S. Mima

LiteBIRD: a small satellite for the study of B-mode polarization and inflation from cosmic background radiation detection

LiteBIRD [Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection] is a small satellite to map the polarization of the cosmic microwave background (CMB) radiation over the full sky at large angular scales with unprecedented precision. Cosmological inflation, which is the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational waves were created during the inflationary era. Measurements of polarization of the CMB radiation are known as the best probe to detect the primordial gravitational waves. The LiteBIRD working group is authorized by the Japanese Steering Committee for Space Science (SCSS) and is supported by JAXA. It has more than 50 members from Japan, USA and Canada. The scientific objective of LiteBIRD is to test all the representative inflation models that satisfy single-field slow-roll conditions and lie in the large-field regime. To this end, the requirement on the precision of the tensor-to-scalar ratio, r, at LiteBIRD is equal to or less than 0.001. Our baseline design adopts an array of multi-chroic superconducting polarimeters that are read out with high multiplexing factors in the frequency domain for a compact focal plane. The required sensitivity of 1.8μKarcmin is achieved with 2000 TES bolometers at 100mK. The cryogenic system is based on the Stirling/JT technology developed for SPICA, and the continuous ADR system shares the design with future X-ray satellites.

Radio-transparent multi-layer insulation for radiowave receivers.

In the field of radiowave detection, enlarging the receiver aperture to enhance the amount of light detected is essential for greater scientific achievements. One challenge in using radio transmittable apertures is keeping the detectors cool. This is because transparency to thermal radiation above the radio frequency range increases the thermal load. In shielding from thermal radiation, a general strategy is to install thermal filters in the light path between aperture and detectors. However, there is difficulty in fabricating metal mesh filters of large diameters. It is also difficult to maintain large diameter absorptive-type filters in cold because of their limited thermal conductance. A technology that maintains cold conditions while allowing larger apertures has been long-awaited. We propose radio-transparent multi-layer insulation (RT-MLI) composed from a set of stacked insulating layers. The insulator is transparent to radio frequencies, but not transparent to infrared radiation. The basic idea for cooling is similar to conventional multi-layer insulation. It leads to a reduction in thermal radiation while maintaining a uniform surface temperature. The advantage of this technique over other filter types is that no thermal links are required. As insulator material, we used foamed polystyrene; its low index of refraction makes an anti-reflection coating unnecessary. We measured the basic performance of RT-MLI to confirm that thermal loads are lowered with more layers. We also confirmed that our RT-MLI has high transmittance to radiowaves, but blocks infrared radiation. For example, RT-MLI with 12 layers has a transmittance greater than 95% (lower than 1%) below 200 GHz (above 4 THz). We demonstrated its effects in a system with absorptive-type filters, where aperture diameters were 200 mm. Low temperatures were successfully maintained for the filters. We conclude that this technology significantly enhances the cooling of radiowave receivers, and is particularly suitable for large-aperture systems. This technology is expected to be applicable to various fields, including radio astronomy, geo-environmental assessment, and radar systems.

LiteBIRD: mission overview and design tradeoffs

We present the mission design of LiteBIRD, a next generation satellite for the study of B-mode polarization and inflation from cosmic microwave background radiation (CMB) detection. The science goal of LiteBIRD is to measure the CMB polarization with the sensitivity of δr = 0:001, and this allows testing the major single-field slow-roll inflation models experimentally. The LiteBIRD instrumental design is purely driven to achieve this goal. At the earlier stage of the mission design, several key instrumental specifications, e.g. observing band, optical system, scan strategy, and orbit, need to be defined in order to process the rest of the detailed design. We have gone through the feasibility studies for these items in order to understand the tradeoffs between the requirements from the science goal and the compatibilities with a satellite bus system. We describe the overview of LiteBIRD and discuss the tradeoffs among the choices of scientific instrumental specifications and strategies. The first round of feasibility studies will be completed by the end of year 2014 to be ready for the mission definition review and the target launch date is in early 2020s.

Development of Superconducting Tunnel Junction detectors as a far-infrared photon-by-photon spectrometer for neutrino decay search

We present the development of Superconducting Tunnel Junction (STJ) detectors as a far-infrared single photon spectrometer, which is motivated for an application to a search for the radiative decay of the cosmic neutrino background (CνB). The photon energy spectrum from the radiative decays of CνB is expected to have a sharp edge at high energy end in a far-infrared region ranging from 14 meV to 25 meV (from 50 μm to 90 μm in wavelength) in the cosmic infrared background and the overwhelming infrared foreground from the zodiacal emission. Thus, the detector is required photon-by-photon detection with sufficiently high energy resolution, in order to gain the best signal-to-noise ratio as well as to identify the edge structure. The following two types of photon detectors are under consideration: an array of niobium/aluminum STJ (Nb/Al-STJ) pixels with a diffraction grating, and STJ using hafnium (Hf-STJ). Each Nb/Al-STJ pixel is required to be capable of detecting single photons in the far-infrared region, and the pixel array measures the photon wavelength spectrum which the diffraction grating creates. Hf-STJ is expected to achieve 2% energy resolution for single photon of 25 meV due to very small gap energy of hafnium.

