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ASKAP status and commissioning

ASKAP status and commissioning. Max Voronkov | ASKAP Software scientist. Kiama - 3 March 2014. Astronomy and Space Science. Some pictures from Ben Humphreys, John Bunton , Aidan Hotan , Dave McConnel and Tom Cox. Australian Square Kilometre Array Pathfinder. Key new features:.

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ASKAP status and commissioning

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  1. ASKAP status and commissioning Max Voronkov| ASKAP Software scientist Kiama - 3 March 2014 Astronomy and Space Science Some pictures from Ben Humphreys, John Bunton, Aidan Hotan, Dave McConnel and Tom Cox

  2. Australian Square Kilometre Array Pathfinder Key new features: • Phased array feed • Multiple synthetic beams on the sky • 3-axis mount Wide field of view Radio interferometer with 36 identical 12m antennas Located in a radio-quiet zone in Western Australian outback

  3. Phased Array Feed (PAF) 188 independent receivers Beamformer computes 36 linear combinations making individual beams on the sky 3-axis mount gives a better stability of the system and simplifies imaging

  4. BETA: first 6 antennas of ASKAP, MkI PAF BETA Beamformer supports 9 beams only First tests were done with two 3-antenna arrays

  5. Current status: BETA and Beyond • Most commissioning efforts goes towards BETA • Most development is towards ADE (2nd generation h/w) • cheaper PAF with better Tsys across the frequency range • less electronics in the antenna pedestals • simpler and more maintainable design in many cases • Number of milestones of general importance • Remote observations from Sydney • Pawsey centre supercomputer is ready Ben’s talk – for HPC matters Aidan’s talk – for info on beamforming

  6. The Pawsey High Performance Computing Centre for SKA Science • AUD$80M super-computing centre • Supports storage and processing of data from the Australian SKA Pathfinder and the Murchison WidefieldArray • Construction completed April 2013

  7. BETA Hardware • DRx can delay stream up to about 5 microsec • Beamformers have an integrator after the fine filter bank (FFB) • H/W fringe rotator is part of the beamformer • Initial setup was two 3-antenna arrays • Antenna 1-3-6 sub-array is compact enough, so it can be used without fringe rotator

  8. Early work with the Software correlator • 16 MHz bandwidth, 1:10 duty cycle and up to 4 beams, 3 antennas • 3-beams (made on Virgo) arranged in a line, 928 MHz, 13h track • 1549-790 (pointing centre, boresight beam), 1610-771 (centre of the most offset beam) + two weaker sources • Delay tracking via DRx • Phase tracking in software • Can’t synchronise with DRx • Calibration on 1934-638 • Each beam separately • Image beams separately • Linear mosaicing • With an idealised beam model • Good data reduction exercise

  9. Many months of artefact chasing The biggest issue was tracked down to the idiosyncrasies of the DDR memory controllers on DSP card Also note the ripple in this spectrum (filter response). It can be (and is now) corrected in the software

  10. Delay tracking controlled by ingest pipeline Simplifies debugging Full control over DRx, H/W fringe rotator and software corrections Can synchronise delay and phase tracking and flag invalid samples

  11. Getting HW fringe rotator to work

  12. Phase is free-wheeling, timing is painful Large phase jumps when we update phase rate parameter Significant mis-timing • Timing becomes crucial, software needs to understand what the hardware is doing • Parameters are loaded on an event but applied when the current 55.296ms block of data ends, correlator knows nothing about it • Tried to operate with 90x55.296ms and 91x55.296ms cycles instead of 5s • Got beating with 1pps interrupts

  13. Investigate timing astronomically Slope corresponds to 14.5±0.4s delay 3 correlator cycles? Track geometric delay/phases via DRx + software for a strong source Set different phase rates and measure what phase we get

  14. Timing – can only account for 2 cycles

  15. Imaging with two 3-antenna sub-arrays Correlator has been repatched into the final 6-antenna configuration two weeks ago • Full 304 MHz bandwidth • 9 beams, stokes I • Beams made using the Sun • Didn’t survive power cycle (most likely due to attenuators) • Calibration on 1934-638 • Separately for each beam • Also considering a hybrid approach where the calibration per beam is done once per day and routine calibration is antenna-based • No isolated calibrators • Delay tracking per antenna • w-projection fixes differential delay across the field well

  16. First (serious) look at bandpasses Bandpass has been calibrated on another 1934-638 scan taken a few hours earlier Frequency-dependent structure of beamformer weights needs a more careful look Wavy pattern is because of confusing sources!

  17. Summary • BETA is coming along - extremely valuable engineering experience • All but one bug found with BETA also relevant for ADE/ASKAP - saved time • Exercise full system, including software. • Learn beamforming and refine calibration model • Timing across boundary of different systems • Source of frustration • Avoid free-wheeling behaviour? • The presence of beamformer as a separate hardware makes synchronisation difficult. Avoid multiple clock domains? • Do as much in the software as possible?

  18. We acknowledge the WajarriYamatji people as the traditional owners of the Observatory site Thank you Astronomy and Space Science Max Voronkov ASKAP Software Scientist t +61 2 9372 4427 e maxim.voronkov@csiro.au w www.narrabri.atnf.csiro.au/people/vor010 Astronomy and Space Science

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