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Atacama Large Millimeter Array Update

Atacama Large Millimeter Array Update. Slides Unabashedly Stolen by Al Wootten NA ALMA Project Scientist From ALMA NA Cost/Management Review January 30 – February 1 2006. The ALMA Partnership. ALMA is a global partnership in astronomy to deliver a truly transformational instrument

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Atacama Large Millimeter Array Update

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  1. Atacama Large Millimeter Array Update Slides Unabashedly Stolen by Al Wootten NA ALMA Project Scientist From ALMA NA Cost/Management Review January 30 – February 1 2006 ALMA NA Cost/Management Review

  2. The ALMA Partnership • ALMA is a global partnership in astronomy to deliver a truly transformational instrument • North America (US, Canada; Taiwan in process) • Europe (via ESO with Spain) • Japan (now including Taiwan) • Key Science goals include • Image protoplanetary disks, to study their physical, chemical, and magnetic-field structures, and to detect tidal gaps created by planets undergoing formation in the disks; • image starburst galaxies as early as z = 10; • image normal galaxies like the Milky Way out to z = 3 • Located on the Chajnantor plain of the Chilean Andes 16500’ above sea level • The way ALMA is being built is via a 50:50 partnership between NA & Europe and a closely coordinated but separate effort from Japan • ALMA will be Operated as a single Observatory with scientific access via regional centers • North American ALMA Science Center (NAASC) is here ALMA NA Cost/Management Review

  3. What is ALMA? • Up to 64 12m antennas • Plus the Compact Array of 4 x 12m and 12 x 7m antennas from Japan • Baselines from 15m to 15km • 5000m site in Atacama desert • Receivers: low-noise, wide-band (8GHz), dual-polarisation, SSB • Digital correlator, >=8192 spectral channels, 4 Stokes • Sensitive, precision imaging between 30 and 950 GHz • 350 GHz continuum sensitivity: about 1.4mJy in one second • Angular resolution will reach ~40 mas at 100 GHz (5mas at 900GHz) • First light system has 6 bands: 100, 230, 345 and 650GHz • Japan will provide 140, 460 and 900GHz • 10-100 times more sensitive and 10-100 times better angular resolution compared to current mm/submm telescopes ALMA NA Cost/Management Review

  4. Where is ALMA? ALMA El llano de Chajnantor ALMA NA Cost/Management Review

  5. Chajnantor AOS TB Toco Chajnantor Road Negro Chascón Macón OSF Honar 43km=27 miles ALMA NA Cost/Management Review

  6. Chajnantor V. Licancabur Cº Chajnantor Pampa La Bola Cº Toco Cº Chascón AOS TB Center of Array ALMA NA Cost/Management Review

  7. OSF Facilities ALMA and Contractors Camps Contractors Camp ALMA Camp Contractors Lay-down area ALMA NA Cost/Management Review

  8. OSF Facilities ALMA and Contractors Camps ALMA camp Contractors recreation room Water tanks Contractors Dormitories Contractors kitchen and dining room Contractors offices ALMA NA Cost/Management Review

  9. Recent Camp Development Dormitories at ALMA Camp ALMA NA Cost/Management Review

  10. Recent Camp Development Contractors Camp dining room ALMA NA Cost/Management Review

  11. APEX - The Atacama Pathfinder Experiment A Vertex RSI Antenna Operating at Chajnantor Bonn 21.10.05 ALMA NA Cost/Management Review R.Güsten

  12. AOS Facilities Access Road AOS Technical Building 85 % complete ALMA NA Cost/Management Review

  13. AOS Technical Building ALMA NA Cost/Management Review

  14. AOS TB Construction (1) General view, January 2006 ALMA NA Cost/Management Review

  15. AOS TB Construction (2) ALMA NA Cost/Management Review

  16. Vertex SEF grading ALMA NA Cost/Management Review

  17. ALMA NA Cost/Management Review

  18. ALMA Status • ALMA has just undergone a major rebaselining and subsequent review • The review declared the technology readiness of ALMA very high and judged that most technical risk has been eliminated • Five years ago ALMA was a "must do" scientifically but with high technical risk pushing the state of the art • We now have: • prototype antennas that meet ALMA’s demanding requirements • receivers with near quantum-limited performance, unprecedented bandwidth and no mechanical tuning • the first quadrant of the correlator completed below cost and with enhanced performance • The baseline includes appropriate contingency for remaining technical risks (e.g. photonic local oscillator, highest frequency cold multipliers) ALMA NA Cost/Management Review

