Freezing cold antenna in the desert (SKA 4)

Sun beating down on KAT radio telescope

Sun beating down on KAT radio telescope

Imagine you are in the middle of the desert with the scorching sun beating down on you with no shade-cover, no water, no electricity and temperatures rising above 50 degrees Celsius? This is more or less the circumstances under which the elements of the Karroo Array Telescope (KAT) have to operate. The only difference is that the antenna feed needs to be cooled down to 20K ( -253 deg C), which is potentially a difference of more than 300 degrees. The cooling of the feed is necessary to reduce total RF noise in the system as every 7 degrees adds 0.1 dB RF noise.

I spoke with one of the project engineers who said that the easy part is to cool the feed to 50 K. They’re using a Gifford-McMahon helium gas cooler for the first cooling stage which can absorb up to 50 Watt of heat energy. The tricky part is cooling it down from 50 to 20 K. This has to be done inside a vacuum otherwise the smoke and dust particles would freeze and clog up the cavity. This creates another challenge, because gasses behave differently under very low temperatures and particles don’t collide as usual. This is overcome by using an ion pump cooling system which uses a strong magnetic field to positively charge all the particles, accelerating them to sputter against the cathode plates and extract the molecules to form a vacuum. See http://www.gammavacuum.com/operation.asp for a more detailed, graphic explanation.

To view previous blogs on the SKA project, please click here.

Author: Robert Kellerman

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