by rick perley - university of...

4 Apr 2007 Pulsar SKA-2007, Thailand 1

The EVLA Project

by Rick PerleyNational Radio Astronomy Observatory

(as told by Scott Ransom)


The Very Large Array (VLA)

• Built 1970’s, dedicated 1980

• 27 x 25m diameter antennas

• Two-dimensional 3-armed array design

• Four scaled configurations, maximum baselines 35, 10, 3.5, 1.0 km.

• Eight bands centered at .074, .327, 1.4, 4.6, 8.4, 15, 23, 45 GHz

• 100 MHz IF bandwidth per polarization

• Full polarization in continuum modes.

• Digital correlator provides up to 512 total channels – but only 16 at maximum bandwidth.

VLA in D-configuration(1 Km maximum baseline)


The Expanded Very Large Array

• The EVLA Project (This is really a new telescope!):– builds on the existing infrastructure - antennas, array,

buildings, people - and, – implements new technologies to produce a new array whose

top-level goal is to provide

Ten Times the Astronomical Capability of the VLA. – Sensitivity, Frequency Access, Image Fidelity, Spectral

Capabilities, Spectral Fidelity, Spatial Resolution, User Access– With a timescale and cost far less than that required to design,

build, and implement a new facility.


Requirements: Electronics

• Continuous frequency coverage from 1 to 50 GHz.– Obtained in eight bands: 1-2, 2-4, 4-8, 8-12, 12-18, 18-27, 27-40, 40-50– Retain the ‘legacy’ low frequency bands (327 and 74 MHz).

• Continuum point-source sensitivity ~ 1 µJy (1-σ in 12 hours)– Cryogenic receivers– Instantaneous bandwidth up to 8 GHz per polarization. – Multi-bit sampling:

• 8 bits @ 2 GSamp/s for low frequency bands (L, S), • 3 bits @ 4 GSamp/s for high frequency bands (C,X,U,K,A,Q).

– Antenna metrology: Holography to improve efficiency.

• Maximize frequency and time stability– Fully digital system, with sampling in the antenna vertex room.


Requirements: Correlator

• At least 28 station inputs, with 16 GHz maximum bandwidth.• Accept input quantization of 1, 2, 3, 4, or 8 bits.• 16384 minimum spectral channels• Full polarization capability. • Frequency resolution variable from 1 MHz to < 1 Hz.• Frequency targeting to zoom in on specific spectral regions with

increased resolution, or to avoid specific regions.• Spectral dynamic range of > 300:000:1

• > 1000 pulsar time bins, of width ~20 µsec.

• Fast dumps, < 100 msec with all spectral channels.


Requirements: Correlator

• VLBI ready:– Delays up to 25,000 km.– Accepts recorded data on tape or disk, or real-time.– Multiple antenna inputs per correlator station input.

• Phased array capabilities – at least 1 GHz bandwidth.• Multiple subarraying for simultaneous real-time or recorded-

time observations, without limit. • And much more…


Requirements: Data Management and Operations

• Part of NRAO ‘end-to-end’ data management• New flexible, common tools for proposal generation,

proposal submission.• All data archived, easy access for all users –

astronomers, engineers, technicians, manager.• Default image generation via pipeline processing.• Goal of noise-limited, full beam images, in all Stokes’

parameters– Requires better algorithms, correction of beam pointing,

squint, and polarization. • Minimize operations costs – preferably hold to present

levels.


Frequency - Resolution Coverage

• A key EVLA requirement is continuous frequency coverage from 1 to 50 GHz.

• This will be met with 8 frequency bands:– Two existing (K, Q)– Four replaced (L, C, X, U)– Two new (S, A)

• Existing meter-wavelength bands (P, 4) retained with no changes.

• Blue areas show existing coverage.

• Green areas show new coverage.

Current Frequency Coverage

Additional EVLA Coverage


The Eight Frequency Bands

8 x 4 x 3

8 x 4 x 3

8 x 4 x 3

6 x 4 x 3

4 x 4 x 3

4 x 4 x 3

4 x 2 x 8

2 x 2GS/s x 8bits

Digitization

2x8.3060 - 9540-50

2x8.455026.5-40

2x8.554518-26.5

2x6.653512-18

2x4.65348-12

2x4.60244-8

2x2.60252-4

2x1.43281-2

IF BW (GHz)

Aperture Effic. (%)

System Temp (K)

Band (GHz)

Blue = System tested and in place, or under installation. Green = Prototypes to be tested in 2007Red = Deferred to end of project


Sensitivity Improvement 1-σ, 12 hours

Red: Current VLA, Black: EVLA Goals


Correlator Specifics

• Design and construction of correlator ‘sub-contracted’ to DRAO correlator group (Penticton, BC, Canada)

• Their design is an extraordinarily flexible machine, with an ‘XF’ architecture

• A 32 station correlator, but more than 32 antennas can be input, with bandwidth reduction.

• Recirculation provided on four inputs for increased frequency resolution.

• Vast number of ways to share resources internally, trading inputs, or sub-correlators, or polarization, for more channels.


EVLA-I Performance Goals

100%

0.12 Hz

2 MHz

4,194,304

16,384

8 GHz

1 µJy

EVLA-I

5 22%(Log) Frequency Coverage (1 – 50 GHz)

3180 381 HzFinest frequency resolution

25 50 MHzCoarsest frequency resolution

8192 512Maximum number of frequency channels

1024 16# of frequency channels at max bandwidth

80 0.1 GHzMaximum BW in each polarization

10 10 µJyPoint Source Sensitivity (1-σ, 12 hours)

FactorVLAParameter

The EVLA’s performance is vastly better than the VLA’s:

These fantastic improvements come at a cost less than ¼ the VLA capital investment, with no increase in basic operations cost!


