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1. The Simons Observatory: Cryogenic Half Wave Plate Rotation Mechanism for the Small Aperture Telescopes

Author

Yamada, K., Bixler, B., Sakurai, Y., Ashton, P. C., Sugiyama, J., Arnold, K., Begin, J., Corbett, L., Day-Weiss, S., Galitzki, N., Hill, C. A., Johnson, B. R., Jost, B., Kusaka, A., Koopman, B. J., Lashner, J., Lee, A. T., Mangu, A., Nishino, H., Page, L. A., Randall, M. J., Sasaki, D., Song, X., Spisak, J., Tsan, T., Wang, Y., and Williams, P. A.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

We present the requirements, design and evaluation of the cryogenic continuously rotating half-wave plate (CHWP) for the Simons Observatory (SO). SO is a cosmic microwave background (CMB) polarization experiment at Parque Astron\'{o}mico Atacama in northern Chile that covers a wide range of angular scales using both small (0.42 m) and large (6 m) aperture telescopes. In particular, the small aperture telescopes (SATs) focus on large angular scales for primordial B-mode polarization. To this end, the SATs employ a CHWP to modulate the polarization of the incident light at 8~Hz, suppressing atmospheric $1/f$ noise and mitigating systematic uncertainties that would otherwise arise due to the differential response of detectors sensitive to orthogonal polarizations. The CHWP consists of a 505 mm diameter achromatic sapphire HWP and a cryogenic rotation mechanism, both of which are cooled down to $\sim$50 K to reduce detector thermal loading. Under normal operation the HWP is suspended by a superconducting magnetic bearing and rotates with a constant 2 Hz frequency, controlled by an electromagnetic synchronous motor. The rotation angle is detected through an angular encoder with a noise level of 0.07$\mu\mathrm{rad}\sqrt{\mathrm{s}}$. During a cooldown, the rotor is held in place by a grip-and-release mechanism that serves as both an alignment device and a thermal path. In this paper we provide an overview of the SO SAT CHWP: its requirements, hardware design, and laboratory performance., Comment: 19 pages, 21 figures, submitted to RSI

Published
2023
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2. Erratum: The Simons Observatory Large Aperture Telescope Receiver (ApJS (2021) 256: 23 DOI: 10.3847/1538-4365/ac0db7)

