The ALMA Main Array Correlator

To make images from millimetric wavelengths joined by multiple antennas, we need an absolutely colossal amount of computer power. Signals from each antenna pair – there are 1225 possible pairs alone in the main array of antennas (50)- should be mathematically compared billions of times per second. You would need millions of laptop computers to perform the number of operations that ALMA carries out every second! This need resulted in the construction of one of the fastest supercomputers in the world, the ALMA Correlator.

The Correlator, installed in the AOS Technical Building at an altitude of 5,000 meters above sea level, is the last component in the cosmic wavelength collection process. It is a very large data processing system, composed of four quadrants, each of which can process data from up to 504 antenna pairs. The complete Correlator has 2,912 printed circuits, 5,200 interface wires and over 20 million welding points. The Correlator is made up of Tunable Filter Bank (TFB) cards. The distribution requires four TFBs for data that arrives from a single antenna. These cards have been developed and optimized by the Bordeaux University in France.

The Morita Array or the Atacama Compact Array (ACA) Correlator

ALMA has fifty-four 12-meter diameter antennas and twelve 7-meter diameter antennas. The smaller antennas, along with four of the larger ones, make up the Morita Array or the Atacama Compact Array (ACA). This enables ALMA to make better observations of broader objects in the Universe, such as giant molecular gas clouds in the Milky Way. The ACA Correlator is designed to process signals detected by the ACA antennas. It consists of 52 modules connected to each other via optic fiber, which are installed in 8 racks in the AOS technical building. The power spectra resulting from the correlation are transferred to ACA data processing computers, transforming photons to photos.

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