Dark Energy Spectroscopic Instrument (DESI) Fiber Positioner Production

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the production and manufacturing processes developed for the 5000 fiber positioner robots mounted on the focal plane of the Mayall telescope.Comment: SPIE 201

Fabrication of the DESI Corrector Lenses

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the DESI corrector optics, a series of six fused silica and borosilicate lenses. The lens diameters range from 0.8 to 1.1 meters, and their weights 84 to 237 kg. Most lens surfaces are spherical, and two are challenging 10th-order polynomial aspheres. The lenses have been successfully polished and treated with an antireflection coating at multiple subcontractors, and are now being integrated into the DESI corrector barrel assembly at University College London. We describe the final performance of the lenses in terms of their various parameters, including surface figure, homogeneity, and others, and compare their final performance against the demanding DESI corrector requirements. Also we describe the reoptimization of the lens spacing in their corrector barrel after their final measurements are known. Finally we assess the performance of the corrector as a whole, compared to early budgeted estimates

The DESI Sky Continuum Monitor System

The Dark Energy Spectroscopic Instrument (DESI) is an ongoing spectroscopic survey to measure the dark energy equation of state to unprecedented precision. We describe the DESI Sky Continuum Monitor System, which tracks the night sky brightness as part of a system that dynamically adjusts the spectroscopic exposure time to produce more uniform data quality and to maximize observing efficiency. The DESI dynamic exposure time calculator (ETC) will combine sky brightness measurements from the Sky Monitor with data from the guider system to calculate the exposure time to achieve uniform signal-to-noise ratio (SNR) in the spectra under various observing conditions. The DESI design includes 20 sky fibers, and these are split between two identical Sky Monitor units to provide redundancy. Each Sky Monitor unit uses an SBIG STXL-6303e CCD camera and supports an eight-position filter wheel. Both units have been completed and delivered to the Mayall Telescope at the Kitt Peak National Observatory. Commissioning results show that the Sky Monitor delivers the required performance necessary for the ETC.Comment: 9 pages, 7 figures, 1 tabl

Overview of the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project.Comment: 11 pages, 4 figure

A Spectroscopic Road Map for Cosmic Frontier: DESI, DESI-II, Stage-5

In this white paper, we present an experimental road map for spectroscopic experiments beyond DESI. DESI will be a transformative cosmological survey in the 2020s, mapping 40 million galaxies and quasars and capturing a significant fraction of the available linear modes up to z=1.2. DESI-II will pilot observations of galaxies both at much higher densities and extending to higher redshifts. A Stage-5 experiment would build out those high-density and high-redshift observations, mapping hundreds of millions of stars and galaxies in three dimensions, to address the problems of inflation, dark energy, light relativistic species, and dark matter. These spectroscopic data will also complement the next generation of weak lensing, line intensity mapping and CMB experiments and allow them to reach their full potential.Comment: Contribution to Snowmass 202

Astro2020 APC White Paper: The MegaMapper: a z > 2 spectroscopic instrument for the study of Inflation and Dark Energy

MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at

Precision alignment and integration of DESI's focal plane using a laser tracker

Ground-Based and Airborne Telescopes VIII 2020; Virtual, Online; United States; 14 December 2020 through 22 December 2020; Code 166573.--Proceedings of SPIE - The International Society for Optical Engineering Volume 11445, 2020, Article number 114456JThe recently commissioned Dark Energy Spectroscopic Instrument (DESI) will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope delivers light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the use of a Faro Laser Tracker with custom hardware and software tools for alignment during integration of DESI's focal plane. The focal plane is approximately one meter in diameter and consists primarily of ten radially symmetrical focal plane segments ("petals") which were individually installed into the telescope. The nominal clearance between petals is 600 microns, and an alignment accuracy of 100 microns and 0.01 degrees was targeted. Alignment of the petals to their targeted locations on the telescope was accomplished by adjusting a purpose-built alignment structure with 14 degrees of freedom using feedback from the laser tracker, which measured the locations of retroreflectors attached to both the petal and the telescope and whose positions relative to key features were precisely known. These measurements were used to infer the locations of aligning features in both structures, which were in turn used to calculate the adjustments necessary to bring the system into alignment. Once alignment was achieved to within acceptable tolerances, each petal was installed while monitoring building movement due to wind and thermal variations. © COPYRIGHT SPIE.This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE–AC02–05CH1123, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the NSF’s National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain, and by the DESI Member Institutions. The authors are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Natio

Impact of distortions on fiber position location in the Dark Energy Spectroscopic Instrument

ABSTRACT The Dark Energy Spectroscopic Instrument, to be located at the prime focus of the Mayall telescope, includes a wide field corrector, a 5000 fiber positioner system, and a fiber view camera. The mapping of the sky to the focal plane, needed to position the fibers accurately, is described in detail. A major challenge is dealing with the large amount of distortion introduced by the optics (of order 10% scale change), including time-dependent non-axisymmetric distortions introduced by the atmospheric dispersion compensator. Solutions are presented to measure or mitigate these effects

The DESI fiber positioner system

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the baryon acoustic oscillation technique. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5,000 fiber optic positioners feeding ten broad-band spectrographs. The positioners have eccentric axis kinematics. Actuation is provided by two 4 mm diameter DC brushless gear-motors. An attached electronics board accepts a DC voltage for power and CAN messages for communications and drives the two motors. The positioner accepts the ferrulized and polished fiber and provides a mechanically safe path through its internal mechanism. Positioning is rapid and accurate with typical RMS errors of less than 5 mu m

Overview of the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project. © 2018 SPIE.This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DEAC0205CH1123, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico, and by the DESI Member Institutions. The authors are honored to be permitted to conduct astronomical research on Iolkam Du'ag (Kitt Peak), a mountain with particular significance to the Tohono O'odham Nation