Upgrade of ALMA Data Transmission System Led by Japan Starts

In 2018, ALMA published the strategic vision for development towards enhancing the telescope capabilities in the 2030s as the ALMA Development Roadmap. The main priority identified in this vision is to broaden the receiver IF (Intermediate Frequency) bandwidth by at least a factor two and to upgrade the associated electronics and correlator. This upgrade is now known as the ALMA2030 Wideband Sensitivity Upgrade (WSU). In November 2022, the ALMA Board approved project proposals for the development of a second-generation correlator led by the United States, and a new data transmission system (DTS) led by Japan.

The implementation of the ALMA2030 WSU will enable new astronomical research with ALMA thanks to the increased performance of the telescope. In addition, the increase of IF bandwidth will translate in a dramatic increase of the amount of scientific data obtained in a given observation time, contributing to the efficient progress of research.

However, the great amount of data will pose a challenge on the data transmission system (DTS), which transmits the obtained data from each antenna, the eyes of the array, to the correlator and total-power spectrometer, the brains to analyze it. In order to proceed with the ALMA2030 WSU, the DTS needs to be upgraded.
This upgrade will be carried out by NAOJ in Japan in cooperation with NRAO in the United States.

In today’s advanced information society, Ethernet is one of the digital communication standards that we often hear about in our daily lives. So far ALMA has used proprietary communication systems different than those used in everyday life, but this causes inconveniences such as not being able to easily obtain replacement components when a problem occurs. To avoid this, this DTS upgrade will be based on Ethernet. In particular, it will rely on the most advanced readily commercially available standard, 400 GbE (Giga bit per second Ethernet). Combining multiple 400 Gbps (Giga bit per second) high-speed Ethernet lines, a high-speed transmission system will be designed which will be able to transmit up to 1200 Gbps data from each antenna to the correlator. Using 400 GbE long-range option will also allow to transmit the data over distances in the order of 80 kilometers, which would allow the increase of the longest distance between antennas in the future, increasing the angular resolution of ALMA and making it a sharper more powerful telescope yet.

■What does upgrade bring?
Celestial bodies consist of various atoms and molecules, each of which emits radio waves at different frequencies. For example, carbon monoxide molecules, which emit radio waves at 115 GHz, are indicative of rarefied gases with low temperatures and densities that float throughout space. Conversely, hydrogen cyanide, which emits radio waves at 89 GHz, is known as an indicator of a relatively hot and dense gas. By comparing the distribution of these two molecules, we can explore how stars are born from environments with rarefied gas. In this way, by observing many kinds of molecules at the same time, various astronomical phenomena are revealed. Simultaneous observation of many kinds of molecules means simultaneous observation of radio waves in a wide frequency band. However, it is technically difficult to observe a wide frequency band at once. Currently, to cover a wide frequency band, observations are carried out many times, divided into narrow frequency bands, which requires much observation time.
By improving receivers to observe a wide frequency band at once and having an improved DTS to transmit all that data at once, it will be possible to observe and analyze radio waves in a wider frequency band with high sensitivity with the same observation time as before. New discoveries that have never been captured before are expected.



About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.