image: ALMA telescope array in the Atacama Desert
Credit: © ESO/C.Malin
The Atacama Large Millimeter/Submillimeter Array (ALMA) in the Chilean Andes is one of the most powerful radio telescope facilities in the world. Researchers use it to study dark and distant regions of the universe in order to better understand how stars, planets, galaxies and life itself are formed. To do this, ALMA measures the millimeter and submillimeter radiation emitted by cold molecular clouds, for example. Molecular clouds are interstellar gas clouds with a temperature of only a few tens of Kelvin, in which stars form when the density and temperature are right.
ALMA has a total of 66 individual parabolic antennas with diameters of 12 m or 7 m, each equipped with high-frequency receivers for ten wavelength ranges (›ALMA bands‹) between 6 and 8.6 mm (35–50 GHz) and 0.3 and 0.4 mm (787–950 GHz) in the electromagnetic spectrum. For Band 2, which covers wavelengths from 2.6 to 4.5 mm (67–116 GHz), the Fraunhofer Institute for Applied Solid State Physics IAF and the Max Planck Institute for Radio Astronomy (MPIfR) have now provided 145 low-noise amplifiers (LNAs). This means that all ALMA bands are now fully equipped for the first time.
With ALMA’s Band 2, researchers hope to gain a better understanding of the so-called cold interstellar medium — a mixture of dust, gas, radiation and magnetic fields from which stars are formed. Complex organic molecules in nearby galaxies, which are considered precursors to biological building blocks, as well as planet-forming disks, will also be studied in greater detail thanks to the improved measurement capabilities.
Unique average noise temperature of 22 K enables highly sensitive measurements in band 2 of the ALMA telescopes
“The performance of receivers depends largely on the performance of the first high-frequency amplifiers installed in them,” explains Dr. Fabian Thome, head of the subproject at Fraunhofer IAF. “Our technology is characterized by an average noise temperature of 22 K, which is unmatched worldwide.” With the new LNAs, signals can be amplified more than 300-fold in the first step. “This enables the ALMA receivers to measure millimeter and submillimeter radiation from the depths of the universe much more precisely and obtain better data. We are incredibly proud that our LNA technology is helping us to better understand the origins of stars and entire galaxies.”
“This is a wonderful recognition of our fantastic collaboration with Fraunhofer IAF, which shows that our amplifiers are not only ‘made in Germany’ but also the best in the world,” says Prof. Dr. Michael Kramer, executive director at MPIfR.
Development, production and qualification of InGaAs mHEMT LNAs for ALMA
At the heart of the LNAs for ALMA’s Band 2 are monolithic microwave integrated circuits (MMICs) based on metamorphic high-electron-mobility transistors (mHEMTs) developed by Fraunhofer IAF using the compound semiconductor material indium gallium arsenide (InGaAs). The technology enables LNAs with particularly low noise temperatures, which significantly increases the sensitivity of the receivers. As the name suggests, low-noise amplifiers improve the quality of incoming signals by amplifying the signal while causing as little disruptive background noise as possible.
Fraunhofer IAF and MPIfR were jointly commissioned by the European Southern Observatory (ESO), which operates ALMA in cooperation with other international institutions. Fraunhofer IAF was responsible for the specific design of the MMICs, their manufacturing, their testing at room temperature and the selection of the chips. MPIfR took over the modules’ complex assembly and qualification, including cryogenic test measurements at 15 K for use in the ALMA Band 2 receivers matching ESO specifications.
Location and operation of ALMA
In order to perform the most accurate measurements possible, ALMA was built on the Chajnantor Plateau in the Chilean Andes. In the Atacama Desert, at an altitude of 5000 m above sea level, conditions for radio astronomical measurements are unique in the world. The high altitude and dry location ensure that millimeter and submillimeter radiation from distant regions of the universe is significantly less attenuated than elsewhere, as it has to penetrate less atmospheric water vapor.
ALMA is jointly operated by ESO, the US National Science Foundation (NSF) and the Japanese National Institutes of Natural Sciences (NINS) in cooperation with the Republic of Chile. ALMA is supported by ESO on behalf of its member countries (Belgium, Denmark, Germany, Finland, France, Great Britain, Ireland, Italy, the Netherlands, Austria, Poland, Portugal, Spain, Sweden, Switzerland, the Czech Republic, and the host country Chile), by the NSF in collaboration with the Canadian National Research Council (NRC), the Taiwanese National Science Council (NSC) and NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
About Fraunhofer IAF
The Fraunhofer Institute for Applied Solid State Physics IAF is one of the world's leading research institutions in the fields of III-V semiconductors and synthetic diamond. Based on these materials, Fraunhofer IAF develops components for future-oriented technologies, such as electronic circuits for innovative communication and mobility solutions, laser systems for real-time spectroscopy, novel hardware components for quantum computing as well as quantum sensors for industrial applications. With its research and development, the Freiburg research institute covers the entire value chain — from materials research, design and processing to modules, systems and demonstrators. https://www.iaf.fraunhofer.de/en.html
Further information
https://www.eso.org/public/unitedkingdom/teles-instr/alma/?lang – Learn more about ALMA
https://www.iaf.fraunhofer.de/en/researchers/electronic-circuits.html – More information about activities in the field of electronics at Fraunhofer IAF
https://www.iaf.fraunhofer.de/en/networkers.html – More information about collaborating with Fraunhofer IAF