1. PACS IIDR 01/02 Mar 2001 Instrument Overview1 PACS Instrument Design Description and System Performance A. Poglitsch

2. PACS IIDR 01/02 Mar 2001 Instrument Overview2 Science Requirements Summarized in PACS Science Requirements Document Main scientific drivers –Investigations of the distant universe: galaxy formation and evolution - history of star formation and nuclear activity –Studies of star formation and the origin of the Initial Mass Function in our own Galaxy –Physics and chemistry of the interstellar medium, Galactic and extragalactic –Giant planets and the history of the Solar System Required observing capabilities –Imaging photometry in 3 bands in the 60 - 210µm range with requirements on sensitivity per detector and field of view –Imaging line spectroscopy in the 60 - 210µm (goal: 55 - 210µm) range with requirements on sensitivity per detector, spectral resolution and instantaneous bandwidth, and field of view

3. PACS IIDR 01/02 Mar 2001 Instrument Overview3 Instrument Requirements Summarized in PACS Instrument Requirements Document High-level requirements on design, performance, and operation of PACS instrument Two basic instrument modes/channels –Imaging photometry –Imaging line spectroscopy Optimization / trade-off for prime science objectives –definition of requirements which enable minimum mission –definition of goals which enhance the performance to strengthen the science of the mission Minimization of risk and complexity

4. PACS IIDR 01/02 Mar 2001 Instrument Overview4 Photometer Requirements Photometric bands with relative bandwidth  <2 Field of view and pixel scale note: equal f.o.v. in both bands is nearly a requirement Image quality –blur: telescope limited; distortion: ±1 pixel; alignment: <1/3 pixel

5. PACS IIDR 01/02 Mar 2001 Instrument Overview5 Photometer Requirements Sensitivity (point source detection) –requirement: 5 mJy (5  ), 1h of integration –goal: 3 mJy (5  ), 1h of integration Dynamic range –detection from 3 mJy to >1000 Jy (goal: 3000 Jy) –contrast of up to 1:500 in one field Post-detection bandwidth –requirement: 0.5 - 5 Hz –goal: 0.05 - 5 Hz Observing modes –pointed observations (fixed, raster) with chopping/nodding –line scans without chopping –line scans with chopping (fixed throw)

6. PACS IIDR 01/02 Mar 2001 Instrument Overview6 Photometer Requirements Calibration and photometric accuracy

7. PACS IIDR 01/02 Mar 2001 Instrument Overview7 Spectrometer Requirements Spectral coverage –57 - 210µm –goal: continuous, no gaps Resolving power –R = 1000 - 2000 Instantaneous bandwidth –  v = 1000 - 2000 km/s Field of view and pixel scale –5 x 5 pixels –9”x9” ±10% pixel scale Image Quality –blur: telescope limited; distortion: ±1 pixel; alignment: <1/4 pixel

8. PACS IIDR 01/02 Mar 2001 Instrument Overview8 Spectrometer Requirements Sensitivity (point source detection) –requirement: 3x10 -18 W/Hz 1/2 (5  ), 1h of integration –goal: 2x10 -18 W/Hz 1/2 (5  ), 1h of integration Dynamic range –detection from ~1x10 -18 W to >10 -13 W –contrast of up to 1:100 (t.b.c.) in one field Post-detection bandwidth –requirement: 5 Hz –goal: 10 Hz Observing modes –line spectroscopy (line + baseline/continuum) chopped unchopped, with frequency switching –range spectroscopy (scan of arbitrary wavelength range); chopped

9. PACS IIDR 01/02 Mar 2001 Instrument Overview9 Spectrometer Requirements Calibration and photometric accuracy Spectrometer implementation –integral-field grating spectrometer –photoconductive detectors –only concept which can fulfill all requirements

10. PACS IIDR 01/02 Mar 2001 Instrument Overview10 Instrument Concept Imaging photometry –two bands simultaneously (60-90 or 90-130 µm and 130-210 µm) with dichroic beam splitter –two filled bolometer arrays (32x16 and 64x32 pixels) –point source detection limit ~3 mJy (5 , 1h) Integral field line spectroscopy –range 57 - 210 µm with 5x5 pixels, image slicer, and long-slit grating spectrograph (R ~ 1500) –two 16x25 Ge:Ga photoconductor arrays (stressed/unstressed) –point source detection limit 2…8 x 10 -18 W/m 2 (5 , 1h) Focal Plane Footprint

11. PACS IIDR 01/02 Mar 2001 Instrument Overview11 Definition of the FOV for the Photometer Physical pixel size: 0.75 x 0.75 mm 2

