The iLocater cryostat and thermal control system: enabling extremely precise radial velocity measurements for diffraction-limited spectrographs

Extremely precise radial velocity (EPRV) measurements are critical for characterizing nearby terrestrial worlds. EPRV instrument precisions of \(\sigma_{\mathrm{RV}} = 1-10\,\mathrm{cm/s}\) are required to study Earth-analog systems, imposing stringent, sub-mK, thermo-mechanical stability requiremen...

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Bibliographic Details
Published in:arXiv.org 2022-08
Main Authors: Crass, Jonathan, Sadagopan, Nandini, Misch, Matthew, Rizika, Alexa, Sands, Brian, Engstrom, Matthew, Crepp, Justin R, Smous, James, Chilcote, Jeffrey, Fantano, Louis G, VanSickle, Michael, Hearty, Frederick R, Nelson, Matthew J
Format: Article
Language:English
Subjects:
Adaptive optics
Circumstellar habitable zone
Control equipment
Diameters
Diffraction
Earth analogs
Multilayers
Near infrared radiation
Operating temperature
Radial velocity
Radiation
Spectrographs
Thermal control systems
Thermal expansion
Thermal stability
Vacuum chambers
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Summary:Extremely precise radial velocity (EPRV) measurements are critical for characterizing nearby terrestrial worlds. EPRV instrument precisions of \(\sigma_{\mathrm{RV}} = 1-10\,\mathrm{cm/s}\) are required to study Earth-analog systems, imposing stringent, sub-mK, thermo-mechanical stability requirements on Doppler spectrograph designs. iLocater is a new, high-resolution (\(R=190,500\) median) near infrared (NIR) EPRV spectrograph under construction for the dual 8.4 m diameter Large Binocular Telescope (LBT). The instrument is one of the first to operate in the diffraction-limited regime enabled by the use of adaptive optics and single-mode fibers. This facilitates affordable optomechanical fabrication of the spectrograph using intrinsically stable materials. We present the final design and performance of the iLocater cryostat and thermal control system which houses the instrument spectrograph. The spectrograph is situated inside an actively temperature-controlled radiation shield mounted inside a multi-layer-insulation (MLI) lined vacuum chamber. The radiation shield provides sub-mK thermal stability, building on the existing heritage of the Habitable-zone Planet Finder (HPF) and NEID instruments. The instrument operating temperature (\(T=80-100\,\mathrm{K}\)) is driven by the requirement to minimize detector background and instantaneous coefficient of thermal expansion (CTE) of the materials used for spectrograph fabrication. This combination allows for a reduced thermomechanical impact on measurement precision, improving the scientific capabilities of the instrument.
ISSN:2331-8422