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Designing an Optimal SKA

Designing an Optimal SKA. Andrew Faulkner . D esigning an optimal SKA around AAs at low frequencies plus dishes at higher frequencies – maximising the science output for a fixed cost. SKA Overall Structure. Mass Storage. 0.4-1.4 GHz Wide FoV. Tile & Station Processing.

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Designing an Optimal SKA

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  1. Designing an Optimal SKA Andrew Faulkner

  2. Designing an optimal SKA around AAs at low frequencies plus dishes at higher frequencies – maximising the science output for a fixed cost

  3. SKA Overall Structure Mass Storage 0.4-1.4 GHz Wide FoV Tile & Station Processing Central Processing Facility - CPF To 250 AA Stations Dense AA ... Correlator – AA & Dish 16 Tb/s Data ... .. 70-450 MHz Wide FoV .. Time Post Processor Control Sparse AA ... 0.8-10 GHz Single Pixel or Focal plane array DSP Control Processors & User interface 12-15m Dishes 80 Gb/s DSP Time Standard ... To 2400 Dishes User interface via Internet

  4. SKA Overall Structure Mass Storage 0.4-1.4 GHz Wide FoV Tile & Station Processing Central Processing Facility - CPF To 250 AA Stations Dense AA ... Correlator – AA & Dish 16 Tb/s Data ... .. 70-450 MHz Wide FoV .. Time Post Processor Control Sparse AA ... 0.8-10 GHz Single Pixel or Focal plane array DSP Control Processors & User interface 12-15m Dishes 80 Gb/s DSP Time Standard ... To 2400 Dishes User interface via Internet

  5. SKA Overall Structure Mass Storage 0.4-1.4 GHz Wide FoV Tile & Station Processing Central Processing Facility - CPF To 250 AA Stations Dense AA ... Correlator – AA & Dish 16 Tb/s Data ... .. 70-450 MHz Wide FoV .. Time Post Processor Control Sparse AA ... 0.8-10 GHz Single Pixel or Focal plane array DSP Control Processors & User interface 12-15m Dishes 80 Gb/s DSP Time Standard ... To 2400 Dishes User interface via Internet

  6. SKA Overall Structure Mass Storage 0.4-1.4 GHz Wide FoV Tile & Station Processing Central Processing Facility - CPF To 250 AA Stations Dense AA ... Correlator – AA & Dish 16 Tb/s Data ... .. 70-450 MHz Wide FoV .. Time Post Processor Control Sparse AA ... 0.8-10 GHz Single Pixel or Focal plane array DSP Control Processors & User interface 12-15m Dishes 80 Gb/s DSP Time Standard ... To 2400 Dishes User interface via Internet

  7. Potential Configuration: Comms links Dishes spread along spiral Core ~5km dia AA Station Central Processing Facility 180km ~250 Aperture array stations Dishes AA-hi ~2400 Dishes Not to scale! AA-lo

  8. Some SKA design parameters.....

  9. SKA implementation analysis Key Science Experiments Physical Parameters: • Flux • Area of sky • Polarisation • Dynamic range • etc Instrument Technical Specification: • Sensitivity • Survey speed • Configuration • Stability Potential Designs: • Collector type • Frequency range • Data rates • etc Modelling: • Variants • Performance • Cost • Power • Risk SKA Design Operational Constraints: • Time allocation • Storage • Power • Operations budget

  10. Science Requirements.... The Design Reference mission http://www.skatelescope.org/PDF/091001_DRM_v0.4.pdf

  11. Design Reference Mission Science Experiments

  12. 39,000 5. Wide Field Polarimetry - 2 Huge.... 15,000 Sensitivity Requirements 12,500 Sensitivity Aeff/Tsysm2 K−1 7. Deep HI Field 8. HI EoR 6. Continuum deep field 10,000 10b, 13b. Pulsar timing 15. Probing AGN via HI abs’n 12. HI BAO 7,500 10a, 13a. Pulsar search 5,000 3. Protoplanetary disks 2,500 5. Wide Field Polarimetry - 1 4. Cosmic Magnetism 9. Galactic centre pulsars 11. Galaxy Evolution via H I Absorption 2. Resolving AGN and Star Formation in Galaxies 0 0.1 0.14 0.3 1.0 1.4 3.0 10.0 Frequency GHz Specified sensitivity DRM 0.4 Derived from survey speed

