November SKA Low Frequency Aperture Array. Andrew Faulkner

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2 SKA Phase 1 Implementation Southern Africa Australia SKA 1 -mid m dia. Dishes 0.4-3GHz SKA 1 -low 256,000 antennas Aperture Array Stations /650MHz SKA 1 -survey 90 15m dia. Dishes GHz Construction 2017 start

3 SKA Phase 2 Implementation Southern Africa Australia SKA 2 -mid m dia. Dishes GHz AA-mid m dia. Aperture Array Stations MHz SKA 2 -low 3,000,000 antennas. Aperture Array Stations MHz Construction 2020 s

4 Sparse: >λ/2 A eff increases as λ 2 Layout irregular Increased skynoise from grating lobes Small beam at high frequencies AA selection 1000 Sparse AA-low Sky Brightness Temperature (K) T sky A eff Fully sampled AA-mid Becoming sparse Aeff / T sys (m 2 / K) Dense: λ/2 Constant A eff Fully sampled wavefront Excellent side lobe control Regular layout A eff /T sys AA frequency overlap Frequency (MHz) Dish operation

5 Basic and stretch SKA Office appointed Consortia to produce the major Elements Low Freq. AA - Science Data Processor - Communications Dishes - Correlator+Beamformer - Infrastructure Integration Issued a Baseline Spec. now as Level 1 Requirements LFAA must meet the Level 1, or Baseline requirements Baseline spec. misses a lot of opportunity from AAs, so LFAA may meet Target requirements (self-imposed ), Low cost or traded with other aspects of SKA1 (e.g. dish performance)

6 SKA 1 -low Baseline specs Strongly configured for EoR Frequency: Bandwidth: Sensitivity : Polarisation: Beam size: Scan angle: 50MHz 350MHz 300MHz 1000m 2 /K ( MHz) Dual (of good quality) >5 (no beam stitching) 45 max. # of beams: Single (!) Configuration: 50% <600m radius 75% <1km radius 95% <3km radius 3 spiral arms of 50km Output Data rate: ~10Tb/s (total)

7 SKA 1 -low Baseline specs Strongly configured for EoR Frequency: 50MHz 350MHz Bandwidth: 300MHz Sensitivity Excludes : 1000m any 2 /K ( MHz) pulsar processing!! Dual (of good quality) Pretends an AA is a metal dish only 1 beam! >5 (no beam stitching) Polarisation: Beam size: Scan angle: 45 max. # of beams: Single (!) Configuration: 50% <600m radius Fixed station 75% <1km size radius 95% <3km radius 3 spiral arms of 50km Issues Restricts parameters for a transient search Limited frequency range No autonomy for stations Output Data rate: ~10Tb/s (total)

8 Technical implementation Antenna: Log Periodic No. of ant.: 256,000 (2 18 ) Ant. placement: Random. 1.5m min. Station size: 256 / 512 / 1024 ant. 35m / 50m / 70m dia. No. of stations: Signal transport: Analogue fibre Processing: Digital Sample res.: 8-bit or 4-bit real Tiles: 16 antenna per Tile Data routing: Switch network

9 Array sensitivity vs. frequency T rec 35K >100MHz SKA Survey Band 1 Credit: Eloy de Lera Acedo EM simulations (CST) and LNA electronic simulations (Microwave Office). Further optimisations to perform

10 Target Implementation Individual Log-periodic antennas single array Analog fibre signal transport from each antenna Individual solar power (+battery) at each antenna Single (large) processing bunker (256 racks) Band selection using ADC baseband or first alias Data routing inside bunker using COTS switches

11 Example bunkers

12 SKA-low: end-to-end Maser Signal & Data Transport Low frequency Aperture Array Central Signal processor Science Data processor Scientists! HPC HPC HPC Bulk Store HPC UV Processor Buffer store Switch Correlator Beamformer Buffer store Switch Beamforming Power Cooling Infrastructure M&C Telescope Manager Central Bunker can integrate: LFAA Beamforming Signal transport Local M&C LFAA Correlator Maser clock

13 Signal flow through AA Antenna & LNA Receiver Signal Processing Antenna structure LNA e/o RFoF ADC 1 st Beamforming Spectral filters Control & Monitoring Station beamforming e/o Data out Clock Solar/copper Power Power Bunker Local Infrastructure Power Monitor & Control Cooling

