Presentation on theme: "May 22/23 2007 SAGE Meeting1 EVLA Hardware Systems: Status and Prognosis Rick Perley."— Presentation transcript:
May 22/23 2007 SAGE Meeting1 EVLA Hardware Systems: Status and Prognosis Rick Perley
May 22/23 2007 SAGE Meeting2 Key EVLA Project Goals Fundamental Goal: By building on the existing infrastructure, multiply ten-fold the VLAs observational capabilities. Full frequency coverage from 1 to 50 GHz. –8 frequency bands with cryogenic receivers. –Two separately-tunable polarization pairs – with no restrictions on their tuning (unlike current VLA). 1 Jy point-source continuum sensitivity (most bands) New correlator with 8 GHz/polarization capability –16384 minimum channels/baseline with full polarization –Full recirculation capability for increased flexibility –128 independently tunable frequency slots. Noise-limited full-beam imaging in all Stokes parameters Completion by 2012.
May 22/23 2007 SAGE Meeting3 EVLA-I Performance Goals ParameterVLAEVLAFactor Point Source Sensitivity (1-, 12 hours)10 Jy1 Jy 10 Maximum BW in each polarization0.1 GHz 8 GHz80 # of frequency channels at max. bandwidth1616,3841024 Maximum number of frequency channels5124,194,3048192 Coarsest frequency resolution50 MHz2 MHz25 Finest frequency resolution381 Hz0.12 Hz3180 (Log) Frequency Coverage (1 – 50 GHz)22%100%5 The EVLAs performance is vastly better than the VLAs: The cost to the NSF for this >10-fold improvement is $59M – about 1/3 the cost of the original VLA.
May 22/23 2007 SAGE Meeting5 Scientific Capabilities Growth Until the WIDAR correlator is available for scientific use (earliest will be mid 2009), new science capabilities come from new frequency access: –L-Band (1.2 – 2.0 GHz) – The new space from 1.74 – 2.0 GHz appears free of RFI! –C-Band: Good sensitivity, but poor polarization outside old frequency range. (Will be corrected by new OMTs). With only 10 days notice, the special C-band call for proposals returned 19 proposals (9 for D config., 10 for A config.) –K-Band: Full tuning range of 18 – 26.5 GHz now available. –Ka-Band: By end of 2008, a sufficient number (~9) of new Ka band (26 – 40 GHz) receivers will be on line for good new science. –Q-Band: The old tuning separation limitation of 400 MHz between IF pairs is gone.
May 22/23 2007 SAGE Meeting6 EVLA Status – End of 2008 In 18 months (at which point the prototype correlator testing should be completed, and the final system under installation), we expect to have on line: BandFinalInterimOld 4/P14010 L41410 S300 C8 X0028 Ku0010 K18010 Ka900 Q18010 Definitions: Final: The system in its final, EVLA State, with full tuning capabilities. Interim: Modern electronics, but old narrow-band OMT, limiting sensitivity or polarization purity. Old: The VLA system, either on an unmodified VLA antenna, or transferred to an upgraded EVLA antenna. Limited tuning capabilities.
May 22/23 2007 SAGE Meeting7 Project Book Requirements Chapter 2 of EVLA Project Book contains all the detailed technical performance requirements. –Sensitivity, stability, pointing accuracy, polarization purity, bandpass stability, and much more. Tests conducted so far indicate we should meet all the requirements. Some requirements will need special tests to determine if we meet specs. New EVLA post-doc (Brigette Hesman) will take charge of acceptance procedures.
May 22/23 2007 SAGE Meeting8 Short-Term Issues of Concern Phase and Amplitude Stability –We believe all major issues affecting stability are understood. –Remaining problems are mainly due to VLA design, and observing methodologies to avoid them are on EVLA Returns web page. Cross-Array (VLA x EVLA) Performance Issues –Hybrid-array performance not ideal. –Some problems will be eliminated upon Modcomp replacement. –Others (closure error, loss of sensitivity due to bandpass mismatch, Doppler tracking) will remain until completion of retrofit process. Modcomp Replacement –Modcomps to be retired June 27. –Although some special modes will not be available in July, we are confident all existing capabilities will be restored shortly afterwards.
May 22/23 2007 SAGE Meeting9 Longer-Term Issues of Concern Optimized High Frequency Performance –Fine tuning of optics (primarily via holography) will be needed to improve high frequency performance. –This work cannot even begin until late 2007, and is likely to be deferred to late 2008. Decommissioning VLA antennas? –In Jan 2009, ten VLA antennas left. –By Jan 2010, only four VLA antennas left. –At some point in 2009 (or 2010?), it will not be worth continuing to operate these. –The committees opinion on when these should be decommissioned will be helpful.
May 22/23 2007 SAGE Meeting10 Frequency Band Implementation The 10 frequency bands (8 Cassegrain, 2 PF) are being installed on three schedules: –7 bands installed during antenna retrofit: 4, P, Interim L, Interim C, Old X, K, Q –2 new bands installed, and 2 bands upgraded in the field, after retrofit: Final L, Final C, Ka, S –1 decommissioned band, and 1 upgraded band, deferred to the end of the project: Ku, Final X
May 22/23 2007 SAGE Meeting11 Bands Installed During Retrofit Five currently existing receiver systems re-installed with few changes: –4 (73.0 – 74.6 MHz) –P (300 – 340 MHz) –X (8.0 – 8.8 GHz) –K (18 – 26.5 GHz) –Q (40 – 50 GHz) 4 and P bands are unchanged, but are now free of internally- generated RFI. X-band is the existing (JPL) system. K and Q bands have same receivers, but different electronics, allowing full-band tuning.
May 22/23 2007 SAGE Meeting12 Interim L and C Bands These new bands are installed during retrofit without their wide-band OMTs: –Design/testing of their full-band orthomode transducers (OMTs) is not yet complete. –Old (narrow-band) OMTs are temporarily installed, limiting sensitivity/tuning range/polarization. L-Band limited to 1.2 – 2.0 GHz. C-Band has nearly full-band tuning, but reduced performance. Tests of new OMT show excellent performance, with installation of these scheduled to begin later this year.
May 22/23 2007 SAGE Meeting13 Bands Installed Following Retrofit Upgrading of Interim C and L Bands to Final Status: –These are upgraded via addition of the final design OMTs –The OMTs will be installed in the field, beginning later this year. C-band OMT deployment has higher priority. L-band OMT deployment likely delayed, pending further study of efficacy of DME removal in 1.0 – 1.2 GHz range. Two new bands: –S-Band (2.0 – 8.0 GHz) Prototype horn being laminated in Albuquerque now, with on-antenna installation by years end. Receiver will not be ready for on-sky tests until mid-2008. –Ka-Band (26.5 – 40 GHz) Receiver under construction now, with on-sky tests by end of this year. –We expect suberb performance from each of these new systems.
May 22/23 2007 SAGE Meeting14 Bands Deferred until End of Retrofit Process Due to supply issues (money, people), two bands had to be deferred to the end of the retrofit process: –X (8 – 12 GHz) –Ku (12 – 18 GHz) Design of X-band OMT now beginning. Receiver tests begin late 2008, deployment begins in 2010. One, or both, of these bands are vulnerable to descope, should contingency become tight.
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