Minutes of the MDC Configuration Working Group Meeting
14 September 1998, written by Tamara Helfer
Present:
Tucson: Darrel Emerson, Tamara Helfer (chair), Simon Radford, Jeff Mangum
Socorro: Bryan Butler, Chris Carilli, Leonia Kogan, Frazer Owen, Michael Rupen, Min Yun
Hawaii: Al Wootten
1. Tamara gave a short overview of the current status on the array configuration work as outlined on the meeting agenda. Tamara and Leonia described features of Leonia's optimization code, which is a minimax for synthesized beam sidelobes.
2. D array: Leonia has run an optimization for worst sidelobe vs. D array diameter, for the case where N=36 ants, D=10m, with a minimum spacing of 12.8m. His results yield a D array with a nominal diameter of about 90m; the maximum sidelobe in such a filled array is about 10-11%.
The group discussed the goal of producing D subarrays with a variety of elongations to enable observations of sources at different declinations. This discussion touched on several points:
a. How to perform the optimization. Leonia currently optimizes for a circular beam at the zenith. He does not take into account any shadowing considerations or noncircular beams. He will think about ways to optimize for a noncircular beam. In the Tucson meeting postmortem, Simon suggested simply scaling the NS coordinates from the optimized circular array as a starting point for an elongated array.
b. Our working assumption is that we will have three D subarrays, with elongations of 1.2, 1.6, and 2.9 (as in the Project Book). Tamara will check with Mark Holdaway about how set those numbers are.
c. Do we want one poured slab or discrete stations for the D array? Simon's opinion was that this is an engineering decision more than a science decision.
3. C, B, A arrays: Tamara suggested that we adopt as the default design philosophy the idea of nested rings/triangles. This was accepted by the group. Tamara will design default strawperson arrays for these configurations, with help from Leonia if he is able to assist (Leonia is not at all funded to work on MMA issues). Tamara will talk to Mark Holdaway about getting started with imaging simulations to test specific configurations. Michael Rupen volunteered to give moral and intellectual guidance for these simulations.
4. The next MDC Configuration Working Group meeting is tentatively scheduled for 4 weeks from today, or 12 October 1998, 11 am EDT.