Update on the Square Kilometre Array
Sean Dougherty, Herzberg Institute of Astrophysics, Ingrid Stairs, University of British Columbia and Russ Taylor, University of Calgary
International Developments
SKA Implementation Plan
The International SKA Steering Committee (ISSC) meeting took place from 26-31 March in San Juan, Argentina. A major outcome of the meeting was an agreed plan for the phased implementation of the SKA. The plan recognizes that four of the five key science goals of the SKA (probing the dark ages and the epoch of reionization, the origin and evolution of cosmic magnetism, the evolution of galaxies and large scale structure, and strong field tests of gravity) are enabled by a telescope operating at the low (~100 to 300 MHz) and mid (300 MHz to a few GHz) frequency ranges. See the most recent SKA Science Case book (http://www.skatelescope.org/pages/page_sciencegen.htm) for details of key science. The mid-frequency range science is enabled by the wide fields-of-view capabilities of focal-plane, phased-array feed technologies on 10-15 m class parabolic reflector antennas. The agreed implementation plan is a phased development of the full SKA,
1) with the “regional demonstrators” initially leading to a Phase 1 SKA to be constructed on the 2012-2015 timescale with a target construction cost goal of €250 M.
2) Phase 1 will consist of 10% of the collecting area of the full SKA over the mid-frequency range from 300 MHz to a few GHz (the upper frequency to be defined by design studies currently in progress).
3) The scientific and technical outcomes during Phase 1 rollout will guide the development and construction of the full SKA on the 2016-2020 time scale.
Two funding proposals, the European FP7 Preparatory Phase (PrepSKA) Proposal and the US Technology Development Program (TDP) Proposal have been awarded funding for the final stages of planning for the SKA. Major funding has been allocated in Australia and South Africa for SKA pathfinder “regional demonstrator” telescopes at each of the proposed sites to be constructed from 2008 to 2012.
FP7 Preparatory Phase Proposal (PrepSKA)
The 2006 European Strategy Forum on Research Initiatives (ESFRI) Roadmap for Research Infrastructures[1], lists the Square Kilometre Array as the next generation radio telescope for Europe, to become operational on the 2014-2020 time frame. As a result, the European SKA Consortium was invited to submit a Preparatory Phase Proposal to the European Union for FP7 Infrastructures. The proposal, “A Preparatory Phase Proposal for the Square Kilometre Array” or “PrepSKA”, was submitted on 2 May 2007. The proposal was coordinated by the United Kingdom Science and Technology Facilities Council and includes seven major work packages with participation by 20 organizations from the international SKA collaboration, including several funding agencies The National Research Council of Canada and the University of Calgary are named participants from Canada. The award of funding was announced in August.
The principal objectives of PrepSKA are:
- to produce a deployment plan for the full SKA, and a detailed costed system design for Phase 1 of the SKA;
- to further characterize the candidate SKA sites in Southern Africa and Australia and to analyze the various risks associated with locating the SKA at each of the sites;
- to develop options for viable models of governance and the legal framework for the SKA during its construction and operational phases;
- to develop options for how the SKA should approach procurement and how it should involve industry in such a global project;
- to investigate all aspects of the financial model required to ensure the construction, operation and, ultimately, the decommissioning of the SKA;
- to integrate all of the activities, reports and outputs of the various working groups to form an SKA implementation plan.
The duration of PrepSKA is 4 years, from 2008-2011. Including the contribution from the European Community (EC) and matching funds from national agencies in Europe, the cost of the Work Packages in PrepSKA total €22.2 M.
Figure 1 - The EU FP7 SKA Paraparatory Phase Proposal is coordinated by a central team in Europe with collaboration from the international entities that are represented on the International SKA Steering Committee.
US Technology Development Program (TDP)
The US SKA Consortium has recently been awarded $12 M USD by the National Science Foundation a “Technology Development Project for the Large-N/small-d Square Kilometre Array Concept”. The TDP proposal was submitted by Cornell University on behalf of the US SKA Consortium, and includes international collaborators. The TDP project is intended as a collaborative but separately funded parallel effort to PrepSKA, explicitly stating that it is the “mechanism for US participation in the international design effort”. The funding is for five years (2007-2011. A prime thrust of the work is the research and development of 10-15m class parabolic antennas for the SKA, including a study of the technical limitations that will define the upper frequency range. The scope of the proposal is to span the current SKA reference design up to an engineering design for construction of Phase I SKA in 2012.
