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Proceedings Paper

The iLocater cryostat: design and thermal control strategy for precision radial velocity measurements
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Paper Abstract

The current generation of precision radial velocity (RV) spectrographs are seeing-limited instruments. In order to achieve high spectral resolution on 8m class telescopes, these spectrographs require large optics and in turn, large instrument volumes. Achieving milli-Kelvin thermal stability for these systems is challenging but is vital in order to obtain a single measurement RV precision of better than 1m/s. This precision is crucial to study Earth-like exoplanets within the habitable zone. iLocater is a next generation RV instrument being developed for the Large Binocular Telescope (LBT). Unlike seeinglimited RV instruments, iLocater uses adaptive optics (AO) to inject a diffraction-limited beam into single-mode fibers. These fibers illuminate the instrument spectrograph, facilitating a diffraction-limited design and a small instrument volume compared to present-day instruments. This enables intrinsic instrument stability and facilitates precision thermal control. We present the current design of the iLocater cryostat which houses the instrument spectrograph and the strategy for its thermal control. The spectrograph is situated within a pair of radiation shields mounted inside an MLI lined vacuum chamber. The outer radiation shield is actively controlled to maintain instrument stability at the sub-mK level and minimize effects of thermal changes from the external environment. An inner shield passively dampens any residual temperature fluctuations and is radiatively coupled to the optical board. To provide intrinsic stability, the optical board and optic mounts will be made from Invar and cooled to 58K to benefit from a zero coefficient of thermal expansion (CTE) value at this temperature. Combined, the small footprint of the instrument spectrograph, the use of Invar, and precision thermal control will allow long-term sub-milliKelvin stability to facilitate precision RV measurements.

Paper Details

Date Published: 9 August 2016
PDF: 10 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 990873 (9 August 2016); doi: 10.1117/12.2233617
Show Author Affiliations
Jonathan Crass, Univ. of Notre Dame (United States)
Louis G. Fantano, NASA Goddard Space Flight Ctr. (United States)
Frederick R. Hearty, The Pennsylvania State Univ. (United States)
Justin R. Crepp, Univ. of Notre Dame (United States)
Matthew J. Nelson, Univ. of Virginia (United States)
Sheila M. Wall, NASA Goddard Space Flight Ctr. (United States)
David A. Cavalieri, Univ. of Notre Dame (United States)
Corina Koca, NASA Goddard Space Flight Ctr. (United States)
David L. King, Univ. of Cambridge (United Kingdom)
Robert O. Reynolds, Large Binocular Telescope Observatory (United States)
Karl R. Stapelfeldt, NASA Goddard Space Flight Ctr. (United States)
Jet Propulsion Lab.s (United States)

Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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