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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:. - PowerPoint PPT Presentation

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ASKAP status and commissioning Astronomy and Space ScienceMax Voronkov | ASKAP Software scientist Kiama - 3 March 2014

Some pictures from Ben Humphreys, John Bunton, Aidan Hotan, Dave McConnel and Tom Cox Australian Square Kilometre Array PathfinderRadio interferometer with 36 identical 12m antennasLocated in a radio-quiet zone in Western Australian outback

Key new features:Phased array feedMultiple synthetic beams on the sky3-axis mountWide field of view

Phased Array Feed (PAF)188 independent receivers Beamformer computes 36 linear combinations making individual beams on the sky3-axis mount gives a better stability of the system and simplifies imagingBETA: first 6 antennas of ASKAP, MkI PAF

BETA Beamformer supports 9 beams only First tests were done with two 3-antenna arrays

Current status: BETA and BeyondMost commissioning efforts goes towards BETAMost development is towards ADE (2nd generation h/w) cheaper PAF with better Tsys across the frequency rangeless electronics in the antenna pedestalssimpler and more maintainable design in many cases

Number of milestones of general importance Remote observations from SydneyPawsey centre supercomputer is ready Bens talk for HPC mattersAidans talk for info on beamformingThe Pawsey High Performance Computing Centre for SKA ScienceAUD$80M super-computing centreSupports storage and processing of data from the Australian SKA Pathfinder and the Murchison Widefield ArrayConstruction completed April 2013

BETA Hardware

DRx can delay stream up to about 5 microsecBeamformers have an integrator after the fine filter bank (FFB) H/W fringe rotator is part of the beamformerInitial setup was two 3-antenna arraysAntenna 1-3-6 sub-array is compact enough, so it can be used without fringe rotator Early work with the Software correlator16 MHz bandwidth, 1:10 duty cycle and up to 4 beams, 3 antennas3-beams (made on Virgo) arranged in a line, 928 MHz, 13h track1549-790 (pointing centre, boresight beam), 1610-771 (centre of the most offset beam) + two weaker sourcesDelay tracking via DRxPhase tracking in softwareCant synchronise with DRx Calibration on 1934-638Each beam separately Image beams separatelyLinear mosaicingWith an idealised beam model Good data reduction exercise

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

Delay tracking controlled by ingest pipelineCan synchronise delay and phase tracking and flag invalid samplesSimplifies debugging Full control over DRx, H/W fringe rotator and software correctionsGetting HW fringe rotator to work

Phase is free-wheeling, timing is painfulTiming becomes crucial, software needs to understand what the hardware is doingParameters are loaded on an event but applied when the current 55.296ms block of data ends, correlator knows nothing about itTried to operate with 90x55.296ms and 91x55.296ms cycles instead of 5sGot beating with 1pps interrupts

Large phase jumps when we update phase rate parameter

Significant mis-timingInvestigate timing astronomically Track geometric delay/phases via DRx + software for a strong sourceSet different phase rates and measure what phase we get

Slope corresponds to 14.50.4s delay3 correlator cycles? Timing can only account for 2 cycles

Imaging with two 3-antenna sub-arraysFull 304 MHz bandwidth9 beams, stokes IBeams made using the SunDidnt survive power cycle (most likely due to attenuators)Calibration on 1934-638Separately for each beamAlso considering a hybrid approach where the calibration per beam is done once per day and routine calibration is antenna-basedNo isolated calibratorsDelay tracking per antennaw-projection fixes differential delay across the field well

Correlator has been repatched into the final 6-antenna configuration two weeks ago First (serious) look at bandpassesFrequency-dependent structure of beamformer weights needs a more careful lookWavy pattern is because of confusing sources!

Bandpass has been calibrated on another 1934-638 scan taken a few hours earlierSummaryBETA is coming along - extremely valuable engineering experienceAll but one bug found with BETA also relevant for ADE/ASKAP - saved timeExercise full system, including software. Learn beamforming and refine calibration modelTiming across boundary of different systemsSource of frustrationAvoid 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?

Astronomy and Space ScienceThank youAstronomy and Space ScienceMax VoronkovASKAP Software Scientist

t +61 2 9372 4427e [email protected] w www.narrabri.atnf.csiro.au/people/vor010We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site