  13. Survey Speed Requirements 12. HI BAO 4. Cosmic Magnetism 1e10 13a. Pulsar search 5. Wide Field Polarimetry 7. Deep HI Field 11. Galaxy Ev. via HI Abs’n 1e8 6. Continuum deep field 8. HI EoR 3. Protoplanetary disks 1e6 9. Galactic centre pulsars Survey Speed m4 K−2 deg2 10b, 13b. Pulsar timing 1e4 2. Resolving AGN & Star Form’n 1e2 1e1 0.1 0.14 0.3 1.0 1.4 3.0 10.0 FrequencyGHz Specified survey speed DRM 0.4 Derived from sensitivity

  14. >3000 2. Resolving AGN and Star Formation in Galaxies 3000 15. Probing AGN via HI abs’n 1,000 Baseline Requirements 6. Continuum deep field 300 11. Galaxy Evolution via HI Absorption Baseline length, km 100 3. Protoplanetary disks 7. Deep HI Field 30 4. Cosmic Magnetism 8. HI EoR 5. Wide Field Polarimetry 10 12. HI BAO 3 10a, 13a. Pulsar search 9. Galactic centre pulsars 10b, 13b. Pulsar timing 1 0.1 0.14 0.3 1.0 1.4 3.0 10.0 Frequency GHz Stated in DRM DRM 0.4 Unstated in DRM - assumed

  15. Comments on Science reqts • Major surveys are <1.4 GHz: below HI line • Only AGN experiments are >500km baseline • Interesting how many want 10,000 m2/K...... • Continuum & Pulsars want as much sensitivity as possible • Transients requirements are not shown • Would like the parameters as a function of frequency

  16. Some design trade-offs......

  17. Tailoring the AA system 1000 Sparse AA-lo Fully sampled AA-hi 100 Aeff Tsky Becoming sparse Sky Brightness Temperature (K) Aeff / Tsys (m2 / K) 10 Aeff/Tsys AA frequency overlap fAA fmax 1 Dishoperation 100 Frequency (MHz)

  18. Ae AA Station Configuration TH_n ….. ….. 12 fibre lanes @10Gb/s each 12 fibre lanes @10Gb/s each Long distance drivers e/o TH_1 e/o Ae e/o Tile Processor - hi o/e e/o TH_0 Station Processor 0 o/e ….. o/e o/e ….. e/o o/e e/o o/e e/o ….. ……. e/o e/o Ae e/o Long distance drivers e/o o/e e/o o/e o/e o/e ….. 1.0-1.4GHz analogue ….. o/e Inputs #: 1296 Channel rate: 120Gb/s (raw) Total i/p rate: 1.5 Pb/s Typical: AA-hi tiles: 300 AA-lo tiles: 45 Total: 345 I/p data rate: 42Tb/s o/e ………... o/e ….. o/e To Correlator ……. ….. Tile Processor - lo e/o 10Gb/s fibre e/o ….. e/o .... ….. ….. e/o Max 4 Station Processors Station Processor n Long distance drivers TL_0 TL_1 1.0 GHz analogue ….. ….. Notes: 1. No control network shown 2. Up to 4 station processor systems can be implemented in parallel 3. Data shown are raw, typ. get 80% data Local Processing e.g. Cal; pulsars TL_m

  19. AA Station performance costs Cost for Field of View, FoV: 10% Cost for Aeff/Tsys: 90% Sensitivity: Aeff/Tsys Survey Speed:(Aeff/Tsys)2 x FoV

  20. AA – Dish Frequency X-over • low flow implies large dia. • Large feed for low freq • Costs high for low freq Frequency AA Dish+feed • Cost increases as ftop2 • Can reduce Aeff at high f • Cover main survey reqts.

