Fiber Positioning Robots for Wide-Field Spectroscopic Surveys.

Large wide-field spectroscopic surveys are ideally suited to study inflation, and dark energy. They require instrumentation that allows multiplexed redshifts measurements of thousands of galaxies. The Dark Energy Spectroscopic Instrument which has been running in survey mode since May 2021 utilizes 5000 computer controlled robotic positions to place 100 micron diameter optical fibers on galaxies whose location on the sky have been obtained in a previous target selection imaging survey. Light collected by the 5,000 fibers is then fed to a bank of 3-arm spectrographs. During the first year of survey operation DESI has already cataloged over 10 million galaxies and is adding more at a rate of over a million a month. Next generation instruments such as the proposed Megamapper aim to go deeper in redshift and to increase the multiplexing to more than 25,000. We will present the current design of the DESI fiber positioning robots and the challenges that a high density focal plane like the one proposed for Megamapper present.