Evaluation of the ALMA Prototype Antennas1

Abstract

The ALMA North American and European prototype antennas have been evaluated by a variety of measurement systems to quantify the major performance specifications. Nearfield holography was used to set the reflector surfaces to 17 µm RMS. Pointing and fast switching performance was determined with an optical telescope and by millimeter wavelength radiometry, yielding 2 ′′ absolute and 0.6 ′′ offset pointing accuracies. Path length stability was measured to be 20 µm over 10 minute time periods using optical measurement devices. Dynamical performance was studied with a set of accelerometers, providing data on wind induced tracking errors and structural deformation. Considering all measurements made during this evaluation, both prototype antennas meet the major ALMA antenna performance specifications.

Mechanical Measurements of the ALMA Prototype Antennas

“…An overview of these performance results was presented in [2]. The current paper presents a more detailed analysis of the mechanical performance measurements made of the ALMA prototype antennas.…”

Wide field aplanatic two-mirror telescopes for ground-based γ-ray astronomy

“…The unavoidable need to reduce the OS weight and its moment of inertia will probably require the use of modern, light-weight, high-strength materials, such as carbon fiber-reinforced plastics, to construct the optical support structure. Alignment of the segmented optical system may require automated edge sensors and actuators, since the tolerances of the aplanatic telescope OS are roughly equivalent to a mm range radio telescope, such as ALMA [ 28], in the range 100-20 µm. Although these requirements are three to four orders of magnitude looser than the diffraction limit to which the positions of the segmented mirrors of the Keck telescopes are maintained, they are far stricter than those of current ACT optical systems, such as VERITAS, MAGIC, and H.E.S.S.…”

Atacama Large Millimeter/Submillimeter Array

“…These prototype antennas were tested at the NRAO's Very Large Array (VLA) site near Socorro, N.M [12][13][14] [15]. Subsequent to the prototype testing phase, antenna production contracts were written in 2005 with Vertex, AEM and MELCO.…”