  19. Front End Key Specifications(and Preliminary Results) * - between 370 – 373 GHz Trx is less then 300 K • Dual, linear polarization channels: • Increased sensitivity • Measurement of 4 Stokes parameters • 183 GHz water vapor radiometer: • Used for atmospheric path length correction ALMA NA Cost/Management Review

  20. Software Architecture ALMA NA Cost/Management Review

  21. Pre-production ALMA Water Vapor Radiometer Operating in an SMA Antenna on Mauna Kea (January 19, 2006) Relay mirrors Photo courtesy of Magne Hagstrom & Ross Williamson ALMA NA Cost/Management Review

  22. System Integration Activities: Prototype Integration Electronics are first integrated as a system and characterized in the lab at AOC, Socorro. ALMA NA Cost/Management Review

  23. Canada • Canada is part of the North American ALMA project • As part of this they are members of the North American Partnership in Radio Astronomy • This gives them the “right to compete” for time on all NRAO facilities including ALMA • They are delivering on of the receiver bands (Band 3) plus cash and software effort to an agreed Value of $20M FY2000 • They are also committed to providing 7.25% of the ALMA Operations costs • Canada will cover all cost overruns associated with their work • As such they were not part of the ALMA rebaselining exercise • Canadian ALMA work is covered by an MOU which empowers the NA ALMA PM and the relevant NA IPT leads to direct their work ALMA NA Cost/Management Review

  24. Japan • Japanese contribution to ALMA – Enhanced ALMA • Atacama Compact Array (ACA) System • Twelve 7-m antennas + four 12-m antennas Higher photometric accuracy • ACA Correlator high sensitivity, simultaneous realization of wide frequency coverage and high spectral resolution • New frequency bands • Band 4 (125-163GHz), Band 8 (385-500GHz), and Band 10 (787-950GHz) [R&D] • Emphasis on submillimeter wavelengths • Contributions to infrastructure & operations ALMA NA Cost/Management Review

  25. ALMA-J plans • Reexamine funding/Value agreements between projects • Complete agreement with ALMA-J – June 2006 • Respond to RFQ – summer 2006 • Late 2006 – 3rd Executive, E-ALMA ALMA NA Cost/Management Review

  26. Enhanced ALMA 12-m array ACA ALMA NA Cost/Management Review

  27. Reviews, Reviews and More Reviews ALMA NA Cost/Management Review

  28. 2008 2009 2006 2007 2010 2011 2012 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 Time Now 1.09 Science Summary Schedule (Data from IPS as of 2006Jan13) ATF Testing June ’06 ATF First Fringes SE&I Reference OSF Integration – Start dates 50th 32nd 1st 2nd 3rd 8th 16th ATF Testing Support ATF Site Characterization Science Support OSF Commissioning Antenna Array – Finish dates SCIENCE SUMMARY ` 32nd AOS 6 Ant Array Evaluation Complete 8th 16th 50th Science Verification OSF/AOS Mar ’09 Early Science Decision Point Call for Proposals / Early Science Preparation Jan ’10 Early Science Sept ’12 Start of Full Science ALMA NA Cost/Management Review

  29. J1148+5251: an EoR paradigm with ALMA CO J=6-5 • Wrong declination! But… • High sensitivity • 12hr 1 0.2mJy • Wide bandwidth • 3mm, 2 x 4 GHz IF • Default ‘continuum’ mode • Top: USB, 94.8 GHz • CO 6-5 • HCN 8-7 • HCO+ 8-7 • H2CO lines • Lower: LSB, 86.8 GHz • HNC 7-6 • H2CO lines • C18O 6-5 • H2O 658GHz maser? • Secure redshifts • Molecular astrophysics • ALMA could observe CO-luminous galaxies (e.g. M51) at z~6. ALMA NA Cost/Management Review