What is the EVLA Not Doing?

• Expanding to provide 10 times the current best resolution (the New Mexico Array). – The ~few Kelvin brightness sensitivity at milliarcsecond resolution

capability provided by the full EVLA did not pass muster at the NSF.

• A super-compact configuration, for low surface brightness imaging (the ‘E’ configuration). – This ~$6M component could easily and quickly be done as a

standalone project. (Lost: 10 µK brightness sensitivity on 12 arcsecond scale at 34 GHz).

• A sub-1 GHz facility. The VLA’s optics system makes it very difficult to implement an efficient wide-band low-frequency capability.– All proposed methods to do this require extensive design and

development – for which we have no budget.


EVLA Design Driven By Four Science Themes

Magnetic Universe Obscured Universe

Transient Universe Evolving Universe

Measure the strength and topology of the cosmic

magnetic field.

Image young stars and massive

black holes in dust enshrouded

environments.

Follow the rapid evolution of

energetic phenomena.

Study the formation and evolution of

stars, galaxies and AGN.

CO at z=6.4

Sgr A*


Strong Gravity and Black Hole AccretionC

redi

ts:

MPE

, Gen

zel e

t al.

Tycho EVLA capabilities– 10-fold increase in sensitivity (rms=1 uJy)– 106 : 1 image fidelity (PSR : SgrA*)– 10’s mas position astrometry– Millisecond pulsar timing

Results from long-term timing and astrometry

– Measure mass and spin of SMBH• Keplerian orbits • Relativistic spin-orbital coupling• Complements Con X Fe-line florescence

– Tests of GR in ultra-strong regime• And alternate theories of gravity

– Probes of the magneto-ionic accretion environment around a black hole

– 3-D imaging capability, through pulsar motions, variation in DM.

No need to wait for the SKA for this project!

MBH

At 22 GHz: rms 20 hours= 1 μ Jyϑscat=2 mas; tscat=1.3 msec

¿} } {} # Detect2−15PSRswithin4000AUof SgrA rSup { size 8{*} } {} } } {}

¿

VLA beam = 100 mas; FOV =±60¿

¿


EVLA : Pulsar Searching of Images?

• It might be possible to (eventually) record visibility data to survey particular regions of the sky (Gal Ctr, GCs, GLAST Error boxes, ...)

• Search time series of images with a total FOV the size of the primary beam and pixels the size of synthesized beams:

– D-array (1 km bl): ~40 synth beams across primary1.4 GHz (55'' / 35') 22 GHz (3.4'' / 2.2')

• Problem is that the data rate is huge:

2 x 8 x (27x26)/2 x 1000 x 1000 = 5.2 GB/s !Initial data rate is 25 MB/s, progressing to at least 1GB/s....


EVLA : Cost and Timescale

• An initial proposal (EVLA-I) to NSF was submitted in 2000. – Goal: To multiply tenfold or more all VLA capabilities, except spatial

resolution. – Funding started in 2001 following NSB approval. – Completion by 2012.

• EVLA-I is a cooperative project: – $57M from NSF, over eleven years– $15M from Canada, (correlator, designed and built by HIA/DRAO)– $2M from Mexico, and – $8M from re-directed NRAO operational budget.

• A second proposal (EVLA-II) was submitted in April 2004. – Primary Goal: To improve tenfold the spatial resolution. – $115M, over 7 years. – The NSF has recently (Dec 2005) declined to fund this proposal.


Phase I Status

• Eight antennas now converted to EVLA standards. – Six of these have passed the acceptance criteria, and are back in the

array for regular observing.

• Antennas will be upgraded at a rate of 6/year, starting 2007.• We think most technical problems are overcome – some

‘gotchas’ undoubtedly still there.

X17

(K)XL23

KXL26

QKXCL24

QKXCL18

QKXCL16

QKXCLP14

QKXCL13


Correlator Status

• Detailed design nearly complete.• Breconridge (the contract manufacturer) has delivered a fully

populated baseline board for detailed testing in Penticton. • Baseline board is large: 51 x 41 cm, 28 layers, 85000

connections, 95000 vias, 1.2 km trace length, 11802 parts. • Station board also populated and in testing in Penticton. • Phasing board design delayed. All other boards completed.• ASIC correlator chip passed (yesterday!) all 30 tests at full

speed! All FPGAs are ready, including the filter. • Prototype correlator (4 stations) expected for on-sky testing in

January 2008.


Software!

• We have major work ahead in software:– Correlator modes and operation. – Telescope scheduling, archiving, default image generation.– Calibration– Imaging

• 2:1 BWR ratio imaging• Polarization (removal of beam polarization)• RFI excision• Multiple-direction self-calibration• Management of non-coplanar imaging• Management of spectral line cubes.

• The EVLA proposal underestimated software costs (if we knew then what we know now …)

• Remaining contingency will be reserved for hardware. • Assistance from NRAO headquarters will be needed to meet the

software requirements.


New Capabilities Timescale

• The old correlator will be employed until the new correlator achieves full 27-antenna capability – mid 2009.

• Old correlator’s limitations remain

• Full band tuning available before 2009, on schedule shown here.


Relationship to the SKA

• There is no specific formal connection between the EVLA and the SKA (and EVLA is 1.3% of a square km)

• But the EVLA Project is indeed a demonstrator for most technical issues for the SKA, including:– Array operation– Digital antennas systems– Wideband multi-bit data transmission over long distance– Management of massive, complex correlators– Archiving– Spatially-variant gain calibration– Wide-field imaging including beam corrections and non-coplanar

imaging.– `e2e’ data management. – Exploring the sub-mJy sky.


The EVLA: A North American Partnership

The EVLA Project on the Webhttp://www.aoc.nrao.edu/evla/

by rick perley - university of...

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