ALMA Wideband Sensitivity Upgrade (WSU)
The ALMA Wideband Sensitivity Upgrade (WSU) is a major initiative to enhance ALMA science potential, instrumentation, and software systems for sustained, high-capability operations through the 2030s. The WSU will dramatically increase the observational capabilities of ALMA and translate to new opportunities across a range of scientific topics. The initiative is well underway, with planned completion of core elements by the end of this decade.
The ALMA 2030 Development Roadmap, a Board-approved vision for ALMA sustainability and enhancement, identified the WSU initiatives as top priority. The goals of the WSU include an increase in bandwidth by a factor of 2 (ultimately x4), as well as increased digital sensitivity and improved sensitivity of key receivers.
The initial and most critical stage of the WSU is the upgrade of the signal chain for increased bandwidth and improved digital efficiency. Future stages will implement receivers with broader bandwidth and higher sensitivity. Nearly every hardware component in the existing signal chain is being replaced in this first stage and includes the IF Switch, Digitizer, Data Transmission System, a new Fiber Optic Cable, and a major new digital correlator - the Advanced Technology ALMA Correlator (ATAC) and a new Total Power GPU Spectrometer (TPGS). ATAC will be located at the Operations Support Facility (OSF) at 3000 m elevation rather than the Array Operations Site at 5000 m where the current Baseline Correlator resides and will provide improved power efficiency and ease of support. The relocation requires creation of a new correlator room in the OSF. The WSU also includes a major upgrade of both online and offline software systems, including a new calibration and imaging pipeline and data processing system. The signal chain upgrade will include at least one new, high bandwidth receiver, Band 2. Additional high bandwidth receivers with improved sensitivity are expected to follow. The entire ALMA partnership is contributing to the success of the WSU; North American contributions to the new signal chain include ATAC, the new OSF Correlator Room, and collaboration on the Digital Transmission System (DTS) with East Asia. A project to develop a prototype of the Band 6v2 receiver is also in progress at NRAO.
An initial project review for the WSU is scheduled for July 2024 and several subsystem preliminary design reviews will be held over the following months.
Resources
- ALMA Memo 621 (arXiv:2211.00195), October 2022
- AAS special session, January 2023
- WSU presentation at NRAO Imaging workshop, June 2023
- WSU press release, February 2023: approval of the development of a second-generation correlator and digital transmission system (DTS).
- WSU press release, November 2023: NRAO and NAOJ partner to produce Band 2 and develop upgrade Band 6
- AAS special session, January 2024: ALMA as a high-z powerhouse: the impact of the Wideband Sensitivity Upgrade
