D'Alessandro, G. and Mele, L. and Columbro, F. and Amico, G. and Battistelli, E.S. and de Bernardis, P. and Coppolecchia, A. and De Petris, M. and Grandsire, L. and Hamilton, J.-Ch. and Lamagna, L. and Marnieros, S. and Masi, S. and Mennella, A. and O'Sullivan, Créidhe and Paiella, A. and Piacentini, F. and Piat, M. and Pisano, G. and Presta, G. and Tartari, A. and Torchinsky, S.A. and Voisin, F. and Zannoni, M. and Ade, P. and Alberro, J.G. and Almela, A. and Arnaldi, L.H. and Auguste, D. and Aumont, J. and Azzoni, S. and Banfi, S. and Baù, A. and Bélier, B. and Bennett, D. and Bergé, L. and Bernard, J.-Ph. and Bersanelli, M. and Bigot-Sazy, M.-A. and Bonaparte, J. and Bonis, J. and Bunn, E. and Burke, D. and Buzi, D. and Cavaliere, F. and Chanial, P. and Chapron, C. and Charlassier, R. and Cobos Cerutti, A.C. and De Gasperis, G. and De Leo, M. and Dheilly, S. and Duca, C. and Dumoulin, L. and Etchegoyen, A. and Fasciszewski, A. and Ferreyro, L.P. and Fracchia, D. and Franceschet, C. and Gamboa Lerena, M.M. and Ganga, K.M. and García, B. and García Redondo, M.E. and Gaspard, M. and Gayer, D. and Gervasi, M. and Giard, M. and Gilles, V. and Giraud-Heraud, Y. and Gómez Berisso, M. and González, M. and Gradziel, M. and Hampel, M.R. and Harari, D. and Henrot-Versillé, S. and Incardona, F. and Jules, E. and Kaplan, J. and Kristukat, C. and Loucatos, S. and Louis, T. and Maffei, B. and Marty, W. and Mattei, A. and May, A. and McCulloch, M. and Melo, D. and Montier, L. and Mousset, L. and Mundo, L.M. and Murphy, J.A. and Murphy, J.D. and Nati, F. and Olivieri, E. and Oriol, C. and Pajot, F. and Passerini, A. and Pastoriza, H. and Pelosi, A. and Perbost, C. and Perciballi, M. and Pezzotta, F. and Piccirillo, L. and Platino, M. and Polenta, G. and Prêle, D. and Puddu, R. and Rambaud, D. and Rasztocky, E. and Ringegni, P. and Romero, G.E. and Salum, J.M. and Schillaci, A. and Scóccola, C.G. and Scully, S. and Spinelli, S. and Stankowiak, G. and Stolpovskiy, M. and Supanitsky, A.D. and Thermeau, J.-P. and Timbie, P. and Tomasi, M. and Tucker, C. and Tucker, G. and Viganò, D. and Vittorio, N. and Wicek, F. and Wright, M. and Zullo, A. (2022) QUBIC VI: Cryogenic half wave plate rotator, design and performance. Journal of Cosmology and Astroparticle Physics, 04 (039). pp. 1-31. ISSN 1475-7516

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Abstract

Setting an upper limit or detection of B-mode polarization imprinted by gravitational waves from Inflation is one goal of modern large angular scale cosmic microwave background (CMB) experiments around the world. A great effort is being made in the deployment of many ground-based, balloon-borne and satellite experiments, using different methods to separate this faint polarized component from the incoming radiation. QUBIC exploits one of the most widely-used techniques to extract the input Stokes parameters, consisting in a rotating half-wave plate (HWP) and a linear polarizer to separate and modulate polarization components. QUBIC uses a step-by-step rotating HWP, with 15° steps, combined with a 0.4°s-1 azimuth sky scan speed. The rotation is driven by a stepper motor mounted on the cryostat outer shell to avoid heat load at internal cryogenic stages. The design of this optical element is an engineering challenge due to its large 370 mm diameter and the 8 K operation temperature that are unique features of the QUBIC experiment. We present the design for a modulator mechanism for up to 370 mm, and the first optical tests by using the prototype of QUBIC HWP (180 mm diameter). The tests and results presented in this work show that the QUBIC HWP rotator can achieve a precision of 0.15° in position by using the stepper motor and custom-made optical encoder. The rotation induces <5.0 mW (95% C.L) of power load on the 4 K stage, resulting in no thermal issues on this stage during measurements. We measure a temperature settle-down characteristic time of 28 s after a rotation through a 15° step, compatible with the scanning strategy, and we estimate a maximum temperature gradient within the HWP of ≤ 10 mK. This was calculated by setting up finite element thermal simulations that include the temperature profiles measured during the rotator operations. We report polarization modulation measurements performed at 150 GHz, showing a polarization efficiency >99% (68% C.L.) and a median cross-polarization χPol of 0.12%, with 71% of detectors showing a χPol + 2σ upper limit <1%, measured using selected detectors that had the best signal-to-noise ratio.

Item Type:	Article
Keywords:	CMBR detectors; CMBR experiments; CMBR polarisation; gravitational waves; CMBR polarization;
Academic Unit:	Faculty of Science and Engineering > Experimental Physics
Item ID:	18829
Identification Number:	https://doi.org/10.1088/1475-7516/2022/04/039
Depositing User:	Dr. Créidhe O'Sullivan
Date Deposited:	03 Sep 2024 16:07
Journal or Publication Title:	Journal of Cosmology and Astroparticle Physics
Publisher:	IOP Publishing
Refereed:	Yes
URI:	Publisher
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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