HERA currently comprises 57 of the eventual 350 elements, with construction proceeding apace. The contract to install the rest of the support poles has been awarded, with the work to be completed before the end of the year. Regular science operations have been underway since mid-October. With the site construction teams set, focus has turned to finalising the new architecture, which will start to be installed in early 2018.
The new architecture features field-deployed “nodes” that can each accommodate 12 antennas. Each node contains a post-amplifier (the “PAM”) and a digitiser/channeliser/packetiser (the “SNAP”) for each signal path. Being deployed throughout the array allows for either:
(a) short lengths of coaxial cable (keeping them short to try and keep the reflections at short timescales) or
(b) longer lengths of analogue optical fibre (keeping them long to keep the reflections at long timescales) to be used.
Both options keep the reflections out of the desirable mid-length timescales. The default approach is to use the long lengths (of order 500m) of optical fibre.
The outputs from the node are 10 gigabit ethernet fibres with the channelised data, which are sent back to the Karoo Data Rack Area (KDRA) back in the Karoo Array Processor Building (KAPB). RF quietness is obviously a key specification, and measurements are on-going to ensure compliance with the stringent site specs. Currently one prototype is deployed for testing and is shown below (with the RF-tight door removed for the photo).
HERA recently held its annual workshop in October — this year hosted by NRAO at the Domenici Science Operations Center in Socorro, NM. The growing team may be seen in the picture below. The team held a comprehensive review of the full system and looked at commissioning data. Software pipelines and finalising specifications for the next generation equipment were key goals. A comprehensive review of the new feed options was conducted, and a Vivaldi-based design from Cambridge University was down-selected.
The new Vivaldi has a 5:1 bandwidth, which allows HERA to instantaneously measure redshifts from about 4 – 27, so the entire evolution from the early Dark Ages through to full reionization is accessible. The image below shows the first design drawing of a deployable structure — the design is currently being finalised with final trade-offs between performance and manufacturability. On-antenna testing will commence in January.
HERA is a partnership to conduct an experiment to detect and characterise the Epoch of Reionization. Partner institutions in the collaboration are Arizona State University, Brown University, University of California Berkeley, University of California Los Angeles, University of Cambridge, Massachusetts Institute of Technology, National Radio Astronomy Observatory, University of Pennsylvania, Scuola Normale Superiore de Pisa, SKA-South Africa and the University of Washington. Additional collaborators are Cal Poly Pomona, Imperial College, Harvard-Smithsonian Centre for Astrophysics, University of KwaZulu Natal, Rhodes University and University of Western Cape. HERA is an SKA precursor instrument. HERA is funded by the US National Science Foundation, the Gordon and Betty Moore Foundation with additional support from the partner institutions.