  21. Central Processing Facility

  22. Central Processing Facility UV Processors Image formation Science analysis, user interface & archive Correlator Beams Visibilities UV data Images AA slice Imaging Processors Data Archive Data switch Processor Buffer Buffer Processor ... Processor Buffer AA slice Buffer Processor Processor Buffer Processor Buffer ... Processor Buffer AA Stations ... Processor Buffer ... Processor Buffer AA slice Buffer Processor Buffer Processor Processor Buffer ... 250 x 16Tb/s ~4.8 Pb/s Buffer Processor Processor Buffer Processor Buffer Science Processors Processor Buffer 2400 x 80Gb/s ... Processor Buffer ...... Dish & AA+Dish Correlation Dishes ...... Buffer Processor Buffer Processor Buffer Processor ~10 Pflop Processor Buffer Buffer Processor Pb/s Tb/s Gb/s Gb/s

  23. The central processing problem….. Data rate, R, from the correlator Each pair of antennas are multiplied together R  Nc2 For each beam R  Nb Must avoid chromatic aberration – need to split bandwidth Df into Nch channels of width df < f D / B R  f / df Longest integration time must sample changing sky due to rotation of the earth dt < 2600 qmax / qD R  1 / dt Quadraticfor baseline length Quadraticfor no. of collectors Inverse Quadraticfor collector diameter Linear for no. of beams

  24. The central processing problem….. Data rate, R, from the correlator Each pair of antennas are multiplied together R  Nc2 For each beam R  Nb Must avoid chromatic aberration – need to split bandwidth Df into Nch channels of width df < f D / B R  f / df Longest integration time must sample changing sky due to rotation of the earth dt < 2600 qmax / qD R  1 / dt Processing cost.... Nb FoV: cheap • B resolution: expensive • D-1 FoV: very expensive Quadraticfor baseline length Quadraticfor no. of collectors Inverse Quadraticfor collector diameter Linear for no. of beams Fewer big stations + more beams is much cheaper

  25. Data rates out of Correlator • For the AA the data rate assumes constant FoV across the band. • Assuming that for the dynamic range the FoV of the station only has to be imaged • Assuming that for the dynamic range the FoV of the dish must be imaged

  26. Processing model

  27. Model for UV processor Highly parallel – 20 TFloppromised in 2 years – assume 50 Tflopin 2018 Operations/sample reqd.: ~20,000/calibration loop Processor: €1000, 5 calibration loops, 50% efficiency, Each processor can operate on ~ 1 GB/s of data Requirement: 100 PFlop (AA) 2 EFlop (dishes) Buffer 1 hr of data  7.2 TB in a fast store Memory est. €200 per TB. Total UV-processing :Cost = €2.5m per TB/s AA < €10m Dishes ~ €125m UV Processors UV data Buffer Processor Processor Buffer Processor Buffer Processor Buffer Buffer Processor Processor Buffer Buffer Processor Processor Buffer Processor Buffer Processor Buffer Buffer Processor Processor Buffer Buffer Processor Processor Buffer Processor Buffer Processor Buffer Buffer Processor ...... Processor Buffer Processor Buffer Processor Buffer Processor Buffer Buffer Processor Gb/s

  28. Technology Roadmapping Processing From Bruce Elmegreen, IBM

  29. Modelling: Design and Costing Tool Also tracks Power & data rate

  30. Hierarchical designs..

  31. Data link cost vslength (16Tbit/s) Introduction second amplifiers (160km) Introduction of first amplifiers (80km) • Large data rate link costs from tool show the combine effect of distance break points for different technologies. • These break have strong implications for cost savings if we change the layout of the Aperture Arrays Introduction of first pre-amplifiers Change from short range to mid range lasers Change from short range to mid range lasers

  32. Changing the collector distribution • Does this matter? Yes. Look at the estimated costs for 250 AA station links, each with 16 Tbit/s. Vary Bmid – distance within which 95% of all stations are placed, cost implications of the order 100 Million EUR. • 95% within 10km, very few stations out to 180km • 95% within 100km, remainder out to 180km

