Locally-developed antennas take UKZN HIRAX project closer to implementation

October 25th, 2019, Published in Articles: EngineerIT

 The Hydrogen and Real-time Analysis eXperiment (HIRAX) has deployed two new prototype telescope dish designs, one aluminium and the other fibreglass, at the South African Radio Astronomy Observatory (SARAO) at Hartebeesthoek.

HIRAX is led by the University of KwaZulu-Natal (UKZN) and hosted as a guest instrument by the South African Radio Astronomy Observatory (SARAO) and managed by a consortium which includes five additional South African institutions: the African Institute for Mathematical Sciences (AIMS), Durban University of Technology (DUT), Rhodes University (RU), University of Cape Town (UCT), and the University of Western Cape (UWC). In addition to the seven South African consortium members, HIRAX has 17 current international partners who provide significant financial and in-kind contributions to the HIRAX project.

HIRAX will be an interferometer that comprises roughly 1000 x 6 m dishes placed in a close-packed, redundant configuration, and will be deployed at the Karoo SKA site. The operating frequency of 400 – 800 MHz corresponds to a redshift range of 0,8 to 2,5.  The dishes will be stationary and will have a 5 – 10 degree field of view and will be periodically repointed in elevation in order to build up coverage of the southern sky.

The HIRAX telescope will enable research in the evolution of dark energy through hydrogen intensity mapping, and research on transient radio sources such as fast radio bursts (FRBs) and pulsars. Dark energy is a mysterious force in the universe that scientists believe is acting against gravity to cause an accelerated expansion of the Universe. FRBs are mysterious millisecond extragalactic flashes in the sky of unknown origin.

A fast radio burst is a transient radio pulse of length ranging from a fraction of a millisecond to a few milliseconds, caused by a high-energy astrophysical process not yet fully understood.

The first FRB was discovered by Duncan Lorimer and his student David Narkevic in 2007 when they were looking through archival pulsar survey data and named after him. Many FRBs have since been recorded. Although the exact origin and cause is uncertain, they are almost definitely extragalactic and extremely energetic at their source, the strength of the signal reaching Earth has been described as 1000 times less than from a mobile phone on the moon.

Fig. 1: Assembling one of the protype dishes at SARAO Hartebeesthoek.

Collaboration on the dish design started in the beginning of 2018 with the purpose of defining final dish requirements for the project. The design of these 6 m dishes has strict tolerances on the shape, surface accuracy, and receiver position. The mechanical design also allows for the manual repointing of the dishes every few months, enabling the instrument to map about a third of the sky over a five-year period while minimising cost by eliminating the need for active drive mechanisms.

The fibreglass dish was designed and manufactured by MMS Technology in Pretoria, and the aluminium dish was designed and manufactured through a partnership between NJV Consulting and Rebcon in Durban. Funding for the HIRAX prototype dishes was provided by the UKZN and the Department of Science and Innovation through the National Research Foundation.

HIRAX will instrument and analyse the two new prototype dishes over the next few months to develop the final requirements for an open tender for the first 256 dishes to be installed at the HIRAX main site in the Karoo.

“After the successful testing at Hartebeeshoek we are looking forward to hosting HIRAX in the Karoo”, SARAO MD Rob Adam said. “We always had the idea that the SKA site would prove to be an attractor for other leading-edge global astronomy projects, and this is turning out to be the case.”

Cynthia Chiang, HIRAX instrumentation lead and professor at McGill University and Fractional Professor at UKZN, said that to deliver high-precision science, HIRAX has stringent specifications that require custom-built telescope dishes. “The two new dishes from MMS and Rebcon represent a significant milestone toward achieving HIRAX’s goals, and it will be crucial for informing the final instrument design.” Both MMS and the NJV/Rebcon collaboration worked hand-in-hand with the HIRAX project to produce prototype designs that will inform final dish requirements for the HIRAX project.

The MMS dish consisting of a fine aluminium mesh embedded in fibreglass was installed in August this year. The MMS dish can tilt in elevation 30 degrees either side of zenith. Designing and manufacturing this dish was a serious trade-off between performance and cost. For this reason, the mount was kept as low and simple as possible and the dish itself as thin as possible without compromising too much on performance. The single piece composite material dish does not need any post-manufacturing setup, and the mount is low enough to facilitate easy adjustment of the dish elevation by one person.

The NJV/Rebcon dish was installed in October 2019. The design intent was realised by a form of laser-cut profiled aluminium elements which provided the parabolic accuracy the project required.  The dish is made of aluminium mesh with an aluminium backing structure, it is fixed in azimuth and can tilt in elevation down to the horizon.

Kavilan Moodley, principal investigator of the project and professor at UKZN, emphasised that through these and future collaborations with industry and the scientific community, the project endeavours to build technical capacity nationally as South Africa increases its radio astronomy portfolio through MeerKAT and the development towards the Square Kilometre Array (SKA).

HIRAX is complementary to the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and will share much of the back-end technology, including FPGA-based ICE boards and the GPU correlator.

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