  30. ALMA into the EoR Spectral simulation of J1148+5251 • Detect dust emission in 1sec (5s) at 250 GHz • Detect multiple lines, molecules per band => detailed astrochemistry • Image dust and gas at sub-kpc resolution – gas dynamics! CO map at 0”.15 resolution in 1.5 hours CO HCO+ HCN CCH N. B. Atomic line diagnostics [C II] emission in 60sec (10σ) at 256 GHz [O I] 63 µm at 641 GHz [O I] 145 µm at 277 GHz [O III] 88 µm at 457 GHz [N II] 122 µm at 332 GHz [N II] 205 µm at 197 GHz HD 112 µm at 361 GHz ALMA NA Cost/Management Review

  31. Bandwidth Compression Nearly a whole band scan in one spectrum LSB USB Schilke et al. (2000) ALMA NA Cost/Management Review

  32. Antenna Designs in ALMA • Three antenna designs currently in hand: • Two will be operated in PSI interferometer in near future: • Vertex (APEX close copy operational at Chajnantor, destiny of this prototype uncertain). • AEC (Basis of AEM design, destiny uncertain). • MElCo prototype disassembled for retrofit to design similar to 3 MElCo production antennas • Four others expected • Production Vertex design (25-32 antennas) • Production AEM design (25-32 antennas) • Production MElCo 12m antennas (3 antennas) • Production MElCo 7m antennas (12 antennas) • For present purposes, only consider production Vertex and AEM designs • As these are evolving, must assume they will be identical to the prototype antennas ALMA NA Cost/Management Review

  33. Antennas • Demanding ALMA antenna specifications: • Surface accuracy (25 µm) • Absolute and offset pointing accuracy (2 arcsec absolute, 0.6 arcsec offset) • Fast switching (1.5 deg sky in 1.5 sec) • Path length (15 µm non-repeatable, 20 µm repeatable) • To validate these specifications: two prototype antennas built & evaluated at ATF (VLA) ALMA NA Cost/Management Review

  34. AEC Prototype Antenna ALMA NA Cost/Management Review

  35. Vertex Prototype Antenna ALMA NA Cost/Management Review

  36. VertexRSI and AEC Prototype Antennas ALMA NA Cost/Management Review

  37. Science Implications • Prototypes accepted from manufacturers • Final technical evaluations complete • Both antennas meet the specifications • What happens with two different antenna "designs" • common mode errors don’t cancel • But differences may help • cost (construction, commissioning, operation) • other ? • Consider: • Surface differences • Pointing • Pathlength • Mosaicking and polarization ALMA NA Cost/Management Review

  38. Science Implications:The Antenna Surfaces Source: AEG Results Both telescopes easily meet specifications (<25 µm); both are excellent antennas. ALMA NA Cost/Management Review

  39. Prototype Pointing Results Source: AEG Results Spec: 2” all-sky; 0.6” offset pointing under primary operating conditions ALMA NA Cost/Management Review

  40. Fast Switching Specification: 1.5 degrees in 1.5 seconds, settling time under 3 seconds. ALMA NA Cost/Management Review

  41. Path Length Stability • Spec: 15/20 µm repeatable/nonrepeatable *Δt = 3, 10, 30 minutes; **Wind-induced, Δt = 15 minutes ALMA NA Cost/Management Review

  42. Science Implications • Pointing • Both antennas meet specifications, but the character of pointing differs • in compact configuration • WIND: wind "shadowing“ may have some effect • SUN: sunrise may have some effect • GRAVITY: both designs are essentially rigid • in other configurations • WIND: differs over the site as will the antenna response • SUN & GRAVITY remain constant over the site • Fast Switching • Both antennas meet specifications • Awaiting redesign of AEC quadripod • If not, effect would be to decrease throughput/efficiency ALMA NA Cost/Management Review

  43. Science Implications • Phase / pathlength / focus • as pointing, but a more subtle effect. • Axis non-intersection may be the dominant effect on pathlength (baseline) prediction, and has no common mode error • Other mechanical deformations would benefit from identical antennas • Gravitational sag, thermal deformation, perhaps other environmental items • Phase effects due to fiber length • Fiber run to antenna is dominant in effective length change (but if monitored and corrected, no common mode) • Polarization matching and primary beam shape • determined by quadripod leg design (shadowing of quadripod legs, but exact shape plays a minor role too) • Lesser effect from the differing arrangement of panels and therefore character of scattering from the edges ALMA NA Cost/Management Review