Development of Superconducting Tunnel Junction Detectors as a far-infrared single photon detector for neutrino decay search

Yuji Takeuchi∗a †, Shin-Hong Kima, Kenichi Takemasaa, Kenji Kiuchia, Kazuki Nagataa, Kota Kasaharaa, Takuya Okudairaa, Tatsuya Ichimuraa, Masahiro Kanamarua, Kouya Moriuchia, Ren Senzakia, Hirokazu Ikedab, Shuji Matsuurab, Takehiko Wadab, Hirokazu Ishinoc, Atsuko Kibayashic, Satoru Mimad, Takuo Yoshidae, Shota Komurae, Keisuke Orikasae, Ryuta Hirosee, Yukihiro Katof, Masashi Hazumig, Yasuo Araig, Erik Rambergh, Jonghee Yooh, Mark Kozlovskyh, Paul Rubinovh, Dmitri Sergatskovh, Soo-Bong Kimi aUniversity of Tsukuba, 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-8571, Japan bInstitute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara,

Development of superconducting tunnel junction photon detector on SOI preamplifier board to search for radiative decays of cosmic background neutrino

Kota Kasahara∗, Shin-Hong Kim, Yuji Takeuchi, Ren Senzaki, Kazuki Nagata, Takuya Okudaira, Masahiro Kanamaru, Tatsuya Ichimura, Koya Moriuchi, Kenji Kiuchi, Yasuo Arai1, Masashi Hazumi1, Hirokazu Ikeda2, Shuji Matsuura2, Takehiko Wada2, Satoru Mima3, Hirokazu Ishino4, Takuo Yoshida5, Yukihiro Kato6, Erik Ramberg7, Mark Kozlovsky7, Paul Ruvinov7, Dmitri Segratskov7 University of Tsukuba, Ibaraki 305-8571, Japan 1KEK, Ibaraki 305-0801, Japan 2JAXA ISAS, Kanagawa 252-5210, Japan 3RIKEN, Saitama 351-0198, Japan 4Okayama University, Okayama 700-8530, Japan 5University of Fukui, Fukui 910-8507, Japan 6Kinki University, Osaka 577-8502, Japan 7Fermi National Accelerator Laboratory, Illinois, 60510, US E-mail: kasahara@hep.px.tsukuba.ac.jp

Development of Superconducting Tunnel Junction Detector Using Hafnium for COBAND Experiment

We present the development of a Superconducting Tunnel Junction detector using hafnium (Hf-STJ) as a far infrared single photon detector for COsmic BAckground Neutrino Decay search (COBAND) experiment. The photon energy spectrum from the decay of cosmic background neutrino is expected to have a sharp edge at the high energy end in a far-infrared region ranging from 14–25 meV in the cosmic infrared background and the overwhelming infrared foreground from the zodiacal emission. We are developing a Hf-STJ which is expected to have 2% energy resolution for a single photon of 25 meV. We have successfully produced a superconductor-insulator-superconductor structure using Hf. However, it is found to suffer from a large leakage current and needs modification of the Hf-STJ to reduce it. We have developed two new types of Hf-STJ: Hf-STJ with an Al layer and Hf-STJ with a new sputtering condition. The leakage current density of two new types of Hf-STJ becomes 16 times smaller than the old Hf-STJ and obtained a response to the visible light. Because of its large leakage current, further optimization is underway.

GroundBIRD: observations of CMB polarization with fast scan modulation and MKIDs

Polarized patterns in the cosmic microwave background (CMB) radiation contains rich knowledge for early stage of the universe. In particular their odd-parity patterns at large angular scale (> 1°), primordial B-modes, are smoking-gun evidence for the cosmic inflation. The GroundBIRD experiment aims to detect these B-modes with a ground-based apparatus that includes several novel devices: a high-speed rotational scan system, cold optics, and microwave kinetic inductance detectors (MKIDs). We plan to start observations in the Canary Islands in 2017. In this paper, we present the status of the development of our instruments. We established an environment that allows operation of our MKIDs in an optical configuration, in which the MKIDs observe radiations from the outside of the telescope aperture. We have also constructed MKID prototypes, and we are testing them in the optical configuration.

Development of the Superconducting Detectors for Applications to Particle Physics and Astrophysics

Atsuko Kibayashi1, Masashi Hazumi2,3, Hirokazu Ishino1, Yoshiaki Kibe1, Satoru Mima4, Chiko Otani4, Nobuaki Sato2, Hiroki Watanabe3, Yosuke Yamada1 and Mitsuhiro Yoshida2 1Department of Physics, Okayama University, Okayama 700-8530, Japan 2High Energy Accelerator Research Organization(KEK), Tsukuba, Ibaraki 305-0801, Japan 3SOKENDAI, Tsukuba, Ibaraki 305-0801, Japan 4Terahertz-wave Research Group, RIKEN, Wako, Saitama 351-0198, Japan