Author

Zhu N., Zhu, N, Bhandarkar, T, Coppi, G, Kofman, A, Orlowski-Scherer, J, Xu, Z, Adachi, S, Ade, P, Aiola, S, Austermann, J, Bazarko, A, Beall, J, Bhimani, S, Bond, J, Chesmore, G, Choi, S, Connors, J, Cothard, N, Devlin, M, Dicker, S, Dober, B, Duell, C, Duff, S, Dunner, R, Fabbian, G, Galitzki, N, Gallardo, P, Golec, J, Haridas, S, Harrington, K, Healy, E, Patty Ho, S, Huber, Z, Hubmayr, J, Iuliano, J, Johnson, B, Keating, B, Kiuchi, K, Koopman, B, Lashner, J, Lee, A, Li, Y, Limon, M, Link, M, Lucas, T, Mccarrick, H, Moore, J, Nati, F, Newburgh, L, Niemack, M, Pierpaoli, E, Randall, M, Sarmiento, K, Saunders, L, Seibert, J, Sierra, C, Sonka, R, Spisak, J, Sutariya, S, Tajima, O, Teply, G, Thornton, R, Tsan, T, Tucker, C, Ullom, J, Vavagiakis, E, Vissers, M, Walker, S, Westbrook, B, Wollack, E, Zannoni, M, Zhu N., Bhandarkar T., Coppi G., Kofman A. M., Orlowski-Scherer J. L., Xu Z., Adachi S., Ade P., Aiola S., Austermann J., Bazarko A. O., Beall J. A., Bhimani S., Bond J. R., Chesmore G. E., Choi S. K., Connors J., Cothard N. F., Devlin M., Dicker S., Dober B., Duell C. J., Duff S. M., Dunner R., Fabbian G., Galitzki N., Gallardo P. A., Golec J. E., Haridas S. K., Harrington K., Healy E., Patty Ho S. -P., Huber Z. B., Hubmayr J., Iuliano J., Johnson B. R., Keating B., Kiuchi K., Koopman B. J., Lashner J., Lee A. T., Li Y., Limon M., Link M., Lucas T. J., McCarrick H., Moore J., Nati F., Newburgh L. B., Niemack M. D., Pierpaoli E., Randall M. J., Sarmiento K. P., Saunders L. J., Seibert J., Sierra C., Sonka R., Spisak J., Sutariya S., Tajima O., Teply G. P., Thornton R. J., Tsan T., Tucker C., Ullom J., Vavagiakis E. M., Vissers M. R., Walker S., Westbrook B., Wollack E. J., Zannoni M., Zhu N., Zhu, N, Bhandarkar, T, Coppi, G, Kofman, A, Orlowski-Scherer, J, Xu, Z, Adachi, S, Ade, P, Aiola, S, Austermann, J, Bazarko, A, Beall, J, Bhimani, S, Bond, J, Chesmore, G, Choi, S, Connors, J, Cothard, N, Devlin, M, Dicker, S, Dober, B, Duell, C, Duff, S, Dunner, R, Fabbian, G, Galitzki, N, Gallardo, P, Golec, J, Haridas, S, Harrington, K, Healy, E, Patty Ho, S, Huber, Z, Hubmayr, J, Iuliano, J, Johnson, B, Keating, B, Kiuchi, K, Koopman, B, Lashner, J, Lee, A, Li, Y, Limon, M, Link, M, Lucas, T, Mccarrick, H, Moore, J, Nati, F, Newburgh, L, Niemack, M, Pierpaoli, E, Randall, M, Sarmiento, K, Saunders, L, Seibert, J, Sierra, C, Sonka, R, Spisak, J, Sutariya, S, Tajima, O, Teply, G, Thornton, R, Tsan, T, Tucker, C, Ullom, J, Vavagiakis, E, Vissers, M, Walker, S, Westbrook, B, Wollack, E, Zannoni, M, Zhu N., Bhandarkar T., Coppi G., Kofman A. M., Orlowski-Scherer J. L., Xu Z., Adachi S., Ade P., Aiola S., Austermann J., Bazarko A. O., Beall J. A., Bhimani S., Bond J. R., Chesmore G. E., Choi S. K., Connors J., Cothard N. F., Devlin M., Dicker S., Dober B., Duell C. J., Duff S. M., Dunner R., Fabbian G., Galitzki N., Gallardo P. A., Golec J. E., Haridas S. K., Harrington K., Healy E., Patty Ho S. -P., Huber Z. B., Hubmayr J., Iuliano J., Johnson B. R., Keating B., Kiuchi K., Koopman B. J., Lashner J., Lee A. T., Li Y., Limon M., Link M., Lucas T. J., McCarrick H., Moore J., Nati F., Newburgh L. B., Niemack M. D., Pierpaoli E., Randall M. J., Sarmiento K. P., Saunders L. J., Seibert J., Sierra C., Sonka R., Spisak J., Sutariya S., Tajima O., Teply G. P., Thornton R. J., Tsan T., Tucker C., Ullom J., Vavagiakis E. M., Vissers M. R., Walker S., Westbrook B., Wollack E. J., and Zannoni M.

Abstract

After the publication of the article, it was brought to our attention that the description of Equation (1) may cause potential confusion. Thus, we have decided to provide a newer reference and added a unit for qtot in the description. The updated paragraph should read as the following:.

