Time: 10:15 EDT (8:15 MDT, 1415UT)
Conference leader: Al Wootten
Past minutes, etc on ALMA Configuration Group Page
Minutes
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Attendees: Wootten, Conway, Guilloteau, Woody, Webster, Butler, Kogan, Sakamoto, Wright, Viallefond, Boone and Radford
Summary
From the 21 November 2000 telecon minutes: "The plans for the layout
of the pads must be finalized by the beginning of construction. We hope
that the first construction funds will arrive on 2001 Oct 1 when the FY2002
begins here."
At its meeting at San Pedro and Santiago the ASAC heard presentations on, and visited the site. Hofstadt urged the scientists to reach a final configuration plan by January 2002. The construction funds have not arrived yet but the construction phase of ALMA does appear to be imminent, beginning possibly as soon as yesterday. Hence, the configuration group should act on the decisions made at its PDR and move on toward a final design decision. A plan for doing this was presented, wherein outstanding issues could be addressed by the end of the year. Biweekly teleconferences will be held, at which progress on designing the intermediate configurations, and the bridge configuation between the large configuration and the inner configuration, will be discussed.
Updates
Philosophy was discussed, spurred by Woody's recent memos beam optimization and Conway's discussion of how this provides a suitable philosophical basis for establishing the grand design of the array. Pad sharing was discussed; to some extent this compromises sidelobes. It was generally agreed that pad sharing is subjugate to scientific considerations but the goal remains to design for 250 pads or less.
Optimization in the uv plane and in the beam was discussed. Boone noted that uv coverage was an important parameter for imaging considerations whereas beam sidelobes could be secondary. An example of a configuration with excellent beam properties and poor imaging properties, or excellent imaging and poor beam properties, will be produced for illustration.
Leonia noted that this is the fundamental problem of radio imaging--how to reconstruct the image. No configuration works which does not provide appropriate uv coverage, but the appropriate uv coverage depends to some degree on the nature of the source to be imaged. We must design a configuration, simulate observations with that on appropriate sources, and select the configuration on the basis of our best results. This was the process at the PDR.
The degree of short spacing coverage in the large configurations was discussed. Guilloteau noted that at least enough were required to effect calibration.
Conway has been making progress on intermediage configurations and will have considerably more time to work on this after 1 November.
Webster mentioned that he is working on designs for the hybrid configurations going out to the largest configuration. He noted that the Project Book has not been updated since the PDR and still refers to 10 km as the diameter of the larger configuration. The Project Book chapter will be updated to reflect the results of the PDR and the expansion of the project to three partners. As a consequence, he has designs to 10km which remain within the pad budget, even perhaps using on 235 pads.
Future Plans
The large configuration is bounded by the constraints of the site, rather than by a number. Leonia demonstrated at the PDR how an array of diameter roughly 14km could be accommodated on the site. Some baselines between the antenna stations he identified and some stations to the extreme SE in Conway's zoom spiral design in fact reach 17 km. The larger arrays should fully employ the real estate available on the site, consistent with the constrains that fiber optic runs will be less than 25 km.
We will arrive at at least one strawman configuration design consistent with the results of the PDR by early December. The Chajnantor campaign of December 2001 will include an ESO engineer, to provide feedback for the final configuration selection. Holidays extend beyond New Year's Day in many countries. URSI and AAS meetings in NA occur 6-10 January. SG is committed 14-18 Jan. A strawman date for this would then be after 20 January. Possible venues include the AOC, with a visit to the Test Interferometer site and whatever part of the Vertex antenna has arrived, Tucson, or ?
The next teleconference was tentatively set for 1415UT on 16 October.