12. PACS IIDR 01/02 Mar 2001 Instrument Overview12 Definition of the FOV for the Spectrometer 47” sampling Pixel scale has to be a compromise –small number of spatial pixels limits field of view –diffraction introduced by image slicer does not allow full sampling –large wavelength range requires compromise Physical optics analysis shows that 9.4”/pixel gives low enough diffraction losses (15% at 175 µm) with acceptable spatial resolution/ Full spatial sampling in the long- slightly offset pointings wave band with two,

13. PACS IIDR 01/02 Mar 2001 Instrument Overview13 0.78 x 0.78 arcmin 2 3.5 x 3.0 arcmin 2 PACS Design: Focal Plane Footprint

14. PACS IIDR 01/02 Mar 2001 Instrument Overview14 FPU Functional Groups Common input optics –filter, focal plane splitter –chopper (observation/calibration) –calibration sources Photometer optical train –dichroic beam splitter –separate re-imaging optics for short-wavelength bands (60-90/90-130µm) long-wavelength band (130-210µm) Spectrometer optical train –image slicer unit for integral-field spectroscopy –anamorphic collimator –Littrow-mounted grating with actuator/position readout

15. PACS IIDR 01/02 Mar 2001 Instrument Overview15 FPU Functional Groups (cont.) –dichroic beam splitter for order separation –anamorphic re-imaging optics to independently match spatial and spectral resolution to pixel scale Photoconductor arrays (2; long/short wavelength) –detectors with fore optics –cryogenic readout electronics Bolometer arrays (2; long/short wavelength) –bolometer assemblies with readout electronics –common 0.3K cooler Band selectors –filters + exchange mechanism (photometer bands) –filters + exchange mechanism (grating orders)

16. PACS IIDR 01/02 Mar 2001 Instrument Overview16 FPU Layout Chopper sGe:GaDetector Red Spectrometer Blue Bolometer Red Bolometer Calibrator I and II 0.3 K Cooler Filter Wheel I Filter Wheel II Grating sGe:Ga Detector Blue Spectrometer Encoder Grating Drive Entrance Optics Photometer Optics Calibrator Optics Slicer Optics Spectrometer Optics

17. PACS IIDR 01/02 Mar 2001 Instrument Overview17 Optical Performance Optical design fulfills requirements regarding –field of view –spatial sampling –distortion –geometrical spot sizes (Strehl ratio) –alignment –internal calibration capability –chopping –spectral coverage and resolution –transmission / diffraction losses

18. PACS IIDR 01/02 Mar 2001 Instrument Overview18 PACS Ge:Ga Photoconductor Arrays 16x25 pixel filled arrays –25 linear modules –integrated cryogenic readout electronics 16 pixel stressed detector module Feed optics: light cone array

19. PACS IIDR 01/02 Mar 2001 Instrument Overview19 PACS Photoconductor Modules Ge:Ga photoconductors –unstressed: 40 - 120µm –stressed: 110 - 210µm –quantum efficiency > 30% confirmed through independent measurement Wavelength (µm) T=1.7K, P=9x10 -14 W, t int =1 s, C int =10 pF NEP [W/  Hz] NEP vs. bias

20. PACS IIDR 01/02 Mar 2001 Instrument Overview20 Capacitive feedback transimpedance amplifier (CTIA) for each pixel, based on AC-coupled inverter stage in silicon CMOS technology 16 CTIAs multiplexed on each CRE chip for each linear detector module CRE chips integrated in detector modules Amplifier noise compatible with background- limited performance in spectroscopy Technical feasibility demonstrated In Out-A CfCf C AC CTIA architecture Analog Bus 18-Bit Shift Register Detectors Clock Switch Control Logic CA2CA18 Sync Reset Sample CA1 PACS Cryogenic Readout Electronics

21. PACS IIDR 01/02 Mar 2001 Instrument Overview21 PACS Short-Wave Bolometer Array Assembly Support 300 mK filter Strap 300 mK Mechanical interface Ribbon cable 300 mK (top view) (bottom view) 2 K buffer amplifiers 16 x 16 sub-array

22. PACS IIDR 01/02 Mar 2001 Instrument Overview22 Bolometer Arrays: 16x16 Subarray Demonstrator Pixel Interconnection circuit with reflectors I/C 1 Multiplexer I/C 2 MOS Followers will be integrated in the interconnection circuit in next models

23. PACS IIDR 01/02 Mar 2001 Instrument Overview23 Bolometer Arrays: Pixel -Mechanical suspension -Thermal link to the substrate -Electrical connection PACS short-wave bolometer pixel efficiency (calculated) pixel architecture