  44. Fiber Length • The effective length of the fiber is dominated by the run up the antenna (see ALMA Memo 443). • Differences in the two designs include • Length of fiber run • Degree of thermal shielding • Such variations are monitored and compensated. ALMA NA Cost/Management Review

  45. Pathlength Effects • Temperature: • Surface RMS changes with ambient temperature from holography: • * VertexRSI: ~0.6-0.7 micron/K. • * AEC: ~0.8 micron/K. • Both deformations had a high degree of structure (like BUS segment print-through for VertexRSI, large-scale 45-degree plus inner-ring print-through for AEC); probably in the noise at highest frequencies, where frequent calibration will be done in any event. • Focal length change due to ambient temperature changes: • * VertexRSI: • 34 micron/C from holography • 36 micron/C from radiometry • * AEC: • 14 micron/C from holography • 20 micron/C from radiometry • All within specification and unlikely to impact science (focus tracked; surface changes small) ALMA NA Cost/Management Review

  46. Quadripods • The optical path from the sky off the reflector to the subreflector intercepts the quadripod. In both designs, the solid angle subtended by the quadripod is minimized and the point of attachment to the antenna is as close as possible to the edge of the reflector to minimize shadowing. • The shadowing profile is less than 1% of the antenna diameter. • Owing to careful minimization of the quadripod profile, the sidelobes will be small and distant from the primary beam. • Beam profiles were calculated from the shadowing profiles (next slide). • Quadripod shadowing is known for the Vertex design (ALMA Antenna Group Report #40), estimated for the AEC design by Lucas. • Reflections are minimized by profiling of the inward edge of the quadripod legs. • Different lateral motion of the subreflectors with elevation in a homologous antenna could effect cross-polarization; amenable to calculation. • Shadowing is measured using holography and is the same for both antenna designs within a few tenths of a per cent. • Integrated power <1% of that in the main beam, hence sidelobe power will be more than 40 dB below that of the main beam. ALMA NA Cost/Management Review

  47. Quadripod-dependent Questions Cross Vertex AEC Three sorts of interferometric baselines provide three sorts of beams: Vertex-Vertex, AEC-AEC, and Vertex-AEC. For the most sensitive imaging, these must all be measured and tracked. The most sensitive images include mosaics and polarization images. ALMA NA Cost/Management Review

  48. Effects of Quadripod Differences • “If one ignores the effects of the sidelobes, it is better to have antennas with different configurations; if you are going to correct for it then it is easier if they are all the same.” –James Lamb • Case One—no correction • The effect of the different sidelobes is small • Since the sidelobes differ, a source won’t be in both at once and the effect on an image is diminished • Interferometric data provide a strong discriminant for sources near the main beam owing to fringe rotation/delay offset • Case Two—correction applied • Worst case is an interfering source in a sidelobe. But with two designs it cannot be in a sidelobe of all antennas at once. One will want to correct for the different antenna patterns ALMA NA Cost/Management Review

  49. Summary • If quadrupod layout is identical, advantage of a single design exist, but is rather limited •  25 excellent antennas + 25 good antennas is better than 50 good antennas •  50 (or 64) excellent antennas is even better • Each prototype met specifications and qualifies as an excellent antenna • Conclusion: The effect of having two designs for the 12m antennas in ALMA is small. Any imaging effect can be dealt with for the most sensitive images which might need additional care. • Cost probably has a greater effect • 2 designs • 2 software interfaces • 2 Assembly, integration, verification, commissioning and science verification • 3 beams to track in the most sensitive applications ALMA NA Cost/Management Review

  50. www.alma.info The Atacama Large Millimeter Array (ALMA) is an international astronomy facility. ALMA is a partnership between Europe, North America and Japan, in cooperation with the Republic of Chile. ALMA is funded in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), in Europe by the European Southern Observatory (ESO) and Spain. ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI), on behalf of Europe by ESO, and on behalf of Japan by the National Astronomical Observatory of Japan.

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