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Supercomputer boost for world's highest observatory

Paul Sutherland, Feature writer
Dec 23, 2012, 8:00 UTC

Sen—A major step forward towards completion of the world's highest telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), has come with installation and testing of its supercomputer.

This colossal machine, one of the most powerful anywhere, is a vital component of the observatory as it will combine and manage the faint signals from space collected by its 66 dishes.

It is housed at an operations centre, the ALMA Array Operations Site (AOS) Technical Building, alongside the many antennas in a room where astronomers can work comfortably, protected against the thin air and inhospitable environment outdoors at 5,000 metres (16,000 ft) altitude.

The supercomputer, termed the ALMA correlator, has more than 134 million processors and performs up to 17 quadrillion operations per second, a speed comparable to the fastest general-purpose supercomputer in operation today

By using it to combine and compare the celestial signals from deep space, European Southern Observatory (ESO) scientists can effectively turn the dishes into one enormous telescope up to 16 kilometres (10 miles) wide, since this is the furthest distance apart that the antennas can operate together.

Confirmation that the correlator is up and running is a major milestone in preparations for the observatory's inauguration in March 2013. The writer visited when a number of dishes were already operating in October 2011.

Data collected by each antenna must be combined with that from every other dish. The correlator can manage 64 of the antennas at a time, carrying out up to 17 quadrillion calculations every second, which is comparable to the performance of the fastest general-purpose supercomputers in the world.

Wolfgang Wild, European ALMA Project Manager for ESO, said: “This unique computing challenge needed innovative design, both for the individual components and the overall architecture of the correlator.”

A wide-angle view of the correlator supercomputer at ALMAA wide-angle view of part of the correlator supercomputer at ALMA. Credit: ESO

The correlator's initial design, construction and installation, was led by the US National Radio Astronomy Observatory (NRAO), the lead North American partner in ALMA, and jointly funded by the US National Science Foundation and ESO.

“The completion and installation of the correlator is a huge milestone towards the fulfillment of North America’s share of the international ALMA construction project,” said Mark McKinnon, North American ALMA Project Director at NRAO. “The technical challenges were enormous, and our team pulled it off,” he added.

A key part of the correlator is a unique digital filtering system conceived and built for ESO by the University of Bordeaux in France. A set of 550 individual digital filters can split the wavelengths of light that ALMA sees to allow observations to be made in much greater detail.

The university's Alain Baudry, European ALMA correlator team leader, said: “This vastly improved flexibility is fantastic; it lets us ‘slice and dice’ the spectrum of light that ALMA sees, so we can concentrate on the precise wavelengths needed for a given observation, whether it’s mapping the gas molecules in a star-forming cloud, or searching for some of the most distant galaxies in the Universe.”

The builders of the supercomputer faced particularly unusual challenges. Since the air is so thin at ALMA's altitude, twice the usual airflow is needed to cool it. Spinning computer hard drives are not used because they rely on a cushion to prevent their read/write heads from hitting the platters. The correlator also had to be designed to withstand earthquakes because seismic activity is common in the Atacama Desert.

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