ALMA Board Approves Development of Next-Generation Spectrometer for Morita Array

In April 2025, the ALMA Board approved the development of a new state-of-the-art spectrometer for the Morita Array ¹, also known as the Atacama Compact Array (ACA), which was designed and developed by Japan for the ALMA telescope. This new instrument, known as the Total Power GPU Spectrometer (TPGS), will be developed by a joint team from the Korea Astronomy and Space Science Institute (KASI) and the National Astronomical Observatory of Japan (NAOJ).

The TPGS represents a major contribution from East Asia to ALMA's ambitious Wideband Sensitivity Upgrade (WSU) program, which aims to double the receiver Intermediate Frequency (IF) bandwidth and upgrade related electronics and software, including the correlator and spectrometer systems.

The team behind the TPGS previously developed the current ACA Spectrometer, which achieved first light in February 2022 and began scientific operations in October 2023 (Cycle 10). Their work was recognized with the NAOJ Director General's Award in 2025. The TPGS development will be fully based on the successful collaboration between KASI and NAOJ of the existing ACA Spectrometer. Eventually, the new TPGS will replace the existing ACA Spectrometer.

Building on this successful collaboration, the TPGS will significantly improve ALMA’s capabilities. It will feature:

• Four times more correlated bandwidth
• 16 times finer spectral resolution
• Ten times higher input data rate from antennas

By leveraging cutting-edge GPU technology and direct data transfer to GPU memory using 400 GbE connectivity, the TPGS will meet the stringent requirements of the WSU and ensure faster, more precise observations.

"The TPGS will enhance processing capacity and reuse proven legacy software from the ACA Spectrometer, enabling rapid development and seamless integration." said Jongsoo Kim, TPGS project manager at KASI.

The project passed its Conceptual Design Review (CoDR) and Subsystem Requirements Review (SRR) in November 2024 and is now moving toward its Preliminary Design Review (PDR), expected in early 2026. Once completed, TPGS will replace the existing ACA Spectrometer.

Additional Information

ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSTC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.

Images

Notes

1. Among the total 66 ALMA antennas, 16 antennas developed by Japan compose the Atacama Compact Array (ACA), nicknamed “Morita Array”. The ACA consists of twelve 7-m antennas and four 12-m antennas, the latter of which forms a group of antennas called the Total Power (TP) Array. The ACA is suitable for precise measurement of the intensity of radio waves coming from diffuse extended objects and the large-scale structure of the universe. ↩︎