The Canadian SKA R&D program on technology an science forms the basis for our collaborations on both the TDP, PrepSKA, and our partnership on the Australia SKA Pathfinder. This convergence reflect the international recognition of Canadian strengths and expertise in key technologies, and the coming together of the global R&D program for the SKA.
The Canadian-Australian Collaboration on the Australia SKA Pathfinder
The Australian SKA Pathfinder (ASKAP) is being constructed in the Mid-West region of Western Australia (formerly called MIRANdA). This telescope (formerly called MIRANdA) is being developed as an international partnership between Australia (CSIRO) and Canada (NRC) to build an array of dishes based on the SKA Phase 1 design. ASKAP will demonstrate high dynamic range imaging over very wide-field-of-view using phased-array feeds on 15 metre antennas, and will make significant advances in the key SKA science. (See June 2007 issue of e-cassi).
The agreement between NRC and CSIRO to collaborate toward the realization of ASKAP was established in November 2006. In May the Australian Government announced an additional allocation of $56.6 M AUD to ASKAP, bringing the total of Australian Government commitment to $101 M AUD for the 2007-2011 time period (see http://www.dest.gov.au/ministers/bishop/budget07/bud34_07.htm for details).
South African Demonstrator
South Africa recently informed the ISSC that the SA government will fund development
of an SKA pathfinder, the “Karoo Array Telescope” (KAT) at the proposed SA site, at a
level of about $100 M Euro. At this point in time the technical specifications for KAT are in transition. However, the KAT planners do not intend to pursue focal plane array technology or a low-frequency aperture plan array. Thus degree of alignment of the KAT with the SKA reference design is uncertain.
Canadian Developments
Canadian Science Activity
The Canadian SKA Science Advisory Committee (chaired by Norbert Bartel) has produced a Canadian science document for the MIRANdA telescope, ranging from Galactic HI and polarization studies through compact objects to galaxy evolution and cosmology, and emphasizing what would be gained from various possible upgrade and expansion paths for MIRANdA. Our Australian counterparts have also produced their own document, and we have now merged of the two science cases to arrive at a document with the strongest possible international appeal and a concerted plan for future development. This science document will be published as a special issue of the journal Experimental Astronomy.
In March there was a meeting held at ATNF in Sydney, Australia on focal-plane array technology for the SKA, followed by a two-day meeting on Science with ASKAP. There was strong Canadian participation in both these meetings, with eleven attendees from Canada, including engineers from HIA and scientists from both the university community and HIA. The science meeting covered topics in both the Canadian and Australian science plans, and was a catalyst in developing the combined science case.
Following the science meeting, there was a face-to-face meeting of the Australia/Canada ASKAP collaboration. A result of this meeting was a joint Communique, a highlight of which was the affirmation that ASKAP is on -- and remains on -- the international science and technology path to the SKA.
Formation of The University of Calgary Centre for Radio Astronomy
In June the Office of the Vice-President Research of the University of Calgary approved the formation of a Centre for Radio Astronomy at the University of Calgary. The Centre
for Radio Astronomy combines groups in the Faculty of Science and the Schulich School of Engineering and builds on a long-standing research partnership between the
University of Calgary and the National Research Council of Canada, Herzberg Institute of Astrophysics. As part of establishing the Centre, the University of Calgary
will provide $2.1 M of direct cash and in-kind support toward a mandate to promote and facilitate Canadian participation in the next-generation international radio astronomy
facilities prioritized in the Canadian Long-Range Plan for Astronomy, including ALMA and the Square Kilometre Array.
Canadian SKA Technology In Canada, SKA-related technology development is targeting low-cost, high-performance solutions in three areas vital to the SKA: wide field-of-view, low system-temperature,
and large collecting area. These three areas are being addressed respectively by phased focal-plane array feeds (the PHAD project), novel CMOS LNAs, and reflector
antennas fabricated with composite materials (the CART project).
