Title: The ALMA Phasing System: A Beamforming Capability for Ultra-High-Resolution Science at (Sub)Millimeter Wavelengths,
Abstract: The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) has
developed and deployed the hardware and software necessary to coherently sum
the signals of individual ALMA antennas and record the aggregate sum in Very
Long Baseline Interferometry (VLBI) Data Exchange Format. These beamforming
capabilities allow the ALMA array to collectively function as the equivalent of
a single large aperture and participate in global VLBI arrays. The inclusion of
phased ALMA in current VLBI networks operating at (sub)millimeter wavelengths
provides an order of magnitude improvement in sensitivity, as well as
enhancements in u-v coverage and north-south angular resolution. The
availability of a phased ALMA enables a wide range of new ultra-high angular
resolution science applications, including the resolution of supermassive black
holes on event horizon scales and studies of the launch and collimation of
astrophysical jets. It also provides a high-sensitivity aperture that may be
used for investigations such as pulsar searches at high frequencies. This paper
provides an overview of the ALMA Phasing System design, implementation, and
performance characteristics.