Most upcoming CMB experiments are planning to deploy between a few thousand and a few hundred thousand TES bolometers in order to drastically increase sensitivity and unveil the
B
-mode signal. ...Differential systematic effects and 1/
f
noise are two of the challenges that need to be overcome in order to achieve this result. In recent years, rotating half-wave plates have become increasingly more popular as a solution to mitigate these effects, especially for those experiments that are targeting the largest angular scales. However, other effects may appear when a rotating HWP is being employed. In this paper, we focus on HWP synchronous signals, which are due to intensity to polarization leakage induced by a rotating cryogenic multilayer sapphire HWP employed as the first optical element of the telescope system. We use LiteBIRD LFT as a case study and we analyze the interaction between these spurious signals and TES bolometers, to determine whether this signal can contaminate the bolometer response. We present the results of simulations for a few different TES model assumptions and different spurious signal amplitudes. Modeling these effects is fundamental to find what leakage level can be tolerated and minimize nonlinearity effects of the bolometer response.
We measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD ...low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at 36
μ
m
at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as 0.24 and
3
×
10
-
5
G, respectively. From the AC amplitude, we compute TES critical temperature variation of
7
×
10
-
8
K and fractional change of the SQUID flux is
δ
Φ
/
Φ
0
|
ac
=
3.1
×
10
-
5
. The mechanical vibration can be also estimated to be
3.6
×
10
-
2
N at the rotation mechanism location.
We laser-ablated sub-wavelength structures (SWS) on 200 mm diameter birefringent sapphire disks to produce broadband anti-reflection coating (ARC). The disks were assembled into a stack of five ...plates making an achromatic half-wave plate (AHWP) suitable for operation between 40 and 140 GHz. We report on the SWS fabrication and transmission measurements of the stack at room temperature. From the measurements, we compute a band average transmission and modulation efficiency for nine spectral bands that correspond to the frequency coverage of the
LiteBIRD
Low-Frequency Telescope (LFT). We also assess the level of instrumental polarization the AHWP exhibits. We discuss paths for further development to minimize the instrumental polarization from the AHWP. This work is a development milestone toward the implementation of an AHWP for the
LiteBIRD
satellite.
LiteBIRD is a proposed JAXA satellite mission to measure the CMB B-mode polarization with unprecedented sensitivity (
σ
r
∼
0.001
). To achieve this goal, 4676 state-of-the-art TES bolometers will ...observe the whole sky for 3 years from L2. These detectors, as well as the SQUID readout, are extremely susceptible to EMI and other instrumental disturbances, e.g., static magnetic field and vibration. As a result, careful analysis of the interference between the detector system and the rest of the telescope instruments is essential. This study is particularly important during the early phase of the project, in order to address potential problems before the final assembly of the whole instrument. We report our plan for the preparation of a cryogenic testbed to study the interaction between the detectors and other subsystems, especially a polarization modulator unit consisting of a magnetically rotating half-wave plate. We also present the requirements, current status and preliminary results.
Abstract
LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and ...fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun–Earth Lagrangian point L2, where it will map the cosmic microwave background polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of $2.2\, \mu$K-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions, and synergies with other projects.
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