM (Jan 2009)
Instrumentation Flight Set Model – FM (May 2009)
Leicester, December
WSO Detector Workshop

30. Previous R&D on photon counting detectors

31. PC-ICCD for ground-based astronomy
Leicester, December
WSO Detector Workshop

32. PC-ICCD characteristics
Array Size
2048  2048 pixel (1)
2048  512 pixel (2)
Pixel Size
13.5  13.5 m2
Spatial Resolution
 25 m 550 nm
 30 m 254 nm
Time Resolution
16.8 ms (1)
4.512 ms (2)
Detective Quantum Efficiency (DQE)
8.2% @ 229 nm
6.8% @ 254 nm
Visible Light DQE
405 nm
Spectral Range (DQE  1%) nm
Dark Count Rate
1.74 cts s-1cm-2
Local Dynamic Range (DQE loss < 10 %)
13 cts s-1 (1)
54 cts s-1 (2)
Global Dynamic Range (DQE loss < 10 %)
cts cm-2 s (1)
cts cm-2 s (2)
Leicester, December
WSO Detector Workshop

33. Spatial Resolution Readout system: FWHMx~ 5 m
Front MCP pore structure fully resolved
Detector:
FWHMx~ 25 5500Å
limited by proximity focus
Leicester, December
WSO Detector Workshop

34. Dynamic Range 10% fractional count rate loss: Local:
13 full frame
54 window
Global:
2.6·104cts cm-2 s-1
9.2·104cts cm-2 s-1
Leicester, December
WSO Detector Workshop

35. Asiago-Cima Ekar
182 cm Telescope + AFOSC (3 filter wheels allowing combination of: photometric filters, grisms, Echelle grisms, polarimeter based on a double Wollaston prism)
 High speed Photometry & spectroscopy of CV & Flare stars
Leicester, December
WSO Detector Workshop

36. Crab Pulsar PFFT=0.0334881±1.5·10-7 s PEF=0.033488256±8·10-9 s
Leicester, December
WSO Detector Workshop

37. 1WGA
Leicester, December
WSO Detector Workshop

38. PC-IAPS 1024x1024 pixel 1024 8-bit ADC on chip (one for each column)
Objective Holder
Electronic Board
CMOS - APS
Light Tight
MCP
Lens Objective HV
Connector
1024x1024 pixel
bit ADC on chip (one for each column)
8 parallel outputs
Up to 500 frame/s full frame (+windowing)
Leicester, December
WSO Detector Workshop

39. PC-IAPS FEE Board
The APS is mounted on a 10 cm x 10 cm PCB board, which also hosts the driving electronics, the real time data processing unit and the interfaces to the host PC. The core of the electronics is a single FPGA, XILINX XCV 800 (800 Kgates equivalent), allowing a very compact design.
Leicester, December
WSO Detector Workshop

40. PC-IAPS FEE Overview
At each clock pulse, the 64 bits data output (8 pixels x 8-bit) are acquired by the data processor.
Synchronous FIFO are used as delay line that allows a concurrent sampling of a pixel together with its nearest neighbors.
Upon initialization, a set of D-Latches is used to map 8 windows of 3x3 pixels, which covers dynamically the whole APS image at the pace of the pixel clock. This allows the whole APS frame to be analyzed, avoiding problems of either fixed or dynamic image partitioning.
The processing system performs in parallel the following tasks on each window:
 Check (discrimination and pile-up rejection criteria) for the presence of a photon event;
 compute the centroid coordinates and transfer them to a PC.
Leicester, December
WSO Detector Workshop