Published
2021

3. The effects of inclination on a two stage pulse tube cryocooler for use with a ground based observatory

Author

Tsan, T, Galitzki, N, Ali, A, Arnold, K, Coppi, G, Ervin, T, Foote, L, Keating, B, Lashner, J, Orlowski-Scherer, J, Randall, M, Seibert, J, Spisak, J, Teply, G, Xu, Z, Zhu, N, Tsan T., Galitzki N., Ali A. M., Arnold K., Coppi G., Ervin T., Foote L., Keating B., Lashner J., Orlowski-Scherer J., Randall M. J., Seibert J., Spisak J., Teply G. P., Xu Z., Zhu N., Tsan, T, Galitzki, N, Ali, A, Arnold, K, Coppi, G, Ervin, T, Foote, L, Keating, B, Lashner, J, Orlowski-Scherer, J, Randall, M, Seibert, J, Spisak, J, Teply, G, Xu, Z, Zhu, N, Tsan T., Galitzki N., Ali A. M., Arnold K., Coppi G., Ervin T., Foote L., Keating B., Lashner J., Orlowski-Scherer J., Randall M. J., Seibert J., Spisak J., Teply G. P., Xu Z., and Zhu N.

Abstract

Ground-based observatories across a wide range of wavelengths implement cryogenic cooling techniques to increase the sensitivity of instruments and enable low temperature detector technologies. Commercial pulse tube cryocoolers (PTCs) are frequently used to provide 40 K and 4 K stages as thermal shells in scientific instruments. However, PTC operation is dependent on gravity, giving rise to changes in cooling capacity over the operational tilt range of pointed telescopes. We present a study of the performance of a two stage PTC with a cooling capacity of 1.8 W at 4.2 K and 50 W at 45 K (Cryomech PT420-RM) from 0-55° away from vertical to probe capacity as a function of angle over a set of realistic thermal loading conditions. Our study provides a method to extract temperature estimates given predicted thermal loading conditions across the angular range sampled. We then discuss the design implications for current and future tilted cryogenic systems.

Published
2021

49. Book reviews.

Author

Randall, M. J.

Subjects
MULTI-User Detection (Book)
Abstract

Reviews the book `Multi-user Detection,' by Sergio Verdu.

Published
1999
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50. The Simons Observatory: Cryogenic half wave plate rotation mechanism for the small aperture telescopes.

Author

Yamada K, Bixler B, Sakurai Y, Ashton PC, Sugiyama J, Arnold K, Begin J, Corbett L, Day-Weiss S, Galitzki N, Hill CA, Johnson BR, Jost B, Kusaka A, Koopman BJ, Lashner J, Lee AT, Mangu A, Nishino H, Page LA, Randall MJ, Sasaki D, Song X, Spisak J, Tsan T, Wang Y, and Williams PA

Abstract

We present the requirements, design, and evaluation of the cryogenic continuously rotating half-wave plate (CHWP) for the Simons Observatory (SO). SO is a cosmic microwave background polarization experiment at Parque Astronómico de Atacama in northern Chile that covers a wide range of angular scales using both small (⌀0.42 m) and large (⌀6 m) aperture telescopes. In particular, the small aperture telescopes (SATs) focus on large angular scales for primordial B-mode polarization. To this end, the SATs employ a CHWP to modulate the polarization of the incident light at 8 Hz, suppressing atmospheric 1/f noise and mitigating systematic uncertainties that would otherwise arise due to the differential response of detectors sensitive to orthogonal polarizations. The CHWP consists of a 505 mm diameter achromatic sapphire HWP and a cryogenic rotation mechanism, both of which are cooled down to ∼50 K to reduce detector thermal loading. Under normal operation, the HWP is suspended by a superconducting magnetic bearing and rotates with a constant 2 Hz frequency, controlled by an electromagnetic synchronous motor. We find that the number of superconductors and the number of magnets that make up the superconducting magnetic bearing are important design parameters, especially for the rotation mechanism's vibration performance. The rotation angle is detected through an angular encoder with a noise level of 0.07 μrad s. During a cooldown process, the rotor is held in place by a grip-and-release mechanism that serves as both an alignment device and a thermal path. In this paper, we provide an overview of the SO SAT CHWP: its requirements, hardware design, and laboratory performance., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Published
2024
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