PHased-Array Demonstrator (PHAD) Steady progress is being made on the PHased-Array Demonstrator (PHAD), a prototype engineering demonstrator of a phased focal-plane array at the Herzberg Institute
for Astrophysics (HIA). PHAD will not have the sensitivity or bandwidth of a science-capable feed system, but will be sufficient to demonstrate the technology and to explore
design issues applicable to a science-ready system. One of the key design features is the ability to store all the data from all of the elements in the array. This enables
tremendous flexibility, both in system diagnostics, and in beamformer algorithm development. Initial beamformer design will be done off-line with a software beamformer
that will work with stored data. Once the algorithm has been tuned, it can be uploaded into the FPGA-based data acquisition system and real-time beamforming can then
be used for deep integrations.
The PHAD array has 180 elements (90 for each orthogonal linear polarization) along with a row of "dummy" elements around the periphery of the array (Fig. 1). The array is
76 cm wide (or 5 wavelengths at 2 GHz) with element spacing of half-wavelength at 2 GHz. The elements are "Vivaldi” antennas, working over the frequency range 1--2 GHz.
There are no active components on the antenna element boards. The array is modular and is assembled by sliding antenna elements into slotted posts supported by the
backplane.
The receivers used in PHAD take advantage of modern radio frequency integrated circuits which provide a large amount of functionality with a small number of components.
For example, on the receiver chip there is, in addition to the usual chains of amplifiers and mixers, a complete synthesizer to tune the receiver. Low-noise amplifier chips are
also on this board.
PHAD is now built, and an extensive series of tests and measurements have started, beginning with array radiation patterns measured in an anechoic chamber. Ultimately, we
are aiming to test the system on a radio telescope.
Figure 2 - The complete 180-element PHAD array assembly, with the array of antenna elements (left side), the receiver module rack (centre), and the data output lines (on the right). This prototype phased-array feed system will be mounted to the new 10-m composite antenna.
CMOS Low-Noise Amplifiers The availability of very-low-noise amplifiers operating at room temperature is key to producing sensitive, low-cost, phased-array receiver systems, since they do not require
potentially costly cooling systems. Although traditional HEMT technology has had little improvement over the past decade, the CMOS technology used in computer chips has
been advancing at an exponential rate described by Moore's Law. As transistors are made smaller, they not only work at higher frequencies, but they also have lower noise.Although this reduction in noise has been predicted for some time, only recently has it been demonstrated. Fig. 2 shows an amplifier fabricated with 90 nanometre CMOS
that has achieved a noise temperature of less than 14K between 800 and1500 MHz, operating at room temperature. This has been attained through a combination of clever
circuit design and careful layout of the chip. This very promising result suggests that as CMOS technology progresses to smaller device geometries, there are excellent
prospects for room temperature CMOS amplifiers to be competitive with traditional cooled low-noise amplifiers. Leo Belostotski and Jim Haslett at the University of Calgary
are leading this work.
Figure 3: Left: the Belostotski-design CMOS low-noise amplifier integrated circuit at the University of Calgary. Right: noise performance over the full 800 and 1450MHz band operating at room temperature is at most 0.2 decibels, equivalent to 14K.
Composite Reflector Antennas The ability to build large collecting areas with cost-effective reflectors having excellent radio-frequency performance remains a significant tecnology challenge for future radio
telescopes. At HIA, the CART project (Composite Applications for Radio Telescopes) is addressing this challenge by applying composite materials and fabrication techniques to low cost-per-unit-area radio-telescope applications.
Work on a 10-m prototype is progressing well. In the past three months, the 3-piece mold for the reflector surface has been installed in our fabrication facility – a renovation of the hanger used to house “BOB”, the aerostat used in testing for the Large Adaptive Reflector. To ensure the fabrication process would work as designed, a section of the integrated reflector surface and beam structure was successfully built. This prompted the lay-up of the first full 10-m reflector, now well advanced (Figures 4 and 5).
By the time you are reading this, the reflector will have been pulled from the mold and placed on a telescope mount for testing. The mount that will be used is from the MV-1 mobile antenna formerly located in Yellowknife, in the Northwest Territories, as part of the Canadian geodetic VLBI array. The opportunity to acquire this antenna arose during the winter months, and one of our engineers spent a week in –30°C temperatures supervising the dismantling of the antenna for shipment to the DRAO site. It arrived in late March and a refit for the CART project is complete.
Figure 4 - The reflector surface of the 10-m prototype laid in the mold. The blue material is foam core.
Figure 5 - Panorama of the back of the completed reflector (yellow), sitting in its mold, complete with structural beams (black).