  33. Impact of changing the distribution • Does this matter? Yes. Look at the estimated costs for 250 AA station links, each with 16 Tbit/s. Vary Bmid – distance within which 95% of all stations are placed, cost implications of the order 100 Million EUR. • 95% within 10km, very few stations out to 180km: 60M Euros • 95% within 100km, remainder out to 180km: 140M Euros

  34. Consider apossible SKA....

  35. 39,000 5. Wide Field Polarimetry - 2 Huge.... Can this reqt. be 5000 m2K-1? This reqt. is ~16 Km2 AA!! 15,000 Sensitivity Requirements 12,500 Sensitivity Aeff/Tsysm2 K−1 7. Deep HI Field 8. HI EoR 6. Continuum deep field 10,000 10b, 13b. Pulsar timing 15. Probing AGN via HI abs’n 12. HI BAO 7,500 10a, 13a. Pulsar search 5,000 3. Protoplanetary disks 2,500 AA-lo 5. Wide Field Polarimetry - 1 4. Cosmic Magnetism 9. Galactic centre pulsars AA-hi 11. Galaxy Evolution via H I Absorption 2. Resolving AGN and Star Formation in Galaxies 0 Dish 0.1 0.14 0.3 1.0 1.4 3.0 10.0 Frequency GHz Specified sensitivity DRM 0.4 Derived from survey speed

  36. Survey Speed Requirements 12. HI BAO 4. Cosmic Magnetism 1e10 13a. Pulsar search Does the science require this? 5. Wide Field Polarimetry 7. Deep HI Field 11. Galaxy Ev. via HI Abs’n 1e8 6. Continuum deep field 8. HI EoR 3. Protoplanetary disks 1e6 9. Galactic centre pulsars Survey Speed m4 K−2 deg2 10b, 13b. Pulsar timing 1e4 2. Resolving AGN & Star Form’n 1e2 1e1 AA-lo AA-hi Dish 0.1 0.14 0.3 1.0 1.4 3.0 10.0 FrequencyGHz Specified survey speed DRM 0.4 Derived from sensitivity

  37. >3000 2. Resolving AGN and Star Formation in Galaxies 3000 15. Probing AGN via HI abs’n 1,000 Baseline Requirements 6. Continuum deep field These baselines are very expensive! Fibre & computing 300 11. Galaxy Evolution via HI Absorption Baseline length, km A few large low freq dishes? 100 3. Protoplanetary disks 7. Deep HI Field 30 4. Cosmic Magnetism 8. HI EoR 5. Wide Field Polarimetry 10 12. HI BAO 3 AA-lo 10a, 13a. Pulsar search AA-hi 9. Galactic centre pulsars 10b, 13b. Pulsar timing 1 Dish 0.1 0.14 0.3 1.0 1.4 3.0 10.0 Frequency GHz Stated in DRM DRM 0.4 Unstated in DRM - assumed

  38. Costs for ‘this’ SKA Collectors 250 x 57m dia AA-hi 250x220m dia AA-lo 1200 x 15m dishes Wideband SP Feeds Costs not Included: Development work Non-recoverable expenses Civil works Power installation Operational Costs Project Management

  39. Costs for ‘this’ SKA Collectors 250 x 57m dia AA-hi 250x220m dia AA-lo 1200 x 15m dishes Wideband SP Feeds Costs not Included: Development work Non-recoverable expenses Civil works Power installation Operational Costs Project Management ~€1.2 Bn

  40. AA-hi Arrays (not inc. station processing) Infrastructure: Cover membrane Steels for Antenna Support Structure Cable Support Poles Velcro Cable Ties Foundations: building poles Civil Engineering Cooling Power Supplies Racking Trenches Infrastructure Build – 3 man years Bunkers ~€1.5M each array, NPV Analogue Data Transport: Connection to PCBs = no. of cables Preparation of cables Cable - total length reqd per station Male plugs PCB Outlet plugs (i.e. PCB inputs to first processor) Install cables in field ~€11 each element, 2011

  41. Summary A great SKA can be built.... .....with lots of work

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