ALMA North America Cycle 4 Study Project Final Report: Diversifying the Applications of the ALMA Phasing System

Abstract

The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) produced the hardware and software modifications necessary to bring Very Long Baseline Interferometry (VLBI) capabilities to ALMA. The resulting VLBI observing mode was introduced to the science community in ALMA Cycle 4 (2017), and two VLBI science campaigns have now been carried out successfully at ALMA. The current Cycle 4 ALMA North America (NA) Study was proposed to lay the groundwork for a variety of enhancements to the ALMA Phasing System (APS) that were not within the scope of the original APP project. These include: (1) devising an improved method for the handling of baseband delays; (2) development of procedures for use of the APS on fainter astronomical sources than is presently possible; (3) development of data acquisition and correlation techniques to allow the APS to be used for spectral line VLBI experiments. These tasks were intended as preparatory steps for a future full-scale implementation project (if approved). Formal approval of this implementation work has now been granted and is funded through an ALMA Cycle 5 NA Development project known as APP “Phase 2” (APP-2). As a result, efforts to implement capabilities designed and explored under the current Cycle 4 Study, as well as a previous Cycle 3 Study award, are now underway. This report provides a status summary of Cycle 4 activities and outlines follow-on work that is continuing as part of the ongoing Cycle 5 Development efforts.