The Atacama Large Millimeter/Submillimeter Array (ALMA) is a set of 66 millimeter wave antenna in the Andes in Northern Chile. All antennas are connected and operate as an interferometer making ALMA the most powerful millimeter telescope in the world. In 2013 ALMA formally marked the end of construction and the beginning of operations. This paper will focus on the impact, on the ALMA control software, of this transition from construction to operations.
The control subsystem for the Atacama Large Millimeter Array (ALMA) must fulfill a number of roles. Principle
amongst these is the ability to conduct observations and the ability to monitor and maintain the health of the hardware.
These two roles impose different requirements on the control subsystem. The ALMA control subsystem uses a design
which explicitly recognizes these different roles and provides capabilities that are targeted at the astronomers, engineers
and other users of the ALMA control subsystem. In this paper we will describe this aspect of the design of the ALMA
control subsystem with emphasis on how the various components of the software interact to meet the requirements of
these different users and produce a coherent control subsystem that can transition from a high level, astronomical
perspective of the array to a detailed low-level perspective with a focus on a particular piece of hardware.
The Atacama Large Millimeter Array (ALMA) is an international telescope project currently under construction in the Atacama desert of Chile. It has a provision for 64 antennas of 12m each, arranged over a geographical area of a few square kilometers. Antenna control and correlated data acquisition is implemented by means of a distributed set of realtime Linux computers, each one hosting ALMA Common Software (ACS) based applications and connected to a common time base distributed by the ALMA Master Clock as a 48ms electronic pulse signal (time event). All these computers require to be time synchronized for achieving coordination between commands and data acquisition. For this purpose, the ArrayTime system presented here implements a real-time software facility that makes possible to
unambiguously time-stamp each time event arriving at each computer node (distributed clock), relative to an external time source of 1Hz and in phase to the TAI second. Array time is the absolute time of each time event, and synchronization of distributed clocks is resolved by communicating the array time, via ACS services, for the next time event interrupt at least once during the operational cycle of the distributed clock. Thereafter, it is possible to schedule
application tasks within a latency range of 100us by extrapolating from the last interrupt and based on the current CPU Time Stamp Counter (TSC) and the estimated frequency of the CPU clock. In the following, we present a description of the elements that constitute the ArrayTime facility.
The Atacama Large Millimeter Array (ALMA) will, when it is completed
in 2012, be the world's largest millimeter & sub-millimeter radio
telescope. It will consist of 64 antennas, each one 12 meters in
diameter, connected as an interferometer.
The ALMA Test Interferometer Control System (TICS) was developed as a
prototype for the ALMA control system. Its initial task was to provide
sufficient functionality for the evaluation of the prototype
antennas. The main antenna evaluation tasks include surface
measurements via holography and pointing accuracy, measured at both
optical and millimeter wavelengths.
In this paper we will present the design of TICS, which is a
distributed computing environment. In the test facility there are four
computers: three real-time computers running VxWorks (one on each
antenna and a central one) and a master computer running Linux. These
computers communicate via Ethernet, and each of the real-time
computers is connected to the hardware devices via an extension of the
We will also discuss our experience with this system and outline
changes we are making in light of our experiences.
We present visibility measurements of the nearby Mira-like star R Doradus taken over a wide range of wavelengths (650 - 990 nm). The observations were made using MAPPIT (Masked APerture-Plane Interference Telescope), an interferometer operating at the 3.9-m Anglo-Australian Telescope. We used a slit to mask the telescope aperture and prism to disperse the interference pattern in wavelength. We observed in R Dor strong decreases in visibility within the TiO absorption bands. The results are in general agreement with theory but differ in detail, suggesting that further work is needed to refine the theoretical models.