24. PACS IIDR 01/02 Mar 2001 Instrument Overview24 Bolometer Readout & Performance 10 -16 W/Hz 1/2

25. PACS IIDR 01/02 Mar 2001 Instrument Overview25 PACS Grating Diamond ruled reflection grating Optical size 320 x 80 mm Used in 1 st, 2 nd, and 3 rd order, angle range 48° ± 20° –1st order (red detector)210 - 105 µm –2nd order (blue detector)105 - 72 µm –3rd order (blue detector) 72 - 55 µm Groove profile optimized for highest efficiency over all 3 orders using PCgrate full EM-code Cryogenic torquer motor drive Inductosyn angular resolver Grating efficiency (above) and resolution (below) 100 ms

26. PACS IIDR 01/02 Mar 2001 Instrument Overview26 PACS Chopper The technical feasibility of the PACS focal plane chopper has been shown Critical components (pivots, motor, sensor) have been predeveloped An experimentally verified simulation model was established, providing input data for optimization and allowing for precise chopper control

27. PACS IIDR 01/02 Mar 2001 Instrument Overview27 Filters/Dichroics Used for definition of photometric bands (photometer) and for selection of grating orders (spectrometer) Low-pass, high-pass, band-pass filters and dichroic beam splitters in multi-layer mesh technology Provided through contract with QMW as part of SPIRE/PACS technology exchange agreement Delivered filters fulfill or exceed transmission requirements Press tools Metal grids Spacers Filter support rings Manufacturing process: Air/vacuum gap filters use annular metal spacers Hot pressed polypropylene filters use dielectric spacers

28. PACS IIDR 01/02 Mar 2001 Instrument Overview28 Instrument Units and Subsystem Responsibilities

29. PACS IIDR 01/02 Mar 2001 Instrument Overview29 Observing Modes Observing modes are combinations of instrument modes and satellite pointing modes Instrument modes: –dual-band photometry –single-band photometry –line spectroscopy –range spectroscopy Pointing modes: –stare/raster/line scan –with/without nodding

30. PACS IIDR 01/02 Mar 2001 Instrument Overview30 Dual-Band Photometry Both arrays operating –full spatial sampling in each band –long-wave array imaging 130-210 µm band –short-wave array imaging 60-90 or 90-130 µm band sub-band selected by filter Raw data rate ~ 1.6 Mbit/s (4 times oversampled) Standard mode for PACS as prime instrument, preferred mode for PACS/SPIRE parallel mode Observing parameters –chopper mode (off/on; waveform, throw) –pointing parameters (stare/raster/scan;nod) –integration time per pointing

31. PACS IIDR 01/02 Mar 2001 Instrument Overview31 Single-Band Photometry One array operating –long-wave array imaging 130-210 µm band or –short-wave array imaging 60-90 or 90-130 µm band Raw data rate ~ 0.3 or 1.3 Mbit/s Test mode for PACS as prime instrument Fall-back mode for PACS/SPIRE parallel mode Observing parameters –chopper mode (off/on; waveform, throw) –pointing parameters (stare/raster/scan;nod) –integration time per pointing

32. PACS IIDR 01/02 Mar 2001 Instrument Overview32 Line Spectroscopy One or two arrays operating –observation of individual lines –long-wave array in 105 -210 µm band –short-wave array in 57-72 or 72-105 µm band –wavelength in primary band determines wavelength in secondary band Max. raw data rate 1 or 2 x ~1.8Mbit/s Observing parameters –scan width (default 0) –chopper mode (off/on; waveform, throw) –pointing parameters (stare/raster/scan;nod) –integration time per pointing

33. PACS IIDR 01/02 Mar 2001 Instrument Overview33 Range Spectroscopy Two arrays operating –observation of extended wavelength ranges continuous scan (full resolution) or steps (SED sampling) –long-wave array in 105-210 µm band –short-wave array in 57-72 or 72-105 µm band Max. raw data rate 2 x ~1.8Mbit/s Observing parameters –start- and end wavelength –resolution mode –chopper mode (off/on; waveform, throw) –pointing parameters (stare/raster/scan;nod) –integration time per pointing

34. PACS IIDR 01/02 Mar 2001 Instrument Overview34 (a) Values for the photometry modes from 60-90 or 90-130 µm / 130-210 µm, respectively. (b) The formal transmission of >1 takes into account the acceptance solid angle of the photoconductor light cones / bolometer baffles which differs from the beam solid angle. Parameters of PACS Instrument Model (Present Best Estimate)

35. PACS IIDR 01/02 Mar 2001 Instrument Overview35 Background, NEP, Spectroscopic and Photometric Sensitivity  Performance requirements (or even goals) met