14 2 x MHz Baseline: SKA-low Station Processing 2 x 6.4 Gb/s per antenna RF over Fibre from Antennas RF over Fibre from Antennas RFI shield TILE Filters MHz ADCs 800MS/s Spectral filters Spectral filters Beamforming Beamforming 2 x 4 Gb/s for 250MHz BW per element Data Switch Data to Correlator TILE

15 2 x MHz Target: SKA-low Station Processing 2 x 6.4 Gb/s per antenna RF over Fibre from Antennas Spectral filters Beamforming 2 x 4 Gb/s for 250MHz BW per element RF over Fibre from Antennas RFI shield TILE Filters MHz MHz ADCs 800MS/s 700MS/s Spectral filters Beamforming Data Switch Data to Correlator TILE Low Band High Band

16 2 x MHz Target++: SKA-low Station Processing 2 x 6.4 Gb/s per antenna Memory RF over Fibre from Antennas Spectral filters Beamforming 2 x 4 Gb/s for 250MHz BW per element RF over Fibre from Antennas RFI shield TILE Filters MHz MHz TILE ADCs 800MS/s 700MS/s Spectral filters Beamforming Data Switch Transient buffer Data to Correlator Low Band High Band Memory

17 Implementation Antenna RFoF Data Network Analogue inputs 16 dual pol. antennas Digitise and beamform

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19 256 racks in 16 aisles High speed switched network Flexible beamforming Overlayed monit. & control

20 Capabilities of the design No. of stations: 1024 or 512 or 256 Core close-up Station dia,: Multiple Beams: 35m or 50m or 70m Flexibly allocated in available data rate Beam forming: Improved apodisation Scan angle: 60 max. No. of Bands: 2 Frequency Ranges: Data rate: 50MHz 375MHz 375MHz 650MHz 10Tb/s Credit: Keith Grainge REDUCING SKA1 system cost and/or IMPROVING performance.

21 Capabilities of the design No. of stations: 1024 or 512 or 256 Station dia,: 35m or 50m or 70m Multiple Flexibly allocated in Beams: available data rate Beam forming: Improved apodisation Better Stations Station Station Scan angle: 60 max. No. of Bands: 2 Frequency Ranges: Data rate: 50MHz 375MHz 375MHz 650MHz 10Tb/s Extended Station Credit: Keith Grainge REDUCING SKA1 system cost and/or IMPROVING performance.

22 SKA-low could observe Pulsars! Imaging: Corner Turning Course Delays Fine F-step/ Correlation Visibility Steering Observation Buffer Gridding Visibilities Imaging Image Storage LFAA Beams Switch Buffer store Correlator Beamformer Switch Buffer store UV Processor HPC Bulk Store Non-Imaging: Corner Turning Course Delays Beamforming/ De-dispersion Beam Steering Observation Buffer Time-series Searching Search analysis Object/timing Storage SKA-low Processing Chain

23 Aims First cross-correlation AAVS 0.5 tests Verify correct interferometer operation and calibration Make a variety of test images Extract key AAVS 0.5 parameters: SEFD, station beam characteristics,. Inform design of future verification activities (AAVS 1) Requires reliable and well-calibrated MWA

24 First AAVS 0.5 image (using MWA) 2 minute integration, wide-field snapshot, centred on 3C444 AAVS 0.5 baselines only (but calibrated using whole MWA) November 2013 No allowance yet for AAVS SKA Low 0.5 point Frequency spread Aperture function, Array pointing or baseline 24 errors

25 AAVS 0.5 System Equivalent Flux Density (SEFD) 3C444 for 3 hrs from 1030 local time, 20/8/ azimuth variation; modest Bad variation around elevation 80 MWA and AAVS 0.5 tiles connected to the same MWA receiver (#7) Good agreement between models and measurements NB: un-optimized AAVS configuration Good Simulation: 2.5 % moisture soil, Trx = 50 K

26 In conclusion.

27 In conclusion. SKA-low can be superb for transients & pulsars! Low frequency aperture array is critical to SKA Wide-band log-periodic antennas give 13:1 freq. range RFoF enables a very flexible architecture Solar power reduces deployment and running costs Centralised processing enables: Flexible station configuration Improved beamforming Simpler maintenance Use of COTS components