The Atacama Large (sub)Millimeter Array, ALMA, is located at an altitude of over 5000 meters on the Chajnantor plateau in Chile. Credit: ESO.
ALMA is an interferometric array of sub-mm radio telescopes located on a high desert plateau in Chile. It is currently the largest ground-based astronomical project with participation from Europe, United States, Japan, Canada, South Korea, Chile and Taiwan. The location of ALMA has been chosen because the altitude and dry desert environment minimises the amount water vapour in the air column above the telescopes. One of the major science drivers of ALMA is to observe the cold universe, in particular the microwave radiation emitted by water molecules in clouds and protoplanetary disks. This radiation is however also readily absorbed by the water molecules in our own atmosphere.
ALMA consists of 66 telescopes with each telescope housing a set of receiver cartridges sensitive to different wavelength bands. NOVA, together with Onsala Observatory in Sweden and industrial partners, is constructing a total of 73 receivers for Band 5, the 163 – 211 GHz wavelength range. Within this band, the thermally excited emission of water vapour can be observed at 183 GHz.
The Band-5 receivers are heterodyne sideband-separating receivers providing vey high performance: The sensitivity is better than 75K over the whole band and better than 55K over 80% of the band. The polarisation separation is -23dB, better than any other ALMA receiver.
The production of 73 advanced astronomical instruments is somewhat atypical compared to other instrumentation projects. A mass-production approach has been taken where a dedicated team of NOVA instrument scientists and technicians assemble and test the receivers in an continuous flow. By early September 2016, 35 receivers have been delivered. The last of the 73 receivers is expected to be delivered by mid-2017.
The NOVA lead for the ALMA Band-5 project is: Dr. Wilfried Boland (NOVA).
Image below: Three ALMA Band-5 receivers ready for delivery. © NOVA.